The exhaust pipe thing will be an easy fix if I just get myself motivated to it. Probably need cut it somewhere and weld back to slightly different angle, or maybe just bind it somehow a bit. Not rocket science.
But what goes beyond my understanding is the pinging problem. I have learned my lesson and I understand pretty much about that problem in general and it ain't anything new to me neither. What is confusing is that Signet's almost bone stock 225 slant is suffering it. I have re-curved the distributor over and over again (both the mechanical and vacuum advance) and now it finally seems to be working okay. I will need to go buy a new vacuum canister with different rate (or ratio or what it is in English) to limit maximum vacuum advance to +10 degrees.
In the beginning it suffered both light and full throttle knock above 2500 rpm. Below that it was working just fine. Now it pulls nicely up to 5k's, but what is weird is that it just don't tolerate mechanical advance over 25 degrees BTDC at any engine speed. I did check every common thing causing detonation like oil leaks to cylinders, spark plug heat range and type (tried few) AFR, and even compression pressure, but there is no one significant problem. (I checked and double check the timing marks as well, that they match the top dead center. Match..) The compression pressure is, however, slightly in the high side for iron head motor, but nothing alarming. Rule of a thumb is that street motor running regular pump gas should not exceed 180psi of cylinder pressure at cranking. 200psi to be the absolute limit for pump gas street motor on premium. Signet's motor is cranking out heathy steady 182-185psi on every six cylinder. As said, slightly in the high side for motor that is intended to run junk gasoline, but nothing alarming.
I finally landed to a spark curve that delivers 7 Deg. BTDC at idle 650rpm and begins to pick up advance around 1200rpm and getting all 23Deg. in at 3000rpm, plus vacuum 10Deg.@60kpa. My current vacuum canister actually delivers +15Deg. but I modified it to limit it to 10 that seems to work ok. Just want to buy new that delivers the right rate with out any mods done.
What can I say.. The spark timing is extremely conservative, but it seems to work well and the motor is indeed very responsive and fun to drive. And works on 95 octane pump gas. (95 Euro norm equals to about 87 in the U.S) The motor actually seems to make much better top-end power than I expected and one thing that might make it less prone for detonation in the upper range could be better exhaust. The 2" pipe maybe become a little bit restrictive causing some back pressure which in turn causes all kinds of problem. Including excessive heat load on exhaust valves and cylinder head that can lead to hot spots and self-ignition. It also causes excessive amount of exhaust gas remaining in cylinders after exhaust stroke which heat up the new mixture making it hotter and more prone for detonation. And aside takes room from new fresh mixture and drop engine efficiency and performance. Oh well.
Anyways. I'm pretty positive about Signet. It runs and drives:) And regardless of all small thing there is left to do... it ain't bad. And damn I love to take on the highway. Love to drive it!
But now it's getting late and I gotta go sleep. I'll put up something more asap. This was just some kind of late night intermission release:D Take care!