Installing larger valves on previously....

I have a set of LT1 heads ported by Lloyd Elliot. They were originally ported with stock valves, totally stock valves, and flowed 271 @60.

Anyway, the question, whether it is advanced or not, want a sure answer, is if I want to install either larger race-flo valves they will obvioulsy need cut for the larger valves, but what happens to the 5-angle valve job done to them previoulsy, is it gone, or will it go unaffected.

Or, if I put stock size raceflos on them, do the seats need recut or ground down to accept brand new valves, or are they drop in, im quite sure that they at least need ground down.

And lastly, what do you suggest, these flow quite "freakishly" for stock valve stock casting lt1 heads (I know flow isnt everythng, but lloyd ported them so everything else is still good), for the valves, keep stock size, go bigger, what kind of valves?

lift Intake Exhaust
.050 36.5 23/0
.100 62.9 48.1
.150 93.3 71
.200 131.7 90.5
.250 163.1 113.6
.300 185.6 126.2
.350 215.7 137.8
.400 234.5 149
.450 248.7 163.6
.500 257.7 172.5
.550 265.1 181.6

Yes your valve job is gone if u descide to cut, I'd keep it the way it is. The flow is awesome & you'll definetly pick up a lot midlift with larger valves but then air has more valve to go around with larger valves so it all depends, I think you'll definetly benifit from some 2.0/1.57's on there but it'll get costly especially if you had a nice valve job there before.

As bunker said the valve job is gone. To correctly go to a valve bigger then a 2.00 you will need to install new seat. That is what I had to do. The trade off seems to be working for me and the bigger valve really is not an issue on a 4 inch bore. I know on the smaller bore LS1 the bigger valve is shrouded to much and the cone of flow is broken up.

To keep the proper Vavle job that was done you should keep the valves that were preped with the heads so all the hieghts are correct and they fit on the seats correctly.

Ok, so it sounds like I should probably stick with the same size valve then, I would only gain a few CFM anyway so Im not too worried about that. But it wasnt clear in your posts whether keeping the same size valve puts me in the same boat with losing the valve job, or if I can put new stock size valves on no problem.

I definitely am not running the stock valves that are in these heads on my new motor.