The case for CFI

Everyone is in love with the GM TBI. Well, i got one and decided it would not be a good choice for my mod-log head because the base is too big and the spacing between the butterflies is too wide. Here is a comparison between the TBI gasket and that of the weber, which is what my head is presetnly configured for. As you can see, I'd have to make a funneling adapter to make it work. Plus, the clearance with the valve cover is questionable.


So I picked up a CFI unit from a 3.8 v-6. Now look at the weber gasket on the CFI gasket.

As you can see, the spacing of the butterflies is nearly perfect. What;s more, the placement of the bolt holes on the CFI and the Weber are different enough to make an easy adapter plate that won't leak at the bolt holes. Of course, if your head is already set up for a Holley, then this is a no-brainer because the mount is identical.

Here is a look at how the bottom of the TBI, the CFI, and the weber compare. this is a 32/36, but I'll be replacing a 38/38. The barrels on the CFI are about 39/39, but with much less venturi it must be capable of much more flow than the weber.


CFI v. TBI. Obvioulsy, the TBI can flow waaaay more than the CFI, and if I had an aluminum head I'd go TBI, but for a log head this should be ample.


Other views:






The "choke" unit. Actually opens the butterflies, so not a choke. More of a crude fast-idle device.


Here is a fast idle actuator. Won't work with the MS (although I'm sure there is a way using a relay or something). I think it is intended to compensate for A/C. Won't be using it.



In the hood clearance competition the Tempo unit wins. Probably a great setup for unmodified heads up to 150hp, too.

my buddy had a 96 ranger I think it was. the IAC motor was remote mounted on a block with some 1/2" hose running to it sorta like a bypass around the thorttle body. just and idea (to avoid the "high idle" deal on the CFI)

I dont know that people are that in love with the gm stuff its just the most common TBI system out there since they used it for 15 years which included 9 years on every truck and suv they made.

Seems like DIY makes a aluminum block that takes a more common IAC stepper. Its just then plumbed in with hose. Problem is on a TBI you need to be careful that you have the throttle blades open far enough to let the fuel past. This is likely the reason the earlier ones used some method of opening the the throttle rather than a bypass like the GM's and MPFI systems do.

Interesting suggestions on the idle circuit. Where would this plumb into? Somewhere after the TB? Perhaps a hole in the adapter plate would suffice?

Voila:
http://www.diyautotune.com/catalog/cust ... -p-69.html

An hole in the adapter would work fine. You want something fairly central, between the bores would be best. If it was more to one side it would tend to lean out that side more than the other. The inlet side needs to be plumed in after the air filter or needs its own air filter.

For those that dont know what we are talking about here is a link:
http://www.diyautotune.com/catalog/cust ... -p-69.html

Any suggestions for a cheap and cheerful bonnet for this thing that will allow me to route a cold air intake would be welcome. I like the chrome options like those from spectre, but these, which are among the cheapest, are still pretty pricey.

http://www.summitracing.com/parts/SPE-98499/

note: the CFI TB uses a LARGER opening aircleaner housing. so be carefull picking a housing.

also some of the smaller bodied 5.0L FPR will fit the CFI (with a little grinding the bigger billet ones will too)

a simple solution is to make a block off plate and drill/tap the upper housing for NPT threads and run the fuel line of your choice.

Fordconvert, do you think I could lose the goofy choke device by using the Jeep IAC stepper as you suggest? That would make a cleaner installation and less stuff to adjust. I just get the feeling that choke is one of those things that would never quite work 100% right.

I would assume that jeep setup would work but unless you get the steeper used the cost will add up. You are likely correct that you will never be happy with the function of the existing parts. You may get it to work but then conditions change and it may not work right. My current setup is running with a on/off solenoid that just bumps the throttle open slightly and it works fine. It was the stock option that came with the holley throttle body I am using. Many 70's carbs had such a device to either kick up the idle for AC or as a anti dieseling fix. Maybe a trip to the junkyards to look for one of those if money is tight?

stepper motor $35, adapter $65. not too bad for computer controlled idle.

$35 must be why they choose to make it for that one. The ones I have had to buy have been closer to $100.

doesn't the CFI have a PCV port on the base? you could run a 1/2" or so hose to a remote ford IAC pretty easy that way.

interesting suggestion xflow. I have two, and one has it and one doesn't. I'll take a closer look, though.

I had a 3.8L CFI that had JUST the dashpot (solenoid) one

5.0L had that AND a VAC one on it (the goofy choke with thermal element)

I would think if you have a fair weather driver you don't need it too much. a year round into freezing temps might though.

I drove my chokeless Turbo setup a whole IL winter (down into the teens) I would just hold it on high idle while it warmed up. Your EFI will handle any temp based fuel enrichment and the high idle should only be needed for a minute or so until you get some heat in the cylinders. I was looking at using my manual choke on the car to do it. No wiring and pretty much free.

Yeah, I still have the manual choke cable in place, doing nothing. using that would be a nice retro touch to my fi system. Real hot rod.

Just wondered if there was any updates on this project.