The 500 and 731/800 kent cams
Turbo Mini Forums

Hi,
I'm looking for a good cam for a 998 turbo street/track application. 7000 RPM at max.
I've been told here the Kent 500 is a good compromise.
I've just spent an hour comparing various Kent/Piper and other cams and found another cam that looks great on the paper: the Kent 731/800

Kent 500 spec:
Mild Road 1500-6000 6.67 8.12 I 252 Deg E 268 Deg 16/56 59/29 110 Deg 0.40 I 0.99mm CF1 / VS2

Kent 731/800 spec
Fast Road 2500-7000 7.67 8.12 268 Deg 24/64 59/29 110 Deg 0.40 I 1.45mm CF1 / VS2

This 731/800 looks great because:
- it has a longer intake duration (so high RPM)
- same exhaust duration (can assume the same expansion efficiency and scavenging)
- same low lift, good for std soft springs and thus less mechanical losses and follower damage
- still not too much overlap (1.45mm, my N/A 998 was running very smoothly with a MD256 1.24mm overlap cam)

Did somebody try this cam ? On which kind of engine ?

Where do you guys buy the 500/800 cams ? I can not find any store in the UK. As GBP is cheap right now (never happened before :) ) I'd like to take advantage of my strong US dollar, before I loose my job LOL.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

please look at the spec of the kent 266 cam which has a tad more exhaust tacked on the end and is better suited for turbo application

minispares North have this cam in stock

MD266 was my choice before we talk there about 500.

MD266 spec:
Sports 1000-6500 I 6.67 E 6.85 I 8.12 E 8.37 I 260 Deg E 270 Deg 24/56 61/29 106 Deg 0.40 I 1.67mm CF1 / VS2

So MD266 exhaust duration is quite the same (lift is higher, good point I agree), while intake is shorter. And TDC lift is higher, bad point for a street car, it starts being too high for a 2.5% CO level. Given the poor exhaust design (lack of space of course) I don't think I can improve scavenging with a high overlap.

However, I'd like to understand your point of view. Am I wrong in my thoughts ?

Edited by alpa on 2nd Jan, 2009.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

I think Wil & Ben use the Kent 500 in their 998 Turbo, it's a reproduction of the MG Metro profile isn't it ?

WWW.TURBO-MINI.COM

Hi,
I don't think anyone in the UK would have looked at it from an emissions point of view. We're allowed up to 3.5% CO at idle and HC 1200ppm.
If the CO passes and the HC fails you're allowed to raise the RPM to get it to pass. Obviously this only applies to pre CAT vehicles.
What's the limits where you are?
Cheers,
Gavin :)

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Have a look at the MD274.

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=123522

Short intake, long exhaust duration, good lift and low overlap due to the 110 degree LSA.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Bat:
In France it's 2.5% for late carb generation, HC is not regulated LOL. Staying under 2.5% is easy. Generally the nightmare starts at about 2mm+lash lift at TDC, which is the rally/race cam range.
I think idle is a good indicator. A good idle means not too much resident pressure at intake opening, which means freedom for boost level and cam duration. That's why I'm looking at the TDC lift.

Paul: your approximations (from the thread you pointed) look very different from the real profiles I measured.

The take-off area is usually very grinder dependent and very different from basic Sin/Cos shapes. Just by looking at this zone one can say if cams are well designed. Of course the rest is important as well, but radical asymmetric-ramp square-shaped cams are rare (Schrick does them for Porsche)

MD274 numbers
Sports Injection 1000-6000 I 7.23 E 7.13 I 8.95 E 8.71 I 284 Deg E 274 Deg 12/56 69/25 112 Deg 0.40 I 0.58mm CF1 / VS2

There is not enough overlap (it's still useful on turbo engines, I think the turbine acts like a vacuum pump), and most important the intake phase is too short. There are more lift, but it's not well tunned to rev above 6000RPM (short intake). On track this makes difference. For pure street car it's certainly not important.
9mm lift is like on SW5. Swiftune sell SW5 with a special set of springs, I have it on my 998, they are harder than std springs (I measured). I think 8mm lift is better because you can keep std springs so have less losses.
69/25 exhaust looks huge. "69" may be better to get a high efficiency street engine (even if I'm not convinced Miller cycle is worth of effort on so poorly designed heads), but in this case I don't see interested in having "25" closing retard, this is where resident gases may come back into the cylinder from exhaust.

MD266 has a good point: higher exhaust than intake lift. Unfortunately intake is not well located (I think) for a turbo application.
The best would be a mix of MD266 and 731.

Sorry for a long text.

Edited by alpa on 2nd Jan, 2009.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

I'm attaching the profiles because my Internet provider is putting me out.

I bought a used 731, I'll measure profiles.

Attachments:

19.12kb

Edited by alpa on 5th Jan, 2009.

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

MD266 has a good point: higher exhaust than intake lift. Unfortunately intake is not well located (I think) for a turbo application.
The best would be a mix of MD266 and 731.
correct! the MG CAM is all the 731 should be


one quote:- of a well known A series tuner stated use a 731 cam and loose all the bottom end and gain very little in the middle and Gain almost nothing at the Top!

std 998 A+, g295, MD266, RHF4, 109hp @0.8bar/5400rpm

a list of Kent can dealers can be found here http://www.kentcams.com/

Lots of the dealers listed will ship abroard.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

I ran the Kent MD274 cam in the 1400 with 1.5:1 ratio rockers and it gave 100bhp at 6800rpm and 87lbft at, I cant for the life of me remember That was on a standard production ECU which was a little conservative at best.

Results with the VEMS ECU gave 100lbft and 95bhp, but recon there was a little more tuning in that.

Jackman runs a Kent MD274SP in his 1293 SPi with a MG Metro type head the usual filter and exhaust mods and that gave 80bhp and 64lbft.

The MD274 cam is not something to dissmiss just on a graph!

Its all about experimentation, its all fine talking about it, but untill you try it, you will never really know. Make your choice, run it for a year then change it. if it doesnt give the reulsts then change it back. That is what engine development is all about. and it doesnt happen over night

i ran a old mg metro cam in mine at 1st running around 18 psi and it felt strong and revved round to 6500 easy n felt liek it was still pulling well

but i recently changed to a 266 and personally i thourght it lacked power!! it didnt feel as though it pulled as strong

ok its only a minimal feeling of difference but a difference none the less

the 266 should be timed in at 107deg ATDC

I thought the MD266 should be timed in at 106deg ATDC?

http://www.minifreunde.at

i timed my one in to kent cams spec which is 106 deg

There is thought that if you time a cam into, say, 107 degrees, using a new chain, it will achieve 106 degrees when the chain has bedded in :)

Schrödinger's cat - so which one am I ???

dont they stretch out by about 3 degrees after a few miles? thats what has been recommended to me anyhow

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

I went for 1 degree (for potential new chain stretch) but my logic was the cam follows the crank so with the AFTER TDC cam reading for measuring the inlet valve lift, I set mine at 105 degrees assuming it will stretch to 106...

Maybe I am going mad.....

Schrödinger's cat - so which one am I ???

well with the 266 my car made 107hp on 6 psi on the rolling road with 1.5 roller rockers and 8.2.1 compression and my own ported head!!

i dont know what it made with the mg metro cam though as i never dynod it with that in.