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John,

There are a couple of variables that still need to be determined. These are:

1) Stroke. The current crank (66mm) had the journals ground and first oversize bearings installed in 1982. As soon as I have the engine torn down, all the journals will be measured for wear and ovality, and I also ordered a metric radius gauge to check the rod journal fillets. The crank was NOT re-hardened at the time so I'm really interested to see what 25 years and 20K miles have done. If the crank is serviceable the stroke will remain 66, if not I'll consider stroking to 70.4 if a good STD/STD and set of rods become available; and

2) Bore. Still can't decide whether to stay with the Biral 80s and have them bored to 81 and have JE's made to fit, get a set of Biral 84's, have them re-bored to 85 and have the heads cut to accomodate the revised sealing surface or go with something that's not original appearing, of which there are a couple options.

It seems somewhat strange to keep the small-valve heads just because the casting number is staring you in the face when you look at the engine from below and then do a cylinder that's not obviously original, as any modern cylinder (a Mahle Nikasil, for example) would be. Given the fact that I can't use external oil cooling for originality's sake I'm leaning toward one of the first two options. . . but the temptation is strong. . . can't resist a bump in displacement. . . while you are in there. . .Help me Grady to resist!

3) Cams. I have really enjoyed following your work and thinking about the correct cam choice on a few threads here. As you say, the small-valve engine's 39/35 valves and 32mm ports can't flow enough to make the most of the Early S cam's higher lift, but the engine can benefit from greater duration and overlap.

Unfortunately, a cam with LOWER lift and longer duration is basically the opposite of the direction in which modern cams have evolved. It seems that the trend is to wider lobe separation for reduced overlap, more lift and greater duration still. If you look at, for example, the DC22, here's how it compares to the Solex and the Early S:



4) Pistons. Since the heads will remain the early deep 2,0 profile, perhaps a lower static compression ratio, basically less piston dome area, would be helpful at ensuring flame front propogation, and a higher dynamic compression ratio in the form of reduced overlap would be a better compromise?

This is a street engine so I would have no problem taking my foot out of it about 6800 RPM, which is the same place my 2,2E starts making noise instead of power.

Decisions. . . decisions. You just know I'm going to HAVE to take this to Peter Dawe for a dyno run once it's built.
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Last edited by 304065; 01-23-2007 at 03:01 PM..
Old 01-23-2007, 02:41 PM
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Quote:
Originally posted by john_cramer

4) Pistons. Since the heads will remain the early deep 2,0 profile, perhaps a lower static compression ratio, basically less piston dome area, would be helpful at ensuring flame front propogation, and a higher dynamic compression ratio in the form of reduced overlap would be a better compromise?
John; That's a very interesting way to look at it. I think that what you should really be interested in is the valve closing point, which is more a function of the Lobe Angle and the duration. You could also take a look at the cam timing, and when combined with the other variables, advancing the cam a touch so that the intake valve closes a little earlier. It would be interesting to get Steve Weiner's or Henry's (does he still post here?) input on that idea.
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Old 01-23-2007, 03:53 PM
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John,

As a starting point I need some data but I can't seem to find it without direct experimentation.

Bruce Anderson says that the 64-69 combustion chamber is greater in volume than the later one, so that when you use 84mm cylinders with 2,0 heads that have been cut to fit the later cylinders, you end up with a compression ratio decrease of approximately .4 of a point.

I know it's obvious but it helps me to visualize it: the deep bowl requires a correspondingly high dome to maintain the compression ratio, which is why the combustion chamber ends up divided in half. The flatter and wider chamber in the 84 lets you run a lower dome on the piston that doesn't split the chamber as much.

edit: Later in Bruce's book when he's running through the compression ratio calculation, he says that 2,0 heads cc between 70 and 75cc.

Where this is all headed is, could you use piston that's had the dome cut down to take the peak off, and still realize a compression ratio around 9:1, which coupled with less overlap, would give you a better flame path.

But to figure that out we'd first need empirical dome measurements for a 911T, 911E, 911S and 906 piston. Just backsolving from published compression ratios isn't enough to start spending money!

The other question that comes out of the discussion is whether reduced overlap has any effect on head temperatures-- I remember reading somewhere that the incoming intake charge was used to cool the exhaust valve on a high-overlap engine like a 911S. I suppose Camgrinder could comment on that one.

BTW, teardown has begun, just ancillaries so far but the real disassembly begins in the next couple of weeks. . .
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Last edited by 304065; 01-30-2007 at 05:13 AM..
Old 01-29-2007, 09:17 AM
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Well, here are some theoretical data. . . dome volumes backsolved into the published compression ratio and Bruce Anderson's estimate of the 2,0 liter head volume, at the high end of the range, 75cc.

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Old 01-30-2007, 06:22 AM
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John,

I have been following along with interest your, John L’s and others discussion. Lots of good ideas.

Here is my 2˘.

I’ll offer encouragement to keep your engine exactly stock and as original. That might even include finding a std/std crank and every little show detail – like CAS’s 911.



For playing, get another engine. With some effort I suspect you can find another 901/05, or at least a serviceable 901/05 case. This allows you to do all the “invisible” mods that will give great performance and multi-100K longevity.

The case can be bored for 90 mm cylinders and clearanced for good windage. You can install the oil bypass and piston squarters. With some original Solex cams you can use the 935/911SCRS double cam oiling. A GT3 oil pump will fit with minor mods. Update the case for jack-shaft shell bearings.

Using the Nikasil 2.7 RS P&Cs with a 70.4 crank & rods and 2.2/2.4/2.7 heads will give you 8.5:1 CR so it will run on almost anything called gasoline.

The 1.83:1 Turbo fan configuration will negate the need for a front oil cooler in most situations. The “Rubbermaid Solution” is ideal for track use.

You can do all of this and appear to be stock. You can even twin plug it and have it not apparent to anyone but the most observant.



With your 2.0 rebuilt and setting with assembly lubricant, it will have a long shelf life. You can also get it broken in again and carefully preserve it for storage with no effect on its functionality.

You can do the same with the original transmission.

The nice thing about your 911 is you can swap the drive train in a 3-hour Saturday morning.

Best,
Grady
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Old 01-31-2007, 08:39 AM
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Wow. What Grady said! Of course, that's easy for me to say since t's not "my" money, but it sure gives you almost everything you want, and perhaps, gives you a bit more latitude for creative hp ideas.
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Old 01-31-2007, 10:11 AM
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Grady, thank you as always for the sage advice, that was just what I needed to keep it original!

I may depart slightly from your recommendation in the area of the pistons, however. Modern "slipper skirt" designs have a great deal less friction than the old 901/01 style with the oil ring below the pin.

Fortunately, I have a "platform" where originality is not an issue-- a 1971 fully prepared race car with 911R-style oil coolers, 901 ZF LSD that is absolutely prepared to the limit of the rule book for PCA club racing. If I were to spend time and money doing a "fun" engine I would strongly consider reclassing the car as a 1973 2,4 S at 2369 pounds or a 71 2,2S at 2249 (my current race weight).

Thanks for following the thread. I have a companion thread with some photographs of the teardown of the engine.
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Old 01-31-2007, 10:28 AM
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John,

Is there a Mahle Nikasil P&C set with 3-ring slipper skirt that will fit your needs? That is the key for low friction and longevity.

How about another approach; build a rule-complying spare for your track car (“2.2S”). Make it where it is a dead ringer (visually) for your stock 901/05. Convert the race car engine wiring, etc. where the engines swap into the ’66 without any change.

This way you have both a spare for the track car and a hotrod for the ’66 and all are easily interchangeable in a few hours.

Best,
Grady
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Old 01-31-2007, 04:20 PM
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Grady, now that is a GREAT suggestion.
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Old 02-01-2007, 06:53 AM
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WOW - This thread is out of my dreams.

I was just asking on Rennlist and elswhere about this same exact thing.

I have a 901/05 that was rebuilt with Mahle 2.2 P/C's but that is where the record ends (maybe the same guy worked on our engines John : )
I assume ( prob making an as- out of u and me ) that they are the original heads as the only mention is that the heads were fly cut - there is a note of new valves but no size or part #.
Solex cams and 40 IDA's with 30 mm venturis and 125 main jets.

Lots of lovely torque there but missing the top end.

Where to go from there ? - 32 venturis and 130 jets to start.
Everything Cramer is concerned with also is my concern:
As stock as can be , mostly street use. Not bigger - but nastier.

I was also very intrigued by the 2000 Rally option (the 901/30) but since I already have 2.2E P/C's I am thinking it might be more cost effective to look for 2.2 E or T heads ( ?)
For cooling - would an SC shroud fit ?

I hope this isn't too much of a hijack (bad habit that)

Maybe we can come up with two different but similar solutions and then meet at Lime Rock to see which works better ; ) you'll have to give me a head start though John.

Best:
John F.
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Old 02-17-2007, 04:28 PM
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Rennlist?

John,

If you crawl under the engine with a flashlight you can look up at the cylinder heads. If you see the casting number in the CENTER of the fins, and the number is R901.104.303.04 then you have original 2.0 heads. Or for a '67, 901.104.305.02. If you see anything else, like the number off to the side and smaller, that means you have heads after 1968, when they started using air injection into the exhaust ports for emissions controls. When they did that a casting boss was added and the part number moved. A 2,2 head will have a "911" casting number prefix, a dead giveaway.

The "nailhead" valves are quite a limitation to making power. We can see that the 901/30 used 39/35 valves and 32mm ports and only made 150 HP with 9,8:1 pistons and S cams. That is, obviously, 10 HP less than the "S" with the larger 42/38 valves and 36/35 ports (for '67-68). As John Luetjen pointed out, no torque curve was ever published for the 901/30 engine so we can only guess as to how well it worked. However, the curve for the 2,2 E is well known, which is basically what a Solex-cammed 2,2 conversion is, albeit with reduced horsepower due to the lack of MFI.

As you probably know the sealing surface was changed when the 84mm cylinders were introduced. So when the heads were "flycut" this is what was done. Here is a picture (thank you Henry Schmidt at Supertec) of a '66 head cut for a 2,2 cylinder mating surface.



You COULD use an SC shroud but it would be far better to get one from Damon at Series 900, he makes ones without the cutouts for CIS injection with the channel and deflector in place. Some say it makes a difference, others don't, until I try both we can only use what the factory did to guide us.

Lime rock? The only time this car will ever see that track is when I go to work the radios for Colasante in his 964 cup. With no external cooling and the little brakes I would much rather use the '71 for Serious Track Work. But autocrossing is an entirely different story John. . .
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Old 02-17-2007, 05:11 PM
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I will crawl under and check - when it warms up a bit.
I will be putting on some SSI's so I'll get a good look then.

The note that they were flycut is what makes me think they were the orig heads.

Have you made a final decision on the rebuild ?

Yes, a 40 year old (stock) car sure makes that downhill interesting, and I was hoping I wouldn't need to use the runoff at the end of the straight -but was grateful it was there.

John
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Old 02-17-2007, 05:46 PM
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Quote:
Originally posted by Henry Schmidt
Imagine theis head with these cylinders.
81 mm Nikasil.
You mean for the flycut 2L ?
By the way, nice pic of that head. I (naturally) wondered what they would look like.

...and for pistons ? S ?
...S cams ? Those DC22's seem like a good one also with the E heads.

Henry - do you sell venturis for webers (and jets) ?
I looked on your site and couldn't find them.

Thanks;

John
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Old 02-17-2007, 06:25 PM
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Imagine these heads with a set of Nikasil 81 mm cylinders

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Old 02-17-2007, 06:30 PM
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Looks like I got "a head" of myself - or ahead of Henry anyway.

I didn't think you could go back down once the heads were flycut ?

John
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Old 02-17-2007, 06:33 PM
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Henry, What size are the ports and valves in that 2.0 head?
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Old 02-17-2007, 07:10 PM
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Valves 42mm in 38 mm ex.
Ports 38mm in and 37mm ex.
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Old 02-17-2007, 07:16 PM
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Henry, those are "S" valve sizes, did you start with an "S" head or a normal head and port from there? I can imagine that changing the seats is quite an operation.
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Old 02-18-2007, 05:52 AM
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I have some ideas........ how high do you want to rev her.......?
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Old 02-21-2007, 09:42 AM
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Juan,

This is a comparatively mild street engine for two reasons:

1) No external oil cooling will be used, 911s didn't get external coolers until 1969; and

2) The rest of the car (suspension, brakes) will remain original, hence I can't let the power-to-weight get out of hand.

I envision driving this car around town, up to the ALMS races at Lime Rock, to PCA Concours Events, to the East Coast Parades, and to some autocrosses. This usage pattern suggests that low-end torque should be my priority, not high-end horsepower.

So I think a realistic rev limit, using the smallest valves ever put in a 911 engine (39/35) and a brand-new set of factory valve springs should make for a practical "safe limit" of 7000 rpm. I would like the torque to peak below 5000 and the power to peak just slightly above there. Seven grand in an "F" second with a 7/31 and a 23.8" tire diameter should be good for 60 MPH, which is about as fast as I have ever gone on the autocross course, and then only at the larger one. Horsepower of 150 would provide a power-to-weight ratio of around 14.5 lb/hp, or right about where my '71E is, perhaps 155 which is around stock SC territory, slightly worse than the 13.64 of the '67S, but with more usable torque.

Fire away with any and all suggestions, I have progressed beyond teardown to inspection and measurement. Once those results are obtained and posted, the design will be locked and "purchasing" will begin.

I know you have EXTENSIVE experience racing and building small bore motors so I really welcome your input here. Thanks!
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Old 02-21-2007, 10:49 AM
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