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Old 11-22-2012, 10:28 AM
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Single exhaust questions.

The engine for my '88 C1500 long bed is finally home from the machine shop and I'll start assembling this weekend. Time to start gathering exhaust components. The engine is an 8.75 to 1 SCR 355 with a Comp XR264HR-10 hyd. roller, basically stock '062 Vortecs, Performer intake, Q-Jet M4ME carb and HEI igntion. I have Doug Thorley ceramic coated 1-1/2" Tri-Y headers and from there I plan to run a 3" single exhaust. I used one on my last truck and it worked nicely but I want to make some refinements this time. It will have 2-1/4" pipes off the collectors into a Flowmaster Y-214300 2 into 1 collector, dual 2-1/4" inlets with a single 3" inlet. Off this collector it will have 3" pipe back to a Hooker Aero chamber muffler just ahead of the rear axle with 3" tailpipe to the back bumper. I'm not sure what the best position for the collector would be. Someone suggested putting an X pipe ahead of the collector to help quiet the exhaust. Seems like that may be overkill but I haven't ruled it out. Space is a concern as the truck has a 4/6 static drop with a flipped rear axle and C-notched frame and I don't have much room for duals or a 3-1/2" single where it goes over the axle but 3" will work with decent clearance. From my research so far a single 3" system done properly will support 350HP, I do not believe I'll be making quite that much. I'm thinking 325 at the flywheel is fairly realistic though.

Any thoughts on placement of the collector and if an X pipe would be of any benefit? Remember this is a pickup truck not a race car......

Here's the "collector"..


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Old 11-22-2012, 11:02 AM
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I think you'll be lucky to have an honest 270-280hp..

g.m.'s base crate is a 8.50 to one engine and is 260

how big a dish is those pistons to get 8.75 with vortec's
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Old 11-22-2012, 11:34 AM
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Originally Posted by gearheadslife View Post
I think you'll be lucky to have an honest 270-280hp..

g.m.'s base crate is a 8.50 to one engine and is 260

how big a dish is those pistons to get 8.75 with vortec's
GM's 350 HO crate engine is basically the same engine as mine but with 9.1 to 1 SCR and a flat tappet hydraulic cam with. It is rated at 330HP. These engines can easily make 375HP switching to a Comp 268HE flat tappet, a 750 carb instead of the 600 they are rated with and a good set of headers. I am running a Comp roller cam of nearly identical duration @ .050" as the 350 HO's cam, tighter LSA and more lift along with KB-118 pistons with a 22cc D-cup instead of the full dish piston GM uses in their crate engines. Factoring in the 12 HP or so loss from the 0.35 lower compression I stand by my 325HP estimate.
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Old 11-22-2012, 11:46 AM
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Thinking of running a similar system on my 96 c2500. I think with your drop and the gas tank layout your going to have a problem getting equal length pipes coming off the exhaust manifolds to your y-pipe. The best position I can think of off the top of my head without going into the parking lot of my work and crawling under my truck would be on the passenger side of the cab, but either way something is going to have to snake over the transmission at a spot that's compromising for a lowered vehicle (mines static 3/4 so not as bad) Just my .02 and I would love to hear a better option from someone else, as I'm in the same boat.

I would skip the x-pipe, as you're going to be joining them in a single exhaust anyways. If you want to reduce noise try using a large case muffler or possibly a cheap glasspack (as a resonator) along with your muffler of choice.

325hp at the flywheel sounds about right to me.
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Old 11-22-2012, 12:07 PM
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good luck..
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Old 11-22-2012, 03:45 PM
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I concur gearhead!
Low compression, tiny headers, stockish carb and intake. He'll be lucky to make 250!!
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Old 11-22-2012, 06:33 PM
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I concur gearhead!
Low compression, tiny headers, stockish carb and intake. He'll be lucky to make 250!!
If you don't care to believe it that's fine, I'm just copycatting an already proven combination that dynoed a lot higher than my estimation. No sweat off my nose.
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Old 11-22-2012, 06:45 PM
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Originally Posted by Valkyrie5.7 View Post
Thinking of running a similar system on my 96 c2500. I think with your drop and the gas tank layout your going to have a problem getting equal length pipes coming off the exhaust manifolds to your y-pipe. The best position I can think of off the top of my head without going into the parking lot of my work and crawling under my truck would be on the passenger side of the cab, but either way something is going to have to snake over the transmission at a spot that's compromising for a lowered vehicle (mines static 3/4 so not as bad) Just my .02 and I would love to hear a better option from someone else, as I'm in the same boat.

I would skip the x-pipe, as you're going to be joining them in a single exhaust anyways. If you want to reduce noise try using a large case muffler or possibly a cheap glasspack (as a resonator) along with your muffler of choice.

325hp at the flywheel sounds about right to me.
Yeah, there's no way to equalize the headpipes. The driver's side can come across where the stock headpipe comes over, ground clearance for the exhaust isn't the issue so much as clearance over the axle. I do plan to take a couple inches of drop out of the rear eventually. The rear sits a little lower than the front now. The truck was already lowered when I got it.

Last edited by Hippie; 11-22-2012 at 06:56 PM.
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Old 11-22-2012, 09:07 PM
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Quote:
Originally Posted by Hippie View Post
Yeah, there's no way to equalize the headpipes. The driver's side can come across where the stock headpipe comes over, ground clearance for the exhaust isn't the issue so much as clearance over the axle. I do plan to take a couple inches of drop out of the rear eventually. The rear sits a little lower than the front now. The truck was already lowered when I got it.
I remember when you picked up it, the flat black one with the nice interior right? Idk if it helps, but I could snap a shot of how the 3" exhaust wraps over my 14 bolt sf.
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Old 11-22-2012, 09:37 PM
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I remember when you picked up it, the flat black one with the nice interior right? Idk if it helps, but I could snap a shot of how the 3" exhaust wraps over my 14 bolt sf.
I don't know about the "nice" interior but it is flat black. Boy oh boy is it flat black......
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