Supercharging?

[nick_968]

ORIGINAL: Peter Empson

In my experience the centrifugal charger suits our cars perfectly, and retain great (in fact improved in my experience) driveability. I'd like to answer some of your points individually below:

-nothing at low revs -

hmm, at idle and below about 2k you're right, but boost builds quite quickly with revs and is doing really good things at 3k and over the power band any enthusiast is likely to want - between 4-6k - it's stonking.

- scary quick at high revs -

not sure the sub 300bhp I'm running is ever scary, but it is highly amusing in a light car, with overtakes being effortless. For the road I really don't think much more power to weight is required (not that it's going to stop me).

- think tuned 944 turbo but worse lag -

Total twaddle. Sorry, but it's unlike any turbo I've ever driven (noting that I've not driven a car with the very latest ball bearing turbos), there's instantaneous response available at any time, forget having to change down to overtake, it just goes. The power is consistent with rpm and the rush to the red line simply makes the car feel like a much faster tuned NA car, which is exactly what I want in a fun car.

So why not a roots? NA 944s of all variants (with the exception of the 944S of course) have great low down torque and the S2 and 968 are kings of this. The gearing/traction is such that it's arguable whether you really want any more low rev torque to keep it easy to drive on the road (and debatable as to whether the gearbox or engine will take well to it). A roots charger in my experience (on other cars, not a 944 - so I'm open minded) doesn't tend to give the feel of a true sports car, there's no 'on cam' type rush to the redline.

If you read my previous posts you will see I am not blinkered into thinking that this is the right choice for everyone, the cost alone to do the job properly will see to that, but I am having more fun than ever before. Of course if anyone ever wants to experience it and they're local they just have to pm me.

Good post Peter. I agree with what you say as the centrifugal SC is basically the best of both worlds i.e. a turbo power curve without the lag as the boost response is directly linked to your right foot. The key is in making the installation work. Boosting an NA car, 968 or 944 is no mean feat and takes a lot of time = R&D. The problem I always had with the SC kits offered by shops was that they did not put the R&D into the product and instead use the first few customers cars as test mules. You car seems to work very well according to what I have heard on the grapevine and the weight loss no doubt makes it even more special.

 

[Peter Empson]

Thanks Nick. I agree, most kits are quite incomplete. For example the SFR racing one has (or had when I last looked) no provision to allow the timing to be retarded, which to me sounds quite ludicrous and was the reason I went with a piggy back.

 

[sawood12]

ORIGINAL: mr brightside

Hmm, this is getting technical. So with Megasquirt i can ditch my barn door MAF and use a manifold pressure sensor and a wide band O2 sensor instead, how does this tell the engine how much mass of air's going in or isn't it working off mass any longer? If it's going on pressure and density (?) does it have to be told the diameter of the throttle body or something? I don't like the sound of this farting around with crank position sensors and stuff, this is why i'd prefer to have it installed by a specialist Porsche tuning shop as i don't believe for a minute that it's as simple as it sounds, you fellas have obviously done this before!

This is what mapping is all about and why the same set up on two different cars will need different maps (so you can't necessarily benefit directly from someone else's efforts) - This is why Porsches standard map is conservative and not optimised, and why there is an opportunity for individuals to tune their cars - this doesn't make them cleverer engineers than Porsche at all like some aftermarket tuners will have you believe. The tricky things with standalone is not the hardware, any semi-skilled grease monkey can buy this kit and install it - it is the mapping that makes it work - and this can only really be done on a trial and error basis and if you get it wrong it can go wrong with style (remember Fen's wrap up?).

This is why the Vitesse set up is such a good bit of kit in my view. There is no point in going standalone unless you are going to get significant gains to make the cost and effort worth the while. The Vitesse kit appears to be pricy on the face of it, unless you're Megasquirting and strike upon a setup that works well fairly quickly negating the need for extensive rolling road testing, the Vitesse kit will easily work out the cheapest option - and it is proved over enough cars now that it works out of the box.

What you need is a centrifugal compressor SC with a CVT drive so the RPM of the compressor is not geared directly to the crank RPM and you can keep the compressor RPM constant at any engine RPM (within reason) and control boost pressure by bleeding off excess pressure - a bit like a wastegate, but on the compressor rather than a turbine. Also IC's work better with centrifugal compressor type SC's as all the compression is done internally within the compressor and not downstream in the intake itself. Don't know if an SC of this type exists.

 

[bertelli_1]

Peter, I was trying to point out the general characteristics of different types of supercharger. I have not driven a supercharged 944/968 - I have driven, tested, tuned and fixed an awful lot of cars with them all types fitted so my opinion is based on experience but at the end of the day its a personal preference.

 

[mr brightside]

ORIGINAL: sawood12
This is why the Vitesse set up is such a good bit of kit in my view. There is no point in going standalone unless you are going to get significant gains to make the cost and effort worth the while. The Vitesse kit appears to be pricy on the face of it, unless you're Megasquirting and strike upon a setup that works well fairly quickly negating the need for extensive rolling road testing, the Vitesse kit will easily work out the cheapest option - and it is proved over enough cars now that it works out of the box.

I didn't know Vitesse was available in any form for a 2.5 NA, i thought it was only compatible with S2 and Turbos? Is it the piggyback board you're talking about or a complete system which replaces your old MAF and Motronic box? If it's a complete system that's great, i know loads of people on here use Vitesse but i'd never considered it due to an assumption of incompatibility.

I've got another question too, do systems like Vitesse and MS allow you to modify your ignition and fuelling parameters?

 

[Suffolk944]

Yes the Vitesse MAF is a complete kit - they do provide a piggyback but thats an additional option and by no means essential. Not sure about the issue of ignition adjustment. The guy who runs Vitesse - John- is very helpful and responsive to email queries sent to him direct, am sure he could fill you in with any tech questions you may have.

 

[TTM]

The Vitesse MAF kit comes with predefined fuel/ignition maps ("images") implemented on a chipboard that replaces the DME chip in the DME box.
The Piggyback allows to adjust fueling over the fuel map contained in each image, but as the kit comes it is not possible to adjust the ignition.

 

[sawood12]

The vflex option which comes with the piggy back incorporates a separate MAP sensor that is able to map ignition according to manifold pressure. Yes, it is primarily targeted and developed for turbo's.

The kit comes in two forms - the simple MAF kit and the piggy back which allows you to further tune the fuelling.

 

[Peter Empson]

ORIGINAL: mr brightside


I didn't know Vitesse was available in any form for a 2.5 NA, i thought it was only compatible with S2 and Turbos? Is it the piggyback board you're talking about or a complete system which replaces your old MAF and Motronic box? If it's a complete system that's great, i know loads of people on here use Vitesse but i'd never considered it due to an assumption of incompatibility.

I've got another question too, do systems like Vitesse and MS allow you to modify your ignition and fuelling parameters?

The Piggyback will work with the standard barn door - I'm using a scivision maf which pretends it's one after all. As far as I'm aware is compatible with all the oval dash 944s (I'm not sure about the earlier ones that have a soldered chip but I guess it might be possible to modify them as well). Whilst the Vitesse stuff isn't 'cheap' the pre and after sales support is superb and this can really make the purchase price seem a bargain (I've had responses on a Sunday and help with assistance with issues totally unrelated to his product - it's clear he's a real enthusiast).

 

[Bob]

Has anyone seen the supercharged 968 for sale at Malton Cars?

It looks fantastic and you would hope it is immaculate for £30,000 yet it only has 340 bhp and 288 torque?????

 

[sawood12]

That's a bit steep surely? It must have more on it than just a supercharger? You could buy an immaculate 968 and install a supercharger kit for not far off half that price.

The 340bhp sounds OK but the 288 ftlb of torque sounds a bit light?

 

[Simon Wilson]

I have run a supercharged 924 in the Porsche Club GB speed championship for many years now and can say with some certainty that the 924/944 makes a great base for such a conversion. It goes well.

In my case I used an EatonM62 and fabricated an intake and intercooler setup. I have Motec engine management and the car makes 245bhp. Its a hoot to drive.

The engine management is necessary to get the best from the conversion and MOTEC, whilst more expensive than some systems, has added smoothness and flexibility. I agree that for the larger models the Roots blowers are perhaps overkill as traction is an issue when cars are lightened and the extra torque may be too much for the std traction levels of an S2 model. However for the smaller 2.0 or 2.5 models the roots is well suited.

I also agree that the roots type gives less of a 'rush' than the cetrifugal types, however I cannot agree that its any less a sportscar feel, quite the opposite in fact as the constant 'push' of a blower when on song is quite addictive.

Happy to let folk know about the conversion if it helps.

Cheers
Simon

 

[Peter Empson]

ORIGINAL: Simon Wilson

I also agree that the roots type gives less of a 'rush' than the cetrifugal types, however I cannot agree that its any less a sportscar feel, quite the opposite in fact as the constant 'push' of a blower when on song is quite addictive.

Happy to let folk know about the conversion if it helps.

Cheers
Simon

That's excellent to know Simon, I'd love to see some pics of the install []

 

[Diver944]

ORIGINAL: sawood12

That's a bit steep surely? It must have more on it than just a supercharger?

The Malton website says it's had the works done - Motec, intercooler, Big Red brakes, Suspension and most importantly the engine has now been rebuilt with low compression so the boost pressure could be upped for over 400bhp [8D]

 

[sawood12]

ORIGINAL: Diver944

ORIGINAL: sawood12

That's a bit steep surely? It must have more on it than just a supercharger?

The Malton website says it's had the works done - Motec, intercooler, Big Red brakes, Suspension and most importantly the engine has now been rebuilt with low compression so the boost pressure could be upped for over 400bhp [8D]

That's more like it - though I reckon your 3.2 would still give it a good spanking though.

 

[Peter Empson]

Simon kindly emailed me a couple of pics of his setup

"Its an Eaton supercharger with full MOTEC M400 Management plus a high power
spark amp.
Power is approx 245bhp and 245ftilbs torque. Weight is 980kilos."

 

[Peter Empson]

and the other pic (I love this!)

 

[Simon Wilson]

Thanks for posting the shots Peter. I should point out that the ECU in the interior shot is the earlier Emerald M3D system. It was good but not as good as the more recently fitted MOTEC system.

Cheers
Simon

 

[Mike_Pollock]

When is your dash going to look like that then Peter?


Must add that Peters engine gives a real solid push and amazing acceleration
on the track, like a well tuned sport engine coming on cam.
Helped but the added lightne

 

[Peter Empson]

ORIGINAL: A9XXC

When is your dash going to look like that then Peter?

Can't say I'm not tempted, there's probably nearly -20kg to be had from going to that extent, I was going to mould a lightweight dash from CF and FG but the stock shape is pretty complex for a beginner, and I really haven't had the time. Maybe next year!