VVT + Supertech pistons = interference engine
#48
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Is this even an issue with an unmodified head? I feel like Sav and Emilio have both posted builds with stock vvt heads and 8.6 supertechs where no issue was mentioned.
Psyber, are worried because of the o/s valves?
Psyber, are worried because of the o/s valves?
#49
The new head has cams, sub, and OS valves and I have a pretty strong feeling it'll interfere so whenever I manage to rebuild the bottom end, I have to figure out this black magic of clay and cam angle.
#50
Ugh - not making me feel good when Psyber is worried too. Here is what I have:
block re-surfaced a couple times (unknown). Supertech 9:1 pistons sit -.001 below deck.
Head re-surfaced a couple of times, and then I went ahead and did some porting and the bowl is at 52mL. So calculations say I'm now at 8.922:1 compression ratio (not that it is relevant).
I have stock valves, manley rods.
So the question now is: How would I be able to manipulate the VVT actuator to manually rotate the assembly and check for clearance? OR, does anyone have timing info that would say "no problemo dude, stop worrying'.
block re-surfaced a couple times (unknown). Supertech 9:1 pistons sit -.001 below deck.
Head re-surfaced a couple of times, and then I went ahead and did some porting and the bowl is at 52mL. So calculations say I'm now at 8.922:1 compression ratio (not that it is relevant).
I have stock valves, manley rods.
So the question now is: How would I be able to manipulate the VVT actuator to manually rotate the assembly and check for clearance? OR, does anyone have timing info that would say "no problemo dude, stop worrying'.
#51
Ugh - not making me feel good when Psyber is worried too. Here is what I have:
block re-surfaced a couple times (unknown). Supertech 9:1 pistons sit -.001 below deck.
Head re-surfaced a couple of times, and then I went ahead and did some porting and the bowl is at 52mL. So calculations say I'm now at 8.922:1 compression ratio (not that it is relevant).
I have stock valves, manley rods.
So the question now is: How would I be able to manipulate the VVT actuator to manually rotate the assembly and check for clearance? OR, does anyone have timing info that would say "no problemo dude, stop worrying'.
block re-surfaced a couple times (unknown). Supertech 9:1 pistons sit -.001 below deck.
Head re-surfaced a couple of times, and then I went ahead and did some porting and the bowl is at 52mL. So calculations say I'm now at 8.922:1 compression ratio (not that it is relevant).
I have stock valves, manley rods.
So the question now is: How would I be able to manipulate the VVT actuator to manually rotate the assembly and check for clearance? OR, does anyone have timing info that would say "no problemo dude, stop worrying'.
#53
Another question for the experts: If I rotate the assembly through its range, and the valve does not interfere with the piston, does that mean I'm good? I would expect that there is a reason why people clay the piston - is it because you need a minimum gap between the piston and valve to make sure the valve doesn't bounce (or thermally expand) and hit the piston while in use?
#54
Another question for the experts: If I rotate the assembly through its range, and the valve does not interfere with the piston, does that mean I'm good? I would expect that there is a reason why people clay the piston - is it because you need a minimum gap between the piston and valve to make sure the valve doesn't bounce (or thermally expand) and hit the piston while in use?
#55
Just to tidy this thread up - my journey (and findings)
1. Piston to Valve clearance, while important, isn't nearly as important as "quench or squish". The gap between the top of the piston and the head surface. My block has been ground down 10mils and I'm using a different piston from stock (9:1 supertech). So I have basically a 0mil delta between top of piston and block surface. So I have a head-gasket-only quench distance. At about 40mils, that is definitely the dominant concern. I've seen lots of info stating you should be greater than 35mils to prevent the piston contacting the head.
2. I have tons of room between the piston and valves. I clayed the pistons and found there was ~0.20" on the intake side and nearly 0.30" on the exhaust side. I'm using stock valves, and the valve seats were reground a couple of times. Crazy amounts of room. Really I'd say Miatas only have a risk if you have oversized valve diameters and/or larger cams.
3. It is in fact an interference fit, but as long as you don't plan on breaking your timing belt, it is a non-issue.
4. I am going to clay it again with the VVT advanced/retarded. I'll get back after this weekend.
Thanks everyone
1. Piston to Valve clearance, while important, isn't nearly as important as "quench or squish". The gap between the top of the piston and the head surface. My block has been ground down 10mils and I'm using a different piston from stock (9:1 supertech). So I have basically a 0mil delta between top of piston and block surface. So I have a head-gasket-only quench distance. At about 40mils, that is definitely the dominant concern. I've seen lots of info stating you should be greater than 35mils to prevent the piston contacting the head.
2. I have tons of room between the piston and valves. I clayed the pistons and found there was ~0.20" on the intake side and nearly 0.30" on the exhaust side. I'm using stock valves, and the valve seats were reground a couple of times. Crazy amounts of room. Really I'd say Miatas only have a risk if you have oversized valve diameters and/or larger cams.
3. It is in fact an interference fit, but as long as you don't plan on breaking your timing belt, it is a non-issue.
4. I am going to clay it again with the VVT advanced/retarded. I'll get back after this weekend.
Thanks everyone
#56
Hey there guys,
Do we know if the same thing applies for the normal(non FM) wisecos 8.x cr?
I couldn't find measurements of the valve reliefs for the wisecos
Any input will be very helpful as I am about to tune it and I really dont want to have bent valves by advancing the vvt
As the engine is built by the previous owner unfortunately I don't have any input if the checked that before final assembly.
Do we know if the same thing applies for the normal(non FM) wisecos 8.x cr?
I couldn't find measurements of the valve reliefs for the wisecos
Any input will be very helpful as I am about to tune it and I really dont want to have bent valves by advancing the vvt
As the engine is built by the previous owner unfortunately I don't have any input if the checked that before final assembly.
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