Need some guidance on n2o 928s
07-06-2005, 02:17 AM
#31
Rennlist Member
first of all, there is not that much difference in the actual hp to the wheels over the operational range to 100mph. probably an advantage for the 2.50 gear box, vs the 2.2, but its not the full percentage, as the gears in the trans are usually different to make the total difference less. as we beat to death, there are trade off with any mix of gears and ratios. a lower numerical ratio will have an greater advantage at the end , and shorter period of each gear while the advantage of the higher numerical rear end gear box will have an lesser advantage through more of each gear. Depending on the target speed, there is a case for most any gear box ratio. Key thing is really gear ratio spacing, which porsche really keeps the same for most all of its models.
so, didnt you mention you were on the NOS? or is your 4.7 US something really special. could it have the euro intake? euro cams?? mine did and got 243 rear wheel hp and was pretty fast. i sure a stronger 4.7 US could have even made more. (ie I was only at 200hp at the rears with headers and 3.5" exhaust, while some other guys were in the 220 range)
mk
so, didnt you mention you were on the NOS? or is your 4.7 US something really special. could it have the euro intake? euro cams?? mine did and got 243 rear wheel hp and was pretty fast. i sure a stronger 4.7 US could have even made more. (ie I was only at 200hp at the rears with headers and 3.5" exhaust, while some other guys were in the 220 range)
mk
Originally Posted by m21sniper
BRIAN: "Sniper
That is a great time for a NA 3 speed auto!!!"
Mine is a 4 speed, and always starts in first regardless of throttle position. I assume the first owner paid good money for that neat little feature, because as i understand it that is not normally the case. It also brings into play the very real possibility that my trans had the lower 2.50:1 gear ratio retrofitted vs. the stock 2:20.
Doesn't sound like much, but a .3:1 lower final drive ratio is actually pretty significant. I also lowered the effective final drive ratio myself a bit(about 3%) by switching to a smaller OD tire(245-45-16), which is also 20mm wider than stock.
"Your car has to have some type of serious engine work...my guess is a 5.0L+ bottom end with Euro intake-heads-cams...plus the stuff you did!"
When i raced Lance he suggested i might have a 5.0 bottom end too. My block is marked M28/20, which is the correct OEM part number for an 83 US, but it's possible it's got some sort of stroker kit in it. I've never had the Valve covers off, so i've no idea what sort of cams i have. If i ever have to pull the covers i'll be sure to write down the cam numbers and post them.
I've also heard from a lot of people that own and have driven 83s that they're freaks, much faster than the published performance listings. I would buy that if i hadn't crushed Heather's 83 US by so much.
"With your lightweight car & those type of numbers you have to be at least 310 (Euro spec) crank HP...probably closer to 330....have you dynoed it? Again my guess is 270+ to the wheels"
I'm not a big believer in dyno's because you can take the same car to three different shops on the same day and get three fairly widely varying dyno numbers. I calculate HP by known track ET and trap speed, then split the difference. That gives a decent enough guesstimate for my purposes. All i really care about is the actual ET though. When ya run a 13.67 you don't need a dyno to tell you you're making lots of power, it's self-evident.
"You should post your times at www.dragtimes.com I posted my runs from march...my best was a 14.54 at 95mph...that was with zero power braking..just floor it and go!"
I ran my best time launching at 1600rpm @ 22psi in the rear tires after a nice burn out, with 50psi in the fronts. Try duplicating that next time you go, i guarantee you'll pick up a 1/4 second or more.
"Not bad for a near stock (only RMB), automatic full weight S4 (3500+ myself)...I figure with some tweaks and a better launch I could drop it down to 14.3 or so...maybe better?"
Maybe as low as a 14 flat if you set the tire pressure and run 100octane gas and bump your timing way up to take advantadge of it. At the track it's all about traction. Our 928s have about a 2300rpm stall converter, so if you can get full traction at 2300rpm you're going to run a much faster time than launching from idle. Perhaps as much as a second if you're lucky. I've seen cars make no change other than slicks and cut that much off their ET before. 80s-90s mustangs GTs are a good example of that. They're seriously traction-challenged cars, and benefit massively from a swap to nice wide slicks.
"Your 0-60 seems kinda slow in comparison to the 1/4 mile times...typically my G-tech reads between 5.9 to 6.1 for my car (6.12 on the 14.54 1/4 run)... But the 55mph shift does slow the times!"
The G-meter times were actually recorded before i did my final weight savings job(i borrowed the g-meter off a friend, i don't own one of my own) or my last day at the track, and i cut a good 125+ pounds off the car since that time(driving seats, dry cell battery, and yanking the A/C system). I'm sure it's a few tenths faster now, but i've not verified that in a timed run. My real powerband is 2d gear. My car pulls very hard all the way to 6500rpm in second, which equates to 98mph. I shift to third about 100 feet short of the traps right in the heart of my motors power band, and accelerate like mad the last 100 feet.
My best trap speed is a 103.1, which oddly enough came on my slowest ET run of the day because of wheelspin at the line. I spun em for a good 20 feet and as a result the motor was in the heart of it's power band when i finally got traction(just shy of 3000rpm IIRC). That allowed me to accelerate through 1400 feet much harder than i would normally do with a good launch from 1600. Helps the trap speed, hurts the ET. On my 13.67 run i think my trap speed was a low 102. It's been over a year, so my memory is a bit foggy. I guess i should dig out my timeslips for the day, but i'm lazy.
That is a great time for a NA 3 speed auto!!!"
Mine is a 4 speed, and always starts in first regardless of throttle position. I assume the first owner paid good money for that neat little feature, because as i understand it that is not normally the case. It also brings into play the very real possibility that my trans had the lower 2.50:1 gear ratio retrofitted vs. the stock 2:20.
Doesn't sound like much, but a .3:1 lower final drive ratio is actually pretty significant. I also lowered the effective final drive ratio myself a bit(about 3%) by switching to a smaller OD tire(245-45-16), which is also 20mm wider than stock.
"Your car has to have some type of serious engine work...my guess is a 5.0L+ bottom end with Euro intake-heads-cams...plus the stuff you did!"
When i raced Lance he suggested i might have a 5.0 bottom end too. My block is marked M28/20, which is the correct OEM part number for an 83 US, but it's possible it's got some sort of stroker kit in it. I've never had the Valve covers off, so i've no idea what sort of cams i have. If i ever have to pull the covers i'll be sure to write down the cam numbers and post them.
I've also heard from a lot of people that own and have driven 83s that they're freaks, much faster than the published performance listings. I would buy that if i hadn't crushed Heather's 83 US by so much.
"With your lightweight car & those type of numbers you have to be at least 310 (Euro spec) crank HP...probably closer to 330....have you dynoed it? Again my guess is 270+ to the wheels"
I'm not a big believer in dyno's because you can take the same car to three different shops on the same day and get three fairly widely varying dyno numbers. I calculate HP by known track ET and trap speed, then split the difference. That gives a decent enough guesstimate for my purposes. All i really care about is the actual ET though. When ya run a 13.67 you don't need a dyno to tell you you're making lots of power, it's self-evident.
"You should post your times at www.dragtimes.com I posted my runs from march...my best was a 14.54 at 95mph...that was with zero power braking..just floor it and go!"
I ran my best time launching at 1600rpm @ 22psi in the rear tires after a nice burn out, with 50psi in the fronts. Try duplicating that next time you go, i guarantee you'll pick up a 1/4 second or more.
"Not bad for a near stock (only RMB), automatic full weight S4 (3500+ myself)...I figure with some tweaks and a better launch I could drop it down to 14.3 or so...maybe better?"
Maybe as low as a 14 flat if you set the tire pressure and run 100octane gas and bump your timing way up to take advantadge of it. At the track it's all about traction. Our 928s have about a 2300rpm stall converter, so if you can get full traction at 2300rpm you're going to run a much faster time than launching from idle. Perhaps as much as a second if you're lucky. I've seen cars make no change other than slicks and cut that much off their ET before. 80s-90s mustangs GTs are a good example of that. They're seriously traction-challenged cars, and benefit massively from a swap to nice wide slicks.
"Your 0-60 seems kinda slow in comparison to the 1/4 mile times...typically my G-tech reads between 5.9 to 6.1 for my car (6.12 on the 14.54 1/4 run)... But the 55mph shift does slow the times!"
The G-meter times were actually recorded before i did my final weight savings job(i borrowed the g-meter off a friend, i don't own one of my own) or my last day at the track, and i cut a good 125+ pounds off the car since that time(driving seats, dry cell battery, and yanking the A/C system). I'm sure it's a few tenths faster now, but i've not verified that in a timed run. My real powerband is 2d gear. My car pulls very hard all the way to 6500rpm in second, which equates to 98mph. I shift to third about 100 feet short of the traps right in the heart of my motors power band, and accelerate like mad the last 100 feet.
My best trap speed is a 103.1, which oddly enough came on my slowest ET run of the day because of wheelspin at the line. I spun em for a good 20 feet and as a result the motor was in the heart of it's power band when i finally got traction(just shy of 3000rpm IIRC). That allowed me to accelerate through 1400 feet much harder than i would normally do with a good launch from 1600. Helps the trap speed, hurts the ET. On my 13.67 run i think my trap speed was a low 102. It's been over a year, so my memory is a bit foggy. I guess i should dig out my timeslips for the day, but i'm lazy.
07-06-2005, 04:47 AM
#32
Banned
Thread Starter
Mark: "first of all, there is not that much difference in the actual hp to the wheels over the operational range to 100mph. probably an advantage for the 2.50 gear box, vs the 2.2, but its not the full percentage, as the gears in the trans are usually different to make the total difference less."
I was referring to changing only the ring and pinion but maintaining your current trans ratios. A .3:1 lower final drive ratio will definitely provide greater torque multiplication and therefore greater acceleration, at the cost of vehicle top speed and fuel economy(My shark gets about a whooping 8mpg in the city).
At any rate, i don't know if my car has a 2.50:1, i only offered it as a reasonable possibility because it's obviously had transwork done to make it always start in first(or it's from a different year entirely). It also shifts very firmly. I used to chirp my 225-50-16s all the time on the 1-2 upshift under moderate throttle.
What i can tell you that my car shifts from 1st at 5500 rpm at 55mph, and from 2-3 at 6500rpm at 98mph. It's been a while since i ran it all the way through 3d(as conditions to do so rarely present themself), so i can't give ya specific speed/rpm figures for the higher gears.
"so, didnt you mention you were on the NOS?"
No, i want to add NOS. Right now it's naturally aspirated. That's what led me to come here to begin with. I seek guidance from folks with first hand NOS 928 experience.
"or is your 4.7 US something really special."
Apparently it's 'something really special' according to the surprise i always encounter from other 928 enthusiasts. In my own experience with various GM musclecars and hotrods i don't consider a mid 13 particularly fast from a V-8 powered car in my 928s weight range. I've owned a couple 12 second cars that were much heavier, and one was a six cylinder, lol.
"could it have the euro intake?"
It has a US intake, though it is possible it's been hogged or perhaps extrude honed. Never had occasion to remove it. It does have a gigantic MAF though(i've never measured it but it looks bigger in diameter than the 3" unit on my Buick T-Type turbo was).
"euro cams??"
No idea what cams are in it. It has a nice lopey idle though. If you want i can post a link to a video of me running it a little bit on a windy road. It sounds nice with the Borla custom exhaust.
I posted the cars known mods and weight reduction measures earlier in the thread.
I was referring to changing only the ring and pinion but maintaining your current trans ratios. A .3:1 lower final drive ratio will definitely provide greater torque multiplication and therefore greater acceleration, at the cost of vehicle top speed and fuel economy(My shark gets about a whooping 8mpg in the city).
At any rate, i don't know if my car has a 2.50:1, i only offered it as a reasonable possibility because it's obviously had transwork done to make it always start in first(or it's from a different year entirely). It also shifts very firmly. I used to chirp my 225-50-16s all the time on the 1-2 upshift under moderate throttle.
What i can tell you that my car shifts from 1st at 5500 rpm at 55mph, and from 2-3 at 6500rpm at 98mph. It's been a while since i ran it all the way through 3d(as conditions to do so rarely present themself), so i can't give ya specific speed/rpm figures for the higher gears.
"so, didnt you mention you were on the NOS?"
No, i want to add NOS. Right now it's naturally aspirated. That's what led me to come here to begin with. I seek guidance from folks with first hand NOS 928 experience.
"or is your 4.7 US something really special."
Apparently it's 'something really special' according to the surprise i always encounter from other 928 enthusiasts. In my own experience with various GM musclecars and hotrods i don't consider a mid 13 particularly fast from a V-8 powered car in my 928s weight range. I've owned a couple 12 second cars that were much heavier, and one was a six cylinder, lol.
"could it have the euro intake?"
It has a US intake, though it is possible it's been hogged or perhaps extrude honed. Never had occasion to remove it. It does have a gigantic MAF though(i've never measured it but it looks bigger in diameter than the 3" unit on my Buick T-Type turbo was).
"euro cams??"
No idea what cams are in it. It has a nice lopey idle though. If you want i can post a link to a video of me running it a little bit on a windy road. It sounds nice with the Borla custom exhaust.
I posted the cars known mods and weight reduction measures earlier in the thread.
07-06-2005, 04:48 AM
#33
Banned
Thread Starter
"again, it depends. i just posted dyno runs at 82 degrees, and actual was actually better than SAE corrrected. I would love to think that the car could run 5% greater hp at 50 degrees[, but ive done dyno runs at 60f with the same results (actual) dont know why, but it sure doesnt seem that high temps hurt much. in fact, my fastest times at Laguna have been in 85 to 90 degree days. (and that goes for Thunderhill at 100F) trade off with tire stick???? thinner air, less wind resistance??? who knows. But, there are trade offs"
That's probably attributable to the cooling effect of n20 on the air charge. That's an advantadge a blown or naturally aspirated engine does not enjoy.
That's probably attributable to the cooling effect of n20 on the air charge. That's an advantadge a blown or naturally aspirated engine does not enjoy.
07-06-2005, 12:03 PM
#34
Supercharged
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See what happens when you leave town for a couple of days... Everone wants to know about NOS!
Well all I can say is that it works! It works very well especially for an OB like my 82. Very fun and will shave about .5~.6 seconds on a 1/4 mile run.
You might want to read my previous posts on this subject. I'm at work right now and busier than a 1 legged man at an *** kicking contest so you'll have to forgive me not linking the posts. If I have time tonight, I'll try and post the link then.
Well all I can say is that it works! It works very well especially for an OB like my 82. Very fun and will shave about .5~.6 seconds on a 1/4 mile run.
You might want to read my previous posts on this subject. I'm at work right now and busier than a 1 legged man at an *** kicking contest so you'll have to forgive me not linking the posts. If I have time tonight, I'll try and post the link then.
07-06-2005, 12:08 PM
#35
Rennlist Member
I dont run NOS on my car now. But, yes, one of the advantages of NOS is 50hp shot when you need it regardless of outside temps.
mk
mk
Originally Posted by m21sniper
"again, it depends. i just posted dyno runs at 82 degrees, and actual was actually better than SAE corrrected. I would love to think that the car could run 5% greater hp at 50 degrees[, but ive done dyno runs at 60f with the same results (actual) dont know why, but it sure doesnt seem that high temps hurt much. in fact, my fastest times at Laguna have been in 85 to 90 degree days. (and that goes for Thunderhill at 100F) trade off with tire stick???? thinner air, less wind resistance??? who knows. But, there are trade offs"
That's probably attributable to the cooling effect of n20 on the air charge. That's an advantadge a blown or naturally aspirated engine does not enjoy.
That's probably attributable to the cooling effect of n20 on the air charge. That's an advantadge a blown or naturally aspirated engine does not enjoy.
07-06-2005, 12:14 PM
#36
Rennlist Member
WAIT a min!!! "giagantic MAF" ???????????????????????
if we are talking about an unmodified 1983 US, then there aint no MAF!! its a very tiny AFM. one that can get some good hp, but it needs euro intake and cams for 250ish HP to the rear wheels
if you have a "gigantic MAF" then you either have a euro 1985,which would explain your fast ETs, or some aftermarket work on the intake or fuel air system.
cant "hog " out the US Throttle body, its limited by casting size. euro is huge, and looks almost identical, unless you look closely at the casting. 2.5" vs 3.5" diameter!!!
MK
[QUOTE=m21sniper
"could it have the euro intake?"
It has a US intake, though it is possible it's been hogged or perhaps extrude honed. Never had occasion to remove it. It does have a gigantic MAF though(i've never measured it but it looks bigger in diameter than the 3" unit on my Buick T-Type turbo was).
[/QUOTE]
if we are talking about an unmodified 1983 US, then there aint no MAF!! its a very tiny AFM. one that can get some good hp, but it needs euro intake and cams for 250ish HP to the rear wheels
if you have a "gigantic MAF" then you either have a euro 1985,which would explain your fast ETs, or some aftermarket work on the intake or fuel air system.
cant "hog " out the US Throttle body, its limited by casting size. euro is huge, and looks almost identical, unless you look closely at the casting. 2.5" vs 3.5" diameter!!!
MK
[QUOTE=m21sniper
"could it have the euro intake?"
It has a US intake, though it is possible it's been hogged or perhaps extrude honed. Never had occasion to remove it. It does have a gigantic MAF though(i've never measured it but it looks bigger in diameter than the 3" unit on my Buick T-Type turbo was).
[/QUOTE]
07-06-2005, 12:19 PM
#37
Race Director
Sniper
55 mph @ 5500 rpm in first gear is very fast (for a 4 speed)....my 4 speed with 2.20 rear end shifts out of first gear at 6200 rpm around 40ish mph...then also shifts out of 2nd @ 6200rpm at around 80mph? Thats why I thought you had the three speed...since those typically go almost 70mph in first gear! I would guess you have at least a 2.20 rear end since 1st gear goes so fast!
Brian
55 mph @ 5500 rpm in first gear is very fast (for a 4 speed)....my 4 speed with 2.20 rear end shifts out of first gear at 6200 rpm around 40ish mph...then also shifts out of 2nd @ 6200rpm at around 80mph? Thats why I thought you had the three speed...since those typically go almost 70mph in first gear! I would guess you have at least a 2.20 rear end since 1st gear goes so fast!
Brian
07-06-2005, 12:29 PM
#39
Rennlist Member
Again, you may have missed the point, but there ARE trade offs in gearing effects to acceleration. just because you have a higher numerical rear end, doesnt you mean you get the advantage of increased torque at all speed ranges. its the ave torque to the wheels over the speed range. (area under the torque curve used.) you say you go through 2 gears from 0-100mph. right now with your hp, you have an optimal gearing. assuming your 1/4mile top speed is 100mph. a higher numerical ratio in the rear of your car, could make for a shift at 90mph, where you would have an advantage from 0-40, a disadvantage from 40-55, then an advantae from 55 to 90, but a disadvantage from 90 to 100mph. (based on guesses of a rear end change) again, we all had a heated discussion on the topic of gearing. bottomline, it really depends on your target speed range. something very important to racers whom choose ratios based on time and distance spent in each gear and expeced speeds based on available hp. as a rule of thumb, you want to find a set of ratios or rear end that gives you engine redline at the end of a straight or distance.
as far as gas mileage, in a stick , top gear plays little on projected MPG, its really about load. sure if you have a 5 speed and you run in 4th at 80mph on a road trip, your MPG will suffer. but , a 8 % change in rear end ,all things being equal, wont do much for Gas mileage differences . thats really a factor or atomization of the gas and air and engine and chassis frictional losses. there are lots of little 4 bangers that rev to 3k rpms onthe hyway and get 40mpg.
I dont think EPA estimates of the GT and S4 were much different, even though one got a 2.2 and the other got a 2.72 rear end.
mk
as far as gas mileage, in a stick , top gear plays little on projected MPG, its really about load. sure if you have a 5 speed and you run in 4th at 80mph on a road trip, your MPG will suffer. but , a 8 % change in rear end ,all things being equal, wont do much for Gas mileage differences . thats really a factor or atomization of the gas and air and engine and chassis frictional losses. there are lots of little 4 bangers that rev to 3k rpms onthe hyway and get 40mpg.
I dont think EPA estimates of the GT and S4 were much different, even though one got a 2.2 and the other got a 2.72 rear end.
mk
Originally Posted by m21sniper
Mark: "first of all, there is not that much difference in the actual hp to the wheels over the operational range to 100mph. probably an advantage for the 2.50 gear box, vs the 2.2, but its not the full percentage, as the gears in the trans are usually different to make the total difference less."
I was referring to changing only the ring and pinion but maintaining your current trans ratios. A .3:1 lower final drive ratio will definitely provide greater torque multiplication and therefore greater acceleration, at the cost of vehicle top speed and fuel economy(My shark gets about a whooping 8mpg in the city).
At any rate, i don't know if my car has a 2.50:1, i only offered it as a reasonable possibility because it's obviously had transwork done to make it always start in first(or it's from a different year entirely). It also shifts very firmly. I used to chirp my 225-50-16s all the time on the 1-2 upshift under moderate throttle.
What i can tell you that my car shifts from 1st at 5500 rpm at 55mph, and from 2-3 at 6500rpm at 98mph. It's been a while since i ran it all the way through 3d(as conditions to do so rarely present themself), so i can't give ya specific speed/rpm figures for the higher gears.
.
I was referring to changing only the ring and pinion but maintaining your current trans ratios. A .3:1 lower final drive ratio will definitely provide greater torque multiplication and therefore greater acceleration, at the cost of vehicle top speed and fuel economy(My shark gets about a whooping 8mpg in the city).
At any rate, i don't know if my car has a 2.50:1, i only offered it as a reasonable possibility because it's obviously had transwork done to make it always start in first(or it's from a different year entirely). It also shifts very firmly. I used to chirp my 225-50-16s all the time on the 1-2 upshift under moderate throttle.
What i can tell you that my car shifts from 1st at 5500 rpm at 55mph, and from 2-3 at 6500rpm at 98mph. It's been a while since i ran it all the way through 3d(as conditions to do so rarely present themself), so i can't give ya specific speed/rpm figures for the higher gears.
.
07-06-2005, 12:39 PM
#40
Rennlist Member
stinky!!
hey, we all know what it takes to do a 13 second 1/4 run. and it aint no 1983 stock 4.7 US 928! it does take around 300hp on a 3300lb chassis. 1983 928 rarely put down more than 200hp at the wheels stock. so, where did 50hp come from?? id say, that "giagantic" MAF is a good place to start!
MK
hey, we all know what it takes to do a 13 second 1/4 run. and it aint no 1983 stock 4.7 US 928! it does take around 300hp on a 3300lb chassis. 1983 928 rarely put down more than 200hp at the wheels stock. so, where did 50hp come from?? id say, that "giagantic" MAF is a good place to start!
MK
Originally Posted by Normy
Anyone else smell a cattle farm around here-?
N-
N-
07-06-2005, 02:45 PM
#41
Rennlist Member
More errors : a 245x45x16 is almost the same diameter as a 225x50x16.
both are about 24.7-9".
the only way you coul have a 3% gearing change is if you switched from one of the above to the same tire in a 17" (or went down to a 15" for the opposite effect of about 3%)
55mph 1st gear
3% tire gearing difference
MAF driven 1983 US auto
Hmmm, lots of questions here!
mk
both are about 24.7-9".
the only way you coul have a 3% gearing change is if you switched from one of the above to the same tire in a 17" (or went down to a 15" for the opposite effect of about 3%)
55mph 1st gear
3% tire gearing difference
MAF driven 1983 US auto
Hmmm, lots of questions here!
mk
Originally Posted by m21sniper
BRIAN: "Sniper
That is a great time for a NA 3 speed auto!!!"
I also lowered the effective final drive ratio myself a bit(about 3%) by switching to a smaller OD tire(245-45-16), which is also 20mm wider than stock.
That is a great time for a NA 3 speed auto!!!"
I also lowered the effective final drive ratio myself a bit(about 3%) by switching to a smaller OD tire(245-45-16), which is also 20mm wider than stock.
07-06-2005, 03:03 PM
#42
Banned
Thread Starter
"Anyone else smell a cattle farm around here-?"
Tell ya what norm, bring your skeptical self to philly and i'll happily lay a whooping on the first Cobra we see...just for you.
Lance (previous owner of a 1983 Euro with a 75hp shot of nitrous) already posted that i beat his Shark by 3 lengths from a standing start earlier in the thread. If that's not good enough for you, then bring your tail to philly and i'll take you for a ride.
Othewise, STFU.
Tell ya what norm, bring your skeptical self to philly and i'll happily lay a whooping on the first Cobra we see...just for you.
Lance (previous owner of a 1983 Euro with a 75hp shot of nitrous) already posted that i beat his Shark by 3 lengths from a standing start earlier in the thread. If that's not good enough for you, then bring your tail to philly and i'll take you for a ride.
Othewise, STFU.
07-06-2005, 03:05 PM
#43
Rennlist Member
what about the MAF? if you have one, it aint no 1983 US
mk
mk
Originally Posted by m21sniper
"Anyone else smell a cattle farm around here-?"
Tell ya what norm, bring your skeptical self to philly and i'll happily lay a whooping on the first Cobra we see...just for you.
Lance (previous owner of a 1983 Euro with a 75hp shot of nitrous) already posted that i beat his Shark by 3 lengths from a standing start earlier in the thread. If that's not good enough for you, then bring your tail to philly and i'll take you for a ride.
Othewise, STFU.
Tell ya what norm, bring your skeptical self to philly and i'll happily lay a whooping on the first Cobra we see...just for you.
Lance (previous owner of a 1983 Euro with a 75hp shot of nitrous) already posted that i beat his Shark by 3 lengths from a standing start earlier in the thread. If that's not good enough for you, then bring your tail to philly and i'll take you for a ride.
Othewise, STFU.
07-06-2005, 03:22 PM
#44
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And didn't Devek build a few 2v strokers, that no one knew where they were, or who owned them?
I mean, there is no reason to call BS on someone who seems to be honest.
We may not know why it's so fast, and it's interesting to find out,
but there is no reason to badmouth someone who is just talking
about how their car is strangely faster than other 928s...
He's got the timeslip to prove it.
I don't smell anything other than burning rubber.
I mean, there is no reason to call BS on someone who seems to be honest.
We may not know why it's so fast, and it's interesting to find out,
but there is no reason to badmouth someone who is just talking
about how their car is strangely faster than other 928s...
He's got the timeslip to prove it.
I don't smell anything other than burning rubber.
07-06-2005, 03:31 PM
#45
Banned
Thread Starter
"Again, you may have missed the point, but there ARE trade offs in gearing effects to acceleration. just because you have a higher numerical rear end, doesnt you mean you get the advantage of increased torque at all speed ranges."
A higher final drive ratio decreases engine torque multiplication, a lower final drive ratio increases engine torque multiplication at any engine speed. Higher = lower numerical rating. Lower = higher numerical rating. Ie, a 2.50:1 is lower than a 2.20:1.
"its the ave torque to the wheels over the speed range. (area under the torque curve used.) you say you go through 2 gears from 0-100mph. right now with your hp, you have an optimal gearing. assuming your 1/4mile top speed is 100mph."
My 928s best ever trap speed is a 103.1mph.
My IDEAL 1/4 mile gearing would leave me just short of redline in top gear at the end of the 1/4 mile. I'd need about a 4.56:1 for that. The extremely high gearing of 928s is what really hurts them as 1/4 mile cars. With no other change but a 4.56:1 rear end ratio any 928 would be much faster in the 1/4 mile(perhaps as much as 2 seconds assuming traction can be maintained, which it most certainly would not), at a great expense to top end(perhaps as much as 40 or more MPH).
"a higher numerical ratio in the rear of your car, could make for a shift at 90mph,"
A higher gear ratio would increase vehicle speed at the end of each gear as well as vehicle top end, and the opposite would be true for a lower gear ratio. Right now my car performs it's 2-3 upshift at 98mph @6500rpm. If i were to switch to a higher gear(ie a lower numerical rating), my 2-3 upshift speed would increase, and it would lower if i installed a lower gear(ie a higher numerical rating).
"where you would have an advantage from 0-40, a disadvantage from 40-55, then an advantae from 55 to 90, but a disadvantage from 90 to 100mph."
Torque multiplication is purely a function of gear ratio. A lower gear ratio provides greater torque multiplication at all engine speeds, end of story.
"as far as gas mileage, in a stick , top gear plays little on projected MPG, its really about load. sure if you have a 5 speed and you run in 4th at 80mph on a road trip, your MPG will suffer. but , a 8 % change in rear end ,all things being equal, wont do much for Gas mileage differences ."
An 8% increase(ie 8% higher) in final drive is about what most Overdrive gears will provide(some a bit less, others a bit more). The 5speed in the 928 is not over-driven, it's 1:1, the same as 4th in the auto cars. Our 928s do not have overdrive. An 8% reduction in engine speed at a given vehicle speed will improve gas mileage on any vehicle. Just how much depends on a lot of factors, but the higher geared vehicle- all things being equal- will have better fuel economy and a higher top speed than one with a lower(ie numerically higher) gear ratio.
As far as my tire size, the 245-45-16 tires i installed are 0.1 inches smaller in diameter than the 225s, which is an effective change of 0.7% in final drive ratio. I don't know where i came up with 3%, it's been a while since i compared the two sizes, and i apparently 'mis-remembered', my appologies.
Link to a handy tire size calculator: http://www.miata.net/garage/tirecalc.html
A higher final drive ratio decreases engine torque multiplication, a lower final drive ratio increases engine torque multiplication at any engine speed. Higher = lower numerical rating. Lower = higher numerical rating. Ie, a 2.50:1 is lower than a 2.20:1.
"its the ave torque to the wheels over the speed range. (area under the torque curve used.) you say you go through 2 gears from 0-100mph. right now with your hp, you have an optimal gearing. assuming your 1/4mile top speed is 100mph."
My 928s best ever trap speed is a 103.1mph.
My IDEAL 1/4 mile gearing would leave me just short of redline in top gear at the end of the 1/4 mile. I'd need about a 4.56:1 for that. The extremely high gearing of 928s is what really hurts them as 1/4 mile cars. With no other change but a 4.56:1 rear end ratio any 928 would be much faster in the 1/4 mile(perhaps as much as 2 seconds assuming traction can be maintained, which it most certainly would not), at a great expense to top end(perhaps as much as 40 or more MPH).
"a higher numerical ratio in the rear of your car, could make for a shift at 90mph,"
A higher gear ratio would increase vehicle speed at the end of each gear as well as vehicle top end, and the opposite would be true for a lower gear ratio. Right now my car performs it's 2-3 upshift at 98mph @6500rpm. If i were to switch to a higher gear(ie a lower numerical rating), my 2-3 upshift speed would increase, and it would lower if i installed a lower gear(ie a higher numerical rating).
"where you would have an advantage from 0-40, a disadvantage from 40-55, then an advantae from 55 to 90, but a disadvantage from 90 to 100mph."
Torque multiplication is purely a function of gear ratio. A lower gear ratio provides greater torque multiplication at all engine speeds, end of story.
"as far as gas mileage, in a stick , top gear plays little on projected MPG, its really about load. sure if you have a 5 speed and you run in 4th at 80mph on a road trip, your MPG will suffer. but , a 8 % change in rear end ,all things being equal, wont do much for Gas mileage differences ."
An 8% increase(ie 8% higher) in final drive is about what most Overdrive gears will provide(some a bit less, others a bit more). The 5speed in the 928 is not over-driven, it's 1:1, the same as 4th in the auto cars. Our 928s do not have overdrive. An 8% reduction in engine speed at a given vehicle speed will improve gas mileage on any vehicle. Just how much depends on a lot of factors, but the higher geared vehicle- all things being equal- will have better fuel economy and a higher top speed than one with a lower(ie numerically higher) gear ratio.
As far as my tire size, the 245-45-16 tires i installed are 0.1 inches smaller in diameter than the 225s, which is an effective change of 0.7% in final drive ratio. I don't know where i came up with 3%, it's been a while since i compared the two sizes, and i apparently 'mis-remembered', my appologies.
Link to a handy tire size calculator: http://www.miata.net/garage/tirecalc.html