UK Spec B with Supercharger

[jslayz]

slipping belt in SC unit ???

[Spec BSC]

slipping belt in SC unit ???

Thanks for the idea might come back to that.
Having the only supercharged Spec B in the uk does have its draw backs that there is no body else to talk to, to use as a sounding board. Then I remembered that I have a customer who supercharged a Fiat Panda from scratch.

Anyway talking to him and going through all the history and outcomes we came up with the following.

There is a boost leak! However it is a constant and prevents the full pressure being achieved but there are no leaks in the inlet tract and its not the bov. The maximum pressure achieved is irrespective of pulley size and has been achieved on two different engines!

What parts have been on both engines apart from the sc equipment?
Answer inlet manifold and EGR valve, infact this egr valve was on the engine that ate the cats so it may well be damaged giving a possible cause for the boost leak.

The egr valve will be junked to see if this makes any difference.

If that doesn't work then just maybe the sc unit with the standard impeller and 56mm pulley just can't deliver the goods but the boost gauge did show 11psi consistently last sunday during a 100 mile trip so Im really hoping its the EGR valve.

[KiDo_Tuning]

Looking great mate well done!
8 pot front brakes - they look sweet as! Are they the original brakes or retrofitted from another model?

They look like K sports - aftermarket brakes (with a subaru sticker). The biggest brakes to be fitted on a lib/leg are the 6 pot brembos on the S402. There's a number of aftermarket BBK options.

S206 had bigger brakes than S402

[Spec BSC]

Blocking off the egr made no difference, had the inlet tract pressure tested, zero leaks.

Tim at raptor has always maintained that they measure the pressure just after the sc impeller so got round to tapping a feed into the body.


The first drive looked promising but with more carefull monitoring the maximum reading at 7000rpm is still only 8.4psi and the 56mm pulley is meant to give in the region of 12psi.

Have spoken to a sc speacilist in the uk and there conclusion is belt slippage as the pulley is not wide enough to cope with the friction they normally use an 8 groove belt on their systems. Going to take a trip up to see them and see if we can get the belt speed measured and take it from there. If I cant get the belt slippage issue sorted with the raptor may well change it.

[jslayz]

slipping belt in SC unit ???

Hey, that is what I thought!
Can you get a toothed belt or chain upgrade???

[vertix]

Interesting, I've also been struggling to make max boost (9/9.5psi). Done countless leak tests, replaced BoV, still not fixed I'm only seeing ~7psi @7k RPM.

I guess slipping belt is the next thing to check..

[Spec BSC]

Interesting, I've also been struggling to make max boost (9/9.5psi). Done countless leak tests, replaced BoV, still not fixed I'm only seeing ~7psi @7k RPM.

I guess slipping belt is the next thing to check..

Have you moved the tesioner on the raptor mounting bracket to its highest position.?

[kiahatsiu]

Has it made 9psi before? Is it possible you are out of the compressors efficiency?

[vertix]

Yep tensioner is set to the highest point, and I have not yet seen 9psi since putting the SC on

[kiahatsiu]

When you had the original pulley on did it hold a constant boost?
I am wondering if your 3.0 4v per cylinder engines are too efficient to see 9psi.

[Spec BSC]

Right been doing a bit more research into belt slippage, found an excellent company in the USA, 928 Motorsport, that deal with all types of sc unit including Raptor.

Heres what they say about belt slippage.

Belt slip and drive pulley sizes: Remember that every time you change to a smaller pulley, you loose tractive force on the belt and the ability to pull a load. To make matters worse - you just increased the load - trying to move more air increases the load on the belt, and now you have even less tractive force to do it with because the pulley is smaller.
Solutions for belt slip:
1) go from a 6-rib to an 8-rib pulley system. If 8-rib, go to 10-rib or a cogged pulley system.
2) if using a sprung belt tensioner, replace with static (solid) belt tensioner.
3) if driving the supercharger from a shared serpentine belt that drives the other auxiliaries, change it so the supercharger has its own belt. The supercharger demands 50 to 100 HP to drive it (depending on model, back-pressure, and rpm) and nothing else in that system (the alternator, the power steering pump, etc) do. So the serpentine system is not designed for that load and you will never get the belt tight enough. If you did, you would overload the alternator bearings into an early failure anyway. It is convenient for kit makers to drive off the serpentine belt, but that only works for light supercharger loads up to about 6-8 psi. Put the supercharger on its own crank pulley with its own tensioner.

Also they can coat the pulley to give more traction, ok the belt will wear a bit faster but hey. So I have ordered some belt dressing which is a temporary fix to see if I can get boost to increase, if so will then consider getting my pulley coated whilst considering re-engineering the belt drive system.

[dan_ashcroft]

Great info, thanks for sharing.
Will be watching, Good Luck!

[vertix]

Looks like your all over it, good work!

Very interested to see how you go with the belt dressing.

[Spec BSC]

So the belt dressing made no real difference in fact there was a drop in pressure! Ordered a new belt and getting the pulley sent off for a coating.

[KiDo_Tuning]

Grant/Purdy is seeing 9.6psi no issues

FYI: I would still rather have air passing the inlet valve into the combustion chamber than pressurising the inlet manifold.