Valves

[Dirtkart90]

Hi, I got a 5hp Flathead 60 over steel bore with p-open cam billet crank, rod, 3hp flywheel head etc. tilly carb on methanol head has cuts for big valves, looking to go as big with valves as possible what size big valves would be recommended before I buy seats and valves and get it machined ? Thanks

 

[flattop1]

I wouldn't go much bigger then whats in it .
Could go 1.375 in 1.160 exhaust.
Source the pieces first before making a decision they may be hard too come by .

 

[Dirtkart90]

I wouldn't go much bigger then whats in it .
Could go 1.375 in 1.160 exhaust.
Source the pieces first before making a decision they may be hard too come by .

Thanks yeah seems like a lot of the parts are hard to come by or out of stock

 

[flattop1]

P open has pretty big lift anyway .
Does it not run strong enough?

 

[Dirtkart90]

P open has pretty big lift anyway .
Does it not run strong enough?

Yeah it runs good just wanted to do a little more and valves are pretty much only things that weren’t done.

 

[flattop1]

Its possible you could leave the seats and go with a slightly bigger valve.
Brian Carlson may have a better idea , of the possibles .

 

[Freezeman]

Its possible you could leave the seats and go with a slightly bigger valve.
Brian Carlson may have a better idea , of the possibles .

What would the advantage of having bigger valves than necessary for seat size? I would think that would reduce flow.

 

[95 shaw]

Sometimes a tapered cut beneath the sealing angle can help flow. Keeps port velocity up, especially at low lift.
Airflow inside combustion chamber is quite different than you would expect in an ohv engine.

 

[flattop1]

What would the advantage of having bigger valves than necessary for seat size? I would think that would reduce flow.

I wouldn't go much bigger then whats in it .
Could go 1.375 in 1.160 exhaust.
Source the pieces first before making a decision they may be hard too come by .

I would agree .
The engine sounds pretty well sorted out .
The reason i asked about current performance.
There are big costs , with small gains hopefully.
Flow bench time or relieving the area between the valves and cylinder if its not already.

 

[CarlsonMotorsports]

Some shops do not have the capability to cut infinite bore sizes for seats like with a small boring bar with an indexible cutter. Most will have specific size cutters that are made for the interference fit of the seats that shop has in stock. You may want to confer with the shop that's doing your machine work prior to purchasing valves and seats.
1.340" IN is still pretty common for Raptor blocks. We may, or may not, have anything larger than that in stock anymore. Give us a call during business hours and Sarah or I can dig through the aftermarket flathead shelf to see what we can find for you.


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