cutting seats for bigger valve question

[DBMonster85]

I never thought of this when I had my intake seat cut to go to a 27mm from a 25. seeing that you cut the seat to go bigger do you need to have the bowl cut as well to actually gain from it all or did I gain anything just cutting the valve seat to go to 27mm. with the bowl being the same size I didn't really help my self did I???

 

[ole4]

When you cut a seat there should be multiple angles to the seat a 30 top cut a 45 or 46 degree seat a 60 degree bottom cut to blend to the bowl and a 75 to open up the seat. If you do not enlarge the bowl you are missing some of the benefit of the larger valve. The whole bowl does not need to be enlarged just the bowl below the seat to about 3/16 - 1/4 inch.

 

[ole4]

Correction 75 blends to the bowl the 60 blends to the seat.

 

[Prowler08]

Depending on your P&P job to compliment your larger valves... Just putting in a larger valves we see about 3-5 cfm difference on the flow bench, cutting at the angles mentioned above was 10-15 cfm difference, P&P, larger valves, and cut properly was 20-25 cfm difference..
Stock cfm was about 45-50 cfm... After all work was done 65-75 cfm... with a 27/25 valve combo...
The biggest difference was at low lift from .050-.200 it got up there a lot quicker in cfm.

Depending on the head you are using... The 14cc head needs a lot of work to flow good, the 18cc head needs work not as much as the 14cc and the 22cc head needs a good P&P and larger valves to be the flowing at its best...

 

[DBMonster85]

Ok. It was a 3 angle so hopefully that will be ok? And it's been ported and unshrouded. I have a 18cc head as well that was just bought complete from N.R. but I did the 14cc head my self.

 

[DBMonster85]

ok ole4 I get what your saying now so no I'm not getting all I could as the bowl below the seat was not touched and that's what my question was.

 

[DBMonster85]

and prowler8 thanks for the flow numbers it's nice to see what does what. and were you gain more flow thank you guys. my bowl need to be opened some but this is now after thought as the head is already on my cruiser. damn it!!!