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Valve / Rocker gap measurement


burndog

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For all you performance / racing guru's out there. I am looking for some advice / recommendations on valve gap for my engine application. I am running a turbo, 15-18psi, mild turbo regrind cam, lot;s of spark and of course retarded timing up on boost at 4500RPM.

 

I just finished my break in period and will be retorking head and adjusting valves. I know stock gap is .008, but would anyone recommend going tighter (.007 or even .006)? I checked them and only a 3 valves would allow a .008 to slide through. But, I can tell those 3 valves are definitely throwing off significant valve train noise.

 

Thoughts?

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I would be interested in what the cam grinder specified as the lift ramps may well be different to the original BMW cam necessitating a different clearance. If no info available I would still go with 8 thou inlet 10 thou exhaust.

'73 BMW 2002Tii,'89 Renault Alpine GTA V6 Turbo,'56 Renault 4CV with 16 TS motor, 

 '76 BMW R90S, '68 BMW R60/2, '51 BMW R51/3, '38 BMW R71

Ipswich, Australia.

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I didn't get the cam spec'd before installing, as it looked in perfect condition. I was told it was a reground stock cam. It has a great little lope at idle and comes on hard just before peak boost at 4500RPM.

 

Question; for a turbo application would one really want to be leaving gap / valve timing that loose? 

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what the cam grinder specified

 

This.  Lash is driven in some part by the take- off and landing ramps.

 

And yes, extra turbo heat WOULD indicate leaving the valves a bit looser.

 

The turbo doesn't really affect valvetrain much, except to put even more loading on the intake springs,

especially on high- speed overrun.

 

In the absence of other data, I'd leave them at .008, and if they're seriously noisy, maybe close them up

not more than a thou...

 

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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More heat? Are you guys talking heat sinking in the head or the increased compression? If the later why would one use different gap for intake and exhaust? Wouldn't both the intake and the exhaust valve be experiencing the same heat increase?

Sent from my iPhone using Tapatalk

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