Hi Everyone,

I'm going through my cast iron 60 degree V6, I noticed that the throat of the port is a little wonky compared to some aftermarket aluminum small block heads I have freshened. After measuring I discovered two things:
1: The throat is TINY. It measured 1.342 inches in the smallest point. With a 1.71 Inch intake valve, that works out to 78.47%
2: The throat is not symmetrical. The widest point measured at 1.410, or 82.45% of the intake valve. That's almost 4% difference in port size.

Has anyone come across stock (or junky aftermarket/ remanufactured) that measure this bad? Anyone want to spitball a percentage of flow that I'm losing?

 

It is definitely better for the Throat to be about 78% of the Valve, than too large (like 93% or larger).

Yes, it is very common for Stock Castings to be wonky and vary quite a bit from runner to runner, bowl to bowl, or port to port.
Modern Castings like the L92/ LS3 and newer are amazing in comparison to the majority of Stock Castings.

 

Yes, I agree that it's better to be to small than to large on the throat. I'm also aware that the heads are a lost cause for any "real" potential. However, with less than 29 Cu In per cylinder, there isn't enough engine to warrant any decent flow through the cylinder heads, so stock "home improved" heads should meet my modest performance goals.

As I'm refreshing the heads, I'm trying to avoid any trips to the machine shop as the performance gains are not worth the cost per $. Both the intake and exhaust valves are being reused, as both are in decent shape and lap in with very little effort. the valve guides pass the "pop" test and wiggle test, so no need for installing new guides. also, the spring locators, keepers, and locks are being reused. Honestly, I will have more money in my spring compressor at $125 than I will have in replacement parts to rebuild both heads.

Does this mean that I don't care about performance? no. I want the cylinder heads to fully support my goals/ potential for this engine. My goal is a good daily driver with plenty of midrange power from 2000-4500 RPM. I'm aiming to open the throat gently to 86-88% across all ports. I'm not looking for anything crazy with these stock heads, just want around 145 CFM intake flow and round 120-125 CFM exhaust flow (82-85% of intake flow) at .450 valve lift. This should be plenty to feed my 2.8 liter more than enough air given the RV style cam with 206@.050/ 0.420 lift Intake and 214 @.050/ 0.447 lift exhaust.

I MIGHT spend a little money and have the heads flat milled if the combustion chambers CC in a little high to gain back compression. But, that is dependent on Piston to Valve clearance.