Supercharger boost pressure.

[zed1015]

Ok. Not very often i ask for advice. In fact this is my first time so be gentle . Maybe i'm having blonde moment but why is my boost gauge only reading vac (in/hg). When blipping the throttle the gauge goes from 0 to -30 and back. Even when holding constant revs the needle never goes into + psi. Gauge feed is from the plenum so surely must be pressurised ?. Am i missing something ?.

[Big Fluff]

Hmmm.. First thought, if you're using a glycerine damped gauge, is to make sure that there is not too much fluid in there. Ideally leave a big bubble in there. Mine was overfilled from the factory (ATP) and gave really far out readings (resulting in smashed pistons etc.).

Negative readings:- When the throttle is opened, the plenum area will become a vacuum as it tries to suck air & fuel in, just like any 'nat asp' engine.

Positive readings:- You'll never get the needle to move into the positive pressure scale unless you really load the engine, and this is only achievable when on the road.! I remember thinking exactly the same when I first rebuilt my turbo bike.
Take it out on the road and you'll see

[zed1015]

Well!. Being a supercharger i would have thought it should show boost from tickover. Gauge isn't the best but just tried a mr turbo one with the same result and even by sticking my tongue on the end of the pipe i can feel suction. blipping the throttle or building the revs up steadily still shows no pressure just less vac.

Went to it this morning and it started first kick, Instant throttle response and revs shoot up like a stroker (sups juice like one too ), Like no Zed i've seen race tuned or not. Something must be working but suppose only a proper road run will confirm that one way or another.

[tlc]

DON'T THINK IT, DO IT.

And take a buddy with a video camera

[Buckle]

Just out of interest - how are you regulating the boost presssure? I guess there is some kind of waste gate / dump valve?

Is an intercooler fitted?

My experience of superchagers is limited to VW G40 Polo's and G60 Corrado's. And they wouldn't achieve any boost reading without loading the engine either up the road or on a dyno.

More Pics!

[zed1015]

Boost pressure is fixed and in direct relation to engine revs . Current gearing should give a max of between 8 to 10 psi and i would have thought it should show + boost from tickover. The engine does sound and feel VERY powerfull /sweet / crisp and free revving etc so maybe all is well. Have upped the engine capacity with 1075 wiseco's so maybe the pump isn't quite keeping up but that sounds a bit unlikely for such a small increase?. Might have to up the blower gearing to compensate ?

[Big Fluff]

You'll never get the needle to move into the positive pressure scale unless you really load the engine, and this is only achievable when on the road.! I remember thinking exactly the same when I first rebuilt my turbo bike.
Take it out on the road and you'll see

I repeat what I said before.... You don't HAVE to take any notice of what I say though.
You're a clever guy, but personally I think it would be a mad move to piss about with the gearing of the charger without first getting a boost reading by taking the bike on the road. You run the chance of blowing the lands out of the pistons at a minimum if you run too high boost pressures.
You asked for advise, and I'm offering that to you. It's your choice though.....

[tlc]

I increased the boost on my Jag by upping the gearing by means of a smaller top pulley.

Admittedly the ECU was remapped at the same time but the difference to before is it now has a distinct powerband from 3.5k.

The wife says what did you do that for as it was alright before.
I just bury my foot in the carpet

I would try on the road as Big Fluff says. It may be that pump losses are more than boost gains in which case it will be necessary to increase pump speed.

Oh and is there a check valve or wastegate device fitted ?

[zed1015]

I repeat what I said before.... You don't HAVE to take any notice of what I say though.

Certainly not dismissing anything you have said ok. Would be nice for someone to confirm either way (preferably another supercharger or drouin owner) whether it should be showing boost or not from tickover as unlike a turbo it doesn't have to spin up high to pressurise. Another source i've spoke to says it sounds like the blower isn't pumping enough and therefore not even making boost higher than the motor is pulling in naturally hence the capacity increase theory and upping the gearing to compensate. Of course i'll only find out once i take it for a spin but until then it's really gonna bug me.

[zed1015]

Oh and is there a check valve or wastegate device fitted ?

It has two spring loaded blow off valve's fitted in the plenum which in theory will never come in to play as the boost is governed directly by engine rpm.

[tlc]

My experience with Super doopers is limited to "do this, and here`s the credit card" but they are exactly the same as hydraulic pumps.

You are pretty much in pioneer territory I guess but does not "suck it and see" work in this case ?

Maybe a dyno run to at least work out if you have the correct fuel air ratio.

There was a Super in Hannover last week. Maybe speak to him ?

You can always ask Kawamick, Z1RII or PeterK who have excellent English and I`m sure will speak to the owner for you.

[zed1015]

Ok. Get this. Gauge SHOULD be showing boost from no load tickover only rising slightly with revs as the pump losses are offset ( in an ideal world max boost would be from tickover). Drouin built these kits to bolt on a stock motor with stock comp, only recommending welding the crank and forged pistons for the highest gearing producing 16 to 24 psi for racing. Looks like the blower was borderline on the lowest gearing for a std motor and isn't pumping quite enough for my motor which has increased capacity and lower comp. So what i have at the moment is a gas flowing device that nearly but not quite gives what a normally aspirated motor takes and if run in this state will still be very quick but lacking a lot of the low down torque associated with a blown motor. So it looks as if i'll have to do some calculated head scratching as to what size pulleys i need to make to get some positive pressure.

[tlc]

Don`t know if these guys could help you Zed ?

http://www.paramount-performance.com/ac ... index.html

They seem to know about Soopered Jags !

[Pigford]

Rob, may be worth contacting these chaps..... The bloke who runs it has a 600cc Bandit with a charger fitted.... Hes had it yonks... & knows his stuff.

He looks a bit like Merlin the Wizard

http://www.blackdragonmotorcycles.co.uk/


This 600cc suzuki bandit runs on bio E85 fuel and the bike primarily is used for sprinting, road use and hill climbing.

Mods include uprated suspension, Remus exhaust, Micron headers, Air shifter, JMC pro/stock adjustable swing arm and an opcon supercharger unit running at 12lb boost on the stock engine, this generates 132 bhp at the rear wheel with up to another 50 horsepower available from nitrous .

Performance figures:

1/4 mile best 9.71 seconds
1/4 mile best terminal speed 142
1/8 mile 6.38@114 mph

Results:

NSA 2006 750 Race Championship 1st place
NSA 2007 750 Race Championship 1st place
NHCA 06 Road legal class 4th place
NHCA 07 Road legal class 2nd place
Dakota Raceway Fastest road bike 1st place

[zed1015]

Cheers for the info but pretty much knew what the problem was all along, Just hoping it wasn't coz it's one more thing to sort out, more cash, more time, one more step away from completion. Then having to wait for the dry 10 minutes of the year to test it out. Think i might start building jet ski's, at least it's always the right bloody weather for running them !.