OK I been reading and following everything I can on getting more HP from my 968. I have a very solid (mechanically speaking) platform that will have new head gasket and the Tip donut replaced shortly.
I am looking to get aprox 300hp, give or take
I see three options to get what I want and the purpose of this post is to get other opinions and weight the Pros vs Cons. I am not looking for all out rebuild or monster HP. So with that here are the options:
1) DS1 Super Charger $4k approx. 325HP(?) no fuss no muss but all in at once.
2) RSBarn N/A Setup $4K approx. 275HP (Pete please weigh in) w- Header/Cat/Exhaust & Chip/some other work. I can build this in stages so easier on the pocket book.
3) Turbo- Mild set up with working parameters similar to what Flash established with the Supercharger setup in keeping injectors and factory engine management but adding a chip. I have been working on this for awhile now and have a lot of the details worked out and will "go public" with shortly. I want to keep 968 as close to stock as possible.
So let the beat down begin, the naysayers, cant be done, your crazy, what alternate universe do you live in stuff begin.
[beat down]
It can't be done. You're crazy. What alternate universe do you live in?!
[/beat down]
<img src="/forum/images/smilies/968/wink.png" class="smilie" alt="" />
I've got a new supercharger on the shelf (still!) and I hope to be able to comment on it soon, otherwise I can't help you with the other two options other than to say I've seen several turbo conversions in person, none of them very nice, and the headache factor alone would steer me away.
In order to save yourself time effort and to reduce the trouble factor, you should ask Flash. I wouldn't consider his association with design one to be a nonstarter or conflict. He has done most of these options or investigated them and has good opinions regarding them.
The big advantage of a turbo is that it has greater ultimate peak horsepower potential than a supercharger. But given that you want to keep the gains relatively modest, and you don't plan to make any internal engine modifications, I don't understand why you would want to go the turbo route over the D1R supercharger. Seems like a lot more headaches, no less cost, even if you do everything yourself, a lot of custom fabrication, and last but not least, turbo lag.
The N/A set-ups are interesting, but I think more of the gains end up being higher in the rpm range than with the supercharger. Fine for a track car, but not optimal for the street.
To me, it seems like a no-brainer: go with the D1R SC (if there are any left).
I'm in the "no-brainer" camp as well (ask my wife). I believe my engine produced about 310 Hp with a fresh top end. There have been soooo many discussions about the finicky nature and huge cost of getting a turbo to
run respectably; yes you can get it to run but after that..... $$$
Supercharge it in the morning, admire it in the afternoon and hit the streets the next day - 100 Km break in <img src="/forum/images/smilies/968/smile.png" class="smilie" alt="" />
Yeah everytime I do the math I come up with the same answer you guys are backing which of course is the supercharger.
The real and only reason I had considered the N/A route was the part by part option for cash flow where as the SC option is all up front.
When you are ready to buy a part for NA, put that cash in a sock somewhere and you'll end up in the same place cost-wise. We need more folks signing up for the SC so I am guessing that it will be a while before we see a new batch. Let D1R know that you are committing to the SC and all be breathing easier (pun intended_).
Doing a turbo conversion is very costly (new rods or pistons to decompress the engine), same for N/A - new cams, exhaust, ECU, etc. Having done a non-D1 supercharger, this is also very expensive (and still in the process of getting right), but required new injectors (above those provided with the kit), a new engine management computer and tune, etc, etc. It does make more power than the 300hp you are looking for, but at considerably more cost and heartache (and the car has been off the road for 4 months of 2011 being modified).
My advice, simply buy the D1 supercharger kit and be happy. I actually have one in a box in storage as I was not confident that we could get the other S/C to work (which we are still playing with). Now I have to wait again until a manual cab comes up for sale (there are only 8 in Australia - 2x 1992 auto's for sale currently - so the D1 kit may not work on these and I would prefer a manual) - and I will fit the D1 kit to that.
I would also go with the D1R kit. I'm currently building my own supercharger setup, and it is certainly going to work out more than the $4,000 for the D1R kit - and no AC on mine.
To be clear about 1 point and this will sound stupid, I would love to get the DS1 setup, right now and be done with it. Problem for me is the $4k up front and its not spending it but having it. I have an end-of-year bonus coming just not sure how much. The price is more than fair and worth it.
If I were to go other option I have a complete 968 engine and could build it on a stand little by little, but I know it would cost me more.
Separate question. If the DS1 kit does not require engine mods, why wouldn't a turbo working under similar boost/engine limitations also work? What am I missing? They are both forced induction, one is belt, other exhaust, bot create boost.
Not trying to be argumentative or combative I just couriuos. On another post Flash was discussing that no "true" 968 Turbo had been done. Would not a Turbo added in the same manor as the DS1 Supercharge qualify?
I was wondering the same thing. In fact, you could ask the inverse question - If you decompress the engine and take the other appropriate precautions, why couldn't a monster-sized supercharger (i.e. what you see in dragsters) produce as much ultimate power as a turbo? But to answer your question, I think you're right - if you keep the engine stock, a turbo would see the same boost limitations as a supercharger, and probably not have the potential to produce appreciably more power.
I think it comes down to convenience, and cost. The fact that the D1R supercharger is a proven system in a bolt-on package makes a compelling case to go with it, given your goals.
For those concerned about a lump sum outlay to purchase the kit. Flash had said something about a layaway plan in his initial post gauging interest for a 3rd batch of Superchargers.
"If enough people line up, then I can start taking deposits. I can do a layaway plan too, so that people can just start sending money and not worry about frittering it away and never getting to the kit."
[color="#282828"]From Flash's last post under Round 3 Supercharger Kit? it looks like an announcement about the next batch is on the way. When that happens I'm sure it will answer many of our questions. [/color]
The issue with a supercharger versus a turbo is how much boost they make and when. A supercharger is driven by the engine crank, so its speed is proportional to the engine speed. So in my case, I am installing a larger crank pulley - which will speed up the supercharger and therefore make more boost (i.e. deliver a greater volume of air into the engine - so more fuel can be added). The build up of air pressure with a supercharger is linear with crank speed (well almost versus a turbo), so there is little engine stress and you can run higher compression ratios. In my case, at 7,000rpm, the supercharger will be rotating at around 50,000rpm impeller speed and will make around 10psi maximum boost (at around 6,000 rpm).
For a turbo, they spin much faster (hence are smaller to make more boost) and boost normally comes in much higher pressure earlier in the rev range. A turbo will spin to over 100,000rpm, will be making full boost at around 3,500rpm and will then have to be wastegated (i.e. bleed of air pressure driving it - and also possibly have a blow-off valve fitted to do the same thing on the air side) to stop it making too much pressure/air delivery. THe more air you push past the hot side of a turbo, the more air you push into the engine, so more air/exhaust goes over the hot side, etc. You have to limit the boost from a turbo, where you design the boost from a supercharger (as it is limited by engine rpm, step-up ratio and supercharger volume).
There is a club member here in Perth that has one of Peter Fitzgerald's (Australia) 968 RS replica's. He has wound down the boost on the engine to make it reliable. It was making around 460hp, it now runs around 405hp at lower boost. There are guys in Sydney with 944 turbo's (2.5 litre engines) getting around 500HP out of these, but only for limited time until they grenade due to the internal loads.
Remember when 1.5 litre F1 cars were making 1,500HP in qualifying trim - then they pretty much threw away the engine.
So yes, you technically can keep stuffing more and more boost pressure into the engine and make more and more power, until the limiting factor breaks. The limiting factor, could be the turbo failing due to the load and rotational speed (i.e. - it literally explodes and then the engine injests it), it could be the oil seal fails (remember the plumes of white smoke from engines when the turbo oil seal would let go), the rod or crank will fail, etc. Another interesting factor is power is torque times engine rpm (with a conversion factor included). So the more torque and rpm's you make, the more power you also have.
Relationship with torque
For a given
torque and speed, the power may be calculated; the relationship between torque in
foot-pounds, rotational speed in
rpm and horsepower is: [img]//upload.wikimedia.org/wikipedia/en/math/4/9/b/49b9b534acdc06c352c3d6bb30fd12da.png[/img]
Where
P is power, τ is torque, and
f is rotations per minute. The constant 5252 is the
truncated value of (33,000 ft·lbf/min)/(2π rad/rev).
Continuing the dialogue;
So, you can run more and more boost into an engine, but the problem is unless the fuel can handle the ignition/compression of the engine, it will knock. So you either have to run an exotic fuel, or ensure that regardless of the amount of boost, the maximum allowable compression ratio is not achieved - or you will have to retard ignition and therefore lose power. This is why turbo engines run lower compression ratio's than naturally aspirated engines.
With my original set-up, the ignition is retarded to prevent knocking (although this could have been due to old fuel), but this was running around 5psi of boost. To run 10 to 11psi of boost, we are dropping the compression to around 10:1 (from the normal 11:1). This will hopefully allow more advance to be dialled back in and therefore make more power. The tuner commented for the original tune, that if you could wind more advance back into the engine - it would have made around 50HP more.
Currently the car is making 209kW (278HP) at the rear wheels (247kW (329HP) calculated at the crank). So if you add back in the 50HP lost through retarding the ignition, this would be close to 375HP at 5psi of boost. Another issue with superchargers is that boost is really the restriction of the engine - not true pressure as such and I am running a high flow exhaust - so boost for the same set-up on a standard car would be slightly higher). Aim at 10/11 psi is around 430HP at crank.
So there are multiple issues to be dealt with when supercharging or turbo charging an engine.
A turbo will also produce a much hotter air charge - which will also lead to pre-ignition, hence the need to intercool the intake air.
Craigawoodman, thats what I'm talking about, Excellent answer! You keyed in on a huge factor I had overlooked which was:
"The build up of air pressure with a supercharger is linear with crank speed (well almost versus a turbo), so there is little engine stress and you can run higher compression ratios"
Now I get why the SC is really a much better "fit" for our cars/application. I knew there was something I was missing and your post nailed it for me.
So with that, by estimate, what is the ceiling/max boost for our car with stock engine mgnt and injectors?
Ah, the answer to your question regarding stock ECU is best answered by Flash, but the answer is almost zero boost. The stock ECU is not calibrated nor does it have maps for forced induction. Flash through doing his Sueprcharger kit had to create a custom ECU map to ensure correct fuel/air mixture and to ensure that the mix did not lean out at partial throttle. Following his posts for his kit, the stock ECU will try to force the air/fuel mix back to 14:1 (stoiciometric mixture) every 1/4 second under partial throttle. So the engine will be running lean most of the time - not good.
Only answer is to run an aftermarket ECU or go with Flash's kit where he provides a new ECU chip which meets Californian emissions reg's. When I bought my kit, it came with a rising rate fuel regulator (i.e. an attempt to shove more fuel into the engine). This is a band-aid at best. Even with the larger injectors provided with the kit - without the rising rate regulator and maxing out the duration for the injector with the aftermarket ECU, the engine was running lean at high RPM - so we went to the next size injector. Once we install the larger crank pulley and run more boost, we might have to go a size bigger again. The aftermarket ECU controls how long the injector is open for to control fuel delivery.
So, my basic understanding is - with stock ECU and stock injectors - bugger all boost can be run and what benefit you got would not be worth it. Have a read of my posts regarding my SC installation and the problems that I have had to go through. As per my first post, much easier to buy a proven product and bolt it up. My end goal was different for this car, but for a daily driver the D1 kit would be excellent.
craig's comments are excellent and spot on.
nothing is perfect. there are other limiting factors to supercharging too. for example, the OEM MAF will probably hold you to about 335. the intake manifold will limit a touch higher, but not all that much. due to the dual resonance design of the 968 intake manifold, 375 is likely going to be slightly optimistic, but a bit over 350 should be achievable, assuming about 9lbs boost, and you can cool it enough. you might have more success with the S2 single resonance manifold.
one has to remember too that the efficiency goes down with a supercharger as the boost goes up. that means higher boost temps, which means intercooling, which reduces boost, which means adding more boost, which means higher boost temps, which means more intercooling...............
when choosing a system, the general rule is:
low end grunt and power = roots blower.
smooth mid-range torque = centrifugal supercharger.
big top end = turbo.
that's exactly why my kit is the way it is. i wanted to find the balance between power, complexity, and reliability. i chose mid-range torque over high end horsepower. but this was for a street car where it's all about mid-range, and not a track car, where upper end would be more important
pick your poison
Flash,
The aftermarket ECU on my car removes the <acronym title='mass air flow'>MAF</acronym> sensor - so reduced inlet restriction (ignoring the additional cost of the aftermarket ECU and tuning). Ninemeister in the UK reportedly made 430hp with a 968 and supercharging.
The more boost - the more likely to have pre-ignition, so fuel quality will become more and more important as you run higher boost levels. At higher boost levels, there is also more parasitic load, so it is not proportional in terms of boost versus increased engine power. Some of the top fuel dragsters need something like 200kW just to drive the supercharger at full boost and the air fuel mixture borders on almost hydraulicing the engine at low RPM it is that rich.
The aim for any engine is to have a wide a range of engine RPM between peak torque and peak HP - as this is the usable range of the engine. If possible a flat torque curve also makes the car easier to drive.
A good supercharged engine will be easier to drive than a turbo as there will be little lag, and no major peak in engine power/torque that gives you that on-off problem with boost. Look at track times between a GT3 and a GT2 - they are normally almost equal. A GT3 will normally be quicker around a race-track than a Turbo 911. This is due to the better throttle response and quicker pick-up than having to wait for the turbo's to spool up. Only on very high speed tracks, where power dictates acceleration will massive HP come into play.
Craig, are you dropping the compression using a 1.4mm head gasket or another way? I had thought about potentially going down this route a little later once I get a basic tune sorted.
Eric,
Yep, dropping the compression ratio through a thicker head gasket, but not the 1.4mm version. It is a custom thickness Cometic gasket, hence why it is taking so long. Both Don (from the old T&D) and Richard from RJP here in Perth have been tick-tacking on what thickness is required to achieve 10:1 compression ratio. It will all depend on how much boost you are going to run. I am still not convinced that the whole pre-ignition issue wasn't just a combination of old fuel (remember the car had been at T&D for roughly 3 months when tuned) and a brand new engine. Once the engine had bedded in some more and with a new dose of fuel - perhaps the problem would not be there.
I have not seen any other articles that have listed issues with the engine pre-igniting under 4.5psi of boost pressure, or even more (the 10psi of the Ninemeister car). But like all things, it is better to be safe than sorry. I will most likely also have to upgrade the supercharger itself as they now have a unit with race bearings, lower drag internals, etc. It looks cheaper to simply buy a new SC unit than send mine back over and have it modified. That way I have a spare supercharger that at a later date I can get modified so when change-outs are required there is no downtime for the car.
For a 944 S2 - I don't think the compression ratio is as high as a 968 - is this correct? If so, you could achieve the same result most likely with a 1.4mm head gasket.
When the engine was rebuilt - you could not get a widefire gasket in 1.4mm. Perhaps another issue.