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Thread: TH350 advice

  1. #1
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    Default TH350 advice

    Guys

    Have a TH350 in the auto trans shop at the minute.
    Case had a small crack in it near one of the dowels, sorather than weld it up, whilst it went in to be checked out they swapped it allover to another good case they had for me.

    Box was pretty much standard inside, just got a few newparts that needed replacing. I think he said the donor case had somethingscrewed in rather than however it was done normally.

    I bought a B&M shift kit for it, and it is drilled forStreet and Strip. Plus I have a B&M 10” Holeshot 3000 converter (2800-3200stall torque dependant).

    This is going in my HK GTS. Basically 10.5-11:1, LT1 alloyheads, Edelbrock Performer, factory 350/350 Quadrajet, HEI ignition, extractors,XY-XA GT resonators, factory exhaust rear part, mild hydraulic cam. 9” probably3.5 gears, maybe 3.7 (just depends what I have) and will run maybe 225/60/15tyres on 15” Pontiac rally rims. Car will have A/C, and if I can wrangle it aRodtech front end with power steering too.

    Is the transmission as described Ok for this duty, or isthere something else I should be doing to it now whilst it is out?

    Note it has an old pan on it now, will buy a bigger pan forit later, and I’ll mount a big cooler up the front with the A/C condenser.

    Please excuse words without spaces, for somereason on this forum I have to type text outside of the forum and then copy andpaste it – it is impossible to type into the “new thread window”, every second character gets missed and Explorer keeps crashing.

    Does anyone need a used TH350 case? Just needs a minor crack repair.

  2. #2
    casual poster Madogg's Avatar
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    That will be fine.
    Probably safe for about 400HP
    I prefer the Transgo shift kits but there’s nothing wrong with B&M
    Those holeshot converters are fun

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    Something screwed in rather than how it is sometimes done, perhaps he meant something like this....

    Adapt-A-Case | A74761DAC Saves your TH350-700r-4L60E Case

    A few different variations of this case saver.

    Pretty sure B&M do the dual feed mod for direct clutch in their kit.
    Only thing I don't like about some of those shift kits is the separator plate is so thin and the pump pick up area in the case is so large, the separator plates distort heavily in the unsupported area.
    I have some plates that almost look like they have been bashed with a hammer they bow so badly

    TCI do a thicker plate in the transcat kit for automatic shifting cars that wont distort.

    I would strongly suggest getting the converter split and hand brazed on both the turbine and impeller if the engines makes a bit of snot, those B&M converters have caused a lot of heart ache.

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    That HD centre support looks like what he was talking about.

    So hand brazed is better than furnace brazed? Will it be OK for 350hp? I wouldn't expect this to make much more than 375-380hp on a dyno, so with exhaust and engine driven accessories it won't be seeing any huge hp figures.

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    Decent converters will have hand brazing for additional support as well as the furnace brazing which is quite light.
    I don't know precisely what body converter you have but they generally are not furnace brazed, seen plenty let go.

    The better converters are furnace brazed and then additional brazing in key area's.

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    The Holeshot 3000 specs say it is furnace brazed. Whether or not that is true I guess is a matter of trust!
    http://www.bmracing.com/products/204...h350-and-375b/

    Also a quick question on stall, to make sure I am doing my calcs right for diff ratio:

    My calcs show me that with 225/60/15 tyres my tailshaft will be doing roughly 3000rpm at 100kmh with a 3.7 rear axle or 2850rpm with a 3.5 rear axle.

    The advertised stall of 3000rpm is based upon an engine that produces 230lbft@2500rpm, approx. stall range given is 2800-3200rpm.

    So I assume my mild cammed 350 will stall maybe 2800 or so.

    I also assume the quoted stall rpm is flexplate rpm, ie impeller speed not turbine speed? So my calculated tailshaft 2850rpm at 100km/h would be maybe 3100rpm at the engine in 1:1 3rd on the TH350? Meaning I could get away with a 3.5 rear axle if I wanted to?
    Last edited by HK1837; 09-02-2018 at 07:01 PM.

  7. #7
    casual poster Madogg's Avatar
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    Stall speed is probably the most misunderstood topic ever!
    Basically, if your car was stationary, the tyre couldn’t slip, and you put it into 1st and floored it, the rpm the tacho hits just as the car starts moving is the stall rpm.
    When the car is cruising down a flat highway with hardly any throttle there should be very little slip in the converter, even at less than the stall rpm.
    Higher stall speed converters are physically smaller so they are a bit more prone to slippage if the car is heavy/going up a hill/towing or you floor it.
    Hope this helps.
    P.s a mate of mine had a 3000 holeshot behind his mild 350. He couldn’t stop smiling when he drove it. Nothing could touch him from the lights!
    Last edited by Madogg; 14-02-2018 at 08:59 PM.

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    What ratio rear axle was your mate running? I would have liked a taller ratio than 3.5 or 3.7 in this car as I've had 3.5/3.55 rear axled cars before with 1:1 top gear and they were not nice cruising over 80km/h. I thought i'd be no chance to fit 3.25 with that converter though.

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    casual poster Madogg's Avatar
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    Don’t know what the ratio was but it was fairly tall.
    3.25 will be awesome.

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    I have two 9” LSD centres here, one is a 3:1 but the other I have not pulled the diff apart. It was from an XW GT or GT-HO so may be 3.25. I have 3.7 gears too. Will probably just buy a Trutrac for it eventually so hoping to run what I have initially.

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