R3W7 Assembly
This shows the Hilborn injectors where I machined them for electronic injectors and tipped the injector angle up from 45 degrees to 37 degrees. This will spray the fuel directly at the back of the intake valve head (when I mount the injectors on a 22 degree manifold). The theory behind this is something I read on Indy car engines where they spray the raw fuel on the valve head....apparently the 'cold' fuel hits the hot valve head and vaporizes as it's being sucked into the cylinder. I guess that sounds good....
I probably would not bother with the expense of EFI but there's no intake manifold that will fit under the hood. In fact, I'm pretty sure there's only 1 (or possibly 2) intake manifold made for these heads and it's a tall one. Plus, I've run the Hilborn in the years past on other engines and I'm a big believer in the straight shot air flow they provide.
Those are the Corvette LS7 type injectors, I like them as they are small.
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Can’t say for sure about EFI and injector placement, but when I ran MFI and alcohol, the nozzles were at the valve cover rail. It’s hard to explain, but on the dyno, loading the engine you could see and feel it struggle a bit. I fought it for a bit but just said screw it, it’s just pig rich until it starts the pull.
In the car, I could “feel” that same thing letting the clutch out and, I could feel it in the 3-4 shift. It would almost vibrate.
I forget what happened but I was at work dealing with a TR and it hit me that I never made the HP/CID I thought I should, and the TR engine I just built was about where I’d thought it should be.
So, I got on the phone and called every MFI guru, whiz bang, bubble gummer and Pro I could find regarding nozzle placement.
Every single one of them, to a man said do NOT move the nozzles up the manifold. They all said the further the nozzle is from the valve, the more chance of fuel/air seperation, which means wall flow, fuel stratification in the chamber and a big loss of power.
Then I asked how a carb can put the fuel in that far away from the valve and not have the same issues, yet everything I’ve seen is the MFI is down on HP/CID to carbs. Most were honest and said they weren’t carb experts so they couldn’t say. One guy, who is a “go to” MFI tuning expert said that carbs make LESS HP, and they have more issues with stratification and wall flow than MFI with correctly placed nozzles. His suggestion was to up the pressure the the nozzles. When I told him I’m at 100 psi at the nozzles at 8500 and how much more pressure should I use he said 60 was plenty.
So I yanked the manifold and moved the nozzles up and inch. You could tell when it first fired it was cleaner. It was a bit fat, so I leaked the barrel valve about 1% less and threw .006 more bypass and .012 more high speed at it, and picked up a fat .1 off the trailer.
That was all in the gear changes. Most of the weird feeling was gone.
Before I went back on the dyno that winter I moved the nozzles up another inch. At that point IIRC we were up 25 HP across the RPM range and that weird vibration/feel was gone.
The time slips matched the dyno numbers. My next move was going to be to move the injectors up into the plenum and put them right over the port. I was going to fab up something to let me put the nozzle further into it was directly over the port.
I think that like the other moves, it would have made more power and I think the gear changes would have been even better.
But, I got sick and quit racing so I never did that.
The interesting thing is when NHRA shoved EFI up Pro Stock’s butt, the big complaint was they couldn’t move the injectors where they wanted them.
I said all that to say that I’m not sure that moving the nozzle closer to the valve is always the best thing. In fact, in an MFI application I know it’s not. It’s not even close.
On the last dyno pulls I was getting close to the HP/CID number I thought I should be making.
I think at this point, I can make more HP/CID with carbs and gas than I can with MFI and alcohol.
Not sure how EFI would respond, but it would be interesting to test. Expensive, but interesting.
EDIT: I forgot to mention the one thing that did occur when moving the nozzles up was idle quality. I could get the engine happy at about 1200 with the nozzles at the VC rail. When I moved the nozzles up, the best I could do was about 1400ish and that was after I leaned the idle out as far as I could. No matter what I did, if I closed the butterflies enough to slow the idle down, and set the BV accordingly it would be lean and stumble giving it throttle. Adding fuel never cleaned it up, and made the oil dirty.
Long after the fact, I decided that the issue was in the ramp of the BV and what position it was in relative to butterfly opening at idle. The higher nozzle placement required less fuel to achieve the same RPM. Leaning out the BV at idle sped the RPM idle up, so you close the butterflies and now the BV is even closer to the lean end of the ramp on the BV. I was going to make another BV but I never go around to it. So moving the nozzles away from the valve MAY cause issues with idle quality. It may not be affected with EFI, or maybe it can be tuned out.