S38 conrods

Devinder · Post by **Devinder** » Mar 15, 2006 12:51 AM

I found a popular connecting rod that is very close to the S38 rod. The Honda H22 rod is the same width, same big & small end size, but 1 mm shorter (143). All the manufacturers (Carillo, Arrow, Scat) make this rod in a 4340 H-beam style. I discussed it with Scat engineering at length and I just bought a balanced set of 6 from them for $400. It's shot-peened and comes with 3/8" ARP 2000 bolts.

M30 guys ordering custom pistons should consider this rod too since the price is about the same as having a set of stock rods rebuilt.

Devinder

<img src="http://www.cscoupe.org/misc/M5/new_engi ... edited.jpg">

Ed · Post by Ed » Mar 15, 2006 7:51 AM

Devinder wrote:I found a popular connecting rod that is very close to the S38 rod. The Honda H22 rod is the same width, same big & small end size, but 1 mm shorter (143). All the manufacturers (Carillo, Arrow, Scat) make this rod in a 4340 H-beam style. I discussed it with Scat engineering at length and I just bought a balanced set of 6 from them for $400. It's shot-peened and comes with 3/8" ARP 2000 bolts.

M30 guys ordering custom pistons should consider this rod too since the price is about the same as having a set of stock rods rebuilt.

Devinder

The H22 rod has been a long time favorite of the M10 crowd. The aftermarket chromoly H22 rods hold up very well to obscene amounts of boots.

Devinder · Post by **Devinder** » Mar 15, 2006 9:43 AM

Ed,

That's good to know -- I was a little worried that I was the first one doing this.

Devinder

Yellow2 · Post by **Yellow2** » Mar 15, 2006 10:44 AM

M10 and M30 rods are the same correct?

m535is · Post by **m535is** » Mar 15, 2006 12:12 PM

In general yes. But you need to be careful with saying yes to this statement because it really depends on the stroke length. The longer the stroke, the shorter the rod has to be to prevent the piston hitting the cylinder head.

On another note, I would like to know which BMW con rod do the H22s match up with.

Ed · Post by Ed » Mar 15, 2006 4:34 PM

m535is wrote:In general yes. But you need to be careful with saying yes to this statement because it really depends on the stroke length. The longer the stroke, the shorter the rod has to be to prevent the piston hitting the cylinder head.

On another note, I would like to know which BMW con rod do the H22s match up with.

The H22 rod is 1mm shorter than an S14/S38 rod. When combined with custom pistons and an S14 crank, you get a very light and strong M10 stroker.

Devinder · Post by **Devinder** » Mar 15, 2006 4:37 PM

m535is Posted: 15 Mar 2006 09:12 Post subject:

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In general yes. But you need to be careful with saying yes to this statement because it really depends on the stroke length. The longer the stroke, the shorter the rod has to be to prevent the piston hitting the cylinder head.

On another note, I would like to know which BMW con rod do the H22s match up with.

Closest fit would be the S38. The H22 rod is 143 mm. The S38 rod is 144 mm.

M30 rods and M10 rods are all the same length -- 135mm. The difference in stroke (from BMW stock 80mm up to 88.4mm) is made up in the piston compression height. There should be no problem running a 143 rod in an M30 -- just make a piston with the S38 compression height + 1 mm.

I will be running the H22 rod with a 92 mm crank so I'm having 29mm pistons made.

If there is interest, I can post all of the dimensions and my calculations.

Devinder

m535is · Post by **m535is** » Mar 15, 2006 4:43 PM

That would be really helpful because I am going to be building a 3.6 L M30 with a 86mm crank and 93.5mm bore. A la E34 M5 3.6L And I am going to use the b35 head and block and will need to get some custom pistons as I am looking to run 10.5:1 or so compression.

Thanks

Devinder · Post by **Devinder** » Mar 15, 2006 6:29 PM

quick calculation for your setup is:

1/2 of 86 mm stroke is 43 mm.
H22 con rod is 143 mm
M30/S38 deck height is 217.5 mm

217.5 - (143 + 43) = 31.5

so you need a 31.5 mm piston compression height (from wrist pin center to top to piston flat part) to have the flat part of the piston level with the block.

From my measurements, BMW likes to run the M30 pistons about 0.3 mm above the deck and the S38 pistons about 0.5 mm above the block. So, for M30 spec, you will want a 31.8 mm piston. For S38 spec, a 32.0 mm piston.

Then you just need to specify a dome shape to get 10.5:1 CR with the b35. I've never measured a b35 piston so I cant help you there.

Devinder

This spreadsheet was for my use but it has the relevent numbers in it:

Devinder · Post by **Devinder** » Mar 15, 2006 6:31 PM

By the way, you need to run Honda bearing inserts with this rod. The Honda crank pin dia is 48 mm just like BMW, but the rod big-end bore is 51 mm instead of BMW's 52 mm.

Devinder

Ed · Post by Ed » Mar 16, 2006 8:28 PM

You can also run a certain forged flat top Mustang piston with custom length rods to build a nice M10/M30. Which is cheaper, custom rods or custom pistons?

Devinder · Post by **Devinder** » Mar 16, 2006 9:11 PM

I think custom pistons are cheaper by far. How much are the Mustang pistons? JE forged BMW pistons are about $900 with rings and wrist pins. I found a shop that has S38 dish and valve relief cad drawings for JE so that should be no problem.

Scat wants about $1500 for 6 rods (either 144 or 135). The others are around $1800. Frank Fahey had a run of Pauter 144mm rods made and he wants $1800 for a set. I saw them at his shop and they do look good, but I think H-beam 4340 will be fine for my stroker.

Devinder

Ed · Post by Ed » Mar 17, 2006 12:41 AM

Devinder wrote:I think custom pistons are cheaper by far. How much are the Mustang pistons? JE forged BMW pistons are about $900 with rings and wrist pins. I found a shop that has S38 dish and valve relief cad drawings for JE so that should be no problem.

Scat wants about $1500 for 6 rods (either 144 or 135). The others are around $1800. Frank Fahey had a run of Pauter 144mm rods made and he wants $1800 for a set. I saw them at his shop and they do look good, but I think H-beam 4340 will be fine for my stroker.

Devinder

I think the Mustang pistons are $300 / set of 8 w/ rings. That would certainly make the H22 rod/custom piston route cheaper.

jason · Post by **jason** » Mar 17, 2006 5:52 PM

I know metric mechanic has a set of high compression pistons made by wiseco. I belive they are 10:1 or higher. Give them a call they might have a kit with h beam rods, forged pistons,with tapered wrist pins. Give them a call or check out their web sitehttp://www.metricmechanic.com I know they can make one hell of 3.9L s54 that screams like a bat out of hell.

Devinder · Post by **Devinder** » Mar 17, 2006 5:58 PM

Jason,

I did talk to MM and their 3.9L pistons are made for use with the BMW 90 mm crank. I have a Scat/Dinan 92 mm crank so those wont work.

Devinder

BDK · Post by **BDK** » Mar 20, 2006 7:06 AM

The s38b38 uses a rod which is shorter than normal to allow for the stroke, I forget the measurement...
just not enough caffeine as their is one sitting beside my pc I just can't remember how long it is....lol...

Hey Rob,
if your building the Monster M30, there are some steel rockers out now that allow for 9000 rpm redline....eventhough 8000 is probably enough....
Korman has them .....

Devinder · Post by **Devinder** » Mar 20, 2006 11:12 AM

142.5 mm

MyE28.com

MyE28.com

S38 conrods

S38 conrods

Re: S38 conrods