1975 911 Handling Improvements

[puddy]

Yesterday I was at Mosport tracking with alot of very nice newer Cayman, GT3's, GT3RS's and other exotics. My old turbo charged hotrod has the power to keep up with some newer cars on the straights but not in even close in the corners. I'm pretty comfortable lapping at around 1:42-43, I may be leaving some time on the table in some corners but others when I try to push a little faster the back end wants to slide out. I have rode along in cars that are much faster and seem to feel almost effortless in handling, then going back to my car and thinking I gotta be able to go faster, then I get sliding and have to back off.

My suspension set up, using R888 tires is:

Front - 1.2 camber
- 255 x 18" tires
- 21mm hollow torsion bar up front
- bilstein shocks, 1 level up from stock.
- Weltmeister thru body sway bar
- WM Strut tower brace

Rear - 1.3 camber
- 315 x 18" tires
- Bilstein coil overs (I can't recall spring weight)
- WM sway bar

I've read good things about the new K3 coil over kits.
http://www.kwsuspensions.com/products/kw-suspensions/variant-3-coilovers/kw-suspensions-porsche-911-g-model-74-89-35271061.html

So the question is, can an older rear-engined hotrod be modified to handle somewhat closer to its modern siblings, without breaking the bank? I love my car, don't want to ever sell her, but want to go faster.

Perhaps I need to fine tune my sway bars a little to start? Any advice is greatly appreciated.

[stlrj]

I bet the newer 911s had suspensions that were unmolested and set to factory...something to think about.

[75 911s]

Not a track guy, but as an armchair quarterback you could have a set of track tires in 15 or 16 with actual slicks. That may help the back stick a little better.

Everyone around here usually preaches driving lessons before blowing money on more 'toys' if you are trying to go faster.

Is the car corner balanced? 18's sound huge.

[Knockdown]

Have you acquired the tools and skills to perform an alignment on your car? After a run on the track, are you measuring tire temps across the tire? Corner balance is important as well, I am considering getting scales soon. Sounds like you might have some room for tuning through sway bars, camber, toe, rear coil overs, corner weight.

[Matt Monson]

Start a thread in the track and autocross forum. The guys who really know track set up rarely visit the tech forum.

[911 Rod]

What is it that you expect the car to do more?
If it goes flat around the corners the sways are fine the way they are set up. Or is it understeering or oversteering?
I work my ass off driving my car and can't keep up to the new cars.
The only way would be to go faster in the corners. Brake later and go deeper in the corners.
I see a few torsion bar cars keeping up the newer cars and I attribute this to the driver.
Drop down a run group and then you can pass cars. lol

[911 Rod]

Sorry just reread and saw you comment about kicking out.
Really you should only be accelerating going straight. So back to my go deeper in the corner comment. Adjusting your sway bars will help too.

[puddy]

OK thanks Rod. It wasn't stepping out under acceleration, just going too hot into an off camber turn 1 or 2 at Mosport, these are very fast corners. Having the back step out is almost a "code brown in the pants moment" both times I breathed off the throttle and widened my arc thru the corner and carried on.

FYI I should have mentioned the car is corner balanced. the majority of my experience is 3 years of PCA events with instruction for the first 2 years, i'm in black run group now.

I have not measured temp across the tires.

I dont necessarily want or need to pass newer cars, but it would be fun to run with newer cars that cost 5x as much

[911 Rod]

If you are going next weekend, grab an instructor.
I'd be more than happy to go out with you or take you for a spin in my car.

[stlrj]

It's also possible that all your improvements could be doing just the opposite of what you have intended. (unintended consequences)

[kevin930t]

There is a guy on the internet that runs a 96 993? That has some suspension mods and break mods that can run with just about anything,i believe his u tube channel is showdown911.I am amzed with his skills.It would be a blast to try and keep up with the new cars but at the same time you have a really special car .

Sent from my SM-N910T using Tapatalk

[tobluforu]

How about loosening the rear bar a tad and go from there. I don't have a car like yours or the skill, but with my welt bars it seemed like there was a fine line of how much I would adjust the rear bar too tight, then bam, too much over steer. Then you have the front bar that you tighten up some, and what about tire pressure? Then you have spool up, when you are coming out of the corner does the car lag some, then hit boost and out comes the rear? If so, can you dial it down any? I'm all about simple, easy, cheap things first.

[Trackrash]

Rear wing.

[Tom Elder]

Hi, Chris
Your inquiry made me smile, bang for the buck lap time at Mosport! Spent loads of time thinking about this issue. I have no experience driving a 911 around Mosport but more the a few laps in, at the time, 10 year old Formula Vees and Formula Fords. After the motor is where you want it, the next best place to apply your dollars, is get the best possible tires. Back to back testing of 3 different brands of shaved street radials, 4/32” on a Formula Ford around Mosport, there was 5 sec a lap difference between the tires. The tires tested were not were not super sticky, barely street legal tires that you can get today. What type of tire are you using now? Good street or a street / track tire.

[racer]

Maybe take a ride in the newer car to see where they are gaining an advantage? Or compare video/data? While your straightaway speed may be comparable, their braking might be superior, allowing them to brake later.. then, with a Cayman, the mid engine balance allows for a higher g? Then again, maybe 40+ years of suspension development have something to say about this? Maybe the immensely stiffer chassis of the new cars helps too? Traction/yaw/stability control does wonders as well.


As for your car.... I see a mix of Torsion bars (which imho, might be too small.. Heck, I ran 22's on my SC! Spring rates would be good to know, and were the shocks revalved to match the tb/springs? How big are the sway bars? What brand tires?

[Tom Elder]

Disregard my comments, I missed that you are using R888

[puddy]

Originally Posted by 911 Rod

If you are going next weekend, grab an instructor.
I'd be more than happy to go out with you or take you for a spin in my car.

Hi Rod, thanks a lot, I'll be at the track next weekend, I'll look for you. What colour is your car?

My car has a GT2 wing, maybe I can steepen the angle?

Tires are R888's with over 2 seasons on them. I usually run them at about 25 lbs front & 27 rear, cold. That usually worked good for me but I've also heard that R888 should be set in mid 30's cold.

I'll check my rear spring rates and sway bar diameters and report back.

[Trackrash]

OK, so you have a rear wing. I have found, in my limited track experiences, that the newer style suspensions are going to be superior to our old torsion bar setups. I remember not being able to stay with Boxsters through corners, even though they were running "street" tires and I had RA-1s.

I will be following this thread. Please keep us up to date on your findings.

[Bill Douglas]

Chris, I think you did really well being anywhere near these newer cars - relax, you're a hero LOL

[Rawknees'Turbo]

Originally Posted by stlrj

I bet the newer 911s had suspensions that were unmolested and set to factory...something to think about.

If you are implying that Puddy (I have another name for him, butt won't use it here ) should set his 1975 car back to its as delivered, full of compromises, cushy street car specks (including super skinny wheels and tires) and that it would then get around a track more quickly, you would be mistaken.

Originally Posted by stlrj

It's also possible that all your improvements could be doing just the opposite of what you have intended. (unintended consequences)

In which alternative universe?!?!