Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 01-21-2020, 02:54 AM   #1
GordonP
Junior Member
 
Join Date: Sep 2011
Posts: 11
Default Larger intake valves

The Model A engine Iím working on rebuilding has larger intake valves and stock exhaust valves. All are inserted.

Whatís the point?

Iím a big believer in stock engines. That said, is their some advantage to this configuration?
GordonP is offline   Reply With Quote
Old 01-21-2020, 05:29 AM   #2
Truckerjim
Junior Member
 
Join Date: May 2018
Location: Outside Windy City
Posts: 19
Default Re: Larger intake valves

Makes the engine breather better for more power and maybe even more horsepower
Truckerjim is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 01-21-2020, 06:15 AM   #3
updraught
Senior Member
 
updraught's Avatar
 
Join Date: Feb 2015
Location: Australia
Posts: 1,252
Default Re: Larger intake valves

It's to keep up with the Japanese who refused to make under-stressed engines.
updraught is offline   Reply With Quote
Old 01-21-2020, 06:49 AM   #4
GordonP
Junior Member
 
Join Date: Sep 2011
Posts: 11
Default Re: Larger intake valves

Quote:
Originally Posted by Truckerjim View Post
Makes the engine breather better for more power and maybe even more horsepower
Doesn't what comes in have to go out through the exhaust valve? Seems to me the only way to get more out the exhaust is to either make it bigger or increase the pressure, no?

Is anybody out there running an engine like this? My first inclination is to have the inserts redone back to stock.
GordonP is offline   Reply With Quote
Old 01-21-2020, 08:26 AM   #5
kenparker
Senior Member
 
kenparker's Avatar
 
Join Date: May 2010
Location: Van, Texas
Posts: 1,066
Default Re: Larger intake valves

nothing scientific, just, my opinion. The air coming in is pushed in - thru the intake valve - by atmosperic pressure and the vacumn caused by piston moving downard. The air moving out - the exhaust - is being pushed by the piston and the explosion and the expanding of the air inside the cylinder. The exploison and resulting expanding air move a lot faster than the air being sucked in by vacumn. clear as mud???


as said above the engine breathes better and is more efficient which equals more hp. I have built several engines with the larger valves and the one currently on the table will have the larger valves. Iffen I wus u I would leave the larger valves alone. Iffen you have insert main or rods I wud also leve dem alone. It would be VERY expensive to conver an engine back to babbit bearings. ken

Last edited by kenparker; 01-21-2020 at 08:31 AM. Reason: more info
kenparker is offline   Reply With Quote
Old 01-21-2020, 08:36 AM   #6
40 Deluxe
Senior Member
 
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 3,129
Default Re: Larger intake valves

If the valves and seats are in good shape, just do the usual regrind. Being larger won't hurt a thing (and by itself probably not help much for power). It may have been done to repair worn out seats. But without a performance cam and bigger carb and intake (such as a B), not likely to make a difference.
40 Deluxe is offline   Reply With Quote
Old 01-21-2020, 06:52 PM   #7
updraught
Senior Member
 
updraught's Avatar
 
Join Date: Feb 2015
Location: Australia
Posts: 1,252
Default Re: Larger intake valves

http://modelaparts.net/special.htm/1.700flowsheets.html

The exhaust valves are too big.
updraught is offline   Reply With Quote
Old 01-21-2020, 08:19 PM   #8
Pete
Senior Member
 
Pete's Avatar
 
Join Date: May 2010
Location: Wa.
Posts: 3,572
Default Re: Larger intake valves

On a FLATHEAD 4 or V8, people that believe the exhaust should NOT be as big or bigger than the intake are living in the past.
Ideally, the exhaust system should be big enough so that NO pressure wave is reflected past the reverse flow dam to the valve seat.
Pete is offline   Reply With Quote
Old 01-21-2020, 09:57 PM   #9
Synchro909
Senior Member
 
Synchro909's Avatar
 
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 4,650
Default Re: Larger intake valves

Quote:
Originally Posted by updraught View Post
I agree, in fact, when I was sold a set of valves with larger inlets, I put them in the lathe and turned them down. Instead of 0.2" larger, they ended up at 0.1 larger. I'm quite happy with the result but that said, I'm no less happy with an engine I did with standard sized valves. Everything else is the same.
__________________
Life is not measured by how many breaths you take but by the times your breath is taken away.
Synchro909 is offline   Reply With Quote
Old 01-21-2020, 11:26 PM   #10
holdover
Senior Member
 
Join Date: May 2011
Location: SW Virginia near the Blue ridge Parkway
Posts: 599
Default Re: Larger intake valves

Exhaust valves (for reasons mentioned above) are usually smaller than intake valves. Increasing valve size does not always increase flow, depending on the engine/head design it sometimes reduces flow across the whole valve lift. An example is the 305 Chevy engine, increasing intake size alone often reduces flow, there is a delicate balance between value size, lift, porting, intake and headers etc.
holdover is offline   Reply With Quote
Old 01-22-2020, 12:58 AM   #11
40 Deluxe
Senior Member
 
Join Date: May 2010
Location: now Kuna, Idaho
Posts: 3,129
Default Re: Larger intake valves

Quote:
Originally Posted by holdover View Post
Exhaust valves (for reasons mentioned above) are usually smaller than intake valves. Increasing valve size does not always increase flow, depending on the engine/head design it sometimes reduces flow across the whole valve lift. An example is the 305 Chevy engine, increasing intake size alone often reduces flow, there is a delicate balance between value size, lift, porting, intake and headers etc.
Don't overlook the fact that the 305 has smaller cylinder bores, thus shrouding the intake valves.
40 Deluxe is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 10:30 AM.