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Need exhaust advice on hot 383 build Ok well i'm thinking about exhaust work now. Since i plan to run longtube headers, i will need to fab up a y pipe to connect to the existing catback exhaust i have BUT its only a single 3inch exhaust and i'm afraid that will choke the 383. I love the sound of it but i dont think its gonna do well on the big cammed 383. The 383 will be stout, custom cam in the high 230's duration, .600 lift, and 11 to 1 compression. hoping for 400whp if not over :) This car will need to breathe, and i've seen guys pick up lots of power by getting rid of their 3in single systems. Since i'm looking for all out power out of this combo, this leaves me to new ideas. Idea number 1 is the idea that i'm really considering at the moment but there is one flaw that has me worried. I'm gonna build a custom y-pipe around the crossmember to look something like this car. http://i2.tinypic.com/8bxuu87.jpg I'm gonna join it into a flowmaster Y-collector 3inch dual inlets, 4inch single outlet. http://www.jegs.com/images/photos/389Y214300A.gif then gonna run a big 4inch single exhaust on back to my current y-pipe splitter. I'll have a Dynomax Ultraflo 4inch round muffler where my current powerstick tube is, and will run a 4in-to-3in reducer cone to join the 4inch single pipe to my 3inch inlet mini y-pipe splitter where the exhaust goes over my axle. seen here http://inlinethumb21.webshots.com/42...500x500Q85.jpg The splitter is single 3inch inlet and dual 3inch outlet. So there will be only a short section of restriction when it goes from 4inch to single 3" then out thru the dual 3inch tailpipes. This way i keep that back half exhaust section that i had made earlier last summer, which i love the way it looks. But that little restriction worries me abit... 4 to 3 inch is tight lol, but atleast it has a lot of exit room thru the dual 3inch outlets OPTION 2, is true 3inch duals. My headers are 3inch collectors so i will NOT neck it down to 2.5 inch. I'll run the tubes just like that ypipe posted above around my crossmember for clearance purposes, and then NOT join them into a y pipe but continue them to the rear section of the car. i'll have some sort of mini h pipe or mini x pipe along the way. I'll get another powerstick to put into the i pipe next to the other tube. it probly will be alot more money since its more piping, and abit more weight. But the biggest concern is that true 3inch duals is OVERKILL for my motor and i will lose power from having too much exhaust flow, if there is such a thing. opinions needed. I will be attempting to do this myself and hope to buy a welder sometime soon. It will be a mig welder. Will it be ok to mig the pipes together or should i have it tig welded up? I dont think i'll use stainless pipe, but rather aluminized steel. |
Re: Need exhaust advice on hot 383 build Think we've might have talked before. You may have checked out this link. http://www.superchevy.com/technical/...exh/index.html Everything you need to know about building an effective exhaust system. However, as 3rd genowners, especially with lowered cars, it's almost impossible to build a really effective system that will perform AND be quiet and managable on the street (speed bumps and driveways). The first photo you've posted is probably the cleanest long tube installation I've seen. I've talked with him earlier and got a few specs. The cut outs seem to be the solution. My only suggestion on an improvement would be to provide some sort of secondary tuning for the collector (after the cut out). Personally, and my 86 is heading to the shop in the next couple of weeks(Altered Images in central Ontario), I'm going to forgo the true duals setup and go with cutouts just for track days. I'll keep a single 3" and one muffler for cruising. My guess is that there's a couple of tenths in the 60' times with a properly spec'd exhaust. The single pipes, shorty headers and poorly assembled systems just kill performance. |
Re: Need exhaust advice on hot 383 build By the way, one small restriction in your system will cripple the potential of the whole thing regardless of how well the rest is built. |
Re: Need exhaust advice on hot 383 build even if that small reducer section is that far from the headers? wouldnt velocity be somewhat slow by then and shouldnt really cripple the system? Maybe i can modify that y pipe section and cut a 4inch inlet into it. But i think i can fab up a true dual system that has decent clearance. I just will use 3 inch pipes and think i can get it to clear. Just hope it aint too much pipe |
Re: Need exhaust advice on hot 383 build what about a cutout behind the big 4" muffler before the reducer/splitter to the back? you'll reap the benefits of a big single setup (simliar scavaging properties as an x-pipe) and have still have the option to go quieter out the back. just a thought, same thought process i used when i did my single 3.5" system on my car now. |
Re: Need exhaust advice on hot 383 build i didnt really want to run a cutout. I want to run the exhaust as is without touching it at the track, basically bolt on my drag wheels and drive to the track and run....no other changes other than the shock settings :) I want to run great times at the track and bring that max performance out on the street. I cant run open headers on the street If open headers make max power, then a full true dual 3inch wont kill performance that much. And i forgot to add, i'lll be spraying this car with a 150 shot or so later down the road. Probly late fall this year. thats probly gonna be over 500whp, so true dual 3inch may not be a bad idea if i can squeeze it all in on the passenger side axle like stock does. It has been done i think i can do it again. |
Re: Need exhaust advice on hot 383 build after reading that article in the above posted link I'm leaning to 3inch true duals. A pipe will flow 115 cfm per square inch of area when under same pressure as what carbs are rated at. That article shows you want a exhaust system that has mufflers that will flow 2.2 cfm of flow per open pipe hp. Since my car should make around 500-520 hp with open headers, I THINK... i need anywhere from 1100 to 1144 cfm of total flow. thats roughly 550-572 cfm per section of a dual system. 2.5 inch pipe is said to flow about 560. 3inch is 812 cfm so i'll go with more for safety. Now when i spray the car, and make near 620-650hp on motor, thats 687 cfm per pipe flow. 3inch duals is still way more than adequate. Now if i get a muffler that only flows 600cfm, my system will be limited to that flow, so the 3inch really wont hurt much if i have good headers with good header collectors. Thoughts on this logic? |
Re: Need exhaust advice on hot 383 build It's not all about the cfm capability, but rather how the exhast can be 'tuned' for power increases. The benefit of open headers is the scavenging effect that results from pressure waves being reflected back to the exhaust port. That's why properly spec'd open headers make more power than a typical exhaust system whether it's a true dual system, 3" pipes or whatever. The race guys will run dual mufflers right at the collector (for an overall collector length of 20 to 40+ inches) and these will contribute to the tuned length of the secondary depending on the type of muffler used. That also means the exhaust ends at the end of the mufflers or the scaveging effect is lost. (no pipe after the muffler to speak of). Any change in the diameter/flow capability of the exhaust whether it's the open atmosphere, a muffler or a restriction will change the tuning that we're trying to find. This dosen't mean you shouldn't run the least restrictive system you can, it's just if you don't follow the basic priciples, then you won't get the full effect of using long tube headers. I think the idea of 3" duals, high capacity mufflers (the 2.2cfm/hp rule) and an x-pipe are the minimum you should be doing. There are a lot of fast cars out there that do just that. It's just that they would be faster still following the advice in the articles. ---------- Personally, I'm going to try and build a terminator box like Vizard did for his friends Vette. If I find there's simply not enough room, I'll place cut outs (maybe electrically activated $$) at the appropriate spot and allow for extentions on those to allow for some length tuning. |
Re: Need exhaust advice on hot 383 build The answer I was trying to find was what if you ran two 3" pipes right over the axle and had the high capacity mufflers there. Does that mean the collectors are now 6 feet long? What effect does THAT tuned length have? I can't get an answer to that one and I've been all over the internet. I have read where the proper muffler (one that behaves like an open atmosphere to the engine) can be placed at the appropriate distance along the collector ( say 20 to 40" like the race guys ) and add tailpipes from there. There's just not enough room in a lowered 3rd gen to do this. Not as far as I know anyway. |
Re: Need exhaust advice on hot 383 build That also means the exhaust ends at the end of the mufflers or the scaveging effect is lost. (no pipe after the muffler to speak of). Any change in the diameter/flow capability of the exhaust whether it's the open atmosphere, a muffler or a restriction will change the tuning that we're trying to find. This dosen't mean you shouldn't run the least restrictive system you can, it's just if you don't follow the basic priciples, then you won't get the full effect of using long tube headers. I think the idea of 3" duals, high capacity mufflers (the 2.2cfm/hp rule) and an x-pipe are the minimum you should be doing. There are a lot of fast cars out there that do just that. It's just that they would be faster still following the advice in the articles. ---------- Personally, I'm going to try and build a terminator box like Vizard did for his friends Vette. If I find there's simply not enough room, I'll place cut outs (maybe electrically activated $$) at the appropriate spot and allow for extentions on those to allow for some length tuning. A pressure wave is reflected either at the end of the exhaust pipe or when a sizable increase in cross-sectional area occurs. Open chambered mufflers such as Flowmasters often appear to the pressure wave much the same as the end of the pipe I planned to run some type of tube like round muffler, or powersticks like i have now since i Love the sound. BUT glasspack/tube mufflers act more like a extension of collector length since it doesnt offer a wide cross-sectional area difference like a open box chambered muffler A glass pack muffler can act significantly different. It does not appear as a pipe end but as a substantial increase in collector length. Result: a reduction of power even though there is no measurable backpressure involved. So if you were to put like a flowmaster 40 series box muffler over the axle, the collector tuned length would be like 6 feet or something very long and would tune max power at a reallly low rpm. Since my car should peak at anywhere from 6000-6500 as specified by the custom cam i wanted, i wont know the specs till i get it tho, i need to add mufflers or resonator boxes at a appropriate length from the collector to tune for that RPM i guess, for max peak hp i assume. since boxes arent profiled well for thirdgens that are lowered like mine, i will have to see what i can throw in the exhaust to simulate that. I am guessing i need a 'collector' effective length of 15-20 inches to peak at 6000-6500rpms or so. Or do i want it farther down like 25-30 to boost 4000-5000 rpms power/tq? This i'm not sure about |
Re: Need exhaust advice on hot 383 build I had a single 3" system with 1 3/4 LTs on my Z28 with a procharged 383 and it made 614whp on a very conservative tune, I also dynoed it with the cut-out open and picked up 0 hp. In my opinion I really don't think you need that much exhaust...for a single setup, a 3.5" system is more than enough or dual 2.5" for true duals. Dual 3" systems are usually more at home on cars making 4 digit HP numbers. Bigger is better sometimes but theres always that threshold. |
Re: Need exhaust advice on hot 383 build thats true... i thought about just fabbing up a Y pipe like the mufflex y pipe if i get hooker long tubes, and connecting it to my existing 3inch catback. Also install a cutout or two. once i get it somewhat tuned, i'll hit the dyno and do before/after runs with cutouts open and closed to see how much that 3inch is killing me, if at all. If it is, then i'll have to scrap the 3inch and do a single 4inch like planned to keep my y-pipe i make. OR sell that off and do the duals sooo many options |
Re: Need exhaust advice on hot 383 build How long would the collector be with the cut outs open? Most applications I've seen have the cut out immediately after the collector which amounts to a collector length of about 12" or less. This would push the tuning effect of the secondary way up in the rev range. The result is the feeling you get when you drive your car to the exhaust shop with open headers and you notice how 'sluggish' it feels. No collector length equals poor low end response. You are right in that there is a compromise when it comes to street cars. |
Re: Need exhaust advice on hot 383 build not sure where i'd put them, but in the original pictures i first posted, it probly be like that which LOOKS to be about 30-36 inches |
Re: Need exhaust advice on hot 383 build So many options is right! I'll go the cut out route myself, seeing as that there is little room for resonator boxes (and I don't like my exhaust dumping out underneath the car) and I'll provide some means of extending the collector beyond the cut out so I can achieve some kind of tuning. You're right on with your assessment of the length vs. rpm. It must be nice to make tons of power and not have to be concerned about maximizing every bit of torque that's available. Procharged 383's can do that for you! |
Re: Need exhaust advice on hot 383 build i'm seriously thinking of just making this a blown motor and not worrying about the exhaust lol i may have to do the cutout idea..i want to do it electronically tho...for ooooo's and awwwws effect. i dont feel like crawling under the car to take off caps on hot exhaust or put it back on when i am ready to leave the track |
Re: Need exhaust advice on hot 383 build I'd say that's a good start. I'd like to build mine to allow for extentions of 12 to 24" beyond where the cut outs are. Remember too that there shouldn't be any appreciable difference in diameter between what the collectors are and what the exhaust pipe is. Half an inch in I.D. is enough to impart some sort of resonance and the whole experiment is out the window. |
Re: Need exhaust advice on hot 383 build There's the expense and reliabilty of the electric cut outs that has to be considered though. Seriously, I'm just trying to break into the 12's with a little 218 degree cam and Vortec heads. I think it can be done with this kind of attention to detail. I know there are easier ways. Supercharging... Nitrous... 3000 lbs, 4.56 gear and 4000 stall gets you that with 300hp! |
Re: Need exhaust advice on hot 383 build
Originally Posted by skinny z
(Post 3619813)
So many options is right! I'll go the cut out route myself, seeing as that there is little room for resonator boxes (and I don't like my exhaust dumping out underneath the car) and I'll provide some means of extending the collector beyond the cut out so I can achieve some kind of tuning. You're right on with your assessment of the length vs. rpm. It must be nice to make tons of power and not have to be concerned about maximizing every bit of torque that's available. Procharged 383's can do that for you! |
Re: Need exhaust advice on hot 383 build I agree with you there. I prefer my car to be a little quieter too. I don't need to attract attention. I am going to explore this as much as I care to afford. It may provide some interesting results. |
Re: Need exhaust advice on hot 383 build i dont mind really loud since this car is more of a fun car now getting less than 4K miles a year if that. I really want good TONE...something that will sound good and i've found what i like with my current system but its not adequate for my car now. that motor did not need any bigger than the 3" system and 1 3/4 LTs. What i've noticed is that exhaust pipe size has become somewhat of a bragging rights kinda deal, sometimes a lot of these guys running stupid pipe diameter sizes have NOWHERE near the mods/power to warrant it....hey look at me with a bone stock 305 but it sounds really killer with my single 4" system I've seen dyno results of a guy that picked up 8-10 whp with a true dual 2.5 inch setup over a MUFFLEX 4inch single. But i've also seen ppl gain little with true 2.5's over single 3's but that was on smaller motors. If i cammed a 350, i'd be keeping my 3inch for a while. I'm afraid this 383 will want more and since i've spent or will be spending money on AFR heads, fully forged lower end, custom grind cam, and other attention to detail, i dont wanna skimp on exhaust. The only reason true 3inch seems logical to me now is that i will upgrade to a bigger motor later, OR add more nitrous, or turbo/blower setup shooting for 600-700+ whp depending. Then i think the dual 3inch would come in handy. But its hard to say since you experienced different results. I got time to research this and will be doing alot. ----------
Originally Posted by skinny z
(Post 3619834)
There's the expense and reliabilty of the electric cut outs that has to be considered though. Seriously, I'm just trying to break into the 12's with a little 218 degree cam and Vortec heads. I think it can be done with this kind of attention to detail. I know there are easier ways. Supercharging... Nitrous... 3000 lbs, 4.56 gear and 4000 stall gets you that with 300hp! 4000 stall seems abit large and so does the gear with that little cam |
Re: Need exhaust advice on hot 383 build I actually wasn't refering to myself with those specs. That's one of the J/Stock class racers who rips off 11's with a combo like that and a 305! My heavy clunker is 13.4@102 with the 218 cam. I'm hoping the exhaust work will bring on the torque and drop a couple of tenths in the 60'. I'd be thrilled with 12.9. You must have had some good bolt ons. |
Re: Need exhaust advice on hot 383 build the car ran good with what it had, and responded well to the stealth ram. had more in it with better tune ( i was really lean) and more gear |
Re: Need exhaust advice on hot 383 build Any further along on the exhaust research? Nice looking ride by the way. Just checked out your web page. |
Re: Need exhaust advice on hot 383 build yes, i took a look under my car today and forgot how low it sits...its slammed lol I dont know if i will be able to run any style of exhaust without notching the subframe which i think will be my only option. The picture posted above showing the nice y pipe with cutouts going around the spohn crossmember is what i wanted to do but instead, i'll tuck the pipes up in the subframe area and just stabilize the car with subframe connectors and such. Problem is that photo above shows the crossmember without driveshaft safety loop. I have a loop up front so getting the pipe to cross back over will be tight, i may have to modify the DS loop. ALSO on the drivers side, i'm not sure what i'm gonna do about the fuel lines that are in my way that are mounted on the subframe. I want to move them somehow but not sure how to do that. I also dont like the idea of running hot exhaust right next to them. i guess i could wrap that section in header wrap to help protect them SO i have no idea what to do now |
Re: Need exhaust advice on hot 383 build whose car is that in the first pic you posted. that is a REALLY nice setup. i would like to do a dual setup like that with longtubes on my car, but it is so low. i would like to contact that guy about the ground clearance of that setup. |
Re: Need exhaust advice on hot 383 build
Originally Posted by Orr89RocZ
(Post 3628093)
yes, i took a look under my car today and forgot how low it sits...its slammed lol I dont know if i will be able to run any style of exhaust without notching the subframe which i think will be my only option. The picture posted above showing the nice y pipe with cutouts going around the spohn crossmember is what i wanted to do but instead, i'll tuck the pipes up in the subframe area and just stabilize the car with subframe connectors and such. Problem is that photo above shows the crossmember without driveshaft safety loop. I have a loop up front so getting the pipe to cross back over will be tight, i may have to modify the DS loop. ALSO on the drivers side, i'm not sure what i'm gonna do about the fuel lines that are in my way that are mounted on the subframe. I want to move them somehow but not sure how to do that. I also dont like the idea of running hot exhaust right next to them. i guess i could wrap that section in header wrap to help protect them SO i have no idea what to do now Cut the Sphon DS loop and replace it with another one that doesn't interfere with the exhaust. When I had my LT true dual installed, I did have to notch my frame on the driver side to gain additional ground clearance but I did not remember having to re-route any fuel lines. |
Re: Need exhaust advice on hot 383 build
Originally Posted by skinny z
(Post 3619590)
The answer I was trying to find was what if you ran two 3" pipes right over the axle and had the high capacity mufflers there. Does that mean the collectors are now 6 feet long? primary. Whenever there is an abrupt change in cross section, a reflective surface, or extreme bend an expansion wave will be created (negative phase).
Originally Posted by skinny z
(Post 3619590)
What effect does THAT tuned length have? I can't get an answer to that one and I've been all over the internet. exactly where the peak will occur without knowing other particulars such as valve timing, header deisgn, secondary diameter, etc. When I fab'd up my collector extension, my TQ peak moved down 400 RPM, and I gained more average HP from 2500 RPM to 5500 RPM. The HP peak jumped to 5850 RPM (from 5700), and the car also improved on the track.
Originally Posted by skinny z
(Post 3619590)
I have read where the proper muffler (one that behaves like an open atmosphere to the engine) can be placed at the appropriate distance along the collector ( say 20 to 40" like the race guys ) and add tailpipes from there. There's just not enough room in a lowered 3rd gen to do this. Not as far as I know anyway. |
Re: Need exhaust advice on hot 383 build
Originally Posted by maroon88iroc
(Post 3637500)
whose car is that in the first pic you posted. that is a REALLY nice setup. i would like to do a dual setup like that with longtubes on my car, but it is so low. i would like to contact that guy about the ground clearance of that setup. https://www.thirdgen.org/forums/exha...s-spohn-c.html very nice setup. not bad clearance, but could be alot better had the frame been notched Cut the Sphon DS loop and replace it with another one that doesn't interfere with the exhaust. When I had my LT true dual installed, I did have to notch my frame on the driver side to gain additional ground clearance but I did not remember having to re-route any fuel lines. I hope to order the headers by next week or so, and then when i get them, mock them up to see how much room i''ll have. But exhaust is the last thing on my mind. I just want the motor done :) |
Re: Need exhaust advice on hot 383 build Anything new with your research? I'm toying with the idea of "improving" my exhaust once again. Especially if the next dyno session makes a nice improvement with the straight pieces installed in place of the catalytic converters. There is a program called PipeMax. Don't know if you have heard of it. Does some nice calculations on exhaust lengths etc. Anyways according to PipeMax my car should have a collector length of either 9", 18", 36" or 72" for the proper tuned length. With the stock style exhaust system I'm toying with the idea of running an 18" length collector on the passenger side and a 36" length collector on the drivers side and have them go into a common resonator box that would be located on the passenger side where the current exhaust runs. Then have the two pipes come out of the resonator box and into the high flow catalytic converters. The idea is to have the resonator box act like "open air" so that I can get somewhat of a tuned exhuast. Not sure how well this would work with the nice shorty headers I have. By the way my headers have a 3" collector that immediately goes into 2 3/4" pipes. Just incase that the exhaust system may be holding things back for some reason. ;) |
Re: Need exhaust advice on hot 383 build i'm trying to figure out where i could possibly place a resonator box to act like open air under my car. If i ran a single 4inch pipe setup, with the ypipe being only 30inchs or less, that wouldnt be too hard to put a box where the y collector merge would be. Just about the I pipe area but thats where i want to put my muffler. So i could use a big open chambered case muffler and that would act like the open air box i'm sure. But that limits me alittle in clearance compared to a tube muffler i want to run, like i have now The other choice for me and the one i'm thinking will happen most likely, was true duals, 3inch all the way, into a x pipe. Maybe i could make a resonator somewhere in that line but again i'm not sure how much clearance i would have. Then i thought does it even matter? I havent seen ANYONE running a street car make a resonator box trying to tune pressure waves at a certain collector lengths. I've seen countless LT1 dynos putting up 400+whp running true dual 2.5 and 3 inch setups, some running single 4inch setups. They dont have a resonator box and have the power i'm after. Now the question becomes how much do they stand to gain with a box somewhere in the system? Most of the cars i've seen DO dyno higher with open cutouts near the collector so in theory, if a resonator box acts the same way as cutouts, which tunes the engine for a target rpm range (Lets say peak rpm for the cam/heads/intake for max hp), then it will make open header HP with a full quiet exhaust :) Then hell yes i will try to fit that under my car The exhaust article states a large cross sectional area difference will reflect pressure wave back. What defines a large cross sectional area difference? What about using gutted cat converters as resonator boxes? they are somewhat wider inside. For me that would make my car look emissions legal atleast but i can get around that legality. Atleast they would fit cleanly and tune my collector length |
Re: Need exhaust advice on hot 383 build 1 Attachment(s) Those are the questions I have been asking and researching. I do know that you need to figure out the best spot for a resonator to get the proper "tune" effect. You might want to invest in Pipemax as I believe it is around $40 and does more than the exhaust systems. Does intake systems and dyno simulations as well. The question is it worth it or just go for the best free flowing exhaust you can. I sure you have seen this picture but it does show a resonator box. In the picture below "tuned collector length" is one of the keys. |
Re: Need exhaust advice on hot 383 build I'm thinking the simplest way is to use two seperate tunes. Open LT headers (that would require extentions that would also need to be tuned) along with a rejetted carb or FI curve and a fully muffled system like a 3" cat back with it's own carb setting for cruising. If your engine is strong enough you can still make that 400 whp with a full exhaust although the books show there's another 10+% available. That's 40 horse and it's significant. A couple of mufflers under the passenger compartment dosen't seem to be option in a lowered 3rd gen so I won't pursue it. If you want to examine the resonator box approach there may be an option as far as I can see. The box has to a minimum of 8 times the volume of one cylinder. In my case that's 350 ci. A 36" length of 4" pipe gets you 376ci. I think you might fit a piece of pipe that size along the trans tunnel. A single pipe or duals from there over the axle and through the muffler and you're done. The sinlge pipe and the muffler have to be large enough to flow about 2.2 cfm/hp to reduce the back pressure. The resonator box should eliminate the need for second tune. I'm just not sure if the engineering is possible. I'll be building something in the next couple of weeks and I think the potential of another 40hp is worth it. |
Re: Need exhaust advice on hot 383 build
Originally Posted by 1989GTATransAm
(Post 3705324)
Anything new with your research? I'm toying with the idea of "improving" my exhaust once again. Especially if the next dyno session makes a nice improvement with the straight pieces installed in place of the catalytic converters. There is a program called PipeMax. Don't know if you have heard of it. Does some nice calculations on exhaust lengths etc. Anyways according to PipeMax my car should have a collector length of either 9", 18", 36" or 72" for the proper tuned length. With the stock style exhaust system I'm toying with the idea of running an 18" length collector on the passenger side and a 36" length collector on the drivers side and have them go into a common resonator box that would be located on the passenger side where the current exhaust runs. Then have the two pipes come out of the resonator box and into the high flow catalytic converters. The idea is to have the resonator box act like "open air" so that I can get somewhat of a tuned exhuast. Not sure how well this would work with the nice shorty headers I have. By the way my headers have a 3" collector that immediately goes into 2 3/4" pipes. Just incase that the exhaust system may be holding things back for some reason. ;) |
Re: Need exhaust advice on hot 383 build Thanks. I have the Dyno Don 1 3/4" shorty headers. The wye pipe is two 2 3/4" pipes into a 3.5" Mufflex cat back system with a Magna Flow 3 1/2" muffler. Should flow pretty good on its own. Just trying for more if I can get a "tuned" exhaust. You are correct on long tubes but they are out of the question for smog purposes. I can fudge some things but not those. :) |
Re: Need exhaust advice on hot 383 build Well once my motor is done and installed, i will see exactly how much room i will have. I gotta see where my longtubes will exit the car and how i will run pipes under the car. I plan on cutting out my crossmember so i can have the 3inch tubes fit underneath it without hanging that low. A 36" length of 4" pipe gets you 376ci. My question is this. How well does flowing a 3inch round pipe into a box like that back into a 3 inch pipe work? Would that create some turbulence? I bet it will sound very different tho :) from a normal piped setup. Also that vette system posted there, with a single long box. having both pipes enter a box like that, how well do you think that is for flow? Could you have just a single small box with BOTH engine banks dumping into it like above graphic shows? Why does he feel it has to be THAT long. I think i'd only have 20 inches to play with under the car...if that. And i dont wanna add too much weight to the car :) What i'm realllly thinking is just building a basic dual setup, then getting that dyno'd, see where my power is at. Have cutouts installed and see if that makes the power difference. IF cutouts work, and i want more power i will fab a small box like i mentioned for each bank and see if there is any improvement. |
Re: Need exhaust advice on hot 383 build The way I understand it, after the properly spec'd collector length and diameter you have to try and simulate open atmospere. That's the resonator box and both collectors dump into there. One box at 'least' 8 times the volume of one cylinder is the general rule. Exiting the box you have to ensure minimal backpressure with 2.2 cfm/hp. 3.5" pipe flows about 1100cfm at typical test pressure so that and an 1100cfm muffler will do it. |
Re: Need exhaust advice on hot 383 build
Originally Posted by 1989GTATransAm
(Post 3705544)
Thanks. I have the Dyno Don 1 3/4" shorty headers. The wye pipe is two 2 3/4" pipes into a 3.5" Mufflex cat back system with a Magna Flow 3 1/2" muffler. Should flow pretty good on its own. Just trying for more if I can get a "tuned" exhaust. You are correct on long tubes but they are out of the question for smog purposes. I can fudge some things but not those. :) It might be possible to build something for track only days where you open cutouts installed somewhere along the y-pipe and build a seperate fuel curve for the newly opened headers and tuned for length collector extentions. You could still try the resonator box idea. The difference with the short headers is the point where the system tunes to. Higher rpm with short primaries and lower with LT's although you should still gain the advantages of utilizing a box. |
Re: Need exhaust advice on hot 383 build 1 Attachment(s) When using PipeMax I used shorty headers and it came up with the "tuned" lengths that I posted above. That was for peak horsepower at 5800 rpm. Anyways I was thinking of making a resonator box 3" tall, 7" wide and 17" long for my 355. I believe there is enough room for it. Here are some more pictures of resonator boxes and how the pipes enter and exit the box. Basically the pipe enters the box with a stub maybe 1/2 to 1" inside the box. The top one shows a funnel exit. The bottom shows a pipe with a bellmouth exit. Looks totally doable to me. Question is will it work? I would have the box and pipes into the box ceramic coated to help keep the heat away from the floorboard. If I could get a 5% gain in power it would be worth it. Edit: I wonder with the resonator box and the high flowing catalytic converters if one could do away with the muffler? My mind is just racing around with thoughts. Hahaha. |
Re: Need exhaust advice on hot 383 build One more thing. During my reasearch someone got the wrong tuned length and lost power. That is why I say the tuned length is very important at least to get it close. |
Re: Need exhaust advice on hot 383 build
Originally Posted by 1989GTATransAm
(Post 3705853)
One more thing. During my reasearch someone got the wrong tuned length and lost power. That is why I say the tuned length is very important at least to get it close. If you don't nail the spec down exactly, then the exercise is useless and you might just as well run what anyone can buy over the counter. If you have a combo that makes tons of power in the first place, then you probably don't miss the 10%hp that's available. That seems to be the trade off between running a typical single cat back exhaust and tuned open headers. Since I'm building a new exhaust from the heads back, then I'm hoping the extra effort will be worth it. |
Re: Need exhaust advice on hot 383 build same here man, headers back so i have to pay attention to what i do. I went thru the effort of getting the best heads i could get, a custom grind cam for max power for the rpm range i want, so its only natural i take the effort to the exhaust side and come up with something thats gonna work best for my setup |
Re: Need exhaust advice on hot 383 build Just for general information. For my 355 setup PipeMax recomends a collector pipe size of 2.639". That includes a 16 gauge wall thickness and would be OD. So the closest would be a 2 5/8" pipe. The 2 5/8" pipes are hard to come by. So I went with the 2 3/4" pipe of 2.75" which are not that common either but available. ;) Bret Bauer in one thread said it was better to be a little bigger than a little smaller when choosing your exhuast pipe size. So something for you guys to consider. By the way PipeMax is only like $40 or $45. Well worth it when desiging an exhaust system. Intake for that matter too. :D |
Re: Need exhaust advice on hot 383 build If i got true dual 3inch, i should have enough cfm flow to handle much more powerful motor than my 383 n/a. on the spray it will be a better match and thats why i'm doing the true duals i'll have to look into that pipemax |
Re: Need exhaust advice on hot 383 build 115 cfm/square inch for exhaust pipe flow tested at standard pressure. Make sure you know the cfm of the mufflers you intend to use. Inlet/outlet size does not necessarily correlate directly to flow. |
Re: Need exhaust advice on hot 383 build Now here's something to consider. If I build system that looks like DTL504's, then without the cutouts I've got a collector that has to be about 40-48" long. If I dump those collectors into a resonator/terminator box made of 4" pipe sized to provide the necessary volume (8x one cylinder minimum) and then into a suitably sized exhaust and muffler (cfm wise) I should have a functional system that behaves like open to the atmosphere headers. The 40" + collector seems out of spec to me although by how much I don't know. Pipe Max would be useful here. I know that reducing the collector diameter to 2.5" (which I'm doing) and lengthening it will push the torque peak down the rpm scale which suits me. I just don't want it outside the limit of my stall speed which should be somewhere around 3000 - 3500rpm. Now here's the interesting part. I've seen 4" cat back systems from Mufflex that use a merge pipe (dual 2.5" into single 4") and then a single exhaust pipe into a muffler in the stock location. Would that 4" exhaust pipe behave like an oversized terminator box? Over volume dosen't seem to be an issue in box design. Provided the single muffler can flow at least 2.2 cfm/horse power (a straight 4" pipe flows 1400+ cfm), then a functional system can be had with purchased parts as opposed to hand built. With the exception of the hand made collector extentions of course. |
Re: Need exhaust advice on hot 383 build I don't think the 2 1/2" to 4" wye pipe would serve as an exhaust termination box as pictured in post #1. I think the inlet of the termination box needs to be on the order of the pictures I posted in reply number 39. If you were to use a 4" piece of pipe as a termination point then the 2.5" collector pipe would need to extend inside it say 1/2-1". I would think that the 4" pipe could also bend some and would not have to be straight for installation clearance purposes. |
Re: Need exhaust advice on hot 383 build Here are a couple of interesting links to tuned exhausts on other forums. Some little tidbits of information in them. http://www.gofastnews.com/board/engi...e-hot-air.html Here is one I started trying to get some information. Couple of tidbits of info in the replys. http://www.speedtalk.com/forum/viewtopic.php?t=10237 |
Re: Need exhaust advice on hot 383 build Good idea! I wanted to look at SpeedTalk to see what they say. A termination box is the addition of a large cross-sectoinal area in the exhaust. a y pipe would seem like that but if i recall right, that article says it just acts like a long collector/primary tube. So if you wanted to run a 2.5 into a 4 inch single exhaust, you will still need a larger tube in there to act like the resonator, like a section of 5inch exhaust pipe, and then go back into the 4inch. I'm still liking the build a small box like muffler for both sides and make that my termination box point. I dont know how much room there is. I dont know what my collector length should be either tho. |
Re: Need exhaust advice on hot 383 build
Originally Posted by 1989GTATransAm
(Post 3707228)
I don't think the 2 1/2" to 4" wye pipe would serve as an exhaust termination box as pictured in post #1. I think the inlet of the termination box needs to be on the order of the pictures I posted in reply number 39. If you were to use a 4" piece of pipe as a termination point then the 2.5" collector pipe would need to extend inside it say 1/2-1". I would think that the 4" pipe could also bend some and would not have to be straight for installation clearance purposes. It would still be possible to use a suitable length of 4" pipe with a fabricated adapter that brings the collectors into the box in the specified manner. It would only need to be 36" long to meet the minimum requirements for a 350. Something along the lines of the piece in the Go Fast News article you attached. I'm only working with the idea of 4" pipe because I know it fits in a lowered vehicle application. |
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