Pelican Parts Forums - Leak down question

Brent

I don't think your current upgrades really added much power. I think the '70 T had the same exhaust as the other 911s through '74? A 3 into one on each side, with a 2 in muffler? And a Permatune isn't really going to do much for power. Better running (which is worth a lot for a daily driver, to be sure), but not horsepower in any significant amount. So you don't have that much invested in go fast stuff here.

Though the Weber 40s are all you will ever need in that department, so that's a plus. You could have your head ports opened up to E/S spec, and your manifolds also can be enlarged to match, if you upgrade to those specs. The MFI the E and S had contributed, I think, to those engines' fine performance, but you'd be close enough with the Webers.

Your T came with cast iron cylinders. If you can get a set of 2.2 or 2.4 Nikasil cylinders which are within spec, that's an upgrade. Then you can look for a set of 2.2 S pistons at 9.8/1 compression ratio. Or E pistions, at 9.1/1. The Nikasils, when used on race motors, actually raised the HP, though on a street motor I doubt you would notice anything. But they handled the increase in heat higher performance produced better than the cast iron.

The issue here is what it will cost. Used parts like these are 40 years old! How likely is it that they will still be within spec? You won't know unless you have them carefully measured. You can hunt up what the cost of a set of E or S Ps and Cs new might be.

You can also hunt up a set of E cams. You could use the S, but they are said to be peaky for street use (the ones I once had I used only on the race track, so I didn't notice because I was never cruising at low RPMs).

So upgrading your T motor to an E/S should give you a nice boost in performance. You might be able to do that on a "budget." Maybe.

You can bore the case spigots out, use 90mm cylinders from the 2.7s, and have a larger displacement. Bruce Anderson talks about this in his book using Euro factory pistons, but nowadays for what - $1,200 or so - you can have J&E make you the pistons you want to work with your carbs, which does away with the issues Bruce talks about with low compression ratios.

Bruce recommends keeping your T head port sizes and T cams for such a motor for street use!

But here is a rub:

The magnesium case you have is only good up to a point. Remember Newton: for every action, an equal and opposite reaction. More force pushing down on the piston, more force pushing up on the heads, trying to rip the head studs from the magnesium. Became an issue with the 2.7s, even those without excessive heat from emissions controls. In short, your case is not what any engine builder would choose for a hot rod motor. But if you shoot for maybe 150 hp (a nice increase from your 120), perhaps it will last.

Then there is the question of the rebuild. If your motor has never had the bearings replaced, doing that now sounds reasonable. You like the car, you liked the motor, why keep worrying about when you are going to see the oil warning light flick on while driving on a freeway some time? And a good rebuild is not cheap, but it leaves you with a near new engine rather than a touched up possibly clapped out one.

From some of this, can you see why folks often decide to find a used 2.7 with head studs which will meet torque specs, and leakdown numbers no more than about 12%, and just drop them in? With your Webers you wouldn't even have to change the fuel pump/supply system. Or a 3.0, which may be one of the most durable of Porsche's engines?

Tough decisions, to be sure.

Oh - no reason to be scared of doing routine stuff like removing and installing engines, or tearing them down, or, for that matter, bolting them back together, yourself. Lots of us have learned, even before Anderson and Dempsey came out with books which help a lot. Wayne's book that you have is especially helpful, as it is aimed at the likes of us in detail. Machining is the tricky part, and we all have that done by real machinists so it is right. Cam timing is tricky at first, but you can find someone to help.

Walt

Walt