305 to 350 swap

[bidle92]

did a motor swap from a 305 tpi to a 350 tpi and it runs a little rough like its missing. Do you need to put a chip for a 350 in the computer or not. What else needs to be changed when doing this swap.

[MattODoom]

You need to swap the PROM chip over to a 350 one, other wise the fuel and spark maps will be off.

[kammi10]

yeah what he said,

[jgardner]

Well with the increase in engine volume what have you done to the fuel delivery? Is it getting more fuel so it's not running lean?

[tenpin842]

Agreed, Stock 305 injectors are 19# 350 stock are 22#.

[WMCCjames]

Well you say it's missing? Is this happening at idle or under accel? A 350 with start and idle fine on a 305 chip and 19lbs injectors. Actually, a 350 will run just fine on a 305 chip as long as the pressure is bumped up on the fuel rail. Is this the right way, no, but it does work. If you miss is happening on idle/low speed you have another problem.

Here's the crazy thing for all you nah-sayers...I ran a 305 chip on a 406 with 60psi fuel for a short while....so it does work, just not ideal.

[bidle92]

It is missing at idle and at a cruise. Check for vacum leaks and for arcing
plugs and wires and found none. Other then that it runs pretty good.

[WMCCjames]

Hmmm.....did you check for a cracked spark plug? Check engine light coming on?

[ezysk]

Guessing you put an entire 350 TPI Engine in, with all its own sensors, fuel injectors and so forth, thus the only thing that remained from the 305 was the computer, is this correct?

Or did you just replace the 305 block with a 350 block?

How did the 350 TPI run before you installed it, did you get to hear it run first?

Is the 350 TPI Cam a stock one, or has it changed significantly?

Just trying to get some more background.

[bidle92]

Its the old 305 tpi stuff from the old motor. Injectors and computer are the 305 tpi. the motor is a 350 from the mid 80's but not out of a tpi vechile. Does not have a cracked plug that would effect the vechile running all the time.

[WMCCjames]

Its the old 305 tpi stuff from the old motor. Injectors and computer are the 305 tpi. the motor is a 350 from the mid 80's but not out of a tpi vechile. Does not have a cracked plug that would effect the vechile running all the time.

No, a cracked plug will act like a random misfire...trust me.

Any check engine light?

[bidle92]

No check engine light. I deal with that type of misfire stuff almost every day trust me I checked

[wezeles]

did you keep the 305 heads too? if so that could be part of your problem... i think most TPI 305 heads are 58CC atleast from 87-89 and the 350 tpi heads are 64cc from 87-89 you just bumped up your compression ratio a bit there if you kept the 305 heads could be fixed with some timing and better fuel.... from 90-92 i think a good chunk of both 305's and 350's used aluminum 58cc heads eaither way something you have to consider

[LS1Formulation]

Aluminum heads only came on Corvettes. They were closer to 60CCs in the real world. Most iron 305 TPI heads were 62-64CC and the 350s were 67-68CC. The compression ratio wouldn't cause it to miss for any reason. With all the tolerances in Gen I small blocks, the CR would not be anywhere near the point of detonation. It's definitely an ignition issue, which may have just let itself be known when the swap was done.