Mad Machinist

Suzuki employs a variable pressure system that works quite well on their GSXR1000.

http://www.superbikes.co.za/images/s...00_Engine2.jpg

http://www.superbikes.co.za/images/s...0_Exhaust1.jpg



Good day,
Mike

racer7088

NO I wasn't referring to you OLDSSTROKER !

arnie

If backpressure is induced, it is done, to achieve a NET gain. Generation of a net gain, by tailoring exhaust wave timing, to their advantage, in spite of, and even though there is a slight giveback, with any resulting extra backpressure.

Bersaglieri

I am somewhat a novice, but could the solution to backpressure end the great header debates that rage on in LT1 Tech? I have spent so much time trying to sort out the Shorty/Mid/LT information that I am confused about what is better for what. Is the LT the true almighty? Or does the Shorty rule the top RPMs. I sure as hell dont know, but does backpressure answer these questions? Also that is why I-pipe diameters are regulated, such as 3in aftermarket b/c a 5 inch one would hurt most 350 applications more than benefit from the extra flow?

-Dustin-

OldSStroker

Here are two recent threads that might help:

http://web.camaross.com/forums/showt...hreadid=215779

http://web.camaross.com/forums/showt...hreadid=232645


The first few pages of the "Myth" thread have some good, and some confusing information. Melkor has some good words.

The second thread discusses flow and pipe sizes.

If you read thru these you might get some of the answers you seek...or maybe just get more confused.

romoranger

i think the easiest answer to the backpressure/no back pressure debate would be that no back presssure, ex: a pipe which would be 8" large would allow the air to eddy and not flow at the highest rate. a certain size pipe, which would be determined by the amount of air which is flowing from the engine would be one which would allow the exhaust gases to travel fastest thorugh the exhaust piping without allowing the the air to eddy back and make an attempt and succeed in making it back to the engine (will not make it back, but will be pressuring the gases behind, therefore limiting exhaust flow). the correct piping size will still have the gases attempting to make it back, but it will still be small enough that it cannot swirl and slow down the gases behind it.

therefore backpressure in an exhaust would be gases flowing through the piping that slow down the gases behind it.
optimal backpressure is exhaust flow in which the gases flowing do not cause a signifigant loss of speed to the gases behind it

sorry about my book, this is just what i learned working on turbo cars, which require no backpressure as torque is not the main concern, and just applied to the way a n/a vehicle creates power

OldSStroker

You must mean no backpressure after the turbine, right? At turbine inlet there is probably significant backpressure, which the engine feels. Like MaxRaceSoftware said above, it depends on where you look at the backpressure.

FWIW, some car engines are turbocharged for the very reason of getting high torque at low rpm and holding the torque curve flat for maybe 2500-3000 rpm. An example would be Audi TC'd engines. WRX seems to get a torque peak around 4000 then drop off and flatten out. It appears to be an engine TC'd for mid-range torque.

If it seems like I'm picking you, that's not the intent. Just disagreeing a little. No offense intended.

MaxRaceSoftware

Will hot burnt exhaust gases "Burn a Second Time " ????

Why would you want hot burnt exhaust gases back inside your engine's cylinders ???

OldSStroker

I wouldn't want it of course. But if there was a NET gain in fwhp from adding a turbocharger and accepting some backpressure resulting from the exhaust gases drivng the turbine, I would accept that.

If there's no turbo in the system, get those nasty hot gasses the hell out of there.

If you want to burn the exhaust a second time (assuming no cats which kinda do that), how about an afterburner?

Larry, how much "extractor effect" do you think Cup cars get from placement of the flat exhaust outlet in the rocker area? It would seem the aero guys could create a low pressure area there and maybe actually measure the depression in the pipes in a wind tunnel. It might be significant at 190 mph.

romoranger

no problem at all oldsstroker, i am not really implying with stock power curves, which is something i probably should have indicated. and yes you are right, i had meant no pressure after the turbine but forgot to say that, i got a wicked concussion the other day so the fact that i am putting out somewaht complete thoughts is an accomplishment in itself today
but you are right about the high-torque at a low rpm, i completely forgot about diesels and the like. once again i should have specified for cars that are usually involved in some kind of racing, (excluding auto-x as torque is of a high concern) my head hurts so i will step down from lowly podium before i say something else dumb

Zero_to_69

Inert gases can't burn, they displace fresh intake charge

Do I get a cookie Larry/Bret/Jon?

Another related question with respect to overkill exhaust pipe volume:

If an exhaust extension pipe measures 4' x 3" (directly off the collector
of the header),
will that volume result in more backpressure due to more "atmosphere"
to overcome?

IE: Does the eddy flow, or reversion have anything to do with
the amount of atmospheric pressure residing in the pipe?

BTW: The above compared to a 2.5" extension pipe on a stock
350 CID small block spinning around 2500 RPM.

romoranger

that question i am going to have to let somewhat else answer, i do not know enough about how much exhaust and air a 350 would flow at 2500. i'll let someone who knows n/a engines and how well the stock pieces and how a piece like that would flow answer this one, no need for myself to point someone in the wrong direction

MaxRaceSoftware

Originally posted by MaxRaceSoftware
Will hot burnt exhaust gases "Burn a Second Time " ????

Why would you want hot burnt exhaust gases back inside your engine's cylinders ???

OldSStroker ..when i posted that , i wasn't replying to your previous post above mine ....but instead was just making a generalized statement towards all the other posts

----------------------------------------------------------------------------

Larry, how much "extractor effect" do you think Cup cars get from placement of the flat exhaust outlet in the rocker area? It would seem the aero guys could create a low pressure area there and maybe actually measure the depression in the pipes in a wind tunnel. It might be significant at 190 mph.

on the Intake side its easier to calculate

Peak_RamAir_HP_Gain = MPH * MPH * Peak_HP * .000001205

Peak_RamAir_HP_Gain = 190 * 190 * 700HP * .000001205

Peak_RamAir_HP_Gain = 30.45 HP gain from RamAir

usually the same psi drop on exhaust side makes at least 1/3
gain of intake side
so approx = 10.15 HP at 190 mph would be a good guess ???

and also 10.15 extra free hp would increase fuel efficiency , BSFC, and gas mileage , and could mean difference between finishing or winning NASCAR race

MaxRaceSoftware

If an exhaust extension pipe measures 4' x 3" (directly off the collector
of the header),
will that volume result in more backpressure due to more "atmosphere"
to overcome?
=======================

the wave passes right thru "medium" in extra length piece

but exhaust gas velocity would be so very slightly effected ,
you would have to have hi-tech equipment to measure

both the wave and the gas's velocity would be disipated
over time

when the collector "dumps" into the local atmosphere
you have the whole entire local atmosphere to "overcome"
it doesn't present a problem the way you are thinking the magnitude might be ?

MaxRaceSoftware

Inert gases can't burn, they displace fresh intake charge

Do I get a cookie Larry/Bret/Jon?
=====================================


Zero_to_69

you get a Star