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Adiquate result from my "slightly adjusted" Griffi
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dnb
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1996 TVR Griffith

PostPosted: Sun Jan 06, 2008 6:33 pm    Post subject: Adiquate result from my "slightly adjusted" Griffi Reply with quote

The engine in question is a 5 litre Rover v8, with a few things bolted on to it... Wink



Not too bad a result. I'm a bit surprised by the antics at 4000 RPM. The only thing that's different beween this and the 260 bhp result in the summer is my own design of isolated runner twin plenum inlet manifold.
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Coops
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PostPosted: Sun Jan 06, 2008 6:37 pm    Post subject: Reply with quote

nice one mate,
glad to see things going the right direction,
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Alley Kat
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PostPosted: Sun Jan 06, 2008 7:06 pm    Post subject: Reply with quote

Nice, and an impressive gain from the manifold too...
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Eliot
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PostPosted: Mon Jan 07, 2008 7:16 am    Post subject: Reply with quote

Good work.
Maybe the air velocity hits a sweetspot at that rpm?
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bill shurvinton
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PostPosted: Mon Jan 07, 2008 11:52 am    Post subject: Reply with quote

Certainly very odd. Above that point the torque curve does exactly what I would expect, below there it is all over the place. Usually results like that are from excessive wheelspin on the rollers. If that isn't the case, then there is something very wrong with airflow in the intake or some wierdy in the exhaust.

With IR setups the torque plot usually has a small hump low down for the airbox (if there is one) then 1 or 2 distinct humps for resonant modes.

Intriguing...
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Eliot
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PostPosted: Mon Jan 07, 2008 1:06 pm    Post subject: Reply with quote

bill shurvinton wrote:
Certainly very odd. Above that point the torque curve does exactly what I would expect, below there it is all over the place. Usually results like that are from excessive wheelspin on the rollers. If that isn't the case, then there is something very wrong with airflow in the intake or some wierdy in the exhaust.

With IR setups the torque plot usually has a small hump low down for the airbox (if there is one) then 1 or 2 distinct humps for resonant modes.

Intriguing...

Its daves own design manifold:

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ChrisJC
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PostPosted: Mon Jan 07, 2008 2:11 pm    Post subject: Reply with quote

Well unless he's got a flat plane crankshaft, that inlet manifold may well do 'funny things'

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dnb
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1996 TVR Griffith

PostPosted: Mon Jan 07, 2008 7:53 pm    Post subject: Reply with quote

The crank is standard, and I am using a standard manifold base (well, almost standard Wink ) so it still has crossovers, so the airflow is correct.

The car was a pain on the rollers - we tightened the straps several times, so it could have been slipping a bit.
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bill shurvinton
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PostPosted: Mon Jan 07, 2008 8:42 pm    Post subject: Reply with quote

In which case I would mark it down to a non-optimal RR and do some manual interpolation of the graph down to 3000RPM
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r2d2hp
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PostPosted: Mon Jan 07, 2008 9:48 pm    Post subject: Reply with quote

That's an amazing increase David. Were the tests done using the same rollers. Did you make any other modifications made as well?
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dnb
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1996 TVR Griffith

PostPosted: Mon Jan 07, 2008 11:53 pm    Post subject: Reply with quote

Not the same rollers, but they were at least both Dyno Dynamics.

The only change (other than fitting the plenums) was to hugely increase the VE table and retard the ignition timing a bit to control the det.

I suppose I should be using 97 RON fuel, but there's no constant source of it here. Sad
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dnb
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1996 TVR Griffith

PostPosted: Sun Mar 16, 2008 12:10 am    Post subject: Reply with quote

I think I have the answer to the jump in torque issue.

There is a term: "Effective wide open throttle". In a NA engine, it means the throttle angle to achieve atmospheric pressure in the manifold. Any throttle opening after this is simply slowing the airflow down.

Effective WOT with these plenums at low RPM is around 30% or so, and the RR test was done with the throttle pegged at 100%. It would be interesting to see results from using a progressive throttle opening in this lower RPM area.
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katanaman
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PostPosted: Sun Mar 16, 2008 12:38 am    Post subject: Reply with quote

Can the VEMS control a throttle by wire? Could be an interesting experiment if it does as I guess thats the whole point of them.
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dnb
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1996 TVR Griffith

PostPosted: Sun Mar 16, 2008 2:20 am    Post subject: Reply with quote

If I have diagnosed the problem correctly, it would indeed be a solution.

No, VEMS can't do fly-by-wire throttles at the moment, and it's not something I'd really want on the car either. (I have a lot of reasons)

I'll stick with feeding the throttle based on vacuum gauge readings for the moment.
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katanaman
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PostPosted: Sun Mar 16, 2008 4:38 am    Post subject: Reply with quote

I guess a mechanical solution would be like the old SU carb, bike CV type arrangement but as a TB. I notice even some of the new bikes with injection are still using a type of CV so you might well be onto something with your ideas.
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