What spec is my engine?

[Neilnaz]

Hi everyone this is my first technical question so it may sound like a stupid question and it may have been asked before (although I have searched on the forum) but here goes anyway:

I have recently purchased a 1971 911T Targa. I have perused through the receipts for work undertaken and found a series of receipts that suggest that the car had a fairly major engine rebuild following engine damage. The receipts show that the engine was rebuilt to 'S spec' with new pistons and camshaft (etc.). I want to know whether there is an easy way to establish whether this is still the case and whether the engine should be kept adjusted to 'S specfication' i.e. timing (etc.).

This work was undertaken in 1989 and I have no paperwork to suggest that there was any further major work carried out since that time.

How can I easily tell whether the compression was raised and whether the cam is the S spec cam (etc.)? I would like to understand whether it is or not so that when adjustments are required they are made to the right specs/tolerances.

The car goes very well but I wouldn't be able to tell whether the car has 125BHP or 180BHP or anything in between. The car does run Weber carburettors which would have been original to the T model.

Sorry for the long question. Is there an easy way to find out what I have?

Regards, Neil

[Bob Kontak]

I am thinking the T in 71 had Zenith carbs from the factory.

The cams have part numbers on them on the chain end but I think the sprocket is in the way.

You could do some research on cam lift for the S and put a dial indicator on the valves and determine if the lift is within spec. S cams will lift higher.

[Neilnaz]

Thanks for your reply Bob. I am in New Zealand and the car came to New Zealand from the UK but may have originated in Germany given the dash clocks (German descriptions rather than English), originally being LHD and a bit of paperwork I have seen.

I think that would explain why the car has Webers as I thought that the European 71T came with Webers carbs. I am going to discuss with a local Porsche specialist to see whether he can verify the specification of the engine. The car is with them at the moment as I am getting the pedal box changed.

At some point in its life it was converted to RHD from LHD and the conversion was undertaken using a RHD pedal box from another vehicle (possibly VW Beetle). The clutch pedal has too much travel making gear changes awkward.

I will confirm on here what we establish.

Regards, Neil

[Bob Kontak]

Originally Posted by Neilnaz

I think that would explain why the car has Webers as I thought that the European 71T came with Webers carbs.

Neil,

They very well may have. I have a neighbor with a 70T that originally had Zeniths. So that alone is the basis for my comment.

Hoping all is still in S spec.

[Walt Fricke]

If you lived in the US, I'd say you ought to put the car on a chassis dynamometer to get rear wheel horsepower and torque curves. That ought to tell you right away if it has S power or
not. But maybe chassis dynos aren't common in NZ?

By checking various specs, you can also make some quick checks. I think the S and T cams are timed rather differently. So just checking cam timing should give you a pretty good idea. Isn't the S up around 5mm? Easy for a shop to do. Easy to do, period, but you need a few tools and some understanding.

[Neilnaz]

Thanks Walt - as I mentioned I will discuss with the local specialist and get them to check for me while the car is with them. I thought that there may be a straightforward way of checking.

I imagine that it is quite possible that the car has been set up as a T for quite some time and adjusting cam timing could release some additional gee-gees with commensurate adjustment of the mixture (etc.).

I am new to Porsche ownership so my imanineering above may be pie in the sky...

I will find out early next week and keep you posted.

Cheers, Neil

[boss11]

[QUOTE=Walt Fricke;7699532]If you lived in the US, I'd say you ought to put the car on a chassis dynamometer to get rear wheel horsepower and torque curves. That ought to tell you right away if it has S power or
not. But maybe chassis dynos aren't common in NZ?

hahaha, in NZ we do have running water, electricity, race tracks and dynos, its not all sheep, cows and Lord of the Rings

[Roger 911]

I would second Bob's suggestion regarding checking the cam lift and duration. Another thing you may want to check is the intake port size. S ports are larger. If they increased the port size, that would be a good sign that they actually did build an S spec motor.

Another less scientific approach...T cams make peak power around 5600 rpm and S cams at 6800 rpm. If your motor is really S spec, it will be pulling like a freight train at 6000 rpm, and still going strong at 6500. If its a T, it won't.

My stock '72T started to run out of steam over 5000 rpms. I replaced the T cams with E cams and it made a noticeable difference, pulling strong to past 6000 rpms.

Good luck!

Roger