J richard

Jack, cool, as long as you've got an H&N couldn't see it in the flic...

In looking back at the 935/936 wheel fans were used extensively to get air out from under the wells...

winders

Jack,

The problem is that you have the potential to generate much more downforce at the rear than the front. The cantilever effect has the rear axle as the pivot and the distance from the rear wing to the axle as the lever arm. This lever is lifting the front end. Shorten the lever and you reduce the lifting at the front. What good is the downforce if you can't use it?

Scott

winders

Faster? Probably not. But it might save your butt if your car gets too loose. Knowing the straight ahead position is a bitch when you shuffle steer. Not knowing the straight ahead position can lead to an off track excursion or crash that you might otherwise have avoided.

Maybe I am stronger than you. My air-cooled 911-based race car with 11.5" bias-ply slicks out front is not too hard to steer with my hands at 9 and 3 all the time. I have no issues at Sears Point or Thunderhill. I have zero toe at the front though. I make it through ~30 minutes races just fine.

Sometimes you get on a track so tight you have to shuffle steer in some corners. But you do it in just about every corner and that is on the Big Track at Willow Springs.

It's up to you.

Scott

analogmike

Quote:
Originally Posted by analogmike View Post
Are you running the same pressures front and rear? Lower front pressure could help add heat in the front tires. I would not be raising the rear end on a 911 unless it was pushing badly. I take it the front is as low as it can go?
I started out with the fronts 3-lbs lower than the rears. By the end of the day, I'd bumped that to a 6-lb gap. (I made a mistake in my initial post where I used the degree sign when I should have written pounds -- I fixed it.)

Yes, the front is pretty low. But as I've been told, rake really only changes a car's aero, with the other effects pretty minor.

----

But lowering or raising changes the roll centers, which changes the handling ENORMOUSLY. I would think that would be much more noticeable than the resulting aero change. Especially the rear ride height makes a huge difference in handling, and also changes toe and camber...

Veloce Raptor

+1

ProCoach

+2

My idea of aero is tunnels...

claykos

Jack,

What size tires are you running? You may actually see a benefit from going to a bit narrower front to help you get more temperature. On my 911s I've been able to get pretty even temperatures front to rear.

You can also work on the front aero. There are other things you can do besides the splitter. Ducting front inlet air out the top or sides will help with downforce.

jdistefa

Jack,

If your front track has been pushed out that much and you haven't compensated for altered scrub radius, then along with a manual rack.... I'd be shuffle steering too! I think there's lots of evidence that you're a very capable driver so I hope people can leave technique alone here

I don't know anyone who runs a 911 from longhood to cup car that runs square hot tire temps.... a few approach it, but I don't think it's a valid goal in and of itself.

I suspect (but don't know for sure) that rake above 1.5 deg in a 911 is primarily an oval track setup for high speeds and big rear wing. Higher than that for mixed speed tracks and I hope you have a high decel lockup LSD

Have you considered using front wheel well 'spoilers'? They're essentially gurney flaps for the leading edge of the wheel wells. See here http://www.flickr.com/photos/sierrac...es/4852752717/

Interesting thread!

jdistefa

Pin the tail on the front end aero

2BWise

Well, I've got no comments as to what direction to go next, but will offer up another consideration. It sounds like when you go out you're simply looking at making any change you can to make the car faster. Correct me if that isn't the case, but it doesn't sound as though you don't have a specific test plan when you hit the track. Have you considered taking a day and simply running four consecutive rake changes and quantify its effect? No other changes just simply adjusting rake and collecting the data. Hell, all you need is a straight stretch of road. Take a day and run up and down the highway! If you fix your ride height sensors so that they're actually functional (sorry, zip ties simply don't cut it) then you can see the actual influence it has and begin to quantify the change as an improvement or not. Lap times are the ultimate measure, but very tough to relate on various days as conditions change. If you can objectively measure what's going on you will be much more confident in the results and with future tuning.

Mahler9th

Some great suggestions here as usual, and from some of the usual people.

You and I have met a few times and of course have interacted in Forums here and PP.

All of this is well and good for discussion. If you are asking about basic things like tire temps, it is possible that your platform is far from optimized. Or it is already pretty optimized, but no one has explained it to you.

Here is additional food for thought:

1. If your goal is to identify opportunities for changes to the car to increase its performance potential, it might be good to consider an hypothesis. For example, you might say that "This car as it stands is capable of 2 seconds per lap faster than I have gone at Willow Springs if I make some tweaks." Of course this would assume that you are driving the existing platform at nearly 100% pretty consistently. Think about the tracks too. I have not driven at Willow Springs, but in 17 years of track driving and racing in NorCal I have seen plenty of clueless drivers struggling at Sears Point because their set up is so biased to Willow Springs. Also make sure your hypothesis is reasonable. Perhaps there is a benchmark car that has a very similar config to yours in your area.

2. While these forums are a great resource, I would still start with the basics. You have a basic platform that has been around and driven in anger since the 70's. It isn't that hard to tap into resources that have been in "money is no object, spare no expense" situations with cars like yours. I am not advocating throwing parts at the challenge, but rather making sure your platform is in line with one of the tried and true "recipes." Scott Winders knows what I mean by this.

It just isn't that hard to tap into professional resources with that experience.... unless the only place you look is here. If I lived down there and drove Willow Springs and similar places, I would start with Cary Eisenlohr. I have not met him, but we have corresponded and spoken on the phone. He has vast experience. If he does not provide a service you can purchase, he can point you in a direction. I am sure there are salty veteran resources in the POC.

3. It may be also good to find a coach who knows your basic platform and can drive it so you can see how close you are to its max. And the right guy can also tell you about tweaks he'd make (assuming it is a he) to increase the performance potential. Up here, a guy like Johannes Van Overbeek could do that I reckon. There are many others. Doesn't have to be a pro driver.

Up here in NorCal, we have a few torsion bar 911s with large displacement air-cooled motors. Several of these cars are on the same recipe having been built and/or modified by the same expert. Our ability to increase performance potential is pretty small, even for cars that are not confined by class rules. We don't have much testing, because the recipe is so good. Time tested, verified. Scott has learned that.

Don't get me wrong, it is always good to question, up to a point. Like, "will I have greater braking performance with Pagid Orange compared to the Hawk Blue pads I am using now, everything else being equal." If cagey veterans tell you "no," it might be good to look elsewhere for opportunities. Sometimes when you ask on the internet, the answers can start you on a path to chase your tail. That's cool too if that is what you want to do.

- Mike

Mahler9th

Also, buy and read the Puhn book. Then read it again. There are other books as well.

But look at the car on the front of the Puhn book. Then ask yourself how that car connects to Kevin Buckler, Eisenlohr, Peter Gregg, Hurley, Jerry Woods, Rich Walton, Mat Lowrance, Porsche AG, Paul Newman, Bobby Rahal, Jeannete, Dave Klym and on and on. Yes and Craig Watkins too!

And how it relates to yours.

jdistefa

^ +993 on Puhn

winders

Just about every driver can improve their technique. I know I certainly can and welcome input when I can get it. If Jack wants to shuffle steer like he does, more power to him. All I did was ask if tried not doing it and commented on why it might not be the best choice to use all the time.

Scott

JackOlsen

In this case, the 3/16" change didn't produce anything distinctly noticeable. The last session produced some faster-than-before segments that lowered my 'best theoretical lap' down into the high 1:26's for the first time ever. So from that perspective, there might be a benefit. It's hard to say much of anything with absolute certainty. I've been driving this track in this car for 13 years now. So I should feel any distinct change. But I made two tire pressure changes and two ride height changes over the course of four hours, and my average lap times were all still within less than half a second. As I've mentioned before, the lap times generally increase as the day goes on, which means you never really have an apples-to-apples comparison. On this day, they went down slightly. That MIGHT mean I made an improvement. But I emphasize might.

I've played with a lot of different ideas over the last decade. My limitation is that it's a street car, so I always want the stuff to unbolt -- to reduce public pointing and laughter.









I did see a benefit going from 315/275 down to 275/255. I just don't have the horsepower for those wider tires.

I've looked into lining the front wheel wells. And putting spoilers ahead of the front tires. I will probably try both of those. Venting is tricky because I'm not willing to cut holes in my exterior panels. (Again, it's mostly a street car.)

Well, my A-arms were cut and extended by that amount -- actually in order to improve scrub radius (it has better scrub radius than the car came stock with 6" wheels now). It's much lighter, steering-wise, than an early Turbo. But in the sweepers it's still a fair amount of work. Or I just have weak arms.

And yes, I'm thinking about the spoilers ahead of the front wheels.

Within my time and budget restraints, I'm pretty methodical. I recently did a few hours of straight line testing on the wing -- looking at front and rear ride heights with different wing settings, making repeated 100-mph runs in opposite directions to correct for wind conditions. And this Friday of testing only involved tire pressure and ride height changes, one change per run, with data and notes. I'm not a race team -- I have to jump out to check my own tire temps. But I think I'm making slow and steady progress. But that's where I'm looking for guidance from guys who have already been down this path. Or something close to it.

Thanks, Mike. I'm looking for input here, but I also have spent many hours in Cary's shop. (He brought my one-off struts back from the Netherlands in a suitcase.) And the car was put together by Tyson Schmidt, who's currently the race guy for Hergesheimer (but is a long-time personal friend). We drove as a team in this car for three years in the Open Track Challenge, so a suspension guy has driven and tweaked things. Nothing in the car's suspension is stock, really. It's got most of the usual mods, and some that are more unusual. But it's a tried and tested car, now. A 1:27 for a street driven car on these tires is a pretty good lap time. I haven't come across anyone with a car of similar power and weight who's quicker than that. But that doesn't mean I couldn't be faster still.

I do think this car has a 1:24 in it at this track (which is the only track I'll be driving at until my kids are older). So that's what I'm focusing on. I'll probably need better rear shocks for that (Bilsteins were a way to save some money) and stickier tires. But I'd like to get a better handle on the car's set up before I make those kinds of purchases.

I ordered the Puhn book. Looking forward to reading it.