what u think

[one-day]

about my compresion 2.o pinto number one 130 psi all the rest 150psi what needs doing

[Toby]

Bin it and fit a nice pre-crossflow!!

 

only kidding - doesn't sound too bad. Supposed to be within 10% aren't they?

 

Tiny bit of oil down the plug hole should tell you if its rings or valve seats.

 

Good luck

[w p e]

tight tappet?

[Vista]

Check your valve clearances as a first easy thing to check, then pour a little engine oil down the spark plug hole of the affected cylinder, and test it again. If the pressure comes up temporarily then you likely have a worn bore or worn / gummed up rings.

 

I assume you have no other symptoms that might indicate a head gasket problem?

[Toby]

tight tappet?

 

Good thinking!

 

You could do this for a living!!

[one-day]

no head gasket seems to be fine but supposed to have a stage 3 head on it and on those figures it seems not to have a stage 3 head on it would i be correct in assuming that.

[Toby]

depends on the cam

 

lots of durration spoils the effective CR

[one-day]

its got an fr30 cam in it supposedly

[Toby]

its got an fr30 cam in it supposedly

 

Wayne?

[one-day]

its got an fr30 cam in it supposedly

 

Wayne?

explain

[Vista]

What figures?

 

Am I missing something? The head stage and type of cam won't affect your peak pressure figures as both valves are closed at TDC on the compression stroke.

[Toby]

What figures?

 

Am I missing something? The head stage and type of cam won't affect your peak pressure figures as both valves are closed at TDC on the compression stroke.

 

It wont affect individual cylinders unless like Wayne said a clearances are wrong or a lobes gone, but the inlet valve stays open as the piston comes up the bore on the induction stroke to allow for inertial filling - more so on a race cam - which spoils low speed filling and therefore the CR on cranking.

[Vista]

Eh? Piston comes up the bore on the induction stroke? Now I'm really confused.

 

I'm probably being over simplistic here but bear with me: -

 

1. Suck: - Piston travels downwards on the induction stroke

2. Squeeze: - Piston travels upwards on the compression stroke

3. Bang: - Piston travels downwards on the power stroke

4. Blow: - Piston travels upwards on the exhaust stroke.

 

Now I'd expect the inlet valve to be open at 1, both valves to be closed at 2, exhaust valve to be opening towards the end of 3 and inlet valve to be opening somewhere midway through 4 (to aid scavenge and piston crown cooling), the exhaust valve then closing as the induction stroke begins (back to one) Your valve overlap is therefore on the exhaust stroke isn't it?

[Toby]

Yes about both valves being open (overlap) for the exhaust scavenging effect to start the inlet charge moving but because the charge coming in now has momentum the inlet valve can stay open past the point of the piston being at the bottom of the bore (duration) and that's where the effective compression ratio is reduced at low rev's. hence potentially a low pressure measured in the cylinders during cranking.

 

The reason I said "wayne" was for some guidance on acceptable pressures with this cam as he might have some experience with that cam - I haven't.

 

It is possible to work out the ECR from the cam timing figures because you can work out how far up the bore the piston is at valve closure.

 

[Toby]

Just been on the KC web site -your cam is pretty mild so I would have expected a little more effective compression ie higher reading. Its all about the whole package too, so, IMO it's a bit OTT to have a stage 3 head with a mild cam (and therefore potentially not great for gas speed.)

 

However - how does it go? Proof of the pudding......

 

If it doesn't go great you could probably do worse things than a bit of a head skim. (Check actual CR and valve to piston clearance)