Van

Charlie, that looks more like a rocker-arm assembly... and you can see, for the "vtec", which is like our "variocam", there are two cam lobe profiles. The large lobe presses down on the follower between the rocker arm - which must have some sort of actuator, probably hydraulic, to engage it with the rockers; and then the small lobes move the rockers a different amount when the central follower is disengaged.

I wonder if there's a way to make some kind of spacer plate that holds a modified cam box a little further away from the head... and then you might have room to develop some kind of roller-follower rocker arm that can push the valves down. Maybe regrind the camshaft so the lobes are smaller for more clearance for the new apparatus?

Van

I was doing a little research - it seems there was a mercedes that used electronically actuated valves?? I can't seem to find pictures, though. And I don't think they're still doing it, so possibly it didn't work that well.

bad_monkey

Solenoid actuation is the next development in F1 etc - a camless valvetrain. Theoretically endlessly variable timing and lift, reduced friction, no need to provide oil for a cam assembly.

It was supposed to be part of the 2008 mercedes c class - they called it "KDI EVT". I don't think it was ever released.

Valeo are making parts for this now...


You can see how it works quite easily. The control would be complex, and require another computer - and there would surely be challenges to overcome when switching a magnetic field so quickly.

The interesting thing is that the magnetic field could positively close & open the valve, but you'd have to be sure of how quickly you could close the exhaust as the piston approaches in order to run any overlap.

An interesting new technology.

bad_monkey

Yarf

Charlie
Does the DME/ECU limit the rpm?
Keith

Van

I saw that video when I was searching. There is also lots of high-speed footage showing springs rotating, valve stems flexing, and valves floating.

Keith, the DME limits RPM by cutting the fuel supply to the engine.

bad_monkey

The rev limiter can be removed by a custom chip - or moved to a higher point for safety. The Rogue Tuning DME mods look promising for this too.

A related issue will be successfully maintaining the correct fuelling at higher RPM - but that's a relatively well known problem across different engines compared to the potential upper limitations of the hydraulic lifter valvetrain.

Dave W.

What's this about a high rpm fueling issue? I haven't heard of this before. At what RPM is it noticeable?

bad_monkey

Well, first issue is that the stock mappings won't "know" about higher RPM.

Furthermore, the way the stock systems were designed, the injectors were batch fire - all injectors fire at once. Fuel sprays behind the closed intake valve and is atomised by heat / drawn in when it opens.

http://www.frwilk.com/the944/injectr2.htm

http://members.rennlist.com/951_race...atchFiring.pdf

I'm anticipating that we might reach the limit of injector duty cycle using this strategy at higher RPM - i.e. always-on becomes not enough. Bigger injectors might work, but I think that there may be some advantage to a reworked injector strategy.

The fuel output is limited by injector throughput and rail pressure - so I reckon some upgrade of these will be needed to support increased RPM / power.

The control aspect becomes of concern where fuel and timing are concerned - I'm kind of counting on Rogue tuning to provide us a reasonably flexible solution at a hobby budget here.

Rogue_Ant

Tuning in...
Higher RPM. The first major hurdle is oil-pump cavitation.

Next, regarding higher-RPM fueling/timing control - this is workable. Many OEM & aftermarket injection strategies utilize batch-fire after a certain RPM or IDC (even ones that utilize sequential injection tend to revert to batch at some point). And regardless of injection strategy, at high RPM, the injection window becomes very short, necessitating the injection event to span over all 4-cycles (2-revolutions) of the engine.

Setting the fuel & timing maps to have better resolution and include higher RPM is not an issue. The M-Tune uses enlarged/enhanced maps. It is just a matter of including the RPM we might need. Ultimate RPM-limit is going to be how fast the DME can actually count all the teeth on the pressure-plate (130 for the 944, 132 for the 951). If you are wanting really high RPM, an overclock of the DME might be necessary (also tested and done). When I get some time, I will do some DME upper-RPM limit testing on my bench.

Injector upgrade is also not an issue. The Honda S2000 (9000rpm red-line from factory) uses ~360cc/min injectors. With the stock 944NA injector being ~240cc/min, an upgrade would probably not need to be very extreme.

MAGK944

When I was with Lotus in 78 they were experimenting with solenoid valve actuation. They used Moog valves at the time, they were precision, fast cycling solenoids (electrically activated, hydraulically driven). The same valves were used in aircraft undercarriage systems at the time.

The problems they had, if I recall correctly, was controlling open/close duration at various speeds, but computer technology has moved on somewhat since then. I bet we are not too far away from camless engines and infinite variable valve technology nowadays.

Cochezz

I have a few questions.

To the OP, Why do you want to increase the RPM?
What are you trying to acomplish and what is the max rpm?


Rogue Ant, any news on the NA mass air flow setup?

MAGK944 what did u do for Lotus in '78?

MAGK944

Kept the tires warm in the paddock for the some guy called Mario Andretti Unfortunately we lost Peterson that year

Van

A guy has asked me about making vinyl graphics for a John Player Special theme for his 996.

bad_monkey

The line of thought I'm following is that given a fixed displacement, one way to achieve more power is to spin up to more RPM.

To do that effectively you need to understand

a) how to avoid functional degradation at higher RPM - e.g. valves not closing, oiling issues etc.

b) how to make use of the increased throughput - fueling/timing/spark/exhaust - this is an area not yet discussed in this thread, and it's good that Rogue could join in here.

What I'm looking for is practical hobby / weekend racer budget methods to achieve an increase in power through higher RPM - and so the limits are likely to be lower than those achieved by full-on builds like Henk's 3.2 16v engine.

I'm going to estimate here that about 8k rpm is going to be the practical limit - maybe a little higher.