Getting A Head

[Mr9146]

A complete set of early mechanical injection heads recently passed through my hands. I copied down this information:

Production Date: 8/66

Part # R901.104.304.05

I have some information on their history, but I am always looking for more. What can you guys tell me? Eric911S, I expect you to chime in here...

Thanks, I'll add more info as I sift through the rest of the boxes...

[Flunder]

Marco:

If they were twin plugged, think those puppies were from a 906E - the version with the early slide throttles.

[Mr9146]

They are twin plug ... with the early peanut plugs.

[Flunder]

Marco;

The 906E used Bosch mfi with slide throttles. This one was owned by Cunningham, Zipper, Polak and is shown in long nose, short tail configuration as when it won Daytona in 1966. Nice!

I assume your heads had the early dome shaped combustion chambers, which when combined with the pop up 10.3 compression pistons required twin plugging in order to propagate a better flame front for proper combustion. The pop up on the piston effectively divides the combustion chamber into tow halves so having a plug on either side was the solution.

The 906 spawned all the good guy bits for the 911R: 906 center oiling cams, Marelli 12 plug dizzy etc. My other guess for the heads is 911R as they could be ordered either with MFI and the slides or alternatively with the 46s on tall magnesium 906 intake manifolds. With carbs, the factory rated the engines at 210 ps and with MFI and slides at 220 ps.

[Mr9146]

Tom, here's what I know about the heads:

They're twin plug (peanuts), MFI (plugged, but not welded), they have HUUUUGE intake ports, they were last used on a 1972 911ST 2.5 longstroke with carbs.

What threw me was the "R" in the part number ... I've never seen (noticed?) that before. Makes me think they are FACTORY hot-rod/race heads. My dad says that they remind him of the heads on his motor, and he knows for a fact that his are factory ST heads, but he's not sure of the part number.

BTW, was that 906 you posted once owned by Warren Eades?

[69Sman]

If you're gonna sell 'em, let me know....please....

[Flunder]

I think Gerald Barnes of Anaheim Hills owns that 906E now.

There are a couple of different factory ST head configurations for the different displacements: the 2247 and 2380 is slightly different than the 2492 and 2466. The former would use 38mm i and e ports, same as 906E and 911R.

On the 2492 and 2466 the ports are almost taken out to RSR specs: the intake and exhuast ports would each be 41mm.

All of the ST heads would have the later more open combustion chamber shape and valve sizes of 46mm i and 40mm e.

When the ST heads were used with Weber 46s, the taps for the injection nozzles were plugged, as you describe.

The 906E and 911R head would have the smaller 45mm i and 39mm e valves and 38mm i and e ports and of course the more closed looking combustion chamber.

Put a mic on the ports and it may give us another clue.

Sounds like a nice set of heads!

[Mr9146]

Stacy - Thanks a lot! Now I'm a flipper

Tom - I really do need to measure the valves and ports to be sure, but the intake port looks to be 40+. The exhaust port, on the other hand, looks much smaller. The early casting date and the "R901" designation threw me off. If these were indeed on an ST I would expect to see a 911 part number. Any thoughts on this?

I will also take some pictures to supplement this thread...

[Flunder]

Marco,

Yes, I agree that ST heads would most likely have 911 part numbers.

The ST race spares manual, the "april 70 SPARE PARTS LIST" shows the cylinder head part nbr as being 911.104.033.01 so I think your heads are more likely from the 906E or 911R or TR era.

No one left things alone for long so the intake ports might well have been enlarged from the original 38mm to 40mm (and matched up with the intake manifold ports) after these heads left the factory. It was/is not uncommon to open up the ports on the intake side only, leaving the exhaust ports a bit smaller to keep peak torque a little lower on the band.

The head pictured is supposed to be a 2.5 ST head (but may be a modified series 911S head). However, you can use the photo to compare the combustion chamber shapes to see if yours have the earlier more dome shaped chambers or the later more open 2.2/2.4/2.7 shape like the photo.

The engine photo is of a longstroke 2.5 (86.7x70.4) that has the 2492/2466 version of the ST heads with 41mm intake and exhaust ports.

[Mr9146]

The crank is definitely a 70.4 and the pistons are 86.7. That I know for sure.

The combustion chamber of the heads I have look much more domed ... the valves aren't as "splayed out" as they are in the picture you posted. In fact, the valves in the heads I have look smaller, too.

Hmmm.....