MFI injectors mounted in TB's or the stacks?

[haycait911]

has anyone had any experience with or seen a set-up where the MFI injector is mounted in the throttle bodies or the ( magnesium ) stacks, instead of the heads.

I've got pretty much an entire MFI set-up for my 3.2. K&N's with hats, '69 S magnesium stacks that had been re-drilled to fit later tb's, '72-'73 tb's bored to 38mm, SC 3.0 big-port heads, and an MFI pump modded to run 3.2/3.4 liters.
thus I've got 46mm at the top of the stacks, 38 mm at the bottom of the stacks, 39mm into the tb's, 38.5mm out the bottom, into 38mm intake port.

I don't really see any way to put the injectors in the tb's. the tip of the injector would be right under the middle of the butterfly plate. not the best spot, I think. better to mount into the side of the stacks. anyone have any thoughts or experience? thanks, Don.

[356RS]

Got your PM Don. As far as mounting injectors in the TB's I don't think there is any room for a good fit. They would have to be made much taller. Mounted in the stacks would work but I see no gain in performance, possibly worse in the lower end range, but maybe some gain in the higher RPM range. Matt Blast sells the high butterfly TB's and there beautiful but the cost is way up there. Are you trying to get somewhere in between the $$ high butterfly's and your idea? Sounds like an interesting motor your building Don.

[haycait911]

I'm motivated by laziness, mostly. it would save me drilling the SC head. also, it would make for a 'bolt-on' set-up that would only need a cam change to run an engine on MFI. I don't really understand the affect on the power curve but couldn't the injection timing be adjusted to compensate?

****or maybe injector blocks between the tb's and stacks would work better.

[304065]

Sell your MFI TBs and get PMO set up for MFI. . . .

[356RS]

Yes, the injection timing would have to be adjusted towards more advance. What cams would you be using with this setup? The PMO's above might be the way to go.

[Flieger]

Above the throttle butterflies can cause the fuel to pool on top when at part throttle and when you get on the power again it stumbles from the excessively rich mixture. Not having an RPM Transducer fuel shutoff will only make it worse. Porsche tried it, found the poor drivability, put them back in the heads where they belong, and found no real penalty in max horsepower.

[Jeff Higgins]

I have to agree with Flieger. It's really pretty easy to drill the heads as required. Monty at Redmond European has a little drill jig that bolts to the intake port that he used for mine.

[haycait911]

thanks guys, I guess I'll stick with the stock set-up and drill the heads. still, it would be interesting to see an injection block/spacer to mount the injector into. it wouldn't affect the timing noticeably and would give a bolt-on option for MFI. D.

[BoxsterGT]

If I remember correctly, Jerry Woods once had injectors mounted up on the top of the air cleaner facing straight down. Aluminum covers w (3) injector bosses mounted 118mm apart for each side of the motor.

Don't remember how well it ran in low engine speed conditions. Perhaps it might help.

Len

[Flieger]

Sounds like the cold-start injectors.

[al lkosmal]

Don,
I have been working on few different intake/fuel management ideas. One of those ideas is to adapt MFI throttle bodies and stacks to EFI. One of the methods I'm looking at is using 930 spacer blocks. Machining the injector port for EFI injector bungs to accept EFI injectors, This would give you retro-cool throttle bodies and stacks and modern air/fuel management..............................but, I think that you could machine and tap these spacers for MFI injectors instead. and using long studs or bolts, mount the throttle bodies on top of them. etc.

Regards,

Al

[haycait911]

hi Al. I looked at the 930 spacer blocks, but I seem to recall that they're quite limited as to bore size. 32-33mm?

[stownsen914]

Originally Posted by haycait911

hi Al. I looked at the 930 spacer blocks, but I seem to recall that they're quite limited as to bore size. 32-33mm?

I think you can bore them out to about 38mm or so. I had the same idea, to use them with some MFI throttle bodies, but I need to bore them larger than 38mm so they won't work for me after all. So I have a set for sale. PM me if you're interested.

Scott

[al lkosmal]

Don,
The set of spacers I have, have a 36mm bore and it looks like they can go out to 40mm or so and still provide a sealing surface. The bottom opening of the 69S throttle bodies, which would be the mating surface to the top of the spacer block, is 36mm......which would mate up perfectly.......or they can both be bored out a little, if desired.

Regards,
al

[356RS]

The 930 injector blocks/flange is a good idea. I think the early ones were made of some sort of heat resistant plastic and would crack when bored more than 34mm. The improved ones were bakelite/phenolic and could be bored out to 36-37mm like Al said. Better yet are the aftermarket aluminum ones that someone makes, can't remember who, that most likely could be bored out to 40mm?
Just remembered who makes them, Turbo-Kraft, offers size's from the stock 32mm to 41.5mm. They come with a phenolic insulator spacer for heat blocking when used in turbo applications.

[BURN-BROS]

I made a few sets of injector spacers for a 3.2 head. Keep in mind that if you put them on a normal head, the relationship between the crossbar and the MFI pump will change significantly. You would have to verify before moving forward.

[r lane]

Don, I am in the process of doing a similar project. Would like to know who did your pump. I have heard it can be done, but have'nt found anyone who has done it. I plan on making a reciever block between the head and and the throttle body to locate the injector. I may have to trim a bit off the intake spigot of the head, and the reciever block will be 12-15mm deep. Havn't mocked anything up yet, but I believe that will work. Would like to hear back from you. Bob Lane