back pressure

series3-2007 · Post by **series3-2007** » Sun Jul 01, 2012 10:19 pm

ive flicked through the previous threads and cant seem to find one on the following, "how much back pressure do i really need for either economy (i know economy doesn't really come with any v8 haha) i love the sound of just the heads no manifolds nothing just sounds awesome, but how much back pressure do i really need, could i get away with coming out the heads into pipes and then straight out, or have i gotta put a box of some description in?? any ideas guys

kiwicar · Post by **kiwicar** » Mon Jul 02, 2012 1:52 pm

Hi
For best power/ economy/ engine life/ drivability emisions the best exhaust back pressure is none! If you can achieve this then you get the minimum of inlet charge contamination and therefore the most complete burn of the fuel in the charge. Also the mixture is the easiest to ignite so you can use the leanest mixture, and as the burn is the most stable with minimum of exhaust gas contamination you can use the maximum compression without detonation which in turn helps power out put and clean burning.
All you now have to do is make the best system for minimum or no back pressure and still keep the neibours happy.
Best regards
Mike

topcatcustom · Post by **topcatcustom** » Mon Jul 02, 2012 2:34 pm

I think the reason people get mixed up with "back pressure" stuff is due to mis-wording on exhaust pulse tuning etc.

The reason you tune an exhaust is so that every pulse from one cylinder emptying into the exhaust proceeds to "pull" the exhaust gas out of the next cylinder, in effect you are using each pulse to draw a vacuum behind it, which sucks the next lot out, and so on. This is why in my mind you need to size exhaust pipes correctly, so you get good velocity. Too big a pipe and you get no pulse speed, too small and it can't travel fast enough to cause a vacuum behind it.

Don't take it for gospel, thats just how I understand it!

kiwicar · Post by **kiwicar** » Tue Jul 03, 2012 9:28 am

Certainly with most V8s this is the main effect.
Mike

SimpleSimon · Post by **SimpleSimon** » Tue Jul 03, 2012 10:29 am

kiwicar wrote:
Certainly with most V8s this is the main effect.
Mike

+1 Often see this topic appear in various places

but generally the same response

ChrisJC · Post by **ChrisJC** » Tue Jul 03, 2012 12:11 pm

And the problem with a dual-plane V8 (like the Rover engine) is that you can't properly tune the exhaust because the firing order is uneven.

Chris.

bigaldart · Post by **bigaldart** » Tue Jul 03, 2012 12:22 pm

put a blower on it and you don't need to worry about exhaust pulses!

Alan

Ian Anderson · Post by **Ian Anderson** » Tue Jul 03, 2012 12:29 pm

ChrisJC wrote:And the problem with a dual-plane V8 (like the Rover engine) is that you can't properly tune the exhaust because the firing order is uneven.

Chris.

Oh yes you can but it takes a lot of pipework and a big wallet!

Ian

ChrisJC · Post by **ChrisJC** » Wed Jul 04, 2012 7:19 am

Ian Anderson wrote:
ChrisJC wrote:And the problem with a dual-plane V8 (like the Rover engine) is that you can't properly tune the exhaust because the firing order is uneven.

Chris.
Oh yes you can but it takes a lot of pipework and a big wallet!

Ian

True. It works very well in a GT40, but not many motors have the space above the bellhousing to bring all the pipes together!

Chris.

stevieturbo · Post by **stevieturbo** » Wed Jul 04, 2012 10:57 am

bigaldart wrote:put a blower on it and you don't need to worry about exhaust pulses!

Alan

The best plan lol