Supercharger tuning strategy pre charger injection

Hi guys,

I've been presented with a setup that I haven't dealt with before and looking to gather as much info before putting it on the dyno.

The engine in question is a Holden 202 with a roots Supercharger, 1bar pulley, wasted spark, 8:7.1 CR, boost spec camshaft. There is no intercooler and the S/C sits right above the exhaust manifold so I'm expecting high intake temps.

The injectors are located to the rear of the supercharger firing directly on top of rotors.

The Main question I'm asking is - Is this method of injection efficient enough to get a well driveable and reliable tune? Or do I need to push for port injection and utilize the pre S/C injectors for water/meth or to just more fuel under boost?

If we tune it with only pre S/C injection, is there a calculation for injector size?

What IAT is the maximum I want to be seeing before lifting off the gas?

What WOT AFR should I target?

Thanks in advance!

There were quite a few versions of that engine, IIRC, with different port arrangements. What are you working with?

The BIG problems that come to mind with the "top" feed to the supercharger is the potential lag between air flow and fuel demand , the potential for fuelling variations from the air distribution vs that of the fuel, and maybe fuel 'drop out'.

Not sure if you'll be able to get a truely driveable setup - but that depends on what one considers 'driveable"?

Depending on the head, and the manifolds, you should be able to get a much better over-all tune with port injection.

Is the supercharger blow-through, or suck-through? The former may have significantly higher intake temp's.

Your suggestion of port for fuel and the "top" for water/meth' might be the best compromise, and it's give plenty of time for the latter to maximise charge cooling.

Whatever you go fo, you can make a rough estimate of the injectors by multiplying the original peak power by the charge ratio, and dividing by the numberof injectors, and comparing that to the suggested power per injector you have in mind.

No real idea on IAT, that may partly come down to the fuel being used and the detonation resistance - maybe 100C?

AFT will depend on the fuel - a lambda of around 0.85-0.9 will probably be a good compromise.

If possible, routing the exhausts away from the 'charger, and using heat shielding and a cold intake will help.

TBH, it sounds like a bit of a Frankenstein's monster - Roots 'chargers are quite inefficient, if you can't pursuade the client to go to a screw or centrifugal 'charger, any chance of having it remounted to the driver's side which would allow the cross-over to be through a charge cooler?

Some short comments:

It will run better with port injectors, but it will run with injectors in the location you have.

It will make more power and operate more safely with cooler air charge, but if you define an IAT limit for your setup and fuel and the driver always sticks to it, again it will run as is.

You've identified areas for improvement so it's really up to how well and reliably the vehicle owner wants the vehicle to be, and what you're comfortable delivering.

Don't Roots type blowers also require a constant stream of fuel across them for cooling and lubrication purposes? Or am I thinking of a different type of blower?