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I have been building engines for about 30 years or so but can't seem to get a straight answer on factory e10 crankshaft strength. I am building a "budget" performer and need to know the crank material ( I.e. 4340 chromoly , 5140 chromoly, ) in order to calculate max stress and RPM that it can tolerate. Also, are any high volume oil pumps available for this engine series? Any insight would be very helpfull.

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If you get near 700 hp, maybe think about oil pump improvements?

 

This guy swapped an m30 rotor into the stock 02 pump, for a bit of an improvement, and he has 740rwhp.

http://www.bmw2002faq.com/topic/119432-m10-dyno-world-record/

 

I can't find where he made any improvements to the stock crank.

 

Sorry that this isn't commonly known information, because these parts don't break.  With a 'budget' build you'll get nowhere near their limits.  Worry about rockers and other valvetrain parts instead (IE HD rockers are working well for me). 

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A completely stock crank can put up with a hell of a lot of abuse. You'll likely destroy main bearings long before the crank lets go. A balanced stock crank is likely good up to 10,000 rpm of continued use. As said before, the bottom end is not what you have to worry about, it's the top end. 

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I have been building engines for about 30 years or so but can't seem to get a straight answer on factory e10 crankshaft strength. I am building a "budget" performer and need to know the crank material ( I.e. 4340 chromoly , 5140 chromoly, ) in order to calculate max stress and RPM that it can tolerate.

I like math and calculations... but have never done it for the M10 crankshaft.

 

My own empirical data: I lightened an M10 crankshaft by six pounds, have run it in a full race engine with nearly 160HP at the wheels for 80+ hours without issue. (Is there a calculation to translate race hours to street hours?)

 

Also: Suggest checking M10 crankshafts for straightness. -KB

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Excellent! All of this info is greatly appreciated. I will be using this for some competition use and running around 8000 peak for 30 minute stretches , and I know most factory cranks will not tolerate that. (American engines come to mind) . I figured they must be pretty good since a google for crank failure didnt reveal much. I already have h-beam rods, forged slugs that are slightly tall so I can machine them for the head once I determine the set up for that. I will focus on the head as you all suggest. Once we start the machine work I will take some pics and post it. At this point we were shooting for a cost of $1000 without machining cost (it's free if I do it) but it looks like it is going to be around $1500 for the build of the long block. Thanks again for all the help!

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Unless you are a serious machinist and can make your own rocker arms, a budget of $1500 is going to hamper your desire to turn 8000 rpm for 30 min.  You talk about how many RPM you want to run but nothing of the HP and Torque you expect to make.  You can turn a stock M10 to 8000 rpm (not for very long) on a stock cam and 1 bbl carb but it will not be making any power up there.  There are other considerations you need to look at.  Is this going to be just a track car or also a street car?  Things you can do on a race engine that does not spend a lot of time at any single rpm can cause problems when you get out of the freeway and cruise for an hour at say 4000 rpm.  There might just be at a secondary harmonic and cause a problem at some point in the rpm range.  (lightweight cranks are not a great idea on street cars).     

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After re-reading, I think he meant that it'd be run hard for 30 minutes at a time, which includes often being at a peak of 8000rpm.  At least I hope.  I don't know what racing series would ever require you to stay at 8000 rpm for 30 minutes straight.  That does not sound comfortable.

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I was making that assumption also, but once again RPM does not let us know how much power he is planning on making.  A lot of people spin their engines a lot harder than the HP or Torque output needs them too.  I know exactly what it takes to make max HP@8000 rpm with a M10 and doing it on a $1500 budget is not going to be easy. 

 

First rule of racing "HP cost $$$, How fast do you want to spend?"

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After re-reading, I think he meant that it'd be run hard for 30 minutes at a time, which includes often being at a peak of 8000rpm.  At least I hope.  I don't know what racing series would ever require you to stay at 8000 rpm for 30 minutes straight.  That does not sound comfortable.

Correct! It will need to turn hard periodically but not continuously. I will run between 5500 and 7500 on a road circuit and naturally aspirated is a requirement. I already have most of the parts on hand and at this point I have about $800 in it. A one barrel carb? Not quite, it is well breathed and well camed. I hoping for 200 hp. Should be easy enough.

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