TO EVERYONE that is making or has made a stroker.

[rwh11385]

http://e30m3performance.com/tech_articles/engine-tech/rod-ratio/kin2.htm

TDC acceleration talk

http://e30m3performance.com/tech_articles/engine-tech/piston-dynamics/dyn2.htm

force on cylinder wall by changing rod length !!!

i know better than anyone that the "if i'm gonna do it, i'm gonna do it big" mindset, but it's silly and unneccessary, and you get in over your head

plus, i know very few logical engineers. (it's always "let's go for overkill!!")

[Sean]

I know Heeter - I know.

Yea, I burning tons of moeny on this. Yea, I'm going for longer stroke.

But - now that everything's apart - I'm just like - FUCK IT - lets get'rdone and have fun with this.

If I knew everything I knew now - I WOULD HAVE thrown the M20B25 into my car and been done with it - but I had to rip off the head and do all this and that before I learned everything I know now - so, no point in just putting a measly b25 back together now.

If the engine is designed right - it should still last a long time.

The reason the BUDGET 2.7i stroker will not last is because you have a long stroke revving up to 6500 rpms and a heavy piston and rod combination, not to mention a short rod with a long stroke.

What I'm doing is similar - an 89.6mm stroke with 135mm rod is only a 1.5 r/s ratio - however, the lighter piston and rod will make it so the engine CAN rev high, without hurting itself in the process.

I know I'm in college, and I know I went from doing a budget stroker to a full blown almost 3.2i stroker - but I'm having fun with this. If I can pull of the money (which I'm still waiting to find out) that's what I'm going to do. I only live once, so I'm going to make the most of this.

I never once said I knew everything. What I do know is that I'm learning. If you think I'm a dumbass, retarded, wasting my money, some ricer, or a loser that doesn't know what he's doing - I figured that. State your opinion, and it'll be heard. But that's it - I'm making my own decision based on what I decide and me only. :D

shorter rods dont rev as high? 130mm rods in my 323i with a 6600rpm factory rev limit would tend to suggest otherwise.

Problem with the 3L motor is with the longer stroke you increase the piston speed at tdc. If you plan to rev the motor to exceedingly high rpms you are going to have to replace the factory forged items with something stronger and make sure you have a good set of rod bolts holding it together.

The problem exists because you can only reduce the piston compression height so far before you sacrifice piston strength. If you ran a 135mm rod a piston with a comp height of 28.8mm is just on the limit of what you want to reduce it to (and a lot of machinists wont produce a piston with a height much less). To run longer rods you would have to sacrifice metal on the crown and lands, thats not a good idea.

You guys are treating this like its all a blanket statement, rod ratio's arent quite that simple and they are only a guide figure, case in point bmw develop quite a few engines with less than ideal rod ratio's, yet they last the distance (why, because it isnt that simple). To investigate the inner workings of your motor package there are a lot more things to take into consideration. Things like how timing is effected, how efficient the engine is going to be at different degrees of the crank, piston speed at bdc and tdc, effects on pressure waves, cam timing and lift, etc. Ive got like 7 pages worth just on calculations relating to the 3L im building and i havent even touched a bolt yet.

You cant start talking about things like rod ratios in simple terms, it just isnt a figure that can be used like that.

if you want a new set of rods, brian crower will make you a new forged set to suit for about $10-$15 more (per rod) than the cost to replace the standard factory rods from one of the many parts places.

Madhatter, I entirely understand there's a lot more that goes into an engine than just a rod/stroke ratio.

What is the stroke on the 323i motor? I never said short rods don't rev high - I said short rods with long stroke don't rev high. If I'm wrong - than oops.

I'm just sharing my thoughts with others, hoping to get some input and guidance on my thinkings, on whether they are right or not.

Brian Crower, where's this at?

[rwh11385]

If I knew everything I knew now - I WOULD HAVE thrown the M20B25 into my car and been done with it - but I had to rip off the head and do all this and that before I learned everything I know now - so, no point in just putting a measly b25 back together now.

*cough* engineer *cough*

there's nothing stopping you from putting in a good m20b25. no matter what you think you've "sunk" into this thinking or process, just evaluate the cost/benefits for the future (not the past)

[Sean]

Also - madhatter - what rod bolts do you recommend?

I've been talking with Metric Mechanic a lot, Jim has a lot of good things to offer. I'm pretty much going to be making the bottom end of their 3200 Sport engine - just sourcing out my own parts.

Another question for you - would you recommend modifying the stock oil system? Like, Jim said they make special bearings that have 360 degree groves for oil in the main bearings as well as special rod bearings. Is this a good idea to look into?

I don't plan on revving increbly high - just like 6500 or so. Even then, it won't happen right away because I won't have a completely worked over head quite yet - so for a while, my car will not have a ton of power - but I just want my bottom end to be set.

*cough* engineer *cough*

there's nothing stopping you from putting in a good m20b25. no matter what you think you've "sunk" into this thinking or process, just evaluate the cost/benefits for the future (not the past)

LOL yea...this is true. THat's a good point. I suppose I could find a good B25 for cheap, like $450-$600. Hell, I spent that much just on everything for the rebuild. But I just feel like I've gone this far...why go back now?

[rwh11385]

The reason the BUDGET 2.7i stroker will not last is because you have a long stroke revving up to 6500 rpms and a heavy piston and rod combination, not to mention a short rod with a long stroke.

What I'm doing is similar - an 89.6mm stroke with 135mm rod is only a 1.5 r/s ratio - however, the lighter piston and rod will make it so the engine CAN rev high, without hurting itself in the process.

135mm rod / 75mm stroke = 1.8
130mm rod / 81 mm stroke = 1.6
135mm rod / 89.6mm stroke = 1.5

so you're going with a 1.5 r/s ratio after thinking a 1.6 one at 6500rpm would be too risky, not long-lasting enough?

you may be decreasing the mass of the piston/rods, but that may still have an increase in force against your cylinder walls.


did anyone mention using i rods and machined i pistons? shit wasn't this a setup back in the hay day? that would give a 1.67 r/s ratio, and i forget what c/r. and fucking affordable.

[Sean]

135mm rod / 75mm stroke = 1.8
130mm rod / 81 mm stroke = 1.6
135mm rod / 89.6mm stroke = 1.5

so you're going with a 1.5 r/s ratio after thinking a 1.6 one at 6500rpm would be too risky, not long-lasting enough?

you may be decreasing the mass of the piston/rods, but that may still have an increase in force against your cylinder walls.


did anyone mention using i rods and machined i pistons? shit wasn't this a setup back in the hay day? that would give a 1.67 r/s ratio, and i forget what c/r. and fucking affordable.

Yea, I'm jumping all over the place.

I understand there will be more force on the side of the piston.

If you think about it though - the S52 runs the identical setup - the 135mm rod with the 89.6mm crank. (yea, there are differences in block design...just pointing that out though.)

[rwh11385]

You don't want to run short rods, stick to the 135mm, and machine the pistons.

http://www.r3vlimited.com/board/showthread.php?t=63141&highlight=machined+pistons

The consensus amongst engine manufacturers is that a ratio of 1.50 is the lowest acceptable rod ratio for a street motor. Realistically, rod ratios between 1.65 - 1.80 are ideal.

http://www.r3vlimited.com/board/showthread.php?t=50434&highlight=machined+pistons

IMHO, I would not go for stroke on an M20. You might get a torquey beast (like Ted's, others), but I can't really imagine the SOHC head flowing that much air for a longer stroke. That's not really my bag, baby... (diminishing returns I would think)

You can throw down for custom pistons or machine "i" ones, use I rods and an eta crank, either bore out for 85mm or not, just go stock bore, and use the money from not throwing down or waiting for a S52 crank on a 284/274 cam (if you desire).

I mean, Jordan put down good numbers and he didn't have to bling out on a huge stroke crankshaft. And don't you already have an eta crank? And I rods?

[madjurgen]

You shouldve waited till you graduated to do this project, then money would no longer be a big issue and you wouldnt have to compromise in certain areas. i couldnt imagine doing this project in college. Im glad i waited, its SO much more fun on an engineer's salary.

You didnt wait, but glad to see you still believe in the 'do it right once' philosophy. I never thought that philosophy came from being an engineer but i can kinda see where it might. So if you find the funds do it. (But lets let nando go through it first, so he makes the mistakes and not us)

[madjurgen]

I mean, Jordan put down good numbers and he didn't have to bling out on a huge stroke crankshaft.

I think this actually serves as inspiration to both Sean and I.

'If Jordan put down such good numbers from a 81mm crank imagine what I can do with a 86/89mm crank, given all other things equal.'

At least thats my train of thought.

[Sean]

Robert, thanks for bringing up those threads, I think I had read them before, but they were good to read again.

Yea, doing this while in college isn't the brightest thing to do, and I would ahve waited - but I had my top end ready to go for my budget stroker, so I needed to get it done - the shit was just laying around.

Once I got into it, I learned that doing it the way i planned wasn't all that great. Then I looked into other options. Although expensive - if the guy that owes me 2 grand pays me, I should be golden. If he doesn't...I'm looking into other means.

If I wanted to, I could go thru with my original plan...and do this project on my spare block when money allows.. Thing is, I have so many spare parts - I got tons of stuff. An extra I casting head and whatnot. hmmm



How much do I ened to shave off of an I piston to get it to fit with the 81mm stroke and 135mm rods? I might have a good deal on s50 rods, so I might just do my eta crnak, s50 rods, and shaved I pistons. yes..no? (Don't say it, I know I'm jumping back and forth - Robert brought up some good points - and it helped to uncloud my mind and think in terms of dollars rather than just straight power)

[DrMcDave]

the engineer thought process is fun. I think your right about overkill though. I first started thinking stroker a long time ago. I was going for a 2.8. I then called jim at MM and he started talking to me about this 3.2 which at this point only 2 exist which to me was kinda scary. The one jim didn't build basically drinks oil but the guy messed up the rings. There is a 3.2 liter ix in ohio built buy some guy i've spoken w/ on the phone a few times.

chris (e30tech owner) and i were going to build these 3.2's but the price keeps going higher and higher. the bottom end can be done for 2k or so+machine work. My concern came in when he spoke of massaging the cylinder walls. I only trusted jim to do this so i was going to send my block down there. then he started talking about lightweight custom rods another 1000 dollars and then his head gasket. The price kept going up and up.

i can't wait to see someone build one that puts out like 260hp

[rwh11385]

nah, think of how constrained the head is and how much it doesn't flow compared to a S50 head. going vertical probably doesn't have as much help to an m20 as a s50/s52.

http://www.r3vlimited.com/board/showthread.php?t=44068&highlight=unichip

Chris's 3.0L stroker - 188.2rwhp (MAF)

http://www.r3vlimited.com/board/showthread.php?t=53015&highlight=unichip

Jordan's - 170ish rwhp / 175ft-lbish rwtq (2.8l with 274, MAF)

David Lengths 3.0L stroker made 181rwhp and 189rwtq.

...that day by day 2.7i with the HOT cam - Peak whp: 160 with m20 afm

I'd build a 2.7i budget stroker with machined i pistons, i rods, eta crank, 284/274 cam, m30 afm (to start), if I hypothetically wouldn't have just done a M50 nonvanos swap instead!

I would rather spend the money on a better cam, MAF swap, and tuning with Unichip or otherwise than worrying about increasing the stroke, which gains are only marginal.

[rwh11385]

I think this actually serves as inspiration to both Sean and I.

'If Jordan put down such good numbers from a 81mm crank imagine what I can do with a 86/89mm crank, given all other things equal.'

At least thats my train of thought.

The problem is the head does remain equal and you're expecting it to still be up to par for the longer stroke and give a proportional increase with the increase in displacement, but that's not possible.

volumetric efficiency takes a shit at some point, and it's probably near or after 2.7 since BMW made their eta that large. i dunno. it's up to the person looking at the results what is worth it...

[rwh11385]

How much do I ened to shave off of an I piston to get it to fit with the 81mm stroke and 135mm rods? I might have a good deal on s50 rods, so I might just do my eta crnak, s50 rods, and shaved I pistons. yes..no? (Don't say it, I know I'm jumping back and forth - Robert brought up some good points - and it helped to uncloud my mind and think in terms of dollars rather than just straight power)

Have Stu ask his dad, or call Pete yourself. He used to or still does it. It's like 3mm or something.

Do you know many companies that allow it to be entirely ran by engineers?? Nah, that'd be crazy. :drink: (unless they have MBAs)

[Sean]

the engineer thought process is fun. I think your right about overkill though. I first started thinking stroker a long time ago. I was going for a 2.8. I then called jim at MM and he started talking to me about this 3.2 which at this point only 2 exist which to me was kinda scary. The one jim didn't build basically drinks oil but the guy messed up the rings. There is a 3.2 liter ix in ohio built buy some guy i've spoken w/ on the phone a few times.

chris (e30tech owner) and i were going to build these 3.2's but the price keeps going higher and higher. the bottom end can be done for 2k or so+machine work. My concern came in when he spoke of massaging the cylinder walls. I only trusted jim to do this so i was going to send my block down there. then he started talking about lightweight custom rods another 1000 dollars and then his head gasket. The price kept going up and up.

i can't wait to see someone build one that puts out like 260hp

I hear ya...I started lusting for that motor.

But, now that I think about it - I'd STILL be cutting corners. I'd get enough for pistons...but what if I decided not to reenforce the oil system, or skimped out on con-rod bolts?

I'm going to hold out. Robert's right...it's just plain retarded to force this all upon myself when I know so little. A 3.2i is a big udnertaking.

Damn...lust clouds your mind quick.