Could a 951 reach 200+ mph?
08-04-2006, 11:32 PM
#46
Rennlist Member
So that means my tach is off by a few hundred rpm. I remember being 6800-6900 at 194mph. If I was really at 7100 my tach is off. Is if off throughout the whole range or it gets more inaccurate at high rpms? Anyone know. Oh, and I do have 265/35/ZR18 tires.
08-05-2006, 12:50 AM
#47
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WOW you keep that thing contained with 265s? I would have figured you for a trick 315 or 305 setup....i just love fat rears...hence my flares.
Back to the 200mph thing - to avoid the big hole between 4-5 using an NA 5th, could adjustments be made starting from second gear on? Less change per gear but overall yield the desired gearing ratio? Hell maybe even go the route the lingenfelter Vettes do and get a 66mph 1st gear
Back to the 200mph thing - to avoid the big hole between 4-5 using an NA 5th, could adjustments be made starting from second gear on? Less change per gear but overall yield the desired gearing ratio? Hell maybe even go the route the lingenfelter Vettes do and get a 66mph 1st gear
08-05-2006, 01:04 AM
#51
Race Director
Originally Posted by guns951
I was referring to the aerodynamic limited speed. Following the mentallity that a brick can only go so fast etc. Where is our "wall?"
08-05-2006, 03:14 AM
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Originally Posted by MPD47
Robby, now that you mention it I think Winslow is running a 295/30. My last set of Pirellis were 285/35R18 though, im positive of it.
08-05-2006, 03:43 AM
#53
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Defastest- I honestly think your car has the power to hit 200mph & I think there are several other car's here that have it too- so don't misunderstand my posts on this. In answer to your question, in my limited experience & vast amounts of reading, it seems they are further off as they go up- I know speedos seem to be- check out many Bimmers for more on that... 
My tach is perfectly on w/my speedo in 5th at all but ~3000rpms- I'm on at 2k rpms & back on by 4k, but at 3k, I'm off by 4-5mph... not sure why... OR how... But, I've checked my speed against MANY radar signs & other cars, etc, & it seems to be prettty much on- at least confirmed up ~127mph & even in the mid 150's (as fast as I've actually had it) it was on by the tach. Anyway, even a 993/996TT can break 190- if we factor in an extra 40HP or so to hit the same speed, since 951 has more drag & FA, then we'd STILL only need 440, w/the right gearing- you're 100HP+ over that.... Oh, & one thing I've never mentioned- I hate the way these rear wheel wells look w/small tire/wheel combos... The pics you used to have on Powerhaus are what made me realize that these cars need more in back- it's one of the most perfect looking rear wheel well areas I've seen on these cars... It seems to be lowered JUST RIGHT w/just the right amount of offset & RD tire, etc... It's perfect & it's what I'm shooting for for my own car... You really spared no expense on that car- it really is amazing- one of the best all around jobs I've ever seen!!! BTW- I'm sending you a PM right now...
Guns, yes, you could, but custom gears, from places like Powerhaus II (no afilliation w/Powerhaus anymore) are EXPENSIVE- on the order of $1800/gear or so... So, you'd really need to pick your gears... A better way to do it is what a few guys are trying to get going right now- a dif FD (ring & pinion)- this would give the same spacing through all gears- done w/the 968 they want, it would give ~189 w/the FD they've picked out (3.22 I think). W/a 951 you could do the same, but better to have more gears to seal the holes IMO- more gears gives more to work with. ALSO, changing out 1st is near-impossible- I called PHII a few years ago to ask about some of this stuff- most places, unfortunately, wont do these things b/c it's so expensive (unless someone REALLY has bucks) b/c MOST people want SHORTER for better accleration at the expense of top end- it's sad really... It would be nice to have the best of both worlds... Keep in mind, cars like Vipers & Vettes can handle those 60-70mph 1st gears, etc, in part b/c of their massive low-end TQ! And, in answer to your question, IF I'm reading you right, a STOCK 951 is DRAG limited to ~155 while a stock Turbo S is drag limited to ~162. To change this by gearing alone, would be tough, as they're really geared pretty well for top speed- you'd be better off tuning the car to peak a little higher in the gear & not lose too much right below in rpms & you could possibly squeeze out the last 5mph of a Turbo S right at redline. Most would just throw in chips & not worry about it, since they'll take a Turbo S to the 6500rpm rev limiter (IF the limiter's not defeated). I'm thinking, that a well chipped Turbo S w/tial WG & full 3" exhaust, should break ~175 w/an S2 (.778) 5th- throw in a larger Turbo & MAF & you might be able to redline that gear ~180 (w/255/50/17's). Again, it just depends on how much HP drop you get right before redline &/or where the HP peaks, etc...
I guess the guy to talk too, if you're seriously considering, is Scott Gomes- he's been wanting to break the land speed record for 951's for years- was planning a 250mph run at Bonneville a few years ago, but not sure what happened... Either way, he's got the record as far as I know at somewhere over 205- I THINK it was 208- in his personal car... He HAD the original Norwood Doom engine for sale a few years back- might still... throw one of those in & go to town...
My tach is perfectly on w/my speedo in 5th at all but ~3000rpms- I'm on at 2k rpms & back on by 4k, but at 3k, I'm off by 4-5mph... not sure why... OR how... But, I've checked my speed against MANY radar signs & other cars, etc, & it seems to be prettty much on- at least confirmed up ~127mph & even in the mid 150's (as fast as I've actually had it) it was on by the tach. Anyway, even a 993/996TT can break 190- if we factor in an extra 40HP or so to hit the same speed, since 951 has more drag & FA, then we'd STILL only need 440, w/the right gearing- you're 100HP+ over that.... Oh, & one thing I've never mentioned- I hate the way these rear wheel wells look w/small tire/wheel combos... The pics you used to have on Powerhaus are what made me realize that these cars need more in back- it's one of the most perfect looking rear wheel well areas I've seen on these cars... It seems to be lowered JUST RIGHT w/just the right amount of offset & RD tire, etc... It's perfect & it's what I'm shooting for for my own car... You really spared no expense on that car- it really is amazing- one of the best all around jobs I've ever seen!!! BTW- I'm sending you a PM right now... Guns, yes, you could, but custom gears, from places like Powerhaus II (no afilliation w/Powerhaus anymore) are EXPENSIVE- on the order of $1800/gear or so... So, you'd really need to pick your gears... A better way to do it is what a few guys are trying to get going right now- a dif FD (ring & pinion)- this would give the same spacing through all gears- done w/the 968 they want, it would give ~189 w/the FD they've picked out (3.22 I think). W/a 951 you could do the same, but better to have more gears to seal the holes IMO- more gears gives more to work with. ALSO, changing out 1st is near-impossible- I called PHII a few years ago to ask about some of this stuff- most places, unfortunately, wont do these things b/c it's so expensive (unless someone REALLY has bucks) b/c MOST people want SHORTER for better accleration at the expense of top end- it's sad really... It would be nice to have the best of both worlds... Keep in mind, cars like Vipers & Vettes can handle those 60-70mph 1st gears, etc, in part b/c of their massive low-end TQ! And, in answer to your question, IF I'm reading you right, a STOCK 951 is DRAG limited to ~155 while a stock Turbo S is drag limited to ~162. To change this by gearing alone, would be tough, as they're really geared pretty well for top speed- you'd be better off tuning the car to peak a little higher in the gear & not lose too much right below in rpms & you could possibly squeeze out the last 5mph of a Turbo S right at redline. Most would just throw in chips & not worry about it, since they'll take a Turbo S to the 6500rpm rev limiter (IF the limiter's not defeated). I'm thinking, that a well chipped Turbo S w/tial WG & full 3" exhaust, should break ~175 w/an S2 (.778) 5th- throw in a larger Turbo & MAF & you might be able to redline that gear ~180 (w/255/50/17's). Again, it just depends on how much HP drop you get right before redline &/or where the HP peaks, etc...
I guess the guy to talk too, if you're seriously considering, is Scott Gomes- he's been wanting to break the land speed record for 951's for years- was planning a 250mph run at Bonneville a few years ago, but not sure what happened... Either way, he's got the record as far as I know at somewhere over 205- I THINK it was 208- in his personal car... He HAD the original Norwood Doom engine for sale a few years back- might still... throw one of those in & go to town...
08-05-2006, 04:19 AM
#54
Instructor
Hi !
944 speedos are definitely optimistic !
According to several magazine tests and measurements done at the time these cars were new, the error is around 8-10 % or so. I still have some articles if anyone is interested.
I have also confirmed this with my own 944:s doing measurements using highway markers.
Speedos should NOT be used for performance comparisions !!!!!
Tommy
944 speedos are definitely optimistic !
According to several magazine tests and measurements done at the time these cars were new, the error is around 8-10 % or so. I still have some articles if anyone is interested.
I have also confirmed this with my own 944:s doing measurements using highway markers.
Speedos should NOT be used for performance comparisions !!!!!
Tommy
08-05-2006, 05:31 PM
#56
Instructor
Yes it is - being a long time 944 NA and S2 owner I finally got this one 1 1/2 years ago. I've been sort of lusting after one since they first came out 15 years ago.......
It is in very nice condition :-)
Cheers,
Tommy
It is in very nice condition :-)
Cheers,
Tommy
08-05-2006, 06:54 PM
#58
Three Wheelin'
Okay, for the non-physics inclined, some useful formulae:
At any speed, the power produced by the motor must overcome driveline friction, rolling friction and aerodynamic drag (assuming a smooth level surface.) We can account for driveline friction by using rear-wheel horsepower (rwhp.)
Rolling friction is relatively constant, and can be approximated by the formula:
Froll = Cr * m * g
where; Cr is the coefficient of rolling friction, and is generally about 0.015 for cars using high performance tires (less for slicks); m is the total weight of the car, and; g is gravitational acceleration (9.81 m^2/s.)
Aerodynamic drag increases as the square of velocity, and can be estimated as:
Fd = 0.5 * Cd * A * rho * V^2
where: Cd is the drag coefficient, which is 0.33 for a stock 951; A is cross-sectional area, which is 20.3 square feet (1.89 square meters) for a 951; rho is atmospheric density, which is 1.2047 kg/m^3 at 68 F and one atmosphere pressure, and; V is velocity.
Power is defined as force * velocity. This is much easier in consistent metric units, but if you trust me on the conversion factors, the minimum rear wheel horsepower required to maintain any given velocity is:
HP = Cd * A * V^3 / 149,200 + Cr * m * V / 376
where: HP is in SAE horsepower, A is in square feet, V is in mph and m is in pounds. If we substitute typical values for a 951, we get:
HP = 0.33 * 20.3 ft^2 * V^3 / 149,200 + 0.015 * 3200 lb * V / 376
Or: HP = V^3 / 22,273 + V / 7.84
So we get the following results:
Speed Drag Resistance Total
(mph) (HP) ----(HP)---- rwhp
50 ---- 5.6 ---- 6.4 ---- 12.0
100 --- 45 ----- 13 ----- 58
150 -- 152 ----- 19 ---- 171
167 -- 209 ----- 21 ---- 230
200 -- 359 ----- 26 ---- 385
235 -- 583 ----- 30 ---- 613
Remember, these are minimum horsepower requirements to maintain these speeds, so you will need extra power to get to the speed in a realistic distance. Also, this horsepower must be available at the rear wheels at the particular rpm your gearing and wheels provide, so all the previous discussions about rpm and power at speeds still apply.
At any speed, the power produced by the motor must overcome driveline friction, rolling friction and aerodynamic drag (assuming a smooth level surface.) We can account for driveline friction by using rear-wheel horsepower (rwhp.)
Rolling friction is relatively constant, and can be approximated by the formula:
Froll = Cr * m * g
where; Cr is the coefficient of rolling friction, and is generally about 0.015 for cars using high performance tires (less for slicks); m is the total weight of the car, and; g is gravitational acceleration (9.81 m^2/s.)
Aerodynamic drag increases as the square of velocity, and can be estimated as:
Fd = 0.5 * Cd * A * rho * V^2
where: Cd is the drag coefficient, which is 0.33 for a stock 951; A is cross-sectional area, which is 20.3 square feet (1.89 square meters) for a 951; rho is atmospheric density, which is 1.2047 kg/m^3 at 68 F and one atmosphere pressure, and; V is velocity.
Power is defined as force * velocity. This is much easier in consistent metric units, but if you trust me on the conversion factors, the minimum rear wheel horsepower required to maintain any given velocity is:
HP = Cd * A * V^3 / 149,200 + Cr * m * V / 376
where: HP is in SAE horsepower, A is in square feet, V is in mph and m is in pounds. If we substitute typical values for a 951, we get:
HP = 0.33 * 20.3 ft^2 * V^3 / 149,200 + 0.015 * 3200 lb * V / 376
Or: HP = V^3 / 22,273 + V / 7.84
So we get the following results:
Speed Drag Resistance Total
(mph) (HP) ----(HP)---- rwhp
50 ---- 5.6 ---- 6.4 ---- 12.0
100 --- 45 ----- 13 ----- 58
150 -- 152 ----- 19 ---- 171
167 -- 209 ----- 21 ---- 230
200 -- 359 ----- 26 ---- 385
235 -- 583 ----- 30 ---- 613
Remember, these are minimum horsepower requirements to maintain these speeds, so you will need extra power to get to the speed in a realistic distance. Also, this horsepower must be available at the rear wheels at the particular rpm your gearing and wheels provide, so all the previous discussions about rpm and power at speeds still apply.
08-06-2006, 07:33 AM
#60
HMMMMMM - I have just tuned my car for a little more top end in my quest for 600 RW, and my transmission is removed.
I wouldn't mind taking a shot at it (or having a REAL race driving buddy do it) - anyone have a suggestion on a box/gear combo that I could buy.
I guess turbo with NA 5th - is that the conensus?
7000 RPM.
I wouldn't mind taking a shot at it (or having a REAL race driving buddy do it) - anyone have a suggestion on a box/gear combo that I could buy.
I guess turbo with NA 5th - is that the conensus?
7000 RPM.