Well I plan on getting a late 80's or early 90's IROC sometime soon and making it just a bit faster than stock. I would like the 350 TPI in it with a 5 (or maybe a 6) speed trans. I believe that all the 350's came with a automatic though. I'm just asking if I should be able to buy a 5 speed 305 and swap the 305 for a 350 or if its better to get one with a 350 auto and go on with the trans swap. I saw a 5 speed with a blown 5.0 on craiglist for $1800 so that got me thinking about it. Never done a big car project but I know a decent about engines and what not like working on my own dirtbikes and replacing things on my grandpas cummins that tend to be a pain. Any suggestions are welcome just would like to here some ideas like what model 350 to go for or the trans models as well. Thanks.

 

I much rather have the 350 engine.

The T5 5 speed was too weak to handle the torque of the 350 and that is why GM didn't pair the two together in the third gens.

My opinion would be to get a 350 auto car if you can and if you want a stick, save up and swap in a T56 6 speed. It's much stronger and will last, where the T5 will not.

 

If the automatic is in good enough shape to handle it you could install a shift kit and manual valve body.

 

You're getting good advice here...let me tell you how I've learned the hard way.


Last month, I bought a beautiful '88 350 TPI IROC-Z, which had the auto swapped for a T5 5-speed.


Bought it on Saturday, and knew the transmission had slight issues going into 4th gear. I flew out to Alaska for work on Sunday, and a week later, got back home, fired up the IROC, and attempted to put it in reverse--no reverse.


So now, I have a beautiful '88 IROC 350 TPI that I've driven exactly TWICE, and now need a transmission, and can't drive the car until I do.


If I knew what these guys are suggesting last month, I probably wouldn't have bought the car..but, it is what I wanted.


So, long story short, be a bit cautious buying a 350 with a swapped T5--since you don't know the history, it might be more trouble than you bargained for.

 

There are better engine options than the L98 but it is passable with a T56 (and shorter rear gears.)
There are better transmission options than the T5 but it is passable with an L98 swap.

I would try and buy the car you actually want with the options you want, and I would err towards the LB9 / T5 car personally. Buying a car that has been modified the least by prior owners is my preference also.

 

Not true GM did not pair them because they decided due to sales numbers it was not worth the money to recert the combo for emissions testing.

There are plenty of t5s on this board living long lives behind 350s. It is a weaker trans and if it is not in good shape it will grenade. In good shape there are plenty of people here putting miles on them

 

I should have been more clear. The transmission is out of my car now, and being rebuilt by a shop that specializes in these transmissions outside of Atlanta. The shop told me that unless they are abused, T5 World Class transmissions will live a very long time behind an L98. In my case, he said it appears that someone found an appropriate T5 from another car, and simply installed it without checking anything out first--the factory stickers were even still on the case. In other words, my 28-year-old transmission, with uncertain mileage failed.


Had I been doing something like that myself, it would have been unlikely I would have installed such a transmission in my personal car without checking it out first--but from what I've learned over the years, most people would.

 

The entire drive line on these cars is weak. Start with a stronger engine and then you have to upgrade the transmission, and then you have to upgrade the rear end. Leave it pretty much stock and it will be fine, but if you want to go fast you are going to have to upgrade most of it. I like a car with 3 pedals in the floor. To me they are much more fun and I can't stand automatics. There are direct swap 5 speed transmissions from Tremec that are much stronger. I would start with the 5 speed car and then upgrade everything. You would already have a car with the correct pedals in it and the right console.

 

I disagree with you.. From everything I have seen and read it was due to warranty claims and torque ratings.

The T5 has a torque rating of 265 ft lbs, 285 ft lbs and 300 ft lbs depending on which unit, what year, world class or non world class, etc.


The 305 made 240-300 ft lbs torque depending on year/model

The 350 made 320-345 ft lbs torque depending on year

The T5 was NEVER installed behind any engine with more torque than it's rated limit...

So this left the 350 with only the auto trans option...

350' came into play in what 1986 for the third gen? Look at how many T5 305 cars was sold after that and before that... It was nothing to do with "sales numbers" behind not using the T5 with 350...

It was the lack of strenght in the weak transmission and more torque from the 350 than the T5 could handle or was rated for.

 

Im doing what Big Gear Head is suggesting, somewhat. Building everything behind the engine rather than risk breaking some nasty stuff. t56 swap on a 5 speed car is easy and awesome.

 

T-5 handles 300ft/tq, AT will handle 400. An LO5, the TBI 350 stock is 210HP and 300ft/tq at the wheels. The L98 is 245HP and 350ft/tq.

I had a T-5 mated to a LO5 and didnt have any problems. Even bought the car with a bad clutch and push started it alot. So that can be done, but definitely not an L98.

 

That's all well and good but I got a different story from some of the engineers that worked on these cars for GM.

 

At this point in history it's not worth worrying about why GM did or didn't do whatever 30 yrs ago. Not a productive line of inquiry and is annoying to see people argue pointlessly over it.

Personally, if I wanted a stick car, I'd buy a stick car. IMO it's easier to swap the worthless 305 out of one and put something with some potential in its place, than to do a good clean non-hack-job auto/stick conversion in one of these cars. Not necessarily true for all cars; but these, the tunnel is made QUITE A BIT different, and just hacking a ginormous hole in it and leaving it without any of the reinforcement and the shape it's supposed to have isn't my idea of a job well done.

The 1st 3 or 4 T-5s I tore up in my car were when it still had the OE 305 in it. The next 10 or so were behind a 400. I finally realized that it simply couldn't withstand being treated like a 4-spd, and the last one I put in, while accumulating a T-56 swap, lasted about 40,000 miles. Frankly, you can tear one up with ANYTHING, even a 6-cyl; and if you baby it, you can make it live behind ANYTHING, even a 400.

That said, if I were going down that path, I would find the best 305/T-5 car I could, preferably a G92 car; get rid of the 305 and the TPI, and exchange it for a better motor and better FI system (NOT a carb); and get rid of the T-5 in favor of a T-56.

The T-56 is AMAZINGLY better than the T-5 in almost every way. Only down side is, you NEED more gear; the weenie stock gears in my car (3.73) are BARELY adequate, and it would be much better with more.

Likewise, if I wanted an auto car, I'd buy one; and assume right up front that the trans is no good and will IMMEDIATELY need a rebuild. Might even get another core and start building it at the same time I got the car.

 

I bought my iroc knowing I was going to swap in lsx/t56 combo. I still wanted a 305/t5 combo. THe t5 feels like crap compared to a t56, it just feels sloppy. Ive built alot of cars over the years and I do have some advice I can offer. If youre going to do a motor swap, I would worry about getting a really nice body over the drivetrain. If youre going to stay with the TPI motor, I would get a 350 l98 and swap in a t56 no questions asked. Swapping in a manual into these cars is cake work.

 

3.73 stock? You mean 3.23?

 

Yes.

No. Not a grocery cart.

 

That about sums it up.

 

Yep 3.73 came stock in a good many of these cars. I have a disk brake open 3.73 rear sitting for sale that I pulled from a 1984 Trans am just a couple weeks ago. PRO code for gear ratio is GT4

 

I had an OEM BW 9 bolt 3.70 unit in my 86 TA w/a carbed 305 and T5. (That was swapped for a 502, TKO 500 and a Moser 12 bolt) and that rear went into my IROC were it broke on my 1st ever 12 second pass (after a long life in the 13's and lots of abuse on the street). The pinion lost a couple of teeth. Interestingly, the 3.27 gear set that went in it's place, helped produce my personal best 60' at 1.7 flat. I think that a well assembled 9 bolt can take quite a bit but once you get into a harder launch with slicks, it will only last so long.

 

Didnt know they offered 3.73s factory. Grocery carts have 3.23s?

 

They not only offered them, they made them standard on certain models. (like mine) Part of the package.

Some do. Lots have even worse than that.

 

Sofa, I don't think I've ever figured out what you drive. Pontiac? Chevrolet? Probably an 83 through 85 model?

 

Yep third gens had everything from 2.73 to 3.73 stock. Just depends on year, model, transmission, engine, package.

Factory installed gear ratios was... 2.73, 2.77, 2.93, 3.08, 3.23, 3.27, 3.42, 3.45, 3.73
The 2.77, 3.27, 3.45 was in the BW 9 bolt, the rest was the 10 bolt rears

 

3:73 was standard gear with the L69 package.

 

It's a 83 L69 Z28.

Night, you should add 3.70 to your 9-bolt ratios; 85 Firebirds w L69 got that instead of the 10-bolt 3.73. Obviously not a very common one though, probably not more than acoupla hundred made.

 

As I recall, just for more info, the 84 L69 was available with auto and 3.42's.

JamesC

 

.

 

all in all the advice in here is not wrong. but here is my experience. i had a nwc t5 in my iroc (mods are in sig) went as fast as 12.9 @ 110 in the quater and still has life in it. my car started with a carbed 305 then hot cammed 350 then the h/c/i 350. i did the t56 swap because i wanted the piece of mind of a stronger trans and the 6th gear. why did my car last this long with the 5spd? why didnt mine blow to smithereens with the slight bit from the gas pedal? idk but what i do know you can still enjoy a t5/350 combo gently, i drove mine hard with no issues when pulled.

i would get a factory 305/t5 car. its easier to find a 350 than a complete t5 with pedals swap.

 

Aw crap, I forgot about that one. You are right, not a very common on at all

 

Like I said, I had a 3.70 BW 9 bolt in my 86 TA. Carbed 305 with a T5.