I got a 71 350 malibu stock intake 670cmf Holley Street Avenger,Hooker headers and, Flowmasters.I curently have 2 1/5" pieing all the way to the back. I was thinking of going 3" but it will cut off right before the diff. I was told that there would be back presure if i did this and i would lose power is this true????

you dont need 3" exhaust for a stock motor.

The engine you describe barely needs 2" pipe, 3" is way overkill. You either were misinformed or didn't hear correctly about the backpressure though, adding 3" will not ADD backpressure, it will eliminate it. Engines need some backpressure to operate effciently on the street.

I hope i dont start anything but I used to think that you needed back pressure,but then ive been told by many people that, that isnt true and a biger pipe the better, So im still not sure who to belive..

My friend, you neen to start listening to some people who know what they're talking about. I think for the engine combo you have, that your ET is very good and only want to start talking bigger pipes when you build a bigger engine! Relax and enjoy the ride that you have. Put good on :cool: performance tires, beef up suspension with shocks and sways, springs etc. Goodluck!

True, you do nedd some backpressure. People who tell you don't are misinformed and probably are getting the most out their combo. It is improtant that since you are going through the trouble of researching things you consider the source, if you are asking the local street racer kids, you are getting the wrong info. I used to be one, they have much to learn.

Some reading on the myth of backpressure...

http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm

http://www.automotivehelper.com/topic13199.htm

True, you do nedd some backpressure. People who tell you don't are misinformed and probably are getting the most out their combo. It is improtant that since you are going through the trouble of researching things you consider the source, if you are asking the local street racer kids, you are getting the wrong info. I used to be one, they have much to learn.

umm my sorce is far from a "Ricer" but he is a MOPAR guy.

I dint get that info from a ricer.....but if I did hed problavely tell me to go with a 5" that wat most ricers have graemlins/clonk.gif ...thanks for your replies.

I think it is common knowledge now that the word 'back pressure' is a mis-used term. The fact remains though that optimal pipe size for maximum performance varies from vehicle to vehicle. Bigger is not always better. We have spent the better part of this winter running more than 60 chasis dyno runs on various street performance vehicles including a 230hp Mustang GT, a stock 160hp Monte SS and a moderately built up 315hp Pontiac GTO and the lower horsepower cars 250 rwhp and less, were slightly hurt by maximum flow mufflers like Dynomax ultraFlows. Conversely, the higher hp (250-350 rwhp) seemed to benefit from these same mufflers. Stock manifolds were on all three of the test vehicles.

Other observations; In ALL of the tests performed on the various cars, peak hp and torque increased by the use of 2.5" pipe vs. 2.25" pipe, increased by the use of Mandrel bent pipe vs compression bent pipe and increased with the use of an X pipe crossover vs straight pipe or H pipe.

In one of the more revealing tests, we removed mufflers and tailpipes from the 315hp GTO and ran an open X crossover that dumped just at the rear.... and LOST both peak torque and hp vs when the mufflers and tailpipes were in place!
We also saw some evidence that the placement of the X reflected deminished effectiveness as it moved further back in the system. However, more testing needs to be done there.

I hope there is some good info you can use here. We will be posting the results of the tests on our website later this week.