jrgordonsenior

You don't mention the year of the GT car but assuming it's an older 911 you're fighting aero, suspension, rigidity, and gearing. In So Cal we have numerous GT cars but only a few actually built to battle with cups. The 'Yellow Bee', very similar to Clay's car only with about 390-400rwhp and a close ratio 5 speed, can beat cups running at 2350lbs or so. Another 76' car with a 4.0 air cooled motor could also beat cups when it's running. He too puts out somewhere near 400 whp at 2300 lbs. It's worth noting that both of those cup killers cost way more than what a 6-cup would have cost new and their respective upkeep is inflated too.

My $02. after racing a cup for 4 years and now racing a 270whp 996 is that cups are the greatest, least expensive bang for the buck available. Mechanicals last a long time and they're very fast right out of the box. They seem to always be running rather than in the shop. I blew a clutch & PP once, and cracked a lower control arm, but that was about it.....

M758

My thinking is that at those hp/weight levels getting that power to the ground is very critcal. Cup cars are well sorted car with good combined package. Being factory developed they will make good use of very bit of hp to carry their weight.


A home built or even pro-shop built GT car can be hit or miss. In theory it is faster due to less weight overall and better power/weight, but it needs to be done right so in the real world is it a tough call on how much faster.

mark kibort

Scott,
I didnt write that I meant something else. I stand by that the close ration gear box, can effectively provide MORE usable HP. What I really was doing was clearifying. Again, not more hp peak, but more usuable HP over a given operating speed range. Does that make sence, and is that accurate to say?

So, unless you are ONLY using your car at "X RPM" as you say, the usable HP will change with a close ration gear box. you will be at a higher HP level for a longer period of time. You will have MORE HP-seconds. (energy) to use and accelerate with. this says that the transmission is not only responsible for torque multiplication, but its ability to keep the engine close to the peak HP range. (not peak torque range). the closer the gears, the more available hp you have over any operational speed range. Yes, hp is the rate of doing work ("hp over a period of time as you say") but more importantly, hp x time is energy. if you can provide more hp over this period of time due to the gear ratios closer overlap with the HP curve, arent you increasing the HP available to the wheels over time, are you not?

again, a transmission has 2 main functions. Multiply torque while reducting engine speed coverting it rotation to wheel rotation, and optimize HP over a given operating speed range via its multiple gear ratios.

quick example: If two cars have identical engines and chassis, but one has a close ratio gear box and we race, what happens in a race. the green flag drops and car (A) punches it from 50mph in 2nd to 80mph to 3rd going from 250hp to 350hp and back down to 250hp.
Car (B) on the other hand, punches it at the same gear ratio and 50mph but then at 80mph, shifts at 350hp and then drops back down to 275hp with his closer ration gear box.
At the point of the post shift, who has more HP? right! car (B) so the gear box created 25 more hp post shift than car (A).
The transmission was responsible for more HP (and of course more torque) at the post shift speed. So, it "effectively " gives you more hp at certain speeds.

M758

Mark,
Vic Elford use that gearing trick at the Monte (or maybe another rally) back in the 60's. He geared his 911 to max out at 100mph or something baking not needing to go any faster. This mean he could keep the car in highest part of the power band for more miles of rally than otherwise. That made his power output higher for every mile and made that car a little faster.

Now if you consider it torque muplication or "effective hp" is makes not difference as torque and hp are mathamatically linked. The fact is that you can use gearing to make the best use output of the engine. Grears never change the output of the engine, but it does change was happans at drive wheels and that is the only thing that make the car go.

winders

Mark,

Again, regardless of what you say:

If you want to say that better gearing lets you use power more effectively, great. But you can't say that better gearing effectively raises the horsepower. A transmission multiplies torque, not power. This is why you should choose shift points to maximize transmission output torque, not engine torque.

Scott

mark kibort

What do you mean regardless of what "I" say? i just wrote a clear picture of when gearing is purely responsible for creating more hp at a particular speed. The car at that point in time at that position at the track, was making more hp at that speed. Now, I know we now are clearly talking symantics. You are actually taking a page out of my play book saying that " gear boxes dont change " hp. the context I use that in , is when folks think just by going up a numerical rear end, they suddenly can accelerate faster, for which I say, "that depends". and then you got the gearing discussion.

now to your point, yes, I can say it "effectively" raises hp, at a particular speed where the HP is greater due to the closer ratio gear box. again, we are not talking raising peak HP engine values, we are talking hp at any point in time or position on the track and overall, in HP-seconds. if it raises the ability to acceleatate over a speed range, you have more HP available, you have used more energy and you have accelerated faster. it raised your average HP. so how about this, what if i said, instead of "effective" I said, Average. since that that is crude integration, closer ratios raise your average HP over any speed range. of course youre absolutey right, and i say this as well, "you use the power more effectively" but isnt that the same as "more effective" HP?

BTW, acceleration = Power/(mass x velocity) right? so, if we are increasing acceleration , at the same speed, and the car didnt change in weight, then we have just increased Power. But again, i understand what you are saying and I never meant to imply that the Peak hp of the engine changes with gearing. you opimize the available hp . how is that?

mark kibort

yes indeed!

Bull993tt

Potomac Club Race - 2010 Summit Point Motorsports Park
Group 1 - Sprint 1
Pos PIC No. Last Name First Name Class Laps Total Tm Diff Best Tm In Lap Color Description Region 1
1 815 SCHWARZ DEREK GT3R 13 16:35.610 1:14.652 8 WHITE GT 73 911 CHS
2 1 33 MARTIEN PHILLIP GTA2 13 16:38.848 3.238 1:15.076 4 WHITE GT 08 GT3 CUP POT
3 1 40 SOYKHER IGOR GTC4 13 16:40.216 4.606 1:14.975 2 YELLOW/RED GT 06 997 GT3 CUP CHS
4 2 919 McCARTHY JACK D GTC4 13 16:47.125 11.515 1:15.626 9 WHITE GT 07 GT3 CUP CTV
5 1 416 ALTMAN HOWARD B GTC3 13 17:09.628 34.018 1:18.038 13 WHITE GT 02 GT3 CUP NNJ
6 3 31 WILLIAMS RAYMOND A GTC4 13 17:13.183 37.573 1:15.495 13 BLUE RED BULL GT 05 997 CUP POT
7 2 722 SKALKA BARRY GTC3 13 17:26.976 51.366 1:17.997 8 WHITE GT 00 GT3 CUP CVT
8 1 14 BURGER JEFFREY E GT4R 13 17:27.100 51.490 1:19.154 6 RED GT 90 964 HUD
9 1 52 PALUMBO CHRISTOPHER R GT4S 13 17:27.747 52.137 1:19.094 13 RED GT 75 911 NNJ
10 3 02 LLOPIZ RAFAEL A GTC3 13 17:29.255 53.645 1:16.994 13 WHITE GT 05 GT3 CUP NNJ
11 4 5 MURPHY ALEX GTC3 13 17:47.425 1:11.815 1:20.302 7 WHITE GT 05 GT3 CUP POT
DNF DNF 630 LIEM GIE GT4R 12 16:18.602 DNF 1:19.154 8 SILVER GT 06 CAYMAN S RTR
13 1 88 AMMIDON III HOYT GTC2 12 16:39.100 1 Lap 1:21.775 3 WHITE GT 97 993 SUPERCUP SCH
14 1 160 WIDRA ERIC A GTB1 12 16:46.291 1 Lap 1:20.708 8 BLACK/BLUE GT 04 996 POT
15 2 00 MINGIS DARREN GTB1 12 16:46.495 1 Lap 1:20.483 8 BLACK GT 02 911 RTR
16 3 140 RYAN ROD GTB1 12 16:48.305 1 Lap 1:21.933 10 LOWENBRAU GT 09 CAYMAN POT
17 1 143 BAUER JOHN GTC1 12 16:51.486 1 Lap 1:22.118 6 RED GT 90 964 EURO CUP MNY
18 4 21 LLOPIZ LINCOLN M GTB1 12 16:55.274 1 Lap 1:21.335 7 WHITE GT 10 CAYMAN S NNJ
19 1 81 RUDTNER WILLIAM GTA1 12 16:57.663 1 Lap 1:17.579 5 BLUE GT 03 GT3 RS MNY
20 5 67 STAPLETON SCOTT GTB1 12 16:58.831 1 Lap 1:22.417 12 WHITE GT 01 CARRERA MNY
21 2 15 MULLIGAN BOB GTC1 12 17:00.155 1 Lap 1:22.291 9 WHITE GT 90 964 EURO CUP POT
22 2 12 AMICO PAUL GTC2 12 17:00.751 1 Lap 1:22.280 12 WHITE GT 97 993 CUP POT
23 2 487 HEALY KEVIN GT4S 12 17:03.456 1 Lap 1:22.918 11 BLACK GT 95 993 C2 MNY
24 3 505 SLOWIKOWSKI WILLIAM GTC2 12 17:05.415 1 Lap 1:23.055 2 RED GT 97 993 CUP CNY
25 3 375 MARMOL RON GT4S 12 17:46.130 1 Lap 1:26.632 9 RED GT 73 911 FST
DNF DNF 82 SHAH MIKE GT4S 11 16:32.407 DNF 1:27.927 7 BLACK GT 96 911 C4S POT
DNF DNF 218 LEVITAS MICHAEL N GT1R 11 13:50.091 DNF 1:14.238 6 ORANGE GT 90 993 POT
DNF DNF 111 PEARE KEITH J GT3R 10 13:12.131 DNF 1:16.821 7 BLACK GT 72 914 NNJ


Potomac Club Race - 2010 Summit Point Motorsports Park
Group 1 - Sprint 2
Pos PIC No. Last Name First Name Class Laps Total Tm Diff Best Tm In Lap Color Description Region 1
1 815 SCHWARZ DEREK GT3R 22 28:11.853 1:15.167 5 WHITE GT 73 911 CHS
2 1 919 McCARTHY JACK D GTC4 22 28:19.745 7.892 1:15.224 19 WHITE GT 07 GT3 CUP CTV
3 2 31 WILLIAMS RAYMOND A GTC4 22 28:19.792 7.939 1:15.190 6 BLUE RED BULL GT 05 997 CUP POT
4 1 33 MARTIEN PHILLIP GTA2 22 28:43.913 32.060 1:14.945 15 WHITE GT 08 GT3 CUP POT
5 1 02 LLOPIZ RAFAEL A GTC3 22 28:46.254 34.401 1:16.727 14 WHITE GT 05 GT3 CUP NNJ
6 2 416 ALTMAN HOWARD B GTC3 22 28:51.781 39.928 1:16.709 19 WHITE GT 02 GT3 CUP NNJ
7 1 81 RUDTNER WILLIAM GTA1 22 29:19.684 1:07.831 1:16.812 17 BLUE GT 03 GT3 RS MNY
8 3 722 SKALKA BARRY GTC3 22 29:26.566 1:14.713 1:18.665 12 WHITE GT 00 GT3 CUP CVT
9 1 14 BURGER JEFFREY E GT4R 21 28:25.432 1 Lap 1:18.781 14 RED GT 90 964 HUD
10 2 630 LIEM GIE GT4R 21 28:25.680 1 Lap 1:19.284 15 SILVER GT 06 CAYMAN S RTR
11 4 5 MURPHY ALEX GTC3 21 28:52.332 1 Lap 1:20.224 8 WHITE GT 05 GT3 CUP POT
12 1 67 STAPLETON SCOTT GTB1 21 28:56.244 1 Lap 1:20.522 7 WHITE GT 01 CARRERA MNY
13 2 21 LLOPIZ LINCOLN M GTB1 21 28:57.629 1 Lap 1:21.015 17 WHITE GT 10 CAYMAN S NNJ
14 3 00 MINGIS DARREN GTB1 21 28:58.237 1 Lap 1:21.175 15 BLACK GT 02 911 RTR
15 4 160 WIDRA ERIC A GTB1 21 29:06.029 1 Lap 1:20.973 20 BLACK/BLUE GT 04 996 POT
16 1 88 AMMIDON III HOYT GTC2 21 29:08.197 1 Lap 1:21.875 16 WHITE GT 97 993 SUPERCUP SCH
17 1 143 BAUER JOHN GTC1 21 29:14.764 1 Lap 1:22.080 13 RED GT 90 964 EURO CUP MNY
18 2 12 AMICO PAUL GTC2 21 29:15.288 1 Lap 1:21.982 17 WHITE GT 97 993 CUP POT
19 1 487 HEALY KEVIN GT4S 21 29:15.494 1 Lap 1:21.769 16 BLACK GT 95 993 C2 MNY
20 2 15 MULLIGAN BOB GTC1 20 28:13.303 2 Laps 1:22.836 15 WHITE GT 90 964 EURO CUP POT
21 3 505 SLOWIKOWSKI WILLIAM GTC2 20 28:37.414 2 Laps 1:24.284 16 RED GT 97 993 CUP CNY
22 2 375 MARMOL RON GT4S 20 29:35.383 2 Laps 1:27.113 11 RED GT 73 911 FST
DNF DNF 40 SOYKHER IGOR GTC4 20 25:30.921 DNF 1:14.252 5 YELLOW/RED GT 06 997 GT3 CUP CHS
DNF DNF 140 RYAN ROD GTB1 18 25:06.848 DNF 1:21.460 9 LOWENBRAU GT 09 CAYMAN POT
DNF DNF 82 SHAH MIKE GT4S 17 25:28.792 DNF 1:28.049 15 BLACK GT 96 911 C4S POT
DNF DNF 52 PALUMBO CHRISTOPHER R GT4S 16 21:27.642 DNF 1:18.928 14 RED GT 75 911 NNJ

bobt993

thxs Derek. Hope to see at Summit in two weeks.

SoClose

To return to the original question...
Not sure if the 310h/p GT car is rear wheel or crank. Big difference. My 3.4L, 335 crank h/p turned a 2:18.4 at Sebring this year (GT3R), with the fastest C3 car qualifying about 1 sec faster. My 75 RSR body work is a huge disadvantage on long straights. Kim's 993 RSR body(3.8L) is equal until about 100mph, then she begins to walk away from me (2100 vs 2400lbs). Same for the 906 Cups. On a shorter track-Mid Ohio, Barber- very equal with 996 Cup cars.
The other issue is GT engine development. Most are in the 100-110 hp/L range. Some are above that. I suspect that in the next few years we will see an increase in the number of GT cars with highly developed engine$.

Geoffrey

My 964 based GT3R race car is 2225 full of fuel and was a ground up build with seam welding and 993 driveline. It has more power than a 996 Cup, will out drag a cup car through about 07 or 08, but loses most noticably in high speed corners. Lap times are similar. My car is a stock aero car which helps in straight lines, but loses when downforce is necessary.

SoClose would have a better idea of how the earlier chassis perform, but I can't see them being as good as an equally prepared later chassis.

310hp to the wheels won't give you the performance to compare to a cup. You'll need more like 350.

Costwise, it is hard to beat a 996 Cup, but to me, it still feels much like a street car with rubber bushings in the suspension.

mark kibort

so, how did you get near 370rwhp with the 993 engine, which would be needed to out drag most of the '07, '08 cup cars I would imagine. I remember Chris with POC had a 2200lb 993 with a near stock motor, which made about 330hp on the engine dyno. he was able to keep up with the cup cars of its day, but that was back in the '03-04 time frame.

38D

http://www.efi101.com/contact.html
(scroll down to "East Coast Instructor")

SoClose

Geoffrey is correct, the biggest losses for me in a '75 chassis are in corner exits, especially longer high speed ones. Just can't hook up the back. Corner entry/mid corner perhaps a little bit quicker than most C3/C4Cup Cars. I believe that older cars are more 'tossable' and easier to keep near/on the limit of tire adhesion, minimizing the lap time loss.
350 rwhp from a 993 engine is no stretch at all.

bobt993

Surprised you don't know about Geoffrey's engine builds and Motec work.