Pitted Combustion Chambers - Buick 300

Wotland · Post by **Wotland** » Wed Nov 12, 2008 6:05 pm

I think your stage 3 heads modified with 1.5'' exhaust valves is the best option as long you use an 2.8'' crank.

But something about valve seat. Three-angle jobs are effective for increasing airflow past the valve on NA engine. But in most cases cutting the valves and seats at three angles greatly reduces the width of the actual valve-seat area. But since the operating temperature of the valve is controlled by its contacts with the water cooled head and as the valve seat is the area of contact through which heat can be transferred from valve to the head, it is important to have an wide valve-seat area on forced induction engine (0.080'' for inlet and 0.100'' for exhaust) to help to control combustion chamber temperature in this area.
Also it allows an good valve-seat seal which is needed under high cylinder pressure.

chodjinn · Post by **chodjinn** » Wed Nov 12, 2008 7:05 pm

So you're saying dont get an 3-angle valve seat job? Sound, less expense and more moeny towards making those roller rockers work

HairbearTE · Post by **HairbearTE** » Wed Nov 12, 2008 7:15 pm

Just to touch upon the thread topic again

Here's a pic of the worst of my buick heads. In actual fact the damage looks far worse in the pic than it actually is but to find these heads with none of these sympoms is rare. I saw a good pair that a guy in preston had and I believe one of the guys on here bought them.

CastleMGBV8 · Post by **CastleMGBV8** » Wed Nov 12, 2008 7:46 pm

That would be me

chodjinn · Post by **chodjinn** » Wed Nov 12, 2008 9:11 pm

The ones I've been looking at are a bit worse than that Marcus. Like you say though, 40yr old alu heads aren't gonna be perfect!

topcatcustom · Post by **topcatcustom** » Sat Dec 13, 2008 12:17 pm

Sorry to pull up this thread but didnt want to start another one so similar, can someone give me an idea of what comp ratio I would have using 300 heads, with comp gaskets on a 4.0 block, and would they go on ok?

TC

CastleMGBV8 · Post by **CastleMGBV8** » Sat Dec 13, 2008 12:35 pm

Tom,

You would need a flat top piston to make these heads usable, cant give you a comp ratio without knowing stroke 4.0 or 4.6 and whether high or low compression pistons.

An example with 4.0 pistons in a 4.6 engine and buick 300 heads would give a comp ratio with tin gaskets approx 8.7/1 and comps approx 8.2/1 which may be ok if blown.

If 4.0 engine a lot lower as suitable piston is a problem without going to a specialised build with chevy rod and pistons.

The final static comp ratio depends on how far the pistons are down the bores at TDC ie, deck height. I have assumed 20 thou for the figures stated but they can be quite a bit lower thsn that.

Kevin.

Is this for a supercharged engine?

topcatcustom · Post by **topcatcustom** » Sat Dec 13, 2008 1:02 pm

Hi Kevin, yes is blown, it is a 4.0 block with 4.0 pistons, crank, rods etc the lot. I had a feeling it would be far too low but just looking at options for heads!

TC