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M54B28 using long rods

40K views 27 replies 12 participants last post by  adiantha evant 
#1 ·
Here is what I am after: an M54B28 block using the longest connecting rods possible to improve the Connecting rod ratio and lower piston speeds over traditional setup of 135mm rods and 2.8l pistons.


M54 allow block, 211mm deck height.

M52B28 Crankshaft 84mm
M50B25 connecting rods 140mm
M54B25 Pistons, 27.75mm Compression height




So, on paper it looks like this:


84/2 =42 + 140 + 27.75 = 209.75




The M54B25 block using the 75mm crankshaft, 144mm connecting rod and, 27.75 CH pistons come to 209.25mm.




So, if I went w/ the 84 crank route with the long 140mm rods then, the M54B25 piston CH would change by 0.5mm. What do you think the compression ratio would yield with something like this? I'd say, it would go up by a full point..? 11.2:1
Do you think, there would be issues with piston\valve contact because of the additional 0.5mm in Compression height?
 
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#4 ·
Thats fine unless you trying to build something thats not worth the hassle.

I hear you wanna use longer rods to reduce friction etc... Have you ever taken a look at asien high revving engines? They have bore/stroke ratios and conrod/stroke ratios that actually shouldn´t even work and they revv like hell and produce power and torque without taking care about those "magical" numbers. :hi:

If you wanna build it to say you build it, then thats fine. If you wanna build it to get power gains, don´t be a fool ;)

You want N/A?

-> https://www.youtube.com/watch?v=Sd5U1yrCEN8 !!! :clap:
 
#5 · (Edited)
You are probably referring to Honda's K20/K24 platform. Hey, you brought up HONDA and, not I... :)

I actually happen to have a fair amount of experience with the K24 block. With it's 87mm bore and 99mm (!) stroke, the 2.4l K24 will rev 8000 rpm with factory internals and close to 9000 with aftermarket lightweight rods. This, btw in a street-tune configuration. At 8500rpm, piston speeds will be over 8000fps. These motors make power all the way to red-line or about 8200-8500 rpm with a fairly flat torque curve from 2500 to 5000rpm. Speaking of pistons, a typical 'street tune' setup consist of 12.5:1 compression ratio running US pump gas 91 octane. I know, in Germany and central EU, 91 octane is used for cleaning your tools and such.. lol! But hey, that's all we get here in the States 91 on a good day.

My thinking is that, if the notorious BMW crank harmonics can be sorted out then, you might be able to raise the rev limiter to about 7800rpm, picking up more power on top. The head flows nicely, a nice port and polish, oversized intake valves, lightweight lifter buckets and you should be able to support 7800, no problems.
IMHO, the 84mm crank is just about perfect. I have yet to hear anyone blowing up either a 2.5 or 2.8l crank in their motors, unlike the 3.0.
Using the long rods will drop piston speeds and side loads and less pounding on the crankshaft. Furthermore, using the M54B25 pistons should help as they are probably lighter than the b30 (haven't confirmed this yet)


Anyhow, I am after more revs. More revs should yield more top end power. 7800 is reasonable.

The video you posted is some Swedish BMW cup car build. Don't know much about it but sounds nice nevertheless.
I am more familiar with WTCC as we have a friend who drives for Honda but used to drive for BMW. Also, a good friend of mine owns a team in Le Mans. They are based out of Switzerland.
 
#6 ·
#9 ·
I collected all the parts, dropped in hte new crank and rods and; it's not going to work! I am actually PO'd about it too.:banghead:
Was my mistake of relying on forum data lol!

Anyhow, as it turns out, the M54B25 Connecting rod length is NOT 144mm rather, 144.98.

I measured the factory setup on the 2.5 block. The Piston Deck height came to 1.07mm below deck.

When using the 84mm crankshaft, 140mm connecting rods and, the original 2.5l pistons, the piston will sit 1.54mm below deck. A frickin 0.54mm difference. Great for Turbo build but, that's not what I am after.

Here is the math for comparison:

M54B25 block: 75mm crank : 2 = 37.5mm + rod length at 144.98mm (instead of 144) = 182.48mm

My Hybrid build using M54B25 pistons: 84mm crank : 2 = 42mm + rod length at 140mm = 182

So, I need to gain 0.05mm to maintain the 10.5:1 CR. How can I do this without going custom parts? By using the M54B30 piston.

M54B30 piston compression height: 28.32mm
M54B25 piston compression height: 27.75mm (currently using)

As you can see, teh difference is 0.57mm


So, with all this being said, I am currently looking for a low mile B30 piston set. If you have them available, let me know please. thanks
 
#23 ·
you missed a very important fact when considering deck clearance... your squishing a lot more air into that same area. so just because it sits .57mm lower doesn't mean that its going to have lower compression.

I'm actually doing the same thing, not because I want a n/a motor to rev to 10k, but I needed to get one back together with parts I had laying around.

I came up with 11.33:1 with a 0 dish input on the piston, however it will probably be closer to 11.1 considering the valve reliefs.

using m54b30 pistons I got a cr of 12:1, the valve reliefs are much smaller so it would probably be very close to that, however I bet you would have piston to valve contact with those pistons. they were designed to sit 2.88mm below the deck, not .68mm. the m54b25 pistons will sit lower as you said so you would not have any worries about piston to valve clearance.

I'll let you now how it all comes out in about 2 weeks, but don't expect anything magical.
 
#10 · (Edited)
you will never notice the difference with the longer rod ratio. a small change just doesnt make much difference. some basic calculations will make this evident.

as for adjustments, machining some off the block, different thickness head gaskets can give some adjustments, a piston that sits slightly proud can have the crown machined to suit
 
#15 · (Edited)
S54 has a much bigger stroke and more revs. Loads are rpm^2 and stroke also has a non-linear effect....so a very different beast.

The harmonic issue is basically stroke and rpm related it has very little to do with rod ratio. it so happens that the engines with the issue have a poor rod ratio but this is a byproduct when using a given deck height the longer the stroke the shorter the rod to achieve the same stack height and the engine will still shake itself to bits even with a 10mm longer rod in an M54B30. An ATI Damper is one of the fixes for this it seems

Let’s put some numbers to this

At 7500rpm m52B28 with 135mm rod vs a 142mm rod

135mm/142mm/% diff

Peak Acceleration TDC (g’s)
3463/3422/-1.2%

Peak Acceleration (near BDC g’s)
1890/1905/+0.8%

Mean Piston Speed (m/s)
21.0/21.0/0%

Maximum Piston Speed (m/s)
34.6/34.4/-0.6%

Peak Rod Angularity (degrees)
17.28/16.48/0.8

it will make so little difference in your particular case its not worth doing for the rod ratio reason.

For sure if youre getting custom slugs then opt for the longest rod that gives the best compression height (shorter the better to a point) but dont be afraid of a shorter rod if you have a long stroke engine, inherently you're going to be revving the engine less anyway all else being equal
 
#16 ·
Keep in mind the bore/stroke ratio and rod ratio of the M54b30 would be fine on the 4cyl. Having a long crank is where the issue is. The less the main and rod journals overlap on the crank the more probounced the issue is which is why the 75mm cranks fare much better.

Even in Grand Am they were replacing dampers frequently because the OEM damper cannot handle the abuse (but is required by regs). Switching to a proper damper is the most effective way to solve the issues.

The problem only really goes away with less cylinders/shorter crank :)
 
#17 ·
Yes, I understand and, I agree. BMW guys don't like when I bring this up but, a Honda K24A2 block with an insane 1.44 rod ratio can spin 8k in race configuration and make power all the way to redline. No issues with the crank, ever.
That being said, not all 6cyl engines have the issue the BMWs have. Just look at the RB26DETT. Its a 6cyl block, punks spin that motor to 9 grand without any failure :)

I finally figured out my build. Here it is:

84mm crankshaft
140mm connecting rod
M54B30 pistons, OEM spec. This will yield about 11:1 CR

You could use the M54B25 pistons as well however piston squish isn't exactly perfect as the piston sits 1.5mm down the sleeve. Still, though, this setup would provide you with about 10.5:1 CR, which isn't bad.

I am putting this project on hold until next spring, as I am in the process of moving. In addition, I really need to finish up my Pro3 first before I start messing with my E46.

I was actually thinking of selling my build as is. if you are interested I can hook you up, man! :)
 
#20 ·
The ATI damper will be part of my build. IMO, it's a no brainer. In the matter of fact, I am thinking of just sticking with the OEM dual mass flywheel as well. Yes, I'd like to have a bit better T response due to lighter Rotating assembly but the dual mass isn't that bad -for me, at least. Plus, it will help with countering harmonics.

To be honest, I probably wouldn't be worrying about this particular build, had I bought a 330 from the get go, instead of a 325ci. But, what's done is done; for now, going to stick with it.


IMHO, the 89.6 crank puts enough side load on the pistons as well as the rod journals that, by dropping the stroke and going longer rods and lighter pistons, over all it would make a difference. I am not shooting for only Peak HP, rather, drivability and reliability and, a flatter torque curve.

Looking at the head, it should flow nicely. Not sure how much but, 200-220cfm is reasonable.. (?) Once the bottom end is sorted out, the engine co9uld potentially make power all the way up to about 6800, I think (?)

Someone mentioned about money being better spent elsewhere.
Well, depending on how you look at it but, in general, I agree! I could have bought 8000 shares of KERX at 3.75 last Wednesday and sell off this morning at about 5.10 a share. That's over 1.25\share gain. Or, instead of spending money on the engine, I could buy TESLA (Nasdaq) January-2016 $270 call options, there's a huge open interest there. currently pretty cheap at 5.27 a call. I bet, those calls will double once TSLA is in the money.
Better yet, since Hilary is openly attacking the Banking sectors as well as Healthcare, might as well just go short on both. :) The bottom line is; Each to their own.. For time being, though, this project is on hold until next spring. But, if I ever get this engine done, I will definitely share and provide you with a feedback even if it result in a "I told you so" scenario... :)

BTW, I am thinking of selling my PRO3 build. I should probably list it under the classified. on the meantime, if you are interested, just shoot me a pm. thanks,
 
#22 ·
I certainly never said you did. :) But the OP seems really obsessed with building a non-S54 that he can rev to the moon, so I wanted to make the point.

Personally, I think there's not much point trying to extract a bunch of revs out of an M54 unless you're constrained to that block for some reason (like a rulebook).
 
#25 ·
I was looking for a way around m54 harmonics and read this. I'd like to see what just getting B30 guts into an iron block would do. In the end, every thread I have read says ATI and Viao's oil pump. I get it, that's probably right. But it's $1500, so people keep looking for ways to use OEM parts to make a motor that doesn't thrash.


I hope you did short banking last year. Would have crushed this year. I shorted energy and that trade stopped working in Q2.
 
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