SETA stroker cam options.....???

[JiXer]

So I just used a piece of solder through the spark plug whole and turned the motor over by hand to measure the valve to piston clearance and I got .082" on the intake and the exhaust didnt seem to register at all on a 1/8" piece of solder (that one was tougher to measure because its to the right of the spark plug hole and its harder to get the solder in there.) .082" is considerably more than the .060" minimum that seems to be the consensus number I keep finding in other threads though I could not find any sort of "official" spec to confirm that.
This makes me think that I could bump the intake lift and/or duration a bit, but I don't know how much it would be worth it with no porting and only 8.5:1 compression.

[digger]

So I just used a piece of solder through the spark plug whole and turned the motor over by hand to measure the valve to piston clearance and I got .082" on the intake and the exhaust didnt seem to register at all on a 1/8" piece of solder (that one was tougher to measure because its to the right of the spark plug hole and its harder to get the solder in there.) .082" is considerably more than the .060" minimum that seems to be the consensus number I keep finding in other threads though I could not find any sort of "official" spec to confirm that.
This makes me think that I could bump the intake lift and/or duration a bit, but I don't know how much it would be worth it with no porting and only 8.5:1 compression.

what cam was that with? i think 1.5mm is ok for the inlet side if it was done with zero lash and you are confident with radial clearance.
a cam with only a peak lift increase is not going to reduce piston to valve clearance much since just either side of overlap is where the problem is not at peak lift when the piston is half way down the hole.
look at the lift at TDC from a cam catalog to see which might cause problems

[JiXer]

Sorry. Should have clarified. This measurement was done with an i cam. This thing is all stock as it sits. Lightly resurfaced i head on a super eta bottom end. And yeah... Totally wasn't thinking about the peak lift thing. :) but that obviously makes sense. What do u mean by "zero lash"? Valves are adjusted to .010" and this was done none cold. And my clearance is actualy 2.1mm.

[digger]

Sorry. Should have clarified. This measurement was done with an i cam. This thing is all stock as it sits. Lightly resurfaced i head on a super eta bottom end. And yeah... Totally wasn't thinking about the peak lift thing. :) but that obviously makes sense. What do u mean by "zero lash"? Valves are adjusted to .010" and this was done none cold. And my clearance is actualy 2.1mm.

zero lash means clearances set to zero rather than 0.25mm. a schrick 272 has a lift at TDC of 1.6mm which is not much more than stock but id have to check the stock numbers to compare precisely. the 284/272 has 2.2mm (due to more overlap) so unlikely this will work.
i advise getting a cheap adjustable cam gear if budget allows this can allow some control over clearances and let you alter the powerband a bit with a given cam

[JiXer]

Yeah. I think thats a good call, but I wonder if I could bump the intake duration and lift a bit with a custom grind and use the adjustable cam gear. I wouldnt want to just pick an arbitrary number. But if I were to do that, say, 276/272 and 1.8mm with the adjustabilty... I should clear. Would it make a difference? Still only pushing 8.5:1.
I'd rather be safe than sorry but if its all the same clearance wise, how much is too much for what the motor is.

[digger]

Yeah. I think thats a good call, but I wonder if I could bump the intake duration and lift a bit with a custom grind and use the adjustable cam gear. I wouldnt want to just pick an arbitrary number. But if I were to do that, say, 276/272 and 1.8mm with the adjustabilty... I should clear. Would it make a difference? Still only pushing 8.5:1.
I'd rather be safe than sorry but if its all the same clearance wise, how much is too much for what the motor is.

stock cam has 1.1mm lift at TDC so you lose about 0.5mm clearance (perhaps slightly more due to faster ramps) going with a 272 schrick which is 1.6mm. you would need to recheck clearance once installed. every 4 dgree of advance takes about 0.5mm of clearance away from inlet side. if you cam is excessively advanced then a bigger cam dialled in may have about the same clearance but i think mostly things end up retarded overtime.

to run a bigger cam amd not reduce the clearance you need to widen the LSA which needs more compression to work properly. A budget 2.7 is never going to be a powerhouse so i would avoid overcamming it in attempting to achieve this.

to run anything more than a 272 i would want about 9.5:1CR as a min, but preferably 10:1.

[JiXer]

Makes sense. 272 may be all I can get out of a regrind anyway. I do think the additional lift may help though considering that this thing lives at 4500-6500 rpm. With the long intake runners and no porting I'd think it would have to help cylinder filling and VE to have that touch more lift. No?

[digger]

Makes sense. 272 may be all I can get out of a regrind anyway. I do think the additional lift may help though considering that this thing lives at 4500-6500 rpm. With the long intake runners and no porting I'd think it would have to help cylinder filling and VE to have that touch more lift. No?

yes it does help. on a stock port lifting too high can make the port stall/backup as the flow separates over the short turn but with a regrind you arent going to be massively more lift over stock so it all helps.

people often say if the headflow vs lift curve flattens out then it makes no sense lifting higher than this but this is usually wrong. there are really only two main cases where lifting the inlet valve too high is bad.
1) the valve train can not sustain it
2) the flow separates at high lifts and the flow stalls when it previously would not have

once the scavenging is done the thing driving flow is piston velocity. if the peak lift is higher then at a given point in time the valve lift is higher as well so the head is capable of flowing more at all points in time (not just at the peak) with the higher lift cam. in effect the head spends more time (in degrees) at its peak flow point

[JiXer]

Yeah. I totally follow that and the touch more lift wont get us in to that situation.