MFI Throttle Plates

Weissach911 · 12-30-2011, 02:51 AM

Does anyone know the mounting hole spacing for an MFI Throttle Plate (Butterfly) as I am just having some blanks for Weber and Zenith carbs waterjet cut and thought I may as well have some MFI type blanks at the same time.

Thanks

tadd · 12-30-2011, 06:41 AM

The mfi TBs should be the same as the head bore spacing which is 118 mm.

I've used that number to make a few things.

t

Weissach911 · 12-30-2011, 06:47 AM

I meant the two small holes that hold the throttle plate to the throttle shaft. somewhere around 18-20mm.

Sorry if this wasn't clear.

Shelby1710 · Shelby1710's Garage

Hi
I just happen to be rebuilding my throttle bodies. Carerra 2.7 1974 are 38 mm diameter choke and butterfly holes are 18mm apart. For my own curiosity, do the blanks need further machining with the waterjet cutting?
Hope this helps

Weissach911 · 12-31-2011, 01:47 AM

Thanks, this is the same spacing as a 40ID3C and a Solex 40Pl. The Zenith 40TIN is 20mm

The throttle plate angle is different on all the plates and I think are as follows:

MFI - 7 degrees

Solex 40Pl - 8 degrees

Zenith 40TIN - 10 degrees

Weber 40IDA3C - 12 degrees - 78 degrees in Weber Money.

I have made a fixture with pins to locate the plates in a lathe and will make 'blocks' to position plates at the various angles so that we can make all of the above throttle plates in varying sizes.

We will start with waterjet cut blanks and then lathe turn to the correct angle with minimum clearance.

Shelby1710 · Shelby1710's Garage

I would be interested in seeing your fixture, as I would like to make some replacement butterflys. Could you post a pic of the fixture. I would understand if you would rather not however. Its hard to find people that can do this in Aus.

Weissach911 · 10:52 PM

I haven't made the fixtures yet but will probably do so in the next weeks or two.

The plan is to make a bar of about 35mm dia with pins for the mounting holes pressed into place.

I will make the pins just small enough to clear the 5mm holes at the chosen centres.

The angle plate I hope to make as a 'loose' piece so we can use the same chuck component for one hole spacing set up but for more than on angle.

The other part we plan to mount in the tailstock of the lathe so we can clamp several paltes in the fixture and turn them all at the same time.

Sorry for the crude sketch.

I believe this fixture will turn the plates with the correct angle and the correct degree of ovality.

Shelby1710 · Shelby1710's Garage

Thanks a lot, much appreciated.

jm993rs · 08-05-2019, 06:37 AM

good thread

Trackrash · Trackrash's Garage

Too bad there was never a follow up on this old thread. I would love to see the jig and how it worked out.

r lane · 08-18-2019, 01:14 PM

I made a set of 40s for a track motor to go in MFI. A bar like you describe, but simpler as I was concerned with one angle. Bob

jm993rs · 08-19-2019, 04:05 AM

im now in this step ...... now need buy or create the plates for conversion the mfi low butterfly with :

hole head 40mm and hole for the stack in 42mm and I ¡´m not sure whats is the size exactly I need make for this .....

please whats is the suggestion from the gurus ???

thanks in advanced !!!

r lane · 08-22-2019, 04:52 AM

I purchased a sheet of brass, Metal Suoermarket I think. Decided the thickness I needed prior to order. Took a hole saw and made 6 discs slightly larger than I needed. The mandrel that the discs will be bolted to can be steel or al. Mill the angle on the mandrel end and index the two holes and tap them at the same angle. All of that has to be very accurate, otherwise the holes in the discs will not be centered, making for a bad fit in the throttle housings. Bolt on the discs and machine them to what ever size you require. Bob