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Old 10-29-2008, 05:17 PM
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Help with my build

I was at a transmission shop today asking about installing a transbrake in a TH400. We got to talking about what it was going in which is an S10 that has the following.

BBC 402 w/Offy tunnel ram & 2 Edelbrock 600cfm carbs
Narrowed 9" Ford w/ 4:56 gears and a full spool
TH400 w/ tranny brake & 4500 stall converter
Hossier 33x16x15 slicks

The motor I think is pretty much stock with maybe an aftermarket cam and some head work done.

The guy says that 4500 stall is too much stall for a BBC. It would work fine for a SBC. He also says that I need a transbrake specific torque converter. My question is, how accurate is he?

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Old 10-29-2008, 05:33 PM
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If you're runnign a BBC with mildly ported stock heads you probably do have too much stall- and maybe too much cam too. It wouldn't bee too much if your engine was built to redline at about 7500, but stock ehads won't give you power up that far.
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Old 10-29-2008, 05:37 PM
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That is alot of stall for that combination. I might think it would be ok for a Powerglide trans car. I think your big block would be better with no more than 3500 stall....if that much. The light weight, 4.56 gears and not alot of motor tells me you need to use the torque a bit lower in the scale.
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Old 10-29-2008, 05:45 PM
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All depends on the static compression ratio and the cam matchup. He may not be making enough torque to stall a lesser converter.
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Old 10-29-2008, 06:02 PM
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Quote:
Originally Posted by S10 Racer
I was at a transmission shop today asking about installing a transbrake in a TH400. We got to talking about what it was going in which is an S10 that has the following.

BBC 402 w/Offy tunnel ram & 2 Edelbrock 600cfm carbs
Narrowed 9" Ford w/ 4:56 gears and a full spool
TH400 w/ tranny brake & 4500 stall converter
Hossier 33x16x15 slicks

The motor I think is pretty much stock with maybe an aftermarket cam and some head work done.

The guy says that 4500 stall is too much stall for a BBC. It would work fine for a SBC. He also says that I need a transbrake specific torque converter. My question is, how accurate is he?
He's standing right by it, or was so he should have a feel for the thing.

Let's start at relationships perhaps as much as everything and more than most anything the converter stall speed selection is dependent upon the power curves that the camshaft dictates on the engine. Everything else from port and valves, carburation and intake, exhaust configuration, vehicle gearing and weight are all contributors as well since these things affect where the best breathing occurs, what the working RPM range is, and how much weight the motor has to giddy-up. There is no significant relationship between a BBC or SBC. One could argue the points of added front end weight, stroke length versus bore, and rod length ratio and all that, but these things are secondary tuning considerations that really only are a effect the top competitors can see any benefit from playing with where hundredths to thousandths of a second have significant effects at the finish line.

So without detail information as to these things, we'd be blind folded, shooting in a dark, concrete room.

As too the transbrake being specific to the converter, I don't see it that way. All the transbrake does is use it's internal system between low and reverse to lock the tranny. This lets you rev the engine to where-ever the converter stall stops it, in your case theoretically 4500 RPM. If this is your engines torque peak, all you've got to do is release the trans brake, finding yourself in low gear and pasted to the seat. The other trick at this point is to keep the rear tires from going up in smoke. This gets to be another one of those things that you have to tune for, obviously, if the torque peak, stall speed, and tires going uncontrollably up in smoke all occur at the same spot then something needs to move to prevent that. Same would go for a bog out of the hole. You want the vehicle to move as quickly as possible between those events.

In any event we need the data related to the first paragraph to provide any useful information.

Bogie
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