I have been chasing this for a while now.

383:
performer eps intake
edelbrock 600 13:1 A/F ratio
World Products S/R torquer heads (2.02/1.6)
lunati voodoo cam: http://www.summitracing.com/parts/LUN-60102LK/
Hooker shorty headers
full 2.5" exhaust with single in dual out flowmaster.
hei (recurved with lighest springs)
tried many different plugs.

Dyno'd 228hp@4200 and 338tq@3000.
timing was set at 34 total.

I have no idea as to why my numbers are so low. Any help?

 

Im going to double check tomorrow but I'm pretty sure the exhaust is 2.5 single from the headers to the muffler.

Is this too small? Anybody know of hp gains from upping exhaust size?

 

600cfm carb on a 383?

 

Small heads, small cam, small carb, small exhaust... I could see those numbers on a Mustang dyno.

 

For the carb, I could choose from that or a vac secondary holley 750. I gained 6hp with the 600. however the holley had a 12:1 A/F ratio.

Is it safe to say that the heads and cam are more high performance than almost all stock heads and cams available for a similar engine? Besides vortecs I know those are better...

What is typically needed for exhaust on out cars to reach 300whp?

Oh and it was on a dynojet, mustang dyno is different correct?

 

You are not getting enough air to support a 383. And yes the exhaust should be atleast 3in cat back system.

 

Why do you think that my top end cannot supply enough air? The intake is good to 5500 and my hp peaks at 4200.

 

Your build would work with a stock-ish 350, and even those mods on a 350 are VERY mild. You're choking your engine with your parts combination, and that's why you have low HP. A 383 needs a good running holley based 750 (QFT, Proform, Holley, whatever), an Airgap RPM or good single plane depending on the power range, 195 runners or larger, and a whole lot more lift and duration to take advantage of the kind of power it could make. Top that off with a set of longtubes as well.

I've got a built 355, and even for MY build I've got alot bigger components than you do and it's not even a dragstrip car. I'm running an airgap rpm, Quickfuel 750, longtubes, and my duration is a mild 230/236@50 with 490/490 lift. That's a MILD build 355. You should have your duration up in the mid 240's@50 or more and the lift to feed it as well. My heads I'm going to be bolting on are also 200CC intake runners. That just gives you an idea for comparison purposes. You've got alot more in your engine, but you're not taking advantage of it because your parts combination don't allow it to breathe.

 

Yea i agree my parts are mild but shouldn't it still make as much or more hp than a stock 350 with maybe a cam? Seems like a 350 can so easily lay down 220whp.

What kind of hp is your 355 putting down?

 

What stock 350?

 

You're still going to make small "stock 350" power because you're running "stock-ish 350" parts. Basically put - you're only making more power than a 350 would right now with the same parts because of your added displacement and stroke. Your engine should be making double what you have now, but your current parts do not support those power levels.

+ I haven't dyno'd my current setup. I've seen alot of other combo's similar to mine and most of them are making around 400-430HP at the flywheel with a similar setup and aftermarket heads of the same caliber.

 

Remember an engine is an air pump, if you can't get air in you can't get HP out.

You need to fill the cylinders with air so you can add fuel to make big combustion.
Hence, HP TQ.

 

"Put it this way, I have the dyno printout to prove it. My 91 Z28 with a 30xxx mile L98 (350) with EdelB headers and an airfoil in the throttle body made 232 rwhp and over 300ft lbs before 4000 rpms.

I'd have to look at a few things with your scenario, the accuracy of the dyno and the tune." AC


"Stock L98's put down 160-170 there??? most put down 215-230 depending on the L98. I'd say his dyno reads very very low.

240whp on that dyno may be closer to 280-290 on others. The biggest thing right now is to check how it runs at a track.

Or find another dyno to compare numbers. But the track times wont lie. IF that car traps well over 106 mph, you know its got the power." Orr89RocZ


These are a few examples of why I think stock or relatively stock 350's make hp in my range. Now if I have a slightly better cam, slightly better intake, aftermarket rotaing assembly, better valves, lets say equal heads, 33 more cubic inches............... why am I not making more hp?

 

Several members have, I believe, sufficiently answered your question of why your 383 isnt making more HP. I will note that while your parts are rated to 5500RPM, theyre only intended to produce low to mid range torque not top end power. What does have me puzzled is your low torque number. 338ftlbs from even a mild 383 seems low. What is your CR? Is your cam installed straight up?

 

I'm no expert by any means, but if nothing else the cam and carb you have seem pretty smallish for that engine to breath well. A Comp XE274 type cam would do better, along with a 750 cfm carb. A little bigger on the exhaust wouldn't hurt either...say a Hooker catback (3" single) would help.

Gotta agree with ASE doc - I also wonder why you didn't manage to get more torque, I would think at least down in the lower range you'd have more than 338 ft lbs....but to me, I'd expect both numbers to be a bit higher even with what you have, so something is def. holding it back...

 

compression is about 9.3:1. I have degreed the cam and it was exactly what the spec called for so I left it as is. No bushings.

So you guys think my intake manifold is the biggest power robber or is my exhaust holding me back?

I used a exhaust size calculator and it said the max hp through a 2.5 single exhaust is like 257 hp... not too sure how accurate this is.

 

That exhaust HP estimation sounds about right. Your exhaust is probably your biggest issue right now. Its also the one part of your setup that will give you benefits without making any other changes. The rest of your engine combo needs to be addressed as a system. The larger carb will only benefit you if combined with a freer breathing manifold, which will only work well with better heads. All of which needs a larger cam. You get the point.

 

s/r torquers arent too much different than stock heads... i'd say those are a huge restriction but the rest of the parts match it well enough. Stock heads do support higher hp. I made 254 running very lean on a stock head bolt on L98 thru an automatic. Stock heads should be good for 280whp with a cam and manual trans..maybe even with an auto.
Definately a mild 383 build. I'd change exhaust first and see what it does...quick test is to run it open headers to see what it does. Then go from there.

Intake and heads are very mild. So is the cam. Different heads/intake could make good gains even with that cam.
I'd try an RPM type intake first with a bit larger carb or even same carb for now. Could see abit better gains than 4200 rpm peak hp which seems to fit inside the EPS intakes operating range. But a 383 needs air and the 170cc runner just wont support much over 5000rpm anyway.

My buddy's mild 350 with stock LT1 cam which is smaller than yours made near 300whp estimated from his trap speeds (97-98 mph in a 83 chevy pickup truck). Vortec heads and rpm intake with 750 double pumper carb.

 

What were you running for an intake and exhaust when you made 254whp?

 

L98 with stealth ram EFI setup. hooker 2055 shorties with 3" single exhaust..no cat.
stealth ram would be comparable to RPM intakes, atleast as far as flow and rpm range goes.

 

Your parts are matched well, but they aren't matched for a built 350, and they're definitely not a good match for a 383. If it were me, I'd change the heads, cam, intake, and modify your exhaust if you want to see significant power gains. It's alot of work (and money), but there's really no cheap way to get what you're asking for.

As mentioned before - try running open headers to see the difference if you want. I don't expect much of a gain, though.

Oh, and one more thing.. if I were you, I'd get a scattershield for that 5-speed if you don't have one already.

 

Problem 1
Small cam. a 219/227 perfect for a mild, 350 TINY for a 383. Get something in the 230 range minimum. And since you have flat tappet you are going to give up a few HP over a roller.

Problem 2.
170CC intake runner. Stock L98's are 165cc IIRC. You want a minimum 200cc head to flow for a 383

Problem 3.
600 CFM carb. Will hurt you on the big end of things especially if you are spinning up to 6k RPM. I'd go w/ a 750 if you change the heads.

Once you make those changes then your exhaust will be hurting you, so you will definitely want to step up to a 3".

13:1 AFR is a bit lean, you want to be around 12.5:1

 

If I run open headers will i risk cooking my starter or any other problems?

I will be looking for an rpm, rpm air gap.... any other good manifolds? Any single plane or stick to rpm?

 

Do not run shorty headers open, since you are carb'd I guarantee you will be shooting flames out of them and that is obviously very risk that you could light your car or what ever is underneath it on fire.

Also The possibility where excessive exhaust duration without sufficient backpressure can cause the air/fuel charge to continue burning across the exhaust valve and into the header primary. Which can trash the exhaust valves. This is also possible if you timing is severly retarded also though.

 

Another concern I would have with running short headers open is cool air reversion across the exhaust valves. I would suggest making short test pipes that would route your exhaust away from the undercar and prevent reversion. About 3' would be a good length.

 

yeah with shorties you will need to fab a quick extension piece to run under the car somewhere

 

Well didn'trun open headers but did measure the lift of my drivers side valves.
I used a magnetic base with a dial guage attached and found the lift of each valve as I turned the engine by hand.

My cam is supposed to have .468 int/,469 exh lift.

INT EXH
.257 .292
.256 .272
.263 .275
.240 .274

I'm going to say these measurements are accurate to +/- .015. But are obviously way off what they are supposed to be.

Conclusion: Cam is junk unless anyone knows of why I'm wrong??

 

230ish duration cam at mid 500ish lift, rpm air gap or victor jr intake, 750 holley mech secondaries or better, 3 inch exhaust, tfs heads, you will have a big smile on your face. I never liked the edelbrock headers, thats just me though.

 

Hydraulic lifters will collapse when no oil pressure is present. Those numbers are probably off because of that so I wouldnt be too worried.

 

True, but I could watch the dial raise as the lifter collapsed, so once it was at max lift the lifter was fully collapsed and as i cranked the motor until the valve was closed the lifter stayed collapsed.

A fully collapsed lifter should give me the same reading as a fully pumped up lifter right?

 

These are all stock numbers
86 IROC-A4+L98 V8 9.5:1 5.7 (350) 220@4200 320@3200 TPI

87 IROC A4 L98 V8 9.3:1 5.7 (350) 225@4400 330@2800 TPI

88 IROC A4 L98 V8 9.3:1 5.7 (350) 230@4400 330@3200 TPI

89 IROC A4 L98 V8 9.3:1 5.7 (350) 230@4400 330@3200 TPI


And on and on and on

 

I dont think so. I made a solid lifter for my motor so i could degree the cam in. If it collapses, you wont see the same lift. I know I didnt see the proper lift of my hydraulic lifters vs the solid one i made that prevented the pushrod cup from collapsing. Think about it...the lifter and pushrod are the only two lengths that act on the rocker to transfer cam lobe lift to valve lift. The rocker has its own ratio to change the lift at the valve but assuming pushrod geometry is correct..
If you change the lifter height and keep pushrod the same, the total lift range that acts on the rocker is much shorter now. Pushrod geometry is important for this reason since too short or too long will change how the rocker tip travels on the valve stem tip.
Try taking a rocker off, and putting the dial indicator on the pushrod tip if possible, and check lift again. You should see a difference if the lifter doesnt collapse.

 

Thats crank hp not whp but I have seen L98's put down 210-230whp depending on the year/condition/vette or fbody....

 

True,but I was adressing a different question not were the power was measured but what 350 block made 220hp.There were stock 302's that made even more hp.

 

Thanks for going into detail, I agree with what you are saying but I'm still not too sure about this.

Here is the question. When the lifter is collapsed, is the valvetrain still tight?
(rocker touching valve and pushrod, pushrod touching lifter)

 

Orr is right on easiest way to do it is using a solid lifter.

Remember lift at the lobe and lift at the valve are 2 different things.

Say your cam card said lobe was .300 lift which youre measuring at the lifter
Multiply that times your rocker ratio (1.5 or 1.6 and you should come up with your total lift that the valve is coming off the seat with. The rocker takes what the cam does and is kind of like a multiplier. Weird way of explaining it but...

.300 lift x 1.5 rocker=450 lift
.300 lift x 1.6 rocker=480 lift

Think even if you got a better head left the cam in, larger dual plane intake and a 750 dp youd notice a night and day difference. Bet its nice and snappy down low as it is now though.

 

Alright did some research about hydraulic lifters and now I see that due to the spring inside the lifter there is always pressure on the pushrod. This is what gave me the illusion that there was not "play" in the valvetrain.

I just switched vehicles for the winter and am a few hours away from my car but in a few weeks I hope to try to figure out the exhaust and see how much it is affecting power.

Thanks for the help guys I will keep updating the thread as I continue...

 

The exhaust is def. killing the performance. Dont waste too much time thinking about it, it has to go. The muffler doesnt flow well and its too small. I had a flowmaster and I measured about 6-8 PSI of backpressure at WOT. I personally like the hooker maximum flow mufflers. Theyre not available as a cross-over design, but the larger one is relatively quiet and doesnt resonate or drone like the flows do. Its a real godsend on the highway not to have to listen to the motor the whole way. Its a tight squeeze to get it in the stock position and only has one outlet, but its well worth it compared to the flowmaster, which is basically designed to just make noise.

As for the intake, get an edel RPM. I tried the performer and performer RPM back to back and the performer makes lots of torque down low, but sucks out top. The RPM costs torque at low RPMs, but is much better at high RPMs.

As for the heads, theyre a bit small for a 383. If you change the intake and exhaust, you can pick up some power, but ultimately you will need better heads if you want to go all out. The S/Rs are decent for a mild 350, but dont flow enough for a 383. your cam is designed to make power in the upper RPM band, but the heads are restricting the flow at that point. The two will fight eachother. I can say from experience that a smallish cam with really good heads is better than a larger cam with average heads. The reason being is that the small port will cause the cylinder to pull more vacuum at WOT, and the increased duration will cut more into the compression cycle, reducing the dynamic compression.

Basically you have a 383 with mild 350 parts on it, and not surprisingly, it makes the same power that a mild 350 would make as it can only move as much air as the parts will allow. Its the ammount of air/fuel the engine can take in and exhaust that makes the power, not the displacement.

 

Remember dynos are just a guideline. Your results on your dyno may differ from other dynos. I can point to dynos all over the country that are "ego killers" and others that are looser than a $3 *****.

Your engine is basically performing where you built it to perform. All I am saying is don't live/die by dyno numbers they are just a guideline. Comparing it to other dyno numbers from another dyno, from another time, in another place, by another operator, non corrected numbers, etc... doesn't tell you much. Even the same dynos aren't comparable from day to day.

 

What exhaust system should I run? I Have to stick with my hooker shorties due to cost. What tools would I need to do a custom exhaust, besides a welder obviously. How do you get accurate angles so you know where to cut?

Or should I go for an aftermarket Y-pipe to a single 3 or 3.5 and point it out in front of the rear tire?

 

Which headers do you have? Depending on the headers, it might be possible to get another y-pipe, but thats usually easier said than done. It also might be possible to modify the y-pipe to allow it to tie into a 3" exhaust. 3.5" would be nice for a 383, but even a 3" would be better than what you have now. If you use resonator type mufflers that dont restrict the flow and dont use a cat, you can probably get by with a 3" exhaust.

Since cost is an issue, flowmaster makes a single 3" exhaust for not too much. It comes with a muffler that you probably wont want to use, but it has full mandrel bent 3" pipes with a single outlet on the drivers side. Doesnt look as nice as the dual tips, but it gets the job done for cheap. The 88-89 single cat TPI one is the one you want to get. http://www.summitracing.com/parts/FLO-17151/?rtype=10

I have this system with the maxflow muffler. I dont think you can do it for much cheaper with off the shelf parts and still have a legit full length mandrel bent exhaust.

 

You're outsmarting yourself.

Forget all that.

Start with the simple stuff:

Advance the ignition timing until it starts to ping. Back it off until it quits, then just a tweeeek more. Make any difference?

Look at your jets. Buy some that are 4 sizes and 2 sizes smaller, and 2, 3, & 5 sizes bigger. Change them. Better/worse? Better: go farther. Worse: go the other way. Repeat until no further improvement is obtained.

Come back and tell us what happened.

 

Was that measured on the dyno with a wideband? Or was it just a guess? If the AFR was ~ that all the way across then the carb is probably OK at this point, even though its on the small side. You could try to go a tad richer as many stations have E10 (depending on the area), which needs to be in the 12.5:1 or so range for peak power. If you want to tune outside of the dyno, a wideband is a good investment. Guys like sofa have the experience to tune w/o them, but for the rest of us, tuning w/o one can be like throwing darts. Theyre not infallible as incorrect timing or misfires can throw them off, but they at least give some good feedback to tell you which direction your going in.

The timing also doesnt seem that bad, but depending on the CR and combustion chamber, it may need more, or even less. My experience with timing is that not all engines may encounter detonation before becoming overtimed. Again this depends on the chamber type, CR, etc. Mine just starts buzzing from having the combustion occuring too early. If its pushed beyond that, the sudden pressure spike during the compression cycle becomes so bad that it causes the PCM to loose sync with the crank position, causing a misfire DTC and an erratic miss. Dyno helps here for the rest of us who may not be used to tuning things by ear, feel, etc.

My personal feeling is that theres probably some more left in it, but Ive used those same induction and exhaust parts, and theyre a bit restrictive for performance, even on a 350.

 

These are my headers http://www.jegs.com/i/Hooker+Headers...460-1/10002/-1

I see that hooker and dougs makes Y-pipes for these headers, but do I want bigger than 2.5 for the Y-pipe too?

 

Yea I have messed with both, tweaked the timing from 30 degrees until it pinged at 38 degrees. I set it at 36 which felt the best.

I bought the jet kit for the edelbrock and messed with that A LOT and got it to where it felt the strongest with no stumbles, and left it there which is what it got 13:1 on the dyno with their wideband.

My combination was the richest jet and I believe the second leanest rod.

 

Just the last portion of the y-pipe after the two intermediaries join together needs to be larger to tie in with the rest of the exhaust. You could leave it at 2.5", but that will still be somewhat of a restriction as the headers will join together in a 2.5" section of pipe that goes back up to a 3" exhaust.

 

Yup, so what, do I have to get, or build a custom Y-pipe to get the flow I need?

 

to be continued in the spring time......

 

i used to have a 2.25 (crushed bends) Y pipe to a single 2.5 (mandrel bends)all the way to the back to a flowmaster muffler, i got a great deal on a brand new Gale Banks 3" cat back (4th gen) and i decided to build my own Y pipe using the mandrel bends from the itermediate pipe, well it took me about 8 hours for the build/install but damn what a difference, i must heve picked up at least 20hp.
If you going to do the exhaust do it right, it pays off

 

Yea thats what I'm hoping for. Your previous setup sounds pretty much identical to mine. I hope I can pick up similar gains. So your case proves that 2.5 is too small. Some guys say that 2.5 is fine, but thats obviously wrong.