Vortec5300

I am wondering on average how much HP you lose/gain when opening and closing a cutout? I know it depends on the mods but...ball park.

I have a borla catback that sometimes I run the block off plate forcing all exhaust through the muffler, sometimes I run with no plates(open cutout). When I dynoed it I had the cutout open but the car is more responsive and better low end with the cut out closed...I am wondering how much HP I am losing by forcing the exhaust through the muffler eventhough the muffler is a straight through style...

Anyone dyno test the two scenarios?

I have LTs, ORY and an MS3 cam

blkZ28spt

Depends on your mods and, even more importantly, the exhaust you are bypassing.

Buddy of mine and fellow tech member recently installed and F13 and opening the cutout gained 2 hp. Exhaust is QTP LT's, ORY and slp dual/dual.

You can't be losing much.

NassyVette

iTrader: (22)

About 5 with a stock car...or so I've been told. You'd probably pick up even more if you dyno tuned it with it open.

2001orangess

i only gained 4hp. mods were slp longtubes, y pipe, lid, pulley. i think that was it

BLACKBIRD8200

I don't know about hp but at the track last week i ran with it open and closed
and with it closed i ran a 13.4 and open 13.2 it that helps

blkZ28spt

What cat-back???

Vortec5300

DAMN 2 tenths?? Thats huge! Thats atleast 20hp. Maybe there were other factors in your passes, cooler temps, etc... or something


Ya the gains depend on how good or how crappy the cat back is. I would think a cammed car would gain more with the cutout open.. My car "feels" considerably better with the block plate in there forcing the exhaust through the muffler. Smoother, more bottom end and it seems to fill that gap in the powerband from 1800-2700rpms. My guess is its killing about 10hp on mine, which sucks because I just lost 18hp from a 4.10 gear install...

ItSStock00

iTrader: (11)

I have a F13 cam only car with 1 3/4 Kooks and when I opened the cutouts I gained 20rwhp...went from 376rwhp to 396rwhp w/o touching anything on back to back dyno runs at Futral. When they were closed it was going through a Flowmaster catback. Thats prob. the main reason.

blkZ28spt

That is definately the main reason. I'd bypass the flowcrapper too!

XtrmLS1spd

iTrader: (6)

With my setup, by running through the dual cutouts, I picked up 40 RWHP over the stock catback.

ItSStock00

iTrader: (11)

Tell me about it, I can't wait to get my Loudmouth reinstalled next week.

ItSStock00

iTrader: (11)

Damn! lol, I am running dual cutouts also off the header collector.