FireInMe17

Can I use a 350 ECM on a 305? Are there any differences and what are they? Do the proms really matter for the application since it is the same engine with just different displacements?

I'm trying to swap my 3.1L V6 to a 305 TPI and I ordered a harness but now I need a computer and I will be switching from MAP to MAF in the process.

This isn't a direct swap either, I'm fitting my 305 with 906 Vortec heads and using 1.6 roller rockers and #24 injectors so would using the 350 ECM give me any performance gains for my application? I know that either way I go I will need to do tuning but I've accepted that. I just want to know if I would be better off with a 350 computer or a 305 computer.

BlueIroc-Z

iTrader: (6)

As long as two ECM's have identical service numbers (i.e. 1227165) they are the same regardless of what engine they were used with.

It's the MEMCAL that makes the difference. And, since you are going to have tuning done anyway, that makes any PROM differences irrelevant. As far as I know the other chips besides the PROM on the MEMCAL control the limp-mode and the cylinder select.

The limp-mode may differ from 305 to 350, but that only comes into play if the PROM is non-functional. And, with the non-stock engine setup neither the 350 nor the 305 limp-mode would be an exact fit.

The cylinder select tells the ECM how many cylinders the engine is, so any V8 memcal would be fine in this regard.

Hope that helps. Best of luck with the swap.

FireInMe17

Thanks. I think I'm going to go ahead and try to get a 350 computer because they use #22 injectors vs the #19 for the 305 and I assume that 350's use a bigger cam than a 305? Because the higher cam profile will be better with the 1.6 roller rockers than the smaller settings for the 305.

ninetyone

iTrader: (2)

You will not need 24 lb injectors either unless you want to run excessively rich and spend more on gas. In my 350, 24 lb inj were way too big.

ninetyone

iTrader: (2)

Sorry ,you will need a 305 prom for that car and 19lb injectors. The computer itself has nothing to do with injectors,etc. It is the prom that contains all of the info/instructions. 350's and 305 tpi's share the same cam also for the most part. Check to see what computer you have now. If you have a 1227730, that one already works with all 305's and 350's and about 20 other GM cars. I think you already have the correct ecm you need, that is ,if you plan to run Speed density. If you are going to run MAF , then you will need the 89' and earlier 165 ecm.

ninetyone

iTrader: (2)

Dude with those vortec heads you know you will need the special Scoggin Dickey lower manifold ,right? It's $400 dollars. Seriously, is that 305 engine a MAF TPI? I would eliminate that factor and go Speed density. Much easier to tune and way less of a headache. Just use your current v6 computer and find a used 305 prom (correct year for the engine) and pick up a set of 19lb injectors. Did you already purchase the harness? Just trying to help you out man

FireInMe17

Already made the switch to MAF and umm yeah...I know I need the intake manifold. I got it. I know I have a 7730 but it doesn't work with MAF so I need to find a 165. I know that #24 injectors are big but that's what the engine had installed when I bought it so that's what I'm gonna use. The MAF harness is on its way to my house now. Honestly, I've had so many problems with my V6 and MAP that I think I want to try something else. MAP sucks haha.

ninetyone

iTrader: (2)

SD is better than MAF , hands down. You can still swap it over to SD and also save yourself money on buying an ecm. With 24 lb injectors your BLM's are going to be low(rich). You may use an adjustable fuel pressure regulator to turn down your fuel pressure as this will help a little bit. How much did you pay for a harness? Who ever installed those 24lb injectors in that engine before you , did not know what they were doing.

ninetyone

iTrader: (2)

I certainly hope that you are not going to try and use 24 lb injectors in a 305! They were too big for my 350 tpi. Oh well, i guess you can get it tuned around that. You just have to change the injector constant. Until you get it tuned tho, i would use an AFPR and turn down the fuel pressure significantly. Cars are a little quicker lean rather than rich.

gerrym

Concur, I'm running 24's in my bone stock L98 '89 GTA convertible... well... bone stock except for headers and a highly tweaked PCMFORLESS tune. The 24's will as you say work just fine if you tweak the tune. With the '89 MAF setup it can be a little injector constant, a little MAF tweak. There is no substitute for a someone who really knows the car, the mods and the ECM doing the correct tweaking of the tune. Even in a completely stock setup. My driveability with the tune was changed in a MAJOR way. Alvin emailed me multiple edits after the initial dyno tune. I picked up a ton of torque from the dyno tune, but many way cool driveability features in the subsequent edits.

GM-