porting a 7m head, cut down the guides, or leave them?

[daver]

Working on a 7M head, general mild port and polish.

Question is particularly on the exhaust side, should I cut the guides down and blend them into the port roof, or leave them alone?

 

[IJ.]

Personally Id leave them full length and just radius em as the length is good from a wear Point of View.

 

[mk3ukr]

Slightly off-topic question. How good are valve guides on 180K miles motor? I want to remove my head for mild porting and installing +1mm valves. Do I have to order set of valve guides in advance or they can be in the perfect condition?
Thanks
Vladimir, 89T

 

[daver]

Good from a wear point of view, but obviously not from a flow perspective. They're actually a significant obstruction in the rather small exhaust ports.

The valve stem itself can't be done much with, unless somebody wants to make custom guides and valves with a thinner stem.

The motor I'm doing this head for however is pretty much a semi-stock 3 season driver, so I don't want to cut the guide or valve life down significantly.

Curious if anyone has ever run a 7m with the guides blended down any significant milage?

 

[figgie]

Good from a wear point of view, but obviously not from a flow perspective. They're actually a significant obstruction in the rather small exhaust ports.

The valve stem itself can't be done much with, unless somebody wants to make custom guides and valves with a thinner stem.

The motor I'm doing this head for however is pretty much a semi-stock 3 season driver, so I don't want to cut the guide or valve life down significantly.

Curious if anyone has ever run a 7m with the guides blended down any significant milage?

absolutly stupid.

the valve stem size is already at at around 5.8-5.9mm. Any smaller and i guarantee you that you will probably start breaking valves.

as for the valve guide. Cutting them down.. pointless. Regardless if they are an obstruction or not. There is a reason why those stems NEVER need replacing. One is due to length.

 

[IJ.]

Ok I'll put it this way....

Is the small increase in flow worth the decrease in performance you get from poor valve seating when the valves can wobble around never seating in the same place twice causing seat wear valve recession and ultimately closing the running clearance then burning the valves?

<Grandpa mode on>
Seen just about every "Performance mod" that can be done at home in 30+ years of building motors and while I don't have a lot of 7M specific data/experience motors are motors and a lot of it still applies.
<Granpa mode off>

 

[group a supra]

Ok I'll put it this way....

Is the small increase in flow worth the decrease in performance you get from poor valve seating when the valves can wobble around never seating in the same place twice causing seat wear valve recession and ultimately closing the running clearance then burning the valves?

<Grandpa mode on>
Seen just about every "Performance mod" that can be done at home in 30+ years of building motors and while I don't have a lot of 7M specific data/experience motors are motors and a lot of it still applies.
<Granpa mode off>

:withstupi