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Quote:
Originally Posted by jpnovak View Post
I bored some MFI stacks recently. I ended up with a straight bore. I could not fixture the stacks well enough to cut with taper ream. The ream is the easy part. I just did not have enough room to jig the parts. I could not cut the taper by hand. Just some downward pressure on the ream due to tool weight was enough to prevent me from taking a cut.

The drill on an extension worked well. I cut in 2mm steps out to 38mm. be aware. That plastic (phenolic) is really hard and will bind easily. It will heat and expand at the cutting edge and then contract behind it binding the bit.

The throttle bodies are basically a plunge cut followed by a blend with a flap wheel.
Thanks for that - it does certainly seem to be some "unobtanium" plastic. So impressive to me that Porsche was using plastic intake manifolds in 1972!!! Obviously they injection molded the entire thing, no machining done post molding.

My backup plan for the stacks is a straight bore, then carbide burr or flapwheel to get a bit of taper. The taper is so slight that the real world difference is likely negligible.
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Old 12-12-2018, 08:43 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #401 (permalink)
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Wurth Rost Off Ice

A little side note, a few hints for stripping the throttle bodies down, an .8mm tip snap-on screwdriver bit is the only way I can remove the screws holding the throttle plates. It's an exact, tight, fit, after bead blasting the heads of the screws to clean off the carbon deposits. And the only way these are coming out without destroying them. They are irreplaceable!!! Try finding a 4mm x .75 pitch screw anywhere on the planet!

Also pictured is Wurth Rost Off Ice, which really works well for getting the 6mm studs out - I'm heating the throttle bodies to 350f before blasting the studs with the Rost Off Ice which seems to "shock" them enough that they come out without issue using the snap-on collet type stud remover.

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Old 12-13-2018, 04:42 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #402 (permalink)
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Another Boring Post

So, here's my setup for boring the stacks. I had to build a boring bar (brazed a random hunk of carbide to the 3/4" tool steel shaft) to reach the depths of the stacks.

I have to laugh, looking at the picture. It looks so simple. Elegant, even. Let me assure you it is neither of those things!!!



If I was a better/more experienced machinist I would have foreseen some of the difficulties with this job. In fact I probably wouldn't have even attempted it. But now I have all these parts and tools so I have to keep going!!

Problem #1. The original plastic stack bore is not concentric with the throttle bore. Witness the carbon buildup on the bottom of the stack. Not an issue when there's a 6 or 7mm missmatch between stack and throttle, but I'm going for 38mm stack and 40mm throttle bore, so have to nail it pretty close.



Solution: the fixture I built has a hole that is concentric with the throttle bore, so that's my target, and I need to dial it in (literally!) with the indicator to ensure the hole in the plastic stack is where it needs to be, about 2mm closer to the middle cylinder than before. Rube Goldberg would be proud. I had to machine an adapter/extension to fit my indicator arm setup into my boring head, just to reach the bottom of the work envelope!!!!

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Old 12-13-2018, 05:23 AM
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Jonny, really appreciate your ability to convey your thoughts in this thread. It’s tough enough to come up with solutions let alone stop and document them. When all is said and done. And the car is complete. Only you will know the many hours of thought and care taken in all phases of this build. Your eye for detail is to be admired and resonates with to be sure many members. The pleasure one achieves in creating a unique look or custom piece for ones own satisfaction keeps my blood flowing.

Andy
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Last edited by acme911; 12-13-2018 at 10:01 AM..
Old 12-13-2018, 09:46 AM
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The angle of the dangle

I went through many pains to figure out the exact angle of the outside funnels in the stacks. Lots of headscratching and thinking and measuring.

I was going to try using the cones from my motorcycle wheel truing/balancing stand to center in the holes then measure the angle directly, but couldn't remember who I've lent it to.

Then I figured I'd take measurements top and bottom and figure it out using (GASP) trigonometry.....

F$#%^ that! I finally just set it up and centered it at the bottom, then the top, then the bottom again, then the top, back and forth until they were within .001" of each other.

The result was anti-climactic:

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Old 12-14-2018, 04:49 AM
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Wow, that’s amazing what the heck you figured out there. I would know how to even turn on a machine like that. Nice work.
Old 12-14-2018, 06:09 AM
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Quote:
Originally Posted by acme911 View Post
Jonny, really appreciate your ability to convey your thoughts in this thread. Itís tough enough to come up with solutions let alone stop and document them. When all is said and done. And the car is complete. Only you will know the many hours of thought and care taken in all phases of this build. Your eye for detail is to be admired and resonates with to be sure many members. The pleasure one achieves in creating a unique look or custom piece for ones own satisfaction keeps my blood flowing.

Andy
It's all about the getting there!!! Glad you're enjoying it as much as I am.
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Old 12-14-2018, 06:27 PM
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Success!!

The first complete test bore/ream of a plastic stack complete. Need to work out a few bugs but it's not bad. Got a nice even, concentric, 1mm step from the throttle bore to the stack. Not easy! But the before and after difference is quite dramatic.







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Old 12-14-2018, 06:31 PM
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Quote:
Originally Posted by merbesfield View Post
Wow, thatís amazing what the heck you figured out there. I would know how to even turn on a machine like that. Nice work.
Thanks! I don't really know what I'm doing but it's coming along. I'm finding my cheapo drill press vise isn't up to the stress I'm placing it under so it's back to the drawing board for a fixture to hold my stack boring fixture at a solid 10 degrees.

While I ponder that I'm stripping my other set of throttles for rebuild. Lots of parts!!


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Old 12-15-2018, 06:36 AM
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Now you just need some IKEA style instructions to put them back together...

Awesome work and very inspiring!
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Old 12-15-2018, 08:31 AM
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Plated Parts

I've finally joined the yellow zinc club. Few things are as enjoyable as sending off parts and having them come back looking like new!



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Old 12-22-2018, 05:57 AM
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Lack of updates

My lack of updates doesn't necessarily mean a lack of progress, lots happening, but not much to share. Been fiddling with MFI stuff which I could write a book about. Luckily someone else has done that. I highly recommend:

PORSCHE 911
MECHANICAL FUEL INJECTION PUMP
1969-1973
A DIY STEP-BY-STEP GUIDE
Repair and calibration of the PED 6 KL... Mechanical Fuel Injection Pump At Home

By Michael J. Burgess

The book is every bit as detailed and descriptive as the title. I'm in the rebuilding phase, yesterday started re-assembling the pump. I mixed up the smallest batch of Gaurds Red Single stage ever and marked the middle of the 6 gear segments with my Loel-Corning Paint pen (a wonderful little device!)


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Old 12-22-2018, 06:07 AM
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The MFI pump is a wondrous and wacky device. The root of it, and how it works, is pretty simple, and it's this portion which you assemble first:



It's really just a variable displacement, positive displacement, pump. It's a miniature 6 cylinder, two stroke engine, operating at half crankshaft speed. One little piston pump per cylinder times 6. The piston rotates and has an angled top edge which covers a fuel supply hole earlier or later in it's stroke, thereby varying the amount of fuel delivered each time it pumps.

After some fumbling around I got all 6 cylinders assembled and the rack assembly working freely. Fascinating stuff.



The book has a few inaccuracies which caused me some pain - the instructions on winding the individual piston barrel springs are contradictory - the springs need to be wound clockwise in order to become tensioned clockwise in the case of 1-3, and counterclockwise for 4-6. In this manner they become more tightly wound around the piston when they are "wound up" and ultimately end up pulling the rack into the pump body (towards the drive end) when assembled.

There is no mention of when to tighten the gear segment clamps to the control sleeve. It has to be done.... I choose to simply eyeball them to midway travel and snug the clamps for a basic starting point. The book pictures the clamp screws for the gear segments facing the rear of the pump when they should face the front of the pump on both sides. Luckily I have a few spare pumps for reference!!



Another helpful hint - before you go any further than this point it would be wise to remove the delivery valves at the top of each barrel and look at the tops of the pistons - it would be really easy to get a piston 180 degrees out and not know it. It would be terrible to have the whole pump apart and have a dead piston!



Another final check is that you can hear the pistonS pump through the delivery valve (an audible "pfft") if you press the followers in and out by hand. The noise changes depending on the rack position (it disappears completely when you go to full lean) so in this manner you can test each piston for proper operation before committing to installing the regulator housing and camshaft.

Fun stuff!!!
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Last edited by Jonny042; 12-22-2018 at 06:20 PM..
Old 12-22-2018, 06:15 PM
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Very cool work there.
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Old 12-22-2018, 06:27 PM
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Bigger is better!!

My recent success with boring the plastic stack (hey, I've done one "test"....) tells me I can get a full 39-40mm at the bottom of the stack which has me thinking.... so I had some 42mm throttle plates made up. This is all the subject of a much longer post about intake tract dimensions and port sizes and camshaft profiles and MFI space cams and etc.etc.etc. but I'm pretty sure that even the 42mm plates are going to be the choke point in the intake.



There's more than meets the eye to a throttle plate. They aren't round, for one thing...



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Old 12-22-2018, 06:36 PM
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Agree with JPN....super cool. Reminds me of the excellent (yes) Alfa SPICA system. John
Old 12-22-2018, 06:39 PM
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Quote:
Originally Posted by jpnovak View Post
Very cool work there.
Thanks Jamie! As you know, I initially got bitten by the MFI bug when I set about putting together a set of throttle bodies to use as the basis for an EFI system using your adapters. So in a way this is all your fault

I am expecting to have untold troubles getting the MFI system (specifically the pump calibration) to work cleanly and smoothly but am convinced once it's dialed, nothing will be cooler, and it will be worth the trouble in the end.

EFI is also my backup plan Those 42mm throttle bodies should feed the 3.2SS with enough air for a reasonable amount of power!
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Old 12-22-2018, 06:46 PM
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Documentation Snafu. Or, how I learned to stop worrying and trust my own eyes...

I think I might have found the source of the confusion between clockwise and clockwise and left and right and up and down..... the left side of the pump is on the right side of the car.

Not of it really matters if you do exactly what they mean, not exactly what they say

From the factory Bosch repair docs:



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Old 12-24-2018, 06:35 AM
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Measure twice, bore once.

Finally got a set of throttle bodies that have six holes within .002 mm. Close enough!

These are 41mm with a 39mm bottom exit. I re-ground my carbide taper tool (thanks to my friend Stuart who gave me some tips) and am happier with the finish and the taper from 41 to 39.

Next I'll do a set of 42mm.

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Old 12-24-2018, 06:39 AM
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Like and thumbs up.
Old 12-24-2018, 07:16 AM
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