Cylinder heads

[couperman]

Hi Matt,

I'm building a blown 350 sbc for my competition coupe and have some early Dart/World Products iron heads that have a really nice porting job done on them, I've fitted new bronze guides and now not sure whether to blend them in or just leave as they are, the engine is a 550/600hp pump gas motor with a 6.71 and 2 holley hp carbs so not looking for extra power just don't want to screw up the porting job but equally don't want to restrict the flow either.
Thanks for your help.
Ray

[Frontenginedragsters]

Hello Ray:
 Air flow is horsepower! Blend the upper portion of the valve seat to the combustion chamber.
Make it a smooth transition to the chamber.
Make sure you have a little extra clearance between the exhaust valve and valve guide.
Gasoline makes for HOT exhaust and the valve grows. Very little if any valve seal on the exhaust side.
Also use a VERY good quality exhaust valve. I see more guys with stuck exhaust valves than any other problem.
Matt

[couperman]

Hi Matt,
Thank you for the prompt reply, I'll get busy with the die grinder then.
I have a set of Manley Valves ready to go in.
How much clearance do you recommend?
Are you suggesting running the exhaust valves with no viton seals or have I misunderstood your reply?

Ray