TT427

iTrader: (1)

Anyone see the cylinder notchec like a BBC sometimes was to deshroud?

TT427

iTrader: (1)

But for the Ls1...

96capricemgr

iTrader: (1)

You can't just go looking for any old example to try to prove your point. CHAMBER shape plays into things and the valve centerlines are spread not an apples to apples comparison.
Besides a lot of testing shows cathedral port heads to hold their own just fine against the "higher flowing" rectangle port heads, flow numbers and peak dyno numbers aren't the true measure of performance.

Sales@Tick

iTrader: (3)

You mean as far as radial clearance of the valve is concerned?

TT427

iTrader: (1)

Yes. I think the 396/402 with rectangles got bore reliefs to help with the bigger valves. It proved to benefit enough to warrant production.

Sales@Tick

iTrader: (3)

I've seen it done before...good point. I still think the 2.08 valve is too large for a stock bore LSx.

Sales2@Texas-speed

iTrader: (5)

You are also ignoring valve position inside the head in that statement. Will a 2.08" fit inside the 3.898-3.90x" bore? Yes. Is it shrouded on a 3.898-3.90x" bore? Yes.

TT427

iTrader: (1)

I would agree.

TT427

iTrader: (1)

This is a stock bottom end ls6 deal, would think a 2.02/.04 would flow all that is needed.

KCS

iTrader: (20)

How does chamber shape play any part in how the bore shrouds the valve? As far as valve centerline is concerned, read on...

Correct me if I'm wrong, but the valve position of the intake valves did not change between the cathedral port and LS3/L92 head. It was the exhaust valve that was offset closer to the cylinder wall. Under that premise, how is it that a valve that takes up 54% of the bore okay, but a valve that takes up 53% of it's bore "too much"?

Sales2@Texas-speed

iTrader: (5)

That's incorrect. They were placed similarly, but not in the same position relative to the bore center.

KCS

iTrader: (20)

How far were the valves shifted?

96capricemgr

iTrader: (1)

The chamber and bore are one piece far as running engine flow is concerned.

Let me guess you are one of those people who believes the flow bench is the ONLY measure of a head and when it doesn't pan out on the track or even the dyno you make excuses about how the cam was wrong or something?

KCS

iTrader: (20)

My mistake! I seriously thought that it was the exhaust valve that was offset, not the intake, so that was a bad example.

Well I can tell you this much, I'm not one of those people that will insult someone because I don't agree with their theories or opinions. I've been around this stuff long enough to see some things that lead me to believe that there is a lot of power left on the table when going with smaller valves in many of these street combinations. As long as the valvetrain is stable, I have yet to see a larger valve make less power.

KCS

iTrader: (20)

Sorry to bump an old thread, but I wanted to retract my previous statement here. It seems that the intake valve placement between the cathedral port and LS3 style heads are actually pretty much identical, if not better on the cathedral head. There certainly isn't enough difference to say a 2.08" valve in a 3.905" bore is closer to the bore than a 2.165" valve in a 4" bore. In fact, they're about the same distance.

On an 862 casting and an 821 casting, I used a machinists square and scribed a line perpendicular to the head along the edge of the bolt hole. Then set a valve in the guide and scribed another line along the edge of the valve. While not the most accurate method, it was certainly close enough to see that there is a negligible difference between the two.

821 casting



862 Casting



So again, I don't see a problem running a 2.08" valve in a 3.905" bore. It's pretty similar to running a 2.165" valve in a 4" bore.

Sales@Tick

iTrader: (3)

What if we don't agree on running a 2.165" on a 4" bore?



Just gigging you KCS.

KCS

iTrader: (20)

Ha! Well then you run those exhaust valves in your intake port and you've got the most deshrouded valve EVER!

Sales@Tick

iTrader: (3)

LOL!

I like a 2.02"-2.06" on a 3.9" bore.

I like a 2.04"-2.08" on a 4" bore(2.10" is OK for a few applications)

I like a 2.055"-2.12" on a 4.030" bore

I like a 2.08"-2.16" on a 4.065"-4.070" bore

And anything 4.080"-4.125"+ I like to see a 2.10"-2.25" depending on application.

That's what I personally have found to work very well across the RPM range of many different applications, but there are no hard rules set in stone.

KCS has more access to flow benches and cylinder head porting tools than I do so I'm sure he has seen more exceptions to these guidelines I like than I have.

mchicia1

iTrader: (5)

2.08" valve in 3.905" bore here.

Runs fine. The heads/intake swap gave me 50 hp across the board, so it's not like they aren't working. I just don't know if it's any better than a smaller valve, but that is what the small bores come with.

KCS

iTrader: (20)

More than one way to skin a cat. I don't know how many others do this, but I like to pinch the cylinder head dowels in so that it gives me some back and forth play with the head. When I put the heads on, I can push the head back towards the exhaust side, pulling the intake valve about .015" away from the bore wall, then tighten the head bolts/studs. Manifold still bolts up fine too.

Not too shabby considering they're the LS3 heads too.