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-   -   Can a 911 be made to handle as well as a Spec Miata? (http://forums.pelicanparts.com/porsche-911-technical-forum/565596-can-911-made-handle-well-spec-miata.html)

911st 09-22-2010 01:13 PM

Camber recovery. Interesting.

Do we need camber recovery on a track car?

I suspect this is more to do with a street car so we do not ware out the inside of the tires.

It would seem that the important point on a track car is the tires are at there best angle to the track and stable at the limit in a corner. Stability from getting the best possible dampening and little change in camber with compression and or front wheel angle (caster created camber gain.)

But that is just what I am guessing.

911st 09-22-2010 01:52 PM

Is it just me or do these race cars look like there do not have much in the way of camber recovery? Expecially up front.

Quote:

Originally Posted by URY914 (Post 5569840)

;)

TimT 09-22-2010 03:57 PM

Distortion from the wide-angle lens used to take the picture

RWebb 09-22-2010 04:29 PM

Camber recovery = gain = ability of suspension to make the wheel lean less than the car does; think it is caused by compression & effects of compression via the linkage geometry

I bet Bill V. can explain it...

mppickett 09-22-2010 04:34 PM

Interesting how many responses this thread has generated. I AX campaigned a supercharged miata that would 0-60 in 4.2 secs. The usual shocks, sways, springs, chassis stiffing mods. It was a lot of fun, but still occasionally got smoked by a well driven NA miata (and several Scoobies). I suspect it was the nut behind the wheel problem.

Our 911 feels totally superior in road feel and corner lean. The turbo and peaky torque adds a much more complicated dimension, but I would never go back. I don't race the Porsche (DE or AX) so my comments are only for the sporty touring feel. Both of my cars weighed roughly the same with fuel (2700 lbs). The 911 is much more satisfying and I can assure you that a forced induction miata is a load of fun.

Flieger 09-22-2010 04:57 PM

Camber recovery is dependent on suspension geometry. It is how much the camber changes relative to the body due to suspension travel in bump/rebound, as one gets in roll. This therefore compensates for the roll and keeps the tire at a more optimum camber.

911st, the camber recovery IS a mechanism that keeps the tire properly oriented to the track surface, which you are so concerned about.

racerfink 09-23-2010 06:03 AM

There's no such thing as a 50/50 Miata. The last time I had my car on the scales, the weight limit was 2350lbs for a 1.6L like mine (with 180lb. driver factored in). My weights were-

Lf-638
Rf-621
Lr-545
Rr-547

Now the minimum weight is 2275 with 180lb driver for the 1.6L. 1.8L's have to run 2400lbs., and the 99 and up cars have to run 2450lbs.

Superman 09-23-2010 07:13 AM

I see the pictures of the white Miata #377, and it sure looks cute. It's probably faster than my '78 911, and way faster than my Ford Ranger. But it better not pick a, autocross fight with this car:

http://forums.pelicanparts.com/uploa...1285254779.jpg


http://forums.pelicanparts.com/uploa...1285254801.jpg


http://forums.pelicanparts.com/uploa...1285254820.jpg

911st 09-23-2010 07:48 AM

Racerfink,

Thx for the real info. Still I suspect the Miata still has a lot of tire per axel compaired to many 911's.

Example, your front axel is about 10% more up front and about 48% less rear axel weight than the assumed 2700 lb 911.

Assuming the Miata runs 205's the 911 would need 225 ft and about 275 to 305's rear to have about the same amount of tire where most SC body track cars run about 225/255's. Again this is a bit simplistic but my hope is it helps convey the point.


TimT,

I wondered if a wide lens was used but thought that would have bent the long straight lines in the picture and to my eye that did not seem to be the case.


All good stuff. Just trying to learn and having some fun!!!

Trackrash 09-23-2010 08:03 AM

What about toe change? The rear of a torsion bar 911 will have toe change when the suspension moves. Is this a factor?

Quote:

I wondered if a wide lens was used but thought that would have bent the long straight lines in the picture and to my eye that did not seem to be the case.
This effect can be done in Photoshop.

Flieger 09-23-2010 09:07 AM

RSRs usually run a lot of static camber because they have little suspension movement due to low ride height and stiff springs. This means not much motion available for camber recovery (or whatever you want to call it), even with very aggressive camber gain kinematic ratios.

Bill Verburg 09-23-2010 09:29 AM

Quote:

Originally Posted by Flieger (Post 5577213)
RSRs usually run a lot of static camber because they have little suspension movement due to low ride height and stiff springs. This means not much motion available for camber recovery (or whatever you want to call it), even with very aggressive camber gain kinematic ratios.

A surprising factoid

from the factory
late RSRs only run -3*35' static camber in front -3*10' in back
late GT3 Cups run 4* f/r earlier versions ran as much as -4*45'/-4* 20' depending on the track, less for high speed venues like Daytona

Flieger 09-23-2010 09:52 AM

Well, a lot compared to a street car, which most people are used to looking at. I did not mean RSRs have a lot of camber recovery, just that the way to get the camber to be optimal in a corner is to use static camber since the suspension does not move much so the roll due to tire deflection can only be compensated for with static camber, or caster if steering input is sufficiently large.

I do not think that the effect is entirely due to the wide angle lens.

J P Stein 09-23-2010 10:43 AM

Quote:

Originally Posted by Superman (Post 5573625)
jwakil is absolutely correct. A talented driver in a pickup truck can beat a lot of Miatas.

Coils can be progressive. Torsion bars cannot. Modern suspensions have 3....maybe four pickup points. Far more effective than older 911s. Porsche went as far and did as much with those older suspension setups as anyone could, but it's still a bad design compared to modern suspensions. Polishing a turd. You get a really shiny turd, but it's still a turd.

Spec Miatas are 2100 lbs? Sheesh! Build a 2100-lb 911, and see what happens. As Dan says, once a guy knows how to drive a 911, they will clobber a Miata. Go Dan, go!

Oh, and for the guy who thinks Miatas are AX bullies.......I guess you need to need to see some 914s driven properly. We can accommodate you at our PNWR AX's.

We got bullied by a CSP Miata at the Packwood Tour again this year.....so did Leeds & Jodi before they broke. Anybody that doesn't think a Miata is more capable AXer than ANY Porsche production car is fooling himself....but no one else.

Given enough time & money you can make a 9eleben faster than a Miata on the track, but it probably won't "handle" better.

Bill Verburg 09-23-2010 11:05 AM

Quote:

Originally Posted by Flieger (Post 5577283)
...
I do not think that the effect is entirely due to the wide angle lens.

I agree 100%, -2 or more is pretty obvious

RWebb 09-23-2010 12:03 PM

Quote:

Originally Posted by J P Stein (Post 5577383)
We got bullied by a CSP Miata at the Packwood Tour again this year.....so did Leeds & Jodi before they broke. Anybody that doesn't think a Miata is more capable AXer than ANY Porsche production car is fooling himself....but no one else.

Given enough time & money you can make a 9eleben faster than a Miata on the track, but it probably won't "handle" better.

- what is the handling comparison between a stock Miata and a stock 911?


- 2nd question: I usually think of the advantage of progressive springing as applying to street cars. They introduce a non-linearity that the driver must compensate for (of course, humans deal with non-linear phenomena all the time), but...

what is the advantage on the track of progressive springing?

Packy 09-23-2010 01:05 PM

Every miata at laguna seca gets killed on the straights by the 911s. Both of the "fast straights" are up hill too. Put slicks on and do some suspension tuning and you'll have no problem taking them on. I drove my 911 at laguna and a friends miata (both had slicks) and I much prefer a 911. I feel like I should have a wig and a skirt on to drive the miata, though it was fun.

On the other hand, I went to an all miata event at Laguna and I saw some 350 hp 1.8 or 2 liter turbo/supercharged miatas that could go. I even saw an LS1-chevy V8 miata, under-tuned puting out only 350 from Flying Miata.

I can't believe this is even a serious question. It's all in the set up of the car and driver. A miata slammed with slicks and sway bars will beat a stock, street tires, "comfy" ride height 911, for sure with the same driver.

DanielDudley 09-23-2010 02:00 PM

Quote:

Originally Posted by RWebb (Post 5577549)
- what is the handling comparison between a stock Miata and a stock 911?

If you are running 225/205s on the 911 and the Miata is running 185s, The Porsche is going to corner way faster. If you are running 205s on the M , LE, or R Miatas I expect the Miata is going to have the edge.

911st 09-23-2010 03:17 PM

Bill!

Check out the braking system on this car.

Why would one want a ballance bar and an adjustable PV?

Quote:

Originally Posted by Superman (Post 5577041)


Bill Verburg 09-23-2010 04:08 PM

Quote:

Originally Posted by 911st (Post 5577911)
Bill!

Check out the braking system on this car.

Why would one want a ballance bar and an adjustable PV?

That's probably a line lock on the central console, used in lieu of a parking brake

Tyson Schmidt 09-23-2010 05:07 PM

Quote:

Originally Posted by 911st (Post 5577911)
Bill!

Check out the braking system on this car.

Why would one want a ballance bar and an adjustable PV?



Because an adjustable balance bar can only adjust the front to rear proportion. It cannot put a knee in the prop curve.

It is still desirable to have a prop valve in the system because it better matches the brake proportions to the weight transfer. More rear bias initially, then at a certain pressure, reduces the rear once weight has been transferred from the rear to the front.

A balance bar can't do that. Having both systems gives you full control.

911st 09-23-2010 06:37 PM

Thought of that but could not find anything from Tilton that dose that.

Adjustable PV:http://forums.pelicanparts.com/uploa...1285295706.jpg

Merlin Line Lock.

http://forums.pelicanparts.com/uploa...1285295763.jpg

911st 09-23-2010 06:39 PM

Thx Tyson.

I love Pelican. Always something new to learn.

TimT 09-23-2010 06:41 PM

Quote:

I do not think that the effect is entirely due to the wide angle lens.
There is some serious wide angle effect in that picture....

Whatever...

Does anyone remember the beemers from a few years back that ran -5 deg or so camber?

lateapex911 09-23-2010 09:49 PM

Quote:

Originally Posted by Tyson Schmidt (Post 5578075)
Because an adjustable balance bar can only adjust the front to rear proportion. It cannot put a knee in the prop curve.

It is still desirable to have a prop valve in the system because it better matches the brake proportions to the weight transfer. More rear bias initially, then at a certain pressure, reduces the rear once weight has been transferred from the rear to the front.

A balance bar can't do that. Having both systems gives you full control.

In my race car (an improved touring SCCA RX-7) I used the prop valve every lap at say, the Glen. The front straight is down hill, while the bus stop us up hill, so i can get better braking with the rears getting different pressure. And, in the rain, I need to adjust it differently as well. Sometimes the track dries out, so....

as for the Miata vs the 911, well, apples to apples (either a stock Miata vs a stock , oh, 89 Carreara, or a Spec Miata vs a mildly tuned 911), the Miata will own the 911 in the entry, the corner, and off the corner. Of course the 911 will own the straight....that's just engine.

I say this having driven both.
The Miata is a great car. Mazda did a wonderful job with it. It just is greater than the sum of it's parts.

That said, most guys I see in 911s at track days are in the way in corners. Having horsepower makes it too easy. To learn how to really drive, they should have something that needs to maintain momentum.

petevb 09-24-2010 10:20 AM

Quote:

Originally Posted by lateapex911 (Post 5578487)
In my race car (an improved touring SCCA RX-7) I used the prop valve every lap at say, the Glen.... And, in the rain, I need to adjust it differently as well. Sometimes the track dries out, so....

This is a sign that you may not have the brake balance working together with the prop valve as well as it could be.

The graph below illustrates:
http://forums.pelicanparts.com/uploa...1285350861.jpg
The amount of pressure required to lock the front and rear wheels at the same time depends on how much weight the car is transferring. The harder the car is stopping, the more weight is transfered off the back wheels and the less pressure the back brakes can take relative to the front before they lock up. This relationship is the blue curve in the graph above.

A car with no bias valve, like a 930, has a fixed ratio to the front and rear- see the green line. This ratio matches the ideal (locks the front and rear at the same time) at one point on the graph. The rest of the time it's off, and for safety they err on the side of locking the front brakes too early. In wet conditions, however, the front brakes lock much earlier than ideal, so total braking is reduced.

A dual master cylinder race car lets you adjust the bias for the conditions, so you can adjust to the red line in the wet, back to the green line in the dry and everything in between. Dual master cylinders are reliable and consistent, but they make for lots of adjustments to stay close to ideal.

A good bias valve and brake setup can virtually eliminate the adjustment by being almost ideal over a range of conditions- the purple line. If either the caliper bias or the bias valve itself isn't quite right, however, you're back to adjusting the valve often to compensate for changing conditions.

lateapex911 09-24-2010 11:05 AM

In the category I race, the rules require stock master cylinders. So, balance is done with pads choice. Calipers and discs are stock as well. We are allowed a prop valve. So, I set the car up with the basic balance to the rear, then dial it back for the 'standard" conditions with the prop valve. Then, in the rain, I have some adjustment left. And I have some adjustment for the steep downhill where the fronts get a lot of weight transfer.

911st 09-24-2010 01:30 PM

Great info guys!!!

racerfink 09-26-2010 06:24 AM

Quote:

Originally Posted by Packy (Post 5577648)
Every miata at laguna seca gets killed on the straights by the 911s. Both of the "fast straights" are up hill too. Put slicks on and do some suspension tuning and you'll have no problem taking them on. I drove my 911 at laguna and a friends miata (both had slicks) and I much prefer a 911. I feel like I should have a wig and a skirt on to drive the miata, though it was fun.

On the other hand, I went to an all miata event at Laguna and I saw some 350 hp 1.8 or 2 liter turbo/supercharged miatas that could go. I even saw an LS1-chevy V8 miata, under-tuned puting out only 350 from Flying Miata.

I can't believe this is even a serious question. It's all in the set up of the car and driver. A miata slammed with slicks and sway bars will beat a stock, street tires, "comfy" ride height 911, for sure with the same driver.

Spec Miata's run DOT street tires. Toyo RA-1's to be exact. Not slicks. Plus, if I put the catalytic converter back on my car, I could drive it on the street.

911st 09-26-2010 07:21 AM

Is the graph in post 66 above why Porsche went to a PV w larger rear pistons with the 3.2 Carrera?

Or is there some other reason?

petevb 09-26-2010 08:00 AM

Quote:

Originally Posted by racerfink (Post 5581841)
Spec Miata's run DOT street tires. Toyo RA-1's to be exact. Not slicks. Plus, if I put the catalytic converter back on my car, I could drive it on the street.

For reference, spec miatas are comparable in weight and tires to spec 911s- both ~2400 race weight and RA-1s. The spec 911s run a bit over 100 hp more and look a couple seconds faster per lap on a track like thunderhill on the same day. They can also be street/track cars. The spec 911s are considerably pricier, of course.

The 911 gains an advantage vs a miata as the power to weight ratio of the cars improves. As power increases traction becomes more and more of a limiting factor. The extra weight over the drive wheels allows the 911 to usefully deploy a much higher power to weight ratio, part of the reason the spec 911 is on the lower end of power to weight ratios for 911 race classes.

Quote:

Is the graph in post 66 above why Porsche went to a PV w larger rear pistons with the 3.2 Carrera?
Yes, that's why virtually all newer cars run proportioning valves on the rear brakes.

Bill Verburg 09-26-2010 08:08 AM

Quote:

Originally Posted by 911st (Post 5581899)
Is the graph in post 66 above why Porsche went to a PV w larger rear pistons with the 3.2 Carrera?

.....

yes, and they continue to use them even on cars that never would hve used one back in the '70s

oops, missed Pete's response

911st 09-26-2010 12:11 PM

Quote:

Originally Posted by petevb (Post 5581961)
For reference, spec miatas are comparable in weight and tires to spec 911s- both ~2400 race weight and RA-1s. The spec 911s run a bit over 100 hp more and look a couple seconds faster per lap on a track like thunderhill on the same day...

Excellent reference info!!!


Looked up a few things.

Spec Miata's run 205/50/15, Spec911 225/245 RA1's.

Spec Miata weigh 2285 to 2450 lbs, spec911 run 2400lbs min.

Suspect Miata puts out about 120whp and a spec911 about 220whp.

Thus about a 19lbs per HP for the Miata and 11lbs per HP for the 911.

2 sec a lap on I am guessing what is about a 2:05 lap time (thus 125 v 123 sec per lap).

Thus it looks like the 911 has about a 40% hp advantage, more gross tire per lb (maybe 20% more) and probably more braking reserve per lb than the Miata.

However, the 911 is only about 2% faster.


What is up with that?

It would be cool to see some data acquisition info comparing from the Miata and Spec 911 on the same track and see the speeds in the different part of the tracks.

Tyson Schmidt 09-26-2010 12:22 PM

I think Infineon would be a better track to compare handling since it is less of a horsepower track than Thunderhill.

I've run a 1:48.47 at Infineon in my Spec-911, and that was carrying an extra 150# of trophy weight, so 2520# with driver. My car dynod @ 205 RWHP.

What is the Spec-Miata record at Infineon?

petevb 09-26-2010 04:33 PM

Quote:

Originally Posted by Tyson Schmidt (Post 5582343)
I've run a 1:48.47 at Infineon in my Spec-911, and that was carrying an extra 150# of trophy weight, so 2520# with driver. My car dynod @ 205 RWHP.

What is the Spec-Miata record at Infineon?

Good question. I think they can run in the 1:54s, but the quickest time I saw in a quick scan was in the 1:56s. I'm sure the spec miata guys can correct me...

Infineon puts more of a premium on putting power down than Thunderhill, which helps the 911's cause.

"Handle better" is certainly a slippery question.
Thought experiment: take a Spec 911 and Spec Miata chassis but equalize hp at say 150 hp: the miata would likely win at most tracks. But if all you did was up the power of both cars to 450 hp while keeping the chassis and tires the same the 911 would handily beat the miata. The miata can't use much of the extra power while the 911 can.

You didn't change the suspension or tires- which car "handles better"?

Tyson Schmidt 09-26-2010 05:04 PM

Spec 911's have run 2:00.xx at Thunderhill. I think in ideal conditions one of us is going to break into the 59's there.

So that's about a 6 second delta at both Infineon and Thunderhill.

lateapex911 09-26-2010 05:13 PM

The Spec Miata is an interesting case, and I think one aspect that is in it's favor is the incredible numbers of them, and the resulting development.
And as a starting package, the SM "kit" (dampers, springs, etc) is pretty darn good, on top of a car that is pretty darn good. Whats interesting to me is that, when you "upgrade" a Spec Miata to Improved Touring allowances, the result is faster, but not by a whole lot. A friend has a well prepped ITA Miata, and holds ITA track records all over the NE. (IT allows 7" wide wheels, which get Hoosier A or R comps, some more engine allowances (mid 130 at the wheels, max), and free damper and spring/bar setups, essentially, at a race weight of 2380) Yet, at a track like Lime Rock, where laps are a minute and change long, it only beats the top SMs of the Runoffs champ level guys by maaaaybe a second or so.

I've driven them, and the cars are telepathic, you think, they do. I find them super easy to get to 98%. Finding the nth degree in speed takes time, and experience.

Tyson, I haven't driven a spec 911, but I have to think it's a much trickier machine to carry speed with. I imagine you've been in both, is that the case?

DanielDudley 09-26-2010 05:13 PM

Quote:

Originally Posted by petevb (Post 5582693)
Good question. I think they can run in the 1:54s, but the quickest time I saw in a quick scan was in the 1:56s. I'm sure the spec miata guys can correct me...

Infineon puts more of a premium on putting power down than Thunderhill, which helps the 911's cause.

"Handle better" is certainly a slippery question.
Thought experiment: take a Spec 911 and Spec Miata chassis but equalize hp at say 150 hp: the miata would likely win at most tracks. But if all you did was up the power of both cars to 450 hp while keeping the chassis and tires the same the 911 would handily beat the miata. The miata can't use much of the extra power while the 911 can.

You didn't change the suspension or tires- which car "handles better"?

Can't use it in the corners you mean. But assuming that they are running a bigger tire front and rear, comparable to the 911, they are going to go into the corner faster, and maintain that momentum. The 911 is going to go in slower, and come out faster. On some corners the 911 will have the advantage, and others the Miata. At least that is how it works with 911s and 928s.

petevb 09-26-2010 06:08 PM

I'm sure you're right on the THill times Tyson. I saw 2-3 seconds same day on a couple time sheets, but those were 2:02s for the 911 spec, not 2:00.

Quote:

Originally Posted by DanielDudley (Post 5582770)
Can't use it in the corners you mean. But assuming that they are running a bigger tire front and rear, comparable to the 911, they are going to go into the corner faster, and maintain that momentum. The 911 is going to go in slower, and come out faster. On some corners the 911 will have the advantage, and others the Miata. At least that is how it works with 911s and 928s.

The faster the car, the more it changes from a "momentum" car to a "slow in, fast out" car. Consider: in a car that can't accelerate at all, the ideal line is simply the largest constant radius arc you can draw through a corner. In a car with infinite acceleration and braking, on the other hand, the fastest line is the tightest line through the corner, so the exact opposite. Obviously the "slow in, fast out" line would be much faster all else being equal.

Thus while it's true that the high powered miata spec will carry more speed through the corner, it's largely true to say that's because it can't accelerate with the 911. And while it's also true that at some point on the straight the high-powered miata will hook up and be able to deploy the extra power, the time down the straight is disproportionately effected by acceleration at the beginning of the straight.

So as power to weight climbs even a miata (or 928, or 951, etc) wants be be a "slow in, fast out" car. They are limited, however, by having ~50% weight over the back wheels, which caps their peak acceleration off the corners regardless of the power available. A 911's peak acceleration will be more than 25% greater, all else being equal, due to where the weight is, so it's that much closer to the ideal "slow in, fast out" car.

At low power to weight ratios this doesn't come into play, as you're rarely traction limited. The faster the car, however, the more you want the weight in the back and the less mid-corner speed is the deciding factor.

911st 09-26-2010 07:46 PM

So simplistically we have a two cars that are close on racing weight but the 911 has about a 40% HP advantage, maybe a 20% GROSS tire advantage, better brakes and it is only about 2-4% faster than the Miata.


I am still guessing the 911 is a bit rear traction challenged compared to the Miata. I think 205/255's would get the 911 to about the same traction per axel.

(The Miata I am guessing has about a 1200 lb axel weight w 205 8.4" wide tires.
The 911 rear axel is about 1440 lb with 245 9.6" wide tires.)

The Miata also has less frontal area to try to push down the straights.


It would be cool is some G readings for the Spec911 and Spec Miata.


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