VX and FI

[Rocking-M]

Not sure I'm in the right section. But advice on setting up VX on a stock 1980 FI
engine with stock compression is what I'm after. I'd like to run FI and
I'm not sure, but I'd like to set up independent throttle bodies for each cylinder and
manage with megasquirt. TB's off a ducati may work if I fab the intake.
Just don't know if it's doable since I've never seen a VX set up up close.

May not need individual TB's. I'm after 180hp rear wheel. I read one of the other
threads and it's doable it seems.

Thanks, Robert

[Guy Croft]

Blowing thru throttles is more complicated than suck-thru because of the issue of throttle closure under pressure and I would avoid it because it won't yield any advantage.

You should certainly inject inboard of the blower and as for inboard manifold (with inj in it) it would be worth trying to equalise the runners - which is certainly not the case on the std Vx manifold. You could, for example, weld injector bosses to a standard 4-branch inlet manifold from a carburetted engine and blow the air into the manifold plenum via ducting from the blower. of course - you'd have to revise the blower mounting arrangement.

And I would run a single throttle plate outboard of the blower with a throttle position sensor on it (and MAP sensor on the inboard manifold). There is no advantage at all to having 4 throttles. It doesn't matter over-much where you point the injectors but given a choice I would point them at the valve heads.

Worth noting that the Roots blower does suffer from a terrific amount of reverse flow and thus I'd consider a long rampipe or 'torque tube') on that throttle plate and I would insist on remote filter and cold-air induction - read this site which will tell you more about this than I can here:

http://www.pipercross.net/fastroad/products.asp

Pipercross (haven't dealt with them in a long time) were, to their credit, one of the first to offer 'roll-back radius' rampipes for Weber DCOE and I tested them against OE Weber ones and found measureable gains..

As far as your intended conversion is concerned you'll likely encounter all sorts of 'ancillary' problems, for a start the Vx blower delivers much more torque than a n/a unit of your type, thus the clutch will almost certainly need changing to an uprated version. All Vx models had a bigger diameter one and whilst it's not necessary to go to those lengths (cheaper for an OE mfr to make a bigger clutch than an uprated one..) your std one won't last long at the 160lbf ft the new one will produce. The head gasket really wants changing to one suitable for the far higher cylinder pressure and temperature - and - importantly the ex valves should be changed to sodium cooled ones. The OE ones are the only type you can get and they are pretty pricey.

Supercharged engines do NOT work well with high (standard) back-pressure ex systems and although you could get away with the std header and downpipes the rest of the system should be junked and changed to a pair of large volume oval straight-thru mufflers.

I have to say, all in all, that given the cost/work involved (taken as a whole) I would not use injection at all, I would use a 40DCOE in suck thru orientation and suffer the OE inboard manifold!

GC

[Rocking-M]

Thanks Guy, I have lots to mull over now. Best, Robert

[petarn_vx]

Hello Guy,

you mentioned you would use a 40 DCOE. I just bought one for my Beta VX, and now I am looking for the right jetting. Could you give an advice for a starting point.

wbr
Peter

[Testament]

Regarding the abarth manifold above that you converted to injection - do you have any information on how the engine performed with this setup, and do you know if it ran batch or sequential injection.

The reason being that I have some concerns about the similar setup I am intending to run on a beta VX manifold with batch injection - i.e. fuel is injected once per cycle. the worry is that will the first cylinder to fire on that cycle "steal" some of the fuel from the other cylinder due to the extremely short runners on these manifolds. my initial thoughts were that it would be ok as the other cylinder would bea "dead leg" at the time but the more I think about it the less sure I am. It would be very reassuring to know that a similar setup has not had any serious problems due to this.

[Guy Croft]

I don't have any feedback because it never got fitted, but it would have been good on batch and/or sequential and it was modelled on the Lancia 037 Evo II which had mechanical (ie: batch) fire.

I'd opt for the same choice as you - batch - with a modified Vx man. The inlet flow and pulse effects are going to be so chaotic (as you indicate) that figuring out when to start and stop inj on sequential and trying to optimise it for all cylinders would be, well, I think, very hard work. Given the simplicity of a batch setup - that's what I'd use. Frankly, as the fuel is being sprayed into the ports it's going to be way better than the std carburetted setup where the gasoline is sloshing around all over the place.

G