[ds968]

Ok, so the are two cars - different models, but with nearly identical hp, same with torque, and almost the same weight ( less than 1% difference in all categories ) , both with approximately the same mileage, and both with engines in top notch condition..and both with manual transmission. Yet, one is not just a little faster, but much faster than the other. BTW, also stock, there are no perfromance mods. This is not in a 0-60 situation, but from rolling starts on..and highway side by side runs with starting points at the same speed. One car simply " walks away " from the other. What could be the key reason given that everything that seems to matter is equal ? Is it the gear ratios ? Or the points in the rpm range where the hp and torque is delivered ? Both of those factors ? Anything else ?



Puzzled..

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[Cloud9...68]

All of the above, and then some... <img src="/forum/images/smilies/968/popcorn.gif" class="smilie" alt="" />

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[flash]

yup



newer computer systems are much better than old ones. a 275hp 65 mustang will get it's ass handed to it by a 275hp hyundai

gearing is everything

aerodynamics?

shifting patterns



there are way too many things to list, and no single rolling start run will be the determinant anyway. if a wimp shifts early, or too late, he'll lose - big

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[ds968]

Not a newer computer issue; also not much shifting involved where one could factor in driver skill as reasons. It was a ' 93 Carrera C2 , so I'm guessing the fact that a rear engine has very little drivetrain power loss to the wheels, as opposed to our 15% or so loss, the almost-immediate torque delivery to the rear wheels must explain most of the reason for the acceleration difference. The 5 speed gearing is also probably not as tall as ours, so that moght have added a bit to it, but as I mentioned, this was a brief take off and no shifting to speak of..to make things worse I was at about 4000 RPM when we both stepped on it, so at pretty sweet band point.. Sigh.

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[MB968]

[quote name='ds968' timestamp='1349050386' post='133200']

Anything else ?



Puzzled..

[/quote]



All other things being equal, in two identical cars, identical HP/torque #'s, it is the area under the torque curve that decides which will win. (Or, if I remember my diferential equations, this would be the derivitive of the torque value, as the rpm value is varied from say 2000 rpm to the redline.) So, if one has a very flat torque curve, and one a very peaky torque, the one that is relatively flat will win.

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[Cloud9...68]

I was incredulous that a 93 Carrera C2 has about the same power as our cars, so I looked it up, and to my surprise, it put out a relatively underachieving 247 hp out of 3.6 liters. Makes me have more respect for the effort Porsche went through to coax 236 hp out of our 3.0 liter four-bangers. So, as Dan says, the cars to have near-identical weight/power ratios. My guess is that the biggest factor in the Carrera's superior acceleration is the the fact that the engine and transaxle are hung out over the rear wheels. I've read lots of reports of 911's out-accelerating other cars with better weight/power ratios, and the reason is usually attributed to the superior traction from its pronounced rearward weight bias.

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[flash]

the rear engine concept will push harder off the line than a front engine.



the car is also slightly more aerodynamic than ours.



again though, i point to the gearing. first, it should have been a 6 speed, not a 5 speed. but, if it was a 5 speed, then, the 993 1st gear is lower than ours, giving it better launch. it's second gear is taller than ours though, making it better at a rolling start too.



wheels and tires will play a roll in these types of comparisons too. you may have had the same wheels, but spacers would add weight, and cost you in launch and acceleration.



then there is the torque curve. note that it is a LOT higher than ours for a LOT wider period. i don't know where you guys are getting your numbers, but the C2 should absolutely womp your butt. even with the mods you have, that doesn't come close to the power of the C2. look at the shapes of the curves too.



here are charts from the owner's manuals



   



vs ours



   

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[ds968]

The numbers are from Porsche - The 93 C2 has 247 hp and 228 ft/lbs and weighs 3100 lbs. ( coupe ). And it does have a 5 speed.

Funny though, I also drove it and it does not feel as fast as it actually is. Once again proof that one cannot rely on seat of the pants , lol. Btw, the 993 is not as fast as this model, it has considerably more weight. Prettier body for sure, and no slug, but bit slower.

Anyway, I was always under the impression that the weight to power ratio was 99% of what mattered, with everything else being of negligible impact. Ha, shows you how little I know ( knew..)

We only accelerated in third gear once going uphill on a highway onramp ( he caught up to me very quickly ) and the second time we were on the highway straightaway, and I was in 4th at 4000rpm when we stepped on it, but did not ask him where he was in which gear and where in the rpm band . Sure, I do have the equivalent of about 48 lbs right on the rotating mass ( wheels / spacers ) , and I had half more tank of gas than he did , so another 60 lbs there, and I'm about 25 lbs heavier too, but my car is also lighter by about 50 lbs that I shed getting rid of the spare tire and the OE catback / mufflers. So back to fairly even, since with my mods I should have about 15 more ponies and 10 more ft/lbs than his car does. But this was not even close in acceleration, he just pulled away by two or three car lengths within the first four or five seconds . Much faster launch. In an ironic twist, that's almost exactly what I did to my friend's 04 or 05 Carrera 4 cab ( which I'm guessing must have weighed a heck of a lot more vs it's hp ) , and thus my previous assumption that power to weight ratio is the only factor that counts..

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[flash]

that chart above is right out of the owner's manual. it shows the same as "excellence was expected" with about 280hp. was this a late year 964 and not a 993? when you said 93, i presumed it was the new 93 model, and not the leftover 964. the chart above is for a 993.



here is the chart for the 964:

   

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[Cloud9...68]

That's an interesting discrepancy between the numbers Dan and I found (on Wikipedia, in my case, which I realize isn't the most accurate source of information, but it's correct for the 968). Flash's curves make more sense, given the 964's 20% greater displacement, and Porshe's reliance on the 911 as it's "image" car. Between this, the gearing, and the rearward weight bias of the 911, the acceleration between the two cars shouldn't even be close.



Edit: Flash's post came across as I was typing mine, although the 964's curves didn't post. According to Wikipedia, the 993 got a big power boost over the 964, to about 280 hp. So a 993 should leave a 968 in the dust, even if it gained a few pounds over the 964. If the Wikipedia figures for the 964's hp and torque are correct, the explanation for Dan's drag race results are probably in the gearing, as Flash states, and the rearward weight bias. And the phase of the moon. And the color of Dan's underwear that particular day...

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[flash]

i'm having trouble finding the right chart - arrrrgh - stand by

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[Cloud9...68]

Hmmm... Peak power is comparable for the two cars, and if anything, the 968's torque peak is broader - it stays about 250 nm longer than the 964. Must be the driver <img src="/forum/images/smilies/968/biggrin.png" class="smilie" alt="" />

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[flash]

yeah- that's the wrong chart too.



gotto go to the dyno. i'll have to look for this later

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[Rap]

Dan doesn't believe in underwear! Slows him down especially in drag races!

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[tamathumper]

But he's #1 in skid marks?

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[ds968]

hey, leave my thong out of this ! ( actually, it started out as boxer shorts but with all the weight gain it's now a thong .. <img src="/forum/images/smilies/968/wacko.png" class="smilie" alt="" /> ) eeewww, you guys certainly did not need that visual.. <img src="/forum/images/smilies/968/tongue.png" class="smilie" alt="" />

but back to the cars - yes it's a 964, not a 993 ( my reference to '93 was the year ) so totally different power. I have to ask him in which gear he was in, because if he was in 3rd, whereas I was in 4th, in spite of being at that 4k rpm "sweet spot", that would have made a difference all by itself, not even to mention the burden of my wheel weights in adding to a launch drag.. still, the difference was very pronounced, much more than I would have expected so obviously the gearing, rear engine to rear wheel power delivery, and whatever else all counted.



btw, if anyone wonders about the extra 48 lbs number on the wheels - the spacers are not that heavy, but the extra long steel bolts needed for those spacers do weigh a lot, a total of 12 lbs, and according to just about every source weight on a rotating mass ( like a tire....or maybe even a flywheel ? ) it translates to a 4 X weight equivalent.

That said, it's a small sacrifice to pay in favor of a major aesthetic improvement.. IMO.

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[Ryan]

I like where this is going

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[tamathumper]

Do they weigh 12 pounds, or do they weigh 12 pounds more than the originals?

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[ds968]

The NET added weight is 12 lbs ( 3lbs per wheel..which does not sound like a lot, but I guess it makes a material difference..) so yes that's the delta over the originals. I have two spacers on the fronts and one spacer on the rear. Off the top of my head I can't remember exactly how many mm, but I THINK it's 20mm total in the front and 15 mm in the rear. In any event, I got the longest steel bolts available for that set up and they're pretty hefty.

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[bombfactory]

The added weight of the spacers and longer studs shouldn't noticeably affect acceleration at all, because the mass is located at the hub, very close to the center of rotation. Now add the same weight out near the wheel rim and you'd definitely feel the difference.

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