Christmas Build, 3.2 Short Stroke, 10.1 CR

[snbush67]

I hear ya. Yes, the spun rod does seem to point to lack of oil, yes, I plastigauged and measured oil clearance.

Maybe installing oil restrictors, still not sure. I do know that there have been a slew of camshafts getting ruined, pitted, grooved etc.

[snbush67]

Ran into an issue installing the clutch on the flywheel. The clutch mounting bolt holes on the flywheel are only partially threaded. I will probably just tap them the rest of the way. I think I will ask for a partial refund.

[snbush67]

The twin plug distributor cap adaptor is looking good. I’m still waiting for the cap and rotor to be delivered.

[snbush67]

Finally got the parts in I was waiting for to finish up the twin plug.

[snbush67]

While turning the engine over by hand I noticed some vibration, sticky rubbing when turning very slowly. The light lube I had given during assembly didn’t hang around for six weeks, so I planned to take the motor apart to lube everything again.

Then I decided that perhaps I could just fill the sump with fresh oil and turn the motor by hand, generate enough power to get the pump working. Well, it worked. I used three quarts of oil and it smoothed out immediately, and after three turns the spay bars started oozing oil.





Moving forward with the installation.

[Henry Schmidt]

Originally Posted by snbush67

Finally got the parts in I was waiting for to finish up the twin plug.

Having built and run dozens of these types of twin plug conversion, we always come up with the same conclusion. The rotors are out of balance and present way too much load on the top shaft bushing. Porsche's resolution to this situation is a support bearing.
Below you have my solution.

[snbush67]

Originally Posted by Henry Schmidt

Having built and run dozens of these types of twin plug conversion, we always come up with the same conclusion. The rotors are out of balance and present way too much load on the top shaft bushing. Porsche's resolution to this situation is a support bearing.
Below you have my solution

I should have expected that you would design something so strikingly similar to the Cloud City catwalk.

I was thinking I may be ok because of two things, my shaft is shorter because the adaptor adds only about 3/4” and that the top rotor track is such that it rides in the groove in the cap which keeps the rotor aligned.

I do see how I could fit a bearing and support though so I’ll probably do that. It looks like yours is a bolt on piece. Is it available as a separate piece?

[Henry Schmidt]

Originally Posted by Henry Schmidt

Having built and run dozens of these types of twin plug conversion, we always come up with the same conclusion. The rotors are out of balance and present way too much load on the top shaft bushing. Porsche's resolution to this situation is a support bearing.
Below you have my solution.

When I posted that picture I misspoke. The distributor I posted was a development between Aaron Burnham and Supertec. Gen I.
Aaron may have some of those bearing plates.
Our Gen II distributor uses a slightly different design. Mounting and bearing plate incorporated in a single piece.

[snbush67]

Thanks Henry. I will take your advice and figure out a similar solution.

[fabracadabra]

Replacement electrical panel looks good. Are the switches to isolate and run just one ignition or the other?

[snbush67]

Originally Posted by fabracadabra

Replacement electrical panel looks good. Are the switches to isolate and run just one ignition or the other?

Yes, they are for one or the other, for tuning and diagnosing. I don’t plan on running on one ignition. Initially I planned to use a single three position switch for upper, lower, or both but that got too complicated, so went with simple on/off switch for each.

[snbush67]

It’s running very smooth. I’m pleased. I have a little more work to do before a road test and tuning.

[snbush67]

Took a quick shakedown drive. Running very rich but smooth. I left the jetting the same but changed the chokes to 40’s.

The timing is set at a basic curve no map set up yet.

PMO 46 on normal height manifolds/40 chokes/ F11 tubes/ 187 Fuel/ 187 Air/ 57 Idles.

12.3 at idle 950
11.4 through 2800
11.8 through 4500
12.2 - 12.6 through 6000

I think 40 chokes are right. I will go up to a 190 or a bit higher air.

[PeteKz]

Well, how does it feel?

My guess is that you can add 5 degrees more timing, all in by 3500.

[snbush67]

I did add exactly 5 degrees. I have a vacuum curve too but turned it off for now. I dropped the fuel jets down to 175, still rich but getting closer.

Feels really good. Spins up effortlessly, really smooth all the way through. Good oil pressure and coolers are working great keeping the temps down, so I don’t have to worry about rpm temperature control. I think that the 40 chokes are going to be perfect, plenty of torque down low and it certainly isn’t lacking anything up top. I’m really hesitant about pushing it too hard, after the last build and the rod bearing incident, every little rattle, ping and tick has become amplified.

The twin plug is a game changer, the idle is as steady as I have ever heard, even dialed it down to 700 rpms and it doesn’t miss. I did switch between running both or top and bottom and there is a drop in rpm’s when switching from both to one, but no difference running the top or the bottom.

Much more tuning to do. I’m still working my day job full time and I can only afford about an hour on afternoon tuning drives in a 110 degree air fryer.

[snbush67]

Took an evening tuning run and did three jet changes, I’m creeping up on the right blend.

I’m tuning from slightly rich and every change gained a few points towards perfection as evidenced by smoothness, torque and horsepower.

I’m sticking with the F11 Etubes, they have shown a repeatable steady progression from cruise to redline.

The AFR goal is 12.8 idle to redline. Thats never going to happen with carburetors. Rules are to finish at redline no leaner than 13.2.

Here’s where I’m at;

Fuel. Air. Light Cruise. Redline Finish.
175 190. 11.3 12.2
175. 200. 11.5 12.4
175. 205. 11.7 12.5
175. 210. 12.3. 12.7

So the next jet change is a 220 air. Stay tuned….

[Old H2S]

That is golden information..

[fabracadabra]

The engine bay looks soo good, very tidy.

Kudos

I didn't know they made a 12 plug 123 distributor. Neat.

[snbush67]

Originally Posted by fabracadabra

The engine bay looks soo good, very tidy.

Kudos

I didn't know they made a 12 plug 123 distributor. Neat.

This twin plug 123, is my adaptation of the 123 single plug into a twin plug distributor. AFAIK this is the first. There is a company in Germany that makes a twin plug distributor and uses two boards from 123 in a single housing.

[snbush67]

Back to tuning……


F11’s ain’t going to work out. I went down the rabbit hole to the end and in I can’t get a decent light cruise AFR# without going way too lean at top end. I went all the way up to 260 airs and light cruise never leaned out above 11.8- 12.2 ish and would lean out to 14 at 5000 rpms, not good.

So now I have F7 and F2 tubes. And I am going to order some F3’s.