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Old 01-06-2010, 11:24 AM
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Need Information on a 1984 305 TPI Engine

Hi All,

I've read some of the threads about the 305 and 350 similarities. My question is, If I buy a 350 crate motor, will my TPI system off the 305 work on a 350? The motor came out of a Trans Am, if it makes any difference.
I thought about rebuilding the 305, but I don't know if it would have enough get up and go in a 1937 Olds 2dr. Sedan; fairly heavy car, so a 350 was my next thought. I'm not trying to build a race car, but would like decent performance. Any suggestions would be appreciated.

Thanks....Jeff

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Old 01-06-2010, 01:42 PM
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Originally Posted by eddi887
Hi All,

I've read some of the threads about the 305 and 350 similarities. My question is, If I buy a 350 crate motor, will my TPI system off the 305 work on a 350? The motor came out of a Trans Am, if it makes any difference.
I thought about rebuilding the 305, but I don't know if it would have enough get up and go in a 1937 Olds 2dr. Sedan; fairly heavy car, so a 350 was my next thought. I'm not trying to build a race car, but would like decent performance. Any suggestions would be appreciated.

Thanks....Jeff
You'll have to pay attention to the heads in terms of center bolt angles 90 versus the later 72 degrees and exhaust cross over for the EGR.

The computer will need a custom chip, at this point you will have two decisions to make whether to keep or change the 305 injectors for 350 as this will effect the chip programming.

You can keep the 305 injectors and reprogram the chip to drive them harder to fuel the 350. This works but shortens injector life. Or you can install 350 injectors with an appropriate programming change on the chip. Injectors last longer when done this way. But either way will require a new chip

Other headache is crankshaft, 84 uses the old and leaky 2 piece seal, 86 and up the tighter one piece. The one piece will require you to use a matching bolt circle flexplate. The converter pattern is the same so your existing tranny and converter only needs the flexplate that matches the crankshaft used.

Bogie
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Old 01-06-2010, 03:23 PM
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IIRC GM didn't start with the TPI until '85. AFAIK this was the only year the manifold would fit the pre-centerbolt heads.
I've swapped an '87 TPI (mass air setup) from a 305 to a 350 with no issues BUT I put it on top of a longblock for an 87 1/2 ton pickup (with stock cam for said application). Raised the fuel pressure to 50 psi (factory setting was 43 psi) to compensate for the smaller injectors and it had zero issues. I don't think you could get away with that if it is a speed density setup.
Later on I decided to install headers/exhaust and a slightly larger cam (blue racer with specs similar to the edelbrock performer cam) and the idle quality suffered. Ended up with a custom PROM from Arizona Speed and Marine, wasn't overly impressed with the chip (mpg went way down and there was no performance gain in the 1/4 vs the stock chip) but it did solve the idle issues.
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Old 01-07-2010, 08:32 AM
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Need Information on a 1984 305 TPI Engine

Thanks for the replys. The engine came out of an 84 Trans Am, so I assumed it was an 84 engine, but I bought the car used, so it could have been swapped in at some point. So, it sounds like I would be better off just buying a 350 and using that instead?
The reason I ask about using the TPI is I bought the wiring harness, the performance chip, headers, and various other parts that fit the 305, so I kind of hate to waste the money already invested. Does anyone have any idea about how well a 305 would move a 3500lb car?

Thanks...Jeff
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Old 01-07-2010, 09:01 AM
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The 305 will work fine. Won't be as quick as a 350 but still ok.
The motor swap I described above was in an 87 IROC Camaro, car weighed 3700+ with me in it, 3.27 gear, 700r4 trans, stock converter. It ran 15.90's with the 305, 15.30's after the 350 swap, and 14.50's after cam/headers/exhaust.
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