View Full Version : Drag Racers: Optimum gearing suggestion


BOLO
02-19-2012, 10:14 PM
To get the best et, is it best to cross the traps at the rpm where the engine makes its peak power? For example, peak hp @6700 rpm--cross traps@7100 rpm? Any suggestions is greatly appreciated, thank you.

Yullose
02-20-2012, 12:10 AM
Your ET is most affected in the first 60ft.

Figure out what MPH and RPM you want to be at... and gear the car accordingly.

If my motor lays over at 7500RPM... I'll want to cross the finish line at 7499.

Tire diameter, RPM (assuming 1:1 trans gear) and MPH will dictate what rear gears to use. It's just Math. :D

Here's a cool calculator I like to use...
http://www.race-cars.net/calculators/mph_calculator.html

JWStevens
02-20-2012, 12:28 AM
What he said! Don't get hung up with the peak number as much as when the car starts to lay over. I'm not really a MPH guy but most people watch it closely.

TA1364
02-20-2012, 10:45 AM
It depends how quick power falls off.

BOLO
02-20-2012, 11:41 AM
So if peak hp is @6700 and stays flat and keep pulling to 7200 rpm before it starts to lay down, that would be the optimum rpm to be at the traps? Also, would 400rpm above peak hp considered optimum shift points as well? I apologize with all the questions.

BOLO
02-20-2012, 12:00 PM
With a 28" tire and a 4.30 gear should cross the traps at around 6700 rpm at 124 mph. And thats at around peak hp as well. Am I in the right direction here?

BlackScreaminMachine
02-20-2012, 01:10 PM
The question proposed here is not specific. "Gearing" requirements are completely subjective to the confines of what the combination of the set up. There is only optimum to the given car setup.

TA1364
02-20-2012, 04:13 PM
If it stays flat untill 7200 and the motor can take the rpm shift it there. If I had to guess there might be 1 more mph going from 6700 to 7200 on a flat graph.

BADHAWK51
02-20-2012, 09:50 PM
Butch, your in the same boat I'm in.4.30 seems to be about right. I go threw the traps at about 6,000 now with my 4.10's and will be close to 6,400 with the 4.30
remember though stepping up the gear will essentially tighten up your converter. something to think about.

BOLO
02-21-2012, 12:51 AM
Butch, your in the same boat I'm in.4.30 seems to be about right. I go threw the traps at about 6,000 now with my 4.10's and will be close to 6,400 with the 4.30
remember though stepping up the gear will essentially tighten up your converter. something to think about.

Jeff, according to my calculations with the times on your sig, you should have been crossing the line @6289 rpm. With 4.30 gearing, you will be at about 6600 rpm at the traps. Have you done any weight reduction on the car? It's very impressive for a full weight car running those times.:nod:

JWStevens
02-21-2012, 01:10 AM
Man it seems like there has been a ton of gearing threads lately. I can tell you its way easier if you've got a Lenco. We had a motor that made peak at like 6200 but it would fall off if you shifted it lower than 8K. Everybody's stuff is different. You look like you're hauling ass where ever your shifting now. Fast car man!

BADHAWK51
02-21-2012, 06:25 PM
Jeff, according to my calculations with the times on your sig, you should have been crossing the line @6289 rpm. With 4.30 gearing, you will be at about 6600 rpm at the traps. Have you done any weight reduction on the car? It's very impressive for a full weight car running those times.:nod:

Butch, I use the wallace racing caculator and it's dead on for my car except the sixty foot. I haven't done any real weight reduction but I'm starting to now as we speak. :devil:

Power to Weight Ratio: 6.70
60 Foot E.T. : 1.53
1/8 Mile E.T. : 6.93
1/8 Mile Trap Speed : 98.11
1/4 Mile E.T. : 10.98
1/4 Mile Trap Speed : 122
1/4 Mile Trap RPM : 6,009

BOLO
02-21-2012, 07:18 PM
Butch, I use the wallace racing caculator and it's dead on for my car except the sixty foot. I haven't done any real weight reduction but I'm starting to now as we speak. :devil:

Power to Weight Ratio: 6.70
60 Foot E.T. : 1.53
1/8 Mile E.T. : 6.93
1/8 Mile Trap Speed : 98.11
1/4 Mile E.T. : 10.98
1/4 Mile Trap Speed : 122
1/4 Mile Trap RPM : 6,009

I didn't think you were crossing the traps at only 6000. I know your stroker is gotta be making its maximum peak power at 65-6700 rpm, maybe a little higher. So you do have to gear it accordingly and be at your maximum power at top end of the track. Jeff, with more weight out, I think you still have plenty on the table. 10.4's, 10.5's easily.:chug:

BADHAWK51
02-21-2012, 07:30 PM
I didn't think you were crossing the traps at only 6000. I know your stroker is gotta be making its maximum peak power at 65-6700 rpm, maybe a little higher. So you do have to gear it accordingly and be at your maximum power at top end of the track. Jeff, with more weight out, I think you still have plenty on the table. 10.4's, 10.5's easily.:chug:


Butch, I don't know about 10.40's but I think once I get it down to 3,300 and put the spool and 4.30's in it will go 10.60's pretty sure.

BOLO
02-21-2012, 08:48 PM
Jeff, you changing your class this year at the Shootout? Mod n/a? You'll be competitive for sure.

BADHAWK51
02-21-2012, 09:35 PM
I'm going to run Extreme street again this year so I can only lose 150lbs to get down to min weight. Then next year lose another 100lbs and go to aftermarket ecu, singleplane and a solid roller then run Mod.

Funds permitting of course. :eyes:

355z28
02-22-2012, 10:12 AM
since im running 3.73s, I wonder if I switch to 4.10s if Ill still have enough gear for nitrous passes.

Jeff if your running a lose 4500 converter and going through the gates at 6000, I would THINK id have room to push to 6800 with 4.10s but I dont know what MPH that would put me at. Is there any good way to calculate for this?

BOLO
02-22-2012, 07:20 PM
since im running 3.73s, I wonder if I switch to 4.10s if Ill still have enough gear for nitrous passes.

Jeff if your running a lose 4500 converter and going through the gates at 6000, I would THINK id have room to push to 6800 with 4.10s but I dont know what MPH that would put me at. Is there any good way to calculate for this?

You'll have more than enough gear for the spray. I have sprayed mine running 4.10 gear/28" tire and 4000 stall, going thru the lights at about 6500-6600 rpm

BADHAWK51
02-22-2012, 08:14 PM
since im running 3.73s, I wonder if I switch to 4.10s if Ill still have enough gear for nitrous passes.

Jeff if your running a lose 4500 converter and going through the gates at 6000, I would THINK id have room to push to 6800 with 4.10s but I dont know what MPH that would put me at. Is there any good way to calculate for this?



Like Butch said, if I hit my car with a 150 shot it would cross between 6500 6600 at somewhere around 133mph.


http://www.wallaceracing.com/accel-calc.php

355z28
02-22-2012, 10:20 PM
That calculator says I should be running 11.90s lol It doesnt like the 388hp and 3700lb weight. Ill take your guys word for it. I might give the 4.10s a shot.

BOLO
02-22-2012, 11:08 PM
Jeff, I was going through the wallaceracing calculator, and it seems even a 4.56 gear will get the car thru the lights at around 6700+rpm. Mike V(Quick95), if I recall uses this gear combo with his 4L60.

quik95lt1
02-23-2012, 10:44 AM
thats correct butch.......i run a 4.56 gear with a 29" tire on the 4l60e however you also must factor in coverter slip to the equation which will be different from one to the next........136mph puts me at around 8000-8100 coming through the traps.......as for the when to shift where to cross deal here is what i go by........

you want to shift the car where the power when it leaves the gear is the same as the power when it enters the gear.......you need to think about this in a acceleration vs. time not just acceleration.......you want to have the highest average power the whole trip down the track......

for example check out the graph below........this is my LS2 GTO with the T-56 trans in it and stock gear........i know my 3-4 shift drops 1350rpm @ ~6500rpm..........you can see where i marked off my shift position on the graph......i shift at 6800 with 400rwhp and come into 4th gear at 5500 with 400rwhp as well even though the car makes a 422rwhp peak at 6300 rpm.....notice how if i connect the two dots where i shift the line is flat.......this is optimal.......this gives me the highest "average" power through out the pull.....

http://i919.photobucket.com/albums/ad38/quik95lt1/ScreenShot170.jpg

now if i lower my shift point to 6300 i will go from 422rwhp down to ~5000rpm where i only make 375ish rwhp......now if i connect my two dots they are no longer straight........my average power is hurt because i didn't shift high enough.....so me going 500rpm past my peak power for my shift is my optimum point.......

the same issue will be encountered if you shift it too high.........you need to do the above calculations based off of your power band and figure out what is best for YOUR application......this is why i am constantly preeching dynos are a tuning tool only and peak power doesnt mean squat......sure i made 422rwhp but im faster than 420rwhp cars that are lighter than me.......why? because through my shifts my average power/torque is fantastic, i never drop below 400rwhp.........and this is what i do with my camaro as well......from the instant that motor goes above 6500rpm i make within 5rwhp all the way down the track, im essentally at peak power ALL the time........with my current converter i drop out of it a little im still not optimized.........my new converter being built by ATI right now should it hit right on the nose...........i make peak power at 7450 with my LT1.......flat power to 8000....right now my situation is this....

1>2 @ 7900 yields 6600 in 2nd
2>3 @8200 yeilds 6500 in 3rd (im over reving to compensate for the low shift rpm in the next gear aka i make the same power at 8200 that i do at 6500)

my new converter should put me here which is right in the butter zone for me
1>2 @7900 yields 6900-7100 in 2nd
2>3 @ 7900 yields 6900-7100 in 3rd
cross traps at 8000 at hopefully ~140mph :D


hope this helps!!!!!!!!!!!

now go get fast and get that tank to the shootout!!!!!!! :D

good luck :D
Mike

BAIN
02-23-2012, 02:26 PM
Thanks quik95lt1!

Someone has finally explained the importance of shift extension with data. I have searched so many times and there never seemed to be a real answer how this works. I have been trying to explain this to my converter builder the since the converter was built. I'm on my 2nd restall now and hopefully they got it right this time. They kept telling me that loosening the converter won't help.

My cam makes peak HP @ 6500-6600 and shift at 7000 with 6 hp difference. The original converter dropped back to 5200 which lost 40 HP from peak. The first restall I went through this information with them again to loosen it up. What they sent me was a converter that dropped back to 5600 which lost 30 HP from peak.

The last restall hopefully they got it right! I told them I wanted the shift rpm to drop back to 6000-6100 where I only loose 8 HP from peak. I think this will pick up some ET staying in my powerband from 6100-7000. I haven't had time to test it yet, but I will post results when I do. I will only be able to test in the 1/8mi though :(

quik95lt1
02-23-2012, 02:50 PM
yea i had a huge change when i reflashed mine........i had a 4000 stall and the car just hit a wall at 10.7 @ 128......just wouldn't go any faster didn't wanna hear it........then i realized it one day, i was on the highway watching a friend race with a 135mph car.......i put my foot in it following them and started reeling him in on the high end.......said holy shit i have horsepower lol.......reflased it to a 4800 and straight off the trailer went 10.38 @ 131...hoping to see 9.7x's with the new converter.......

BOLO
02-23-2012, 05:27 PM
Thanks Mike for chiming in, and thank you for explaining this more clearly, and showing it in a graph makes it even easier to see and understand how it works. And Jeff, you gotta check this out.

BAIN
02-23-2012, 06:24 PM
Quik95lt1 what were your 60's with the 4000 and 4800?

BADHAWK51
02-23-2012, 10:36 PM
Thanks Mike for chiming in, and thank you for explaining this more clearly, and showing it in a graph makes it even easier to see and understand how it works. And Jeff, you gotta check this out.



I have been wanting to do this for a while. I need someone to go to the track with me a log some runs it's to hard to watch the tach during wide open blasts to see the rpm drop between shifts.

quik95lt1
02-24-2012, 07:23 AM
Thanks Mike for chiming in, and thank you for explaining this more clearly, and showing it in a graph makes it even easier to see and understand how it works. And Jeff, you gotta check this out.

no problem!!! :D


Quik95lt1 what were your 60's with the 4000 and 4800?

4000 went 1.43-1.45's with the front wheels
4800 goes 1.30-1.32 on the rear wheels
im hoping my new one will go 1.24-1.26's

heres a video of the 4000 converter........car just didn't have it......you can hear it wake up at 6700 or so......then fall way out when it shifted......as well as on the launch it just wasnt there.....
http://www.youtube.com/watch?v=eMudvBlvLqg&list=UU11WqJz3gA4KgQWBLLosb0A&index=32&feature=plcp

heres a vid of the 4800 ......
http://www.youtube.com/watch?v=c_OYvnzkJNQ&feature=related

now add a 29" tire to take care of the overrev situation on the top end and you get this.....
http://www.youtube.com/watch?v=sC42Bbre0tQ&list=UU11WqJz3gA4KgQWBLLosb0A&index=4&feature=plcp

I have been wanting to do this for a while. I need someone to go to the track with me a log some runs it's to hard to watch the tach during wide open blasts to see the rpm drop between shifts.

data logger!!!!

Wicked94Z
02-24-2012, 02:46 PM
hey mike, a 1.30-1.32 on the back tire is around a 1.22-1.24 on the front tire. I think a 1.26 on your current motor setup with a better converter would bring 9.70s. Get a TH350 too :D

quik95lt1
02-24-2012, 03:00 PM
the goal is 9.60's :D i hope ur right......plus i got another 15-25hp in the works lol

BOLO
02-24-2012, 09:08 PM
the goal is 9.60's :D i hope ur right......plus i got another 15-25hp in the works lol

Very impressive Mike. I think you have one of the fastest naturally aspirated LT1 in the country.:devil: Definitely up there with the big dogs like Rick Abare, Ed Wright, and Joe Overton to name a few.:D

LS6CamaroA4
02-25-2012, 09:17 AM
Approximately 200 rpm past peak would be optimal. Same on shiftpoints.

Yullose
06-06-2012, 11:03 PM
~snip
Mike
Sorry to dig up this old thread, but given your excellent detailed explanation and dyno graph... I wondered how best to target shift points and gearing with a graph that looks like this:
The rev limiter is at 6600 so there was no point in pushing it beyond what was logged on the dyno.
The car is a '05 Vette with 4L65 / 3.15 gears and 27" tires.
http://i1169.photobucket.com/albums/r504/yullose/DSC004192.jpg

Wicked94Z
06-14-2012, 10:23 PM
need to get rid of the limiter before you need to worry about optimizing shift points

StraightTimeStirrups
09-17-2012, 11:13 AM
What is your guys opinion on a bolt on car gearing for the 1/8 mile? My local track is an 1/8 mile and I dont imagine hitting a 1/4 mile track for awhile. I would like to know what you guys would think would be a good rear end gear for this car? I am going to be building a 9" for the car so I will have a separate third member for a 1/4 mile if I ever get the chance to run at one.

For a Bolt On Track ONLY Car, what Rear Gear would you run for each track?

1/8 Mile Gear

1/4 Mile Gear

Mighty Whitey
09-17-2012, 04:57 PM
What have you changed since your 11.04@122 pass?
If nothing has changed, and you know your rpm at 122mph, then you can directly relate that to what the fear change will do, just give yourself a little extra room to play with considering the converter will act a little different with more/less gear.
But yes, if you trapped 122@6700, and your motor pulls to 7200 then peters out, then I would try gearing it to run as close to 7100 as possible)

BTW, that website with the calculator's is a little off. Says my car with a 3143 race weight and 344 rwhp would only run 12.17@111mph. Over a full second, and 9mph off. Lol

deerslayinrednek
09-22-2012, 11:45 AM
What have you changed since your 11.04@122 pass?
If nothing has changed, and you know your rpm at 122mph, then you can directly relate that to what the fear change will do, just give yourself a little extra room to play with considering the converter will act a little different with more/less gear.
But yes, if you trapped 122@6700, and your motor pulls to 7200 then peters out, then I would try gearing it to run as close to 7100 as possible)

BTW, that website with the calculator's is a little off. Says my car with a 3143 race weight and 344 rwhp would only run 12.17@111mph. Over a full second, and 9mph off. Lol

All of the calculators I've saw use flywheel HP and not RWHP

BOLO
09-22-2012, 07:12 PM
What have you changed since your 11.04@122 pass?
If nothing has changed, and you know your rpm at 122mph, then you can directly relate that to what the fear change will do, just give yourself a little extra room to play with considering the converter will act a little different with more/less gear.
But yes, if you trapped 122@6700, and your motor pulls to 7200 then peters out, then I would try gearing it to run as close to 7100 as possible)

BTW, that website with the calculator's is a little off. Says my car with a 3143 race weight and 344 rwhp would only run 12.17@111mph. Over a full second, and 9mph off. Lol

If I can recall on my 11.04@122 run. With 4.10 gear/4000 stall and 28" tires, it was crossing the traps at only 61-6200 rpm. I think there's alot more if can gear the car to cross the traps at 7000-7100 rpm.