22 replies to this topic

[topwaxer]

Does anyone know how much boost these kits are running as i was told 12 psi ish and that you need a compression ratio of 7.8 - 8 /1 to make sure the engine doesnt pink. does this sound about right ? has any one installed this kit that can confirm this. are there any pullies that can lwer the boost at all ? if so available from where ?
Thanks in advance

[spikyrob]

its not 12 psi, more around 8, if it was, you could have a pully machined to drop the pressure, from what i'v read the M45 supercharger is horribly inefficient above 10 psi anyway because of the heat it puts into the air one of the supercharger/turbo gurus will be able to explain why, how and more lol

Rob

[topwaxer]

Are you sure as i was under the impression that on a 998 it gives higher boost than on a 1275 as the engine is smaller. please correct me if i am wrong. would running a 998 at compression ratio of 8-1 with 12 psi of boost make much power ?

I am not sure what to do as i have a compression ratio of 8.5 but the engine is still pinking
could it be anything to do with the wrong plugs or is this solely a boost / compression issue ?

Cheers

[Turbo Nick]

its a not properly setup issue, will be down to timing and fuelling.

[topwaxer]

what compression are you running for 15 psi of boost ?

[Turbo Nick]

8.7:1, will be upping it to about 20psi on the same CR aswell.

[Sammy D]

You'll get about 8psi.

I fitted the 15% smaller top pulley and now it's on 10psi. Supercharger whines a lot more but engine gets hotter. I def wouldnt want any more boost than ten with a supercharger.

by the way, I have a 1293 and a comp ratio of 8.5, so quite low really.

[topwaxer]

Please correct me here as i am a little confused, if a supercharger pulley produces 8 psi of boost on a 1273 engine then that equates to more boost if the same is used on a 998 as the engine is smaller.

if this is so then i will need a bigger pulley to slow the supercharger down creating less boost

If by any small chance i am correct in what i am saying then where can you get a bigger pulley for the supercharger

[Sammy D]

Please correct me here as i am a little confused, if a supercharger pulley produces 8 psi of boost on a 1273 engine then that equates to more boost if the same is used on a 998 as the engine is smaller.

if this is so then i will need a bigger pulley to slow the supercharger down creating less boost

If by any small chance i am correct in what i am saying then where can you get a bigger pulley for the supercharger

No, think about it, it runs off the crank.

Lets say I'm getting 9 psi at 6000rpm of the engine. That means when the crank is turning 6000 times a min, the supercharger will be kicking 9psi. Put it on your 998, and when your crank is spinning at 6000rpm, you'll still be getting 9psi. Bore size has nothing to do with it.

All you'll need to fit it to the 998 is either a 998 decompression plate or a suitably modified head.

[topwaxer]

ok i understand thank you.

Have you any idea why it is pinking then as the CR is currently 8.5-1

Could using the wrong plus be causing this

i dont need a special dizzy do i as i am using the standard one


will it still run ok with CR of 8-1 , if i try that to stop it pinking

[Sammy D]

Don't worry too much about the CR, idealy you want it no higher than about 8.7 at the most.

If it's pinking it's likely to be ignition. What sort of engine speed does it pink at? Higher in the revs? Generally a standard dizzy will be too advanced further up the revs with the charger.

I'm using megajolt so can set it up spot on by plugging it into a pc. Maybe something to look into to do yourself.

[topwaxer]

so would altering the advance curve on the dizzy cure this ? as as you rightfuly said it is fine at low rpm but starts to pink as more revs are put on

or is there a better dizzy to buy that already has a better curve ?

[Turbo Phil]

Try backing off the timing & see if it still pinks. Is the fuelling spot on ? You'll never get a dizzy with the correct curve, you need to have one tailored, or better still fit megajolt or similar & map it properly.

[Brett]

No, think about it, it runs off the crank.

Lets say I'm getting 9 psi at 6000rpm of the engine. That means when the crank is turning 6000 times a min, the supercharger will be kicking 9psi. Put it on your 998, and when your crank is spinning at 6000rpm, you'll still be getting 9psi. Bore size has nothing to do with it.

the boost pressure on the 998 motor will be higher, the displacement min-1 of the supercharger is the same at 6000rpm no matter what engine it is on but the displacemant of the 998cc engine is less than the 1293cc engine (obviously )

lets make up some numbers:
at 6000rpm the displacement of the supercharger is 12000lpm,
displacement of the engine at 6000rpm is 5988lpm (1l engine)

because the supercharger in question is of the positive displacement type the 12000l is put through the 1 litre engine resulting in twice the pressure of the atmosphere in the cylinder (12000/5988 = 2.004) 2.004bar in the cylinder is 1.004 bar more than normal 1.004bar=14.75psi so there is 14.75psi of boost for the 998cc

now the same for the 1293cc, the supercharger's displacement is still 12000lpm but the engines is 1.293(in litres)x6000=7758 now 12000/7758 = 1.55 bar in the cylinder this is 0.55 bar more than normal or 0.55bar boost 0.55 x 14.7 =8.085psi

now by sheer coincidence i happen to have used the correct(ish) figures and imo the difference is there to see

because the supercharger is positive displacemant (it physical displaces the volume) it is in theory just simple maths, however turbo's are hugely different and its down to compressor flow (they dont displace just 'pump or blow') and compressor maps are needed.

EDIT: lol i sound a bit harsh, im not having ago sammy, its late, (or early )i have just finnished work and fancy to solve the boost issue

Edited by Brett, 22 October 2008 - 07:04 AM.

[topwaxer]

ok then i understand what you are saying.

So what are my options then

1. chargecooler kit ?
2. lower the compression from 8.5-1 to about 8-1 to stop it pinking
3. Lower the boost

am i correct in assuming these options will help in stopping the engine pinking ?

Unsure how i could lower the boost as not sure what size pulley i would need to achieve 8psi boost ( using your calculations need to shift about 9500 L per min)
has anyone done this before and knows what pulley size to use ?

i was told by jonspeed that i needed to reach compression ratio of 7.8-1 / 8-1 hopefully this would stop it pinking but then will the car drive ok ?

i saw on vmax scart website that they do a charge cooler kit has nayone used this kit? is it any good ? in theory this should help to stop pinking right? and also produce more power with a denser charge ?


To be honest i am more than a little hacked off with jonspeed for selling me this kit running at 14 psi boost when really it should be running under 10 psi or less. It seems that they have set this kit up for 1275 and above and are selling it to people with 998's without telling them the whole truth. I thought i was paying them for their engineering expertise when it now turns out that that isnt quite the case. And i am now left with trying to sort this out.

I would be interested in other peoples thoughts