LS4GXP

iTrader: (2)

Quick question here about cutouts with a N/A motor.

I had bought a 2005 GXP when they first came out. 303hp 323TQ LS4 grand prix. I installed a cutout where the cat was. With the cutout open and closed the car always trapped at 102mph, but with it open i would lose 1-2mph in the 1/8th.

So my question is, Before i start my exhaust will it be worth spending the extra money for an electric cutout, will it be a worthy gain for the price they go for?

joeblue83

iTrader: (8)

on my car I placed the cutout right after the y pipe meets. On the dyno there was a 60 hp difference between the 3.5 inch cutout being open and closed. When its closed its going through a 3 inch edelbrock catback

LS4GXP

iTrader: (2)

60hp seems alot, i didnt notice any difference with my LS4 at the time, and i placed it after the Y. Was alittle slower on the bottom end

joeblue83

iTrader: (8)

my 3 inch pipe was a little dented over the axle, but the dyno showed 60 hp loss with it closed

LS4GXP

iTrader: (2)

whats your compression? Not sure if that would matter or not, I didnt really look into the specs of the LS4, rather i ddont even know if the compression ratio would make a difference.

60hp is alot of feel in the pants lol and am sure alot more MPH in the 1/4. Like i said i lost mph but still trapped the same

duckmanquacker

Like i said i lost mph but still trapped the same


That tells me that you've lost some low end torque but gained at the top end. going with a timed cutout would probably help. IE closed at launch and open mid strip.

LS4GXP

iTrader: (2)

so you guys telling me 300$ IS WORTH IT FOR AN ELECTRIC CUTOUT?

joeblue83

iTrader: (8)

why not just do a manual cutout, only cost like 30 bucks

LS4GXP

iTrader: (2)

had a manual one on my LS4, hated it. Sucked taking it off and putting it on. And i lost bottom end tq and mph.

its electric or its nothing

joeblue83

iTrader: (8)

how can you lose bottom end tq and mph with a manual one, as compared to a electric one, when they are the same minus the work it takes to take the end off???

LS4GXP

iTrader: (2)

manual you take off before you drive the car (obviously) so you lose bottom end grunt, 0-60ish

electric you open up after 60ish and you wont lose the lower end tq


Makes sense too me seeing i lost 2-3mph in the eighth with it open yet still managed to trap the same speed regardless if i had it open or not.

Still trying to adjustify if the electric is worth $300.

joeblue83

iTrader: (8)

my car was the opposite. At the track with the cut out closed I had a higher 60 ft along with 1/8 and 1/4 that were also higher

LS4GXP

iTrader: (2)

no clue, unless its different with carb and F.I.

I ran my car a good 50 times at the track, everything stock but the cutout and muffler.

constant 2.2 - 2.3 60ft
constant 13.7 -14.2 ET
constant 102mph traps regardless and 80mph in 1/8th

cutout off the 1/8th dropped to 77-78mph everytime

skinny z

WHERE you put the cut out is the important thing.
Using a program like PipeMax, it can be determined where the "sweet" spot is (so to speak).
So many guys complain that running open headers (or cut outs) on their cars results in no bottom end. Well no *****. The tuning of the exhaust via collector length is one of the most misunderstood aspects of engine tuning that I can think off.
Unless you have access to such a program, the only way to determine the proper location is through trial and error. Track or dyno. Check out the quicker cars at the track or look closely at a high horsepower engine strapped to the dyno. Undoubtedly you will see collector extensions on the order of 18"-24". That's for pressure wave (exhaust pulse) tuning. Free hp if you know what you're doing.
In certain cases, (as mentioned above with damaged exhaust) any cut out MAY provide an improvement. The same would apply if the catalytic(s) were becoming clogged or if the exhaust were hugely restrictive for the horsepower being developed.

88IROC350TPI

I installed one of those $20 3" summit brand cutouts into my I-pipe it's installed pretty far back it dumps under the rear passenger seat... the car has picked up .25 and 2mph... The car will usually go 11.50-11.60's @ 119mph N/A through the single 3" exhaust and went 11.25 @ 121mph one night with a crappier 60ft with the cutout open.

LS4GXP

iTrader: (2)

Are your guys motors carb? would that even make a difference between FI ?

skinny z

It depends on the amount of overlap ground into the cam. From my understanding, EFI cams typically have a wider LSA which in itself reduces the amount of overlap. The actual cam specs would be required so as to make an educated answer.

UnderCover89TBI

iTrader: (25)

i feel a loss of lower end torque. i run mine open just a bit and it feels good throughout