Do hardened Exhaust seat lower head cfm?

[Robert M.]

Hello all.

I've a 1970 with the L-46, (the 11:1 compression 350 hp)

About 20 years ago the heads needed work, and the machinist reccomended that the 186 heads have hardened exhaust seats installed because of the phasing out of leaded gas, so I agreed. Last weekend while bench racing, a friend suggested that the hardened exhaust seats really hamper the airflow of the exhaust ports, greatly reducing the overall efficiency of the head, and pocket porting of this set of heads would be a waste of time and money, better spent on modern replacement heads.

Anyody have any thoughts on this?

Duke or Clem?

PS. This car is a driver, and will never see a judging field.

[Tracy C.]

Re: Do hardened Exhaust seat lower head cfm?

I can see no basis for your buddies theory. A hardened seat would have no effect on the airflow through the intake or exhaust ports. The head is counterbored to remove the old seat and a new hardened one is installed in it's place.

tc

[Tracy C.]

Re: Do hardened Exhaust seat lower head cfm?

I can see no basis for your buddies theory. A hardened seat would have no effect on the airflow through the intake or exhaust ports. The head is counterbored to remove the old seat and a new hardened one is installed in it's place.

tc

[Clem Z.]

Re: Do hardened Exhaust seat lower head cfm?

no need for the hardened seat inserts BUT to answer your question EVERY set of aluminum heads have inserts for both valves and there are plenty of high flowing ones. back in the early days of BBC cast iron heads we installed "venturi" type exhaust valve seat inserts which were good for about 20/25 HP. these venturi type exhaust valve inserts were standard in ZL-1 aluminum open chamber heads

[Clem Z.]

Re: Do hardened Exhaust seat lower head cfm?

no need for the hardened seat inserts BUT to answer your question EVERY set of aluminum heads have inserts for both valves and there are plenty of high flowing ones. back in the early days of BBC cast iron heads we installed "venturi" type exhaust valve seat inserts which were good for about 20/25 HP. these venturi type exhaust valve inserts were standard in ZL-1 aluminum open chamber heads

[Joe C.]

Re: Do hardened Exhaust seat lower head cfm?

Bob,

It is unfounded. The valve seat, whether it be cast iron or hardened steel alloy, will have the same configuration. One of the best things you can do, is to have a 3 angle valve job done. The main restriction is in the bowl area , ESPECIALLY IN THE EXHAUST VALVE. I was able to open up my exhaust bowls by removing almost 1/8" annulus of cast iron just downstream of the exhaust valve.

The best resource for you to learn about smallblock Chevy heads....their applications, differences, configs, and porting methodology, is: "How To Build & Modify Chevrolet Small-Block V-8 Cylinder Heads" by David Vizard. Where all of the tricks are explained.

Joe

[Joe C.]

Re: Do hardened Exhaust seat lower head cfm?

Bob,

It is unfounded. The valve seat, whether it be cast iron or hardened steel alloy, will have the same configuration. One of the best things you can do, is to have a 3 angle valve job done. The main restriction is in the bowl area , ESPECIALLY IN THE EXHAUST VALVE. I was able to open up my exhaust bowls by removing almost 1/8" annulus of cast iron just downstream of the exhaust valve.

The best resource for you to learn about smallblock Chevy heads....their applications, differences, configs, and porting methodology, is: "How To Build & Modify Chevrolet Small-Block V-8 Cylinder Heads" by David Vizard. Where all of the tricks are explained.

Joe

[Robert M.]

Re: Do hardened Exhaust seat lower head cfm?

Well, the concensus here seems to be that the hardened seats don't affect the airflow. As usual, my buddy is full of "it".
I will pass on learning to do port work on my own heads. I will contact a local speed shop to inquire about the potential airflow gains that can be had for these heads, and what it might cost to reach a leavel of performance comparable to the Vortec heads, and beyond.

[Robert M.]

Re: Do hardened Exhaust seat lower head cfm?

Well, the concensus here seems to be that the hardened seats don't affect the airflow. As usual, my buddy is full of "it".
I will pass on learning to do port work on my own heads. I will contact a local speed shop to inquire about the potential airflow gains that can be had for these heads, and what it might cost to reach a leavel of performance comparable to the Vortec heads, and beyond.

[Mark #28455]

You will not beat the Vortec heads

Sorry to burst your bubble, but the vortec heads have a vastly superior port casting and combustion chamber shape. If your goal is racing, just buy the vortecs and bolt them on (but you will need the matching intake as the vortec intake ports are quite a bit taller). Trying to do that much port work on the stock heads is just not worth it! You can still improve on the old castings quite a bit by pocket porting.

When the vortec heads came out, all the dirt track racers in my area who were racing under the rules that required stock cast iron head castings sold off their "double hump" heads and switched to Vortec heads - the difference was that great.

Good luck,
Mark

[Mark #28455]

You will not beat the Vortec heads

Sorry to burst your bubble, but the vortec heads have a vastly superior port casting and combustion chamber shape. If your goal is racing, just buy the vortecs and bolt them on (but you will need the matching intake as the vortec intake ports are quite a bit taller). Trying to do that much port work on the stock heads is just not worth it! You can still improve on the old castings quite a bit by pocket porting.

When the vortec heads came out, all the dirt track racers in my area who were racing under the rules that required stock cast iron head castings sold off their "double hump" heads and switched to Vortec heads - the difference was that great.

Good luck,
Mark

[Duke W.]

Re: Do hardened Exhaust seat lower head cfm?

It think it comes down the the specific design of the inserts. Aluminum heads are designed for inserts, but CI heads are not. This can make a difference as a minimum amount of material should be removed to install inserts on CI heads, so they might overhang the port.

A recent flow test on some reworked 462s with exhaust seat inserts showed less flow than expected, but it appeared more grinding, which includes grinding the inserts above the seating surface will yield the proper geometry and expected flow.

Basic pocket porting techniques have been in publication for over 30 years - The Chevrolet Power Manuals, How to Hot Rod SB Chevies, and David Vizard's books. These are the primary refereneces, and anyone who attempts to optimize head flow, which is the best single modification you can make to any OE engine, should have and thoroughly understand these references.

Grinding cast iron is a time consuming task and seat inserts are even harder, so it will increase the job time, but if done properly I think the results should be the same as iron head without inserts.

On a set of 1.94/1.50" valve SB heads you want to see about 220/180 CFM at 28" H20 depression in the 0.4-0.5" lift range. (OE is about 200/140.) Add about 10 CFM per side with the 2.02/1.5" valve set.

And to repeat basic advice, inserts are not required for a road engine, so if inserts have not already been installed, don't install them.

Duke

[Duke W.]

Re: Do hardened Exhaust seat lower head cfm?

It think it comes down the the specific design of the inserts. Aluminum heads are designed for inserts, but CI heads are not. This can make a difference as a minimum amount of material should be removed to install inserts on CI heads, so they might overhang the port.

A recent flow test on some reworked 462s with exhaust seat inserts showed less flow than expected, but it appeared more grinding, which includes grinding the inserts above the seating surface will yield the proper geometry and expected flow.

Basic pocket porting techniques have been in publication for over 30 years - The Chevrolet Power Manuals, How to Hot Rod SB Chevies, and David Vizard's books. These are the primary refereneces, and anyone who attempts to optimize head flow, which is the best single modification you can make to any OE engine, should have and thoroughly understand these references.

Grinding cast iron is a time consuming task and seat inserts are even harder, so it will increase the job time, but if done properly I think the results should be the same as iron head without inserts.

On a set of 1.94/1.50" valve SB heads you want to see about 220/180 CFM at 28" H20 depression in the 0.4-0.5" lift range. (OE is about 200/140.) Add about 10 CFM per side with the 2.02/1.5" valve set.

And to repeat basic advice, inserts are not required for a road engine, so if inserts have not already been installed, don't install them.

Duke

[Robert M.]

Re: You will not beat the Vortec heads

Racing is not the goal. The goal is to maximize performance, and fun, on a stock, matching numbers L-46. In a little afternoon book store browsing, I found that Vizard was able to achieve some very good flows with the 186 heads. I also learned that TPI Specialties is only 6 miles away from home, and they will do head work. So I'll speak with them next week. Doug Rippie Motosports is also in the area.

The Vortecs are fine heads, BUT they require a new intake that will raise the stock carb and air cleaner. So would my stock hood close? Probably not. I like my stock Delco radio, so I'd need to modify my ignition shielding support. That shielding really does work inspite of what the experts on the other boards say.
The Vortecs lack a heat riser. I live in Minnesota, and enjoy spring and fall driving, and some of those days get a little cool. So I'd need to convert to electric choke. The Votecs are center bolt valve covers. Throw away my beautiful stock finned aluminum's for some homely center bolt's? Nope. All that costs money. and it adds up to a significant amount.
The Vortecs are not a cheap alternative.

[Robert M.]

Re: You will not beat the Vortec heads

Racing is not the goal. The goal is to maximize performance, and fun, on a stock, matching numbers L-46. In a little afternoon book store browsing, I found that Vizard was able to achieve some very good flows with the 186 heads. I also learned that TPI Specialties is only 6 miles away from home, and they will do head work. So I'll speak with them next week. Doug Rippie Motosports is also in the area.

The Vortecs are fine heads, BUT they require a new intake that will raise the stock carb and air cleaner. So would my stock hood close? Probably not. I like my stock Delco radio, so I'd need to modify my ignition shielding support. That shielding really does work inspite of what the experts on the other boards say.
The Vortecs lack a heat riser. I live in Minnesota, and enjoy spring and fall driving, and some of those days get a little cool. So I'd need to convert to electric choke. The Votecs are center bolt valve covers. Throw away my beautiful stock finned aluminum's for some homely center bolt's? Nope. All that costs money. and it adds up to a significant amount.
The Vortecs are not a cheap alternative.