Exhaust back pressure ?

I know i have lots of questions ,but here is another.I know alot but i dont know everything. Would back pressure help with torque on my motor.I dig the sound and the Up Your *** at***ude of the open headers on the street ,but i wanna have all the power i can at the DOTD .I have all the **** i took off which was a 3 inch dual Flowmaster 3 chamber set up that dumped in front of the rear axle with turndowns.I have changed so much since the exhaust were on it i dont know if it will help me or not.My set up is this.A 2700 # car ,302 H.O. with 4 valve relief flattops(im guessing aroun 9.5 -10 to 1 compression ),E 303 cam with 1.72 roller rockers,mildly milled and gasket matched Edelbrock 1.90/1.60 heads,prehistoric set of tri Y headers ,that were cut on a bit to fit the Falcon, Hopped up 600 Holley on a torker single plane ,Mallory dual point and promaster coil, 4 speed toploader ,and 3:55 gears.Dont like the sound of Flows .I could weld the tailpipes back together and put it back on but there really isnt a place to test it real hard around here ,from 0 to over 100.The Falcon doesnt like beat up roads at high speeds...

 

I have seen bracket cars with long header extensions, and a cross over. Every time I ran my camaro with open headers in high school, I lost my jump on the line, and top end mph. It sure sounded cool though!

 

I replaced the stock exhaust on my caddy with dual 3" with V-Force muff's and dumps. Lost a noticeable amount of low end torque, but gained top-end. Sounds so bad-***ed I don't care though! 472 cubes belching out those pipes sets off car alarms in the parking lots....... hee hee hee.

 

Oh, forgot..... my point was that yes, exhaust backpressure does affect torque. You'll probly gain torque by reinstalling your 3" exhaust. And "they" say Flomasters make more HP/Tq than open headers.

 

I wander if i could do almost the same thing by installing some reducers on the header flanges and keep the open header sound?

 

I would think you'd be ****in' fumes running any exhaust that exits in front of your cabin area, those g***es will **** you up! Look in the Jegs catolouge for Car Chemistry header inserts. Thats probly what your looking for. They're a baffle setup, and cost as much as mufflers, but should work for what your describin'.

Later- John

 

I was wondering why i cough all the time .I will probably get wrapped around a telephone poll long before i get blacklung from the fumes.They are long tubes that exit about where the seat is.I will look in to the baffles,thanks...

 

I think that this **** about losing torque with a bigger exhuast is a subject that has been done to death with a whole lot of misinformed **** over the years!.
You want REAL info from the REAL EXPERT?
Read this!.
http://www.geocities.com/motorcity/track/6992/vizard.html

Then again the fact i can smoke most the ricers around here who have big shiney things on the back of their cars may point to something...

 

Often any loss caused by biggger pipes with reduced back pressure is related to the fact with the exhaust being much more efficient the engine is lean now, Rejetting will likey give you more than you ever had before. Nobody though ever seems to bother. D

 

That link didn't work for me.. I'm interested in the info though if you could PM me it. Thanks.
-Anthony

 

Yeah, the theory as I've always understood it is that if you make changes to the exhaust system to make it less restrictive you have to compensate by rejetting. That's exactly why you often lose power rather than gain any when you suddenly make the exhaust so much less restrictive. How else do you think race cars get optimum performance with open headers?

 

Man, here I thought I was giving usefull information derived from personal experiance!! Ha Ha! Seriously though, ALOT of people say that backpressure affects your torque, I've seen tons of magazine artical dyno tests that seem to point to that. But I guess we don't live in magazines, and to tell the truth I did not re-jet my carb after the exhaust install. Good luck decoding all the different opinions!! lol

Later dudes- John

 

Thanks for the info guys .What your saying pretty much is that there is really no lose of power without exhaust .You just need to tune the jetting the way your gunna be driving it (with or without the backpressure of the mufflers).

 

There is a loss of power with no exhaust, if you're not running WOT. But dynos don't do a good job of capturing power in light load, low throttle situations. But since it's a low throttle situation, do you care if you've lost 10 ft-lbs? probably not, you'll just crack 10 more ft-lbs out of the throttle.

Personally, I find it hard to believe you had any backpressure with a 302 that's got 3" dump pipes. That's awful free flowing. Given everything you want out of the car, consider the header inserts mentioned above, with 2.5" mandrel bent straight pipes dumping at the axle. The smaller pipe will remove some of the lowest db that vibrate the car, but lack of mufflers will give it that agressive sound.

Good luck

 

The power of the HAMB: "The GeoCities web site you were trying to view has temporarily exceeded its data transfer limit. Please try again later."

 

They said I would lose bottom end, with my zoomies, at the track...I stuck 'em on, made a few p***es...I gained 500 rpm, and my sixty foots were better...On the other hand, my old Fairlane consistently ran better, upstairs, through the mufflers...no affect on sixty foots, but, a couple tenths off the e.t.'s, and gained a couple mph...??? no re-jetting...( my coupe is a bit rich, though, through the headers/gl*** packs, so, it seemed spot on with the zoomies...no more tears!)

 

I think this probably varies from combination to combination. More than a few pretty serious racers have gained e.t. by adding header collector extensions, and others get no gain at all. I think it is one of those deals that need testing to determine what your car likes.

Popular Hot Rodding had a project car a number of years ago that got collector extensions. They hated the way it sounded; that is, until they got the time slip, and had gained three tenths on e.t. I guess it depends what is most important to you, the sound, or how it works.....

 

All the Ford racers at Gulfport Dragway say Fords like more back pressure than Chevies. They say to add real long extentions on your collectors paint a stripe on them run your car then cut the extentions where the paint stops burning off.

 

Thanks guys for the positive feed back .Im gunna try the extensions Judd .How long should i start with ruffly before i test them to cut off ?

 

I've seen significant gains in power on milder motors WITH exhaust. It's been my experience that if it's not a big cam/headed/compressioned motor that needs open exhaust, it'll run much better with. Your combo might even perform better with 2 1/4 to 2 1/2 inch instead of the mentioned 3 inch

 

Thanks ,thanks ,and more thanks guys .Ya 'll are making me smarter by the minute .I think i will weld the tailpipes back in place and try it .I have a set of old cherry bombs .Will these work for the experiment,instead of the blowmasters ( cant stand that signature sound ,it makes me want to put a cap on my head backwards and buy a new Stang )?

 

Thank you, it will vary depeneding on cam, heads, intake, and just about everything else in the engine. Cylinder scavenging can be destroyed and raw fuel can be drawn through the engine without being burnt...

I've seen the same thing on dynos, specifically with Harleys. Straight pipes don't make power, they lose it without big cams, headwork, and on and on. Now a good 2 into 1 can show huge improvement, guess it doesn't sound right to some people. I haven't had the dyno time with a car personally to show the results, but I have seen the time slips....

 

I think Cherry Bombs would be fine

 

I don't like the Flowmaster sound either. It is worse to me with small cubes and big pipes. Magna Flow straight throughs do it for me.
Smokey

 

I haven't tried it yet. I ordered the 15" collectors for my fender well headers might try them strait and get extentions if the burn off completely. I'm trying to figure a way to get it quiet enough for the street with out mufflers maybe something that will fit in the collectors

 

I hate quoting myself. It seems egotistical... Anyways, it beats typing all this again...

Here's that thread...

http://www.jalopyjournal.com/forum/showthread.php?t=186324

 

Hey Judd tell me about the drivetrain in your Comet ,if its not to personal a question ,and your E.T. ,mph, shift points etc.I am just curious and would like to make a few comparisons ...