Drive versus Overdrive in the quarter mile

Tom Kelly

Active Member
Joined
Jun 23, 2016
It's spring and time to continue my testing and tuning (now with my soon to be installed wideband a/f sensor and powerlogger) Always looking to protect my precious rebuilt motor so I still anguish a bit about doing the whole run in drive even though the calculators say I am way safe even up to 115 mph with my 27 inch MT's. I am planning to tune in drive (i.e. 3rd gear) but I was wondering about the ET and mph penalty for using OD. My experience last year was that in OD the car shifted to 4th just before the light (maybe 100-150 feet) and I felt a noticeable let down as the rpm's fell that 30%. I suspect the effect that late in the run would be to hurt mph more than ET. What do you all think?
 
I thought R is the race mode :). Kidding. Leave it in drive.
In reviewing past threads to see if this was already covered I noted a member who remembered a friends car with "S" and he wondered if it was a Pontiac. I remember my 55 Olds 88 that I raced at Westhampton Dragway in Long Island in the 60's had an "S" in between L and D. We called it Super. If I remember correctly my Olds ran in L S/A (L stock automatic which was considerably down the food chain) My memory is more fuzzy about performance but I think it ran about 18.0 seconds at about 74 mph. And it had a 2 barrel carb. Lots of torque and a tight tranny.
 
I remember reading that starting in 2nd then banging 3rd had some advantage?


Been a few years since I read that... but that’s how I take mine down the track
 
I remember reading that starting in 2nd then banging 3rd had some advantage?


Been a few years since I read that... but that’s how I take mine down the track
Tricks of the past have evaporated under bracket racing now that we all worship at the altar of consistency. That' s why clutch shifiting is only for the very daring (or very expert) of us weekend warriors
 
It's spring and time to continue my testing and tuning (now with my soon to be installed wideband a/f sensor and powerlogger) Always looking to protect my precious rebuilt motor so I still anguish a bit about doing the whole run in drive even though the calculators say I am way safe even up to 115 mph with my 27 inch MT's. I am planning to tune in drive (i.e. 3rd gear) but I was wondering about the ET and mph penalty for using OD. My experience last year was that in OD the car shifted to 4th just before the light (maybe 100-150 feet) and I felt a noticeable let down as the rpm's fell that 30%. I suspect the effect that late in the run would be to hurt mph more than ET. What do you all think?

Does your rebuild consist of stock pistons?? If so they don't enjoy revving over 5500 much because of how much they weigh... They will crack if not careful
 
I kept getting bigger tires until I had 28” tall tires on the back. Leave it in drive. I didn’t think it would pull the 28” tires but It did. I tried 26” tires and let it shift in 4th and it was slower. I would be looking for 29” tall tires if I was running the 1/4. Mine is just a daily driver with 28” drag radials now.


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I did a burnout while in "R" at the track.............. twice. True story. :confused:
 
Leave it in Drive or like stated , leave in 2nd and shift to third.
Stock pistons are very heavy and will crack if over revved or over boosted like Clint stated. If your trans is stock and the engine is mostly stock then its probably shifting on its own under 5000 rpms.
Built and balanced roller cam engines will take more rpms. i shift at about 6100 and at the end of the quarter mile i am just above 6100 at 139 mph. All engines are different with what they like for rpms.

Bryan
 
Leave it in Drive or like stated , leave in 2nd and shift to third.
Stock pistons are very heavy and will crack if over revved or over boosted like Clint stated. If your trans is stock and the engine is mostly stock then its probably shifting on its own under 5000 rpms.
Built and balanced roller cam engines will take more rpms. i shift at about 6100 and at the end of the quarter mile i am just above 6100 at 139 mph. All engines are different with what they like for rpms.

Bryan
My 86 GN now has about 5,000 miles on a rebuilt engine. Engine was balanced (it looks like you could put a full wine glass on the intake and it wouldn't spill at idle) forged pistons and a comp cams roller cam. New 2800 lockup converter (I'm thinking lockup will not engage at WOT so rpm's will be higher than just doing the tire/gear/speed calculation). I Run 27" MT streets (255/60/15) at the track. I am midway through tuning for the track. I have run it at 12.7 @110 with 20 psi boost (alcohol) but had to ease off due to detonation noted on the scanmaster so I know it will do much quicker. (That was last year) I am about to install my new wideband a/f and powerlogger to go to the next level. My goal is only to get into the mid to high 11's at I guess about 115. So the rpm calculator says with our stock rear and at 115 mph I should get just over 5,000 in drive (3rd). Assuming 5% (good guess?) slippage at WOT that would be about 5,250 max rpm's. Not too far off from taking 115/139 (your speed) times 6100 (your rpms) which gives about 5,050. I am guessing your converter locks up at wot? I don't think mine does that as it only seems to lock up when I let up on the throttle at about 46 mph and not if I am accelerating. This all sound reasonable? I will not worry if I max out below 5500 rpms with my set up.
 
I run a non lock up PTC 17 blade. I run 112.6 in the Eighth mile. You should be fine. I run Mickey Thompson 275/60/15 pro radials that are 28".

Bryan
 
Always looking to protect my precious rebuilt motor so I still anguish a bit about doing the whole run in drive even though the calculators say I am way safe
cant go by that unless you have real slip numbers,i have seen 49 combos blow through converters and wing the motor in 3rd.the load on a tight converter in 3rd is much higher and i suggest to go rich.i put a 49 combo into the 10s and the way i drove it was i manually shifted every gear:)1st gear i took to 6100,then dropped the shifting down 1000rpm gears 2 and 3 with a runout in 3rd.the car would go 1.4 60fts and 330 like it was on a mission with 125mph trap speed @3800lbs.yes stock shortblock with a stock cam.that was the fastest way to get that combo down the track.on the street i short shifted 1st gear;)to avoid wheelspin and held 2nd longer that was the way the car had to be driven on the street for the fastest passes.the car will go faster if properly driven leaving it in drive all the way through will never net the fastest passes.
 
Here is my reminder to put it in DRIVE at the track. It hangs from my rear view mirror. If you don't know what it is, you too, will soon have a souvenir of your own...

Sophisticates, do what you will......
 

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Here is my reminder to put it in DRIVE at the track. It hangs from my rear view mirror. If you don't know what it is, you too, will soon have a souvenir of your own...

Sophisticates, do what you will......
My mirror has been known to hit me in the face on launch
 
Here is my reminder to put it in DRIVE at the track. It hangs from my rear view mirror. If you don't know what it is, you too, will soon have a souvenir of your own...

Sophisticates, do what you will......
Did it get replaced with the billet piece.
 
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