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Discussion Starter · #1 ·
I have heard rumors that the stock exhaust manifold is restrictive. I guess my question is how much power can you make with the stock manifold before it becomes too much of a restriction? Or a better question would be, what are the highest horsepower numbers that you have seen with the stock exhaust manifold?
 

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I think the turbos you need for high-power apps necessitate a new manifold anyway. I mean you could make a custom manifold for the ct26, but the turbo would be your problem, not the mani. A few of the bigger turbos use adapters, but many require a whole new set-up. So basically your turbo will determine the manifold
 

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Moderator, l337 M0d3r4t0r
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I'm with trent.....

445 rwhp here.. We'll see what happens when I get my intercooler form RRE next week and 27PSI.
 

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someone did 520rwhp off a T04B and adapter. supraspeedmkIII i believe it is.
 

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Asshole MKIV owner.
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MKIIISupraGuy said:
someone did 520rwhp off a T04B and adapter. supraspeedmkIII i believe it is.
Correct. When I had a stock exaust manifold and a T04B and adapter I dynoed 520rwhp/492rwtq. But the car made well over 550rwhp many many times with the stock manifold. It's good for at least mid 500's rwhp. It's not as bad as many people make it out to be.
 

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Discussion Starter · #7 ·
520 RWHP on the stock manifold. Now thats impressive.
 

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Actualy, the stock manifold is better than quite a few headers that I've seen. I know the RPS one for sure has incredible poorly designed colector, I'm sure that the stock manifold is better. If you are running anything with an intergral waistgate, I say stick with the stock manifold. It utilises a split pulse design which is decent. It would probably perform better if the divider in the center of the manifold outlet was taller, but for a factory casting, it's pretty good. Aftermarket adapters I've seen for external waistegate turbos are not the best designs either. This is a problem as you become tight on space. I think if you extrude honned, pollished and ceramic coated the factory manifold with a well designed adapter for external waistegate, you could run a large turbo and still have decent throttle response (respectivly) through the factory manifold. I wouldn't be surprised to see 600 or more hp through it.
 
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Would it be beneficial what-so-ever to match port and polish the exhaust mani? I'm gonna run a 60-1, would it help at all??
 

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AEM SP63
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bigdough666 said:
Would it be beneficial what-so-ever to match port and polish the exhaust mani? I'm gonna run a 60-1, would it help at all??
Extrude hone your manifold, you'll see quicker spooling like no other.
 

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aka FredMk3
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humm how about extrune hone/ported stock exhaust mani with a 60-1 with a like 12° or 15° exh clip. quicker spool up with a bit stronger high end?
 

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The stud-bosses really impede the flow thru many (all?) of the runners. There's a good opportunity here for a high-flow direct-swap manifold. On the factory unit, there is not too much space left for honing, but as observed, even a slight improvement is very noticable.

Like many other stock parts, if you push enough boost, you CAN still get high numbers with it, but as a system component, it's still a bottleneck.
 

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i tend to agree with Jeff. it may not impede you from getting high numbers, but whos to say you wont get highER numbers with a replacement?

a basic ex mani is on my project list....
 

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"Extrude hone your manifold, you'll see quicker spooling like no other"

I got flamed here for doing that 3 years ago. Worked KILLER. Port match it to a ported cylinder head with honed upper and lower intake like I did and you will be very pleased. With a nice turbo elbow it will really work nice.
 

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aka FredMk3
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Great!

FredTurbo said:
humm how about extrune hone/ported stock exhaust mani with a 60-1 with a like 12° or 15° exh clip. quicker spool up with a bit stronger high end?
so does my idea make sense?
 

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I put the gasket between the turbo and manifold on the manifold and outlined the opening w/ a marker. Then ported the manifold to match the gasket. Looks like a worthwhile mod, I had to remove a fair amount of material to match the gasket w/ the manifold.

Dale H
87T
 
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