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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Tue, Nov-27-2012, 06:47:56 PM   #1
SliM3
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Default Forged Con-Rod Alternative - Discussion

Greetings M3nthuiasts,

I wanted to start this discussion in hopes of getting feedback, theories, foreseeable pitfalls, (dis)advantages, etc. concerning possibly using forged aftermarket connecting rods designated for motors other than the S54.

A little background surrounding my initiative to find a lower cost option for a built S54 sorta stems from my previous SC400 project, which is indefinitely delayed due to the purchase of my ///M. I was looking to build a nice high-revving, moderate HP NA motor using the capable 1UZ-FE platform which Toyota based on CART/IRL design. No doubt the engine was up to the task but the aftermarket parts, particularly the rods, were very few and far between and the cost of eight was astronomical.

After searching and finally having discussions with a fella in Australia who was a resident 1UZ DIY expert, in stepped a proven alternative. Using his set-up and recommendations as a base I quickly picked-up a set of Lentz forged Winston Cup rods complete with 3/8" Carr bolts, EDM holes for wrist pin lubrication, passed NDI, and had been used for one race (682 miles total). The rods were estimated to be around $2,300 and I purchased them for roughly $350 for the set.

Anyway, enough of the non-essential info. I guess the best way to approach this, is to post what I have found for the S54 so far and what may constitute as an alternative forged rod to use.


OEM ENGINE MEASUREMENTS:
198 cu.in. / 3246cc

-Block-
Bore = 87mm/3.43"
Stroke = 91mm/3.58"
Deck Height = 216.9mm/8.54"
Bore Spacing = 91mm/3.58"
Head Gasket Thickness = .762mm/.03"
Comb. Chamber vol. = 33cc

-Crankshaft-
Main Journal dia. = 60mm/2.36"
Rod Journal dia. = 49mm/1.93"

-Connecting Rods-
Length (c-c) = 139mm/5.472"
PE Width = 19.91mm/.784"
BE Width = 19.91mm/.784"
Pin dia. = 21mm/.827"
BE dia. = 53mm/2.086"
Weight = 632g
Piston Weight = 470g

I have found that the closest match are rods used in a Honda K20 motor (Civic, Integra). Here are some pertinent measurements:

K20 crank rod journal dia. = 48mm/1.89"
Rod Length = 139mm/5.472"
PE Width = 19.81mm/.780"
BE Width = 19.81mm/.780"
Pin dia. = 22mm/.866"
BE dia. = 51mm/2.008"

As you can see from the measurements they are damn near identical, but obviously some machine work is in order:
  • S54 rod journals ground down 1mm/.04" (which really equates to 1/2mm -or- .02" material removed)
  • Piston pin bore size enlarged by 1mm/.04" (will require matching sized pin)
  • Rotating assembly re-balanced
  • Possibly reducing rod journal width, but this is up for discussion, as I think .05mm/.002" clearance on either side of the rod is negligible. (please give your thoughts)

From a cost benefit perspective you've got plenty of brands to choose from, of course keeping in mind that you'd have to buy two sets. However, if there is more than one person looking to run the same brand you can sell your left over rods to that person, who then only needs to purchase 1 set of four

Another perk is that you just can't be underwhelmed by the aftermarket support for Honda motors, so finding the right sized bearings is not a problem. Heck there are so many choices out there, that it may negate the need to remove as much rod journal material as originally proposed. I'm just beginning to delve into part/size availability, however Honda's yellow bearings look like they maintain .0015" clearance on a 48mm rod journal dia.

So what I'm looking at are the K1 lightweight rods which are going for about $410 (x2 req'd) a set on ebay. They are roughly 460g, compared to OEM 632g, and when coupled with a lighter piston, say JE's 308g, I'd have a pretty nice lightweight rotating assembly. In fact I'd be looking at shaving almost 2kg total weight from the rotating assembly. There's also the option of running SPS-Carr bolts for extreme RPM.

Well, I'll end it here and hopefully you guys can toss this around and leave some feedback.
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Old Tue, Nov-27-2012, 07:09:35 PM   #2
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Default Re: Forged Con-Rod Alternative - Discussion

I'd want to know the exact material spec and strength of both. The S54 travel distance/sec at 8000 RPM exceeds most street engines. The angles and forces applied by the S54 piston diameter and stroke are possibly close per cylinder on a Honda engine, but I don't know them much at all. I'd be concerned w/o knowing these things that the rods may not handle the forces.
Why do you not want to use the stock rods, do you have an engine with one failed?

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Old Tue, Nov-27-2012, 07:14:43 PM   #3
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Default Re: Forged Con-Rod Alternative - Discussion

Quote:
Originally Posted by SliM3 View Post
So what I'm looking at are the K1 lightweight rods which are going for about $410 (x2 req'd) a set on ebay. They are roughly 460g, compared to OEM 632g, and when coupled with a lighter piston, say JE's 308g, I'd have a pretty nice lightweight rotating assembly. In fact I'd be looking at shaving almost 2kg total weight from the rotating assembly.
Shaving 4-5 lbs off the rotating assembly would be pretty sweet. Does the K1 weight of 460g include the bolts?
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Old Tue, Nov-27-2012, 08:21:29 PM   #4
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Default Re: Forged Con-Rod Alternative - Discussion

Quote:
Originally Posted by RedM3/4 View Post
I'd want to know the exact material spec and strength of both. The S54 travel distance/sec at 8000 RPM exceeds most street engines. The angles and forces applied by the S54 piston diameter and stroke are possibly close per cylinder on a Honda engine, but I don't know them much at all. I'd be concerned w/o knowing these things that the rods may not handle the forces.
Why do you not want to use the stock rods, do you have an engine with one failed?

ADS
Hey Red, have a look at this article, particularly to the piston motion and rod comparison sections. Some pretty interesting stuff. I know the thresholds and conditions are a lot higher than the S54 but I think it can relate, one way or another, to both the high revving K20 (8600 redline) and S54. Both motors have pretty different approaches to rod:stroke ratios, with the K20 being 1.61:1 and our motors at 1.53:1.

Quote:
Originally Posted by drunk hal View Post
Shaving 4-5 lbs off the rotating assembly would be pretty sweet. Does the K1 weight of 460g include the bolts?
Don't quote me hal, but I think that may be with the ARP2000 bolts. AND, I failed to include the addition of piston rings. Do most manufactures quote piston weights with or w/out the pins? Add that in if they don't.
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File Type: pdf NASCAR Cup and FIA Formula One Engines.pdf (327.8 KB, 29 views)
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Old Tue, Nov-27-2012, 08:29:13 PM   #5
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Default Re: Forged Con-Rod Alternative - Discussion

Just a FYI the K1 rods are a China made rod. I actually have one right next to me right now for a motor for someone. Fit and finish are like any other cheap Chinese rod. The beam of the rod looks a little small compared to the competition. The crank end usually needs some machine work. I would rather have a stock rod over the K1.

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Old Tue, Nov-27-2012, 08:35:04 PM   #6
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Default Re: Forged Con-Rod Alternative - Discussion

Interested in this.
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Old Tue, Nov-27-2012, 09:02:40 PM   #7
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Default Re: Forged Con-Rod Alternative - Discussion

Keep your cheap Chinese rods. I'll stick with the factory cracked and forged rods.

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Old Tue, Nov-27-2012, 09:22:11 PM   #8
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Default Re: Forged Con-Rod Alternative - Discussion

The greater point is still to pull from other fitments that might be more cost effective....but you go boy.
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Old Tue, Nov-27-2012, 09:54:13 PM   #9
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Default Re: Forged Con-Rod Alternative - Discussion

I'd have a hard time justifying the savings (~$800 not including time and labor to machine/modify?) over something like a Carrillo that is made for this application.

I also see little point in touching the rods unless going stroker.
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Old Tue, Nov-27-2012, 10:02:25 PM   #10
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Default Re: Forged Con-Rod Alternative - Discussion

Quote:
Originally Posted by drunk hal View Post
I'd have a hard time justifying the savings (~$800 not including time and labor to machine/modify?) over something like a Carrillo that is made for this application.

I also see little point in touching the rods unless going stroker.
By the time your done buying the K1 rods and doing the machine work on them its not even really worth it. Carrillo and Pauter both make a off the shelf set of rods.
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Discussing Forged Con-Rod Alternative - Discussion in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)