At those distances id want to work out what the possible difference if any could be between a pumped lifter. Id also imagine the 1mm clearance is probably to do with cars like pl/kr running belt drive to deal with the stretch at higher rpm.
Ok, so an update. I got the car rolling a couple of nights ago, and it runs beautifully in general. It sounds much better than the previous build. Possibly due to valves not contacting pistons, cam chain not being slack, etc. . Anyway, I got the car on the road, and started mapping. I wanted to set a config error with the req fuel value straight. Somewhere along the line, that value got messed up, and that meant I had something like 122% VE in the top end, according to my map. I also figured that the new cam timing easily could mean that my map would need fiddling anyway. I have borrowed a KnockSense unit (http://www.viatrack.ca/) from a friend, and had mounted that as well. I haven't calibrated it yet, but just took it for a spin. As soon as I got up to ~4500 rpm @ WOT, the knock indicator lit up. I tried backing off the timing, and it did seem to help. This supported my suspicion that maybe the issue is not with top end detonation, but more mid range. Right now I have removed almost 10 degrees from around 4500 rpm and up. Later on I discovered that from around 5500 and up, I couldn't really make the light go off,. Just to test it out, I tried with as little as 10 degrees advanced all over the map. This suggested issues with noise of sorts. I feel that the cause and effect at around 4500 was definitive though. Secondly I mounted a set of det cans. In this case I have made them from a mechanics stethoscope. I took a long drive (long enough that I forgot about fuel level, ran dry and hard to run ~4 km. in the middle of the night), and listened intensely - but I couldn't make out anything at all. Tried the 10 degrees again for a baseline, and tried around 20 degrees where the KnockSense unit lit up - couldn't tell the difference in sound. I do have a race coming up this Saturday, and at this point, I have the ignition at 16 degrees from 3200 rpm and all the way up. It actually does seem - from the butt dyno - that it runs better than previously. Judging from the VE-table, it would seem that my torque curve has gotten flatter as well. The typical dip at around 4500-5000 rpm that the 1.8 16V's with the big intake all seem to have, has been smoothed out compared to before (it was pretty signification in the old map). I attribute the change in the shape of the torque curve, to the changed cam timing - and obviously this can explain the improved seat-of-the-pants feeling. My next steps involve messing around with the calibration of the KnockSense unit, and see what conclusions I can draw from this. Depending on the results of that, how conclusive they seem to be, etc., I may re-make the det cans, experiment more with those, and then may it's time for the dyno. Right now the results of the steps immediately in front of me, will determine the next steps - unless someone has some brilliant point that I haven't thought of .
Holy thread revival. Playing with my 2L 8v 'budget' race engine build. Block minus 1.5mm 2E pistons decked back to reduce the bowl cc. 1st prelim dummy build Piston No.1 now 0.8mm out of the top of the block Gasket 2.0 uncompressed, say 1.8mm compressed So 1mm clearance, going to verify with the soft solder build Sound alright? I think so Jon
I've just had to do this with Tim's latest race engine. The hydro race cams have 4.amm of lift at TDC so we had to pocket the pistons by 2.25mm, and sink the valves 1mm to get our 1mm clearance. Squish is 26thou. It's been a challenge having to work backwards to get everything to clear. Even taking 1mm off the valve stem leaving very little between the follow stem and the valve spring cap. All good fun though
