Should I rebuild my 70 911E with a 911S engine?

[YTNUKLR]

My 70E had some junk (fuzz and bits of metal) in the motor and so I took it apart. It needs pistons/cylinders plus all the normal parts to rebuild a 40-year-old engine that was never apart. The car has the original motor to the car (#620-0937)

I have a 2.2 S original MFI system (correct fuel pump, throttle bodies, etc.) which has got me thinking.. I would need new pistons anyway, and besides that, the only cost is porting the heads out to 36mm, and re-setting the cams and distributor to 911S specs. when they are serviced. Not too much extra to "upgrade" to 911S specs.

I have never driven a 70E in original configuration. It sounds really good and I think it would be better for driving on the street than the 911S, I am not racing the car. Well, sometimes! But for most of the time, the 911S is going to be more cantankerous, isn't it? Or is it about the same as the E for the most part, and the S just has some cream up in the top of the rpm range?

Would you be more or less interested in a matching-numbers 70 911E that was very nice, but had a 2.2 S Specification engine? Is the S motor a bonus to a buyer or would they rather have complete original specs.?

Thank you for the advice,

Scott

[356robo]

Build it as an E but put in S pistons. Best of both worlds.

[304065]

Scott-- remember everything we know about volumetric efficiency-- if you port the heads larger and use the bigger TBs and stacks from the "S" you have effectively increased the cross section of the intake tract. That will have a tendency to flow better at high RPM, where the greater duration of the "S" cams can be put to use achieving good VE.

The reason the "E" comes off the corners so well is because of the smaller ports, which keep the gas velocity high at lower RPM and achieve good cylinder filling, but they run out of breath at higher RPM.

If you look at the torque peaks for both engines this is borne out-- the E peaks around 4400, the S around 5300 or something like that, and you can feel it in the seat of the pants when that point is passed.

So, if your plan is to drive around town or AX the car, you may want to stick with the E setup. If you intend the car as more of an occasional use country driver where you can let it off the leash, or do track time with it, then by all means build to "S" specifications.

Talk to John Dougherty (camgrinder over on the PP engine rebuild forum) about what you really want to accomplish with this car, he can point you in the direction of "modern" camshaft profiles. I am using the Supercup on 102 lobe center, this is basically a modern lobe profile with similar duration to the Solex, the lobe center of the 911E with significantly more valve lift, earlier in the cycle, than the factory cams. There is more area under the curve and as such better cylinder filling down low and up high. Anyway, through careful camshaft selection you should be able to accomplish an improvement over the stock setup.

AND while you are in there I would do twin plugs, part of what makes an "S" so cool is the higher compression. If you are porting the heads it's cheap to twin-plug them and go to 10,3 to 1-- and the insurance of twin plug will help with the reformulated Panther Pee that is passed off to unsuspecting Californians as a motor fuel.

Now THAT would be a motor-- twin plug high compression with modern camshafts and the unmistakable howl of "S" MFI-- I would expect just under 200 horsepower.

As long as the case and gearbox match it shouldn't matter to a buyer, and if the combo really WORKS it's a major plus when you go to sell, there is nothing like the power of a well-tuned MFI setup.

Good luck!

[j911brick]

If it were me I would keep the car original and build it as an E. There is no shame in a nice E motor and I think it would be more attractve to a collector. If you think you want an S motor then build a separate one and throw it in there. S motor will be like money in the bank.

[Tom F.]

My vote is that you rebuild it as an S.

[Richardnew]

If it's a street car keep it in the E configuration.

Richard Newton
My 911

[Scott Clarke]

I was in the same predicament, and I built a short stroke 2.5 with the E cams and 36mm ports/TBs. If you are buying pistons anyway, why not 90mm? I wish I had the heads modified for twin plugs, though. I couldn't afford the whole system at the time, but John is right in that having the heads machined is cheap, and the rest of the system could be added later without tearing apart the motor.

I must say, though, that I often wonder what the motor would be like with mod S cams (that's why I opened this thread). As it is, it pulls very nicely from about 3K to 7300. I'll probably leave it alone. It works.

[YTNUKLR]

I see there is an obvious consensus

John Cramer - I would like to hear how those cams work for you with, I presume, standard 911E MFI(?) I like an optimized cam, but don't want to modify the MFI space cam to make it happen. I do remember the lesson in VE from early discussions on Pelican and that is why I asked. I have driven a 2.2S but I was wondering if the E is really a lot more potent at lower rpm. It sounds like "yes"...

I will have to look into what the dynamic CR would be if I put 2.2S pistons in with otherwise 911E parts or that supercup/102 cam. Seems like that could work and give a workable dynamic CR, 8:1 perhaps (9.6:1 or so static). It is pretty cheap to machine the heads for twin plugs (~$250) but it is NOT cheap to install 2 CDI's + 12-pot distributor (~$3200) or electromotive ($1000 + it looks stupid) so I want to keep the stock ignition. IMHO twin plugs is really a big deal on a Turbo, but I feel the bang for the buck on a N/A motor is pretty bad and that money should instead go towards a 2.5 short-stroke upgrade if you want the short crank and early feel, or the 2.7RS spec (+ high compression) if you just want more of everything.

As cool as a hot rod is the reality is this car will be driven on the street and run in the 3500-6000 range. To me that means I don't want S cams, even though they are fun. I think the car will be pretty quick and fun nonetheless..

j911brick - My goal is to keep the original matching engine working or at least in workable shape so that it wouldn't be much work to make the car 'original' if I ever need to sell it :crosses fingers: I may be looking for a house in the next 5-7 years though, we'll see. I agree a spare 911S engine is not a bad investment, but I don't have the kind of cash necessary to have a separate motor that I won't be using. And if I had to dump the car due to unforeseen circumstances, it would be worth a good amount less if the original motor is in pieces...

Mr. Clarke - I am not opposed to swapping parts (MFI, heads, cams, even pistons) on a motor, but I just want to build one engine.. The sky is the limit but I don't want to bore my case for 90mm barrels because it stresses the case and can't be undone. If you added twin plugs you will probably pick up 15 hp, not worth it to me for the money. I would change the gears (short gears) and machine the flywheel instead. If you build a high-CR engine that requires race gas on single plugs and/or a large-bore 3.2+ engine, twin plugs is good. But twin plugs is less good on a motor that will otherwise run on street fuel already...and $3k will buy you lots of race gas, anyway...

[Scott Clarke]

I bought a late 7R case for my motor, so I didn't pay anything for the right size spigots or for the oil bypass mod. It was very affordable. My original, matching numbers, case sits on a shelf.

[raspy2point2]

Which is more valuable? More power from a bored out engine or original configuration. I thought the S was the collectible car and therfore to be left original. That is why I bought a 911L so I could hot rod the engine and not be worried about what I was doing the the value of the car. Is that what is happening now--all 65-73 cars are more valuable left alone?