Q&A Porsche discussion

[lakatu]

Nthfinity, thank you again for responding. I appreciate your insight and comments. It has been helpful sharing ideas back and forth on this subject.

It makes sense that the fins would cause a vortex and that would be beneficial in increasing down force by facilitating the exit of airflow out the back of the car.

I’m not sure about the details or conditions on how the down force figures for the GT2, GT3 & CGT were calculated. But I believe that they were under the same conditions or velocity.

[nthfinity]

perhaps this has already been covered, but if it has, i think ill incorperate some of whats been said recently concerning the 911 aero...

quite obviously, the 911 has been one of the most successfuly track day cars for the enthusiast boy racer, but the question is how good is it... so good/bad, only a skilled professional can 'safely' touch the cars limits, while retaining control? or a car a great learning curve is invovled?

i ask this because of the cars dynamics; both weight bias of the rear, and lack of adiquate d/f of the rear. ill break this down to low speed, and high speed corners with the latter discussed first. I have read that the car, when driven near the limit exibhits under-steer on a corners' entrence, and over-steer on the exit. this makes sence, as the lack of pressure on the front wheels limits the turn-in of the vehicle, especially considering the lack of cornering loads on the rear. however, once the load is built up, the rear would like to swing wide.
quite obviously, this would be a safe way to incrementally improve one's ability.

high speed turns are another story altogether, and have a wider possibility of uncirtainty, i think. As speed is built up much higher, aero becomes increasingly important. i would think that one could brake somewhat deeper (later) in the corners to reduce lap times, as additional forces are forcing the front wheels to girp, and have more turn-in capability, and sustain more of lateral g's adequatily... perhaps almost evoking nuetral steer initially with a good front lip design. the problem herin arises to change the 911's cornering dynamics. due to the fact the car is rear engined, the design becomes flawed in my mind for high speed corners. to some degree lift could reduce the friction of the rear tires, under lateral loads, which in turn allow the rear to get away much more quickly, and almost unexpectedly once grip is lost... perhaps oversteer before the exit of the corner, or mabey even still in the entrence.

i would think to compensate for this danger, a driver would end up braking earlier, rather then pile the loads on the front, rather then the letting the rear get away while braking... then accellerating again to load up the rear, and evoke understeer at the entrence to make the car handle more like that of a low speed turn... i am unsure.

to me this would make the 911 the ideal car for low speed turns, but almost bordering on dagerous on high speed turns.

[st-anger]

MOVED:

posted by revvv_pshhh

What would you have to do to get a GT2 Wing on a 996 TT ? Price, process. Also where would you get a GT2 front bumper to put on a 996 TT? just curious

AND

so what exactly are most of the biggest differences between the two cars besides the AWD in the turbo. I really appreciate it, i hope this hasn't been a thread before

[netwolf232]

Auto-Cross Weight Reduction Question:


This is my first season of auto-cross racing and I am currently in a very competitive class. I race a 1985 944 and am allowed to strip up to 100lbs from the car without any point deductions. Would it be advisable to do so seeing that the car supposedly has a 50/50 weight distribution and the bulk of the weight reduction would be on the rear of the car? I guess to summarize my question, is removing weight from my car going to unsettle it if more is removed from the rear than the front? Thank you for the help and let me know if this post should be made in another forum.

-Andrew

[novass]

Sadly, our resident Porsche expert, ST-Anger wont be around for a few months. I would suggest trying to remove stuff that you can easily put back in just to see if its worth your time. You could always offset the removal by taking away the same amount from the front as you do in the back, i.e. lexan rear window and fiberglass hood. My roomate has a 83 944 (I know its the worst model year for that car) just sitting in our garage, I keep tellin him to take autocrossing or something, but he is too damn lazy.

Keep us posted cause I for one would like to know how it turns out, hopefully I can use the info to convince him to race his car

[lakatu]

Originally Posted by netwolf232 Auto-Cross Weight Reduction Question: This is my first season of auto-cross racing and I am currently in a very competitive class. I race a 1985 944 and am allowed to strip up to 100lbs from the car without any point deductions. Would it be advisable to do so seeing that the car supposedly has a 50/50 weight distribution and the bulk of the weight reduction would be on the rear of the car? I guess to summarize my question, is removing weight from my car going to unsettle it if more is removed from the rear than the front? Thank you for the help and let me know if this post should be made in another forum. -Andrew

Definitely the right section for this topic .

Based on my knowledge and conversations with st-anger I would have to say that shaving the weight should benefit the car and not dramatically change the balance of the car. A lighter car should be a net positive as far as handling and acceleration. Any change in handling balance I believe could be adjusted for by adjustable sway bars and changing the relative sizes of the contact patches between front and back.

For example, I am guessing that less weight on the rear might have the slight affect of increasing understeer as the rear may have more grip than the front after shedding the weight. If this was a problem you should be able to use adjustable sway bars to balance this out or use slightly larger front tires to increase front grip.

St-anger has indicated that tires are the biggest factor in increasing lap times see http://www.motorworld.net/forum/show...=185697#185697 . So you might want to look first at upgrading tire size and tire compound for autocrossing applications. You might also look at the weight distribution and changes that Porsche made to tire sizes or sway bars sizes of the normal verses the Clubsport version of the 944/968.

[netwolf232]

Another issue I have is that I am currently running Falken Ziex 512 in 225/50/15's all around. This is the most rubber I can get in without any points deductions. I am not at all impressed with these tires, they get extremely greasy when hot and have a very sloppy feel to them. I have heard nothing but good things about the Azenis tires but the problem is they only come in a 205/50/15. Since I would be mounting these on an 8in wide back and 7in front rim would this stretch the tire out a little giving it some increased tread width? I figure for $50 a tire it couldn't hurt to try them and the Azenis are what most of my competiton is using.

-Andrew

[nthfinity]

Since I would be mounting these on an 8in wide back and 7in front rim would this stretch the tire out a little giving it some increased tread width

i think not... cirtainly, it would weaken the sidewalls abilityt o cope with high g cornering.

one thing to concider may be to have un-equal between the front and rear; very few serious sports cars have the same width up front, and in back.

if the same tires compound is up front, as in the rear, and same width, i would tend to think this would lead to oversteer at the limit.
but you must remember that the rear contact patch in this case is also supplying the power to the pavement, which would balance the car out earlier in the exits of the turn. sometimes the most rubber upsets the cars dynamics while turning then assisting it.

as far as your weight reduction question; i would tend to think that in auto-cross situations, the low speed turns would have negligable effect on the delecate balence... and its cirtainly helpful to improve bushings, sway bars etc. as lakatu recomended.

[st-anger]

MOVED:

posted by XxTwstedMethodxX

Hey everybody, I'm 17 and anout to upgrade from my Civic to either a Boxster, or and M Roadster. I deffinately have a thing for overall quality and looks, but I'm torn between the two. Would you guys suggest going with the slower Boxster, or should I get the BMW. Which is more refined? And which one is more acceptable to mods? Thanks, Aaron

Are there any other sport cars, better than these two, out there that i can get for 23-25K ?

[TransAm]

Boxster - slightly more refined, slightly better build quality and probably handles a bit better.

You'll find a better M Roadster (less miles, newer) for the same amount of cash.

I had a 3.0i Z3 (225hp), I just preferred it over the Boxster - I didn't think there was that much in it, although I nearly went the way of VTEC before I actually bought the Z3. I was more torn between either of the Germans or an S2000 than between the Porsche and the BMW.

[revvv_pshhh]

what exactly are the differences between a 996 Turbo, Turbo S, Turbo X50. i know these are very quite similar but what are the exact difference in these 3. Im sure they all have the same turbo but how high is each one boosted? Does anyone know how much boost you can run on these turbo's when modified?
thanks
Mike

[nthfinity]

http://www.motortrend.com/roadtests/...he/index1.html
some interesting info on the X50, and 955TT.
straight from 'porsche news'

[lakatu]

Over the past year I have had a few interesting PM’s with st-anger. Some of them led to postings in PC and others didn’t. Since st-anger isn’t currently available to provide insight and information I thought, with st-angers permission of course, I would share some of our discussions with others by posting them in PC.

I debated as the best way to present this and finally just decided to present them in chronological order since they somewhat build on each other. Some are more interesting than others but I will try and edit them so that the interesting stuff is highlighted.

This PM was concerning a lap time of 8:32 for a 965 turbo on the NS and related to a previous post by st-anger in "Porsche Discussion"

Originally Posted by lakatu I have been working on a response to your response concerning the 965 8:32 time. But as I was writing it, it started to contradict the direction I was planning on heading with the Fundamentally Flawed article. The 8:33 time for a 320 hp 965 compared an almost identical time of 8:32 for a 1992 365PS also tested by SA. I am guessing here that the 365PS car is a 965 Turbo S however, I thought they had 376bhp. I know there is a difference between PS rating and bhp and maybe that is what accounts for the difference in engine ratings. The point though that I thought was interesting was that the times are almost identical while the power to weight ratios are very different. Assuming that it is the 965 Turbo S then I believed it weighed around 2850 lbs giving it a 7.6 lbs/hp while the 1991 965 weighed 3275 lbs giving it 10.2 lbs/hp. While there were surely differences in track conditions that make a comparison from 1991 & 1992 difficult I personally think that the times would be fairly comparable if run on the same day. Combine this point with the fact that newer 911 models are faster on the NS (993=8:28 & 996=8:17) just confirms that what you had said is true that the limiting factor for NS runs is tire adhesion see http://www.motorworld.net/forum/show...t=tyres#185697 . Certainly, Porsche with the 993 & 996 have been able to increase tire adhesion through suspension refinement and the results are obvious.” Okay here is where I get confussed I was planning on saying in “Fundamentally Flawed” that the rear engine design of the 934 & 935 is superior in braking and acceleration and slightly at a disadvantage in cornering. I have arrived at that conclusion based on reading the opinions of racing car drivers that drove the cars during that era. However, I have seen a few comments that indicated that the 934s and 935 weren’t at a disadvantage but they never indicate that handling was a area of superiority. Okay, so my thought for “Fundamentally Flawed” was that maybe only 20% of the time around a course the car was experiencing lateral acceleration and that maybe it was slower in the turns but that the physics equation for lateral acceleration [a=(v^2/r)] meant that the speed differences between taking a turn with a 50ft radius at 1g and 1.25g is 27.3 and 30.5 mph. So you lose 3mph through 20% of the track but you gain more than that in braking and accelerating advantages. As a result, your average speed verse competitors is higher, and a 934 or 935 lapped faster. So the clash is that I planned on saying that lower cornering speeds were of little consequence and that seems to be completely opposite to the comparison of the 965 NS lap time difference verses newer 911 models. So any thoughts? Where have my theories gone wrong? I'm not looking for you to reply to all of the questions in this post other than why the two points are opposed to each other. Especially as it relates to different 911 models on the NS and suspension improvements increasing times.

Originally Posted by st-anger yep, right a 1992 Turbo “S” has 380hp, I calculated 3.4kg/hp ( 7.5lbs ) and 4.5kg/hp ( 9.9lbs ) so what´s your source on the Turbo S lap time, I never dealt with all this, but find it quite interesting, cause I know of a 8:15 from WR in a ´91 964RS coming with 260hp and ~1230kg, so more or less same power/weight ratio as 965, sure WR is good for quite some bonus time on NS, but that the Turbo S isn´t significantly faster than the 965 AND the RS ... kinda strange… I only have to think of the tyres, sepecially dimensions, and just because of them the “S” should be faster… well, can´t figure out what´s wrong here i´m afraid… just one thing: i´d say without having 500hp you gain ALL the time with higher cornering speed, so lower cornering speed is always bad…

More to follow on this discussion. I will save that for a later post.

[TT]

Originally posted by pzgren:

I found this article today on http://elfer-club.jafc.de/showthread.php?postid=4937

There's is mentioned that there are several reproaches against porsche tuner gemballa. if believing to this reproaches it could happen that it could come to a spontaneously fire in your engine compartment. i read in another forum that they had another accident like this with another gemballa porsche.
what do you think, something wrong with this tuned cars or could that happen - bad luck for the owner?





hope you'll understand my english

[nthfinity]

well, i think there are several things, most of which i can only stipulate.

for one, high performance engines already generate massive amounts of heat... one reason, i think that porsche moved to a traditional water cooled engine. also, with a Turbo, or a GT2, the turbos themselves generate even more heat to the intake. and a third point is the porximity of space, and cooling around the engine is quite minimal... particularly the cramped space from the exhaust headers, to the tips is fairly confined.

when it comes to being a tuner of these cars, generally, the power is upgraded quite segnificantly via turbos, ECU... etc. so higher boost levels inherently mean increased frictional forces on the air being drawn in, and charged. this is where intercoolers come in... cooling the air has several effects, one the volume of the oxygen is lessened, and more bar. can can be mixed with more fuel for more power.

in maintaining intercooler design, perhaps the device isnt designed to those tolerences, and 'heat soak' begins happening in less fluid areas of the intercooler... and the excess heat may cause damage to other parts.

running at higher power/boost, exahaust velocities could put more of a strain on the exhaust headers under load could build up heat as well, and cause possible fractures, or vaporized seals...

just some speculation, but i think the problem could have been helped with a redisign of various parts needing cooling specifically.