Sure. If they utilize properly sized merge collectors and the tube lengths were correct for a stock cube engine, the exhaust valve timing and valve sizing.

 

LIKE KOOKS 1 7/8s?

 

Not likely.

 

Low end torque requires a fairly short duration cam with a fairly late exhaust valve opening event. This way, you don't dump the combustion pressure from the power stroke too soon. You are trying to fully harness the power stroke before dumping the spent gases out of the cylinder. Small diameter primaries aid in retaining the pressure in the cylinder for any given cam and related valve timing events. However, as the RPM's increase (let's say above 4,500 RPM's), then the small primary tubes begin to be a choke-point as they try to flow the higher gas volume rate. You can't have it all, that's a given. For a given cam and head combination, the induction and exhaust systems further tailor the torque/HP RPM curve. For instance, tri-y headers broaden the power band while lowering peak power and limiting upper register power.

Steve

 

testt

 

I'm curious what you guys think I would gain switching from my current 1 3/4 primaries to 1 7/8. My power drops off pretty quick after peak and low end torque is good I have to ease it off the line running 275 mickey thompsons drag radials. I'm concerned more with track times then Dyno numbers, but here's my graph let me know what you think. This is a 408 through an A4 trans. Thanks!

 

The exhaust side of an engine is a "bell curve" meaning proper exhaust scavanging yeilds best power, too little makes less, too much makes less. The exhaust side of the engine is the combination of the exhaust valve diameter, the exhaust port volume, the exhaust duration, the primary pipe (header) diameter and length and lastly the secondary pipe diameter and length if applicable (exhaust system). On the same engine dyno I was able to see the results of 4 heads tested with Hooker 1 3/4" headers and Kooks 1 7/8" same cam, same intake, just changing heads and headers.

The results did not surprise me, I have had many conversations with Junior at Kooks and he believes exactly what I had found and believe. The TEA ported heads had stock exhaust valves of 1.55 diameter and made MORE POWER everywhere with the Kooks, which is what we had witnessed with our own chassis dyno. The new TFS heads carried a 1.575 diameter and didn't seem to care which header was on it, they both made almost the same power. The AFR 205 heads with a 1.60 valve diameter made LESS POWER everywhere with the Kooks headers, which I think was due to OVER scavenging.

We also had done some back to back testing of our own LS6 heads on a chassis dyno, one with 1.57 exhaust valves and smaller port and one with 1.60 exhaust valves and a bigger port, both with 1 3/4" headers. The bigger exhaust port/valve head made more midrange torque and less HP. Which leads me to believe it was being over scavenged as well.

 

03 Z06
switched from 1 3/4 Kooks to 1 7/8 Kooks. Both fully tuned and same engine temp -1 7/8'2 made 10hp/10tq more everywhere in the power range.

02 Z28 H/C car
Switched from Kooks 1 3/4 to stepped 1 3/4 to 1 7/8's - gained 8hp/5tq down low and 15hp up top.

On both Cars the bigger headers made more power everywhere.Thats fact for me

 

i ordered a pair of the s/s race 1 7/8-2x 3 1/2 kooks. hopefully they fit easy. all i have to do to get them now is call and say i approve of the shipping cost. thanks for all the post's i just hope i can sleep at night after spending northwards of 1k on headers alone. im gonna be drooling at my car again with these new editions(ms4,headers,true duals,125 wet shot) kinda a big step in power, now my ls1 should finally have more power then my 1st gen small block in the 84 though-and actually have some traction.