200 mph hurdle !
Discussion
A techie question, from reading through the forum.
According to GM the LS7 powered Corvette has a top speed of 198 mph, but there seems to be very few Ultima owners who have cracked 200 even using the same or similar chevy motors. Jeff Schwartz did it but needed a twin turbo 1000bhp Ultima to do it. Is this a gearbox or other issue ?, how many owners know their cars are capable of that figure ?
It seems strange that a car with a such low drag coefficient and excellent power to weight ratio struggles to achieve it, following various threads I know one or two forum members have given up trying.
Your thoughts appreciated
According to GM the LS7 powered Corvette has a top speed of 198 mph, but there seems to be very few Ultima owners who have cracked 200 even using the same or similar chevy motors. Jeff Schwartz did it but needed a twin turbo 1000bhp Ultima to do it. Is this a gearbox or other issue ?, how many owners know their cars are capable of that figure ?
It seems strange that a car with a such low drag coefficient and excellent power to weight ratio struggles to achieve it, following various threads I know one or two forum members have given up trying.
Your thoughts appreciated
Captain Slog said:
A techie question, from reading through the forum.
According to GM the LS7 powered Corvette has a top speed of 198 mph, but there seems to be very few Ultima owners who have cracked 200 even using the same or similar chevy motors. Jeff Schwartz did it but needed a twin turbo 1000bhp Ultima to do it. Is this a gearbox or other issue ?, how many owners know their cars are capable of that figure ?
It seems strange that a car with a such low drag coefficient and excellent power to weight ratio struggles to achieve it, following various threads I know one or two forum members have given up trying.
Your thoughts appreciated
its a good question! I find it strange, even by baby ultima does 170mph and pulls all the way till it hits the 6k rev limit. I guess the elements make such a massive "brick wall" at these kind of speeds.According to GM the LS7 powered Corvette has a top speed of 198 mph, but there seems to be very few Ultima owners who have cracked 200 even using the same or similar chevy motors. Jeff Schwartz did it but needed a twin turbo 1000bhp Ultima to do it. Is this a gearbox or other issue ?, how many owners know their cars are capable of that figure ?
It seems strange that a car with a such low drag coefficient and excellent power to weight ratio struggles to achieve it, following various threads I know one or two forum members have given up trying.
Your thoughts appreciated
Taking a guess here... At an RPM somewhere between your peak torque and peak HP is where your engine is going to stop accelerating your vehicle. If geared properly for the RPM and there's enough power, you will crack 200.
If you have just enough power, it then becomes a function of time and distance. It might take 5 miles to reach 200 in a lower powered vehicle, while Jeff's 1,000 HP GTR (at 6,300' above sea level) did it in well under 1 mile.
If you have just enough power, it then becomes a function of time and distance. It might take 5 miles to reach 200 in a lower powered vehicle, while Jeff's 1,000 HP GTR (at 6,300' above sea level) did it in well under 1 mile.
You need a lot of power to fight the drag (600bhp plus) and the right gearing. I think if you have the right gearing and not enough power you bog down at say 170mph plus.
Im sure there is a website that with the correct inputs
1 the cars coefficency
2 the cars bhp
3 gearbox ratios
will give you figure for 1 top speed
2 150 mph to max in seconds
etc etc
one problem i cant bloody remember its address
Im sure there is a website that with the correct inputs
1 the cars coefficency
2 the cars bhp
3 gearbox ratios
will give you figure for 1 top speed
2 150 mph to max in seconds
etc etc
one problem i cant bloody remember its address
Has anyone taken the rear wing into account for the Vmax calculations? It sure does its job very well to produce big amounts of downforce, but what are the effects for a high speed run?
I`ve seen other drivers remove the rear view mirrors in order to reduce drag, it always helps a little. Removing the rear view mirrors from a GTR sure won`t help a lot, but who knows about the rear wing? I wouldn`t try it out though as it may be vital for such speeds as is a front splitter...
I`ve seen other drivers remove the rear view mirrors in order to reduce drag, it always helps a little. Removing the rear view mirrors from a GTR sure won`t help a lot, but who knows about the rear wing? I wouldn`t try it out though as it may be vital for such speeds as is a front splitter...
I only needed 1000 hp because in the competition I was in, I had to do 200 in less than one mile (i did in 4700 ft) at 6439 feet altitude.
For example, mostly stock corvette LS7 ZO6 at this event will to 168 in the mile, I did 211.
My old 500 hp LS6 engine In my GTR was good for 193 in two or three miles and was gearing limited at that with .76 top gear and 6500 rpm.
Our 650 hp LS7 makes big power to 7500. with std gearing in the 50/52 or 996 turbo transaxle, puts top speed at 222 mph.
For those who desire way beyond 200+ we install a .68 top gear in the trans with our twin turbo LS7 puts it at 250.
The trans the Factory supply I believe have .92 top gear which limits top speed to more sane levels.
For example, mostly stock corvette LS7 ZO6 at this event will to 168 in the mile, I did 211.
My old 500 hp LS6 engine In my GTR was good for 193 in two or three miles and was gearing limited at that with .76 top gear and 6500 rpm.
Our 650 hp LS7 makes big power to 7500. with std gearing in the 50/52 or 996 turbo transaxle, puts top speed at 222 mph.
For those who desire way beyond 200+ we install a .68 top gear in the trans with our twin turbo LS7 puts it at 250.
The trans the Factory supply I believe have .92 top gear which limits top speed to more sane levels.
actuary said:
In a word, gearing. My standard G50 doesn't let me get past 180, even at 7500mph. Otherwise 200 would be a breeze ...
Pity a replacement / reworked box is so ££££.
Could be wrong ... but....in the "old days" the g50/50 set up used in the sports/spyders would give 28mph per 1,000 rpm in 5th. Mine does anyway, so my top revs are 6k hence, 168mph max (more or less) - I would have thought you should get 28x7.5 = 210mph -( with enough run up/road!) I think there is a thread (long time ago) about this..... Unless your gearing is different ??Pity a replacement / reworked box is so ££££.
Hi SHF,
My gearing is not quite so tall. I've hit 150 many times (on closed roads, of course) and that equates to 6,000 in 5th. If the speedo is accurate, and I think it is (in car footage at Avon raceway vs radar speed at the line etc) then it's more like 25mph per 1000. So 7,500 is tantalisingly close but no cigar. Amerspeed say keep the revs below 7,600 to 7,700, so a 8,000 rpm run is a no go. In any case, I don't want bits of SBC flying off at 190+mph.
Perhaps I should whack up the rear tyre pressures to get some extra radius as the back .. or perhaps not ...
Will have to settle for the next mini V-max run, say a 3/4 mile or 1 mile drag race where a winning speed of 170 might take first place. With the short gearing and 640 bhp, the GTR is still accelerating very well as it reaches the limiter in 5th.
Tony.
My gearing is not quite so tall. I've hit 150 many times (on closed roads, of course) and that equates to 6,000 in 5th. If the speedo is accurate, and I think it is (in car footage at Avon raceway vs radar speed at the line etc) then it's more like 25mph per 1000. So 7,500 is tantalisingly close but no cigar. Amerspeed say keep the revs below 7,600 to 7,700, so a 8,000 rpm run is a no go. In any case, I don't want bits of SBC flying off at 190+mph.
Perhaps I should whack up the rear tyre pressures to get some extra radius as the back .. or perhaps not ...
Will have to settle for the next mini V-max run, say a 3/4 mile or 1 mile drag race where a winning speed of 170 might take first place. With the short gearing and 640 bhp, the GTR is still accelerating very well as it reaches the limiter in 5th.
Tony.
actuary said:
Hi SHF,
My gearing is not quite so tall. I've hit 150 many times (on closed roads, of course) and that equates to 6,000 in 5th. If the speedo is accurate, and I think it is (in car footage at Avon raceway vs radar speed at the line etc) then it's more like 25mph per 1000. So 7,500 is tantalisingly close but no cigar. Amerspeed say keep the revs below 7,600 to 7,700, so a 8,000 rpm run is a no go. In any case, I don't want bits of SBC flying off at 190+mph.
Perhaps I should whack up the rear tyre pressures to get some extra radius as the back .. or perhaps not ...
Will have to settle for the next mini V-max run, say a 3/4 mile or 1 mile drag race where a winning speed of 170 might take first place. With the short gearing and 640 bhp, the GTR is still accelerating very well as it reaches the limiter in 5th.
Hi Tony.... still lets not forget that 170/180mph is still rather nippy! Enjoy!
Tony.
My gearing is not quite so tall. I've hit 150 many times (on closed roads, of course) and that equates to 6,000 in 5th. If the speedo is accurate, and I think it is (in car footage at Avon raceway vs radar speed at the line etc) then it's more like 25mph per 1000. So 7,500 is tantalisingly close but no cigar. Amerspeed say keep the revs below 7,600 to 7,700, so a 8,000 rpm run is a no go. In any case, I don't want bits of SBC flying off at 190+mph.
Perhaps I should whack up the rear tyre pressures to get some extra radius as the back .. or perhaps not ...
Will have to settle for the next mini V-max run, say a 3/4 mile or 1 mile drag race where a winning speed of 170 might take first place. With the short gearing and 640 bhp, the GTR is still accelerating very well as it reaches the limiter in 5th.
Hi Tony.... still lets not forget that 170/180mph is still rather nippy! Enjoy!
Tony.
shithotfast said:
Hi Tony.... still lets not forget that 170/180mph is still rather nippy! Enjoy!
true... but my old M3 worth about 3.5k can do that kind of speed if you remove the 155mph limiter.... wont be as quick to get there though.but the simple fact is that there is not a place in the UK were you can reach more than those speeds unless you can get to them with 1.5miles which takes a lot of power..... anyone know how fast the Z06 gets to at brunters? my guess is 180mph ish.
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