mk1-forum.net

I recall posting a similar question before and receiving some good responses however my post seems to have disappeared so apologies for asking this again (but in a slightly different way this time).

I am building an A series for fast road use and possibly some light competition (Targas). The engine is based around a 1300GT motor which I have had bored to 1330 and I'm using Minispares 9.75CR pistons. I've had the std block decked by 5 thou - pistons are now nominally flush or just below the block surface. I will aim for 10.25:1 static CR by adjusting the head.

The rotating assemblies have been fully balanced and I am using a Minispares light steel flywheel, matching backplate and orange diaphragm. The gearbox is a rod change with 3.4 diff and sc close ratios.

Initially I will use a standard MK3 S head, skimmed and overhauled as required but I will probably go for a modified head later - ported but retaining std size 'big valves'. The carb will be a 1.75 single SU on an MG metro manifold. Exhaust is a twin box RC40 with LCB.

I asked my machinist to supply a nice road cam which would give good torque and not be too lairy. He supplied a new Kent cam and followers - he is a Kent agent so they have not given the cam any of the recognisable numbers but the spec sheet says:

CAM PRO PLUS Cam Card Report 23/03/2015

--------------------------------------------------------------------------------



Spec. Value

---------------- -----------------------------------------

File x:\Kent Cams profiles\Kent pushrod mechanical profiles\P01 - P99\P39.CPP

Lobes I1

Lobe Separation ----- Cam Deg.

Checking Height 0.40 mm

Valve Overlap ----- Crank Deg.



Intake Exhaust

------------------- -------------------

Centerline 106.00 ATDC 106.00

Open 18.60 BTDC 52.57

Close 52.57 ABDC 18.60

Duration 251.2 Crank Deg. 251.3

Area 539.5 mm Deg. 540.0

Lash 0.400 mm 0.40

Rocker Ratio 1.50 1.50

Peak Cam Lift 7.2950 mm 7.29 mm

Peak Valve Lift 10.5425 mm 10.54 mm

Lift @ TDC 1.142 mm 1.142 mm


What does the above equate too, approximately in common parlance? I thought MD246, some opined it is similar to a SW5?

Anyway I am about to install it but have started to get second thoughts about this cam. I have the following questions:

1 Can anyone offer an opinion on how this engine will perform and what it's characteristics will be using this cam?
2 If I fit this cam should I used 1.5 ratio rockers?
3 If I use this cam would it be suitable for a future ported head or is it best with a standard Cooper S type 'big valve'
4 If I wanted something a bit more 'fun' or characterful, what would be the next step up from this cam
5 I was going to re use the existing timing gears and have bought an IWIS chain. However, having now checked closely the smaller gear has some slightly gnarled teeth and I am going to change it or both - would the Minspares steel pulley set be a good choice? (will use offset keys to time the cam)
6 Any advice on timing this cam for best performance?

Any other comments or observations appreciated as ever!

Cheers

Jon

These timing figures are almost for sure from the Kent246 ,

i've used this cam on a "basic" 998 engine.. cam and 12G202 head ( cooper sized valves ).
Cam is great... very very torquey, engine performance is better than a stock 1275 SPI.
It goes out of puf close to 6K, i was expecting a bit more revs for a 998.. maybe it is not timed in as it should.. i was in a hurry and timed it at 108º full lift.

Cheers
Luis

That cam, especially with 1.5 rockers, gives a rather high lift and rather short duration - for a "performance" cam. Short duration makes for a more torquey cam and high lift limit your maximum engine speed. With the large displacement, this would work well in a Land Rover.

This doesn't really match well with the "performance" catagory, and certainly not with the balancing and light flywheel you have done.

Rather go with a Kent 266 for fast street or Kent 276 for racy street. I personally prefer standard rockers with offset bushings as they don't foul a standard valve cover.

Bigger engines do however tolerate more radical cams than smaller engines.

I'm using the MD266 in a very similar spec engine, overall valve lift is quite a bit less but changing from A+ sintered rockers to std forged rockers with offset bushes really transformed it - gives a lot more grunt mid-range and top end. But this is still only 8mm valve lift, I might just try the 1.4 lift rockers...

But the MD266 is a 30 year old profile, I have not tried the more modern short-duration cam profiles with higher lift so cannot really compare.

Couple of comments about the build spec:
- at CR 10.25:1 it will likely need fed 99 octane fuel
- I'm running blue clutch diaphragm, this works fine with std clutch plate
- you will also need to tweak advance curve, I'm using 12-14 deg static plus 10x2 mech advance all in by 3,500 crank rpm

carbon wrote:- at CR 10.25:1 it will likely need fed 99 octane fuel

Mr Vizard reckoned in the Third Edition of his book, ©1999 (Page 228),
that a 250 degree inlet duration cam at about 10.25:1 CR will run OK
with 96 Octane with a heated manifold...

Ian

ianh1968 wrote:

carbon wrote:- at CR 10.25:1 it will likely need fed 99 octane fuel

Mr Vizard reckoned in the Third Edition of his book, ©1999 (Page 228),
that a 250 degree inlet duration cam at about 10.25:1 CR will run OK
with 96 Octane with a heated manifold...

Ian

I wouldn't normally disagree with DV, but the MG Metro used 10.5:0 and 252 deg cam. With a water heated manifold they were prone to running-on even on the 98 octane fuel then available. Marginal at best.

I think that the factory may have cured this problem...

According to my 1995 issue Haynes Mini book, page 304:

"Anti-run-on valve (1990-on Cooper models) - Removal and refitting"
Removal
114 The anti-run-on valve is mounted onto a bracket in the right-hand
rear corner of the engine compartment. Its function is to prevent the
engine running-on ('dieselling') after the ignition is switched off.
<SNIP>

I'd bet that using one of these would soon sort out the problem,
Ford were using them for years before this, as I understand it...

I used to get overrun myself, but with a low enough idle and a
programmable distributor I am not getting this any more on an
11:1 CR engine with a 270 degree cam and a water heated inlet
manifold, with 97 octane fuel.

Previously, I controlled the problem on my 1993 Mini by using the
"fumes-return" pipe to the tank as an actual back-feel pipe. I have
two pumps, one normal, the other plumbed into the bottom of the
carb float bowl and back to the top of the tank via the second pump,
using the other/smaller pipe between the tank and the front.

Turning the engine off was a case of turning off the forward pump
then turning on the reverse pump, and waiting for it to run out of
fuel, typically about 3 to 5 seconds.

This system has 4 benefits:
1) I can run a "silly" configuration if I want to and I don't get overrun.
2) I have a fairly robust "anti-theft" setup as the engine won't even
start with an empty float bowl.
3) If I am in traffic and the under-bonnet temperature is getting a bit hot,
I can send the hot fuel back to the tank to be immediately replenished
by the forward pump. When I next "drag" away from the lights, I then
don't suffer from the embarrassing "too-hot-fuel-bogging"...

I can actually drive at up to about 40mph with both pumps running.
The forward pump is a higher capacity pump than the reverse pump.

4) I am always carrying a spare fuel pump. The two are mounted side
by side, so swapping them over is simply a case of rearranging the pipes.
This has got me out of the poo, before now...

The original idea came about because I wanted a cure for No.3.
All the other factors were just beneficial side-effects.

Ian

I'm changing to a 276.

Does anyone wish to purchase a brand new unused Kent MD246?

Jon