enough backpressure????

[bubu]

help me a little
i have stock manifolds on my 4.3 but i had my Y pipes done to 2 1/4 inches , then removed my cat and put a freeflow muffler( out off a dakota r/t) (hey im a technician at a DODGE dealership) in it with the original exhaust from the muffler back...

i have all the minor external mods...

do you think it doesnt have enough backpressure???
thanks

[Dimemaster]

You have too much back pressure. Any back pressure is too much with a 4-stroke engine. Exhaust tuning is where the power comes from, not back pressure.

[eriks98s10]

really? i thought not having enough back pressure would hurt your engine/horsepower...

[SweetS10v8]

really? i thought not having enough back pressure would hurt your engine/horsepower...

This is the about the worst wives tail ever....

An engine is an air pump. The more air you can get in and then out, the more power it makes. Its the most basic thing you can learn about an engine.

[Dimemaster]

Exactly! When was the last time you saw an AA/FD with mufflers, or even collectors for that matter. Ever actually hear an AA/FD? How wide is it's powerband? Not very. Their engines are tuned for maximum power at a specific rpm, and they run nearly the entire race at that one rpm, using a combination of slipping clutches, gear ratios, and high-growth tires to keep the engine at that rpm. If you looked at the final drive ratios considering tire size at the line and through the traps, you'll find a spread far beyond the range of any street transmisson. Since the driveline allows the engine to run at only one speed, all tuning is done for that engine speed. You can do that with straight pipes to some degree. Another issue for race engines is the exposure of the hot exhaust valves to cool air blowing up the port. Instant bent valve if that happens. Some pipe is necessary to protect the valve from cold air.

Keep in mind that a well-tuned exhaust will still have back pressure. The more tuning favors gains in low speed torque and a wide power band, the more back pressure you get at high rpm. Compromises must be made, which is why full blown race headers don't make power on stock engines.

Some people look at the back pressure of a well-tuned exhaust and see that it is more than a straight pipe, and come to the incorrect conclusion that back pressure increases performance. Many people have preached and posted on and on about how back pressure increases power. Tuning will actually increase back pressure over a straight pipe, but the potential performance gain from tuning is a lot more than the loss from a little back pressure caused by tuning.

That said, a bit of back pressure MIGHT help an engine with a lot of cam overlap improve throttle response a bit because of the reduction of intake gases blowing right out the exhaust during valve overlap. However, that back pressure will reduce high rpm power to a significant degree, especially with dual pattern cams. In this case, the engine builder has the wrong cam in the first place. A slightly milder cam will provide the increased throttle response with less loss of high rpm power.

If back pressure created power, then ricers would stuff potatos in their fart cans and go even faster than a snail.

[flyinbryan06]

i doubt it but there is a posibilty that u dont have enough backpressure, if the truck is not responsive then thats probly why..


why exactly are u asking this, u never posted a problem??

[bonecrushins10]

i thot back pressure messed with your torque an top end
not enough low torque , to much not a nice top end

[daryl]

You want some back pressure but not too much; it comes down to the engine you are dealing with and what gains you are looking for. More backpressure is more low end torque which what 4.3s mainly are, less is good if you want to use the higher rpm (HP) more...all depends what gains you are looking for. I really doubt you have lack of back pressure though.

[93s104x4]

Everyone is right when they say that less backpressure is more power. The only reason for concern with backpressure that I know of is the fact that some vehicles' engine control modules cannot cope with too much or too little backpressure through the exhaust, and therefore cannot calculate the proper fuel mixture and will run poorly. (the 87-91 Ford trucks are notorious for this.)
In short, if you are having no problems with the way the truck is running, you probably did it a favor by opening up the exhaust.

[alscrimp]

Also remember that some of your emissions work off of back pressure built into the exhaust. EGR for one.

[kevint]

If back pressure created power, then ricers would stuff potatos in their fart cans and go even faster than a snail.


ooo, high pitched fart-very appealing to the ladies :D

your reference to the A/FD's and race engines in general is also very true. theres a reason why they have 2-3/8" primary tubes, and why 'collected' headers have 5" collectors.

Basically, everything Dimemaster said is true. Racing has been around long enough for every theory to be tested-big bore exhaust, large-plenum volume intakes (tunnel ram), 4 disk slipping clutches (what allow the A/FD's to run at the same rpm the length of the track). but I digress.