NO EXHAUST......ok?

[Mr Whippy]

It's really a myth that an engine needs backpressure to make *power*... It needs the least amount of backpressure to make it's *PEAK* power - wherever that is in the RPM band, but as always with engines, it's a compromise, you want the backpressure there to prevent the valve overlap from sending half the mixture out the exhaust at low RPMs to keep up the midrange torque, but unrestrictive enough at high RPMs to allow the valve overlap to keep gas velocity up to let inertia keep pulling the gasses out the cylinders after TDC combined with the pulse tuning of the exhaust.

But that was probably more a problem on carb or manifold injection petrol engines than direct injection diesels which inject fuel when the valves are shut any way.

I would hazard a guess that a car would make more torque all over the place, and boost sooner, with no exhaust, vs with an exhaust fitted.

If there are gains had from removing back pressure, and then at a certain point ADDING restriction makes you gain power again, I'd be rather surprised!

Dave

[Ruan]

Oh no absolutely, I was more referring to petrol engines there... Diesels really don't suffer from valve overlap, however, if they have a restrictive exhaust, they cannot get the gas out fast enough... The more you de-restrict the exhaust, the more power you'll make... I was pointing out that on a Diesel, it really won't make any difference.

The only time you'll see gains is if you tune the exhaust so that at a certain RPM it'll help pull the gasses out - just like blowing over a bottle, you can tune it to a certain frequency... Same as the inlet... But naturally this is ALL pre-turbine wheel...

[samass]

I now know the fire ring is still decent; the back box had come off along time ago and leaking into the cabin; we must have broken it when we changed the turbo

so its not blowing from the fire ring? or it is, but it wasn't, and we broke something?

'scuse my worn out mind...

[Mr Whippy]

Oh no absolutely, I was more referring to petrol engines there... Diesels really don't suffer from valve overlap, however, if they have a restrictive exhaust, they cannot get the gas out fast enough... The more you de-restrict the exhaust, the more power you'll make... I was pointing out that on a Diesel, it really won't make any difference.

The only time you'll see gains is if you tune the exhaust so that at a certain RPM it'll help pull the gasses out - just like blowing over a bottle, you can tune it to a certain frequency... Same as the inlet... But naturally this is ALL pre-turbine wheel...

Yeah, some fancy manifold might help you out I suppose. The early manifolds on the Td's are a bit crappy really, they have like a big collector that then feeds to the turbo which can't do much good for anything but those were the days.
The later cast tubular type ones seem the best all-round compromise before you go for a fancy battery area mounted jobby

Dave

[Ruan]

The later ones are shite IMHO - have you seen the bore of where the collector comes out!!!

The earlier design isn't THAT bad considering, they are just a triangle, but they've pulled 200+HP before now...