|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
01-09-2022, 12:34 PM | #1 |
Senior Member
Join Date: May 2010
Location: Camarillo, CA and Pine Grove, CA
Posts: 2,832
|
Big Valves and porting?
For street use is there a noticeable improvement by porting and bigger valves?
__________________
1921 Runabout 1930 Tudor Early 1930 AA Speed costs money. How fast do you want to go? |
01-09-2022, 12:42 PM | #2 |
Senior Member
Join Date: Jun 2010
Location: (Old)Shasta (Redding) CA
Posts: 385
|
Re: Big Valves and porting?
Yes,, most noticeable if you are using enlarged intake system of some kind
__________________
Connoisseur of Rust |
Sponsored Links (Register now to hide all advertisements) |
|
01-09-2022, 12:47 PM | #3 |
Senior Member
Join Date: May 2010
Location: Santa Rosa, CA
Posts: 1,278
|
Re: Big Valves and porting?
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.
|
01-09-2022, 12:56 PM | #4 |
Senior Member
Join Date: Jun 2010
Location: Temecula, CA
Posts: 4,084
|
Re: Big Valves and porting?
I always do a little porting but think bigger valves are not worth the expense for street use.
|
01-09-2022, 03:34 PM | #5 |
Senior Member
Join Date: May 2017
Location: Denver Area
Posts: 433
|
Re: Big Valves and porting?
|
01-09-2022, 04:40 PM | #6 |
Senior Member
Join Date: Mar 2012
Location: Ohio
Posts: 1,954
|
Re: Big Valves and porting?
Sponsored Links (Register now to hide all advertisements)
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. |
01-09-2022, 08:29 PM | #7 |
Senior Member
Join Date: Jan 2012
Location: Western North Carolina
Posts: 3,893
|
Re: Big Valves and porting?
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.
__________________
A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. |
01-10-2022, 09:06 AM | #8 |
Senior Member
Join Date: May 2010
Location: Long Island, NY
Posts: 3,462
|
Re: Big Valves and porting?
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 Bidonde Last edited by Bob Bidonde; 01-10-2022 at 09:13 AM. |
01-10-2022, 09:30 AM | #9 |
Senior Member
Join Date: May 2017
Location: Denver Area
Posts: 433
|
Re: Big Valves and porting?
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. |
01-10-2022, 09:38 AM | #10 |
Senior Member
Join Date: Apr 2015
Location: Saint Cloud Mn
Posts: 745
|
Re: Big Valves and porting?
Bigger cam? Is there enough room for a bigger cam.
|
01-10-2022, 10:08 AM | #11 | ||
Senior Member
Join Date: May 2010
Location: Eastern Tennessee
Posts: 11,508
|
Re: Big Valves and porting?
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.
Quote:
Quote:
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). |
||
01-10-2022, 12:54 PM | #12 |
Senior Member
Join Date: Jun 2010
Location: 34.22 N 118.36 W
Posts: 1,052
|
Re: Big Valves and porting?
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
__________________
As Carroll Smith wrote; All Failures are Human in Origin. |
01-10-2022, 01:18 PM | #13 | |
Senior Member
Join Date: Jun 2010
Location: Temecula, CA
Posts: 4,084
|
Re: Big Valves and porting?
Quote:
You might want a copy of my '4-bangers and me' book. e-mail me at [email protected] for info on it. |
|
01-10-2022, 01:21 PM | #14 | |
Senior Member
Join Date: Aug 2021
Location: alberta canada
Posts: 585
|
Re: Big Valves and porting?
Quote:
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
__________________
old ugly my old father-in-law told me. "listen close when people tell you how to do stuff they may know something. then do it the way you want." |
|
01-10-2022, 01:53 PM | #15 |
Senior Member
Join Date: May 2010
Location: NJ
Posts: 6,177
|
Re: Big Valves and porting?
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.
|
01-10-2022, 05:40 PM | #16 | |
Senior Member
Join Date: May 2010
Location: Camarillo, CA and Pine Grove, CA
Posts: 2,832
|
Re: Big Valves and porting?
Quote:
If I read this correctly a bigger intake with intake porting and leaving the exhaust valve and port stock is your suggestion?
__________________
1921 Runabout 1930 Tudor Early 1930 AA Speed costs money. How fast do you want to go? |
|
01-10-2022, 05:42 PM | #17 | |
Senior Member
Join Date: May 2010
Location: Campbell,CA, USA
Posts: 318
|
Re: Big Valves and porting?
Quote:
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. |
|
01-10-2022, 05:55 PM | #18 |
Senior Member
Join Date: Mar 2012
Location: Ohio
Posts: 1,954
|
Re: Big Valves and porting?
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? |
01-10-2022, 05:55 PM | #19 |
Senior Member
Join Date: Mar 2012
Location: Ohio
Posts: 1,954
|
Re: Big Valves and porting?
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? |
01-10-2022, 06:43 PM | #20 |
Senior Member
Join Date: May 2017
Location: Denver Area
Posts: 433
|
Re: Big Valves and porting?
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. |
Thread Tools | |
Display Modes | |
|
|
Sponsored Links (Register now to hide all advertisements) |
|