I got a question. I have a 350 in an 86 IROC that has been rebuilt with flat top pistons, Pro Topline 200cc heads,Comp 1:6 roller tips, XE274 cam, RPM Airgap, Holley 750 DP. Also has a T-5 and right now a 3.73 rear. Have a 4.10 rear I'm setting up right now. Last thing I haven't modified is the exhaust, because of various reasons it has always been put off for something else. From the manifolds all of the way to the gutted cat and 2.25" I-pipe. The car feels good now.

How much is this holding it back, 20 hp? More or less? I read guys saying that the stock exhaust is holding back their LG4 and I'm kinda like

Also for this setup is the Hedman shorties with the Y-pipe modified and a 3 inch cat back about right? Thanks for any input.

 

I have allways thought the exhaust system should be the first upgrade unless you are doing everything at once. I can tell that your exhaust system is holding you back big time. I would bet you are loosing way more than 20HP. The biggest single seat of the pants improvement was when I put headers on my car. Allen

 

I'd guess it's costing you at least 50 HP. Probably more. Maybe ALOT more. HP comes from RPM, and that is precisely what you are losing.

It would be really fun to go get a dyno printout now, and one after headers and a cat and cat-back.

That way, you could tell us all exactly how much difference it makes.

 

Thats what i was going to say, about 50hp or so. After you reach the power limits of the stock exhaust it really starts hurting power quickly. Swap in some headers and atleast 3" all the way back, and you will be suprised at the power increase.

 

Yes, shorty headers work really well and a 3" intermediate pipe to a high performance muffler will make a huge difference.

 

The more power improvements you do to the engine without touching the stock exhaust, the more power it will rob you of.

 

Thanks for the info guys. It ran a best of 14.05 @99.7 mph last fall with a 600 Edelbrock and 3.42 peg leg rear. Sounds like there is quite a bit left to get out of it with an exhaust upgrade. Wouldn't mind getting a 12 second time slip with it someday.

 

With good flowing exhaust it will probably break into the 12's.