11-03-2018, 11:46 AM
(This post was last modified: 11-03-2018, 11:55 AM by Speedex750.)
Hi Z, yes the Jack French pub analogy is a good one, later inlet closing gives a little more at the top end - but depending on how much you've retarded it - you might loose a little bottom end. I believe the gain comes from getting more charge into the cylinder before the valve shuts - the dynamics in the inlet system are still trying to get past the valve when it shuts, just like the pub landlord slamming the door when you fancy that last minute pint.
I would start by checking what you've already got in terms of timing with an accurate positioning of TDC and the opening and closing times for an inlet and exhaust with a DTI. There seems to be a variability in the accuracy of timing gears, keyway to gear tooth, and you could try different crank gears and see what effect they have. The definitive way is to rotate the gear and broach a new keyway but a simpler alternative is to make an offset key from an old flywheel or halfshaft key. From memory a 10thou offset gives about 3 degrees change to the timing.
As to what to set it to - I've seen a number of different standard timings so I'd be interested in what you find. It seems to me that the 'right' timing is for maximum inlet lift at 110 degrees ATDC. I wouldn't go more than about 5 degrees retarded from that but I'm sure we'd all be interested in how you get on?
Hope helpful. Dave
I would start by checking what you've already got in terms of timing with an accurate positioning of TDC and the opening and closing times for an inlet and exhaust with a DTI. There seems to be a variability in the accuracy of timing gears, keyway to gear tooth, and you could try different crank gears and see what effect they have. The definitive way is to rotate the gear and broach a new keyway but a simpler alternative is to make an offset key from an old flywheel or halfshaft key. From memory a 10thou offset gives about 3 degrees change to the timing.
As to what to set it to - I've seen a number of different standard timings so I'd be interested in what you find. It seems to me that the 'right' timing is for maximum inlet lift at 110 degrees ATDC. I wouldn't go more than about 5 degrees retarded from that but I'm sure we'd all be interested in how you get on?
Hope helpful. Dave