Compatibility of Block and Internal Engine Parts.
01-08-2018, 01:25 AM
#1
Racer
Thread Starter
Compatibility of Block and Internal Engine Parts.
I have a question concerning internal engine parts and block compatibility. I recently started an engine rebuild with an M28/42 engine off a 1987 S4 car with automatic, "something" happened along the way with that block. Managed to get a complete engine from a 1986 32V car, a M28/43 engine for an automatic. What is compatible and what isn't?
So before I got my hands on that engine I asked Greg Brown about compatibility on 43/42 block and he said that blocks are the same with the exception of the two studs in the valley, which the 42 doesn't have and assuming they need to be removed so that the under side of the plenum can fit under. BUT, the 43 block I got didn't have the valve covers. So.....without having to buy covers can I use everything else from the 42 into the 43 block?
The differences I physically see is that the 42 block has bolts on heads to hold both items together. The 43 has studs. Is that an issue?
Pistons on 42 have a deeper cut on piston top for the 4 valves than the 43. So assuming pistons need to be used with the matching heads
Had also read about the pistons that Porsche had made that fell into two categories. I've labelled each piston from each block with its matching number. How can I make sure there's no issue?
And lastly, how the hell do you guys know all the answers? Other than the WSM's what else do you guys smoke or snort to know this knowledge?
want to be a 928 guru like all you guys!
RV
So before I got my hands on that engine I asked Greg Brown about compatibility on 43/42 block and he said that blocks are the same with the exception of the two studs in the valley, which the 42 doesn't have and assuming they need to be removed so that the under side of the plenum can fit under. BUT, the 43 block I got didn't have the valve covers. So.....without having to buy covers can I use everything else from the 42 into the 43 block?
The differences I physically see is that the 42 block has bolts on heads to hold both items together. The 43 has studs. Is that an issue?
Pistons on 42 have a deeper cut on piston top for the 4 valves than the 43. So assuming pistons need to be used with the matching heads
Had also read about the pistons that Porsche had made that fell into two categories. I've labelled each piston from each block with its matching number. How can I make sure there's no issue?
And lastly, how the hell do you guys know all the answers? Other than the WSM's what else do you guys smoke or snort to know this knowledge?
want to be a 928 guru like all you guys!
RV
01-08-2018, 03:52 AM
#2
Rennlist Member
If you put S4 heads onto an 86 engine it will give you 12:1 compression. Not great for a street car without access to high octane race gas.
You will need to transfer your pistons over to the other engine if they are the same tolerance group. Otherwise you will need to find a set of S4 pistons that fit the bore of the S3 engine.
If you don't, your car will no longer be able to detect knocking and always run -6 degrees timing because the pistons will be too "noisy" for the sensors.
The main difference of the engines is that the bores on the 86 block are significantly thicker and stronger. So you could bore the engine out more, or run more boost in it if you choose to.
You will need to transfer your pistons over to the other engine if they are the same tolerance group. Otherwise you will need to find a set of S4 pistons that fit the bore of the S3 engine.
If you don't, your car will no longer be able to detect knocking and always run -6 degrees timing because the pistons will be too "noisy" for the sensors.
The main difference of the engines is that the bores on the 86 block are significantly thicker and stronger. So you could bore the engine out more, or run more boost in it if you choose to.
01-08-2018, 08:48 AM
#3
Rennlist Member
I would not do anything and get the proper engine/short-block - an S4. Seriously. You'll be light years ahead in the end.
01-08-2018, 05:56 PM
#4
Racer
Thread Starter
Again, please go easy on me. New guy learning here, so the part that I forgot to mention that I also paid attention to was the two points where the knock sensors would be connected to on the ‘86 M28/43 block. The two are plugs that don’t allow for the bolts to be attached to when the knock sensors are mounted. Can’t they be removed and be replaced with the ones on the 87 M28/42?
RV
RV
01-08-2018, 07:00 PM
#6
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
although the cylinder bore is nominally 100 mm the variables of machining and plating the pistons ended up with different sizes.... so Porsche selected pistons which best fit the actual bore size. Basically three ranges of sizes as I recall and you SHOULD run the right piston in the right size or it will be too loose or maybe too tight....neither of which is a good thing.
