Stainless Steel Exhausts

Partly, and mostly, but not entirely. Improving the flow at the exhaust is good, but only if you have also gas-flowed the inlet and exhaust manifolds too (yes, ans perhaps looking at trimming on the heads themselves to get rid of any stepping where they meet the manifolds). The science (The little bloke at RPI does this quite well) is to ensure a good, clean flow throughout the entire process. Improving the flow at one point is ok, but will only provide marginal results compared to improving the flow throughout.

Erm, if that makes sense :-)

It makes sense! - but there seem to be a fair few people with saab turbo's saying that just improving the exhaust makes a difference.

I don't think that the 'proper' gas-flowing (of both the manifolds and the head) is quite so important when you have a turbo engine. Something to do with the forced induction I think. It makes a difference, but not as significantly as on an n/a engine.

(steve said he was building the exhaust for a 200tdi earlier)

I'm not an expert, but i've been playing with and researching turbo engines recently. I've got a ported, polished and slightly improved head ready to go on one when i get round to rebuilding it :) - so i can put forward an educated opinion at a later date! (until then i reserve the right to regurgitate things ive read and heard elsewhere!)

On or around Thu, 25 Aug 2005 00:44:08 +0100, Tom Woods enlightened us thusly:

I reckon it still makes a difference. The gas flow is gonna be better, whatever - many modern exhausts are restrictive in order to make 'em quiet, though.

You're right, its the 200Tdi project I'm thinking of. I thought polishing ports wasn't a good thing, for aerodynamic reasons, the rough wall REDUCES friction rather than increases it ? Can you "port" a 200TDi and make a worthwhile improvement I wonder.

Steve

On or around Thu, 25 Aug 2005 12:57:58 +0100, steve Taylor enlightened us thusly:

I suspect this is more about turbulence - too clean a gas path on the inlet, especially in a petrol engine, is supposed to lead to poor mixing. However, in a diesel, that may be less relevant.

however, matching ports so there's no big step in the side would be helpful, I think.

I see a niche market for snake oil magnets on the exhaust manifold here.

I slightly lied about the polishing bit. He's cleaned it up but still left it with a rough finish, as he (the engine guy) said the same as you - that this was better. I trust the engine guy as he's been doing it for years!

so steve Taylor was, like...

That's right - a slight roughness to the surface produces turbulence which (for reasons my O-level physics didn't cover) actually reduces friction. It's the reason that golf balls have dimples.

Shaping ports to manifolds (inlet and exhaust) is worth doing, gives the gas a fair chance of shooting though without banging its head on the step.

Any idea if 200Tdi's need this kind of treatment as a matter of course Rich ?

Steve

Not specifically, but any engine will benefit from what is effectively hand-finishing a product which is fairly crude from the factory. With the

Whether it would be worth the effort, I can't say.

Well, after a bit of searching and ringing around I went for the large bore twin pipe system from Rimmer Brothers. Considering a Land Rover main dealer wanted almost £700 for a mild steel exhaust I consider £569 for a stainless system with a lifetime guarantee money well spent. It's all a bit bright and bling for me (I like understated cars) so I'll be painting the rear silencer boxes black over the next couple of nights. Now just got to find time to fit it!

Here's hoping the burble at tickover with this system is as nice as my TVR Griff 500 (yes, I know what I said about understated cars!).

Regards

Alan

The burble from Grumble is music to the ears for a petrolhead - better than the Tuscan, or my Seven... (yes, yes,yes, I'll get mi overalls)