MFI questions

[Zeke]

I'm going to buy the FI book from Pelican. But before it gets here, I have a couple of questions to toss out.

I guess I figured that MFI was MFI until I began to read about slide valve vs. butterflys and different space cams for different size/cammed engines.

So is an MFI setup off a say a 2.4 T not anywhere the performer of the MFI off an S? Can said T unit be made to run with something like a higher compression, bigger cam RS motor?

[Tim Walsh]

yes can rebuild your T MFI pump so that it will work well with a larger motor and different timing. But you will have to get it rebuild and have a new spacecam installed.
just my uninformed $0.02 others will know much more than I

[Bobboloo]

As Tim pointed out a T injection pump can have the space cam swapped for an S type. Also, have you checked out all the info in the Pelican tech articles on MFI. The bible for MFI (Check Measure Adjust ) is there and you can download it.

[Tyson Schmidt]

Like others have said, you can swap the space-cam in the pump to an "S" space-cam.

But the expensive part is having the throttle bodies opened up to "S" spec. to match the pump. It's about $1000. Then you'll need "S" intake stacks. You can buy the "S" stacks, or find a set of early magnesium stacks and have them enlarged.

And then there's the port size in the heads. You'll have to enlarge them to 35mm. About $300 for a macine shop to do that if you bring them the heads.

[jluetjen]

Slide Valves and "High Butterflys" are pretty much for pure race engines. Slide Valves are cool because at WOT they don't have a shaft running through intake like a butterfly system. Barrel throttles have the same benefit. I believe that the downside of both of these systems is that they can easily jam if dirt gets into the mechanism. Not a big deal on race engines which are kept clean and often rebuilt - but definitely a big deal on a street engine.

I'm not sure what the deal is with the high butterfly systems except that I suspect that it optimises the system around a certain harmonic or something esoteric like that. Unless you have an engine engineered to be optimised for the same set of parameters as the high butterfly system, I doubt that it will do anything noticable for you compared with a properly optomised stock style MFI system.

In order to make things like high butterflys work better then a stock style system, you generally have to spend quite a bit of dyno time figuring out the correct recipe.