Dragaholic

iTrader: (180)

I know there is a gear calculator above and I actually have it under my bookmarks, however, it really doesn't work for automatics, especially with big stalls and no lockup. It calculates for 0 (zero) slippage.

I have a Protorque converter that needs to be restalled for the new setup as it was built for my cam only motor. On the dyno, it showed to flash around 5700-5800 rpms. I'd imagine at the track it's going to be more as it will have more load.

Anyhow, last Sunday I went to the track to make a couple of tests hits. Well I didn't make it to the end of the track. I was hitting the limiter just past the 1000 ft. mark. I passed the traps at 133 mph on the limter the last few hundred feet. I would think that if I dead hooked, that it would have been worse, as in riding the limiter sooner than the 1000 ft. mark.

So my question is, how do I determine what gear ratio I need using a 30" tall tire, pulling 7500 rpms, and trapping somewhere around 140 mph? I currently have a 4.56 and it's too much. Thanks in advance.

1SlowFormula

you have a way to figure out average converter slipage by using those same calculators, just measure your MPH when you hit the limiter, or at least when you have a chance to look at it if you are not logging your runs. That way you have an idea of where your baseline is. Then you plug you numbers into the calculator and subtract you actual RPM at that MPH from whhat the calculator shows, then run your numbers through a calculator the selects optimal gear ratio, then cross check that ratio with the first calculator then add in your slippage and see if that gear is too much...

1SlowFormula

Just going off the numbers above, and it looks about right from the things I have seen with converter slippage, it looks like your slipping about 700+ RPM's.

feeding the numbers into my calculator setting you max trap RPM to 6800 to account for the slippage and it comes back with a 4.264017959040345 optimal gear ratio, and feeding that back into the standard gear calculator, at say a 4.30 gear, it shows you trapping a 140 MPH at 6750 RPM's so if you account for slippage you will be right about on and might have to extend you limiter 100 RPM or so.

but agin this is based off of the average of 700 RPM slippage that shows above and I have seen before...

Dragaholic

iTrader: (180)

I have nothing to log my runs with, but hopefully I'll have something in the next few weeks.

I didn't get a chance to look at my tach to see what mph I was at when I hit the limiter, but then again, the stock tach sucks and is off.

I can say that the car went through the traps at 133 mph, spinning at the launch.

Is that anything to work off of?

Dragaholic

iTrader: (180)

Oops, my post was a minute too late.

Anyhow, with a 4.30 gear shows to trap 140 mph at 6750, with 700 rpm slippage would put me at 7450 would be pretty close. My limiter is set at 7800 right now and I really don't want it to go any higher than that. Maybe I should do a 4.10/4.11.

1SlowFormula

oh hell with you limiter set at 7800 then you should be pretty good with 4.30 gears, that is unless you are still planning to go faster in the future, but I would say the 4.30's are good for you now because unless you have an incredibly loose TC that slips about 1000 RPM's, (I doubt you do) that puts you right about where you want to be.

so let's guess your at a max of 800 RPM slippage, you would still be good to run up around 145 MPH with them and stay off the limiter... My initial numbers were made assuming your limiter was set at 7500.. but there is a good 6+ MPH wiggle room between those 300 RPM..


***EDIT***
But please, try and get out an measure the ammount of slippage you have first, although you should be pretty good unless it's over 1000 RPM's of slip.

TeEnAgE pHeNoM

iTrader: (6)

Ideal converter slip would be about 6% . Your 4.56 gear with a 30 in tire should be 7000 rpm @ 138 mph with 6% slip should put you around 7500 through the traps or 7700 @ 140

Dragaholic

iTrader: (180)

TeEnAgE pHeNoM, I'm not saying your method is wrong because I don't have anything to back it up with, but it doesn't work for my application. I was on the limiter the last few hundred feet of the race. My limiter is set at 7800 and passed the traps at 133 mph. I didn't dead hook either. I did a 1.9 60 ft. and the car usually 60 fts. in the 1.30s. I have yet to make a solid 60 ft. hit with the new setup. I would think it should be in the low 1.30s high 1.20s, but who knows.

Using the f-body.org/gears calculator, 30" tire, 4.56 gear, 7800 redline, should put me at 153 mph. But I was no where close to that number. My car couldn't run that mph with the power I make. I say it'll probably run 140 mph, but again, who knows.

I'm not too far off, so I know that I'm either going to need a 4.33 or 4.11.

Would too much stall be a factor in why I'm hitting the limiter so soon? I don't know what exactly it flashes to or stalls to, because I come right off the converter on the launch (transbrake).

rufretic

iTrader: (37)

That gear calculator is way off for me too. I have 28" tires and 3.73s. I trapped 138 and was hitting the limiter. My limiter is set at 7250. The calculater said I'm good to 161 @ 7200 in third, so it wasn't even close. I think once you throw a converter into the mix it really throws that calculator off. I'm thinking if I go up to a 30" tire I should be ok. I would think for your set-up a 3.73 might be a good option because it should get you through the traps and it might help you get better traction for a better 60'. It sounds like you could probly get away with 4.11s but it might still be close.

mrdragster1970

.

Too early in the morning for all this math. As a general, very general rule. I have found each step is worth about 300 RPM, if you don't make any other changes. I have every gear from 3.90-4.88 for my fast car, & it has been very accurate with my combinations.
So if you need to drop the RPM at the stripe, either tighten up the converter or drop the gear. Example, 4.30 = ~300, 4.10 = ~600.

Another thing, when I slip more on the hit, I cross the line at more RPM. The lower my 60', the lower I cross the stripe. Good luck.

.

Pro Stock John

iTrader: (34)

I think another question for Dragaholic really is, should you change the gear and the converter at the same time...

Dragaholic

iTrader: (180)

mrdragster1970, what do you mean each step is worth 300 rpms? Do you mean each gear ratio drops the rpms down 300 crossing the traps? I don't know if your method will work for me either. I'm not making it to the end of the track, so I can't say what I would be crossing the traps at. If I'm on the limiter already at the 1000 ft. mark, then I can't say well I need to drop 300 rpms or a gear size, to make to the end because I don't know if that will work.

Pro Stock John, I'm going to say no. I'm going to change the gear first, then get one of those Autometer tachs that has playback and records driveshaft speed, THEN send that info to Joe at Protorque so he knows exactly what to do with the converter.

Dragaholic

iTrader: (180)

I hope I made a good choice. I went with a 4.11 to stay on the conservative side in case I add more power with a bigger cam, swap over to solid roller, etc. I'm sure the 4.30 would have been a better choice for now, but again, if I decided to add more power later, then there's a good possibilty that I would have to change it again.

RAGENZ28

iTrader: (5)

I was going to say you could have maybe tried to figure the mph of what you should have run from the 1/8th miles mph and et, but you already have gears so hope they workout for you.

Dragaholic

iTrader: (180)

Well I don't have any solid numbers for the 1/8th mile either. I have yet to hook and get a clean pass with the new tires. The converter is way off too and that will be changed once I make some more passes now that I have a dual channel tach that has playback.

1SlowFormula

the 4.11's are a safe choice and like you said if you are adding power later anyway you can grow into them, so to speak...

car_fixer

i would go with the 4.11's, that should match up pretty well, i trap at 7300 rpm and 28 inch tires at 146-7, you should have the converter gone through, it sounds like it may be ballooned a bit, it has pretty high slip on the big end if you are hitting the limiter that soon. I dont know what setup you have right now, or how many runs are on it, but do you know what range you engine makes power in? you dont want to trap too far past you hp peak.warren johnson says 3% for a rule of thumb by the way...dont know how many runs the guy has made, but at least a few lol, I do know i need a 3.90 gear, I am way past the hp peak on my setup, but I also need to switch headers, I have pretty much determined i dont want to turn the engine any more rpm either, so i can understand why you say that.

Dragaholic

iTrader: (180)

1SlowFormula, exactly my thinking.

car_fixer, keep in mind though, I'm running a 30x10.5x15 tire as opposed to your 28". I also won't trap as high as you either. I'm guessing around 140. The converter has probably around 40 passes on it (just a guess), but it was built for the old motor/setup. It definitely has to be changed, but I need to log some runs with my new dual channel tach before I send it in. The tach will give me info to provide Joe at Protorque so that he knows how to set it up.