Steve Y

Yes this is correct. My point was you lose low rpm torque with too little backpressure and drivability is affected. I put an off road H-pipe on a '95 5.0 and lost a ton of low end and drivability.

Projectz28

maybe the problem wasnt the H-pipe. I'm not saying you are completly wrong here. Heck I'll go along with it... but if you have drivability problems from opening a cutout or putting on an H pipe.... I'd start looking elsewhere for problems and not blaming it on backpressure. Lets assume it is true, the 5 ft lbs you loose at 1600 rpm is not going to cause a drivability problem. You probably wouldnt even know it. If you do then you have lost alot more than that 5 ft lbs.... a cutout or H-pipe didnt make the engine fall on its face at low rpm.

Plain and simple, if you lost enough tq at 1600 rpm to cause a drivability problem, look elsewhere. I have yet to see proof that you loose low end tq from a cutout. even on an engine dyno you would not see this as they dont run WOT from 1000 rpm. Same goes for a chassis dyno.

back to the original post.... this has been argued on this board for years... the simple truth... open the cutout and your times will improve.

Steve Y

I put the H-pipe on, lost a ton of low end (probably 25+ ft lbs). Put the stock H-pipe back on, and gained a ton of low end back. Yes an open cutout will improve times, but I bet from idle to 2500 rpm you will lose torque. When drag racing, the motor is usually above 4000 rpm almost all the time.

Capn Pete

For things to be optimum, you probably need to do more than simply open up the exhaust and expect the best #'s. I think by opening up the exhaust, you will let the air flow better through the motor, and probably lean out the fuel mixture. Maybe the case with your 5.0L was that the fuel mixture down low was affected, and maybe not suitable for the opened up exhaust?? I'm not saying that is the exact case, but all my point is, is that maybe there are reasons why a car will lose low end torque by opening up the exhaust that could be compensated for somehow?

Just like cams and heads have to be "matched" somewhat, maybe a super free-flowing exhaust on a mild engine is "too much"?! (in the case of low end torque anyway).

12SCNDZ

My personal experience is a .2 second difference with the cut-out open. 12.25 with it closed...12.05 with it open.

Frank

Deadcarny

the reason open headers lose power is because of scavaging problems. not sure how it works, but i have seen open headers lose power at levels all the way across the boards. this holds the same affect as too large of a exhaust port or too large of a primary, I guess the exhaust comes out the valve into a large open area and just sits there. I am not an exhaust or physics specialist by any means, though. I have never seen a drop in power from a cutout that was mounted back under the pass seat on an f body. with my car, I usually dyno from 3500 up, but i did dyno once with a bolt on motor from 2300 and up capped and uncapped. the capped run was made 6 minutes prior to the uncapped run.

uncapped:
hp was up at the start and came even around2600 before rising again. after 2900 rpm, HP stayed RIGHT AT 9HP above the capped run all the way to redline
Tq was dead even at 2300 and by 4000 there was a 10 ft-lbs gain that stayed there till redline. TQ was dead even from 2300-2750!

i think it is safe to say that tq would have been dead even down to 2000, and below 2000 if there was any drop in TQ it was minimal and would not be noticed. I think the whole thought of losing a lot of tq and drivability is because the noise it creates plays mind games with you at the lower rpms....when it sounds like an old shrimp truck (work truck) you think to yourself about how weak it is. tap the gas and see how the throttle responds and you will se that there really is not a difference.

Steve Y

Last month's 5.0 Mustang magazine (I know this is a Camaro board, but and engine is an engine, pretty much) had an interesting test. They did all the bolt ons on a car like mine. Very early in the test, the car lost 10-15 rwtq below 4000 rpm with the addition of an off road x-pipe. It made more torque and power above 4000 rpm with this pipe.

Got-LT1

This may very well be true, but I still feel that if the exhaust is matched to run only an open cutout you will not lose ANY torque.

BTW: The article is not mine, I found it a while ago, and I don't agree with everything, but I do agree with the jist of it.

ianfromMA

just to start off why that whole paragraph sucks...you are sucking through a straw. and engine is BLOWING exhaust. also, it PULSES, it does not come out in an even flow. what that guy said makes sense to me.

and to who said it results in a loss of torque below 2000 rmps. why would you ever be below 2000 rpms in a race?

12SCNDZ

Steve,
You seem to be big on fact vs. theory. Here's a dyno sheet that disproves one of your theories. Mid length headers make MORE top end HP than LT's do.

http://www.geocities.com/max_wylde/dyno.html

Next FACT. My car drops 2/10 with the cut-out open. My 60's are identical with it opened and closed. 60 ft. times are a pretty good indication of low end torque, right?

You've tried this in other threads. You come off as being an expert about things you know nothing about. I hate to point out the obvious AGAIN, but you own a 14 second Mustang! I could eat a cheeseburger and tune the radio while racing something that SLOW! Do us all a favor, leave the PERFORMANCE questions to those that know about performance.

Frank

Steve Y

Sucking, blowing, steady, pulses, it doesn't matter. Bigger tubes offer less backpressure than smaller tubes. That's why your paragraph sucks.


You wouldn't. Some of us drive our cars around town and like low rpm torque.

Steve Y

Oh god, you again. In some cases they probably do. Not in all cases.

If you have tons of traction, probably.

Fact: off road H or X pipes usually cause a stock engine to lose low rpm power.

I never said I was an "expert." I just said too little backpressure results in a low rpm torque loss. Dyno a stock LT1 with stock exhaust, then with 12" long headers open to the air. I bet you the 12" header would cause a loss of low rpm torque. What does driving a 14 second Mustang have to do with knowledge? Nothing. What does driving a 12 second Camaro have to do with being an egotistical jerk? In your case everything. The speed of someone's car has nothing to do with their knowledge, genius. You are probably the type of moron that thinks big short runner intakes help low end torque also. Have you ever read a dyno chart? Can you even read, or is someone reading posts for you and you dictate back for them to type. I get dumber everytime I read one of your posts. I'm putting you on the "don't feed the trolls" list.

WS Sick

Steve, show me a Dyno that measures torque at 2000 or below and then we can go prove your theory. I think youre confusing pulse tuning with back pressure.

12SCNDZ

Gee, Steve, It's a a shame you can't undestand FACTS! What I post are facts. Read back through them. I post about how my car runs and what each difference I make to the car affects performance. Some day, maybe you'll understand REAL WORLD performance when you get out of the 14's.
See, I was once like you...Oh wait...That was in high school...but anyway. You know? Read every magazine, and hope someday you'll have a real car.
You telling me what I'm doing wrong would be like me trying to tell Pat Musi what he's doing wrong...Just because I read it in a magazine?! I know Pat wouldn't listen to someone who has a 12.0 second car...So, Steve, why should we listen to the THEORIES of a 14 second Mustang owner? The speed of my car has been used for comparison purposes.
Yea, Steve, I can read. See, I read all the 5.0 vs. LT1 and later 4.6 vs. LT1 and LS1 articles. That's how I knew not to buy a Mustang. Obviously you missed those articles. Should we analyze it further? We know girls like Mustangs...Lacking in other departments, Steve? Hey, relax, I hear Viagra is cheaper than a Mustang.

I joined this thread to state facts. I also made light of the fact that you have no clue what you're talking about.
So, you want to know if I can read? Yea, Steve, and I can also tell you that I've probably forgot more automotive knowledge than you'll ever have. See, I'm not new at this...I've been around drag racing, and cars my whole life. I've seen first hand what works and what doesn't...As a matter of fact, for the past 14 years, I've been a Professional automatic transmission builder.
I'm at the track atleast twice a month, if not more. I attend all 3 NHRA events in my area each year, and I participate in many
F-body, EFI, and GM events every year. I ran at 4 different tracks last season.
BTW, you got Bob Cosby involved in one of our other threads. Funny thing is, Bob seems like a really nice guy, and his car is very impressive. I'm not afraid to give credit where credit is due...The only problem is, Steve, you're not due any!

Frank

Steve Y

What is your I.Q., 20? That's the problem with these car boards. There are too many uneducated grease *****. What does all this drag racing experience you have, have to do with the FACT that too little backpressure causes a low rpm torque loss? Nothing. The speed of someones car has nothing to do with knowledge. I know plenty of people that go out and buy a 9 second crotch rocket. Do you think that all of a sudden they know everything? Yeah, Mustangs aren't real cars and LT1 Camaros are . I know all about LT1s, LS1s, Cobras, Mustang GTs, etc. I have been driving, racing, and wrenching on LT1s for 9 years. Yeah, people that drive Mustangs have problems with the ladies. Nice stereotype Cooter. I've been racing and going to the track for 14 years. I would never step foot in a transmission shop that had you on site much less trust you with my transmission rebuild! I'm really hurt that some internet retard isn't going to give me credit.