81Malibu said:
every engine has a certain rpm range where its able to make the best torque, its torque that gets the car moving, If you gear the car so it spends almost all its time spinning in its most efficient power band, and youll maximize the engine's ability to put power to the pavement, gear the car so it spends most of its time below that power band or set the transmission and gearing so it shifts to the next gear well below, the horse power peak and efficiency suffers.
now obviously factors like car weight, exhaust restriction,engine compression limits due to low octane fuel, and tire diameter will effect your results, and valve train stress, transmission shift points and piston speed and port cross sectional areas tend to limit engine rpms on the upper end of the rpm range.
the higher the torque the engine produces the higher the converter stall speed is likely to be but its never an exact ratio relationship
Keep in mind when selecting a new performance torque converter that there are design limitations and strength limits to all designs, if your old engine made about 370 ft lbs and stalled near 2500 rpm, and
your new engine makes 470 ft lbs of torque thats about a 25% increase, in torque.
so you might, quite reasonably expect or guess that the stall speed would jump about 25% from 2500 rpm to near 3125 rpm,
( example 2500rpm x 1.25%-3125 rpm)
While that sounds reasonable, the real world is not as predictable.
In my experience it won,t necessarily jump a totally predictable amount,
simply because there is a wide variation in the torque converter designs,and engine torque curves and cam characteristics, compression ratios, displacements etc.
Id expect it to jump a bit less, to maybe nearer too 2950 rpm from my experience.
this is based on what I've seen when guys bolt the same converter and transmission they formally had behind a performance 350- 383 SBC
behind a new 454-496 BBC engine
ID also point out that occasionally youll find a converter that worked just fine behind a SBC,
fails when you introduce it to a 25%-50% torque increase with a BBC swap,
taking the effort to read through, these posted links and sub links posted below,will help
http://garage.grumpysperformance.com/index.php?threads/race-front-rear-suspension-related-info.1198/
viewtopic.php?f=71&t=741
viewtopic.php?f=71&t=555
http://tire-size-conversion.com/tire-height-calculator/
http://users.erols.com/srweiss/calcrgr.htm
http://www.car-videos.net/info/tirespecs.asp
http://www.magneticlynx.com/carfor/transc.htm
http://users.erols.com/srweiss/calcrpm.htm
viewtopic.php?f=71&t=10690&p=46305#p46305
you have approximately a 27" diam. tire, with a 3.73:1 rear gear youll turn about 3300 rpm at 70mph and about 3650 rpm with 4.11 gears
swapping to a 200r4 will allow you to accelerate nearly the same but in od even with 4.11 gears spin about 2800rpm in OD at 70mph
and only 2500rpm in OD with 3.73:1 rear gears with the 200r4
personally ID look in salvage yards for a good reusable 200r4 or at least a core to build
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