Inliners International Forums General Discussion Blown and Injected blown injected 270 GMC with MegaSquirt

Hi, I'm in the beginning stages of this build. The motor itself is already built, it was originally an old sprint car race motor, then in a FED for a stint, now in my '53 chevy truck. it is on a engine running stand now where I will add the blower and injection. Blower is an eaton from a Jag. Due to the shared ports on these motors I assume I will just run a sort of TBI setup since the head design won't take full advantage of multi-port...but would like to hear others opinions. as well this will be a low boost driver, nothing crazy here, 5 to 8 lbs boots. One main question I have is I have had this idea of using say 2 large injectors, where just the tip of the injector is machined into the intake plenum similair to a port injected injector. Of course placement would be between the single butterfly and before the separate intake runners start to separate. have always thought of using GM TBi injectors for this project but they aren't very friendly unless you use the whole throttle body and the fuel runs though various cast pieces. Anyone done this before?

Ferd used some 160# injectors on mid-late 90's crown vics with propane injection.

These injectors are usable with gas Ok and you can find them on Ebay.

Each injector will support 300HP... so 2 of them would be LOTS!

Suggest spraying against the inlet air flow to give the fuel a chance to vaporize...

wow 300hp per injector...yeah 160# is a lot of fuel. i don't have a exact HP in mind, but would be happy with 300hp or so. I don't want to turn up the boost too much so i have to worry about head gaskets. I'm going to take the head off and CC everything to h\get an acurate CR before I do any boost calculations. this motor wasn't built by me so just going on what teh previous owner said...which he didn't build it either...it runs fine on pump gas so can't have too much compression. I can relieve the chambers and smooth the piston crowns if i have too to lower the CR, or go with a thick copper gasket...and O-ring.

I have seen discussions on high output injectors and idle quality. this is a hotrod engine with a solid lifter Isky, assuming the .050 numbers are in the 230 degrees or so it's not going to idle like a stocker anyway(as said, not sure of actual specs but will pull cam to spec it). I just wonder if a ,say a pair of 120# injectors will idle OK. Trick Flow has these and should support more than enough for my initial plans and are affordable:

High performance fuel injectors from Trick Flow®.

Fuel Injector, TFX™, 120 lbs./hr., 4\1A Peak and Hold Circuit Driver, Each


Features:

Driver Type 4\1A peak and hold
Fuel Rail O-Ring Outside Diameter (in) 0.590 in.
Injector Advertised Flow Rate (lbs/hr) 120 lbs./hr.
Injector Impedance 2.2 ohms
Injector Plug Style Bosch/Amp-style
Manifold O-Ring Outside Diameter (in) 0.590 in.
O-Rings Included Yes
Outside Diameter (in) 0.971 in.
Overall Height (in) 2.830 in.
Quantity Sold individually.
Seat to Seat Height (in) 2.153 in.
Wiring Harness Included No

It'll be fine, you may have to mess with the number of injections/engine cycle to find the best setup. MS will run 2 Low Z injectors just fine.

efi-diy, I have thought about another option which I'm sure has been done. I have several old multicarb intakes. One is a cool fenton with two old school propane throttle bodies on it that would be easy to put an injector on each where the large propane inlet is....only thing is I'm not sure if that would be quite enough flow(both are one barrels). will have to check the dia when they arrive in container in a couple weeks. Another option is the intake which is currently on the motor wchich an old McGurk 5 carb intake. I coul drunany number of throttle bodies here( for instance off newer motorcycle)....the question being is how would one go about setting up the injection....can it be done progressively with middle openig first( run multiple TPS with progressive?)...or would you need to have all open in parallel and use one TPS? Say you have 3 throttle bodies or 4 or 5...due to the sharing of ports for certain cylinders ther is more flow in the center of teh intake than at the ends....would the center throttle bodies get more flow than teh ends and therefore cause trouble with AF ratio in different cylinders???

The dual inlet will work fine. The 5 holer parallel is easier to tune abiet harder to drive.. sequential is possible but needs more time to tune as you may need to add a secondary fuel table.

One TPS is fine - put it on the primary.

Remind me if the GMC is a 12 port head...

unfortunately it is not a 12 port. it is similiar to a 235 head with 3 intake ports and 4 exhaust ports. With the 3 intake ports, each one sharing 2 cylinders, I guess the twin tbi would have pretty even dispertion as the throttle bodies are set in between each of the runners. as well if I ran the big intake I could just run three TBIs sitting right over the ports...of course at this level of performance having the multiple tbi setup is really just for looks as I assume having a pair of injectors shooting into the inlet plenum would be just as efficient as one injector in each tb.....the multiples would just look more old school.