Supercharging 944NAs, Rimmer ain't the only out there!!!!

[TheStig]

Ok for those of you who are looking into more power for their NAs as I am but can't find the Rimmer supercharger, I have finally proposed a plan to research on bolting a VORTEC supercharger on a 944 without and major re-modifications! The solution is simple if those of you have viewed a supercharged 928 before! Seeing that i have gotten a scholarship for 2 thousand at SDSU it gives me money in my pocket and i will use it to research into this idea!!!! WOHOOO!!!!!!!!

I HAVE EXEEEERRRCCCCCIIIISSSSSSEED THE DEMONS! HEHEHHEHEHEHEH!!!!!!!!!



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Porsche. Es gibt keinen Ersatz.

[wolfrpi]

Don't bother - its centfrigal and you have a small displacement motor. The hp might be much more but the car won't accelerate that much faster.

Erick

[TheStig]

Honda Civics do it with 1.8s and 2.0s, I'm sure there is a way to run a low boost on the car without blowin a piston through the hood.....i would say around 3-6 psis. and i have one spare motor to mess around with



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Porsche. Es gibt keinen Ersatz.

[TheStig]

I saw a 924S with a Carrera GTR conversion at Willow Springs with a Paxton supercharger, obvious centrifugal...at least i think. I don't really know if they make other types.. I'm new to supercharging and reading up on it more. but I"m sure you can get a centrifugal to work right on a 2.5L motor.



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Porsche. Es gibt keinen Ersatz.

[wolfrpi]

Like I said you can get the big hp numbers with centrifugals, but they are only at the higher rpms for the most part. Pick up some import mags and you'll see what I mean. The torque curve is diagonal, as opposed to flat. In the Civics its real bad because the motors rev so high, the supercharger has to be geared to survive at high rpm.

I'm not trying to be a *****, but I am telling you that centrifugal is not the way to go for your car. You'd probably be lucky to turn a 15.0 in the 1/4 mile - very lucky. And that is still damn slow considering my car should turn mid to high 12's and chipped 951s run mid 13's.

A recent issue (february 2001) of sport compact car has a whole mess of supercharged cars tested and compared.

The 270 wheel hp civic turned a 14.4 quarter (centrifugal)

The 180 wheel hp neon turned a 14.7 (roots type blower - just like rimmer).

If you look at the torque curves you'll see why the neon is almost as fast with a lot less hp.

They even had a Jetta VR6 with ALL the tricks including a centrifugal blower which ran only 15.0 in the quarter.

A Toyota Solaro with a roots type blower was also tested and put out 243 to the wheels and turned a 14.5 - just about the same as the civic, but with an auto, probably 500 more pounds, and with 30 less hp. If you look at the torque curve you'll know why.

You know why centrifugals are so popular now? Because hp sells! Why else do we spend so much on MAF's, turbos, exhausts? The only problem is the HP from a centrifugal is very decieving - It's only achieved at very high rpms.

Anyway, good luck with your search.

Erick

[EGSMachine]

so, in other words, develope your own and find out for yourself. there is a couple of ways you can offset where the boost comes up in a Centrifugal, that you can't do with a turbo. get the initial gearing internal to the charger so that it reaches its optimum RPM sooner. then you can play with external pully sizes to vary that. don't let Wolfpri discourage you. do a roots type if you want. roots are more liear in thier boost and more predictable and drivable.that is the real reason that they are popular. however, if you drag race then Centrifugal is the way to go, since you will have the engine screaming the whole run anyways. see what you can do though, but i would invest in a couple of books first.

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84-9445m

[wolfrpi]

Trust me on this one - I've seen the torque curves. Here in Southern California there is just about every type of hot-rod from supercharged civics to older Porsche 911 Bi-turbos. You see just about every conceiveable piece of machinery out here. And you learn - sometimes the hard way (by getting your but kicked). I can tell you one thing though - no street driven centrifugally supercharged civic, prelude, VR6 Jetta or whatever is EVER going to hang with a chipped 951.

Buying books is a good idea - but you should first look at the scc issue I mentioned. There is a complete write up on the issue of supercharging. I think it might have been even Bosch that did not understand by people centrigally supercharged cars. Apparently the design is more akin to applications involving heavy machinery that tends to only moderately vary rpm.

With a properly tuned 951 you can have 400 ft-lbs of torque at 3500 rpm - the only thing that could come close is roots. If a centrifigul produced this much torque at 3000, the head would fly far, far away from the car by 5000 rpm, let alone 6000 rpm, or even the 7000 rpm of my 951.

The advantage with the turbo is that you can bleed off the exhaust gases through the wastegate above a certain rpm point to compensate for this and to keep the boost constant. In the above centrifugal you may be running 20 psi of boost at 3000 rpm (which is acceptable) and 30-35 psi by 7000 rpm (which is totally unacceptable). The above 1/4 miles times are illustrative. I don't mean to discourage you, but this is free advice.

The solution for the centrifigal is to run a variable speed gearbox so that the unit can act more like a turbo and keep appropriate shaft speeds across the rpm range. I believe there is a company that makes such a unit although I'm not sure of their name. Rototech?

Anyway, Good luck in your search for HP!

Erick

[Texatl]

EuroSpec, the more info you all gather the better. If there is an issue with low end boost there are two options.
1) Gear up the car (like the mustangs do)
2) Look into a roots type (positive displacement or twin screw) supercharger...

Kenne Bell and Eaton make roots type superchargers that you can mounts like the centrifugal types, between the MAF and the intake (or on the intake). Eaton makes the supercharger used on the Thunderbird supercoupes (and the Jackson Racing 'charger for hondas). Those superchargers mounted on the side of the engine and run an intake tube to the intake, you almost couldn't see it on the car. The Kenne Bell mounts on top of the engine, low profile to fit under a mustangs, camaro's hood. Both have a long snout (??) to use the serpentine belt, so there is no extra belt and pulleys to install. Also both of those supers have their own lubrication so there is no tapping into the oil pan (like the vortech)...

Get an FMU from paxton or vortech to boost fuel pressure, and an MSD adjustable boost retard, which will allow you to dial back timing as the boost comes on (example - have it set to pull 1 degree of timing for each pound of boost, or more or less, etc...)

Heck we should be able to fit one of these, I just saw a kit for a PT Cruiser...

Example of side mounting a roots SC-

[TheStig]

I was just looking at the Whipple website this morning and saw their twin-screw supercharger. I have heard that some 944s with the Whipple have had between 210-224 horespower depending on how much boost and the pulley on there. The only thing is...how do you mount the damn thing?



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Porsche. Es gibt keinen Ersatz.

[AMCPorsche924Powerhaus!]

horsepower smorseshower, it all depends on what you are after, are you doing 0-60s? are you sitting at 4400 RPM all the time and needing the power then? What do these superchargers do for torque ? when adn how much? maybe it puts your torque kick at a higher rpm which will make ya even slower at the line..any torque specs on these things?
HP figures mean **** unless you look at the curves like wolfpri is saying and the torque curves too. If it ain't a flat curve then the power is only gonna happen once your up on high the tach, so the 0-60 will suck but on track you don't need 0-60, it all depends on what you're after.

[Texatl]

On most roots (twin screw, positive displacement, etc...) superchargers, all the hp AND torque increases are full force by 2500-ish rpm.

[Porsche 951 Fanatic]

Why couldnt he make it so that on his centrifugal when the manifold pressure hits 20PSI it bleeds it off? like so it hits 20PSI at 3000RPM then the wastegate for the intake opens and lets the extra gasses escape? so when he is at 6000 rpm and boost is 40PSI, its regulated by the wastegate deal? so he really has 20PSI?perhaps before the throttle body and AFM so that all the measurments stay accurate?

[Texatl]

You can do a waste gate, sort of... You can get a blow off valve, BUT usually a blow off valve is used when you release the accelerator, but have boost built up, which by closing the throttle body, etc starts to build even more pressure and usually breaks something - like the TB or your impeller (centrifugal types). But, logically you could have a blow off valve set to say 20 psi and to bleed off anything above that.

[Scott R]

They make a device for this purpose, my supercharger has one, it's a boost bypass diaphram. Works off boosted pressure from a air nipple drilled into the positive boost side of the intake. So when it gets to high the diaphram opens and cuts the boost down and lets more normal ir in. But I have no idea who makes this piece, it has no markins on it whatsoever.

[TheStig]

951 you have a good point there with the bleed off and wastegate. What if i were to do something similar to a turbocharger.....a blow off valve???? that could bleed off alot of boost from that centrifugal. Could applying the boost on smoother have to do with using any kind of CPU processing unit for this supercharger? i need ideas!!!



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Porsche. Es gibt keinen Ersatz.

[EGSMachine]

books, man, books. Barns and Noble, Books a Million, walden.

[Texatl]

Try this....

http://cgi.ebay.com/ebaymotors/aw-cgi/ebayISAPI.dll?ViewItem&item=593028334&r=0&t=0

Is this what you were talking about????

[Scott R]

Thats cool. That relief valve is even better then my vacum assisted valve on mine. And only $30 think I will pick that up.

[TheStig]

Yea thats what i'm talking about! Huntley Racing sells one that relieves boost from the motor at up to 20 psis. More than fine for a centrifugal supercharger =)



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Porsche. Es gibt keinen Ersatz.

[Wrecked944]

Has anyone tried the "electric supercharger" yet? Seems like a "why didn't I think of that" sort of product. Here is the website...

http://www.electricsupercharger.com

It is on my "to do" list...maybe later this Summer or early Fall.


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Janus Cole
1980 911SC & 1987 944