Any gain to be had ?

[JSF55]

Was under the pop checking out the grinding marks left on the exhaust box after going over the kerb and looking at the Y piece ,it's SD1 down to this, i could easily upgrade from 2" to 2.5" but would there be any gain ?

[ramon alban]

but would there be any gain ?

It very much depends upon what your requirements are.

For 'balls out' power you might like to increase the overall diameter (and keep on increasing it) at the expense of driveability and economy, or by keeping the original exhaust properties, settling for something smooth and economical.

Here is a small extract from an essay I wrote on the subject of RV8 exhaust systems.

The average owner (like me) does not have any idea of optimal exhaust pipe sizing and
considering the random nature of an exhaust system, things like bends or kinks in the piping,
temperature fluctuations, differences in silencer design, routing over axles, etc, make selecting a
pipe diameter little more than a guessing game for anyone other than trade professionals, and
even then, I doubt the best QuickFit technician would be able to tell “ ‘ay from a bull’s foot”.

Sadly then, we have to rely on perceived wisdom and the best anecdotal evidence seems to point
at the following: - For engines making 150 to 250 horsepower the generally accepted maximum
diameter is 3”. For 250 to 350 horsepower, then 3 to 3 ½ inches is used. Over that, 4 inches is
needed. If a Rover V8 ever gets up around 400 to 500 horsepower an open exhaust beckons. That
should sort out the neighbours.

If you want to read the whole essay go to this link

http://www.vintagemodelairplane.com/pag ... ust01.html

and download the accompanying PDF - its a good read!

[JSF55]

Thanks Ramon, i had already read your write up, i just wondered if anyone had tried something similar, suppose i could always try john

[Darkspeed]

I can't quite get a feel for what part of the exhaust you are referring too - Likewise what is the tune of the engine - how much power is being put through it.

[JSF55]

Ah .... i found a pic ! thats it on the left

engine is +20 3.9 crower 50229 cam 500 eddy and manifold, bit of porting on the heads, 75 shot of nos on the strip but car used a load on road. it's also running an zf4hp22 auto, john

[Darkspeed]

What is the diameter of the pipes that form the V - they look a slightly bigger diameter than the outlet from the headers
The 2-1 collector looks very short - and are you saying that the final pipe out of the car is 2"? OD or ID

[POAH]

engine is +20 3.9 crower 50229 cam 500 eddy and manifold, bit of porting on the heads, 75 shot of nos on the strip but car used a load on road. it's also running an zf4hp22 auto, john

what sort of power are you running without the N2O?

[JSF55]

What is the diameter of the pipes that form the V - they look a slightly bigger diameter than the outlet from the headers
The 2-1 collector looks very short - and are you saying that the final pipe out of the car is 2"? OD or ID

The piece where the V connects is 2 1/2" o/d, the 2-1 collector is the standard SD1 piece, the rest of the system is 2"o/d out with one Jetex stainless box

[JSF55]

engine is +20 3.9 crower 50229 cam 500 eddy and manifold, bit of porting on the heads, 75 shot of nos on the strip but car used a load on road. it's also running an zf4hp22 auto, john

what sort of power are you running without the N2O?

I've estimated it at about 230-240 bhp, got a Innovate MTX so never taken it too a rolling road