Useful 3.2L M104 Specs and using Honda Connecting Rods - PeachParts Mercedes-Benz Forum

Turbo E320 · #1 09-08-2010, 10:38 PM

Ok so I found this data on the M104 thanks in large part to MAG58.

BorexStroke 89.9x84mm or 3.54x3.3in
Deck height 217.625mm or 8.567in
Rod length on 3.2L 145mm or 5.708in
Piston deck height on my 97 3.2L M104 .014" or .375mm ABOVE deck
Piston Dish -8.75cc on "X" stamped 3.2L pistons
Compressed HG thickness .022" or .5588mm
Combustion Chamber volume 48cc on 3.2L
Compression Height on X stamped 3.2L pistons 1.22in or 31mm
Piston Pin bore 22mm or .866in
Rod Journal Diameter 1.889" or 48mm
Rod Big End Diameter 2.009" or 51mm
Rod Thickness .867" or 22.02mm
Headgasket Bore Diameter 91.55mm

Deck height from what I've seen can be found pretty easily(I think, let me know if I'm wrong), by taking the stroke divided by 2(as stroke is the distance between the main and rod journal centers times 2) plus the rod length center to center plus the compression height minus the piston to deck clearance.

for my e320 I got 42 plus 145 plus 31 minus .375 = 217.625mm which just so happens to match MAG58's measurement

With all the other measurements that comes to the stock 10.2:1 compression ratio in RSR, CSG and Eagle's compression ratio calculators. Now if I used a rod that was exactly 2mm shorter than the stock M104 rod, say a 143mm Honda H22a rod(same pin, rod journal and big end diameters), then your looking at a compression ratio of 8.8:1 with the stock pistons. This was the method of lowering the compression on the M104 Twin Turbo kits of the 90's.

With a set of forged pistons in there you have the capability of 150hp per cylinder or 900hp since cheap SCAT H-beam H22a rods are rated at a reliable 150hp per cylinder.

The best off the shelf piston I have located in America is the Ford 4.6/5.4 90.2mm piston which requires the block to be honed a little but not enough for an expensive torque plate to be used. It would give a compression ratio of 7.8:1 to 9:1 because of it's huge range of dish options from -5 to -18cc.

MAG58 · #2 09-08-2010, 11:18 PM

Quick thing to remember is that you only want the 2468 cylinder pistons (passenger bank) from the ford mod motor since the pins are offset in the piston to go along with engine rotation. It's also probably helpful to note the crank is offset towards the passenger side 1mm to allow the point in time where the gasses are expanding more efficiently to come closer to being the same as the point in time where the mechanical advantage the piston/rod has on the crank is the greatest...

Turbo E320 · #3 09-09-2010, 12:33 AM

Good point MAG I, admittedly, did not know that about V-8's. I only went as far as thinking it was to match the valve pockets correctly. Kind of embarrassing to me as I have built several of them...

I also remembered I finished building my friends Scion TC with Carillo/K1 Rods that are about the universal thickness for import H-beams. I remember taking a pic of them with a 95 E320 rod/piston and found it. There would be no block clearance issues as you can see.

Joreto · #4 09-09-2010, 02:50 AM

Good info on the conrods. I've also been thinking about using rods from another make which would fit our engines, but haven't had time to find ones that match (pin, rod journal and big end diameters).

400Eric · #5 09-09-2010, 08:09 AM

Quote:

Originally Posted by MAG58

Quick thing to remember is that you only want the 2468 cylinder pistons (passenger bank) from the ford mod motor since the pins are offset in the piston to go along with engine rotation. It's also probably helpful to note the crank is offset towards the passenger side 1mm to allow the point in time where the gasses are expanding more efficiently to come closer to being the same as the point in time where the mechanical advantage the piston/rod has on the crank is the greatest...

This brings up something I used to know but had forgotten about. In the old days, racers used to reverse the pistons in V8s, running the pass side ones in the driver's side and vice-versa to optimize the leverage effect at TDC. It was an effective trick, the engines made more power (especially more low end and mid range) with the only downside being a little more noise from increased piston slap. (Which of course is the reason why the OEMs put the offset there in the first place..... to reduce that noise even though it cost a bit of power.) So with all this in mind, shouldn't Turbo E320 actually run the pistons from the driver's side bank? Or does that offset crank business change all the rules here? Was that offset crank business done for that same more power effect? Maybe a piston reversal would help to increase that effect? Or was the offset crank done to reduce noise in which case we would be putting things back right again by offsetting the offset thereby canceling it? Remember, MB did always tend to be a little too oriented towards the quiet, luxury side of the equation. Like I said though, I forgot all this stuff!

Also, not to split hairs, but aren't Fords still numbered 1234 5678?
Regards, Eric

Turbo E320 · #6 09-09-2010, 10:51 PM

Have a set of H22 Eagle H-beams headed my way. With the New ARP hardware they use the rating is up to 200hp per cylinder reliably

. Cost was $460

. I'm so excited now. Now I'm just wondering whether I should go ahead fashion off the shelf pistons to fit or have Wiseco make me some for $960.

EDIT: Nissan KA24DE 4-valve pistons look inviting.

Turbo E320 · #7 09-10-2010, 12:10 AM

Just received a kick to the brain. When I said the ford pistons would be a good choice I didn't even have the 4 valve per cylinder COBRA in my head! The combustion chamber is of a similar volume and the head looks to have a similar pattern so if clearance was ever an issue, it shouldn't be now. I believe I will be getting some passenger side Cobra pistons and boring the block slightly over to 90.2mm.

MAG58 · #8 09-10-2010, 01:34 AM

Comp height on KA pistons is pretty damn tall. I don't really see them working too well.
I'd also be leery of 90.2mm. I know it's pretty much a hone difference, but 91mm C36's do seem to have big issues with keeping the blocks stable under boost. Just my $.02
Did you get 4 or 6 h22 rods?

400Eric · #9 09-10-2010, 03:18 AM

Quote:

Originally Posted by 400Eric

This brings up something I used to know but had forgotten about. In the old days, racers used to reverse the pistons in V8s, running the pass side ones in the driver's side and vice-versa to optimize the leverage effect at TDC. It was an effective trick, the engines made more power (especially more low end and mid range) with the only downside being a little more noise from increased piston slap. (Which of course is the reason why the OEMs put the offset there in the first place..... to reduce that noise even though it cost a bit of power.) So with all this in mind, shouldn't Turbo E320 actually run the pistons from the driver's side bank? Or does that offset crank business change all the rules here? Was that offset crank business done for that same more power effect? Maybe a piston reversal would help to increase that effect? Or was the offset crank done to reduce noise in which case we would be putting things back right again by offsetting the offset thereby canceling it? Remember, MB did always tend to be a little too oriented towards the quiet, luxury side of the equation. Like I said though, I forgot all this stuff!

Also, not to split hairs, but aren't Fords still numbered 1234 5678?
Regards, Eric

Hello? Anyone? I believe I've brought up some valid stuff to think about and decide on before you go any further and start ordering stuff.

And Mag, I would like to see your opinions on the questions I posed above. It may not seem like it, but I do respect your opinion. Just because I keep you honest sometimes does not mean I don't respect your opinion. Please post up!

Turbo, since you are probably going to have to end up ordering custom pistons anyway, why don't you just have them shove the piston pin a little further up into the piston and/or have them make you a nice big dish and get your lower compression that way instead of shortening the rods. Reducing rod length reduces your rod ratio and that is NEVER a direction you want to go in.
Regards, Eric

kynsi · #10 09-10-2010, 06:43 AM

One thing which caused broblem in my high (saab) piston is that oil sprays need room. And pin come very low. And also piston skirt hits cranck.

MAG58 · #11 09-10-2010, 01:57 PM

Not ignoring you Eric, I just didn't have time to put together a reasonable response. I can prattle off about block strength and bore diameter all day long since it's been my main focus on turbocharging these engines.

Back on the topic at hand however, I am not sure if the crank centerline offset means the M10x's pistons are offset or not. The effect of this I don't think has been documented amongst many oem circles because I do not think that crank offset has been really considered a factory feature in oem motors until quite recently (Go MB!)

A solid explination of the reasoning behind piston offset is located here:
http://www.motorcycleproject.com/motorcycle/text/cows-offset.html

And a pictoral of offset is shown, courtesy JE, here:
http://www.jepistons.com/TechCorner/Pin-Offset.aspx

I may be completely off my rocker here, but I feel that the offset of the crank away from the direction of rotation will reduce major thrust on the piston, something that would be offset further by correct piston pin offset or practically negated by running them backwards (thank you smokey). I'm not sure I'd be willing to deal with the increased major thrust loading in the name of power when running a turbo, but it does make for an interesting topic. Should this be the case, I could run the 141.5mm rods, my stroker crank (WIN) and a set of honda H series pistons for a smokey approved wrist pin orientation. That could be fun.

I don't see a big issue with 143mm rods either, the R/s ratio on that in a 3.2 is still 1.70. Not the spot on perfect 1.75 of the 145mm rods, but still damn good. 1.53 rod/stroke ratio isn't the greatest, but is the exact same as the B18B or 454 chevy. Cant argue with those motors.

kynsi · #12 09-10-2010, 03:34 PM

Mag, am I right: offset block and offset piston can handle lower rod ratios (pressure) in theory?

Other thing what happens whith ex. side offset pin is that a load which comes from load of combustion pressure is moved more to piston skirt which is a lubricated part unlike compression ring area.

My opinion...

400Eric · #13 09-11-2010, 06:56 AM

Thanks for the links Mag.
Please keep us posted and informed on your build's progress and the results of your crank and piston pin offset research and what you decide to do as a result of that research.

I'm also impressed that you know it was Smokey who was the first one to reverse pistons

Quote:

Originally Posted by MAG58

1.53 rod/stroke ratio isn't the greatest, but is the exact same as the B18B or 454 chevy. Cant argue with those motors.

Sorry, but I have to disagree with you on this one though. I can and have and do and always will argue with the 454. Very over rated engine. It has the worst rod length to stroke ratio of ANY American V8 ever made except for another knappy Chevy: the small block 400. The 454 Chevy is only able to accomplish what it does because of the support and work of hot rodders and the aftermarket. In fact, that same statement can be applied to all pre-LSx based Chevy V8s. Did you happen to see that big block shoot-out that Car Craft did back about ten years ago? They took all the American big blocks and built them as similarly as possible. The 454 ended up in the bottom half when all the dyno room smoke had cleared, keeping company with the 455s from Pontiac and Oldsmobile. Incidentally, those three big blocks were/are the three with the worst rod length to stroke ratios and the worst bore to stroke ratios of all the big blocks. Also, ironically, the smallest displacement engine [cough440Moparcough] with the shortest stroke and longest rod ratio made the most torque, blowing another long held myth about short rods and long strokes being the best for torque production.

In another very extensive comparison done in about 1993, Trailer Life magazine compared three similarly equipped pick-ups and found the 460 Ford to be superior to the 454 Chevy in just about every way, even noting how the engine oil temps stayed higher in the Chevy and lower in the Ford, especially when pulling a heavy trailer, a side effect I believe of the increased side loading caused by the 454's rotten rod ratio. (The V10 Dodge won that comparison BTW.)

Even the Chevy 350's ratio of 1.64, while not too terribly bad, is still the worst ratio of ANY American V8 it's size (340-360 ci) ever made. (Go ahead and try to find one that is worse.) In a factory crate motor shoot-out done years ago by Hot Rod magazine (it was the late 80s or early 90s), the 360 Mopar thoroughly spanked the 350 Chevy despite the fact that the Chevy was sporting Chevy's latest trick of the week Corvette based aluminum heads while the Mopar had to make do with a set of pedestrian iron pre-magnum truck heads. (Mother Mopar wins again!) Yet, inexplicably, the Chevy myth lives on.....

Sorry to get off track but this worship of Chevys really gets me boiling. They aren't all that. Never have been.

Back on track though, I wouldn't drop a rod ratio below 1.59 under any circumstances. I in fact really don't like to see a rod ratio below 1.7 despite the fact that my beloved 401s come in at 1.59. I agree that 1.75 or better is even better. For reference even the short deck, short rod 5.0 M119 comes in at 1.75, the tall deck, long rod 5.0 M119 comes in at 1.82, and the 4.2 M119 comes in at 1.89.

And I'm sure you know how much Smokey believed in long rod ratios. I believe, like he did, that rod ratios are far more important than most folks realize. Even the Chevy engineers recognized the error of their past ways and lengthened their rods (and the resulting ratios) on the new 4.8-6.2 LSx engines.
Regards, Eric

MAG58 · #14 09-11-2010, 10:20 PM

I surprisingly agree completely, Personally my favorite motor at the current is the 6.1L hemi and before that was the ol' 385 series Ford's. Cant beat those motors.

But the point I'm at is that there is physically not enough room for a decent rod/stroke ratio. The cost to get my diesel crank welded, re hardened, and turned down would make the cost skyrocket to the point where I might as well have a custom crank made. There has to be a minimum compression height to run any sort of forced induction (if you follow engine masters, you'll know some people have pushed the top ring and second ring together and run an oil control ring under it, just like F1, with a tiny compression height.

I know all about smokey. My old man was an SCCA lead tech when smokey tried to run his 7/8th size camaro through road racing tech, and more famously when they drained the gas after a race, he got in the car, fired it up, and drove off since he had extra fuel capacity stashed elsewhere.

I also know that smokey ran in displacement limited catagores (He turned those little DZ302's TIGHT back in the day) in which case, moving the rod/stroke ratio to a maximum for the displacement afforded will yeild the most power. But in a non displacement limited class, an increase in displacement on a street motor that will not live at 8500 rpm(SSSSSSS

) will produce a much more responsive midrange that extending the rod/stroke ratio simply will not be able to produce.

Also of note, by the time you do all the work to maximize rod/stroke ratio, you're still going to be doing it on mediocre hydraulic lifters which have crippled the high speed stability of the engine, ask JayRash. IMO money in getting custom parts machined vs off the shelf adaptations is much better spent in the top end of the motor. At least in the case of the M104.

400Eric · #15 09-13-2010, 04:13 AM

I agree the 385 is a great engine. 6.1 Hemi ain't bad either, although I sure wish Mopar would discover the joys of aluminum's viability as an excellent material to make blocks out of.

I also agree that, if forced to choose between displacement and ideal rod ratios, it is more productive to go with displacement. That's one of the main reasons why I love the 401 AMC so much...... it's a great, biggish displacement engine in a very small package.

The way I understand it it was actually one of Smokey's NASCAR Chevelles that he drove away in after they drained his gas tank and the extra fuel was in the frame rails.
Regards, Eric