MSefi.com read only forum (Jan.15,2018)

what year tbi should i be used for the version 3??

Version 3 what?

What engine are you planning to put it on?

What is your goal or plan to do with this engine?

MegaSquirt-II Programmable EFI System PCB3.0

Its going on my mopar 360 making around 350ish hp.

Its in my 88 wrangler that i offroad. Going to put a chevy TBI on it.

If you can afford it I think starting off with MS2 on a V3 + board is a good idea. The version 3 boards have been out long enough now that they are proven to be reliable. They are also support most (if not all) the current options and features.

300 HP is pretty much the limit of 2bbl throttle bodies and getting that out of them starts to push the limits in trying to get full range out of them. If you get them to run full throttle the are border line on idle and idle good but dont run well wide open. You just dont have much headroom so you have to get everything right. The larger GM throttle body only came on the 454s and are not nearly as common as the smaller ones so you often end up having to pay a lot more for them. The 454 was also the only one that used the 90 lbhr injectors, again rare= expensive. If you have to get by cheap you may be better off looking on Ebay for a Holley Projection throttle body (or system and resell or junk their ecu). There were 670 cfm 2bbls that are basically the same as the 454 ones. Thats what I am currently running on my caddy 500. Holley also made/makes a 4bbl. The one I have has 4 85 lb injectors in it and I am concerned about getting it to idle well. Large injectors have a problem where they can not open and close fast enough to deliver a tiny amount of fuel (like at idle). I think I can find a way to work around it with fuel pressure or staging but have not had time to play with it yet. If you are willing to spend some real money there are several people that make throttle 4bbl throttle bodies. there are 2 or 3 that use the bosch (multiport) style injectors. The ones I have seen start around $350 without injectors. There is a company called Auto-nomics that makes throttle bodies and other intake stuff, they even sell their stuff with MS harnesses.

What have you done to your motor to get 350 out of it? To get around 1 hp per inch out of those older motor designs is a bit harder than you may expect. I would guess that would take something not even close to a stock cam, high compression, head and port work, aftermarket intake and exhaust all designed and sized to work as a system. If thats just your ultimate goal and for now you are running it closer to stock you could get away with running a TBI off a chev 350/5.7. Those were very common and should be easy to find cheap. You will then get it running and get the hang of tuning and such. You will also get some ideas on things you may want to do when you rebuild the motor (lots of stuff 'they' will say cant be done or wont work because 'they' dont know how flexible MS is!). The limiting factor will be the GM TBI but since you wont have much invested in that one part it wont be a big deal to throw it away later when you need to upgrade to something like the Autonomics one or maybe even a multiport system.

Are many (or any) of the people you off road with running EFI? And are they running stock factory systems?

The most common GM TBI's were used on the trucks (vans, suv's) from 87-95. From what I can tell the bodies were more or less the same for the 4.3, 5.0, 5.7. Only the 454 was larger. Injectors varied depending on the application but were physically interchangeable. Fuel pressure regulator guts may have also varied but should also be interchangeable. MS can interface with any of them.

A universal or spread bore (thermal quad) intake works better because of the size of the throttle bores but there are adapters to fit the holley square bores also, I just dont like the idea of having that sharp of a bend but I guess that far from the intake ports would be better since any fuel that hits the walls at that point will have a good chance of getting mixed again on its way to the valve.

Another thing to think about is with the large 2 bbls is they can be a little too responsive. Wet pavement is sort of a problem for me at the moment (especially when cops are around). I hope to help that when I get the spark control working and maybe some non linear throttle linkage.

wow great info!

Yes my 360 is not stock. I have a more aggresive cam that gives me great low end response.... this is what you need when off-roading. I have seald power hyp. flat top pistons with 5cc valve reliefs. Compression is somwhere around 10:1. Edelbrock dual plane intake. Heads had some work done por and polishing but don't know the flow numbers. Running block hugger headers.

Now I do not know if its 350 hp. But a car mag. did the same build and they were making around that power at the crank.

i did the math and i flow about 581 cfm at 100% ve

But really you only flow about 80% of that, so that would make it 423 cfm.

I would need a 1.7" bore ~ 43mm with 80lb injectors.

I know you don't want to run them 100%, so I would need 100 lb injectors.

The largest injector I have ever seen listed (that I believe) for the GM's is 90.

I think the big body is around 50mm. So the small one is likely in the range you are thinking.

Is this your daily driver?

No this is not my daily driver. Would a 90lb injector be ok to use??

Its good that this is not your daily driver. Its much easier to work through problems without the pressure of needing it to get to work in the morning.

You may be able to gain the extra fuel my messing with fuel pressure. Im not sure what the GM's use for the fuel pressure regulator. Raising the pressure will get you more fuel but that may make idle worse because large injectors already have trouble operating fast enough at idle with lower pressures. I would think higher pressures would make it worse. You may have to try some external variable setup.

Well if i can't find 100lb injectors I guess i'll have to work with 90lbs.

I heard the chevy/gm tbi uses around 13 or so psi and you can bump it up to 20 somthing.

I wonder what affect my cam will have on the idle with the injectors??? hmmm i guess i'll have to play around with it.

Cam at idle should not be as big a problem as with a carb because you are not depending on vacuum to draw the fuel in you only need flow to carry the fuel the injectors dump in.

true true.

I guess i'm on a hunt to see what size tbi injectors i can find.