Thread: More torque for V8D1

Hopefully all you guru's out there can give me a bit of advice. I own a 3.9V8i (auto 1996) recently converted to LPG. I have almost completed my 6500 km trip towing an 18ft caravan (about 1700kg) and this has highlighted that my D1 could do with a bit more torque to handle the towing. There doesn't seem to be much loss of power on gas compared with petrol and as it's only got 146k on the clock the engine is still in pretty good condition. But I have wondered if there is any fairly inexpensive fixes for this.
I have thought maybe
1. A snorkel to improve air intake temp.
2. A better (larger, free flowing) exhaust
3. Perhaps putting a longer throw crankshaft but this will of course be much more expensive.

I would appreciate any comments, particularly on the crankshaft replacement - will a 4.0 or 4.6 one fit straight in?

yeah i suppose it can become expensive, although ive already done the megasquirt conversion and dont mind knocking up a few mounts so it would be way less expensive than a capa kit

also the capa kits are centrifugal superchargers (like a turbo with a belt driven compressor instead of using the exhaust gases) their characteristics are more like those of a turbo in that they need to spool up to get to the sweet spot

the m90 is a roots style supercharger which has a fixed displacement, 90 cubic inches per revolution so the pressure increase is always the same no matter where in the rev range, assuming it doesnt choke the engine (hard to do with a 3.5)

the roots style has the advantage that it produces instant boost off idle, and hence much more low down torque, a downside is that they are usually mounted in place of the intake manifold which means intercooling in that setup can be a challenge, if i were to do it (and i am, just waiting on a good deal for an m90 from US ebay) i would make up a bottom plate that adapts to some 2.5" piping and run the supercharger off to the side, possibly above the passenger side exhaust manifold, you can run them sideways or even upside down if that is easier to work, then you just run the outlet from the intercooler straight into the current intake manifold, so you eliminate the problem of getting an even distribution of air into each port

although with my EDIS coil packs and LPG injection it may take a bit of working out to get it all to fit in the engine bay, its getting cramped in there now

but before all that i will be getting a cam from Tighe cams that produces more low down torque and a stronger midrange, my stock cam is stuffed anyway (worn lobes) and my lifters rattle like nothing else so i can maybe justify it as 'maintenance' haha
IIRC, the price from Tighe was $280 odd with a 3 day lead time, and Holden v8 lifters fit just fine in place of expensive rover items