Deadcarny

wow, this thread really went to crap...

the topic of the post was pretty simple "Cut-out @ TRACK"!! The original poster was only concerned about at the track and now people are bickering about under 2k RPMs! Lets just let this rest guys.

Capn Pete

In the blue corner, we have STEVE! And in the red corner, we have FRANK!

*ding! ding! ding!*



C'mon boys, don't get this locked. I'm sure there is a fine line between theory vs reality, and sometimes BOTH can be right, and sometimes "theories" may actually be true.

If an accurate test could be setup, it may be true that a car with high flowing exhaust and too little back pressure may actually perform worse for in-town, city driving. However, I think everyone agrees that on a race track, where engine RPM's are always kept high, the better flowing exhaust will out-perform a more restrictive exhaust.

Hence, at the track un-cap your cut-out.

Mikie

Yeah,
I come in here to view everyones opinions on the backpressure view and I see Frank bashing Steve again for no reason.

Man why are you so obsessed with b!tchtalking Steve?
I swear to God if you dont stick to the topic instead of bashing him with quotes about how slow he is then Im gonna talk to Jason D. and see what can be done about people like you.

I could see if Steve made a remark about your car or the LT1 in general , but he didnt.

GIVE IT A REST ALREADY DAMMIT

Mike




Now on to the backpressure thing....
It was my understanding that a cut out will improve 1/4 mile times by moving the curve higher. I think you lose nothing , but it feels like you lose during normal driving since the curve is higher.
I think that is why they made the electric cut out and that should solve the problem.
This is merely an opinion and for God sake it could be wrong , but since Im in an LS1 I hope not to be ridiculed and flamed for my observations

Bob Cosby

E-gads. Just a couple of comments...

A famous Pro Stock drag racer once said that the seat of the pants is the worlds biggest liar. Wise words.

I no longer have an LS1, never had an LT1, and have never had a 'cutout' that I could cap or uncap. However, in my old 88 Coupe, I used to disconnect the mufflers at the track, essentially the same thing as "uncapping" the exhaust. On a Mustang it is real easy - to bolts per side, and then just let the muffler pipes hang down. The exhaust exits the H-pipe (or X-pipe) where it would normally bolt to the mufflers.

Anyways, that was always worth a tenth at the track. The problem with using that as a basis for increased power is that tracks vary, weather varies, track conditions vary, and even your driving can vary. I finally tried it on the dyno just to see what it was worth (if anything). Results. It should be noted that at the time, the car had 1 5/8th headers, 2.5" off-road H-pipe, and the stock catback (yes, stock). No doubt that was the "cork" in the exhaust system, and getting rid of it (via disconnecting) helped quite a bit. As an FYI...
at the time of that dyno, the car ran mid 12's @ ~105-107 mph at a raceweight of ~3150 lbs.

I did the same thing a while back with my near-stock 99 Cobra. The difference is that it had stock exhaust manifolds (restrictive), an aftermarket catalytic X-pipe (more restrictive than an off-road pipe), and a Magnaflow catback (less restrictive than stock mufflers). Disconnecting the mufflers resulted in virtually no difference in HP anywhere in the rpm band. I do not have a scan of those dynos because there simply wasn't any real difference.

Conclusions:

In the case of the 5.0, the exhaust was really "corked up" by the stock mufflers. Getting rid of that restriction helped noticeably and measurably.

In the case of the Cobra, the restrictions in the exhaust were elsewhere in the motor, ie the stock exhaust manifolds and the catalytic X-pipe. In addition to this, the aftermarket catback flowed quite well. Taken together, unbolting the mufflers did little to nothing for performance.

I would think that this info could be applied to most any typical n/a motor.

EDIT: Here is a thread from LS1Tech that references gains seen by some of the racers over there.

Steve Y

Yes, this is all I was trying to say. There is a dyno test in last month's issue of 5.0 Mustang magazine that supports this. They had a car like mine with a cat-back, K&N, removed silencer, etc. Then they installed an off road x pipe. The car lost as much as 10 rwtq below 4000 rpm. It gained as much as 5 rwhp above 4000 rpm. So for in town driving the loss of low end is probably not worth the small gain up high. At the track it is likely a different story.

Steve Y

So how much e.t. and mph would I likely gain if I put cutouts on my car? Right now the whole exhaust is stock. Where should I place them for best performance? I was thinking in the H-pipe right after the first set of converters (there is no room further upstream).

shocker45

i have a 67 camaro with a 355. i gained .1 in the 1\4 mile by installing a h-pipe.
i havn;t gone to the track since i got cut-outs. but i have a noticable torque loss under 2500 rpm. it might be in my head. but it feels a hell of a lot slower comin out of the hole.

WS Sick

For comparissons sake my best freind has an 86 T/A the exhaust consists of 1 3/4 SLP headers and 3 inch Ypipe dumped into a 3 inch pipe through the cat area into a 3 inch cat-back. The motor is a 10.5 to 1 compression 383 TPI motor (big runners, ported plenum and base, monoblade) his heads are ported 292s.
its an auto with 3200 stall and 3.73 rear gears. through the exhaust he ran a 13.2 @ 108 mph, with the cut out open he ran a 12.72 @ 113 mph. Another frieind has a 2002 WS-6 that has shorty headers, cat-back, lid, freemods and a cut-out. with the cut-out closed he peaked at 324 ft #s of torque and 318 hp. with the cut-out open he peaked 338 torque and 327 hp with the graph above the closed #s all the way accross and absolutely leaving the other #s after 3500 rpm.
Bob has a good point about efficinecy of what you have. Its obvious your exhaust can only flow so much so if you go past that point it will do no good. Also pulse tuning is very critical. A very renouned builder (David Vizzard) said that ion some cases a length of pipe with a box on the end of it (not a muffler just an open box) with the outlet the same as the inlet but of a certain volume, helped scavenge the exhaust better and create more poer than a stricktly open header that had turbulance., the back pressure was also reduced with the box.

Steve Y

WS Sick

If you come over I'll see if he'll let you drive it.

You didnt understand a word I said did you?

WS Sick

Read some of this Steve, its pretty interesting.
http://web.camaross.com/forums/showt...hreadid=215779

Steve Y

Where do you live? Maybe I will come over. You said the car gained .5 and 5 mph with the cut out open over a VERY free flowing exhaust. That would mean 40-50 horspower over a VERY free flowing exhaust.

WS Sick

It was not a free flowing exhaust, The motor your questioning was far outpacing the ability of the exhuast to scaevnge the system. If you look at an F-body exhaust system (even with larger dia. peices added) the system if far far from optimal for a 350 much less a 400 plus horse 383.

I live in Kingfisher Oklahoma about 30 miles NW of Oklahoma city , name is Perry Peterman, there are three Petermans in the book (related to all of em) so I'll be easy to call. Dont call after 9 the kids are in bed.

Steve Y

1 3/4" headers and full 3" exhaust with no cats is restrictive to a 383?

WS Sick

3/4 inch SLPs and their Y into a SINGLE 3 inch pipe is restrictive on a 350 that sees over 5800 rpm.
Let me put it this way, with a pressure gauge hooked to the pipe before the cut-out with the cut-out closed we had 11 psi (5 is border good). with the cut-out open we had 2 PSI.
There is a book out there by a well known and well respected individual named David Vizzard "How to build Horsepower" volume 1. He put a set of headers and pipes on an 80 Z with a pellet type converter and the 70 hp 350 stocker. He reduced the backpressure by I think it says 6 psi and he gained 27 hp with that crappy motor.