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  #1  
Old 05-24-2015, 09:07 PM
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Honda H22 DOHC Vtec rods in a M104

I've found references to using Honda H22 DOHC Vtec rods in a M104 to reduce compression when building a turbo engine. Today I pulled apart an apparently running H22 motor and one rod was bent.

I was under the impression that stock H22 rods were good enough for moderate boost in a M104 but seeing a stock H22 bend one puts that in doubt. Stock a H22 is 50 HP per cyl so I'd expect them to hold a 300 HP M104.

The car looked like someones regular driver, was unmodified, automatic, showed no signs of water in a cylinder, rod bearings were in great shape. Rod bending direction was as if the rod grabbed the crank. The bend is severe enough that I wouldn't reuse it and engine running was probably mostly unaffected.

Is the H22 prone to bending rods? When others say to use Honda rods are they referring to aftermarket Honda type rods? Thanks
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Old 05-25-2015, 12:45 AM
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So here's the question: for all the work of making those weaker rods work, would it be worth it given that you should most definitely be able to get 300hp safely out of a box stock 104 with your choice of FI?
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Old 05-25-2015, 08:49 AM
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From what I've read the only real work is making pin spacers to convert the rods from crank guided to piston guided. Supposedly the H22 rods are 2mm shorter making them an attractive drop in replacement for a turbo M104. Past that I'd either use stock M104 or aftermarket H22 rods.

I've seen bent rods in an engine before. Having raced Formula Ford ( 1.6 British Kent engine ) I've had rods from stock engines that were bent during forging but were machined to proper lengths! This doesn't seem to be the case with the Honda rods but I need to remove them from pistons and compare end to end lengths.
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Old 05-25-2015, 09:58 AM
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Besides the difficulty of doing something like this and a few other things that it would do why?
What kind of power goals do you have? And why would you not just have lower compression pistons made? The pistons are the weak link in the engine by far and the correct way of reducing compression while keeping things like quench and rod ratio correct. Besides they are shinny.
But honestly you can get a lot of power out of a stock m104.
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Old 05-25-2015, 12:47 PM
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Because it would be responsive as all hell with a shorter stroke... Decrease lag time. Yeah?
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Old 05-25-2015, 01:43 PM
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Quote:
Originally Posted by Lucas View Post
Because it would be responsive as all hell with a shorter stroke... Decrease lag time. Yeah?
Huh? How do you figure?
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Old 05-25-2015, 01:53 PM
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Originally Posted by MAG58 View Post
Huh? How do you figure?
MAG58:
Some folks really should stay behind the plow.
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Old 05-25-2015, 05:49 PM
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Other posts speak of Honda rods ( I haven't read through them lately. ) , I had thought these were worth a look even though quench is lost. From what I recall, the M104 doesn't have much quench anyway so what ever is lost might not mater much. The Turbo Technics conversions allegedly used shortened stock M104 rods.

http://www.peachparts.com/shopforum/performance-paddock/284473-useful-3-2l-m104-specs-using-honda-connecting-rods.html?highlight=honda+rods

http://www.peachparts.com/shopforum/performance-paddock/178881-turbo-technics-e320-parts-list-installation-reviews.html?highlight=honda+rods


There is a multi stage approach to what I'm doing. Build a slightly turned up motor, work it out in a test mule then drop it into the good car. Build a stronger motor for the test mule for track days.

I'm not tied to any specific type of build yet other than the good car mods need to be reversable ( RE car body isn't hacked up ) I'm somewhat resistant to supercharging only from a packaging stand point for the good car motor. To throw more into the mix, I have a 97 C36 ME 2.1 engine computer and a long stroke crank from a 350 diesel so with the addition of a reground cam I could make a pseudo AMG motor for the good car.



The good car: 97 SL320 with M104 ME2.1 722.6. It really needs more low end zip to make up for small displacement as the motor really doesn't do much below 3,000 RPM.

The test mule: 92 300SL that is currently motor and trans less.
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Old 05-25-2015, 11:28 PM
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Based on the above I would not say you are looking to make a ton of power. Bottom line is that your can run 400+hp through a stock m104 all day long. I think if you opened up the gap on the piston rings you could probably run more than 500hp pretty reliably with a good solid tune.
I am not saying any of this as theory but what I have experienced. I made well above 400hp on a junkyard m104 for many years of fairly abusive driving and trying new things and I can honestly say that I would not even blink at this power level.
If I was going to run long runs say mile or road course something long I would open the rings up anyways.
And any thing you do for trying to copy a 3.6 engine will be way more expensive than just buying a 3.6 engine. They are readily available any day of the week for a couple thousand dollars. For a few more dollars you can just buy a whole c36. Getting the diesel crank modified and new rods and pistons and custom cams will be 2-3 times that.
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