Maximum Engine RPM
 

To all the guru's here on MSF.


Regarding my engine build I'm curious to know what has been shown to be the maximum engine RPM that is safe to run on these engines. I know with the long stroke you wouldn't want to push it too far but is it possible to safely go to say, 7500rpm?

I'd like to make full use of my built motor, balanced and forged bottom end with PNP heads paired with a GTX3076. The motor currently will be using an otherwise stock valvetrain. If I wanted to run at 7500rpm, would I need to upgrade my cams and or valvesprings?

With the ability to harness the power of the EBCS would having a reverse tapered boost curve negate the necessity to change the cams? I'd like to maintain as long and as flat of a torque curve as possible if that makes any difference.

With upgraded rods you can probably get away with 7500rpm, its party due to the stroke and partly the rod length... in guru terms the rod angle is too great.

The valvetrain question is alot more tricky. Off the top of my head the intake valve has an area of ~1.4" which * 24psi = 33.6psi acting on the valve at 24psi. Iirc the intake valve spring has ~42psi seat pressure. So 8lb of pressure is all that is holding the valve closed. When you think of how fast a valve has to move to follow the cam profile at 7500rpm, i dont think it can be done with that spring pressure, even with the stock cam. Iirc the Cosworth duratec valve spring is the beefiest spring available, i think its in the low 50psi range but dont quote me on that.

What about shorter rods and using boost to make up the difference with regards to dynamic compression?

I ask because it seems that would keep torque in check, too.

I'm running Carrillo Forged Pro-H Beam Rods w/CARR Bolts for my build. Do you think they should be able to hold a 7500rpm redline or is that still pushing it too far.

As far as seat pressure goes would I see any downsides to upgrading the springs to say a 60lb beehive or a 70lb dual spring? Would I have increased wear or anything to be concerned about?

^^^ stiffer valve springs will create more heat on the valvetrain components and more strain on the VVT / chain system. The DCR VVT might be up to the task but there aren't really that many people around here running stiffer valve springs. 06speed6 might actually be the only one. If he is...

So this still be somewhere uncharted territory then.

Ah well, I'll what the engine builder says and we'll go from there. I'll probably start with the 60lb beehive springs. See what happens.

got to be carefull with chain stretch too. I heard Mazda revised the material of the chain. Some stretch.

If we had a non interference engine without VVT and belt drive instead of chain I would run stiffer springs and rev the thing up to hell without any concerns. On this engine it's a lot more riskey. Once one the valves starts to float you are toast. How long the chain will last with stiffer springs before it starts to stretch is also a crap shoot.

You can try lightening the intake valves like one of the Ukrenian guys did on this forum. That's also what I did except I went even further and lightened them to the same weight as the exhaust valves which is 45 grams. I am gonna shoot for 7500 red line once the engine is built.

The point 06speed6 makes regarding boost pressure against the inlet valves is a good one but not completely measurable the way he portraits it IMO. The inlet valves have a slope and also you need to discount the diameter of the stem from the surface area. I think, and I repeat, I think, that boost pressure is not a large factor inhibiting float on the intake valves.

I don't know what valve springs some of the built evos run, but I know they can rev stroker 2.3L engines to 9000 rpm at 30+ psi of boost.

http://i1211.photobucket.com/albums/...20115-1804.jpg

http://i1211.photobucket.com/albums/...20115-1837.jpg

http://i1211.photobucket.com/albums/...20116-1233.jpg

*cough* supertechvalvetrain *cough*

yeah. If you want to pay 2k+ go for it.

the dude built/balanced a motor and did pnp work on the head. why not spend the extra money and do the whole thing right? trying to ghettoup the valvetrain to withstand the rpm he wants rather than upgrading smartly is just asking for trouble, IMO.

Plus, with the supertech valvetrain, you should be able to rev 8k no problems. Engine management allowing 8krpm right now is a different story (same with cams)

IIRC, mazdagarage pat runs his motor to 8k. He wants to run it to 8500 but is afraid of fueling. His valvetrain is stock i think, minus his lightened valves. I will try to dig it up

Here we go:

I subtracted some valve area to account for the stem.

Iirc that isnt the installed height that supertech lists for their springs, so the correct seat pressure is lower than the numbers they give. Dual springs are fine for track cars, but if yours is street driven they arent so great. They generate alot of extra heat and they wear out alot faster than a single coil spring. Ide recommend a single coil spring for the street.

A shorter rod would make it worse.

IMO this is the way to do it. No need to worry about overloading the timing chain and too much heat this way.

I'm running half a supertech valvetrian already, upgrading the rest of it just makes sense to me. The builder just told me unless I changed the cams the was no piont in changing the springs.

So all i would really need to do is lighten the intake valves and I should be fine.

So which is it?
And what's a 1/2 supertech valvetrain?

I'm running the exhaust valves, guides and seals. Stock everything else.