AJAKE7796

My tranny is coming out in the next week or two. I have a modified euro 3.0 Carrera running stock cams, SSI's, twin plugged, boat tailed case, the dual inlet single outlet non-stainless dansk muffler is on it now. Last fall we put it on a Dyna pack chassis dyno and I got 180 HP at about 6800 rpm. Well stock the 930-02 CIS engines were 200 BHP at the factory. If we figure 13-15 % power loss to the rear wheel it would seem I should be making more HP with my modified engine. The engine is tight and has just had the valves adjusted. I've been told conflicting information about mufflers, they need back pressure, they don't need back pressure. Can some shed some shed some light here?
Thanks AJAKE

Chuck Harmon

You gotta have some back pressure. I had an 83SC ROW stock with 200,000 miles
on it when I dyno'd 183hp....you got some issues somewhere !
I had a cat by-pass and a Bursch muffler on my SC when I dyno'd it.
Good Luck
Chuck

art

I don't think the twin plug ignition will neccesarily give you more power. You have stock cams, etc and 180hp at wheels is only a 10% loss through the chassis from the theoretical 200 hp, so this seems pretty good.

Don't think of exhaust in terms of 'backpressure', think in terms of pipe diameters enhancing (or reducing) power or torque under certain conditions. A smaller dia pipe will flow faster, and thus enhance low rpm but will choke at higher rpm. A large pipe will not flow very efficiently at low rpm, but will not be restrictive at high rpm. This all assumes that pipe lengths are properly tuned (like SSI) to begin with. People confuse the relative restriction of a smaller pipe by using the term backpressure to describe it.

AJAKE7796

It's a bit clearer. Now that I look at I understand it as I would understand friction loss in differend diameter fire fighting hose. I've had the car for three years. I know who built the engine and a lot of money was spent on the car. It's impossible to know the real story as of this day, but I suspect the car was running a high compression set up for the track because I did discover it had recent new stock compression pistons and cylinders, wrong year gas tank, a RS lightweight flywheel and a carefully concealed welded plug for a electric battery switch cut out switch in the proper location for racing. Last year the car got a proper sorting out and I mean proper. It just would have been so much easier had I got the real story. The good news is I love the car and more importantly trust it. This year I need to learn to handle it at speed so I know the outer envelope. And tweak it a bit more if need be.....