Naah. Im just a stupid racer, done stupid things and trying to lear how to read burn patterns from 20€ piston.. My cams are like 258@seat/178@1mm and 9.3mm lift, so i dont have valve train issues.LotusElise wrote: ↑Fri Sep 23, 2022 10:23 amYou mean slow on valve lift, in such a way that scavenge phase get the name worth and lift harder later with the aim to let the piston design need no valve reliefs?
Two things why this won't be the optimum:
- cam lobe design need very consistent acceleration, once you begin slow it is hard to get it back without going to the edge on materials, you would loose lift potential and duration, seating is one of the most sensitive moments for cam designers, the profile before dictate what it needs in the end to seat the valve smooth so that bounce is reduced to min. at high engine speeds. Otherwise we need even more FMEP eating valve springs. A smooth but stepped lobe profile isn't good for the wear and the dynamics of the valve and valvespring. What you do wrong in the beginning can only be healed with higher valve spring forces in some portion. Nothing we want have for highest power output everywhere.
I fear this is not leading to the holy grail. I talk about 100 ftlb/liter torque. I've reached already with my first attempt in NA racing 104 ftlb/liter peak torque (almost 209 ftlb peak torque on a 2-Liter NA engine) and from 4500-8200 rpm over 96 ftlb/liter. I know to get there and still searching on ways to take that level to higher engine speeds for the next attempt I am working on.
- TDC valve lifts of 5-7 mm are typical for NA engines in the 4-valve field. If you go lower you loose in the midrange engine speed. At 10,000 rpm you still see 3-4 mm@TDC with a R/S-ratio of 1.7 and a 86 mm stroke and a 13:1 CR in a 50 ccm head that means still touching the piston without reliefs
On a 2-Liter NA engine .5mm lift@TDC is enough to make 1.5ft lbs/cid from 4000rpm-5500rpm. This is done using modified oem parts and 15-16bar cranking press measured by our gage. My experimental stuff has gone up to 19-20bar using similar cams. There is power hidden on a exhaust side...
Attached is a picture about chamber matching the piston above, approximately 1.3mm quench clearance. I just go for bigger exhaust valves.