kent safe until 8000 revs

[eric]

Is it possible ?

 

What specs needed ?

[combine]

A lotter revs for a crossflow !

[Pezky]

lots of steel bits.......

[Klunk]

Hi Eric ,

 

Yes it is possible but, as Q102 says, you'll need a lot steel and forged components to be safe.

 

I have one such engine at home that came out of one of my old caterhams. It would easily rev to 8000 and sounded absolutely sublime 🥰 . Allegedly it would rev to 9000rpm but I didn't fancy the potential rebuild cost. From their website, Kent Cams do one cam suitable for upto 9300rpm!!

 

Don't forget that to make use of the revs you've got to have a top spec head as well, to flow enough air, otherwise it's a waste of time and money.

 

Regards,

 

Giles

 

PS. I could be persuaded to part with my engine if your interested?.....

 

 

 

[eric]

I already have an ali head,

Forged pistons and conrods

steel flywheel

Duplex chain

 

The question is, do I need a steel crankshaft ?

[cskip]

Yes you need a steel crank. With the correct Cam and other bits, it is possible to Rev to 8500 rpm safely. The higher you go after that increases the rebuild frequency.

[eric]

It is just for fun ! The pleasure to use high rev on a track but occasionally

[rj]

Roger King will know

[eric]

I think the cam will be the kent 234 or the A2

[Graham Perry]

You will struggle to get a really useable 8000 revs easily out of a 234. Mine was well sorted and was past its best at 7200. Regular 8000 revs really needs a steel crank and a better cam. You are then into bigger carbs and better oil pumps.

 

As said above Roger occasionally pops by, he may read this and advise.

[eric]

yes but the 8000 revs are not the absolute target, it is a way to have a safe engine and the mental pleasure to have an engine able to reach high revs or so.

 

Could be prefect if the engine is about 140 /150 HP wit a lot of torque at low revs and good road manners. (smooth slow running and good sound when revving high, an engine with 2 faces )

[elie boone]

I think that with a 234 cam you will strugle to see 140bhp, unless you go 2ltr but that would be expencive.

 

So you want torque and high rev then you will end up with something like a Kawa 1400 or similar with added lightness

 

Edited by - elie boone on 26 Dec 2012 10:29:14

[Drumster]

My RK 1800 x/flow (AX block) with forged pistons and 234 cams (among other things) made a healthy 140bhp and the limiter was set to 7,200, and that lasted 50k miles until it went bang, but that's another story ☹️

[bstark]

My 1700 with a 234 is nearly 140bhp at just over 6,000rpm but is dropping as it heads towards 7,000...

 

Probably better with a 244 as long as you have 3D ignition to keep it all nice and driveable.

[Pezky]

When I had the xflow, power tested at Northampton Motorsport at 150 bhp

Engine was 1700 RK, forged pistons, 234 cam and Megajolt 3d ignition. Seem to recall max power at 6ish but still had power 7, wasn't willing to go past that

[eric]

today with a 1600 , twin 40 webers, std pistons, CR 9.4 : 1, std con road , std crankshaft,

O/E flywheel 5.9 kg, a stage 2 Burton Head , A2 cam, the engine goes very easily to 7000 revs . Engine professionally built by a race engine motorist

 

But in fact, the 1600 are scarce, the most of the engine are 1700 cc nowadays ...

[Roger King]

Merry Christmas everyone.

 

The highest revving Crossflow I ever built pulled 9400rpm on track. This was in the early 1980's in Will Hoy's Clubmans car. They were limited to a four speed gearbox and we were racing at Zandvoort when it had its very (very) long straight. Basically, you had to gear the car for the rest of the circuit and it would then hit whatever revs it was willing to achieve on the straight. Normally we'd have stopped in the high 8000's, but with four gears we had no choice on that track. Incidentally, the engine was fine afterwards - and we won.

 

That was with an A8 race cam which is one of the now old-fashioned generation of profiles with relatively low lift and long duration. This meant that valve gear accelerations were fairly modest compared with the more modern high lift, short (ish) duration race cams like the 264. The valve gear would dismantle itself with the modern type cam at those revs. In truth, the A8 was all done by around 8000rpm, but it hung on reasonbly well beyond that. The 264 will give similar power, but with vastly improved mid-range torque so it's generally quicker, though much harder on things like the valve springs.

 

The engines were of course all steel. Don't forget that the bottom end of the Crossflow is basically identical to a BDA, so there are no problems with high revs there; it's just the heavy valve gear that suffers.

 

I believe that the old Formula Junior engines of the early 1960's used to rev to 11,000rpm. They were Pre-Crossflows, but the engine is fundamentally the same in terms of valve gear. They were however 1100cc ultra short stroke jobs with fairly small (and therefore light) valves and had the likes of Cosworth developing them.

 

Edited by - Roger King on 28 Dec 2012 21:05:14

[eric]

Hello Roger

 

Thanks for the reply, may I understand that for high revs it is safer to stick with lower lift cam, the old style A profile cam than the more modern kent 234

[Roger King]

For extreme revs yes, but 8000rpm is no problem at all with high lift, short duration profiles. You will need to spec the correct valve springs (not necessarily the ones mentioned in the camshaft catalogue) and you need to pay attention to reducing the mass of the valve gear as much as possible. This means using 9/32" diameter valve stems, using the lightest valve retainers you can find (aluminium is ideal, but they need replacing every few hundred miles - titanium is a good compromise), removing any excess mass from rockers, pushrods, etc. I'm assuming here that you are going for a 254 profile or above. The 234 and 244 are less fussy.

 

The good news is that all of the above will give you an engine that revs more freely and the cam profile will give you much better mid-range torque and much better emissions. This is to the extent that it is perfectly possible to drive a well set up carburettored engine with a 264 round a multi-story car park - you won't do that with an A8! I ran a 7 with a 264 as my everyday road car for a few months; the only thing I found tricky was the fact that it had a full race clutch so pulling away from rest was a little awkward. In the end I learned that to pull away you either had to give it some welly and leave rubber, or trickle away very gently (yes, with a 264) until the clutch was fully engaged.

 

In the past it was just assumed that a highly tuned engine would be undriveable at low revs so people put up with horrible lumpy idles and no grunt below 4000rpm. In reality this isn't the case and if the engine is injected (and properly mapped) it is even less the case.