What's up people I am in a bit of a pickle here. I love my firebird I loved restoring it and everything about it. But it accelerates way to slow and I could spend hundreds just building my V6. But a friend has a parts 89 formula not 100$ its an L98 or not but the way they described it I am sure it is. Now they need the shell to restore their other car and they may sell me everything I need to swap my V6 over. Problem is the motor is seized. So I would probably get it dirt cheap with transmission and everything else. I plan on taking a few years and slowly rebuild this motor. And when its done drop it in one winter when the car is parked. I would most likely have to bore it out and everything but for a practicly free motor is it worth it? I would like to do An L98 because it would be easier to swap I would imagine with my current fuel lines and such and my neighbor has a 91 GTA with this motor and he is getting better MPG around town then me but not much better. The power of that engine just pulls that weight so easily while its hard for the 3.1 to accelerate. I love the feeling of my buddies LS1 spinning tire up the road and before I know it I'm already at the end of the street. Just to have that power. BUT I am still stuck on the fact that I can save all the bullshit of swapping a motor and build my v6. Do a cam headers some heads that sorta thing. And I plan on rebuilding my rear end (273s) and making them posi. If I did that or put a completely different rear end in would I have to worry about my speedometer ??? I also know the rear ends are junk in the third and 4th gens and heard about a Ford 9" rear end swap what is my best option ???

Any answers to my questions and all help would be appreciated.

Oh and one other thing DO NOT suggest me selling my car for another one I have way too much sentimental value in this car I've had it since I was 12 and took five years restoring it

Thanks guys

 

Don't know about all your other questions but I can say that the only thing that will mess up your speedometer with a rear end swap is if you either: A) change the gear ratio, or B) change your tire height.

or both, of course, haha.

There are plenty of companies that will sell you the speedometer gear that you need to make everything correct again though.

 

With the 3.1 you'd be much better off with 3.23 or 3.42 gears. You need to swap the gears in the trans if you change ratios. Posi is a great improvement but you don't need a Ford 9". The rear ends are not junk they're built for the application work fine when used as designed.

 

What do the transmission gears have to do with my rear end gears. My Buddy's changing his gears in his Ls1 from 273 to 373 doesn't have to touch his transmission.

 

So I would be better off getting 342s instead of building my 273s as a posi?

 

He'll have to if he wants his speedometer to work correctly. The equipment that tells your speedometer what to read is in the transmission, and it's majorly affected by the gear ratio.

Depends, 273's will give you better mileage, 3.42's will do better on the strip.

posi is a must either way.

 

If you're getting a posi unit then you can add whatever gears you want. Make sure of what rear end you've got. Should be a 10 bolt with 28 spline axles I think but open it up to make sure. I like the 3.23 (3.27 if 9 bolt) as an all round compromise but I'm building another axle with 3.73 gears for auto-x. I'm trying to get set up so the axles can be swapped fairly easily. And I've already got the little plastic gears that go in the trans to match the rear end ratio. Do plenty of reading so you get to know what's what.

 

My friend can rebuild my rear end with my 273s and when I swap my motor I'll get the rear end from the parts car. I just would enjoy a posi more and hopefully get a bit more leverage. How would I tell what gears the parts car has though it's an 89 formula. And if the car isn't a 350 I'm just going to build my v6 and eventually get a crate motor. So many decisions to make I want to be prepared

 

So I guess I'm keeping my current gears just rebuilding them as posi now what about the seized L98, I'm thinking if the block is good I'll take it and swap it or if not or its the 305 I'll just build my V6

 

The rear ends in the thirdgen's are great, they can handle close to 500hp, so what are you talking about? Also, the v6 rear end is no different than the v8 rear end, they are the same car. SAME

 

FYI, the v6 cars have better gear ratios in their rear ends. The v6 cars all come with either 323 or 342's. I used a v6 rear in my 350TPI bolt on car and it worked great!!

 

Gear ratios change depending on production engine/transmission options but other than that, it doesn't matter what engine came in the car, a third gen 10 bolt is the same weak 10 bolt. It went through a few changes over the years but it's the same 10 bolt.

 

I thought they were crap because of the fact they have issues vibrating and making sounds and just breaking my friend is having that issue with his ws6 and I think my rear end is vibrating but it might be a lot of things. He also completely rebuilt it. He ordered a new rear end should be in today. And my v6 is just a base auto trannt so im pretty sure they are 273s and when I go to the 350 tpi should I just take the rear end from the donor car to match the transmission so my sledometer would work or change the gear for my current rear end. I know all the rear ends work and withstand the power from all the engines.

 

If you take the engine, tranny, speedometer gear(it's at the end of the speedometer cable that hooks into the side of the transmission) and rear end from the donor car and put them all in your car then your speedometer will work correctly.

Honestly if you can get the whole instrument cluster with the speedometer cable that would be your best bet.

 

Sounds good to me I don't know much about rear ends and my friend will do all the work needed on them and I plan on taking everything I need so that sounds like a plan

 

A common complaint about vibration is caused by the OEM steel driveshaft. Installing an aluminum one normally removes the vibration but the OEM ones are not very strong. You can also get your steel one rebalanced or if it's in poor condition, have a new shaft made.

 

The vibratiom only started recently and only occurs when I am going 70mph and accelerating over that and how much would a new drive shaft be and are they the same in the v8s?

 

If the vibration only started recently you may have lost a wheel weight or the u-joints on the drive shaft may be bad or you may have bent an axle. Did you hit a curb? In any case you need to check the spinning parts. Maybe get your wheel balance checked first. That's the easiest/cheapest to deal with. Then check the drive shaft. Next easiest/cheapest. Hope it's not a bent axle shaft.

 

Haven't hit any bumps Havent bottomed out but new england roads are **** and our first thought was a sticky weight coming off a rim and I get them balanced free so that will be my first thing to do

 

Both the 89 formula and the 90 firebird will have the electric speedo. Swapping speedo gears is small potatoes compared to the rest of the work involved. Don't worry about it. Acquiring the TPI motor with ECM and harness, along with the tranny, for next to nothing is a good deal anyway you look at it.

The only sure fire way to be certain of the rear end gear ratio is to open the cover and look. The ratio will be stamped on the ring gear in whole numbers, just divide the big number by the little number.

I'd focus on getting everything I needed for the swap. You seem to be instead focused on the small stuff now, and the speedo gears certainly fall into that category.

 

Yeah your right I just like making sure its possible to get everything working right as if the motor was stock. I'll let you know how it turns out I should be contacting them about the car soon enough

 

Grab a good 350 short block from one of the millions of 90's trucks instead of rebuilding the seized engine

When stripping the formula, don't cut any wires, you'll need the engine harness as a whole. Repin it to match your year

You will have to add a buffer box to get the speedo working, but that's a small issue to be solved much later down the road. Same with the v6 to v8 tach

 

Deffinitly won't do a truck motor though I almost did when a friend offered the 350 out if his 95 tahoe till he found a crack In the block. I'd like it to look orignal but if that seized motor is cracked too I'll buy a crate motor and just strip the formula of everything else. Thanks for the advise

 

Whats wrong with a truck 350? The shortblock is practically identical to the L98 in the formula. Trucks are the absolute most common 350

 

Nothing is wrong with them other than they did not come stock if the cars I want it to be like the motor came in the car and I am very famillar with the l98s not to mention the motor will cost nothing and i will get the transmission I want. If i had a car that didn't have a motor in it I would get anything I'd could get my hands on but not my dream car

 

Even if you do have 2.73s, which I'm 100% sure you don't unless the rear has been swapped out, you do not want them. I hate the 2.73s in my car, they really kill it. More suited for grandma's Caprice than a performance car.

3.42 are ideal for a TPI thirdgen. If you are going to go through the trouble of getting a posi and ripping apart the rear end, you might as well put some decent gears in the car.

 

Whatever I have right now I have a posi unit now out of my Buddy's 4th gen that had the wrong gears he thinks are 273 and since I need a posi I'm having the gears i have now rebuild so my ratio does not change so I don't have to go through the bullshit of taking my tranny apart to make my spedo work and when I swap the motor I'll take the formula gears put them in my rear end and drop the formula transmission in and I'm golden. The swap is a few years away at the least and posi is a must for me right now anything to help