Ignition Timing & Compression Ratio's
Discussion
I've currently got a timing problem with a 2000 Griff 500, simply put it wouldn't stop pinking. This had been rectified by the dealer, but has mostly been achieved by winding the igntion advance right back. This has killed the performance of the car (quote from TVR mechanic, "this is the slowest Griff 500 I've ever driven").
First a simple question, just for my information, what way does the rotor arm in the dizzy rotate? In which case, which direction of rotation of the dizzy housing will advance the ignition?
Now something a little more technical, I've been told that this problem is more than likely caused by too high a compression ratio (although it is yet to be measured). What does this mean and what are the possible solutions to this?
As a footnote, with the timing set at 28 degrees at 4000rpm (no vacum advance) and running Super Plus (which I always use) + Millers octane booster, the car will still pink a bit, but performance is a lot better.
Neil
First a simple question, just for my information, what way does the rotor arm in the dizzy rotate? In which case, which direction of rotation of the dizzy housing will advance the ignition?
Now something a little more technical, I've been told that this problem is more than likely caused by too high a compression ratio (although it is yet to be measured). What does this mean and what are the possible solutions to this?
As a footnote, with the timing set at 28 degrees at 4000rpm (no vacum advance) and running Super Plus (which I always use) + Millers octane booster, the car will still pink a bit, but performance is a lot better.
Neil
Thanks for the replies, I now have all the information I need.
For those how don't read the TVRCC Email List on yahoo, here is another good reply from a respected source:
There's lots of things that can cause pinking - retarding the timing isn't the best way to go to cure it though on the griff since you can only alter the total timing across the whole rev range, so you'll keep from pinking at whatever revs this is a problem, but lose power everywhere that pinking isn't a problem if you see what I mean. you could lower the compression ratio, but as the griff breathing is compromised to begin with if you can't get much mixture in the chambers you have to squeeze it hard to get the power back at high revs. assuming the engine is in good condition with no faults / heads not skimmed too far / etc then try reducing the intake temperature by lagging the exhaust manifolds and intake pipes, fit a lower operating thermostat and a "water-wetter" to reduce engine temp (don't use a high antifreeze concentration as this reduces the water's ability to transfer heat) - after that you're probably better off going for a mapped engine ecu rather tha major engine surgery so you can slightly overfuel to cool the chambers under load whilst still running a weak cruise mixture, and only retard the timing in the pinking-critical range, so getting your power back.
joolz.
Cheers,
Neil V
For those how don't read the TVRCC Email List on yahoo, here is another good reply from a respected source:
There's lots of things that can cause pinking - retarding the timing isn't the best way to go to cure it though on the griff since you can only alter the total timing across the whole rev range, so you'll keep from pinking at whatever revs this is a problem, but lose power everywhere that pinking isn't a problem if you see what I mean. you could lower the compression ratio, but as the griff breathing is compromised to begin with if you can't get much mixture in the chambers you have to squeeze it hard to get the power back at high revs. assuming the engine is in good condition with no faults / heads not skimmed too far / etc then try reducing the intake temperature by lagging the exhaust manifolds and intake pipes, fit a lower operating thermostat and a "water-wetter" to reduce engine temp (don't use a high antifreeze concentration as this reduces the water's ability to transfer heat) - after that you're probably better off going for a mapped engine ecu rather tha major engine surgery so you can slightly overfuel to cool the chambers under load whilst still running a weak cruise mixture, and only retard the timing in the pinking-critical range, so getting your power back.
joolz.
Cheers,
Neil V
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