i have never been a fan of a dual purpose car - i have always said "keep the street car the street car, and if you want to play on the track, get a track car" - this is for a number of reasons, not the least of which is reliability once you start modding - safety is another big one - there is no way to stay on top of the items on the car that could cause issues on the track, if you are driving it every day - a track car goes through a complete inspection before and after each event - a street car gets driven to the track, more often than not forgoing any inspection at all, and items wear gradually, so are often missed
no chance i would do an ls1 - while fun at the onset, it doesn't take long to realize the gearing is all wrong, the chassis isn't up to it, and the extra weight is a drag, requiring a complete redo of the transaxle to change gearing, bracing to properly handle the stresses, and a rework of the suspension and brakes to handle the new loads - quite the project to do it right - i've done a number of different V8 conversions, a couple of which were a real blast for a while to drive, and i've have seen and driven countless others - in the end they are all the same - no matter what anybody says about it, after a couple of years, those conversions always rattle and run weird - that's why they constantly come up for sale - sounds great on paper, but not so great in reality - if you get it done right, fun for a while though
but, that is exactly why i designed the SC kit the way i did - i was trying to hit the best compromise i could, refusing to give up on reliability, and instead choosing to give up some top end power to get it
So far the only thing untouched on my car is the engine/tranny (save for air box mod and chip).
I'm not a big fan of trailer queens, nor am I keen on the idea of putting my car on stands for a couple of months while working on major changes. I like the idea of a complete kit as it is a weekend job with instant satisfaction.
What I'm looking for is to know, and not just in general but rather for each specific available kit, what gains that are possibly attainable given the amount of time, money and labour invested. Creators of both of the two latest kits have been clear about money vs result and regardless of the level of final tinkering and tuning included it is always something that can be done, especially as hours when working on your own car is cheap.
No, turbo is not for me at this time. It would be cool to build a smooth running 16 valve turbo but so far I haven't seen a turbo retrofit with constant and flawless performance every time and all the time. The easy solution would be drop in a complete 951 driveline but where's the fun in that?
i'm just having a hard time imagining actually using any more power - as it stands now, i have a hard time getting what i have to hook up on the ground at launch - it pulls so hard through the lower gears that you are hanging on for control - it's not like big block chassis twisting torque, but it's enough to see that with less suspension, tire, or attention paid, that somebody could get into trouble in a hurry
i know it's the natural tendency to want more, to want to tinker, or even to think about some target horsepower number, but it's not horsepower that makes a car go fast - it's torque, and having that torque over a wide and accessible band
so again, i would look to what the car will be used for - then determine what power you want, and where you want it - that will help you decide on what to do from there
i'm not going to recommend one kit over another - only you can decide what you want - i have in fact recommended against my kit to a few people, because they either want more than it can offer, or they drive in such a manner that it would not be of particular benefit to them anyway, or they are not prepared to do what is needed to ensure safe operation
one thing that you need to consider carefully though, no matter what you do, is how much time you really want to spend tinkering - keep in mind that if you are tinkering on a forced induction kit, it means that you are not driving it - unlike a normally aspirated engine, you can't run a forced induction engine when it isn't right, without serious risk of very expensive damage - tuning is as much art as it is science too - it doesn't happen quickly or easily, nor without a fair amount of expense - i've got over $4k into tuning this one, and i still have one more map to work on this week before i call it done
lots to think about - go slowly and consider everything
I obviously haven't driven Flash's car, but I think I know where he's coming from, and it makes a lot of sense. I know I've told this story a few times, so please bear with me, but when I was tracking my car, I had gotten to where my times, while greatly improved from where I had started, had stagnated. I mentioned this to the owner of the track, a retired racer of 25 years (his last ride was a Ferrari GTP car) took it for a spin, as was only able to beat my time by a few tenths of a second [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img] [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img] [img]style_emoticons/<#EMO_DIR#>/biggrin.gif[/img] . He told me my car is decently set up, but that it's limitation is that it simply doesn't have enough torque (he actually used that word, as opposed to "power") to pull it out of the turns properly. Now, I'm sure there is plently to be gained through more upgrades to the suspension as well, but this experience really shows how much our cars are limited by their relative lack of torque, which I'm sure the D1 SC goes a very long way toward curing.
Not to get too far off subject, but even though the D1 SC is primarily intended for the street, I'm sure it would do wonders for a dual-purpose car as well. I know, I know, a dual purpose car is not the ideal (I would give my eye teeth for a dedicated track car, but I don't have the money, nor the space to store it), but my plan is to add the SC, the chassis brace, some racing seats, upgraded shocks and struts, along with a few other mods, and essentially turn it into a streetable track car. If and when I get the means to build a dedicated track car, I'll put the 968 back to more streetable trim. My favorite thing about the 968 is its versatility, and I think the D1 SC just adds to this quality and really completes the car.
I have been playing around with supercharging on the 968 motor for 12 months now. My car is a race only car, but this is my 2 cents worth on making more power with a supercharger:
For a road car, even a road car occasionally driven at the track for fun, I would think that any of the kits are more than adequate for performance which doesn't compromise daily driving. However, if you are buying a kit for that purpose you want to bolt in on and just enjoy it, so obviously the more complete it is the better and it sounds like Flash has put in a lot of effort and gone a long way towards achieving a trouble free bolt on performance experience. Sounds like a good price too. The other kits probably work fine too, but maybe haven't been thought out as completely and may or may not require more tinkering to get to a trouble free state.
Once the focus becomes much more performance orientated the kits are all a compromise. Boost is boost regardless of whether it comes from a supercharger or a turbocharger. Different ways of achieving it, different boost curves and different levels of byproduct such as heat and drag, but the subject is still forced induction and the engine issues for performance are pretty much the same. I would start by saying that for big power levels turbocharging offers a much easier pathway with a lot more hardware availabe to easily arrive at a setup that does what you want it to do in terms of boost delivery.
In theory you can also achieve big power with a centrifugal blower, but if you pursue more power with one of the existing kits, or even want to use kit level power outputs in aggressive all out track racing where the engine spends it's life bouncing off the rev limit (my case), you will have to modify existing kits and you run into problems straight away. The problems such as controlling heat and tuning are common to all forced induction engines turbo or supercharged. For more power you need intercooling, proper tuning control and to run any more than kit level boost on pump petrol you have to build the engine for it in the same way as you do with a turbocharger, better pistons, lower compression ratio etc etc.
Assuming you do build your engine properly, getting the right boost delivery with a centrifugal charger is more difficult than with a turbocharger. To start with belt slip is a major issue, especially with the puny little 5 inch crank pulleys on the 968 motor. There is a reason big Vortech setups on V8s use 8 and 9 inch crank pulleys. With our tiny little crank pulleys you need an even tinier supercharger pulley to spin the head at a decent speed to make boost. The Procharger C2 in the SFR kit is a very good head and is theoretically capable of 1100cfm, but only if you spin it closer to it's design limit of 80,000rpm. You can't possibly achieve this on an SFR kit with standard pulleys. The "7psi" pulley is a tiny 2.55 inches in diameter. That gets you about 62,000rpm with a standard crank pulley and even then you will get a lot of belt slip with the standard 6 rib belt and belt routing. To make more boost you would need even tinier pulleys and slippage would be cronic. I had a 2.38 inch pulley made (theoretically a "9psi" pulley), and even with cross grooving, much more belt wrap and belt spray it slipped so badly it made less consistent boost than the 7psi one. So unless you are prepared to modify your belt and pulley setup you will never make big boost. I am currently having a custom 7 inch 8 rib crank pulley made for my new engine, which is currently being built. But this is a case of engineering something I already have to work better. It is not a better route cost wise than starting with a turbo in the first place.
Even if you can spin a centrifugal head to the right speed to get the boost you want, you still miss out on easily adjustable low end boost of a turbo. If you gear it with pulleys to spin at maximum rpm at your redline you will get more boost earlier in the rpm range, but you will likely produce too much boost at the top end. It is possible to control the boost with intake side relief valves,which I am also trying out, but it's not too efficient to spend power to make boost then just dump it.
I have already started down the supercharger power path and will just keep going as much for the fun of playing with it as anything. You can afford to play with a car that isn't a daily driver. It's interesting to try and do something different. I also really like the instant throttle response and linear power delivery for track racing. Flash is right however, the kit power is perfect for a very fun road car but if you want more power than the kit offers go turbo. It will be cheaper, easier and get you to your desired result a lot quicker in the end.
Thanks all for the very informative responses.
So, to sum it up:
With a super charger kit there are some gains to be had, largely depending on how complete the kit is to begin with. The more finished it is, the lesser the gains to expect. It seems that going stand alone management could provide the most gain, mainly since the stock ignition is a weak spot, but it is not necessary and not worth it cost-wise unless you take into account the fun in tweaking and learning by working on your car.
For larger hp/torque numbers turbo is the way to go. Large numbers can be achieved with a super charger as well but the cost and effort speaks against it.
OT: If I where to swap the engine for something else it would not be for a V8 but rather a 3 or 4 disc turbocharged rotary. Not gonna happen this season though... [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]
Yeah a 3 rotor wankel would be pretty cool. 20bt's can be had pretty cheap IIRC.
there isn't a direct correlation between being more finished and lower numbers - the reason the numbers come down on our kit is deliberate - it is to accommodate the nominal conditions we will find in the engines - we did an early run that was a lot higher, but it was very dangerous, and way out of injector
if you really wanted to tweak this thing, and were prepared to tear your motor apart and make some significant changes to do it, you could easily get 350hp out of it, and probably as much as 375 - i plan to do just that for the track toy
a bigger head unit could make even more, but that means more compromises
the ignition isn't really a problem at all, and there is no reason to go standalone - people say that because they don't know how to, or just plain don't want to tune the motronic - fortunately, now i do - it's actually a pretty decent unit, though a standalone would be easier to manipulate, due purely to newer software and and a better usb interface
that being said, a turbo still has a LOT more flexibility and capability for big numbers
I didn't mean that your kit is capable of lower numbers, I meant that the level of completion implies that it is more optimized out of the box - hence there are fewer things to attend to and that means less to gain form such work.
Hmm, I always thought of the ignition to be a bit stupid (as it always turns out that I am). But for me, an easy-to-understand interface and good support is important, I doubt that Bosch would take me serious if I called them with generic questions about the Motronic. [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]
lol - no worries - when you said "The more finished it is, the lesser the gains to expect" i thought you meant that the more complete the kit, the lower the output - that would actually be backwards, though in my case, i am deliberately limiting the output to try to avoid catastrophe
good luck getting anybody at all to give you any information about the motronic - everybody i know who knows anything about it is being very cagey about giving up any info - presumably this is to protect their income from tuning, but i have a hard time imagining that they are deriving any real income anyway
Ok, given all of the threads covering supercharging and wanting to get more power for my 968 in motorsport events to bloody a few noses of GT3 drivers, etc, I thought I would go and do some research. There are a couple of good books I have found on supercharging and it is all good stuff. Biggests issue is boost pressure versus premature detonation (knocking) and also heat of air charge. So to run bigger boost, you need to cool the air charge.
For higher RPM applications a centrifugal supercharger is better, but you still need to run an intercooler. Lindsey racing has a novel intercooler which effectively replaces air piping, but you need to place the water radiator (as it is a water-to-air intercooler) somewhere. If I can get an intercooler (water-to-air) option, I will look at how I can get something like 380hp. Ninemeister in the UK have put an article out quoting 430hp from a 968. I still want reliability (car currently need a new clutch - friction disc material came off clutch at Bathurst) and possibly gearbox work because of it.
God knows if the end product will be drivable on the track or not, but the standard car does not need a lot of throttle modulation currently - so the chassis should be able to handle a lot more power.
Once I do a bit more research and some calc's I will see where I get to. but for sure, bigger injectors will be required to fuel the thing.
It should be a lot cheaper than a $25k Powerhaus engine, and hopefully easier to drive on the track.
Interesting topic and I think both Bob and Steve pretty much have it covered. While there always seems to be a bit of discrepancy between hp numbers from country to country, 350hp in anyone's language is a lot in these little old forgotten Porsches. They do indeed continue the tradition of boxing above their weight class.
My friend and mechanic is putting together a 'budget' turbo S2 motor. Aftermarket rods, 8:1.0 c/r Alusil compatible pistons, SFR intake, making up a cross pollination of S2 and 951 exhaust headers himself, and going to run off a Vitesse Piggyback. This will still cost a pretty penny, (although about 15% cost of some other builds I know of) but should result in 400whp day in day out. Running on E85 with the 16v head and low c/r pistons will go a long way to eradicating knock. The biggest thing he might have to consider now is uprating the suspension and brakes to keep up with the extra hp.
I would think that with some similar rods and lower c/r pistons you could utilise some extra psi with the s/c, but as Steve points out, the crank pulleys might be an issue? If this could be overcome then realistically you should be able to achieve some numbers north of 400hp. To control it I would go standalone and just put the time into tuning. I would also run E85 on a secondary map for track days. It really does burn a lot cooler and respond to extra ign and it's way cheaper than Racefuel. There's many of us running around on E85 for some years now to no obvious detriment to the motor and supporting components. Here's a good thread about a guy in Sweden who has worked up to running his 3L 8v 951 at 9:5.1 E85 and well over 500whp European. He is running conservative boost for a turbo car of max 1.3bar / 19psi. Guys with their EVOs etc are running 35psi + nowdays. So we're all pretty conservative by comparison. There are of course mechanical reasons for this also.
EDIT: I was going to leave a link to the Swedish guy's car on Rennlist, but I guess that's verboten here? Anyway, search under the username Corleone in the 944 turbo section for an interesting read. Unlike many of the closed modded scene, he's quite open about his build.
If I was going to s/c a car I'd get one of the D1s with c/r of approx. 10:1.0 running E85 at say 1 bar. That would be interesting. Looking at Steve's race videos you can see just how effective this route can be!
you can't think about a centrifugal unit like a turbo - while it's built very similarly, it's not anything like it in operation
the issue with a centrifugal unit is its upper end limitation - this is a flow issue - boost is a function of turbine speed - it can only spin so fast - the C2 procharger (which is what has been used) can only turn 80k max - that present a boost limitation - it is rated at only 375hp max - the C94 rotrex has a bit over a 100k limit - that puts it at 400hp max, assuming everything else is perfect - there is a bigger rotrex though, just as there is a bigger procharger - you just have to choose the right one for your application
p.s. - intakes won't make that much of a difference - neither will headers - a few here and there, but not like on a normally aspirated engine or a turbo - those things are flow pressure dependent - a centrifugal unit is not
when thinking about boost, and designing the kit, 10lbs is a LOT of boost in the centrifugal world
The god thing about a supercharger is that boost is proportional to engine speed and there is normally a small amount of boost at idle (depending on type of compressor used). Heat is the biggest issue with supercharging and the various type of blower create more of less heat. If you want to run 10 lbs of boost - this as per Flash's post is a lot and will most likely require intercooling. The good thing about supercharging is that as long as the overall boost level is not too high, you do not have to reduce compression ratio - so you have low down torque and you get no lag as such.
As per Flash's post, you need to match the supercharger to the application, if you are overboosting a small supercharger, you make way more heat and it is inefficient. Much better to get the right size supercharger and operate it in the most efficient zone of it's efficiency curve (thereby creating much less heat) and much less chance of pre-ignition (knocking).
When it is all said and done - cooling the air going into the cylinder is the best way of preventing pre-ignition, so for any high boost application, you need to intercool. Same for throttle off - it is not like a tubo, where you need to wastegate to prevent overboosting - you use a wastegate to drop the excess air from the compressor.
I have a couple of good books on Supercharging that I am working my way through. All in all an interesting subject.
Flash,
How do you calculate the hp limits you project for the C2 and Rotrex?
The maximum impeller speeds don't directly relate to horsepower potential as it depends on the size of the charger obviously. The big Vortechs spin quite slow in comparison to the Rotrex and C2 but make much bigger flow figures and power potential.
I notice on the Rotrex site they quote the 94 as having a 250-400hp range and flowing a maximum of .37kg/s (approx 641CFM), whereas Procharger quote 1100CFM for the C2. The 175-375hp is quoted for the C2 as the base range of the naturally aspirated motor it suits, but the supercharged power output is a theoretical maximum of 725hp. The C2 is a bigger head with more flow and power potential than the rotrex as I read it.
i am not calculating them - those are directly from procharger and rotrex - in speaking with them, they have been very clear that the volumetric efficiency, step up ratio, and impeller design of the unit is what determines the specs they posted
if you want 400, you'll be changing to a bigger unit
by the way, pete has been playing with an SFR system that blew an engine - no chance of going over 400, no matter what pulley - contact him for details, as i don't want to make comment on another system here
So Craig, are you going to S/c your car? Pretty sure I had a short chat with you when you came down to Eastern Creek last month with the PCNSW day.
Very nice car and it would be a beast with a puffer on there.
I have the Black be-winged 951. Turned a respectable 1.47 but got held up....hahah, that's what they all say...[img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]
Steve, have you got any more videos of late?
Patrick
Hi Patrick,
No videos lately. The car has been off the road for a few months now for pre season rebuild. (Our season starts at th end of October). I ended up giving up on having an engine built and shipped, it was ridiculously complicated and expensive to ship parts from Dubai to the US for work to be done and a lot of builders couldn't get it done in my time frame anyway. Right now I am waiting on pistons and parts to arrive and am rebuilding a spare engine I have locally. Dropping the CR to 9:1 for a bit more boost tolerance.
I have rewired the car completely and am installing a multi- wideband setup for individual cylinder tuning on the Motec which will be interesting. Shooting for absolute reliability and driveability in the 1 hour races rather than outright power as I am still limited to about 315whp in GTC category or 340whp if I step up to GTB. Still, I figure the setup will be a good foundation for playing with later if I want to test the power limits of the C2 for myself.
Patrick,
I want more power as I am pretty close to the limits of what I have done to the car overall. I have done brakes, suspension, etc and the last part of the equation is to chase more power, I have the corner speed and braking to keep up with more modern cars, but get blown away on the straights. The 968 for sale that was making 250hp at the wheels naturally aspirated was of interest, but in terms of power per $ - supercharging seems to be the way to go. I would love the 500HP Powerhaus turbo engine, but big HP turbo's are rarely good on a track due to excessive lag. I believe that the proportionality and lack of lag of a supercharged engine will probably be better for the track.
As per the threads, getting the right supercharger, which will fit (and keep the A/C for QLD) will be a challenge. It will need to be intercooled - so another challenge. THe engine needs a refresh and cams inspected and a new timing belt and water pump (a financial challenge). I have been looking to boost power for around two years. I didn't do it last year as it would have changed my classification (I needed a standard weight and output car to be in E class) and I ended up winning the overall club championship. This year has been pretty dissappointing (both competition wise and reliability wise), so it makes sense to get the car sorted this year - but I am bloody busy and my mechanic is 550km away (and the car has almost lived there this year).
So the intent is there, the finances are slightly lacking (I have to do my tax and I am not sure if this will be good or bad). All up, I will need around $10k plus to do the required maintenance and supercharger - and there is a nice 968 convertible for sale. Nothing happens when you want it to or can afford it.
Craig
I thought the power output on our fantastic cars was limited by the transmission. And, that a turbocharged engine is more dangerous to the tranny's internals than the smooth power delivery of a supercharged engine. If those two statements are true, then you could have a 500lbf supercharged engine with a higher safety margin, tranny-wise, than a 500lbf turbocharged engine. Or, you could have a more powerful supercharged engine with the same safety margin, again tranny-wise, as a 500lbf turbocharged engine. Or, you could get a different transmission, but you have to draw the line somewhere I guess [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]