Author Topic: Limits of stock valve springs (Read 6958 times)

nobrakese36 · « **on:** November 13, 2006, 01:30:25 AM »

What is the highest m42 dual valve springs an be taken too?? Whats the highest anyone has gone with them??
thanks

Febi Guibo · « **Reply #1 on:** November 19, 2006, 01:44:15 PM »

I have new beehive valve springs (not cheap) and my motor revs fine to 7600 rpms... its more insurance than anything

*new* stock should be good to 7000 rpms.

cecotto · « **Reply #2 on:** November 20, 2006, 09:25:52 PM »

I have no information on the stock valve springs.

But i think to ask that question one would also have to know:
* Camprofile
* Moving mass
* You already brought up the RPM

If you have installed a sports or race cam, chances are that it will have higher lift, and steeper flanks. This results in a quicker acceleration and faster velosity. And thats exactly what the springs are made to be in controll of.

At some time the mass of the valve, lifter, retainer and collets, will surpass the built up force in the spring. And shoot the valve off the cam profile. This is whats called valve float. Which you're probberly already aware of.

When i were planning my rebuild, i investigated this some as i thought that it would be relatively simple to do some math on the parameters. And this way predict at which rpm valve float takes place. But my digging only brought out more questions. As i realized that professional tools takes a very large ammount of parameters into account when simulating the valvetrain. Even the bottomend is simulated to bring in harmonics and what not into the equation. (And i'm not an engineer). I decided to just pay-up, and have the cam-grinder decide. It's a small price to pay, when building an expensive engine.

Also you should be aware that hydraulic lifters can pump-up when reving them past what they were intended for. So moving to mechanical operation is often done on high reving engines. Having sorted out the top end you should have a look at the bottom end.. How are those rods going to hold up??

Sorry to have brought up more questions, and no answers.. It just looked like the question i asked my self not too long ago. I found opinions on the subject. But none that i would trust my money(engine) with. Remember changing the profile changes the whole picture..

nobrakese36 · « **Reply #3 on:** November 20, 2006, 10:37:46 PM »

Thanks check out my build for what i am running, would you say the MM bee hives and heavy duty lifters are worth it? That is probably what i will run,well thanks

asubimmer · « **Reply #4 on:** November 20, 2006, 10:58:22 PM »

the stockers can at least do 7200, the markD is set there. My chip goes to 7200 also

nickmpower · « **Reply #5 on:** November 20, 2006, 11:32:20 PM »

i think ikm goign with the MM stuff. I think the lifters are just m50/ latter 318 lifters though

GuySchalnat · « **Reply #6 on:** November 21, 2006, 11:22:36 PM »

I think the problem is that the limit does seem to be 7200 rpm with the stock engine (my understanding is that the harmonic balancer flies apart soon thereafter, but I could be wrong about that), and anybody who builds a higher reving engine tends to put aftermarket springs in. Especially on a 16 year old engine. Besides, that is over 10% higher then the stock redline, so it seems BMW wouldn't have necessarily put in springs that can handle more then 7200.

-Guy

bmwman91 · « **Reply #7 on:** November 22, 2006, 02:41:37 AM »

The crank damper thing WAS widely accepted as truth for a long time. A few quite knowledgeable and experienced people on here debunked it though...maybe one or 2 people had it come apart, but it was probably damaged or totally crapped out from road salt or something. A damper in good condition should be fine beyond what the motor can do.

The REAL worry is the hydraulic lifters. Above 7200RPM the can cause valve float from the immense oil pressure. You need solid lifters if you are planning on going beyond 7200RPM.

e9nine · « **Reply #8 on:** November 22, 2006, 11:03:30 AM »

For those of you guys concerned about revving high - are you doing any other headwork to aid? Each time i read of cams and other accessories no one seems to have done any port and polishing or valve jobs? I am no expert in this area but my curiousity lies in no one seemingly doing headwork?

With the stock bottom end plus a worked head in addition to cams and higher rev limit, shouldn't that make for a nice combo?

I don't mean to thread jack as this seems in line with the discussion at hand.

GuySchalnat · « **Reply #9 on:** November 22, 2006, 04:11:46 PM »

Quote from: bmwman91;14282

The REAL worry is the hydraulic lifters. Above 7200RPM the can cause valve float from the immense oil pressure. You need solid lifters if you are planning on going beyond 7200RPM.

Ouch. I wonder if, in an autocross car which bounces off the limiter often, I should keep it a bit below that, just in case? Or can I bounce off the limiter at 7200 safely (at least as far as the lifters are concerned)?

And I wonder if I should replace the lifters first?

I understand about parts that may fail if already marginal. I had the alternator belt tear apart bouncing off the stock limiter (6520 or something), but that doesn't mean the belt won't handle higher rpm's. It just means that I should change my belts more often in my autocross car (I'm now thinking once a year, and why not? it isn't that expensive), and carry an extra belt with me to events.

-Guy

tim_s · « **Reply #10 on:** November 22, 2006, 04:25:27 PM »

I've done a decent flow job on a late m42 head. it was originally built for my e30, but i ended up donating it to another m44 project!
TBH there's not too much wrong with the standard head, i enjoyed flowing it though and the finished article looked very pretty! next time i do one i need to pay more attention to the m44 head, as having taken one apart there's some interesting stuff going on.
I dunno about lifter overpumping being that much of a problem, I've rev mine to 7,2k and its still pretty strong.

Vladi · « **Reply #11 on:** November 22, 2006, 05:00:18 PM »

I try not to hit 7000rpm too often. Had the engine since the begining of august and only hit it once, like I,II,III.

e9nine · « **Reply #12 on:** November 22, 2006, 05:05:54 PM »

I have had a Mark D chip for close to a year with no ill effects. Mind you the fact I can rev to 7200 rpm doesn't mean I do it religiously. I view the higher rev limit as an accessory to holding gears. Most times I shifts btwn 6500-7000 when possible. At the track it I would hit the limiter in 3rd more than any other gear when I tried to determine the best points to short shift into 4th as needed.

Tim S. Care to summarize the plus-side of the m44 head? Is it plug and play with regards to the m42 bottom end?

nobrakese36 · « **Reply #13 on:** November 25, 2006, 12:38:26 PM »

My head has been port and polished, i have forged Pauter rods, forged JE pistons,fully balnced crankshaft ,new bearings, resurfaced oil groves,and much more, I plan on running e34 m5 valve springs which are the same dimensions as e30 m3 springs which can rev to around 8000 rpm,as for lifters i will run standard(e36 m42 lifters) and eventualy upgrade to MM lifters.

Author Topic: Limits of stock valve springs (Read 6958 times)

GuySchalnat

GuySchalnat