Higher max RPM

[mmg]

Hi,

Has anyone tried going up with the max rpm limit? How much more RPM can the the engine take without modifications to the valvetrain?
Stock limitter seems to be at 6700. I would like to use more rpm to make better use of my hybrid turbos at low gears

 

[Thomby]

I do like a high-revving engine, and ours may well be good for 7000+ mechanically, but our turbo setups are oriented toward low end spool/torque. What you'll see more of is recommendations to short shift closer to 6000 before the stockers fall off.

I'm not sure what your hybrid turbos involve (bigger turbine, or compressor, inside stock housing?), but the combined manifold/turbine housing has a severe narrowing (1.1-1.2"?) which is why we haven't seen 800-1000+ hp big turbo builds.

Meaning, you may be tapped out on flow ahead of redline, so higher revs would be futile. Have you dyno'd your car with the hybrids to see what the power curve looks like up high?

Jump to about 4:15 here:

 

[mmg]

Turbos are only slightly larger, +4mm inducer wheel, +1,7mm exducer wheel
Nothing crazy, designed to make a tad over 500 hp efortlessly on pump fuel without crazy tune, methanol etc
I fell I need just a little more RPM on 2nd because there is a large difference in gearing from 2nd to 3rd
Question is if anyone has tried that and how much more the valvetrain is willing to take

 

[Thomby]

The argument for shifting lower, say 6000, is that power drops off quickly enough, and our 8-speed's gears are so close that the rev drop is minimal enough, that trading (say) 6000-6500 for 4700-5200 is a worthwhile increase in power. Check out the dyno examples below, and how flat power is from ~4500-5500.

Your turbos should flow more efficiently, but I'm not sure if that will translate to power that continues to increase at higher revs (despite the manifold/housing restriction), or if it will just shift the whole curve upward proportionally, meaning you'll still have the dropoff and benefit from lower revs.

Which is why I'd recommend a dyno, to see how it behaves up there. And maybe ping a couple of the performance shops to see if they've had any luck with higher revs on bigger/hybrid turbos.

 

[mmg]

thanks but the question was if some extra (say 500) rpm would hurt the valvetrain or is considereded safe. 7000-7200 rpm limit for example

 

[rtv900]

thanks but the question was if some extra (say 500) rpm would hurt the valvetrain or is considereded safe. 7000-7200 rpm limit for example

nobody can say dude, you'd have to try it to see
obviously they'll float at some point, and floating doesn't necessarily mean they'll hit if it's just a tiny bit
it will simply progress from whatever speed the springs can't keep them on the cam
So go ahead and bump up 500 and see

also, the rods are under considerable stress at high rpm too, so it's not just valves that can float
for all you know the valve springs are plenty stiff and you'll end up bending a rod or trashing a bearing

 

[mmg]

thanks
I don't want to be the first one to try
hence questioning