This might be way more detail than you need, but the information is all there:
If you tell me what the original compression ratio was, and what the original bore and stroke were, and what the bore and stroke are now, we can figure it out without measuring the head displacement - assuming you didn't shave it.
3.142(pi) X 42.5 (the radius of your stock cylinder) squared X 83.5 (the depth of the cylinder) = 473882.33 cubic millimeters or 473.88 CC.
So, if your stocker is 10:1, the space in the head (plus gasket profile) would have to be 47.39 CC, or one tenth of the cylinder space.
473.88 X 4cylinders = 1895 CC, which is what our owner's manual's say is the displacement for our M44 engines.
I guess this means car companies don't count the space in the head as displacement. Makes sense, as the piston does not go in there, so that area is not displaced.
This is a long way of saying your head has 47.39 CC of space in it, so the next thing is to calculate the new bore and find out what it is in ratio to that.
I posted this somewhere here a while ago, but I have no idea where I put it...
Hope it is helpful.
Determine displacement (D) of your engine…
Formula:
D=π/4 (B)2 x S x N
Where D= displacement B=bore S=stroke N=number of cylinders
Example: six cylinder engine with a 3.5 inch bore and a 3.75 inch stroke.
D = π/4 (3.5)2 x 3.75 x 6 = 216.4753688 Cubic Inches (or just 216.5 rounded)
That's great for inches, but what about liters?
For metric units (liters) we must convert measurements to mm (or record them directly in mm), then convert cubic mm to cubic centimeters (if you want to know the CC's of the engine) then finally to liters if you want to know that.
There are exactly 25.400 mm in each inch. If you remember that, the rest is easy…
There are 1000 cubic millimeters in a cubic centimeter
There are 1000 cubic centimeters in a liter.
Therefore (using the same engine above, converting inches to mm):
D = π/4 (88.9)2 x 95.25 x 6 = 3547395.723 cubic millimeters / 1000 = 3547.395723 cubic centimeters / 1000 = 3.547395723 liters, or rounded, this is a 3.5 liter engine.
The above equation is fun if you have already or plan to over-bore your engine. Even if you over-bore in inches (typically 0.010", 0.020", 0.030", 0.040" or 0.060" at most US engine shops) you can convert these numbers easily to mm, and plug them into your equation where the base numbers (numbers in engine manual or blueprint) are in mm. Simply multiply buy 25.4 to get mm.
Example, for a 0.020" over-bore, we simply add 0.508mm to our bore size (in the example above, that's 88.9mm) to get a revised bore size (89.408mm in the example) and a new displacement of 3588.053221cc or (rounded) 3.6 liters.
Wasn't that easy?
Now, for the pistons, I would say you need to get a sample of both (dealer may order one of each for you) and mic them up. Put the wrist pin in place and mic from the bottom of the wrist pin to the top of the crown on both for a general idea.
Another option is to call Mahle and ask them for specific dimensions on the pistons they sell. There are also several custom piston manufacturers out there too; however if it is a slight overbore, you may be able to get by with oversize rings for a lot less cash...
BUT, unles both pistons are flat-top (and they are not) it is very difficult to determine actual combustion chamber volume, which controls compression ratio.
Poor-man's way of doing it: Get head studs and nuts from ARP (loose the stretch bolts) and a crap-load of head gaskets. Put the head on with no gasket (and no nuts) and turn the engine over and see if you collide the valves with the piston crown. If not, add a gasket and put it back together.
Now check compression. I don't know the pressure/ratio conversion, but I beleive it is done in bar, so 10:1 compression (stock M42) would be 10 bar, or 145.377 PSI maximum (130.8393 for 9.0:1 etc.). If it is higher, add a head gasket, and try again until you come back to 10-10.5. I personally would not go any higher than 10.5 because I think the knock sensors would not be able to cope (but it might be able to go up to 11.5) unless you wish to run 100 octane from now on. If you run crap fuel, the ECU will retard timing to a point that the extra compression is wasted, and you will have spent a lot of money for nothing. SO, be prepared to shell out for more expensive (and less available) fuel from now on.
You may need a longer cam chain, or a well-worn one (but if excessively worn, it will destroy the sprockets) with a double (or triple) head gasket, so keep that in mind as well...
I looked into all this stuff before I did my engine swap. Bang for the buck (especially at todays prices) is all swap, all day long (My manual is still $65.00 shipped by the way- shameless plug...).
__________________ "Speed's just a question of money. How fast you 'wanna go?"
BUT, unless both pistons are flat-top (and they are not) it is very difficult to determine actual combustion chamber volume, which controls compression ratio.
Thanks for the responses guys. I can't afford a swap and I love my 40 mpg highway that I get with my light-footed cruising. Plus my 205 hp to the wheels is nice too . Though for those interested, I have heard nothing but the best about Jim's manual.
Just to repeat my plan, my goal is to do this:
Stock M44 bored for S52 pistons.
If CR is too high, I might get 135mm pistons.
I would like the CR to remain between 8.5 and 10.0:1 in order to keep it supercharged easily. 8.5:1 will allow me to step boost up.
If anyone knows, or knows how to calculate these with STOCK S52 pistons and STOCK M44 rods, or STOCK S52 pistons and 135mm rods instead of stock 140mm rods, I would greatly appreciate it.
Numbers for reference: Stock Bore: 85mm Stock Stroke: 83.5mm Stock Rod length: 140mm
S52 Bore: 86.4mm Eagle H-beam Rods: 135mm
According to other posts, S52 pistons will have to be decked in order to fit properly with ok NA compression.
Could I go to the dealership and ask to see two sets of pistons? I doubt they would have them, but could they order them? I wish there were an expert I could talk to about this for free with a bucket of pistons and rods... haha.
The machine work would likley be the most expensive- you might find four used good pistons and rods on eBay, as when you money shift it, it usually kills 2 pistons...
__________________ "Speed's just a question of money. How fast you 'wanna go?"
When you miss-shift an S52 (and it happens often on the track) you over-rev and throw the valves into the piston, killing the pistons (the two up) and the eight valves corresponding. It also breaks one or both cams (they are hollow, and a bit brittle) and a host of other valve gear.
AKA the "Money Shift"
For what you want used pistons would be fine. Plus you would not be out a ton of cash during the experimentation process...
Did you call Metric Mechanic or some of the other rebuilders to see what they have to say about this idea? They would have 4 and 6 cylinder parts laying around (might have good used stuff cheap too) to make some observations for you. Offer to send them $100.00 or so for their trouble, and I think you could gain a lot of information about your project.
__________________ "Speed's just a question of money. How fast you 'wanna go?"
Ah yes... I overrevved my dad's S52 once to almost 8000 rpm, but luckily nothing bad happened... the valves were still nice and straight. I also overrevved my old M44 a little bit (to around 7800 rpm) for a very short time and it was fine. I wonder what the limit is to these motors for short time overrevving.
I'm not willing to find out first hand if I can avoid it...
Normally, it happens going into a corner, when you go from 5th to 1st rather than third (normally caused by soft tranny mount bushings) and the revs go sky-high.
I bring mine to 7 grand (Dinan software installed) with no issues at all, so I could see a short run to 8 being OK. 10 grand might be a problem. Plus, only one small part has to fail, and the entire system crashes. "Only as strong as the weakest link" so to speak...
__________________ "Speed's just a question of money. How fast you 'wanna go?"
Just to update: I sourced S52 pistons and they're sitting in my room. This summer I'll have them cleaned up and decked. Then, they're going to go to a machine shop with my extra engine which will also be cleaned and bored out to 86.4mm, the rods and pistons will be lightened. Head will be ported and polished after being flow-benched to make sure it's got lots of good air flow. DASC manifold will also be flowed. Valves will be ground and the seats will be re-done. Not too major of a change, but it should be like a new engine with a little extra pep. The extra flow and lighter mass should also allow me to bump the redline up to 7.2k which would be awesome. Just enough to let me hit 60 mph in 2nd gear.
I'm so tired of the 5.85 sec 0-60 because of the 3rd gear shift!!! I need lower! 5.4 or less!!!
Just to update: I sourced S52 pistons and they're sitting in my room.
Cool!
Quote:
Originally Posted by pnosker
This summer I'll have them cleaned up and decked. Then, they're going to go to a machine shop with my extra engine which will also be cleaned and bored out to 86.4mm, the rods and pistons will be lightened.
Which rods are you using? The stock M44 ones? Is it a good idea to remove material from these with a larger piston? Will the 'lightened' piston weigh less than the M44 piston, or more? Are the con rod lengths compatible? Will the rod-stroke ratio change with changing rods?
Quote:
Originally Posted by pnosker
Head will be ported and polished after being flow-benched to make sure it's got lots of good air flow.
With a forced-induction set-up, is this required? Is a 'rougher' intake runner better for better air-fuel mixing at increased velocity?
Quote:
Originally Posted by pnosker
DASC manifold will also be flowed. Valves will be ground and the seats will be re-done.
Are the valves being up-sized? With the bore increase, will the combustion chamber be machined to match? (maybe it is a close bore, I don't know the numbers off the top of my head) Cam increase?
Quote:
Originally Posted by pnosker
Not too major of a change, but it should be like a new engine with a little extra pep. The extra flow and lighter mass should also allow me to bump the redline up to 7.2k which would be awesome. Just enough to let me hit 60 mph in 2nd gear.
When I was auto-xing with my stock engine I could get up to ~62 in second... I basically never shifted on most courses! What can't you get to 60 in second now?
Quote:
Originally Posted by pnosker
I'm so tired of the 5.85 sec 0-60 because of the 3rd gear shift!!! I need lower! 5.4 or less!!!
Sounds like an interesting project! I would be very curious to see the dyno results once it is all said and done. I am thinking about a boost increase, up-sized injectors and a total re-map. I assume you have this in the plan, but it wasn't mentioned. With that bore, I would also think a longer duration cam would be beneficial to you. Not sure who makes what for that engine, but Schrick would be top of my short list...
I looked into a lot of this before deciding to do my swap. I am very curious to see what has changed in the last six years or so...
__________________ "Speed's just a question of money. How fast you 'wanna go?"
Boring out M44 
). 
. Though for those interested, I have heard nothing but the best about Jim's manual.
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