tuning options for jellybean GEO 3 cyl

[34blazer]

was talking to a member of pennocks this afternoon about possibly swapping in a 7730 into his geo prism. he is planning on possibly adding a small turbo and wants to tune it properly. just curious if there would be any issues. and would a v6 memcal need to be modified for cyl select?

[RobertISaar]

prism with 3 cylinder? did he metro-swap it?

i don't think there would be a good V6 MEMCAL to start with.... the 1.0 3 cylinder used a 73.9mm bore, which is far below any GM engine i can think of. and IIRC(since i've looked into it before) the only models that got knock sensors were factory turbo models.

[34blazer]

oops, i meant metro, sorry. besides the knock sensor/filter issue, would a GMECM like the 7730 be able to run this engine?

[34blazer]

looks like $12P could support this.

http://delcohacking.net/forums/viewt...=356&hilit=12P

[RobertISaar]

i don't see any reason why any 7730 native code couldn't handle it if setup correctly. it's a single-injector TBI engine, i imagine operated in peak/hold, or does it have a resistor in the injector circuit?

coming up with a base tune would take a while, but it's completely doable.

[1project2many]

Hard to say what to start with. 96d is the correct value for knumcyl (number of cylinders) for a three cylinder engine. I seem to remember later Metros being PFI. Either way I think I'd set the memcal to use single point tbi firing mode and I might try using a TBI cal, too.

[RobertISaar]

the turbo 1.0s were MPFI(and i think all of the 4 cylinders were as well), but all of the N/A ones, even up to ~2001 or so, all have TBI from what i'm seeing in the wiring diagrams.

there's a single fuel injector, with a fuel injector resistor.

i think it would be interesting to put a turbo manifold set on a N/A engine....

[daleulan]

There might be an issue with a low cylinder-count engine... you might find you need sync MAP sampling so you'd need software that supported it. The MAP fluctuations can be a bit high on low cylinder-count engines and that can cause some very strange problems when you are close to multiples of the 12.5 or 6.25ms loops in terms of engine speed. Some software has sync MAP reading and some do not. I've seen both TBI and MPFI versions of that engine, they used MPFI on the turbo version, cold be dynamic range issues on a single-injector TBI with a turbo. Peak-and-hold instead of a resistor might improve the performance maybe enough for mild boost but I don't know for sure.

[RobertISaar]

most TPI/MPFI native software runs sync MAP up to 4800 RPM for that exact reason... i imagine by that RPM, even on the 1.0, it won't be an issue.

[34blazer]

ive never heard of syncronizing MAP sampling before. where can I read up on this?

[RobertISaar]

not much to read about.... just that the MAP sensor reads are synchronized to happen when reference pulses are received.