Big Valves and porting?

[Chris Haynes]

For street use is there a noticeable improvement by porting and bigger valves?

[Jerry in Shasta]

Yes,, most noticeable if you are using enlarged intake system of some kind

[PC/SR]

Yes, but then the carb and intake become restrictions, and of course then you need a bigger cam, and after that.....Do not know you goal, but IMHO just porting and valves are not worth the performance increase without the other stuff. For a quick and easy HP increase, get a HC head, or downdraft carb.

[Jim Brierley]

I always do a little porting but think bigger valves are not worth the expense for street use.

[GeneBob]

Originally Posted by Jim Brierley

I always do a little porting but think bigger valves are not worth the expense for street use.

Jim,
Is there a guide or YouTube video or something to show where and how much porting is done? I have wanted to do some porting but don't know how.
Thanks,
Gene

[Gene F]

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It depends. For one thing, if you even think you want them, at time of rebuild is the time. It's not that much more money.

Once you drive an A with improved brakes, and a thought out pattern of improvements you don't want to drive anything else. It also depends on how much you drive it too.

[nkaminar]

My car: Down draft Weber, high compression head, Pierce manifold, insert bearings with pressure lube, balanced crank. high lift cam, and big intake valves. I am guessing 80 horsepower. I tired the stock intake and carburetor but it really reduced the power. The engine has to be viewed as a complete system with all the components working together. See https://www.modelaparts.net/dyno.htm/dyno.html for some dyno tests of different add on's.

[Bob Bidonde]

Porting is not reversible and it reduces the compression ratio. For a street runner, I doubt porting is of any significant value, but I am guessing.

[GeneBob]

Bob,
From what I have read, flathead V8 porting is a whole different ball game from what is done for the Model A 4 cylinder. For the 4 cylinder, it was suggested that you do not port inside the combustion chamber volume. But that's about all I have found on this.

[daren007]

Bigger cam? Is there enough room for a bigger cam.

[BRENT in 10-uh-C]

Originally Posted by daren007

Bigger cam? Is there enough room for a bigger cam.

Yes. The head of the valve typically will hit the roof of the combustion chamber before the lobe is too big to fit through the cam journal bores.

Originally Posted by Bob Bidonde

Porting is not reversible and it reduces the compression ratio. For a street runner, I doubt porting is of any significant value, but I am guessing.

Bob, what you are showing in the picture is what is termed as 'Relieved' which is done to unshroud the valve. It has been my experience that most port work is done under the head of the valve and out of the combustion chamber area.

Originally Posted by GeneBob

Jim,
Is there a guide or YouTube video or something to show where and how much porting is done? I have wanted to do some porting but don't know how.
Thanks,
Gene

The science of this is much greater than what most people can show on YouTube. Matter of fact, most content you watch on YouTube relating to a Model-A is generally not very accurate anyway, so that is probably not the best source of information.

With regard to porting, if you want to do porting, you need to buy/build a flow bench which is basically a manometer that tests resistance of flowing air. If you have mega-deep pockets, you can even map the ports on your block and have them digitized. Then using sophisticated software, it will create a simulation of the airflow in both dry and wet scenarios. Afterwards the computer will make changes to find what is optimal for a certain RPM range. Just going into the port or bowl area and hogging out metal does not necessarily increase airflow or horsepower. Likewise there are very basic areas of blueprinting that will net gains in most areas on a Model-A block. Some of those items are port matching in the intake manifold to block ports, blending valve guide areas, and creating multi-angle valve seats to assist flowing air. Pete Samuelson would be a good one to interject his thoughts on this too.

It is mine & several other's opinion that the 1.500" Model-A exhaust valve & port is too large which cuts down on the scavenging effect it can have. Also, I tend to take the stance that most stock intake seats are damaged enough where a seat insert is necessary to have a good valve support. For the same labor expense, I can increase the seat area to support a 1.750" valve instead of cutting and installing a 1.625" seat insert (-which holds the 1.500" valve).

[johnneilson]

Do larger valves and porting increase flow? Yes, but very limited.

The cylinder head chamber design has more of an effect on the flow.
As previously stated, there are many other factors, manifold, carb and exhaust all contribute.

It will take a stout bottom end to utilize all of the HP possible, but that is another topic.

John

[Jim Brierley]

Originally Posted by GeneBob

Jim,
Is there a guide or YouTube video or something to show where and how much porting is done? I have wanted to do some porting but don't know how.
Thanks,
Gene

Gene, Not that I know of, but basically you just need to smooth the castings and enlarge them slightly, especially near the valves. Use of a high RPM die grinder is the best tool for this. Some use of JB Weld or similar to direct the air flow can help. IMO bigger valves are not worth the expense and trouble unless you want to race.

You might want a copy of my '4-bangers and me' book. e-mail me at [email protected] for info on it.

[old ugly]

Originally Posted by Bob Bidonde

Porting is not reversible and it reduces the compression ratio. For a street runner, I doubt porting is of any significant value, but I am guessing.

porting for higher performance engine is probably good when combined with all the other components
but the reliefs like on this fh8 , you wouldn't do that to a model A. the valves are already higher than the top of the block.
ou

[Tim Ayers]

Originally Posted by old ugly

porting for higher performance engine is probably good when combined with all the other components
but the reliefs like on this fh8 , you wouldn't do that to a model A. the valves are already higher than the top of the block.
ou

I know little about Model A's, but it also seems the head chamber design on most heads is quite different than a V8 head. Seems like there is a lot more space than their V8 counterparts.

[Chris Haynes]

Originally Posted by BRENT in 10-uh-C

It is mine & several other's opinion that the 1.500" Model-A exhaust valve & port is too large which cuts down on the scavenging effect it can have. Also, I tend to take the stance that most stock intake seats are damaged enough where a seat insert is necessary to have a good valve support. For the same labor expense, I can increase the seat area to support a 1.750" valve instead of cutting and installing a 1.625" seat insert (-which holds the 1.500" valve).

Brent.
If I read this correctly a bigger intake with intake porting and leaving the exhaust valve and port stock is your suggestion?

[Terry Burtz, Calif]

Originally Posted by Chris Haynes

For street use is there a noticeable improvement by porting and bigger valves?

Before porting and enlarging the intake valves, compare the intake ports on your new engine to the intake ports on a stock Model A engine.

Your new engine has larger intake ports that have a more streamlined path to the valve.

If you modify the ports, keep in mind that the water jacket has a nominal wall thickness of 5/32 inch.

[Gene F]

My car has the bigger valves, and the Stipe IB-330 higher lift cam. When you stop, and turn right onto a ramp and step on it you can feel the acceleration.

It's a choice Chris. Have you thought about going for a spin in one of your local club chapter members cars so you can see the difference? Granted you only need, or want to feel that difference at certain times. One of the guys in our club and I went for a spin in my car. I pulled over and put him in the drivers seat. At the first light he said "man you got some really good brakes on this A". I did tell him beforehand, but he was still surprised. My point is I'm a big try it before you buy it kinda guy whenever possible.

So what do you think Chris, got a buddy in your local chapter?

[Gene F]

My car has the bigger valves, and the Stipe IB-330 higher lift cam. When you stop, and turn right onto a ramp and step on it you can feel the acceleration. Especially when going up a grade.

It's a choice Chris. Have you thought about going for a spin in one of your local club chapter members cars so you can see the difference? Granted you only need, or want to feel that difference at certain times. One of the guys in our club and I went for a spin in my car. I pulled over and put him in the drivers seat. At the first light he said "man you got some really good brakes on this A". I did tell him beforehand, but he was still surprised. My point is I'm a big try it before you buy it kinda guy whenever possible.

So what do you think Chris, got a buddy in your local chapter?

[GeneBob]

Brent, I was hoping this thread would peak your interest and thank you for adding some information. I am not trying to flow an engine for Bonneville, just looking for where the typical Model A port issues are to look for some improvement. I suspect there are some places to look at in the ports that are common problem areas.



Jim, I will look in your book. I frankly forgot to look there.


Thank you both you have valuable experience.