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wil_h

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Betwix Harrogate and York

1st Oct, 2010 at 12:39:28pm

looks like this

Fastest 998 mini in the world? 13.05 1/4 mile 106mph



On 2nd Jan, 2013 fastcarl said:
the design shows a distinct lack of imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


Paul S

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Formerly Axel

Podland

1st Oct, 2010 at 01:15:07pm

Yes, you would need to open up the chambers like that to get the benefit.

Here's a picture of a standard 25.4mm valve compared to a 29mm in a 12G295.


Not much of a gap around half the circumference of the 29mm valve.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

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Near Paris - France

1st Oct, 2010 at 05:09:02pm

But let's consider that you block 30% of each valve (inlet and exhaust) anyway ?

Rusty by nature

On 23rd Jun, 2008 paul wiginton said:
They said "That sounds rough mate." I said "Cheers it cost me a fortune to make it sound like that!"


fab

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Parisien Turbo Expert

Paris\' suburb

2nd Oct, 2010 at 07:44:58am


gt17 design is as stated improved over old turbines, the point is :this design isn't an high boosted one, it's a shopped gt20 turbine wheel a la vnt, a gt20 one would make full/higher boost earlier but would certainly tame higher end because of a bit more restriction, whatever on a a series it does make a nice boost curve and release high power.

manifold wise it's a balance between inlet boost and exhaust tip.. not that easy, anyway a 180 bhp turbine/volute, wg, is still bigger than the inner branch of a turbo manifold then guess where's the restriction

On 1st Oct, 2010 wil_h said:
Just thinking about manifolds.

If you plonked any of the turbo manifolds we use on an NA engine you'd expect a drop in power compared to an LCB, so there is some restriction.

However, in our case, there is a further restriction beyond the manifold in the shape of a turbo, so the manifold is not the most restrictive part of the exhaust system. so in my eyes any improvements you make to the manifold will be pointless as you still end up at the same restriction.

At the top end of the rev range the waste gate will be open, can these be made more efficient?

I think Pauls comment on the efficiency of the 17 turbine is relavent.

My personal opinion is that some of the graphs above show reasonably well optimised engines with minimal drop off in torque and way better than an NA motor.

Paul S

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Formerly Axel

Podland

4th Oct, 2010 at 10:03:35am

Well, the other three 998 Turbos running at the weekend have 29mm exhaust valves and did not seem to suffer from it in any way, so i think that I will be going a similar route with the head as Wil_h's above.

Cam wise, I now have an MPi cam to measure to see if Rover improved the lift profile over what seem to be near standard timing figures.

Tempted to go side mounted turbo as well from what I saw at the weekend.

EDIT: Also my torque curve has changed significantly according to the new figures, no longer flat but peaking at around an estimated 120lbft at 4500rpm (measured 107 at the wheels). Hence a total rethink is needed.

Edited by Paul S on 4th Oct, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."
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