I have a 91 z28 with a 305 tpi and 700r4 tranny.I'm looking to get a 350 for it but was wondering what I would have to change?would the stock tpi unit be okay and the stock computer or would they have to be changed.also jegs has a good deal on a 350 but it says 86 and earlier.can I use any 350 block or does it have to be 87 and newer?also if I went to carb would I have to change the intank fuel pump and would the stock distributer be alright?

 

Yes, if You keep it TPI, Your gonna have to use the 87 and later long block for the TPI intake and etc to bolt right up. The older blocks are not as good as the 87 and ups anyways, because they use a 2 piece rear main seal that usually ends up leaking and most arent pre machined for a roller camshaft which all newer TPI motors have. Their are plenty of 350 longblocks out there that you can find new or used for a good deal so look around. And Im pretty sure that the only thing You'll absolutely need to swap out are the 305's 21 lb. injectors for the 350's 24 lb. injecors. U might need to get a new chip reprogrammed for the bigger motor and injectors as well.

 

can I get a 86 or older block and use the heads from the 305 so I can keep the tpi?

 

I dont think the 86 or older block would even bolt up to your 305 heads due to the bolt patterns. Besides, the last thing you want are 305 heads on a 350. your compresion ratio would skyrocket to somehere around 11 or 12 to 1 and you might not be able to run on pump gas. Not ta mention, You would be way down on horsepower with those crappy little heads!

 

The '91 TPI system is speed density or manifold vacuum sensing type, which is very sensitive to changes to assumptions to the PROM tables. So, you would need to get a 350 PROM, or learn to do your own programming (suggested). You will also have to change the injectors to at least 22 lb, and the knock sensor & module to 350 parts.

You can use most any block, but the factory roller cam type, '87-up, with one-piece rear main seal crank, '86-up, would be more desired. Cams are plentiful to accommodate the computer. You could use your 305 heads, or find L98 heads, or go aftermarket. The easiest would be L98 heads.

If you go carb, your distributor will not work unless you do some sensor input manipulation (have never heard of it being done). You wouldn't have to change the in-tank pump, you can use a return-style regulator to bring the pressure down to 4-6 psi. If you plan on using an engine-mounted mechanical, you should plan on dropping the tank and removing the in-tank pump.
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You need to do some actual research on this topic. Basically, everything you said is untrue:

- Bolt pattern is unchanged.

- CR would be around 10.0:1.

- The only things "smaller" about 305 vs. iron L98 350 heads are the chambers and intake valves. The ports are identical. 350-size 1.94" intake valves are fairly simple to have installed.

With basic porting and valve unshrouding, 305 heads are very good performance enhancing parts for a 350.

 

https://www.thirdgen.org/forums/tbi/...ml#post2999529

See if this helps.

 

That's a TBI thread, so only the non-TBI-specific information applies.

 

I thought the head bolt pattern changed from perimiter to center bolt style after 86... And I've heard of people who have used 305 heads with flat top pistons and have achieved an undesirable compression ratio.

 

The valve cover bolt pattern changed, not the head bolt pattern.

 

For reference, the '86-1/2 up Vette L98 engines had 58cc aluminum heads, 12cc dish pistons, for a 10:1 CR. 4-valve relief flat tops typically have around 6cc volume. You don't need much dish, typically what the factory has, to maintain decent compression with 58cc heads on a 350 engine. Control quench, pump gas will be fine in such an engine.

 

hey, i was just wondering what a flat top 355 w/ 416 heads would to compression wise, you had mentioned dished pistons making 10:1 but by brother has a 355 w/ 416 heads and he is having problems with it pinging only after it warms up and at moderate throttle or load. would the compression ratio dramatically change from dished to flattop?
Thanks
Joe

 

that module, anywhere where you can buy one, or would you have to find it in a car, and where would it be at?