24 replies to this topic

[RedRallyMini]

Strange... I know somebody who's been using it for +- 50 000km, he never had any problems...

[Cooperman]

Be very careful of heads with those valve sizes as they can and often do crack between the seats. In fact I have a beautifully gas-flowed one with those valve sizes, but it's cracked and only of use for holding the door open in a high wind. Just a tiny crack and the head is scrap as they cannot be repaired. On rally cars I never use valves bigger than 35.6 mm inlet and 30 mm exhaust in order to keep reliability.

[RedRallyMini]

Be very careful of heads with those valve sizes as they can and often do crack between the seats. In fact I have a beautifully gas-flowed one with those valve sizes, but it's cracked and only of use for holding the door open in a high wind. Just a tiny crack and the head is scrap as they cannot be repaired. On rally cars I never use valves bigger than 35.6 mm inlet and 30 mm exhaust in order to keep reliability.

 

Is it really that sensitive?

[Cooperman]

It certainly is. Most of the racing Minis with 37 mm inlets have the valves offset to get the necessary clearance and prevent cracking. You won't gain much on a road car with that head either as it won't perform at its best below about 7000 rpm. Below that a 35.6/29.5 mm head will be at least as good so long as the gas-flowing is well done and the carburation is right.

[Turbo Phil]

That head will be almost utterly pointless on a standard 1275. With ports that size gas speed at low RPM will be slow making the engine gutless low down. It's a different matter if you're building a high revving race motor, but for an almost standard road engine I wouldn't fit it. You'll proabaly find it's slower than it was before at the kind of RPM you'll be using on a standard cam.
As for the "Fuelcat" it's probably about as good as the mesh bags you used to be able to buy full of lead balls to drop in your fuel tank & run on unleaded ! Lol
If you do run the head use a dose of Castrol Valvemaster when you fill up, this is actually proven.

Phil.

[RedRallyMini]

So the message is: "Don't buy it!"

[The Matt]

I wouldn't run that on standard ish engine spec. I ran 11.25:1 in my 1380 and didn't have any major problems when using octane booster, lead additive and megajolt to really fine tune the ignition timing. But I didn't run valves that big either. Mine were the 35.6mm ones (IIRC). I've heard of the issues with non-offset big valves but not seen the physical damage myself.

As a side note though, Valvemaster smells lovely!

[Cooperman]

It is possible to run 37/29.5 valves without offsetting the valves, but there is always a possibility that a crack will appear.

To have any chance of delaying what is probably the inevitable it is necessary to ensure that the mixture and timing are absolutely spot-on as the operating temperature is critical and if it runs slightly lean or slightly retarded from optimum then it will crack, sooner rather than later.

It is very expensive to do such a head and when it cracks a lot of cash has been spent. Maybe not if it saves a few tenths of a second per lap and lasts for a few races, but not really for road, or even rally use.

[Turbo Phil]

It's not just a matter of the chance of it cracking it's just that spec head is completely wrong for a standard cammed 1275. It will most likely perform better with a standard head low down.
It's not a matter of whacking any old head on, or if big is good, bigger will be even better. The head needs to be tailored to suit the engine spec, valve lift & RPM used.
If retaining the standard cam, the actual inlet port, for example, can be left almost standard size.

Phil.

[RedRallyMini]

That's why I ask this, because I know nothing about it and you guys, the experts, know everything about it.