Early E/S Motor Rebuild Questions - Why'd They Do That?

[t6dpilot]

I have some questions about why my engine was built a particular way. Hopefully you Pelicans can help me understand "why'd they do that?" The engine is a 69E case with 2.2S pistons, cylinders, ect. The only things that didn't go 2.2L are the heads - they are 67S heads and were used because they were available at the time. It also seems that a 6500 RPM (?) limiting rotor was installed versus the proper 7300 RPM S rotor. Well, it cut out at just over 6k as if it were rev limited.

Additionally, the oil system was "updated" to include an updated pump and later model oil tank. External oil cooler in place, but not plumbed to front fender - stock location in front of engine. Finally, a mid year fuel tank was used.

My questions are these:
[list=1][*]Will I have detonation problems with the 2.0S heads versus using 2.2S heads?[*]Should I change to 2.2 heads in the future or am I good to go with the 2.0 heads? Obviously, I would like to keep it the way it is.[*]I bought an S dizzy rotor. Have not run it yet and am wondering if I could have problems with 7300 revs using a 2.0 head on 2.2 pistons/cylinders?[*]Can someone explain what an updated oil system is and why do this? Also, why the later model oil tank?[*]Any reason to use the mid year fuel tank other than increased volume?[/list=1]

Sorry, if my questions appear stupid. The car is a hot rod and I am still learning about what mods are done and why. Drivability, cost/value/fun factor, cool factor, maintainability, ect. I would ask the builder, but I would probably want to spend more time on the phone than he wants to spend, so I figured I would ask for your opinions and see what arises. Thanks alot.

[t6dpilot]

Whooopps, forgot the fuel delivery system - Weber IDAs

[304065]

My answers:

1) Just like in airplane engines, whether detonation occurs is a function of a number of variables such as timing, load, operating temperature, fuel octane, static and dynamic compression ratios and a bunch of other factors like carbon buildup, hot-spots on the heads that could cause preignition leading to detonation, etc.

That being said, the factory changed the combustion chamber size and shape in 1970. Whether they did that to facilitate the inclusion of larger valves, i.e. 46/40 vs. the 45/39 of the 1969 911S, or whether the later design was intended to facilitate better single-plug combustion, we may never know. What we DO know is that the 2,0 heads have a reputation for being "prone to detonation" and so people usually leave them alone, unless some rule requirement dictates that they use period parts. This second factor is exactly the reason why 69S heads are so expensive today.

2) A set of 67S heads is worth more than a set of 2,2 T or E heads and is probably close to a set of 2,2S heads. Unlike the 2,0 heads where the valve sizes changed as follows:

'64-68 "normal" 68T and L heads, 39/35 valves, 32/32 ports
'69 T and E heads, 42/38 valves, 32/32 ports
'67-68 S heads, 42/38 valves, 36/35 ports
'69 $ heads, 45/39 valves, 36/35 ports.

Now, with the intro of the 2,2 liter engine, all the valves were 46/40 and the ports were 29* for the T , 32 for the E and 36/35 for the S.

*Not what the charts show but I think Tyson measured and they were 29.

Anyway, you could get a set of "T' Heads and have them overhauled and ported and come close to breaking even on the sale of the 67S heads.

Of course it all depends on originality. In my own case, I can't have a non-original-appearing engine, so I am using the original heads. In your case, in order to use 2,0 liter heads with 84mm cylinders they must be flycut to accomodate the later sealing surface, so your current heads are useless to a restorer unless Henry's special conversion kit is used. But you would definitely find interest from the hotrod community.

Bottom line: Bigger valves flow better but not THAT much better. I wouldn't tear the engine down if that's the only thing bothering you.

3. "Safe limit" is a function of reciprocating mass weight, valve train inertia and the power curve of the engine, among other things. "S" cams get interesting above 5300 rpm. I rev my 2,2 E to 7000 regularly in races and it hasn't made expensive noise (yet). If you aren't confident, don't do it.

4. "Updated oil system" could mean many things. To me it means someone has performed the "oil bypass modification" which routes excess oil back to the pump's pressure-side inlet rather than dumping it into the bottom of the case. This resulted in less oil to scavenge so the pressure side of the pump was made larger. Also, in 1971 Porsche installed piston squirters in the main bearing webs of the case to reduce piston crown temperatures. As part of "updated oil" these squirters should have been installed.

If you mean a "Carrera" tank then there has been some sheet metal modification to the starboard engine compartment wall to allow installation of a larger tank. It is a well-known problem with early 911 tanks that the oil-out location is at the rear of the tank, so when you brake hard, oil sloshes away from the pickup for the pressure pump and it momentarily sucks air, turning the low-pressure light on and starving the bearings of oil. NOT good. The larger tank is probably an attempt to fix this. Oil tanks also rust out, you could have had someone trying to save money if a later tank was available cheaply.

5. Later tanks are like 80l instead of 65l, that's the only reason I can think of.

[304065]

Weber IDA's are a retrograde step from MFI. Usually when you change displacement and cams, you need to change the space cam inside the MFI pump to compensate. Because MFI, in the days before the Internet, was not widely understood by non-professionals, Webers were often substituted, with a loss of 10 HP. The thing to do would be to get yourself a set of MFI 2,2 heads, port to "S" specs, find an original 2,2S injection system and look out.

[kenikh]

I am curious if the 2.2S pistons were cut for 2 liter valve pockets, since the valve angle of the engines is different. Is it even encessary due to the high dome heads and low dome pistons?

I would also be curious what the static CR of this set up would be (intuitively it would be low due to the aforementioned piston/head types).