Need A Little help Please

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Dart 67 sedan

Dart 67 sedan

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Ok put on your thinking hats and help me decide on rear gear. I'm running a 410 W2 race head engine that's been set to run in the higher power band. 6800 to 7200 trouble is I'm going thur the lights just shifting into 3/rd gear, with 727 trans with 5000 stall. Shifting to second at about 330 foot wit 1.4/ 1;5 60 ft. Need gear right? Question is 4:88 or 5:13 I can only afford one new setup. 4:56 in the car now. running 7:10 99 mph. 2800 pound car. New gear I'd hope would get me into the mid 6's
I think that is within reason. So any suggestions will go a long way to helping me. thanks guys
 
It's simple math really. And naturally, I don't have that formula in front of me or my slide rule.

Let me see if I can find an online calculator I can trust.
 
You didn't give the tire diameter. I'll guess at 30 inches but you need to give all the data if you want an actual number.
 
I just tried the Wallace calculator and I don't like it. HP doesn't matter in choosing a gear ratio. It's RPM and tire diameter.

I hate online calculators.
 
car is takin so long to get up to revs 6800 at 330 foot engine isn't in power band yet that's why I'm thinking lower gear. W2 race heads[closed chamber] and 640/640 lift at 272/280 . got to get those revs up or am I wrong
 
Dart 67 sedan said:
car is takin so long to get up to revs 6800 at 330 foot engine isn't in power band yet that's why I'm thinking lower gear. W2 race heads[closed chamber] and 640/640 lift at 272/280 . got to get those revs up or am I wrong
Click to expand...


I'm not sure. If it is slow building engine speed it could be a tune up issue. You sure the converter isn't junk? That short tire should need a 4.88 but without the math I use I wouldn't trust that. A 5.13 isn't out of the question.


Most guys don't run near enough gear. I'd rather have a bit more gear and cross at 7500 then to enough and cross at 6800.

Transbrake?
Two step?
 
Running a foot brake class no trams brake or two step. Converter seems to be working as it should flashes as they tell you to do it . Tune up maybe only everything seems and I say that loosely, to be right.
 
The online calls are all saying 4.56 gear. What crap.
Every one of them.

Just junk.

A frigging slide rule is more accurate.

No wonder no one can pick a gear anymore.
 
Flashes to what?

What’s the current rpm at the stripe and speed?

For that sized cam, and 1/8 mile racing...... I’d be looking for about 5600-6000 flash stall.
 
Some rough maths with a 28" tall tyre and 5.13 gears would give you 6160rpm at 100mph over the eighth mile with no converter slip at all. If you estimated say 5 percent slip it would be just under 6500. If you are aiming for more mph it could be up to 7000rpm so i think 5.13 would be good over the eighth mile unless you have a lot slip.
 
What rpm does the engine stop pulling/shift point at? If your trapping at 99, you should be close to 6.60s
 
Correct me if I am wrong here. I crunched numbers and came up with the OP is crossing the line at 5420 RPM......I know that does not seem right
I got there like this:

one rev of the tire is 7.33 ft
99 mph is equal to 8712 ft per min

8712 divided by 7.33 equals 1188.63 rev per min of the tire
1188.63 times 4.56 equals 5420 rpm of the engine

don't seem right.......
 
105mph, 28” tire, 5.13’s, 10% converter slip would put you right about 71-7200.

Current combo at 99mph/4.56’s is 5420........ driveshaft rpm.
Plus whatever the converter slips.
 
I/4 mile combo on an 1/8 mile run. I think the whole combo is mismatched
5.13 gear and good 5500 stall converter would help.
 
Almost sounds like the converter is too tight.
 
anyone care to guess what intake and carb the combo is using
 
I'd be looking into converter,i run a 4.10 with my 28 tall tire shift @ 6600 and am hitting 2nd by 100' or less you need to get that stall up.You will prob want more gear as well for 1/8 mile but you need to get into that power range right at the hit and keep it there.My flash is prob about 5k and drops back to 5800 on the shifts but i'm only 6600rpm shift.
 
The other aspect not being discussed is....... the combo seems to be underachieving.

410 with W2’s should easily be in the 575-600hp range.

If the motor were making the power, and the car running the proper speed in the 1/8...... the 4.56’s might be fine.

Using these inputs:
575hp
2800lbs
350ft track elevation
70deg
50% humidity
29.70 observed baro

Results: 6.44@108.8
108.8 with 28” and 4.56’s...... plus 10% converter slip is 7100rpm
 
Last edited:
Vaild point for sure PRH,his stated 60' time seems soft for combo,my car and driver is 3350lbs with some eddys on it and mid 1.4 so maybe something in combo
 
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