Don Terrill’s Speed-Talk

If you built a few restricted class engines with 'no porting' rules you'd start to see the usefulness of offsetting stuff..........

the 2017 honda crf450 heads are offset 3mm on both intake and exhaust. sbc

Restricted heads, no porting, lol, 99 % of them have port work done to them as well as the "valve job any".

For me, a concentric valve job from the top of the chamber cut to the bottom of the bowl cut then shaping to and from all that is the way to go.

KnightEngines wrote: ↑Tue Nov 07, 2017 7:55 am If you built a few restricted class engines with 'no porting' rules you'd start to see the usefulness of offsetting stuff..........

You got that right!

jcisworthy wrote: ↑Tue Nov 07, 2017 10:55 am
For me, a concentric valve job from the top of the chamber cut to the bottom of the bowl cut then shaping to and from all that is the way to go.

I think it is interesting you feel strong;y that it is "not for you", yet you have not implied it does not work.
Isn't that like saying
"yeah it makes the car faster but it's too much work?" LOL

Same thing can be achieved using an extra thick valve seat, it just ends up thicker one side than the other.
that raises the question....is it OK for a valve seat to be thicker one side than the other?? I think it's ok, but I don't really know.

Its an interesting idea. But doesn't mean it works on everything. Just because 1 manufacturer offsets the seats, doesn't mean it will apply to everything. It could be simply based on the engineering constraints they had, it was worth 6-8 cfm or whatever. But, throw porting in the mix, and the gain disappears, and adds a lot of complexity.

One won't know until one tries.

modok wrote: ↑Tue Nov 07, 2017 7:57 pm

jcisworthy wrote: ↑Tue Nov 07, 2017 10:55 am
For me, a concentric valve job from the top of the chamber cut to the bottom of the bowl cut then shaping to and from all that is the way to go.

I think it is interesting you feel strong;y that it is "not for you", yet you have not implied it does not work.
Isn't that like saying
"yeah it makes the car faster but it's too much work?" LOL

Same thing can be achieved using an extra thick valve seat, it just ends up thicker one side than the other.
that raises the question....is it OK for a valve seat to be thicker one side than the other?? I think it's ok, but I don't really know.

It just does not make sense to me to move over so the bowl cleans up more evenly while making the air flow into the seat angles more unevenly.

I cannot picture that as a scenario that will flow more air and or make more power but I certainly could be wrong.

Moving over would be simple for me because I do valve jobs on my knee mill so not much more work for me really.

It would have to be scienced out with a ton of trial and error though.

How much do you move over? How deep do you bring the bowl cut in, where do you bring the bowl cut in? Bring it in on an extra wide seat, the first angle below the seat, the second angle below the seat, what angles and widths on the bowl cutter and how many?

On and on and on it goes where it stops nobody knows lol