Ted75zcar

iTrader: (2)

F man that is good thinking! I bet you get more lift range as well. Man, that is good thinking. Was it original, or is that a common knowledge approach (the base circle with ST valves thing)? I don't know how much time I spent setting up my lash... was a lot.

psyber_0ptix

iTrader: (4)

When doing the SUB conversion, the shop said that there was no space for a shim on stock cams. The valves where too long. Moving to the 33/34mm base circle aftermarket cams allowed the completion of the conversion. 949 states that tipping valves or guess/check shims is pretty standard. The shop wasn't comfortable with tipping supertechs and the caps would otherwise interfere with the retainers. Lot of magic had to happen to get these to work right. It didn't look like it was possible with stock cams.

Ted75zcar

iTrader: (2)

I did the SUB conversion, went the 949 "PRO" route, guess my measurement and control methods were not up to 949 snuff because I still had to custom shim every valve to hit the max cold lash spec +/- 0.000/<0.001(ish)

it was a total biznatch

AA-Ron

I tipped mine so I could just buy one shim size. all that work will need to be reconfirmed if/when I put new cams in.

Cometic tells you the compressed operating thickness for the head gasket you choose. I believe OEM is .031. Assuming your machine shop provided you the amount removed, you can theoretically take the amount taken off the head + .031 (OEM squish) to find the thickness needed. then you would not effect compression or valve to piston clearance.

sixshooter

iTrader: (12)

Higher lift than Stock cams may experience interference on what was previously a non interference engine. Oversized valves can cause this as well.

Davezorz

iTrader: (2)

To my knowledge, there has been no work done on the head/block

I think i was adjusting the valve lash, and i went to spin the intake cam around to close the valves and check clearance on #4. I spun it such that the cam lobes would open the valves completely before closing(non-interference motor, right?), and I could not get the lobe to pass completely over the lifter. I thought this was odd, so i moved #4 off of TDC, opened the valves all the way an gently rotated the crank, and it would not move to TDC. I checked the other cylinders, and I could feel it just barley touch on #3 (i felt light resistance, but the crank would spin all the way around with the valves open). #1 and 2 cleared the valves completely.

one thread discussing this on a 99 here:
https://www.miataturbo.net/engine-performance-56/wtf-interference-bp4w-84727/

I made a post about it years ago, but people just seemed to think it was carbon buildup. I just buttoned it up and ran it. I just assumed the early motors were non-interference, but maybe as mazda raised the compression and made other adjustments, it may not necessarily always be true.