[Guest]

Hey Rally Bob

In one of the other posts you said that the maximum lift for a stock valve train is about .430". I measured a cam today that had .436" lift. (It is the cam I emailed you about.) When I checked for coil bind or the retainer hitting the valve guide there was tons of clearance. Have I gotten a weird head? (It is a "early" 4 bearing head.) Or, is there some other limitation (like valve toss) with the stock springs? By the way, this engine is using forged pistons with extra valve/piston clearance so that is not a problem.

I'm posting this so everyone can see the answer.

Thanks (again) in advance

TGSI Racing

 

[Guest]

Numerous factors can affect this. Early heads DID have different valve springs that later heads. Solid cams used springs that were 82 lbs seat pressure and about 150 open pressure. Later hydraulic springs were around 95 lbs seat pressure and 180 open. I've always checked with these later springs. Depending on the valve job (sunken seats in the head will increase the valve spring height proportionately), or whether a machinist has shimmed the springs or not, these numbers will vary. I've always measured the clearance at around .450 before coil bind. Keeping in mind you want to retain a clearance before binding, .430 is about the limit, at least with a hydraulic cam. Solids will also take into account valve lash, you have that extra valve lash as a cushion before binding comes into play. (So a .430 lift cam with .014 lash will have only .416 lift at the valve, not including seat recession...plenty of room before valve spring binding)

But I prefer to keep the extra clearance by speccing a low-lift cam with OEM springs, as using a performance cam with OEM springs will often run into valve float sooner than stock because of more aggressive opening ramps. This will 'toss' the valve open higher than rated lift, and the resultant spring bind will yield catastrophic results on the valve train. Broken springs, weakened springs, piston/valve interference.....these can all result.

RallyBob

 

[kwilford]

repaired thread...

 

[RallyBob]

Gotta flip them around Keith, I answered TGSI before he asked the question according to the sequence posted here!

Bob

 

[kwilford]

yea, the order on some were screwed up in the import, and I just ain't clever enough to fix that