Fast road cam geometry & clearance

[Lynxified]

Hi All,

I've aquired a Catcams 228 0312 cam.
Currently doing a testfit in my spare engine, and have some geometry and clearance questions.
This cam gives around 13mm lift, with 3.85mm claimed at TDC.
It also has a reduced base circle to archieve this.

This means I've got to wind out the ball studs to get the spec'd clearance of 0.25mm.
What's the minimum engagement of the studs in the head before I should look at getting extended studs?
Currently It looks like they've got about 8mm of thread in the head.

Second question is regarding clearance from the valves to the piston around TDC.
What clearance between the valve and head should I maintain as the minimum?
I imagine there's some expansion happening as the engine heats up and the rods stretch under high revs, and i'd rather not have them meet

engine in question is a 205.

[Miniliteman]

Isn't the 2280312 a F2 Speedway cam?
For any cam with a small base circle I would use longer ball studs.
W.r.t. the valve to piston clearance Graham will know best, just make sure to measure it not only at TDC but around it. As just after TDC the valves start to open quickly whilst the piston is only slowly moving down.

[Graham]

Hi All,

I've aquired a Catcams 228 0312 cam.
Currently doing a testfit in my spare engine, and have some geometry and clearance questions.
This cam gives around 13mm lift, with 3.85mm claimed at TDC.
It also has a reduced base circle to archieve this.

This means I've got to wind out the ball studs to get the spec'd clearance of 0.25mm.
What's the minimum engagement of the studs in the head before I should look at getting extended studs?
Currently It looks like they've got about 8mm of thread in the head.

Second question is regarding clearance from the valves to the piston around TDC.
What clearance between the valve and head should I maintain as the minimum?
I imagine there's some expansion happening as the engine heats up and the rods stretch under high revs, and i'd rather not have them meet

engine in question is a 205.

re ball studs, i would of said 5 full threads in the head would be the absolute minimum,

valve to piston clearance, you should really work on a minimum of 1.5mm inlet 2.0mm exhaust, at high rpm the piston and rod will grow by around 0.75mm, cutting that clearance down significantly. so in theroy you would still have plenty, but you need to allow more, thermal expansion might actually change valve lift but also you need some spare in case of an over rev.

Leon is correct, you need to check not only at TDC, but around it

[Lynxified]

Lovely answers both, can work with those.
Definitely will measure the full rotation I'd already seen/read about it.

Cam should be more of a tarmac rally cam, but I'm initially planning to stick to the 32/36, which should temper it a bit.
Its more cam than I was looking for, but the price was right ��

[Miniliteman]

A tarmac rally cam with 3.85 mm lift at TDC will not work with a 32/36 carb. And not really advisable with any carb for road use.

[Graham]

A tarmac rally cam with 3.85 mm lift at TDC will not work with a 32/36 carb. And not really advisable with any carb for road use.

it would be better to say it wouldnt be a good choice, at high rpm it would work, perhaps not as well as a cam with less overlap but it would work in a fashion.

however it wil be a pig at at the lower end of the rev range, and will probably idle about as well as a cement mixer with a missfire!

[Miniliteman]

The 32/36 will start to smother (spelling?) the airflow probably at the same rpm the cam will start to work.

[Graham]

The 32/36 will start to smother (spelling?) the airflow probably at the same rpm the cam will start to work.

i did run a 32/36 on an engine with a GTS4, it made 163bhp from memory, which wasnt that bad, until i say same engine on 45's made 30bhp more

[Lynxified]

I was worried about the cam being too much, seems like I was right there.
These are the full specs of this cam:



Now, I see two options here, either change carburation, or pick a different cam.
I'm on a unported (unleaded) head, standard size valves, just overbored .5mm and decked, which should put compression at roughly 1:10.1

I'm not looking for a race engine screaming at 7000rpm, I'd rather have something with good down low torque and drivability on the streets.
What would you recommend I'd move towards?
If the cam would be as easy to swap as on a CVH I'd just try it out and see how it behaves, but I don't fancy having to take the head off multiple times just to try a cam.

[Miniliteman]

I'm not looking for a race engine screaming at 7000rpm, I'd rather have something with good down low torque and drivability on the streets.
What would you recommend I'd move towards?

Burton BF134.

[snapper1]

Doesn’t sound like the camshaft you have chosen is in anyway suitable for your intended purpose and rpm limit, it will make peak power near 7k rpm and not produce any torque below 3.5k rpm.
my experience with cam changes is that you need to look at the engine spec as a whole, in your case it’s a standard engine with 10-1 compression and you want it to perform on the road, other camshafts, a good tuner and maybe look at Grahams YouTube channel to see what combinations could work for you.

https://youtu.be/kYrheF0ta1Q