Head porting & cam question

[wirihana]

I recently purchased an early aluminium engine case, and the vendor has offered some other parts that he has,


"a complete set of 1974 heads, ported to 39.5 intake and 35 exhaust (original porting and flow bench work done by Fumio Fakaya – Ferrari f1 master head builder)
906 Cams
930 Oil pump"


I have a set of mahle 90mm 10,4:1 P&C's and was planning on a 2.7 twin plug DC-40 build for my 1969 911. I have not bought any cams yet, and have a stock set of '74 heads I was going to twin plug and port to match the cams I decide on.


My research suggests that:


The 906 cams in a 2.7 will still be too peaky, and make no sense if i want to keep the 7300 redline for the 70.4 crank;

the 39.5 ports are too large for a DC-40 (or even slightly hotter cam);

and a 4 rib pump would be sufficient for my needs.


Is this correct?

your advice/thoughts please, what sort of build would those heads suit?

Thanks (and stay safe!)

Nathan

[lvporschepilot]

Your research is indeed correct, only with that setup I might go to a DC44 or DC60. That setup will run very well.

[jpnovak]

Did they give you flow data?

So... Flow data will be CFM (or other volume/velocity) vs valve lift. Size the cam so that the lift (intake and exhaust) match the flow data curve. Too little lift and you can not take advantage of the airflow. Too much lift and you are stressing the valve train.

Then pick duration of exhaust lobe to match your desired peak torque/HP. This will define the driving characteristics. Too much duration and the peak power will be in the upper rpm range. This hurts low-end torque and can make the car more difficult to drive on the street at low rpm. Of course, gearing and car weight are huge factors here.

Then match lobe center to your induction system and compression ratio. Dynamic compression is a big part of the equation for safe cylinder pressures.

A good cam shop/engine builder will help with this.

[roblav]

25 years ago, I built up a 2.7RS type engine with webers. Porting was done professionally to your sizes. 8.5:1 with S cams. What a sweet engine... driving characteristics were like a 2.0 Solex engine but with more grunt. Your compression is higher, so you'll likely need a cam more aggressive than S. Maybe a Mod S not quite to the 906.

[stownsen914]

39.5 is on the aggressive side for an intake on a 2.7, but as stated it all depends on the flow.

A 930 oil pump is a great pump but not really necessary for a smaller bore normally aspirated engine.

Re: cams, it's generally accepted that more modern grinds will give a more usable power band than 906 cams will.

The early alum. cases are very stout for a small bore motor, but make sure it has the updates done to it or you'll spend a small fortune in machining. A few that come to mind: oiling updates, piston squirters, updating to use the later style layshaft (unless the case comes with one of the hard to find early layshafts), updating to use the later style chain boxes (unless it comes with a set of the early ones). Also check whether it's been bored for the 2.7L cylinders if that's what you're doing.

[wirihana]

Thank you for your replies,

Jamie, I have read your build threads over the years, really great work!

I will ask if he has any flow data, and see if i can gather any other information. Otherwise i will pass.

I have DC-30 cams in my current engine, (2.2 S pistons on a 70.4 crank, PMO's) so will probably end up contacting John to choose a cam, and go from there to get some heads made to match to his specs. His DC 43-102 carburetor type or DC 44 look interesting.

It is a pretty standard, old school build (2.7 carb'ed twin plug) so not looking to re-invent the wheel, but want to do it properly. Longevity and reliability are key, hence the alloy case and Mahle P&C's as a starting point. The case has been bored out by Ollies, piston squirters, intermediate shaft bearings, and oil bypass update all performed, It comes with its original shaft plus chain boxes and covers, so I can use those or update the studs to use the later versions. I think I can use later mag. covers on those early boxes for pressure fed tensioners?

Apparently the case was originally built up for a Socal driver who auto-crossed his '67, and didn't want these updates done on his original case.

Lots of decisions still to make, especially on which twin pug system to use. There are so many options today. I want a distributor, not COP. I would like to maybe ditch points and be able to program/map an ignition curve. Another thread for another time I think.

Thanks again for your comments.

cheers

nathan

[stownsen914]

Yes you can update to use the later chain boxes. I believe the later tensioners don't fit the early boxes.

[drgouk]

Fumio is a very famous Cylinder head porter from Riverside, orginally worked for Joe Vittone at EMPI in riverside porting VW heads. He is now retired. His VW heads always comand good prices.

[wirihana]

received this message from the vendor, which sounds promising,

"Will look up the flow data on the heads and forward to you.

Engine was originally built for an autocross car and we did not use the 906 cams. We used a cam grind for a 993 called super sport which is essentially a higher lift version of the early solex grind.

Heads were designed for a power band between 4,000 and 7,000."

Did a quick google search on Fumio, He was referred to as a "headsmith" of HP aircooled VW heads. pretty neat stuff.

[Reuben.L]

Sounds fun.
We have a JB racing twin plug dizzy at work that might do the job. Would need to check what case it fits for you on monday. Its unused, was supplied as part of a project but wasnt correct.

Reuben.