Twin exhausts?

The Original Tom · Post by **The Original Tom** » Tue Jul 03, 2007 7:35 pm

Did a spot of off-roading the other day (see here for pics: http://forum.difflock.com/viewtopic.php?t=11430 )

Whilst I was there, I got talking to a guy with a challenge 90 that amongst other cool toys, was sporting 2 exhausts. They were either straight through or had a single cherry-bomb each.
I was astounded at how different it sounded to the other rover V8's there (not just that it was about the twice as loud!)
I now want to do twin exhausts on mine. It's really easy as I can just use straight pipe.
My only stumbling point with this is: what's it like on performance?

Cheers
Tom.

Lewis · Post by **Lewis** » Tue Jul 03, 2007 8:44 pm

I don't think there'll be any impact on performance, in fact, if you build a good system with a link pipe (that joins both sides, I belive to aid scavenging from the cylinders or smooth the gasflow) you might gain power!

To counter that, a single system can make excellent power as well I believe (but stand to be corrected) - didn't some of the RV8 TVRs use single systems?

Although heavily silenced, was the difference something like this:

http://www.youtube.com/watch?v=zr-QbMpX0_M

RV8 Stag, twin exhaust system (no link pipe, mind)

And this:

http://www.youtube.com/watch?v=nV8F7zCBQu8

Single system, twin silencers (now most of them have gone, now it sounds like : http://www.youtube.com/watch?v=B0ssM-bndf4

)

Anything like that? Or did it sound really American and burbly - a bloke I saw around here once had an RV8 on a single system with a cherry bomb and it sounded very rorty...

The Original Tom · Post by **The Original Tom** » Tue Jul 03, 2007 9:02 pm

It was a really raw, rasping sound, with plenty of pop and bang on the over-run. Enough to shake the soul at 20 metres or so

I guess most like the last video, but you can't capture such an awesome sound accurately without some very expensive audio equipment

Plus it was a standard looking engine, on twin SU's and had a snorkle on the air intake.

Mark · Post by **Mark** » Tue Jul 03, 2007 9:59 pm

Kind of off topic

But this sounds too good to be true

http://www.corsaperf.com/flashc5.htm

Mark

kokkolanpoika · Post by **kokkolanpoika** » Wed Jul 04, 2007 6:58 am

I have read that twin system gives more top end power.. Single system is good low/mid range power.. Also single pipe share idling/ engine exchaust voice.. Not so awesome sound that twin system.

ChrisJC · Post by **ChrisJC** » Wed Jul 04, 2007 6:59 am

He probably didn't have a balance pipe, which will not help performance at all.

I had two independent exhaust systems, exiting vertically up the back of the truck cab on my landie. It sounded great, but was undriveable on account of the racket. I changed to a single system with two straight through silencers, and now it just sounds purposeful.

Chris.

tetlow · Post by **tetlow** » Thu Jul 05, 2007 8:34 pm

I have a twin system with a balance pipe just after the sump.
It sounds nice but I was told that the balance pipe made very little difference to power just gave a better burble.

I must admit I only fit the twin system for the looks and sound not any power gains.

Dave

The Original Tom · Post by **The Original Tom** » Thu Jul 05, 2007 10:45 pm

I only want the twin one for sound and looks too

Was just thinking that if I'm gonna lose a noticable amount of power it's not worth it. If I were to gain power, or could easily, then it would be a bonus, but not of great importance.
By a balance pipe, do you just mean a pipe that joins the 2 exhausts together at one point? If so, whats the point? Then you just have a single tailpipe system coming out of 2 pipes.
I thought these guys were talking about a set of crossovers, that would put alternating cylinders into the same pipe, helping resonance.
e.g firing order is 1-8-4-3-6-5-7-2.
But banks are 1-3-5-7, and 2-4-6-8.
The ideal would be to put cylinders 1-4-6-7 into one backpipe, and 8-3-5-2 into another, so each obtains regular pulses...
(pulse-gap-pulse-gap-pulse-gap-pulse-gap, repeat)
...which are good for scavenging. But this requires a lot of specialist fabrication and plubing, which is placed nicely to get ripped off on an off-roader like mine.
Also, because of the regular pulsing, I'd be worried about it starting to sound like a 4 cylinder!

The normal way (or at least the way I was thinking) was to feed each bank into a different pipe. This provides a pretty crappy irregular set of pulses...
(pulse-gap-gap-pulse-gap-pulse-pulse-gap, repeat)
and
(gap-pulse-pulse-gap-pulse-gap-gap-pulse, repeat)
...which aren't so great for scavenging, but is much simpler to implement and gives less twisted pipes to get torn off by a poorly placed tree stump.

Tom.

ChrisJC · Post by **ChrisJC** » Fri Jul 06, 2007 7:10 am

A balance pipe is just a pipe between the two independent exhaust systems. There's probably an optimum place for it, but I don't know where that is! Probably just after the downpipes turn horizontal.

Chris.

tetlow · Post by **tetlow** » Fri Jul 06, 2007 7:41 am

My balance pipe is just after the sump about 1 foot after the pipes go horizontal. The pipe is perpendicular link between the two systems.

I believe the theory is that, as the 5 7 and 8 4 parts of the firing order means you have two firings consecutively on the same bank, the crossover pipe allows the higher pressure pulse to escape into the other system. This gives you more power (back pressure drops) and a smoother note, but don’t quote me . A little knowledge is a dangerous thing.

Dave

Ian Anderson · Post by **Ian Anderson** » Fri Jul 06, 2007 8:23 am

Yes a full 180 degree cross over is great!

I have one on the GT40

And hopefully have some snarling to post next week following Gurston Downs

Ian

The Original Tom · Post by **The Original Tom** » Fri Jul 06, 2007 8:33 am

I would say that the optimum distance is the same as most things with exhausts: an exact multiple of the distance between exhaust valve seat and cylinder head-exhaust manifold face. A well tuned exhaust is an exact multiple of this value long, with any silencers / cats starting at an exact multiple. Each exhaust / cat is classed as 'free air' so the distance multiples start again after each, and their lengths is not taken into account.

On this basis I guess the link pipe should be at a multiple of thie distance, and its length should also be a multiple of this distance.

But hey whadda I know, I'm not the exhaust tuning specialist (but the bloke who told me that used to tune cars for a South African team)

Tom.

TVRTASMIN · Post by **TVRTASMIN** » Thu Jul 19, 2007 5:30 pm

I've read somewhere that with a twin pipe system you paint the two pipes, and where the paint starts to burn off or shows the hottest part, this is where the balance pipe goes.

Post by **katanaman** » Thu Jul 19, 2007 6:16 pm

TVRTASMIN wrote:I've read somewhere that with a twin pipe system you paint the two pipes, and where the paint starts to burn off or shows the hottest part, this is where the balance pipe goes.

I think that's where the collector should go not a balance pipe.

JP. · Post by **JP.** » Thu Jul 19, 2007 6:52 pm

TVRTASMIN wrote:I've read somewhere that with a twin pipe system you paint the two pipes, and where the paint starts to burn off or shows the hottest part, this is where the balance pipe goes.

This is where you'll have to cut your exhaust to get max performance assuming you have a max performance engine. In this case you don't have mufflers and balancing pipes at all......