Spring Install Heights - Advice pls?

[Spenny_b]

Hi gang,

I'm in the process of checking the re-worked heads that I had done (long story short - I don't trust the guys work) for my 964 Turbo.

The heads have been built using Schrick valves, springs, spring rotators (platforms), Ti retainers and associated keepers. The shims were re-used from my original teardown.

The cams I'm now using are stock 964 N/A, replacing stock 930 cams.

Now, what I'm not certain about, is which set of figures I should be working from. The Schrick documentation below, simply says a max installation height of 34mm (Mine are p/n 0013 02 064)



However, looking in Bentleys Technical Data Without The Guesswork, on p15-8 it gives the following:

Valve Spring Height Specification
Intake = 34.5 +/- 0.3mm
Exhaust = 33.5 +/- 0.3mm

Which would you guys be working from?...a specification with a +/- tolerance seems more correct, is it strange that Schrick only give a max height?

The Porsche specs above don't specify whether this is for M64 or M30 engines....so I guess that the spec relates to the spring and not the cam (or profile of the cam, more specifically)

Or do I go by what Schrick states, as this is what will get their spring working correctly?

As they were assembled and given to me, 9 of the valves were 33.x mm, whilst 3 valves were well in excess of 34mm (#1 Exh, #5 Inl, #5 Exh)

Last night I reassembled the 3 taller valves using some of the spare shims. I now have all 12 set between 33.60mm and 33.94mm

Thanks for any advice!

S

[cgarr]

Can you find out what seat pressure you need? I like to set them to seat pressure as long as its within the spring spec and no binding.

[Spenny_b]

Originally Posted by cgarr

Can you find out what seat pressure you need? I like to set them to seat pressure as long as its within the spring spec and no binding.

Hi Craig, thanks for the suggestion. I was speaking to one of my mates today about this (he builds race engines with another mate who's doing my MBE mapping) - he said the same about setting install heights dependant upon the spring base pressure for their racing Duratecs and Hayabusa's.

Any idea where I'm likely to get the spring pressure info from?

Is it a specification of the cam (to maintain lobe contact), or again, one from the spring manufacturer?

Anyone out there with this info?....964 N/A stock cams, no regrinds or repair work....

Cheers
Spencer.

[docrodg]

Seat pressure would be a cam spec. You may try the regrinders, they may have the spec. For some other engine types out there you typically get seat pressure and nose pressure (pressure at max lift) for the aftermarket stuff.

[Spenny_b]

Thanks docrodg....I know my mate who's doing the mapping has very good relationships with Kent Cams over here in the UK - they may be able to get something.

Cheers
S