12a bridge, n/a tranny?
 

Hey guys i am starting my fb track car project and i am going bridgeport with 48ida n/a, i have searched the archive and stuff but its all about the tII tranny and n/a fc tranny on turbo cars, My question is, Is the FB tranny or the FC n/a tranny strong enough for a full bridge with a 48 ida and custom exhaust and so on, but keeping it n/a. Thanks in advance guys

Yes. The bridged NA engine won't have the low end torque that the turbo will. Assuming you aren't drag launching with wider/sticky tires, you should be good.

just to piggyback Trochoid ... in all fairness, you could pretty much fuck up a tranny (or rear) with a good clutch and good tires with a stock- or streetport. i have seen it happen. the point is, the bridgeport itself won't kill the tranny, so go ahead and use the N/A tranny.

thanks guys, my worry was that. I wont be dragging its a track car but road racing so is not as harsh on the tranny torque wise.

A bridge won't make enough more torque over a regular N/A that it will significantly hurt trans life. Mine is doing about 145ft-lb at the wheels, extrapolate from that how you will.

What seems to kill the transmissions is driving it on the street and letting it buck. That really hammers on everything and loosens up the bearings. That, and trying to shift hard at high RPM. The synchros don't like shifting over 7k or so. If you're gentle on the thing and let the synchros do their work, it'll be fine. Ram the shifter and you'll fill the lube with metal and that will eat the bearings too.

You'll have better success with an FC trans, just because they have a better (but LOTS more expensive to replace) bearing arrangement. The problem with the FC trans is that it's really a 4 speed with a hugely tall overdrive, early FB units have a useable 5th gear.

if anything it seems like the T2 trans is good for big tq numbers, but high rpm shifting the tired old used POS's die pretty quick.

if you're into a little machine work the miata gearset is nice.

if you're into more fab work the Rx8 trans has the same ratio's as the old competition transmission, with a granny gear 1st

other than that i agree with PJ

so let me get this straight, you guys are saying that the fb tranny will hold the tourque but not the high rpms, i am gonna road race it so there will be considerable downshifting and so on, and also the fc is a bit stronger bearings but the ratio sucks, so for road racing a miata transmission or an rx8 transmission would be better?

a bridgeport only adds about 15-25 lbs ft of torque over a stock port, which is no big deal. it does add the tq higher in the rev range, so it makes big hp.

the FB/na fc trans handles the shifting better than say a turbo trans

yeah but since peejay is saying that the synchros in the fb and fc dont like to be shifting over 7k, the bridge port will be over 8.5k so thats what i am concerned now.

technique is important! but the Na tran's seem to do a little better than the turbo boxes

The Miata transmission would be better just because it has the nicest ratios of any smoothcase trans, and they do have double-cone synchros on some of the gears (maybe only 1st?).

NO synchronized trans will like shifting at high RPM. Making the gear ratios closer will help. Downshifting is far easier than upshifting since you can rev-match a downshift far faster than you can match an upshift. Again... upshifting you have to wait on the synchro to do its work. Be gentle to it and the trans WILL last a good long time.

For drag racing or autocross or rallycross where the straights are short and the difference between winning and losing is measured in hundredths, you ram the shifter and you replace transmission fluid and/or transmissions frequently. You have the luxury of not having to do that.

The FC 1-4 is slightly better than FB, but 5th is just way out there.

Why?

well, what i know about bridgeport is that they produce most of their power up in the revs from 7k to 9.5k. thats why i was a bit concerned, correct me if i am wrong on that. but if you say that if you let the synchos do their job, i should be fine, then using good gear oil and changing it frequently should hold it for a while then ill just get another tranny when the first one goes.

They make good power there but they also make good power EVERYWHERE. The powerband becomes more an issue of how safe you feel.

For example, my half bridge makes more torque at 3000rpm than my streetport (same ports) did at peak, which was in the 6000rpm area. I specifically did the bridge BECAUSE it would increase midrange grunt so well.

The dyno plot says peak power is at 6800 and falls rapid off after that. Which is odd, because I get my best 1/4mi speeds shifting at about 8700, and at the autocross today I learned that it will pull very strongly indeed to 9500 :)

so your saying that i should be fine if i just let the synchros work. Thanks for the advice.

i agree with that too. i got a chance to drive the P port shifting at 4000ish rpms, back to back with a stock port sterling carbed 12A, shifting around 7k.

the P port feels stronger.

I've been running my trackcar (1980 12A Bridgeport SA) for 5-6 years now, and i can tell; high rev shifting will kill all gearboxes, i tried all types.

And yes, good lubing (and venting with a catchcan) will help, and so does your shifting technics, carefully shifting and stuff (you will end last, but hey, the gearbox was pleased with the handling :D )

But if you drive on the track, it will break, it's mainly the high rev shifting that will either wear out the synchros or the shiftforks.
The strenght of the gearbox does not matter, a bridgeport does not have torque or turbo

Beste choice is a gearbox with as low-milage as possible, and / or a FULLY rebuild gearbox.

cheap, reliable and fast ; Pick Two :wink:

thanks for the advice, ill stick with the fb tranny then since the 5th gear of the fc sucks. Another question that just popped into my head, Were should i set my redline on a bridge? 9k to be safe or were? thanks

Set the redline as far as your scattershield can hold. I got 2 scattershields, one over the belhousing/gearbox, and 1 on the inside of the chassis, from the gaspedal to the shifter.

I 've set my shiftlight to 9500 RPM, but i can see in the tacho's memory that i've got peaks to 10.500 RPM...... I guess sometimes i'm not shifting fast enough....

Without a scattershield, i would not reccommend going over 8500 RPM, so set the shiftlight enough before that.
I must say that i don't have a rev limiter and i 've disabled the stock warningbuzzer (at 6800 Rpm) :D

in addition iron stock type apex seals don't like more than 7000.

upgrade to carbons, and you're good to 8500ish

after that you should have the stat gears and oil pump and pressure mods like the competition book

dont worry about that, i am doing the engine to hold the rpms, i am putting 3 window bearing, hardened stationary gears upgraded oil pump, carbon seals, racing rotor bearings, the whole deal, so thats fine.

ill look into the scattershields and put 2 and set my redline at 9k for safety and after a dyno and seeing were it peaks ill put it to about 9.5k. thanks alot for the advice.

thats what i did, glen, who did the balancing, said i could take it to 11, which means you need the scatter shields!

yea, i will put a scatter shield no doubt, but since they dont sell one for fb that i know off, i am gonna make my own out of 1/2 thick steel plates, i am gonna do kinda of like an exoskeleton around the tranny tunnel, just in case anything happens it will hit the 1/2 steel and not go inside the car, i think 1/2 is thick enough right?

another question, is of topic, but how much was the balancing? what did you get balanced the rotors and e-shaft?

i was actually thinking about just a blanket, the cool thing about the FB is that the clutch is ahead of the firewall, so if it comes apart you're not in the direct line of fire.

i sent my stuff to Arizona Rotary rockets. i think the whole thing was in the $500 range, but i'm not sure, it was a few years ago already.

i bought new rotors, shaft, seals, etc etc the only used parts are the oil pump sprockets and dizzy gear

do you think it will be fine if i use the old rotors and shaft considering that they are in spec without much wear? i am getting new seals and all, but just using the rotors shaft housing ans so on according to their condition.