7500 RPM reliably
I don't think he's near 900whp yet, but I've seen 900+whp through a 2.5" Corsa exhaust. Look at the CTSV guys making 750+whp and running 9's with a completely stock exhaust, doesn't seem to be a huge restriction. They argue all day if headers are even worth it, they just turn up the boost or spray it. If its that big of a concern get a boost actuated cutout for way less than a full exhaust.
I think he said based on his ET/MPH and fuel consumption he was near 900fwhp. Would be really easy to test though. Dropping the exhaust and running open headers is free. I don't even know if they make a 1 7/8 header for the GTO. Just interesting to see whats to gain there.
So 750whp at best... 1 3/4 headers do that and more all day every day. 
Thread Starter
Joined: Jun 2005
Posts: 2,265
Likes: 671
From: Oskaloosa, Iowa
Just one guy in a tiny garage with limited tools doing all his own work and having fun...Just to trigger you some more my bro charger combo...I'm the slowest guy of the local group of friends I hang out with so that keeps me humble.
I'd put down a Benjamin it picks up a couple tenths and 1.5 mph in the 1/4 running 1 7/8 to cutouts. Whether or not that's worth the cost is up to OP. Considering the other items being talked about replaced, it would be cheap lol.
Thread Starter
Joined: Jun 2005
Posts: 2,265
Likes: 671
From: Oskaloosa, Iowa
From what I’ve seen it seems that header primary size does more than cat back exhaust diameter. Saw a friend pick up a ton with 2” primary, but when they dropped the exhaust on low boost he only picked up 19 rwhp if I remember correctly. On high boost dropping the exhaust gained a ton though. This was over 1700 rwhp with a gear driven Procharged 427 dart block combo though. Most events he does requires full exhaust and mufflers except for turbo cars aren’t required to run an exhaust or muffler.
From what I’ve seen it seems that header primary size does more than cat back exhaust diameter. Saw a friend pick up a ton with 2” primary, but when they dropped the exhaust on low boost he only picked up 19 rwhp if I remember correctly. On high boost dropping the exhaust gained a ton though. This was over 1700 rwhp with a gear driven Procharged 427 dart block combo though. Most events he does requires full exhaust and mufflers except for turbo cars aren’t required to run an exhaust or muffler.
Last edited by ddnspider; May 28, 2021 at 09:20 AM.
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11 Second Club
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My recipe for 8000rpm shifts reliably.
1/2" diameter hendrick .165" wall pushrods (total overkill), PSI dual springs, dell west titanium retainers, dell west titanium valves x16 with 7mm stems (overkill, but beneficial), dell west 0.075" thick lash caps (required), and wait for it... low mileage OEM gm ls2 lifters with new gm retaining cups. And my trustworthy fuchs 15/40 diesel oil that has never let a factory ls lifter fail me yet.
I'd turn it to 8200rpm, but on the stock gen4 rods i think 8k rpm will do to give it a chance at living a long(ish) life.
Vid: https://www.bitchute.com/video/KifIxIIZCKCA/
1/2" diameter hendrick .165" wall pushrods (total overkill), PSI dual springs, dell west titanium retainers, dell west titanium valves x16 with 7mm stems (overkill, but beneficial), dell west 0.075" thick lash caps (required), and wait for it... low mileage OEM gm ls2 lifters with new gm retaining cups. And my trustworthy fuchs 15/40 diesel oil that has never let a factory ls lifter fail me yet.
I'd turn it to 8200rpm, but on the stock gen4 rods i think 8k rpm will do to give it a chance at living a long(ish) life.
Vid: https://www.bitchute.com/video/KifIxIIZCKCA/
Thread Starter
Joined: Jun 2005
Posts: 2,265
Likes: 671
From: Oskaloosa, Iowa
I do have long term goals of 6 bolt heads/block and a much bigger blower which would make the exhaust more effective long term as well.
I respect your advice/input you haven’t steered me wrong in the past. You also do it without the huge ego and always rambling that anyone who does it different than you is dumb because you are better at this than anyone else lol
You aren’t wrong. I’m happy with the sound and how quiet it is right now though. My cam was custom with all things considered except for my recent intake change. With 248 exhaust duration I wonder if my improvement from an exhaust change would be less than normal.
I do have long term goals of 6 bolt heads/block and a much bigger blower which would make the exhaust more effective long term as well.
I respect your advice/input you haven’t steered me wrong in the past. You also do it without the huge ego and always rambling that anyone who does it different than you is dumb because you are better at this than anyone else lol
I do have long term goals of 6 bolt heads/block and a much bigger blower which would make the exhaust more effective long term as well.
I respect your advice/input you haven’t steered me wrong in the past. You also do it without the huge ego and always rambling that anyone who does it different than you is dumb because you are better at this than anyone else lol
Yeah if it's already 1-3/4 and dual 2.5" there may not be a lot of room to grow with the exhaust at this point.
Could always try open headers with extensions on them to see if you pick up anything.. as a starting point to see if the exh is worth fooling with.
Could always try open headers with extensions on them to see if you pick up anything.. as a starting point to see if the exh is worth fooling with.
