Orr89RocZ

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.


I'm gonna join it into a flowmaster Y-collector 3inch dual inlets, 4inch single outlet.


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


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.

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1989 IROC-Z L98
My 383 HSR mod list
"383 Stealth Ram Buildup Pics "
"My Ride Pics"
"Car Domain"
Exhaust Idle/Rev
11.47 at 118.5 mph Best mph 119.1

skinny z

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.

skinny z

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.

Orr89RocZ

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

mw66nova

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.

Orr89RocZ

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.

Orr89RocZ

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?

skinny z

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.
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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.

skinny z

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.

Orr89RocZ

Like that article mentioned, the tuned length is effected by muffler placement due the idea of pressure waves as mentioned here

It appears the pressure wave reflects back when it hits a large cross-sectional area difference, and that helps scavenge the exhaust out of the cylinder.

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
So the article suggests using resonator boxes to act as a pressure wave reflector when using mufflers such as this, OR if you have chambered box style mufflers over the axle.

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

leeperryracing

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.

Orr89RocZ

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

skinny z

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.

Orr89RocZ

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

skinny z

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!

Orr89RocZ

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

skinny z

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.

skinny z

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!

leeperryracing

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

skinny z

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.

Orr89RocZ

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.

I dont know why your blown 383 didnt pick up power with more open exhaust....just doesnt make sense to me.

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.
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YOu dont need a whole lot to break 12's you'll have it easily with that combo. i went 12.9's with bolt on L98, 2800 stall 3.42 gear at near sealevel like conditions for my area good day for me

4000 stall seems abit large and so does the gear with that little cam

skinny z

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.

Orr89RocZ

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

skinny z

Any further along on the exhaust research?
Nice looking ride by the way. Just checked out your web page.