Technical Hydra Performance 135 Leichtbau State of the Art Thread

[kayzrx82]

That is a kit specced for a different BMW engine, not an N54. VAC just did the research to find out the bolts dimensions would work on an N54, marked the price up, and sold them as N54.

When you use ARP rod bolts you are supposed to use ARP torque specs, not OEM. the ARP spec ended up being a lot higher than OEM on mine.

Ive never seen ARP hardware used on a stock n54 rod but it can be done as long as you dont distort the bore of the rod. The ARP tightening / stretch specification is to get the fastener just short of its yield point to achieve the fasteners rated clamping load. If the rod isnt designed for that clamping load it can distort the large end bore of the rod. If you want to use ARP spec I would tighten the rod caps with the ARP hardware to ARP spec with the bearings installed off the crank. Check with a bore gauge and make sure you aren't distorting the rod. If your having a shop do it, they should know this already.

 

[Hydra Performance]

To sum up real quick:
The OEM N54 rod bolt PN interchanges with a whole bunch of other BMW engines going all the way back to the early 90s. When you follow ARP's instructions and torque to their spec (which @Aaron said was a fair bit higher than stock), you end up distorting the big end bore of the connecting rod somewhat. This is not a huge deal and is usually rectified by resizing the big end bore accordingly, however this is not possible with cracked rods like ours so you end up running reduced bearing clearances - not ideal on a high-revving motor. With that said I don't think the factory rod bolts need changing out. FWIW the S55 uses the same rod bolts and runs a 7500rpm redline from the factory, food for thought...

 

[Torgus]

FWIW the S55 uses the same rod bolts and runs a 7500rpm redline from the factory, food for thought...

You would have to imagine BMW is not running that bolt at it's limit. There is design margin in every component and for good reason. Probably good up to 8k or beyond if you ask me. It's not a known failure point on any of the BMW engines is it?

 

[JimboFresh206]

M30's and m10's have issues, but they are studs/nuts and thats only if you re-use the old nuts.

glad too see others here know about the pro's and cons of re-sizing rods.

I always see ARP rod-bolts listed when people mention builds and it makes me cringe a bit

Can you line hone this block with the bed plate design? would ARP mains be of any benefit?

Reminds me a lot of when people would run "Metric Blues" for head studs lol

i love this thread

 

[langsbr]

I am using ARP rod bolts on my stock-rod N54, so we'll see I guess.

While I see the concern on the ARP rod bolts on stock cracked rods, it's been done for YEARS in the LS world. There are the same concerns there with the rod end distortion but so many have used ARPs for so long, I think it might be a slight holdback from the old SBC days.

 

[JimboFresh206]

http://www.m3forum.net/m3forum/showpost.php?p=1067114028&postcount=72

kinda interesting. I think there were two types of s54 rod bolt, not sure which one is closer to the n54.

 

[fmorelli]

This thread is a gold mine. Thanks to everyone in the dialog.

Filippo

 

[Panzerfaust]

To sum up real quick:
The OEM N54 rod bolt PN interchanges with a whole bunch of other BMW engines going all the way back to the early 90s. When you follow ARP's instructions and torque to their spec (which @Aaron said was a fair bit higher than stock), you end up distorting the big end bore of the connecting rod somewhat. This is not a huge deal and is usually rectified by resizing the big end bore accordingly, however this is not possible with cracked rods like ours so you end up running reduced bearing clearances - not ideal on a high-revving motor. With that said I don't think the factory rod bolts need changing out. FWIW the S55 uses the same rod bolts and runs a 7500rpm redline from the factory, food for thought...

Yes the rod bolts are the same across various generations but have had revisions along the way so I'm not certain that the current ones are the exact same as the e36 ones were in the 90s, but they're obviously excellent in their own right. I know a lot of what you're recommending comes from theory and knowledge based on your experience with engine building (which I have little-to-none) on other platforms, but I would have to imagine distortion of the rod ends would also have a lot to do with the materials, quality and build of the rods themselves. While the bolts are used all over, our rods themselves are pretty specific. I definitely believe that you've seen ARP bolts might distort rods on other engines, but when factoring in how hearty the N54s stock internals are based on being able to double or go even higher with the HP and TQ levels, surely they're stronger than many other engine's rods in regards to distortion I would guess considering the strength of engine parts are based on metallurgy, thickness, build quality, design etc- that's kind of why we're all where we're at in the first place with these cars, right? You're obviously addressing the design part of that, but I can't help but assume the other factors would play a big role too - but again, I'm aware I could be wrong.

Again I'm not trying to blindly dismiss any of your knowledge or recommendations and I'll be the first to admit you know more about engine building than me. However I was specifically recommended to use the ARP fasteners by both a very large reputable company who designs parts for and builds engines for a wide variety of car uses (VAC) as well as my shop who have used them on everything from older restorations, to their built vortec and cams S54 to DD or track oriented N54/55s and current gen M cars without issues AFAIK. I could maybe see the argument that VAC might suggest them because they sell them, but my shop gives me all parts at their wholesale/supplier cost and have never steered me towards anything they see as unnecessary or a waste of money - even recommending I don't go with poly engine mounts from one of their suppliers when I was specifically looking to because they've seen the hot side melt on street cars multiple times.

I know some of the N54 engine builders offer CARR or ARP hardware even when not doing upgraded rods and I haven't heard of any issues, but if you have and could link some I would actually appreciate it and might skip going that route. I just figured while I was doing a minor engine refresh with some upgrades, I'd go with another small upgrade that I was highly recommended to use by two different knowledgeable and experienced companies who specialize in BMW engine building.

You would have to imagine BMW is not running that bolt at it's limit. There is design margin in every component and for good reason. Probably good up to 8k or beyond if you ask me. It's not a known failure point on any of the BMW engines is it?

Agreed there - they certainly can handle quite a bit and there's obviously an overhead in mind when designing and deciding what parts to use. But since I'm running much higher HP/torque resulting in higher cylinder pressure levels plus soon to be higher RPMs and doing a small refresh it sounded like a solid recommendation.

While I see the concern on the ARP rod bolts on stock cracked rods, it's been done for YEARS in the LS world. There are the same concerns there with the rod end distortion but so many have used ARPs for so long, I think it might be a slight holdback from the old SBC days.

I think so too - just like many people were afraid of coated bearings for a few years despite them being run in tons and tons of actual race cars under harsher conditions than most of us will put our cars through even with bigger builds. But I'm inclined to think if either are installed properly by a knowledgeable and experienced mechanic, chances of issues are small. These companies likely did a lot of research and testing before and wouldn't continue to keep making or selling these parts if catastrophic engine failure from simply using their parts happened, but what do I know I guess?

 

[langsbr]

just like many people were afraid of coated bearings for a few years despite them being run in tons and tons of actual race cars under harsher conditions than most of us will put our cars through even with bigger builds.

What made you go coated rather than wpc? wpc seems to be very popular among the m3/m5 crowd when replacing bearings and since it's a treatment and not a coating, it's less likely to impact tolerances which I'd prefer since bmw already runs very tight.

 

[Hydra Performance]

From the gem of the post @JimboFresh206 linked to earlier, keeping in mind that S54 rods are stouter/more rigid than ours, that's 25-40% of your rod bearing clearance right there, and >6x as much rod distortion than stock! Moral of the story, don't throw aftermarket parts @ sensitive engine internals without a clear understanding of the changes you are making. To paraphrase David Vizard, the race engine builder's job is to toss a bunch of ill-fitting or mismatched parts together and make them fit perfectly...

 

[Panzerfaust]

What made you go coated rather than wpc? wpc seems to be very popular among the m3/m5 crowd when replacing bearings and since it's a treatment and not a coating, it's less likely to impact tolerances which I'd prefer since bmw already runs very tight.

A variety of factors - namely that the coated bearings have been proven in high performance applications for years and my shop both recommends and is familiar with them. I'm sure the micro shot-peening method of WPC bearings is great too, but I'd heard they might not hold an oil film quite as well on bearings despite shot peening reducing friction on most metal-metal parts. The internet is full of great information, but sometimes it's best to go with what your builder recommends - theres going to be different opinions from everyone, and if my shop (and VAC and other racing companies) has used these on tons of high performance street cars as well as straight up race-only cars getting the snot beaten out of them and will stand behind them, I'm comfortable with the choice.

The fact that I got them at the wholesale price didnt hurt either

From the gem of the post @JimboFresh206 linked to earlier, keeping in mind that S54 rods are stouter/more rigid than ours, that's 25-40% of your rod bearing clearance right there, and >6x as much rod distortion than stock! Moral of the story, don't throw aftermarket parts @ sensitive engine internals without a clear understanding of the changes you are making. To paraphrase David Vizard, the race engine builder's job is to toss a bunch of ill-fitting or mismatched parts together and make them fit perfectly...

View attachment 21047

That's actually from an S65, not an S54 - and if you read the rest of the thread (the OP specifically, and then a few posts down from the post Jimbo and you linked) that info was posted in, youd see that not only was there slightly increased bearing clearance with ARP hardware and less bore distortion than noted in that graph but significantly better bearing wear results using coated bearings and ARP hardware vs OEM. The OP shows a stock bearing using stock rod bolts with significant wear at 6k miles, versus VAC bearings and ARP hardware @ 30k miles looking like they're fresh out of the box bearings. Here's a link for some good reading and discussion: https://www.m3post.com/forums/showthread.php?t=1073979

I'd still like to see N54 specific evidence because every platform is different and we're comparing NA rods to FI rods, but if we're going off of that thread linked, the general consensus seems to be you'll have less wear and tear going the route I chose - to the point that the commonly known s65 rod bearing issues seem almost completely addressed.

 

[kayzrx82]

A variety of factors - namely that the coated bearings have been proven in high performance applications for years and my shop both recommends and is familiar with them. I'm sure the micro shot-peening method of WPC bearings is great too, but I'd heard they might not hold an oil film quite as well on bearings despite shot peening reducing friction on most metal-metal parts. The internet is full of great information, but sometimes it's best to go with what your builder recommends - theres going to be different opinions from everyone, and if my shop (and VAC and other racing companies) has used these on tons of high performance street cars as well as straight up race-only cars getting the snot beaten out of them and will stand behind them, I'm comfortable with the choice.

The fact that I got them at the wholesale price didnt hurt either

That's actually from an S65, not an S54 - and if you read the rest of the thread (the OP specifically, and then a few posts down from the post Jimbo and you linked) that info was posted in, youd see that not only was there slightly increased bearing clearance with ARP hardware and less bore distortion than noted in that graph but significantly better bearing wear results using coated bearings and ARP hardware vs OEM. The OP shows a stock bearing using stock rod bolts with significant wear at 6k miles, versus VAC bearings and ARP hardware @ 30k miles looking like they're fresh out of the box bearings. Here's a link for some good reading and discussion: https://www.m3post.com/forums/showthread.php?t=1073979

I'd still like to see N54 specific evidence because every platform is different and we're comparing NA rods to FI rods, but if we're going off of that thread linked, the general consensus seems to be you'll have less wear and tear going the route I chose - to the point that the commonly known s65 rod bearing issues seem almost completely addressed.

It doesn't matter if the rod is NA or FI it depends on the design of the rod and what clamping force it was designed to handle. Over torque any rod past it's designed clamping force and you will distort the bore of that rod. Arp hardware can be used but use caution as to what torque or stretch spec you are using. You need to bore gauge the rods especially if you intend on clamping it more then it was designed to handle. Aftermarket rods have their specs and lubricant you use when applying torque or stretch. They tested it with those specs / lube to ensure you get adequate clamping force without distorting the bore and that it is repeatable. As I mentioned earlier, the stock n54 rod bolts on the stock rods are more then adequate for the rpm these motors are turning stock. Increasing cylinder pressure will not affect the rod bolts as much as reciprocating weight and rpm will .Unless your increasing the weight of rods , pistons ,pins etc or/and increasing rpm, their is no need to attempt to throw arp hardware and torque them to arp spec on the n54. Comparing arp hardware used on the s54 s65 s85 motors that have a higher rev range than the n54, is no where close to the same use case. Those rods are designed for high rpm and therefore need more clamping force and are designed to take the hardware to do so.

 

[GreyNBlueE92]

If only we could use those engine's rods.... I know the liklihood is slim, but it might be worth looking into if somebody has them laying around... I haven't built any BMWs so this is just speculation. Just a thought others might not have "thunk" of

 

[Panzerfaust]

It doesn't matter if the rod is NA or FI it depends on the design of the rod and what clamping force it was designed to handle. Over torque any rod past it's designed clamping force and you will distort the bore of that rod. Arp hardware can be used but use caution as to what torque or stretch spec you are using. You need to bore gauge the rods especially if you intend on clamping it more then it was designed to handle. Aftermarket rods have their specs and lubricant you use when applying torque or stretch. They tested it with those specs / lube to ensure you get adequate clamping force without distorting the bore and that it is repeatable. As I mentioned earlier, the stock n54 rod bolts on the stock rods are more then adequate for the rpm these motors are turning stock. Increasing cylinder pressure will not affect the rod bolts as much as reciprocating weight and rpm will .Unless your increasing the weight of rods , pistons ,pins etc or/and increasing rpm, their is no need to attempt to throw arp hardware and torque them to arp spec on the n54. Comparing arp hardware used on the s54 s65 s85 motors that have a higher rev range than the n54, is no where close to the same use case. Those rods are designed for high rpm and therefore need more clamping force and are designed to take the hardware to do so.

I think we're arguing the same thing on many of those points - like I said, I'd like to see results on an N54 specifically because they're different engines, but since that was the only information anyone provided I mentioned the other things in the thread. Once again I'm not an engine builder, and I understand that the design of the rods in regards to clamping force is a bigfactor, but I also cant help but imagine that the metallurgy also plays a part in potential deformation which is the only reason i mentioned NA vs FI rods. I dont know the metallurgy of either of the engines rods, but we do all know the N54s internals were over engineered for the stock boost it was running as evidenced by what we can run on stock bottom ends, so while I could be and am open to being wrong with solid evidence because it could save me some hassle, but with what I do know I cant help but think the rods could likely handle the ARP studs being torqued to spec vs the OEM bolts being torqued and then spun further/stretched.

As far as the latter part of your post, the whole reason I am going upgraded bearings and ARP hardware is because of doing cams and springs so I will be revving higher than stock. I certainly understand the concern with making sure everything is done properly there - and while I'm not an engine builder, thankfully my mechanic is and his shop has built plenty and they're the ones who recommended that setup, as I mentioned. I have faith in them doing it the right way from their experience and lack of issues, plus the lack of issues posted online about using ARP hardware. The bolts might not have been specifically designed for the N54, but I doubt a company like VAC would continue to sell and recommend bolts for stock rods if they knew they were causing significant problems.

 

[kayzrx82]

I think we're arguing the same thing on many of those points - like I said, I'd like to see results on an N54 specifically because they're different engines, but since that was the only information anyone provided I mentioned the other things in the thread. Once again I'm not an engine builder, and I understand that the design of the rods in regards to clamping force is a bigfactor, but I also cant help but imagine that the metallurgy also plays a part in potential deformation which is the only reason i mentioned NA vs FI rods. I dont know the metallurgy of either of the engines rods, but we do all know the N54s internals were over engineered for the stock boost it was running as evidenced by what we can run on stock bottom ends, so while I could be and am open to being wrong with solid evidence because it could save me some hassle, but with what I do know I cant help but think the rods could likely handle the ARP studs being torqued to spec vs the OEM bolts being torqued and then spun further/stretched.

As far as the latter part of your post, the whole reason I am going upgraded bearings and ARP hardware is because of doing cams and springs so I will be revving higher than stock. I certainly understand the concern with making sure everything is done properly there - and while I'm not an engine builder, thankfully my mechanic is and his shop has built plenty and they're the ones who recommended that setup, as I mentioned. I have faith in them doing it the right way from their experience and lack of issues, plus the lack of issues posted online about using ARP hardware. The bolts might not have been specifically designed for the N54, but I doubt a company like VAC would continue to sell and recommend bolts for stock rods if they knew they were causing significant problems.

I'm not disagreeing with you. As I said you can run the arp hardware just check things if you plan on going past the BMW specified torque.

Keep in mind you cant use the fact that because rod A takes a certain amount of abuse or its taken x amount hp past its stock intended level as a green light to over-torque or over clamp the rod bolts. Metallurgy is not the only factor that determines if a rod is designed for NA or FI. Go by what the rod manufacturer specs. They alone have the cad models, FEA testing , and have done the math to know what clamp load , rpm range , hp load at a given rpm the rod was designed for. As far as the stock N54 rod goes, BMW has a spec for it so that it will maintain its shape when torqued. There is a safety factor built into the rods but that has very little to do with what clamp load it was designed to handle and that safety factor does not scale the same when it comes to the designed clamping load the cap was designed to hold without distorting. The safety factor of the stock rod decreases as you increase hp levels and even more so when you increase revs. Load on the rod bolts isn't linear when it comes to rpm. Reciprocating weight vs rpm is an exponential trend. Even High end aftermarket rods can have their big end bore distorted (squashed out ) from over torque. ARP bolts have a tensil strength 215,000-220,000 psi. High end rods made with 4340 chromoly have a yield psi of 125,000. This is why you check clearances with a bore gauge especially if your going to use a fastener and a spec the rod was not intended for.

 

[JimboFresh206]

Link fixed*

 

[Hydra Performance]

Moving on to the drivetrain now, here's a shot of my 3.91 large-case 215K rear diff conversion in progress, the first of its kind to my knowledge, complete with Mfactory clutch-type diff, vented rear cover, and DEFIV-style lockdown-bracket. Diff comes with a stronger 86mm CV joint flange on the pinion end, eliminating one weak point. It also comes with a drain plug @ the bottom of the case, and taper roller bearing instead of plain ball bearings supporting the diff carrier. Ring gear bolts are 12mm as opposed to 14mm, necessitating a bushing to take up the slack, and it just so happens that an OEM BMW dowel pin, PN 11111743118 happens to fit the bill PERFECTLY! Also included a screenshot detailing my expected speeds/gear with the 3.91 rear end running an 8100rpm redline on a 6MT with 245/45/17 rubber. Looks ideal on paper, remains to be seen how well this bears out in practice...

 

[Aaron]

I can't see that pumpkin will be anything above positively miserable to drive. The stock 3.08 is already poorly matched to a FBO car, let alone one with more power.

Personally, I'm swapping to a 2.56 rear.

 

[GreyNBlueE92]

Any reason for such a small tire? I was thinking of going with at least 255 setup. Looking at squared if it's possible...

 

[Hydra Performance]

@GreyNBlueE92
Because I'm running a square 8.5" setup on a narrowbody 1er. 245/40F and 245/45R. I preferred the longer contact patch of a 245/45 over the wider one of a 255/40 on the rear axle. In an ideal world I would run a 9.5" rear but 275/40 doesn't give you such a wide variety of tire choices in this day and age sadly.