i have a 1988 firebird with a 2.8 v6 and a 5 speed t5, i want to put a 350 in it but the tranny wont handle it so what tranny should i swap in along with the 350?

the 350 is a 1989 350 with a mild 2500-6500 rpm cam
vortec heads, weiand dual plane low rise intake
750 carb, stock 4.000 bore with flat tops, probably around 9.5:1 CR with forged crank and rods, headers and single 2 1/2 exhaust

the rear is stock with which i believe the v6 had 2 gear choices, 3.23 and 3.42, what tranny should i match up to my car? i have a TH400 and a crossmember to mount everything but it doesnt matter, ill get whatever crossmember or whatever is necssary, i just want to know what will give me the most from my car, its probably 70% street, a weekend warrior car

 

hello? anyone? i really need to know guys

 

A t-5 is susceptible to failure behind a 350 (though if you baby the T-5, it should last well enough). Most members would recommend an after market manual transmission if you chose to run the car hard and frequently.

JamesC

 

Personally I think your looking at this a little backwards. A th350 or 400 both have a 1:1 3rd gear so that doesnt change. And changing gear ratios in a trans is not that easy. Swapping gears in the rear axle is very common. You should find the trans that will support your motor (a TH350 or 400 both will if you want an auto) and then select gears in the axle to match your motor combo and driving habits.

 

i meant my rear gears are 3.23 and 3.42 (i think) i have a th400 but idk how it will perform in front of those gears with this engine, thats what im looking for, i know you cant change em in the tranny, i just the most low and mid range torque available to me, i still want speed too though, sorry this is so confusing lol and whats the weak point in the v t5's?

 

the weak point in t5's is the case is not strong enough and theres no way to fix that. If you go with a trans that doesnt have overdrive you'll be at around 3000 to 3300 at 70 mph with those gears. with an overdrive like a 700r4 youll be at around 2200 to 2400 with those gears plus you get lockup with the overdrive trans and that helps alot.

 

a th 350 with a 3:23 rear will be good. (monte ss came stock that way)

th 350 with a 3:42 is going to near 3k rpm at 70 (ok for weekend car )

a healthy 700r4 if properly set up , tv cable, vette servo, would be great with either ratio
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IF YOU HAVE TO GO WITH A USED TRANSMISSION, a th 350 with a shift kit is your best shot.

the th 350 dosent melt if the tv cable geometry is a little off and is stronger.

 

Also, your T5 isn't an option since it's a V6 tranny - maybe could get a V8 bellhousing to connect, but ultimately it will fail unless babied.

If you want to remain manual, T56 is the way to go - its the 6speed from the 4th gens.

If you want to swap to automatic, options are TH350, TH400, 700R4. As mentioned, TH350 and TH400 are 3 speeds, and will get less gas mileage on the highway. 700R4 is 4 speed, getting better gas mileage.

TH350 and TH400 will need different crossmembers as you are aware - of course I think you'll need a different crossmember regardless of which tranny you choose (unless you use the TH400 you have since you mentioned having a crossmember for it already).

To give you an idea, I have the 700R4 behind a 350 similar to yours (probably not as fast as yours), and I have 3.42 rear gears - at 70mph I run about 3100 RPM's with the torque converter locked, about 3400 RPM's without the TC not locked. I get about 17mpg with my setup. With a 3 speed, you'll run higher RPM's (lower gas mileage). The 3.42 or 3.23 gears are fun and save some gas on the highway over 3.73's - you'll tell very little difference between 3.23 and 3.42.

 

your t5 will work with your engine most likely, just do NOT grind gears, if you miss one or grind one that trans. WILL turn into scrap metal in a hurry

 

That doesnt sound right at all. Are you sure your tach is accurate? My stock tach reads about 500-750 RPMs high in that range, and some are far worse than that.

 

That sounds about right to me, but only if he is in 3rd gear at 70. In 4th it should be lower than that.

 

Is anyone ever sure that their stock tach (or any other guage) reads right in a 3rd gen? LOL It could well be off, all I can tell ya is where the needle points. Or - maybe the speedo is off, and I'm running faster (I did swap out speedo gears too).

Seems like in this neck of the woods, no one can wake up in time for work - no matter how fast I'm going on the highway some 25 year old with a wrinkled shirt and loosened tie in his Lexus is beating down my door trying not to be late yet again.

 

Way lower...I got 373's and run 2400 rpm at 70 in overdrive all day long!