333pg333

Bit of a hypothetical one here, but I got to thinking yesterday after being at the track with some Cup Cars amongst others and even though my car felt about as good as it ever has in isolation circulating, once one of these beasts came up and swallowed and spat me out in very quick time while I'm wringing my little car's neck, I wondered why are they just so much faster than our cars.

Now of course this is a pretty open and loaded question and of course we all know most of the answers. But it is an interesting exercise just the same. I asked one of the drivers why are they so much better. Is it the grip, chassis, chassis/body rigidity, torque, aero, suspension package, transmission...he just said...yes.

So in the effort of making inroads on these cars naturally we all think, well if I make a 3L motor with 500hp and my car is as light or lighter than a Cup, then I must be faster than them. Wrong. However I still want to catch up a little. One of the obvious things I noticed was how there is virtually no transition time in a Cup between turning, stopping, and going. It made my car which is on 800/900lb springs feel like I was driving an old Caddy from the 70's. Where we have to wait for the car to catch a set, then often slowly apply the power, they just simply turn and mash. Where we are coming into a twisty off camber corner and have to brake and wait...wait some more...almost there...ok, now apply some gas. They just tap the brakes and power away. Even our method of heel toeing vs sequential loses a lot of time...plus a high compression motor just has that engine braking that we lack.

So I thought, well why can't I bridge the gap a little more. When I've caged the car and stripped as much out of it as possible, why can't I go up to say 1400lb springs? Of course we have a much older style of suspension especially in the rear. No multilink etc, but I'm thinking the multilink would be most advantageous when comparing street cars with springs of e.g. 250lb where the deflections are much more pronounced. On cars with over 1000lb springs where there would be very little movement by comparison, then wouldn't the disadvantages be a lot more minimised? Our rear McPherson strut trailing arms are essentially off a rear engined VW. So you know when they're on a lift you see the wheels drop down and go into positive camber. With modern multi link/arm suspension you don't get the same loss of camber. The arc is a lot straighter up and down. So if we have a stiffer lighter body and stiffer springs, will this not be more similar to the twin a arm rear suspension in it's rate of camber movement? Therefore won't it be maintaining max contact patch allowing the 12" rubber to do it's thing also?

I know this sounds simplistic and I'm sure Jim and others will come on and set me straight, but I'm going to give it a try next year once the body is sorted out.
I also realise there is a case of diminishing returns. Eventually you will run out of traction with too stiff a setup. Interestingly a couple of our friends who race overseas, Henk in Thailand, and Steve/Dubai in, well, Dubai, they have rear springs over 1000lb/in so it's clearly possible that this is ok. (Current Cup cars have spring rates of over 1500lb to put this into perspective) When you see original footage of the 944t Cup cars they roll and slide and have no visible downforce and sure, for the time they were great, but I'm sure that we can up the ante and live to race another day so to speak. Having said all that, I'd like to swap out to a twin A Arm setup oneday too. Don't think that would be so terribly hard really.

You can see in this clip at the end where the Cup Car passes me at the end of the straight. He had been close to me before we turned onto it so it took him the length to catch and pass me, but then he just smoothly drives away. He wasn't even one of the quick ones on the day. On the day I was driving about as well as I can overall and the car was going really well too, but I just have no hope in hell against these guys. Would 200hp extra really help? Possibly make me slower? Guess having 12" Michellin slicks vs 10" Nittos could make a bit of difference too although I have to say again how much I like the Nittos.

I realise people will be bored with my clips, but it's the best way I can illustrate my point. You can cut to the chase (so to speak) at around the 8min mark.


http://www.youtube.com/watch?v=fLi7RFFWFmM

Chris White

Here are a couple of things to think about -
The upper limit to spring rates is determined by track smoothness. Rough tracks will not let you run high spring rates.

The higher the spring rate the greater the weight transfer.

The main reason people go to a higher spring rate is to minimize suspension movement. Street based track cars always have a compromise in suspension design to allow movement, as the suspension moves is will change its alignment – bump steer other things will change the toe, camber and the relationship between the two wheels.

In reality the optimal suspension is the softest rate that keeps the alignment in check and the wheels on the ground. Softer sprung cars will allow you to get on the throttle earlier but may not be as steady.

And last but not least….you need to get on the throttle much earlier….if the rear is stepping out making the rear stiffer will not help…

ritzblitz

This.

I love the idea of trying to make the 944 suspension as good as possible, but trying to make a 944 turbo as good as a 997 cup is a little crazy. You would be trying to make a street car as good as a purpose built race car.

Another thing to consider is that it's turbo vs NA.

Oddjob

Over the years, the usable range of spring rates on 944s has increased. Both because of available shock damping and improved tire technology. But, as with Chris, you can go too stiff. Which is based on several factors, as mentioned track surface, shock valving car weight and tires/wheel size.

There is also concern with the modern tires, 18" wheels (low profile tires), solid suspension bushings, stiff shocks and spring rates, and hard use - that the old 944 suspension parts and body pickup points will and are failing from fatigue at a much higher rate.

So there are consequences of going stiffer, both performance and safety-wise.

Horsepower can be a great equilizer, and adding 200 hp will make a big difference. It wont make the car slower, but it can make it much more difficult to drive to and at the limit. So there will be a learning curve re-adjusting to the added hp, and the brakes and suspension may need to be upgraded to handle the power increase.

You are giving Nitto's too much credit. There is a significant performance increase between full racing slicks and any of the DOT R-comps.

Regardless, dont try to compare or build your car to be competitive w/ 996/997 Cups - it will be an incredibly frustrating and expensive effort.

They are in a different league performance-wise, and building a higher hp motor, dropping a couple hundred pounds, and increasing spring rate in a 944 will not get you close to a current cup.

My 951s are not slow cars and these two 996 Cups (and any other well driven one) are 8-10 seconds a lap faster at my home track. The 997s are faster yet.

https://rennlist.com/forums/showthre...ferrerid=15894

The "produced" video is pretty cheesy, but gives a feel for the performance of the modern cup cars.

http://www.youtube.com/watch?v=vdA0rjwfwao

George D

Patrick,

I would give these folks a call. http://www.raetech.com/Suspension/Susp_Design.php They have a VERY competitive 951.

Oddjob

George,

Raetech work on or build any production based 944/951's ? Dave Finch's old SCCA race car is an N/A motored fully tube framed car.

George D

I don't know. I believe Finch only raced the above mentioned car. He was in collaboration with Porsche in the late 80's with their motorsports activities. Thought Raetech may have some insight to offer Patrick.

Patrick could send Dave a nice e-mail. You never know what insight he may have to offer.

Patrick is asking good questions. To build a suspension for the 951 to be competitive with modern Porsche Cup Racing cars, he needs good advise, a big stash of money, and.....really good advise.

333pg333

Well don't mistaken me for thinking I can build a Cup beater, just bridge the gap a little. I realise that it's not just a matter of throwing on a set of 1500lb springs and thinking that'll do and of course track surface is very much in the mix.
To Jim's point about the suspension pickup points failing, that is constructive analysis. I would imagine there is a way of bolstering ours? I have very little, if any rubber left in my car as far as bushings/bearings go. In reality our entire bodies probably flex too much to go crazy with suspension rates, this is really what the question was about. Just seeing what you guys thought was possible in effect.

Jim is that your car in that video clip? This is a fast Cup car no doubt and the camera angle doesn't hurt any.

A couple of things Chris. You say with higher spring rate, there is more weight transfer. I'm not sure I understand this? I would think that there is less, not more? Aren't we restricting transfer more? That's the idea from my angle.
As far as going for softest as possible is optimum, I also have to say that I feel that I can get onto the throttle earlier now with my new stiffer springs than before. You don't have to wait for the car to roll, set, and go. Now that period is shortened and I am getting on the gas earlier. You say that I need to get onto the gas much earlier though. Are you referring to me or just in general? I don't think I can get on too much earlier than the clip. I am at risk of losing adhesion...I'm pretty sure. I compared it to the pro driving my car last time and he does get on a little earlier in some corners, but he was also on Hoosiers. Granted, there's always room for improvement though.

George, I'd love to do something with Raetech but that's a whole other league. In truth this question is really just to get people's opinions like Jim, Chris', yourself and a few others to what is possible, what isn't. We know that Dubai has 900/1100lb so perhaps he's at the limit?

mclarenno9

You cannot reduce load transfer unless you lighten the car, change track width/wheelbase or lower the CG. With stiffer springs/shocks you will increase the rate of load transfer so that the car reacts quicker to changes in direction.

I don't know how much faster a full slick would be, but it would definitely be faster!

333pg333

Car will be lighter, stiffer, have wider wheels, and possibly slicks.

ritzblitz

Youd consider tubing some of the car and relocating suspension pickup points. But with the amount of money some of these extreme mods cost, you might as well just buy a cup car

George D

Patrick,

Have you driven your car with DOT racing tires? This will give you a significant step up in handling. Purchase a set of light track dedicated wheels with good racing tires or just mount some if you have good roads on the way. These tires will pick up stuff you don't want flying off at speed.

Give it a shot. I think you will be happy.

Eric_Oz_S2

Patrick,

The 944's are not very torsionally stiff and certainly I suspect no where near as stiff as a cup car. You would probably need to brace the car significantly to achieve a similar stiffness. Is this something you would plan on doing?

The cup car will also always have a benefit out of corners due to the rearward weight bias.

I think you would still struggle to keep up. A lot of money goes into a cup car to make it that fast, eg $40,000 engine rebuild every 40 hrs or so is the norm.

I don't see how even stiffer springs would help that much without bracing. I would guess that the chasis would become the "spring" through flexing.

Eric

333pg333

George, yes that's all I drive on. I run R spec Nittos or similar on the car all the time. I don't drive it on the street much at all these days. I have to run a silencer in the exhaust and the car has plenty of squeaks and rattles as there is not much left of the insulation now. The R spec or DOT tyres are a big step up from road tyres and I believe that slicks are another similar jump up in performance. I sometimes use Hoosiers at the track on non club days. These are generally somewhere inbetween the Toyo 888s and a slick. I must say that I find the Nittos pretty close to the Hoosiers, but my Hoosiers were a bit tired so perhaps I need to try some fresh ones again.
The other issue is moving up to slicks and their available sizes. Generally they are a 'taller' tyre. Meaning a larger circumference. This may introduce other issues. I wonder what slicks are available for our cars to fit various bodykits? I will be widening my bodywork to accept wider wheels so need to work on some options.

I'm sure you're correct Eric. Just another part of the equation. Where a cage will do a certain amount of stiffening, in reality to do it properly would mean stripping, new bracing/welding, possibly tubing etc. I won't be doing all of these mods, but may wind up with a few changes. Just bolstering the pickup points would be one.

thingo

I think you just have to address each issue, the cup car has come through a long evolution that began around the time that the 968 was ending production.
It has improvements to the chassis, aero, drivetrain, suspension and brakes.
They are a lot incremental improvements, but no one would build a new sporstcar with the engine in that position.