Valve and cam timing

[olefud]

Hey, I don’t know if it will live or not. The highest piston speeds I’m aware of are in NASCAR and they go 500 miles. There are a few generalities that may be helpful.

A while back modest cost engine pressure wave modeling code that handled supercharging was available. It did a pretty good job of getting you in the ball park and is a lot cheaper than cut and try with your engine.

As to cams, keep in mind that the strong intake pressure will negate much overlap by flowing out the exhaust. Just a touch for scavenging is all you need. Also, with the dense air/fuel charge, you probable will need a good bit of blow down to avoid losing power during the exhaust event.

Actual timing and lift is a function of intake/exhaust flow. With supercharging the exhaust needs all the help it can get. All things equal, two EX valves would seem the better approach (not that you have the choice) since the supercharging can cure many of the intake problems. For the same reason a lot more exhaust cam and flow is the better course.

[Tommy Cookers]

EPI Inc (in USA somewhere) have a very good website including the source material for a RCE article comparing engines, F1 with NASCAR

It shows the need for Titanium rods for the intended RPMs, also IMO you will need rings that won't flutter.

(I only have paper copy of article now, so you'll need to search for EPI)

[olefud]

Quick question. Do you have head flow data for the boost you’re using? It’s not too difficult to back calculate the general RPM at which the engine runs out of breath.

[blake5180]

thanks for all the tips so far. indirectly every response has paved the path for what looks like a promising season for testing.

I have got my computer simulations working and am finding some very interesting things. I now understand that RPMs aren't the most important thing. even with an overdrive limited vehicle. hopefully by computer sim i am only a cam shaft away from a seriously powerful engine.
the only thing is i am having trouble believing that closing the lobe center lines to ridiculous amounts, and as a result having about .350" of lift at overlap will make these huge torque and HP figures I am getting.

as for the flow, it is about 500cfm @ 0.8" lift we make 45lb boost max while our competitors make 50-60lb

Thanks again for the feedback!!!

[riff_raff]

thanks for all the tips so far. indirectly every response has paved the path for what looks like a promising season for testing.

I have got my computer simulations working and am finding some very interesting things. I now understand that RPMs aren't the most important thing. even with an overdrive limited vehicle. hopefully by computer sim i am only a cam shaft away from a seriously powerful engine.
the only thing is i am having trouble believing that closing the lobe center lines to ridiculous amounts, and as a result having about .350" of lift at overlap will make these huge torque and HP figures I am getting.

as for the flow, it is about 500cfm @ 0.8" lift we make 45lb boost max while our competitors make 50-60lb

Thanks again for the feedback!!!

blake5180,

The high manifold boost pressures will help relieve some of the dynamic loads on the piston and conrod around intake TDC. But the recip mass dynamic loads increase exponentially with rpm. While you can make the valvetrain survive at the operating frequencies you propose by reducing valve lift and duration, you cannot do the same for the piston/conrod recip masses with a given stroke length. Even with an ultra-lightweight aluminum piston and titanium conrod, the conrod bolts will quickly fail in fatigue with the level of dynamic loads created in your 4.1" stroke engine at 11,000+ rpm's.

With a pure drag race engine, IN/EX overlap is not so much of a problem. With a well designed header, any intake bypass flow from overlap will end up being pushed back into the cylinder by the header's acoustic reversion. The thing you need to watch out for with overlap is any contact between the intake and exhaust valve heads, and contact between the piston crown and intake/exhaust valve heads.

Lastly, don't forget to include the significant additional load on the exhaust valve face created by cylinder combustion pressure at the point of EXOP, when you analyze your valvetrain components.

Good luck.
riff_raff

[Tommy Cookers]

I agree that the conrod 'big end' bolts won't last long; I never thought that they would.

The task is on a par with F1, as I believe I said before. Piston etc accelerations are no higher (and no lower !). Friction will be high at the very high piston speeds, but this is not a problem in the quarter mile.

I didn't say 11500 rpm IMO is the best or easiest thing for a 4.1" stroke.

We agree that good luck will be useful to this application !

[strad]

I've spun small blocks to over 10 grand so the RPM isn't in my opinion the biggest obstacle..I don't know that the heads even supercharged will support the flow needed. Look the the runners in a Hemi drag head..MASSIVE,,probably twice the area of the most you could hog out a set of Ford three valve heads.

[elmerfud]

Try a one cylinder test first, i think the latest moto guzzi v twin was modelled on a nascar engine and is good for 9500rpm (i recall).

Titanium valves, 16mm lift, beryllium copper seats, forged pistons, low tension rings, maybe a steel rod.

Ambitious!