More 1/4 mile stuff

[McAttack]

Although the car had only about 14k miles when I got it, it was NOT new and I am the 3rd owner. To the best of my knowledge, the only thing the 2nd owner did was put on performance springs and sway bars (which he threw in BTW). So w/o pulling the thing apart, how do I know if the R&P is not OEM?

Also, not sure what Factor X meant by purging the NOS. I'm still on my 1st bottle and have only used it on the strip (MOSTLY lol) Anyway, I'm planning on 2 more visits this year. 1st will be another midweek rental which will give me all the runs I want. And finally Import Wars October 12th in NH.

On a last note, I did try to record my runs w/ a camcorder. While the camera managed to get perfect pictures of my glove box for the runs (DOE!) You CAN hear the engine and shifts. ALL of the runs had me hitting 5th b4 the traps.

Someone asked me in an earlier post if I was getting all 8k. While I responded yes right away, I have to admit can't be exact. If it makes a diff, some may have been 78 or 7900 at some points. The rev limiter obviously made me very aware when I went over.

RE: weight, I removed the spare tire (the cars not mine) and tools. I didn't remove the engine cover although I will next time. I tip the scales at 197lbs (corrected!)

I'm also planning on attending the Upper East NSX Rally in a few weeks. I'm hoping some of the more experienced New England NSXers will be able to advise me.

I appreciate your observations. I'm learning a lot

 

[Lud]

For nitrous to work well, especially right away, you want the lines full of liquid, not gas. "Purging the system" means activating a valve to purge the lines of air/gas and fill them with liquid shortly before you are going to use nitrous.

If you don't have a bottle heater, at the ambient temps you mentioned your FIRST run is probably only getting 75% of the potential of the nitrous setup, and consecutive runs are probably even less as the bottle cools down from use. At 40 degrees bottle temp you are getting maybe 25hp out of your 50hp nitrous shot.

I am not aware of any gear setup, including 4.55 R&P on a 5-speed, or 4.55 R&P on a 6-speed, that would require you to shift to 5th with a 112 MPH trap speed. At what point in the run are you making that 4-5 shift?


[This message has been edited by Lud (edited 08 September 2002).]

 

[McAttack]

Originally posted by Lud:
For nitrous to work well, especially right away, you want the lines full of liquid, not gas. "Purging the system" means activating a valve to purge the lines of air/gas and fill them with liquid shortly before you are going to use nitrous.

If you don't have a bottle heater, at the ambient temps you mentioned your FIRST run is probably only getting 75% of the potential of the nitrous setup, and consecutive runs are probably even less as the bottle cools down from use. At 40 degrees bottle temp you are getting maybe 25hp out of your 50hp nitrous shot.

I am not aware of any gear setup, including 4.55 R&P on a 5-speed, or 4.55 R&P on a 6-speed, that would require you to shift to 5th with a 112 MPH trap speed. At what point in the run are you making that 4-5 shift?


[This message has been edited by Lud (edited 08 September 2002).]

I do not have a bottle warmer. Similar to Tampa Bay NSX I'm Sooooo close to the finish but can't make it in 4th. Tried once but the rev limiter kicked in...

 

[Lud]

TampaBayNSX-R has a 6-speed with 4.55 R&P, not a 5-speed. So his 4th gear is shorter than yours on a 5-speed to begin with, even if you have short gears in addition to 4.55 R&P.

If TampaBay/Scott is 50 feet from the traps when he shifts to 5th with his setup, you should be able to stay in 4th all the way through if you are at the same speed... 50 feet isn't much at 110+ MPH. So something else must be going on. Unless he had really tall rear tires and you have short ones or something...

Either that, or their timing system is out of calibration!

I also suspect Scott would be better off if he did not make that last shift. His top speed in 4th is higher than his trap speed, which means he is losing a little time and speed at the very end versus just staying at 8000 RPM in 4th. But since he only got one run he didn't have a chance to experiment.

Regardless, I think it's safe to say you definitely do not have the stock gearing in your car.

[This message has been edited by Lud (edited 08 September 2002).]

 

[Sketch]

Originally posted by McAttack:
So w/o pulling the thing apart, how do I know if the R&P is not OEM?

You should be able to calculate your gears based on MPH, RPM, and tire diameter. I don't know the math, but you can probably find it on the net somewhere.

Or just plug in possible NSX trans gearing numbers into a web-based calculator like this:
http://www.slowgt.com/Calc1.htm#RPMInGear

You don't need a dragstrip to do it, just go out and drive your car at a steady speed and record the RPM. Calculate your tire diameter ((width in inches * aspect ratio * 2) + rim height), and plug in the numbers.

There is one potential complication to this, is whether your speedo and tach are accurate. If your overall tire diameter is not the same as for stock NSX wheels/tires, your speedo will be off. Your tach might just not be accurate, like my 91. I found out when I had my car dyno'd that 8000rpm on the tach was really only 7600rpm. I seem to recall a thread where a few people mentioned their tachs were off by a couple hundred RPM.

This brings another possibility to mind. If your tach is off, you could be shifting earlier than you think you are?

Obviously if your rev limited kicks in shortly after 8000, this isn't an issue.

---

Edited to fix URL link. Hmm, what happened to HTML code being on?


[This message has been edited by Sketch (edited 08 September 2002).]

 

[sjs]

OK, first tell us if it's a 5-speed or a 6-speed. We really haven't heard that yet. As I said above and Lud has also noted, the 5-spd isn't close to needing 5th at 112 even with a 455. But the 6-spd is off by just a couple MPH which could be tires, just a couple hundred RPM under redline, or a combination of these. If it is a 5-spd then I'd say you are shifting way early, just no way around it I can think of.

 

[BadCarma]

Originally posted by Gerry Johnson:
Drive into your lane, do a slight wheel spin to clean the dirt off the tire's, "not a burn out" unless you are running brackets don't worry about your reaction time concentrate on leaving the line. Reaction time has nothing to do with the ET and MPH, you can sit their as long as you don't break the beam for as long as you like.

everything you say is true.you can sit there forever and when you launch it wil not effect anything till you break the sensor.but if you are running against another driver backet or not it does matter getting your hole shot down
david
ps love your car

 

[CapeCodMass]

McAttack,

I have a few observations (since I watched you run 3 times and taped you twice on video...)

• You spin far too much on the line (like I do). Try taking off like you are leaving a traffic light and a cop is behind you... It will be "bogg" city but the s/c nos should help that out.
• In October I'll be up at Epping for Import wars and if you'd like I'll ride along once to watch. I have a tape of a run when you ran 13.99 and I swear you broke before the traps... since Epping does a lousy job of painting a finish line (and at 110+ you pass the time towers before they light up) you may be braking too early.
• Lastly, and this is just my opinion... Beat it like a borrowed Iroc!!!. F granny shifting! If it breaks down I can give ya a lift home (if mine doesn't die too).
  
  Take it easy...
  
  Remember - The true definition of Orgasm - The point at which the fear of death is overcome by the thrill of speed.

 

[CapeCodMass]

By the way.. I have a bottle warmer and it has a minimal impact on my times... 3 with 3 without all average the same (within .05 of each other).

The purge is nice for show.. (It just blows the NOS in the line out so that the first hit is "pure") Again, we aren't dragsters... Without the purge we may have a 1/2 second delay until the "Good" NOS hits the solenoid...

By the way, since I don't care about braking parts I am buying a set of DOT drag radials... You're welcome to make a pass on them if you'd like (it will cut down our spinning to a managable amount - hopefully). I just don't want you to hold me responsible for a busted axel

.

 

[sjs]

OK, I’m a dunce. Last night I realized that I made a really dumb mistake with the simulator.

I was using RWHP figures as quoted by people rather than grossing it up for approximate crank HP. I’ll try to rerun them this evening but that will only further support that McAttack is missing something.

 

[McAttack]

Originally posted by sjs:
OK, first tell us if it's a 5-speed or a 6-speed. We really haven't heard that yet. As I said above and Lud has also noted, the 5-spd isn't close to needing 5th at 112 even with a 455. But the 6-spd is off by just a couple MPH which could be tires, just a couple hundred RPM under redline, or a combination of these. If it is a 5-spd then I'd say you are shifting way early, just no way around it I can think of.

I have a '99 6 speed

 

[McAttack]

Originally posted by CapeCodMass:
McAttack,

I have a few observations (since I watched you run.....

[*] You spin far too much on the line
[*] In October I'll be up at Epping for Import wars and if you'd like I'll ride along once to watch. I have a tape of a run when you ran 13.99 and I swear you broke before the traps
[*] Lastly, and this is just my opinion... Beat it like a borrowed Iroc!!!.
B]

Good to hear from you Tim.

I am practicing my launches, you're right...

I'll be at Import Wars as well. I WILL take you up on your riding shotgun.

I didn't even consider I was breaking too soon. Didn't even cross my mind....

Beat it like a borrowed IROC? THAT'S IT!!! I was only beating it like a rented mule!! LOL


You have mail.

 

[Lud]

OK if you have a 6-speed then strike my comments about not needing 5th then if you have 4.55 R&P, which you obviously do.

I thought you had a 5-speed for some reason.

But what I said about Scott then applies to you - that if your trap speed is 112 you may be better off not shifting to 5th. You'll have to experiment.

All the little things like purging your nitrous and using a bottle warmer may not make much difference, but they do make a difference all other things being equal. All those little things add up in the end. But if there are other major problems like lots of wheel spin, definitely work on those first because there is much more to gain there.

 

[TampaBayNSX-R]

I was fortunate to have my run video taped at the starting line by my fiancee. I have watched it about twenty times and it looks like the leave was about right. I dumped the clutch at 3,000rpms, or as close to that as I can recall...I was pretty wound up after waiting almost 5 hours to run, the car spun the tires for about ten or fifteen feet and then hooked up. The 1-2 shift saw more wheelspin for about ten feet and then I was on my way. The wheelspin was smooth, no hopping and I didn't lift...just drove through it.

I agree with you Lud about the extra shift costing me. I hope to try running it through the lights in 4th soon to see if I get a higher trap speed. I may save a couple tenths and gain a couple mph that way. I'll post results when I do.

 

[McAttack]

Scott, I think you said in an earlier post that your tire pressure was 20 PSI. I don't think I went that low. I was to 22. But one constant I have is wheel hop. VIOLENT wheel hop. That's what broke my CV joint the first go round. I'd go with a set of drag slicks but I think there are other areas I can focus first which will provide a greater return for the investment. Just writing this makes me want to head up there right now!

 

[marksink]

Hey... you guys are all missing one thing...

a slipping clutch!

I am the previous owner of this car... A slipping clutch would account for what McAttack is seeing, and hitting the rev limiter way to soon, shifting too early, and having a slow time.

mark

 

[McAttack]

Originally posted by marksink:
Hey... you guys are all missing one thing...

a slipping clutch!

I am the previous owner of this car... A slipping clutch would account for what McAttack is seeing, and hitting the rev limiter way to soon, shifting too early, and having a slow time.

mark

Howdy Mark! Good to hear from you! (It was tough to see the look on his face when he handed me the keys but no doubt Mark will be the proud owner of a 2003+ NSX down the road)

I sent you a private email but for the sake f this thread....the clutch is the Comptech Powergrip II w/<3k miles on it. The car is my daily driver so if it could slip under extremes but be ok to and from work, this may be right? Don't know much about clutches....

 

[marksink]

The clutch could very well hold for daily driving and not on the track. 2 Reasons. Repeated launches will heat up the clutch, and the more this happens within a certain period of time, the more likely it is to slip. Second, clutch slips start in higher gears at first, and when the engine is making lots of torque. If it's getting bad, you should be able to place the car in 5th, or 6th, take the engine to where it makes max toruqe, and floor it. If it slips, revs will rise quicker than they should, and letting of the gas will shows the revs drop back to where they should be.

If you think it may only be slipping on the track, say when you hit 8000 RPM in 4th, dont shift into 5th, but let off the gas instead. If your revs below 7000 rather quickly, it means the clutch was slipping.

mark

 

[sjs]

A slipping clutch is pretty obvious. During normal street driving it is true that it may seem fine until you get into the meat of the torque curve, but at the strip where you're launching it hard from a dead stop it would slip then if at all. If you're lighting up the rear tires on a sticky drag surface and don't smell a very conspicuous odor then I think this is not the most likely answer. I won't bet against it because I wasn't driving, but a slipping clutch has a very distinct feel and smell.

 

[sjs]

McAttack. grossing up your HP & torque to 450 and 350 at the crank and assuming you have a 4.55 yields the following:

3k dump launch: 12.19 @ 118.25
3k slip launch: 12.89 @ 117.73

Note: "slip" here refers to a launch technique of slipping the clutch slightly ranther than dumping it and spinning the tires more, not a worn and slipping clutch as recently discussed.

As you can see, even a lousy launch has only a minor impact on trap speed but a big hit on ET.

Dropping the shift point by 300 RPM to 7700 has only a small impact, changing the dump launch to 12.29 @ 118.16. But of course if that last one takes you needlessly to the next gear then it makes a much larger difference.

Just for reference, plugging the stock R&P value of 4.06 into the original dump launch yields 12.20 @ 120.89, nearly identical ET as the 4.55 but a higher trap. So the extra shift costs the same amount of time as the gain from a lower diff through the entire run, assuming fast efficient shifts of course.

 

[Attitude Adjuster]

Originally posted by McAttack:
Howdy Mark! Good to hear from you! (It was tough to see the look on his face when he handed me the keys but no doubt Mark will be the proud owner of a 2003+ NSX down the road)

I sent you a private email but for the sake f this thread....the clutch is the Comptech Powergrip II w/<3k miles on it. The car is my daily driver so if it could slip under extremes but be ok to and from work, this may be right? Don't know much about clutches....

Macattack,

Are you running a supercharger and NOS 50 shot?? Is your bottom end rebuilt? Who setup you NOS system? About how much does the NOS system runs? Is it a wet or dry system? Thanks for the info.

I'm running a CTSC with stock exhaust, dali clutch and ran a best 12.3 @ 114 mph. I since changed my rims to 18X10s and just the short gears and with hot humid air ran a best of 12.7 @109. I'd like to try NOS if it's safe.


------------------
Kenji Ligon
91 Red CTSC NSX

 

[8000RPM]

Originally posted by Attitude Adjuster:

I'm running a CTSC with stock exhaust, dali clutch and ran a best 12.3 @ 114 mph. I since changed my rims to 18X10s and just the short gears and with hot humid air ran a best of 12.7 @109.

So your trap speed went down by 5mph.

I am wondering how much each of the following contributed to the decrease in trap speed:

- Going with larger wheels
- Short gears
- Hot humid conditions

I am trying to figure out the effects of larger wheels (such as 18x10s) on trap speed... Can anyone else provide more reference points?



[This message has been edited by 8000RPM (edited 10 September 2002).]

 

[McAttack]

Are you running a supercharger and NOS 50 shot?? Is your bottom end rebuilt? Who setup you NOS system? About how much does the NOS system runs? Is it a wet or dry system? Thanks for the info.

[/B]

I have a '99 NSX-T 6 speed w/about 18.5k miles on it(as of today). I'm running a CTSC w/the upgraded boost kit (9PSI) and a wet NOS 50 shot flowing from a 10lb polished bottle. Also CT I/H/E and PG II clutch. The bottom end has not been touched. NOS setup was done locally. NOS injects pre SC so I think it's actually more than a 50HP gain. It engages ONLY at full throttle by means of a computerized throttle sensor. The setup w/labor was about $2300. Throttle sensor was about $500. alone.

RE: being "safe" time will tell. The 9PSI CTSC was pushing it which is why I only went with a 50 shot. The fact that it only comes on at wide open along with the fact that 2 months later I'm still on my 1st bottle of NOS "gives me hope"

 

[McAttack]

Originally posted by Lud:
.....if you have 4.55 R&P, which you obviously do.

With Mark Sink's chiming in, that likelihood just went WAYYY down. The original owner was a woman who put 2k miles on it before she sold it to Mark. If anyone was going to add 4:55's it would have been him (and he didn't)

I HAVE A STOCK R&P !!!!

 

[Lud]

Then you have some serious issue with your car, because 4th gear on a stock 6-speed does not redline until around 130 MPH.