The V8 Owners Forum -

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



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.

nice one mate,
glad to see things going the right direction,

Nice, and an impressive gain from the manifold too...

Good work.
Maybe the air velocity hits a sweetspot at that rpm?

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...

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:

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

Chris.

The crank is standard, and I am using a standard manifold base (well, almost standard ) 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.

In which case I would mark it down to a non-optimal RR and do some manual interpolation of the graph down to 3000RPM

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

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.

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.

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.

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.

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.