Author Topic: Engine rev limit (Read 10914 times)

sheepdog · « **Reply #15 on:** January 09, 2008, 12:17:25 PM »

That safety margin is why I said 7k is about the limit.

Many of the parts can hit 8k. That is not a question, the problem is that some may not. You may start pumping lifters, over-stressing bearings, and more. Any idea how good your oil system is? How about bearing condition? Timing chain?

If it were all brand spanking new, yeah, you could probably do 8k for short bursts, probably hit 7500 for a touch longer, but on a 130k+ mile engine... No.

May want to take a look at some of the bearings in the engine and read the Metric Mechanic engine manual. There are quite a few things in this motor to hold you back from ramping up the revs and keeping your engine living a healthy life.

kowalski · « **Reply #16 on:** January 09, 2008, 11:12:00 PM »

i hit 7,600 on an engine with 340,000 km's on the bottom end. the top end has reground cams and thats about it. i did it once by accident, but i've been driving ever since with no problems, i held it at 7,600 for good couple of seconds though.

Boyracer · « **Reply #17 on:** January 10, 2008, 03:01:45 AM »

Well, it is quite pointless to argue about few hundred RPM's because this is no exact science and there are sooo many variables (age of valve springs, used oil etc).

Also, power targets and purposes of the engines vary from person to person. Somebody wants the car to last until a million miles and somebody needs to have 200 hp for one track season.

Only way to know for sure is to try it out... That is not very constructive practice because when you have found the limit it is too late. But since complete M42's are going for few hundred �'s so the loss of engine is hardly an end of the world anyways.

I think the guy here (ludiagsm?) who turbocharged his M42 revved it all the way up to 8500 with a stock valvetrain? Bottom end was obviously modified to take the stresses but I think that shows that atleast the hydro lifters, valve springs etc do not abrutly stop working bit past 7000. They might not last for another 10 years but when you can have spare engines for a cost of 5 tanks of fuel, hey, you might as well take some risks

BrandC · « **Reply #18 on:** January 10, 2008, 06:28:52 AM »

Say you're engine is built to rev to 8000 rpm, how would we make sure it has sufficient oil pressure? Febi, how is your oil pressure holding up at those revs?

Oversteer · « **Reply #19 on:** January 10, 2008, 06:53:01 AM »

I've ordered a chip that has the rev limit changed to 7K, so I was wondering if it was safe to rev it there.

I think that 7K is enough for what I'm planning, cause I won't go radical about engine spec, keeping it standard with the chip and a KN panel filter. Plus, I'd need another rev counter!:D

sheepdog · « **Reply #20 on:** January 10, 2008, 02:07:56 PM »

Quote from: Boyracer;40898

Well, it is quite pointless to argue about few hundred RPM's because this is no exact science and there are sooo many variables (age of valve springs, used oil etc).

Also, power targets and purposes of the engines vary from person to person. Somebody wants the car to last until a million miles and somebody needs to have 200 hp for one track season.

Only way to know for sure is to try it out... That is not very constructive practice because when you have found the limit it is too late. But since complete M42's are going for few hundred �'s so the loss of engine is hardly an end of the world anyways.

I think the guy here (ludiagsm?) who turbocharged his M42 revved it all the way up to 8500 with a stock valvetrain? Bottom end was obviously modified to take the stresses but I think that shows that atleast the hydro lifters, valve springs etc do not abrutly stop working bit past 7000. They might not last for another 10 years but when you can have spare engines for a cost of 5 tanks of fuel, hey, you might as well take some risks

Exactly.

N�R-SPEC · « **Reply #21 on:** February 05, 2008, 11:00:32 PM »

i'm willing to bet an M42/44 is well capable of 11K.

dry sump, solid lifters, lightweight valvetrain components, heavy springs, light flywheel, edged crank, ITBs, SA EMS, larger injectors, serious internal balancing, high duration cams, high comp pistons, 4-1 manifold, ect, ect.. should turn out rougly 300 to the flywheel.

how long would it last? 10K miles maybe. and it wouldn't idle. if you bought a few longblocks from the JY, you'd be able to swap parts over to new motors. would it be worth it? i doubt it. why bother making 300hp at a super high rpm, when you could make 300hp at 4-5Krpm with forced induction and have the motor last 100K miles. the only way i'd build a high strung M42 is if that's what was required by a sanctioning body of a racing organization.

swiss318is · « **Reply #22 on:** February 06, 2008, 03:04:33 AM »

Quote from: N�R-SPEC;42268

....dry sump, solid lifters, lightweight valvetrain components, heavy springs, light flywheel, edged crank, ITBs, SA EMS, larger injectors, serious internal balancing, high duration cams, high comp pistons, 4-1 manifold, ect, ect.. should turn out rougly 300 to the flywheel.

yes, do that and then you have a s42 engine! only some "small" changes to a m42b18 engine!! ;-)

!after a telephone with my racecarbuilder! set your rev limit for an m42b18 with stock hydros etc. to 7000rpms just to stay on the save site! think on your tiny oilpump! :-)