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Old 05-21-2018, 06:57 PM   #776
Turbo, what?
klr142's Avatar
Join Date: May 2004
Location: OR

I've only made it through just over a tank of gas since I did the work and never got around to doing the back to back tests.

Initial thoughts are that I was not blown away by the result of my SINGLE groove experiment. Performance is basically unchanged(expected only an improvement around idle and maybe under 2000rpm), but there does seem to be improved detonation resistance. So at least it has that going for it.

Initially the idle was worse with reduced idle vacuum. It was acting as if I put in a larger camshaft. I'm pretty sure the valves are at about the same clearance as they were before, but during the downtime the buckets did get mixed up and I did have to reshim a couple. One intake might be a little tighter than before, but I doubt it's enough to make a difference. After the car learned through the tank of gas, it improved and the idle is now higher than before, MOST of the time. Sometimes it doesn't idle higher and it has low vacuum, other times it's comparable to before but the idle rpm is higher(indicating it's more efficient?). I didn't adjust the base idle setting on the throttle after doing the work. Low rpm performance doesn't feel much different, and may have even felt worse at first. I may or may not be able to lug the engine around more at really low rpm and low throttle openings with less interior rattling, but it hasn't been the larger difference I was hoping for.

As far as the detonation threshold goes, I used to have a lot of detonation when running the stock fuel tune and the advanced ignition timing. Even when it was cold out(<40° F) I had problems running that "tune" combination. I have continued driving the car in ambient temps over 65° F without issues. Maybe even as high as 75°. So, I would definitely call that an improvement!

My thoughts on the grooving experiment as a hole(for this round), are that doing ONE groove is not enough.

ONE groove may work ok with additional chamber modifications, such as reducing the squench pad near the spark plug and unshrouding the exhaust valve. Both of which reduce the need for grooves.

In a stock combustion chamber, I think TWO or THREE grooves is required for optimal results.

Njål's head is pictured above in post #758 and he had the desired results. Coupled with a K camshaft, he had a massively flat torque curve with good performance and no detonation until PAST MBT while running over 12:1 static compression in a B230. SEE HERE

I'm not sure what I'm going to do at this point. I may pull the head to add some more grooves, or I may just run it as is. Or I may pull the head, add some more grooves and take another mm off the head to bump the compression up some more with new valve stem seals as at least one is leaking some.
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