Building A High Revving Engine

[Z_FromDownUnder]

I've been wanting to get this off my chest for awhile now. Basically, the art of creating a High Revving NA engine is simply put down to a 'race' spec camshaft and nothing else is though of, although there are many factors that contribute to how high your engine will REV.

 

To start with a good quality camshaft will provide the most noticeable increase in possible REV limit. It will allow for more air to enter and allow for exhaust to leave without constriction. This will be the most effective step towards a higher revving engine because it will allow for clean and efficient explosion in the cylinders. Without a better camshaft, the amount of air entering the cylinder will be greatly restricted due to severely shortened time the valve is open for at higher revs.

 

E.G. At 3000rpm the Engine's crankshaft spins 50 time a second or once every 0.02 seconds

if the camshaft allows for 20 degrees of inlet valve opening then

20/360 (20 degrees of total 360 revolution) x 0.02 seconds = 0.0011111... seconds the valve will be open (not that long even at relatively low RPM).

 

At the target 8000rpm+ the time the valve will be open for is down to a tiny 0.0004166 seconds with is certain camshaft

 

This shows the extreme decrease in time the gases have to more a high RPM so EVERY DEGREE COUNTS at High RPM. Often these extra degrees that after market camshafts give you will overlap the intake and exhaust valves which is necessary at high RPM but will kill engine efficiency at low RPM, which is why you never chose a 'Race' camshaft for street.

 

The Camshaft is sometimes called the brain of the engine, but if you are looking for high Revs then the brains body needs upgrading. This means redoing the Valvetrain this is because the sort of wear that is experienced at high RPM is a lot higher than that the stock components where spec'd for. There are many things that can be done to the valvetrain for it to work efficiently, but the first thing that should be addressed is those springs, quite a few camshaft manufacturers require a complete replacement of stock springs when the shaft is installed to keep warranty. With new springs, the tendency for the valves to float open will be nullified. Port polishing will reduce restriction posed by rough surface allowing for greater flow. If possible the use of lighter components in the valvetrain will be of benefit as well.

 

So now that the revs have begone to rise, whats next, well unfortunately from now on redesigning is the key word to higher RPM.

 

Don't get too scared yet, this step is probably the least demanding of the redesign stage, it evolves changing the cylinder dimensions, most people will tell you that a 'square' design is best for a revving engine, but this is false. Rather, it is the most efficient because it provides good torque down low (thanks to a high stroke) and good power up top (thanks to Bore), but we are looking for power up top only, the torque down low will only be killed off by inefficient burning thanks to that nice new camshaft (if you when't to the extreme with the camshaft the your idle could just engulf that power with 'race' idles above 1000 rpm!!!). We want the power up top, so your first move should be to overbore (most people would already have done this before this stage), this should provide a nice displacement increase as well. But, and theres a big but, that stroke it becoming a bit of a pain at these RPM,

 

E.G. if you add 1mm to stroke at 8000rpm this equals:

1mm per stroke so 1mm x 8000rpm = 8000mm or 8m of extra travel per cylinder or 48m per minuet in total

And you have to remember that for every mm of travel, energy is lost rubbing against the walls of the block

 

So the answer is simple, don't increase or decrease or destroke your engine, but don't go crazy, there will be a stage where the decrease in displacement of cylinder will outweigh the power gains of Higher RPM producing less power.

 

Whilst we are messing with the internals, a custom set of pistons, rings, conrods and crankshaft (if destroking or for extra safety). Conrods are a must with high rpm as they can rip them selfs apart from inertia forces taking down your block, pistons, crankshaft and basically all your work for the last how long. You should get all your parts custom made with reduced mass in mind but never compromise strength. With reduced mass, inertia forces should decrease, allowing for overall safer RPM's.

 

Now this is the big part of redesigning. We are going to take on the Valvetrain again but this time with maximum RPM in mind. Design ideas best for High RPM are as follows

A lobe per Valve Camshaft- This nullifies certain rocker arm arrangements, for overall a stronger setup. This involves changing the valve setup to suit.

 

Creating a five valves per cylinder set up- this involves a great deal of redesigning and needs to be started from scratch for best results, this should be used in conjunction with a lobe per valve arrangement

 

Double Overhead Cam- Necessary as with the setups above, you cannot fit 30 lobes on a single camshaft

 

Crank/Camshaft fired Ignition- involves setting the ignition timing to be physically done by a separet lobe on camsaft for very precise timing.

 

After all this (and all that money) you should have a race engine capable of 10,000RPM+ and a truly unique engine:)

 

Have Fun

[ozconnection]

Ummmm, does any of this apply to an L series or is it just a general banter?

 

Your summary isn't particularly specific and therefore a lot of assumptions and generalizations have been made. To build what is truely a 10,000 rpm engine takes a lot more planning than what you give in your description, particularly in terms of reliability and functionality.

 

Still, throw enough money at 'it' and you might find what you're looking for.

 

Let us know how you get on.

 

Cheers.

[johnc]

This post has nothing to do with the L6 so I'm moving it.

[hoov100]

I hate to say it, but thats a whole lot of nothing to do with building a rev bomb, maybe you could use some of it as an outline or an intro to to a write up.

 

 

Also, just for anyone who's just getting into car's the more RPM you have, doesnt mean the more power your going to make, also, its going to be useless to have a motor that rev's to 10k RPM if you make peak power at say 4k RPM's, generally speaking of course.

[MAG58]

I'm just going to go ahead and play devil's advocate here.

 

Have you thought about mean piston speed? More importantly, piston acceleration? This will kill a little wind-up motor way before it runs out of weeze in the top end. Also what about rod/stroke ratio? The little hawn-der engines have pulled of just north of 10k with a not perfect rod/stroke ratio, but they don't exactly last greats amount of time at that range.

 

The only motorcycle mfg that used a 5 valve arrangement was Yamaha and IIRC they switched back to a 4 valve motor in 06 because they realized they didn't need it as 4 valves flow plenty, once again, keeping the bottom end in it is way more difficult at this point.

 

 

You want to make a motor that LOVES revs? Ditch the pistons. Get a 13B rotary, put a bridge port or peripheral port on it with some lightened rotors and hardened stationary gears a decent set (PTS, etc) of apex seals and go wind it up like a sorority girl at homecoming.

[Bart Hoedemaker]

Yep, Rotary, less moving internal parts, than piston.

 

But if you want to go for a screaming piston engine, and top end power. It's 90% about the heads " breathing capacity " and 10% block part. Most important here is the short stroke and high compression ratio.

 

You also want a good fuel mixture, notice " stand off injectors " on F1...

The rest... all engine parts have to be lightened the most as possible.

[260DET]

Bloody hell ZFDU, perhaps you don't realise that there is nothing new in what I think you are saying and most people on this forum have some basic mechanical knowledge, at the very least