Start with balancing & match weighting everything

 

Is it more about damping vibration then and stopping the engine shaking itself apart at higher rev speeds?

 

From what I understand (and there are more knowledgable people on here on this site than me) yes.

If the reciprocating parts are balanced so when they spin the load exerted is even (or as even as can be) around the thing then you will be able to spin it at a higher speed because the load on the crank (in this case) is more evenely spread.

 

The problem is vibration pounding the main bearing shells into the soft mag alloy crankcase, leading to loss of oil pressure and early engine failure.

You will need a counterweighted crank for starters. The stock casting is only good for around 5000 rpm max no matter how well it is balanced.

Then you'll have to balance the entire crank / pulley / flywheel / clutch rotating assembly, the rods and the pistons to a very high tolerance (Probably 1 gram or less).

VW engines that rev that high on a regular basis generally have a limited lifespan. Probably not the most sensible idea for a regularly driven road car.

Of course the engine breathing all the way from air filters to tailpipe will have to be heavily modified to enable the engine to reach those sort of rpm's in the first place, but I assume you knew that already.

Dave.

 

Thanks for the replys guys all makes sense to me, im assuming the balancing part is a specialist thing for most parts due to special machinery needed?

 

yeah it's a specialist job but only cost me £60 for the whole crank assembly, i measured the pistons and rods myself,

as said above that'll help with reliabilty at high revs but then theres the fact of getting the engine to rev that high in the first place,

may i ask why you want 8k rpm, just being nosy

 

Once you get into the high RPMs, the valves will want to 'float' so you'll need heavier springs to keep them shut when they should be. This means more wear on the cam and valvetrain leading to the need for more frequent attention/rebuilds.

 

you will want to send the crank assembly off to be balanced. you need the flywheel and pully on there, the clutch SHOULD be balanced already, but send it off as a precaution

do you have some kitchen scales and a file? then use them to balance the conrods, and the pistons with pins

you will be wanting to get some dual valve springs, not necessarily stiff ones, you just need more control of the valves otherwise they float.

you won't be able to rev high with the stock inlet system so chuck it in the bin and get yourself some nice twin carbs.

if you have the thing apart then it's worth the extra expense of a bigger cam.

and that should give you a higher revving engine, however I personally wouldn't like to let a stock crank or rods see over 7k too often tbh.

 

Thanks guys, im thinking of building a big engine from scratch so will bear all this in mind.

the 8000rpm figure was just a random one although I was working out gearbox ratios at the time and figured at 8000rpm the car would be travelling at about 170mph not that it would be in one piece at this stage mind

 

Big engines usually mean low revs and small engines, high revs. If you want a BIG engine Remmelle are reputed to be developing a 3.6litre with 108mm pistons and 98mm crank. The Pauter super pro engine is 3.5litres is super special and still only revs to 7,800rpm. It must be the basic design of the horizontal flat 4 that limits revs as even Subaru limit the rev ceiling whereas its contemporaries with IL-4s can see 12,000+rpm.
Bigger engines have bigger reciprocating masses to damp out and with a H-4 engine, little space to do it in.

 

8000 rpm for a vw aircooled engine would not be a very streetable motor, lumpy idle, and probabily cough & splutter until about 2k revs! You would be better doing a turbo'ed engine, which would give you more grunt at relativily lower revs.

 

Physics is your main problem at those kind of revs.
As the revs increase the momentum of the pistons moving in and out greatly increases. The forces passed through your conrods are going to be trying to the push and pull the crank out of it's bearings.
Air cooled engines simply don't have enough support on the crank to handle the high revs. That coupled with a cast crank that will flex under high loads gives you even more problems.
You also have the issue of case strength. T1 mag cases simply are not strong enough and were never designed for this.
Aftermarket aliuminum cases offer greater strength, plus using a forged crank will give you a good basis for a high reving engine.
Balancing will then help further but you must uprate your conrods and bolts of course.
6-7k is then easily achievable but 8k, that's going to be very expensive.

 

Hi mate 8k revs is at the extreme of what is possible with these flat four engines.
Even modern subaru engines don't rev anywhere near that and achieve 300hp.
If you want power and reliability go for an injected turbo set up.
Not cheep. But you wont be rebuilding it every 5000 miles.
Hopefully.

 

what are you using the car for?

as you say 8k is 170mph and a stock beetle will die at that pace lol

 

My 2387 motor revs eeasily to 8K. My soft limiter is at 8k and my hard limiter at 8200prm

Apart from ballancing..you need to be able to supply the engine with enough air to allow it to reach those rpm and still make uasable power.. big ports, big cam etc. you will also need big valve springs to keep the VW heavy valve train under control. I run chevy srings on my motor with 5mm longer valves to allow me to run .600 lift at 8000rpm.

 

respect!!

 

A Beetle engine can be made to achieve high revs, most of what has been said is true. Assuming you have everything in place to make it rev it will only last a short while. The biggest problem is the design of the crankcase, it was made to handle 40hp! get the case to support the crank properly and it will last a lot longer. Everything should be lighter and balanced, single not double valve springs.
I never broke a std crank but the std rods let go at 9500rpm!

 

A Beetle engine can be made to achieve high revs, most of what has been said is true. Assuming you have everything in place to make it rev it will only last a short while. The biggest problem is the design of the crankcase, it was made to handle 40hp! get the case to support the crank properly and it will last a lot longer. Everything should be lighter and balanced, single not double valve springs.I never broke a std crank but the std rods let go at 9500rpm!

Rob,
if i have dual bugpack hi-rev spring kit, is it ok to use only the outer springs...?
Engine is 1641, 110 cam, swivel feet, bolt up shafts, gene berg oil pump, twin 34ict's pertronix flame thrower II dissy, HV coil, full flow, Balanced crank assy, lightened f/wheel and equaliser 5.5lb pulley.
Thanks

 

Most of the above is sage advice, it also helps if you are deaf