MFI Throttle Bodies Corroded

[kclem19]

I'm in the process of rebuilding my 72 911 t targa with the 2.4L MFI. My throttle bodies are corroded. I've bead blasted them and they are much worse than I thought. See pictures.







I was planning on converting to EFI using the MFI throttle bodies, but I think these are past the point of no return. The plan was to boost the compression to 9.5:1 with the 964 cam profile with megasquirt EFI. Now that I've uncovered how bad my throttle bodies are, I believe my options are:

1. JB weld the TBs and get them "good enough"
2. Attempt to design and fabricate my own thottle bodies (my friend is a machinist) and copy the style of the PMO TBs
3. Find a set of old carbs and rebuild them
4. Purchase PMO TBs (which I'm hesitant to do because I've already got the heads re-worked and I only want to buy PMOs once. Therefore, I'd want to by a bigger throttle bodies and port the T heads to match if I go with PMOs, but thats going to blow my budget or can the PMOs be ported relatively easily in the future?

The engine will also have the following:

• 4 rib oil pump
• case savers
• oil bypass mod
• hydraulic assist cam chain tensioner upgrade
• 85mm 9.5:1 JE Piston with Biral cylinders
• 72 MFI T heads rebuilt
• cam profile TBD

Any thoughts?

Thanks,
Kelly

[HawgRyder]

If your machinist friend is up to it...you could bore out and sleeve the throttle bores.
He could make you aluminum sleeves for the throttle shafts (bore out the old throttle shaft bore and then press in the new ones so that the new ones are larger diameter on the outside where the spring goes..and have the correct ID for the throttle shaft).
These would need to be "stepped" to work properly.
The end result...new throttle shaft bores...and a nice clean main bore of the correct size.
He could also incorporate a space for an O-ring to prevent shaft leakage.
Bob

[The cap'n]

Rather than spend what could be an amazing amount of money reconditioning what you have, you might want to try to find some good repairable TBs from a boneyard, a private party, or some place like Competition Engineering in Lake Isabella, CA. (That last because I think he has some ...) If you're not in a rush, any good Porsche swap meet should have some for sale by one of the vendors.

The Cap'n

[kclem19]

Originally Posted by HawgRyder

If your machinist friend is up to it...you could bore out and sleeve the throttle bores.
He could make you aluminum sleeves for the throttle shafts (bore out the old throttle shaft bore and then press in the new ones so that the new ones are larger diameter on the outside where the spring goes..and have the correct ID for the throttle shaft).
These would need to be "stepped" to work properly.
The end result...new throttle shaft bores...and a nice clean main bore of the correct size.
He could also incorporate a space for an O-ring to prevent shaft leakage.
Bob

What about getting two sets of street bike throttle bodies? I can make an adapter between the heads either out of aluminum or 3D printed (if there's a robust enough plastic to hold up). Velocity stacks could be 3D printed as well.

There are a few options with throat diameter (38mm, 46mm, 52mm) using the GSXR throttle bodies that are separated so the 4th off of each pair can be removed. I'd want to keep the other three with the original spacing so the throttle linkage wouldn't need to be modified.

Thoughts?

[kclem19]

Originally Posted by The cap'n

Rather than spend what could be an amazing amount of money reconditioning what you have, you might want to try to find some good repairable TBs from a boneyard, a private party, or some place like Competition Engineering in Lake Isabella, CA. (That last because I think he has some ...) If you're not in a rush, any good Porsche swap meet should have some for sale by one of the vendors.

The Cap'n

I'll check with Competition Engineering.

I'm located in south Louisiana. Are there any swap meets within 250 miles of New Orleans?

Thanks,
Kelly

[HawgRyder]

There are several ideas on ITBs....do a search on here for them.
Using them will set your engine apart from stock...so...if you don't care about "original" looks...go for it.
If..on the other hand ...you want it to look original...your choices are limited...rebuild what you have ..or like the Capn says...find good used ones.
There are several companies that make parts for carbs that can cure some problems for you...like needing a slight overbore to clean up the surfacces.
Holley carb company sells new throttle plates in many sizes...so if you have to overbore you might not need to sleeve back to original size.
Good luck with the project.
Bob