305 ECM for a 350? Will it work?

I have a 730 series ECM In my 91 Z28. I just changed the bottom half of the motor from a 305 Tpi to a 350 tpi ( Speed Density not mass air ). Finally got it to start but it's not running well. Can this ECM run a 350 or do I need a chip? If I need a chip, can I use the same ECM housing? Please help!

yes, the ECM should be the same part number for both, the difference is the PROM chip, it is hard wired with a matrix of info based on the engine and lots of testing. It is expecting a certain range of info for a given temp and air density. therefore spaying a given ammount of fuel. It does not measure air flow, so it dosnt know that its now a 350 and is only spraying enough fuel to fire a 305, so your engine is running lean, the O2 sensor picks up on this, and fires out a warning to the computer, who probly is in limp home mode because it thinks something is horribly wrong. Either buy a 350 prom, or reprogram the one you have to the new specs. for a speed density, this is a lenthy process, you have to do the fuel, and spark curves from scratch, while the engine is running, and refine them untill they are as close to optimum as possible. your best bet is to go ahead and put in the 350 cam, and 350 PROM chip, and it should be close to factory settings, and run MUCH better than it is now. but even without the cam, the PROM should make a much better running engine. but you dont have to change the ECM. just plug and play and it should work, wont be perfect, but will work. just make sure the 350 PROM is from a 91 camaro with the same intake and as many of the same options as possible, drivetrain wise. the 91's used a 128 bit PROM, while 92's use a 256 bit, and 90's use a 64 bit. crossing them will not yeild happy results. hope i helped. good luck.

Thanks a lot. I really appreciate the help. it was more info than I've gotten in a months time. I will post again when it all goes together. One more question! How about the starter and distributor. Should they be changed as well? As you can see it's my first motor I ever built myself. Although everything esle went really well!!

Starter and distributor should be fine.

Great. I kind of figured that the starter and distr. would be ok. Thanks to all for your help.

your very welcome zstreet, good luck and hope it all works. and yeah, just to confirm, the starter and distributor are the same.