2.5 vs 3 inch exhaust video - ZR-1 Net Registry Forums

LGAFF · 05-19-2016

https://www.youtube.com/watch?v=_PVXvHkr-Vs

XfireZ51 · 05-19-2016

The one thing I would suggest is that they should have gone the next step. They should have adjusted the AFR to optimize just to compare apples to apples.
The 2.5" was fatter so I am curious as to what would happen if you leaned it out a bit.

-=Jeff=- · 05-19-2016

I liked the Clamp with the O2 fitting in it.

I agree with Dom, adjust the A/F to be apples to apples

Also this will lead to the obvious corsa vs B&B debate.. mufflers and resonators are different too.. both are not the same design like that video

Paul Workman · 05-19-2016

Very interesting.

These tests were on a 454 BBC w/ 2" LT headers. So, here's the first thought popping into my head:

Similar results, far as which makes more power/torque were recorded on the Dynojet by Pete, cid unknown.

However, Marc performed a similar test on a Dynojet comparing the 3" system to the Corsa (again, cid unknown) with opposite results - the Corsa came out on top. (If a baseline w/ open headers was done for either, IDK)

So, the question: What would the difference be on a 350 LT5 for the two diameters vs. what would the difference be for a 427 or 441 cid motor?

One thing seems pretty clear tho... The 3" to 2.5" restriction at my mufflers (Magnaflows) prolly ain't doin' me nuttin' good!!!

And, good question, Dom, w/ regard to the two different test results: Pete's vs. Marc's.

Thanks, Lee.

mike100 · 05-19-2016

Well...even the stock LT5 pipe size is 2.7" (not counting he resonator restriction etc.), but putting a 2.5 pipe on a 600hp 454 is undersized for all but a stock 230hp truck mill. If that thing is .030 over it is probably 468 cubes.

There was one comment that the dyno plot is at wide open throttle and those gains were across the board for that one particular load condition, but I can tell you from previous experience on a solid roller chevy 350 w small headers that it had less off idle punch and a softer midrange throttle response on dual 3" than with dual 2.5" pipes. Of couse it gained 3 mph in the 1/4 mile- but driveability wasn't the same for sure.

05-19-2016	#1
LGAFF Join Date: Mar 2007 Location: Crystal Lake, IL Posts: 7,194	2.5 vs 3 inch exhaust video https://www.youtube.com/watch?v=_PVXvHkr-Vs __________________ LGAFF 90 #966-150K miles-sold 92 #234-sold 1987 Callaway TT #17 1991 ZR-1 #1359

05-19-2016	#2
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Re: 2.5 vs 3 inch exhaust video The one thing I would suggest is that they should have gone the next step. They should have adjusted the AFR to optimize just to compare apples to apples. The 2.5" was fatter so I am curious as to what would happen if you leaned it out a bit. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

05-19-2016	#3
-=Jeff=- Join Date: Jul 2007 Location: Bartlett, IL Posts: 7,169	Re: 2.5 vs 3 inch exhaust video I liked the Clamp with the O2 fitting in it. I agree with Dom, adjust the A/F to be apples to apples Also this will lead to the obvious corsa vs B&B debate.. mufflers and resonators are different too.. both are not the same design like that video __________________ 1990 Corvette ZR-1 #1051 Watson Headers (2" Primary) - Flowmaster Cats - Borla Catback Late Model IH - Plenum Coilovers - 4.10s Custom Interior NCM Lifetime Member #978

05-19-2016	#4
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: 2.5 vs 3 inch exhaust video Very interesting. These tests were on a 454 BBC w/ 2" LT headers. So, here's the first thought popping into my head: Similar results, far as which makes more power/torque were recorded on the Dynojet by Pete, cid unknown. However, Marc performed a similar test on a Dynojet comparing the 3" system to the Corsa (again, cid unknown) with opposite results - the Corsa came out on top. (If a baseline w/ open headers was done for either, IDK) So, the question: What would the difference be on a 350 LT5 for the two diameters vs. what would the difference be for a 427 or 441 cid motor? One thing seems pretty clear tho... The 3" to 2.5" restriction at my mufflers (Magnaflows) *prolly ain't doin' me nuttin' good!!!* And, good question, Dom, w/ regard to the two different test results: Pete's vs. Marc's. Thanks, Lee. __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

05-19-2016	#5
mike100 Join Date: Feb 2011 Location: San Marcos CA Posts: 1,802	Re: 2.5 vs 3 inch exhaust video Well...even the stock LT5 pipe size is 2.7" (not counting he resonator restriction etc.), but putting a 2.5 pipe on a 600hp 454 is undersized for all but a stock 230hp truck mill. If that thing is .030 over it is probably 468 cubes. There was one comment that the dyno plot is at wide open throttle and those gains were across the board for that one particular load condition, but I can tell you from previous experience on a solid roller chevy 350 w small headers that it had less off idle punch and a softer midrange throttle response on dual 3" than with dual 2.5" pipes. Of couse it gained 3 mph in the 1/4 mile- but driveability wasn't the same for sure.