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Discussion Starter #1
Drag car only. 01 Formula Firebird. 408 LS1. 3470 race weight. Currently running a turbo 350 with a TCI trans break. 500 hp to the wheels. Spraying another 250. fixing to go to 300. This set up has been working well, but the clutches only lasted about 20 passes this go round.
Some people say it be be time to go to a 400. I'm looking for opinions from folks that have gone from a 350 to a 400. How did it effect your E.Ts. I am also thinking about going with a power glide. But don't know if that would wise at my current space weight.
Thanks in advance,
Roger.
 

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800hp at the wheels with a th350 is about at its limit if not passed it. I would go th400 with the weight of your car. N/A?
 

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Discussion Starter #4
Lol. I know the 400 is a stronger transmission and will handle the power better. What I am more looking for is, what will the performance drop be? I've always heard the 400 is a power robber. Thanks for the input guys, keep it coming.
 

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Lol. I know the 400 is a stronger transmission and will handle the power better. What I am more looking for is, what will the performance drop be? I've always heard the 400 is a power robber. Thanks for the input guys, keep it coming.
I am in the same boat as you. I am going from a powerglide (which is close in weight to the TH350) to the TH400. The only way to minimize the ET drop if not eliminate it all together is to lighten the TH400 internals. That requires using 2 aluminum drums and lightening the planetary assembly. The owner of the racing trans shop said that once he does all that to the trans it will lose at least 15 pounds of rotating weight. He said from what he's seen, unless you have one of those super trick $7000 TH350s, the difference between a TH350 and a lightened TH400 will only be about .02 in ET. However if you are slipping the clutches as bad as you say, you may actually go faster.

John
 

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If the combo is tuned rite I don't know if you'll see any loss in et. You start buying lightend parts for them 400 and they get real pricey. Are you bracket racing or heads up stuff?
 

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If the combo is tuned rite I don't know if you'll see any loss in et. You start buying lightend parts for them 400 and they get real pricey. Are you bracket racing or heads up stuff?
I believe he told me $800 each for the drums and I'm not sure what it was for the lightened planetary. I think he was lightening a stock set so it would be cheaper than an aftermarket straight cut set. Depending on the RPM you may have to lighten it anyway. I turn 9200-9400 RPM so it is a must for me, otherwise they can grenade from spinning all that weight too fast.

John
 

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If you have a T350 and a T400 both sitting there, both being setup for the task at hand and do an A-B test on the same day in the same car, there will be no difference in performance unless the car was benefitting from the TH350's starting line ratio. The TH350 has a 2.52 low and the TH400 has a 2.48.


Hutch
 

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No. Only turning about 7k.
I'm not sure what the RPM limit is with the stock components. You would have to ask a transmission shop about that. I would think you would be ok though.

John
 

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My car went faster going from a non t-brake 350 to a th- 400 with a brake
NOW I REALIZE MOST OF THIS WAS DO TO BETTER 60 FT WITH THE T-BRAKE
But,it lost no mph
It picked up et exactly double that of what it picked up in 60 ft,so i'd say there was no power loss

Oh and now i want to go back to a 350 since i think it would need the lower 1st gear on motor lol
 

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Discussion Starter #14
If you have a T350 and a T400 both sitting there, both being setup for the task at hand and do an A-B test on the same day in the same car, there will be no difference in performance unless the car was benefitting from the TH350's starting line ratio. The TH350 has a 2.52 low and the TH400 has a 2.48.


Hutch
Thanks for the response.
What would the 400 need ,parts wise, to make it up to the task? :)
 

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Discussion Starter #15
My car went faster going from a non t-brake 350 to a th- 400 with a brake
NOW I REALIZE MOST OF THIS WAS DO TO BETTER 60 FT WITH THE T-BRAKE
But,it lost no mph
It picked up et exactly double that of what it picked up in 60 ft,so i'd say there was no power loss

Oh and now i want to go back to a 350 since i think it would need the lower 1st gear on motor lol

Thanks Cross Breed. I've been watching your build. I've been wanting to step up to the bigger Trick Flow heads on mine. What ETs are you running now? At what race weight?
Are you still running the 4 barrel intake?
 

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its been 9.90s at 6000ft plus d/a in denver
but i think im driving through my converter
 

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Jim
you never listen to me ,so i assumed you didnt want my help;)
 
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