What new piston and cylinders do I need to use on my rebuild
 

I’m preparing to rebuild my 1974 911T 2.7 stock engine with 8:1 compression ratio .I’ve been looking through the online listings for all of the companies selling Porsche parts and specifically looking for the piston and cylinder sets. But it seems like all of the cylinder and piston sets I found are almost 9.5 to 1 compression ratio‘s, and I’ve noticed all of these sets price ranges are from $4,000. To $6,000. I’m not looking to increase the horsepower of my engine I’d basically like to keep my engine and the parts stock I really don’t wanna spend $4000 to$6000 for a set of cylinders and pistons, I do have a budget that I must stick to.
The only thing I found online that looks close to what I might need to use is a MAHLE original piston and cylinder set with rings and wrist pins. Part# 911-103-949-01 The listings say it’s for 1974-1977 911/ 911S - with 8:5.1 compression ratio.
My main question is can I use this piston and cylinder set with the 8.5 to 1 compression ratio to rebuild my engine without having to buy upgraded S cams and doing modification work to my CIS fuel injection system. Thank you Marion Fisk

You’re only going up 1/2 point on CR. You can use either CIS pistons or RS pistons, both are 8.5 CR
2.7 CIS cams have little value, used, so, they won’t break the bank, be sure to check the numbers on the cams you take out, they might already been replaced with S grind.
Bruce

Oregon - by 1974 Porsche did not have the lower end T motor in its model lineup, as it had had since when - 1970? Instead it had a 911, and a 911S. You have the non-S, it would appear. At some point (1976), it stopped that silliness, and called the normally aspirated 911s just 911, and the top model was the 3.0 Turbo. Bruce is assuming you don't have a turbo, as am I. So you have the non-S derated model with a lower CR and less peppy cams. And he's right - a good used 2.7S cam ought not to cost much. Good can pretty much be determined by inspection - pits in the cam surfaces, uneven wear side to side. You might throw in new or reground rockers to go with the cam.

For pistons, since you don't need more power, well don't worry about compression in your price range as long as you don't get the purposely low compression turbo pistons. The higher CR will be fine - you can adjust the CIS if needed. If you take Bruce's advice, and buy a used "S" 2.7 cam (not the fabled early S cam from the 1960s), the most you might have to do is richen the mixture a bit. But the CIS automatically adds more fuel as it senses more air moving into the cylinders, so this ought to work.

What is wrong with what you have? What are your leak downs and compression check readings? Have you got it apart? Are the cylinder bores oval or damaged? Have you measured ovality? Are the pistons buggered up? Valve seating and guide wear? Time for new bearings? Doubtless an engine that old could use a bit of sprucing up so it can run better and perhaps use less oil, but - - -. Lots of things can't be figured until you inspect and measure.

The usual rebuild issue is Alusil vs Nikasil. Nikasil is preferred, but not essential. If your cylinder bores are out of spec, you can have them plated and machined back to spec with Nikasil, which would require - it seems - pistons made for Nikasil.

Re-ringing is pretty straight forward, though complicated for Alusil by divergent opinions.

I agree a guy doesn't really need more power. When I got my '77 in 1985 I thought, coming from an old beetle and a bus, that I had died and gone to heaven. But I didn't get to work or the grocery store any faster, and other than the mountain passes, all using that extra power got me was speeding tickets. However, this forum would be a dull place if no one wanted more.

Bruce - RS pistons? Whatever they are, aren't their tops designed for MFI, without the swirl for CIS? I've got 10.3:1 CR factory 90mm race pistons in one of my cars, using carbs - maybe those are RSR?

Walt, yes the RS pistons are made for the S cams of the early vintage and MFI
The swirl pistons are for CIS injection. Both are 8.5 compression.
I don’t know anything of 10.3 except Euro Carrera. But, we can build them all….
Bruce

Bruce - my 90mm race pistons were made by Mahle for Porsche's racing operation. My 1992 Andial catalog calls them a special application item (along with similar pistons for higher and lower displacement engines. Not a street engine application. I don't recall where I got the set used from a race shop, but when a replacement singleton was needed, Andial had it. It doesn't show up in the other Bruce Anderson's book or Frere, but is (was) real. 10.3:1 was Porsche's nominal CR for its race engines back then. When I tested the CR, it was somewhat lower, though I could have adjusted that.
Not something that M. Fisk is going to run across.

Thank you for your replies Walt and Bruce.
Walt you ask what is wrong with my engine. Well the first thing is I think it’s consuming way too much oil, And it will smoke badly when I’m downshifting and decelerating. Also since last year when it began smoking on decelerating I will find an oil film in the tail pipe that I never had before. I just performed a oil change on the car a few weeks ago and I’ve driven it 528 miles since then and I’ve had to add about 2 1/2 quarts of oil to keep it filled to the halfway mark between maximum and minimum. In December 2021 I did take the car into a Porsche shop and they checked out the engine they told me that the valve train is very noisy, they performed compression test cylinder number one at 130 psi, #2 125, #3 103, #4 147.5, #5 146, #6 154 psi.
Leak down: #1,0%, #2, 6%, #3 37%, #4 8%, #5 8%, #6 0% . So the report told me low compression on cylinders one and three very low on cylinder number three significant leak down on cylinder #3. their recommendation was will need engine overhaul with correction of oil leaks.
But at the present time I cannot afford to have somebody else rebuild my engine so I thought I may need to just do it myself. In May of 2019 two months after I purchased the car I did have a Porsche mechanic check out the compression and leak down at that time while he was checking why my valve train was very noisy and he installed the hydraulic chain tensioners to the Engine. The mechanic who performed the hydraulic chain tensioners for me told me that he didn’t think I needed to rebuild the engine I could just do a top and rebuild. Also as far as I know I have no broken head studs in the engine. As far as I’ve been able to figure out I am the fourth owner of the car, when I purchased the car the odometer was reading 84,843 miles. But the auto dealer that sold it to me said he could not guarantee that that was the total original miles, The engine could have 200,000 miles for all I know. Thank you for any good advice you can give me. Marion fisk

The oil consumption sounds like it may be due to worn valve guides. Some models/years had guides of a more durable material, some less (the early 3.2s especially notorious for this?). I've forgotten about the 2.7 for this, if I ever knew. But someone on this list knows that without looking it up. You might do a search - 2.7 valve guide wear or something. Porsche said something like 500 miles per quart was OK for the 3.2s (perhaps not wanting to face up to the rapid guide wear?). Way high for most owners' tastes. However, your 2.5 quarts per 500 miles sounds like way way too much.

A pure top end would involve removing the heads (which you can do), disassembling them, measuring the valves and guides, grinding valves and seats if not too worn, and replacing if necessary. Removing the guides you could probably do (lots of instruction available on how best to do this). Replacing them is a lot harder, and calls for a lathe and very good measuring skills, so most let a shop do the removal also. Removing and replacing the valves calls for a tool to compress them, and isn't the easiest DIY job, so giving heads to a shop for this work is pretty common.

If you are a machinist by trade, and have a lathe and mill and all that stuff, that's different. I've got a Snap-On valve grinding machine (friend's shop went out of business and it was only a grand), but my ROI is negative, as I used it once over maybe 15 years, and I didn't entirely trust my results.

One of the key results of a proper leakdown is the location of the leak. 34% is pretty bad. But where was the air coming out? If those rings are shot, lots of noise if you listen to your oil tank with the cap off (a hose stuck in your ear works as well as, or better than, a mechanic's stethoscope). There is always some leakage into the engine's sump, but by checking different cylinders you can get an idea of what is normal, and what is a lot louder. In fact, for this you don't really need the leakdown gauges - just a way to blow compressed air into a cylinder at TDC firing, and listening. Similarly, putting your hose into the tail pipe should pick up exhaust valve leaks, and into the air filter should get intake valve leaks. Very important stuff if you want to know ahead of time what you are facing. If you can get access to a compressor you can do the leakdown or leak location yourself - the two gauge tool to do this isn't expensive, or you could borrow one.

A benefit of doing this again is that the 34% might be a fluke - sometimes a bit of carbon sticks on a valve seat and keeps the valve from closing all the way. Of course, you can't count on knowing that. However, if that 34% were to go away, you may have the option of driving for quite a while more without fearing a catastrophe. If the 34% is from a valve (exhaust would be the most likely), well that's different - a burned valve or seat is only going to get a lot worse and may lead to much bigger problems.

Perhaps the shop which did the leakdown noted which cylinders leaked where?

If bad rings are the issue, once you have pulled the heads off it isn't a whole lot more work to remove the cylinders - if leakage past the rings is indicated by the leakdown. Then you can measure things, and see if you can just re-ring, or some part or parts need replacing.

Then you are faced with the question of bearings. To start on that, what are your oil pressures? You could also have an oil analysis done - it can indicate if bearing wear is a problem. At that point tearing the whole engine down isn't a lot more work - the usual slippery slope even for someone with modest goals.

And for all of this, an engine stand and yoke is a very good investment. You can do all this corrective work with the engine sitting on some pieces of wood on your garage floor, but having it up on an engine stand, with the ability to rotate the engine, will speed up all your tasks by maybe a factor of 2 if not more?