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aka hulk
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Discussion Starter · #1 ·
have a question on gearing,my new eng combo has not been dyno'd, right now i run a 4.10-rear gear,29.5/10-5 tire,and she traps @ 7300, @ 146-147mph,i shift @ 7500, as anything less she will drop 1-mph in eight, and trap,so my question is do i need more gear? lets assume my peak hp-is @ 73-7500 rpm, do i wan't to gear so it crosses traps above that rpm?right now its a guess as i can't dyno anytime soon,so next option do i wan't to gear it,any opinoins would be helpful.thanks in advance.

eng. specs 565
bmf out of box350's fully cnc'd
1100-prosystems-dom
bullet 283/294 in/[email protected]
855/in 820/ex-lift
t-400 trans chance 8-inch [email protected] off brake.
any more info just ask.
 

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I have a couple of questions.
Where you race do you get 60', 330' 1000' and 1320" times and mph?
You say anything less then 7500 RPM shift it drops 1 mph.
What about if you shift at like 7700?
At the top end does it feel like it is still pulling or do you feel it go flat before the finish line?
 

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I know a lot of folks like to have a rule of thumb for this kind of thing, but in general, most engines I've worked with like to be run harder upstairs thru the traps, than folks would figure from the dyno sheet....

As for the engine being particular, or sensitive on the shift, you might consider that it is the converter..... the engine is falling off too hard on the shift recovery....

What are your incrimentals?
 

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have a question on gearing,my new eng combo has not been dyno'd, right now i run a 4.10-rear gear,29.5/10-5 tire,and she traps @ 7300, @ 146-147mph,i shift @ 7500, as anything less she will drop 1-mph in eight, and trap,so my question is do i need more gear? lets assume my peak hp-is @ 73-7500 rpm, do i wan't to gear so it crosses traps above that rpm?
I'd say you need more gear. FWIW, mine makes pk [email protected] and pk [email protected], but power doesn't start to fall off till after 7600. I shift at 68-7000 on 1-2, 7800 on 2-3, and cross ~7950-8100 (depending on weather). The converter falls back to ~6400 (1-2) to 6700 (2-3). If power drops like a rock after pk, then maybe gear it to cross 300 past pk instead of 6-800.
 

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aka hulk
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Discussion Starter · #5 ·
60-1.32
330-3.78-3.80
660 5.86-5.90
660-mph 117-118
1000-7.67-7.70
1320-9.20-9.30
still feels like its pullin upstairs,also @ shift drops about1200 first to second and 1000rpm from second to third if that helps
I have also [by accident] shifted @7500-7600 and it didn't go slower or any faster as far as i can tell.
 

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7am on a Monday morning with only 1 cup of coffee and here I am doing calculations :smt115

147mph *5280ft/min = 776160 ft/min / 60 min/hr = 12936 ft/min
[29.5” x 3.14] / 12 in/ft = 7.72 ft/rev x 1.07 (growth factor) = 8.26 ft/rev (tire)
12936 ft/min / 8.26 ft/rev = 1566.1 rpm (tire) x 4.11 = 6436.6 rpm (drive shaft)
7300 motor rpm – 6436 drive shaft rpm = 864 rpm converter slippage

If you went to a 4.33 gears @ the same mph you would have
1566.1 X 4.33 = 6781 rpm + 864 = 7645 rpm

Try shifting around 7700 -7800 rpm. If you don’t see it dropping off the 4.33’s might work well for you. My only suggestion is if you going to rev it higher and with the cam you have listed do yourself a favor and work out a schedule when your going to change valve springs!
Chris what do you think?
 

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My rule of thumb is, Turbo 400 1-2 shift 200 under peak HP 2-3 200 over peak HP and go thru the lights 500-600 over Peak HP

PG 300 over 1-2, 600 over thru the lights
 

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My rule of thumb is, Turbo 400 1-2 shift 200 under peak HP 2-3 200 over peak HP and go thru the lights 500-600 over Peak HP

PG 300 over 1-2, 600 over thru the lights
This might work on a peaky small block, but sure dont work on "my" bigblock......

Originally geared to trap 6600, with 6100 peak power.

Now geared to trap 6150, and picked up 3/10ths!!!
 
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