Twin exhausts

DaveEFI · Post by **DaveEFI** » Thu Jan 08, 2015 11:12 am

On an RV8, what are the pros and cons with having two entirely independent exhausts (left bank and right bank) over combining them at some point? Ignoring material costs.

Spongo · Post by **Spongo** » Thu Jan 08, 2015 2:10 pm

OOOOOOeeerrrrr big can of worms but from my very basic knowledge a balance pipe is required between the two to help the scavange effect that the exhaust pulses create, these help draw them away from the engine and make it breath better. The actual distance that the balkance pipe is from the engine can also effect the engines "breathability" as well.

I am sure there will be many more people with more knowledge than me to come up much more detailed answers

v8250 · Post by **v8250** » Thu Jan 08, 2015 3:49 pm

Spongo wrote:OOOOOOeeerrrrr big can of worms but from my very basic knowledge a balance pipe is required between the two to help the scavange effect that the exhaust pulses create, these help draw them away from the engine and make it breath better. The actual distance that the balkance pipe is from the engine can also effect the engines "breathability" as well.

I am sure there will be many more people with more knowledge than me to come up much more detailed answers

"wot ee said, gov'..."

I have this point to address on the MG - twin tail pipe exhaust system c/o MGOC/made by Double S in Devon; but has no balance pipe or x-over. And that does not make for a good V8 system. Nor, in fact, is it a very nice sound.

My previous V8's I've always fitted a 1.5-1.75" balance pipe where a x-over is impractical, normally located close to the narrow point of the bellhousing. It must be of a flexible joint/pipe material. Too small/big a pipe dia and the scavenge pulse is either too weak or too strong resluting
in loss of efficiency and ultimately power.

Google search 'v8 exhaust x-over / h pipe', there's a lot of good tech data out there. Also worth reading up on v-twin and 2-stroke engine exhaust systems as both rely of the exhaust frequency to gain/maintain power.

As an aside, I've always had a 'thing' for pulse jets. Have you seen this?
The crazily great Colin Furze

cammmy · Post by **cammmy** » Thu Jan 08, 2015 3:53 pm

Depends on the tune you are going for really. The best is to actually merge both into a single pipe for (from memory) 18" - 24" before splitting them again.

Spongo · Post by **Spongo** » Thu Jan 08, 2015 4:12 pm

Thats what my Rangie has its merged into a single silencer

"honestly officer" then splits into 2 again before blasting out of the back

ChrisJC · Post by **ChrisJC** » Thu Jan 08, 2015 10:28 pm

I did two separate systems on my Landie for a bit. Very noisy and sounded rubbish. The balance pipe made it sound much better.

Chris.

v8250 · Post by **v8250** » Fri Jan 09, 2015 8:12 am

ChrisJC wrote:I did two separate systems on my Landie for a bit. Very noisy and sounded rubbish. The balance pipe made it sound much better.

Chris.

This +1.

Dave, thought it would be good to share some different sounds of exhaust for all.

1. MGB V8 conversion with no balance pipe/x-over with a slightly livelier cam. To me, and it's a personal thing, this is not a good sound at idle and low rpm.

2. MGB V8 with Cherry Bombs - this does sound sooooooooooooo good!

3. Conventional V8 with single sports...it sounds very good

4. And finally, some old codger in a home brewed special...would your bonnet look as good...? And maybe struggle with the neighbours...

'Hello Perry...'

Pitschi · Post by **Pitschi** » Fri Jan 09, 2015 8:25 am

Spongo · Post by **Spongo** » Fri Jan 09, 2015 1:39 pm

There is a not very scientific way of finding out where the balance pipe needs to be, go for a fast blat and see where the exhaust is hottest, that was what I was told many many many years ago. Dont think this was exactly very well constructed as an idea but if it works

Devonrod · Post by **Devonrod** » Fri Jan 09, 2015 4:36 pm

I have a balance pipe around the gearbox area, straight across, between the pipes, not ideal but my exhaust goes where I can run it, then there is a kick up the width of the pipe, then straight through oval 18 inch boxes just before the rear axle then the pipes go under the axle to the rear, its not noisy at all, sounds great.

Ian Anderson · Post by **Ian Anderson** » Fri Jan 09, 2015 6:54 pm

Rover 3.9 V8
Full 180 degree cross over

Basically take the middle 2 pipes from each bank and put them into the other side collector

It then pulses alternatively down each pipe

Or sounds like 2 straight 4 engines in perfect unison

Ian

volospian · Post by **volospian** » Fri Jan 09, 2015 9:51 pm

No balance pipes on mine (although it's not an rv8). Mind you, each header goes straight out the side of the car in to a 5" side pipe. I think it sounds fine

unstable load · Post by **unstable load** » Sat Jan 10, 2015 5:36 am

Spongo wrote:There is a not very scientific way of finding out where the balance pipe needs to be, go for a fast blat and see where the exhaust is hottest, that was what I was told many many many years ago. Dont think this was exactly very well constructed as an idea but if it works

I was told to give it a spray of aerosol paint and go for a blat. Where the worst burning of the paint stops is where the pipe needs to be.

Same for tuning a 2-stroke pipe, cut the tailpipe off at the hottest point.