sidescreen Posted April 21, 2011 Report Share Posted April 21, 2011 Hi Guys, Just a question about advance timing, seems to be a bit confusing for me. The manual is telling us it must be 4 degrees static or 10 degrees with a running engine with about 850/1000 rpm. These figures are based on "old" petrol with an octane number of 80. But how much would it be in your opinion with our modern 98 fuels....? Looking forward to your answers ! Regards - Raymond Quote Link to post Share on other sites
TomMull Posted April 21, 2011 Report Share Posted April 21, 2011 Hi Guys, Just a question about advance timing, seems to be a bit confusing for me. The manual is telling us it must be 4 degrees static or 10 degrees with a running engine with about 850/1000 rpm. These figures are based on "old" petrol with an octane number of 80. But how much would it be in your opinion with our modern 98 fuels....? Looking forward to your answers ! Regards - Raymond My amateur opinion is to stay with the original specs, particularly if it runs well, does not "ping" nor run-on after shutdown. You might be able to advance a couple of degrees with high octane fuel but I don't think you would gain much,. if anything (stock cam, I assume). Again, my opinion. Tom Quote Link to post Share on other sites
PhilJane Posted April 22, 2011 Report Share Posted April 22, 2011 Hi All, I have read a few posts on setting up the ignition timing and it's interesting to hear that our experts set up the ignition timing by finding the detonation point (lugging up a hill in 3rd gear)ie by 'feel' and backing off a couple of degrees, rather than set to a fixed ignition timing. Is that due to the different states of engine tune or the different fuels being used? I was hoping to set my ignition timing with a timing light, but find there are no fixed recommendations. Is it 10 deg. BTDC at 800 rev/min? Thanks, Phil. Quote Link to post Share on other sites
Ashley James Posted April 22, 2011 Report Share Posted April 22, 2011 According to the book there is a round hole in the rear flange of the fan belt pulley on the crankshaft and when this is aligned with the pointer, the points should just be opening on the firing stroke and the timing is, I think, 7 degrees BTDC static. However some engines have been enlarged, which raises compression, some have the pulley assembled wrong so that the hole is in the wrong place and some have been converted to a narrow fan belt which needs a different pulley. All of which means it's more difficult to time the engine. I'm a beginner with TRs, so will send my distributor to the Distributor Doctor to make sure it's advancing correctly and then I'll use the marks. Mine may pink because it started life as 1991cc and is now 2187cc. Stuart will probably correct me if I'm wrong. Ash Quote Link to post Share on other sites
67_gt6 Posted April 22, 2011 Report Share Posted April 22, 2011 (edited) I'm a beginner with TRs, so will send my distributor to the Distributor Doctor to make sure it's advancing correctly It's certainly crucial to know that you have the correct advance in the distributor - by which I mean both the curve and the total number of degrees (which should be 10). I bought a new distributor from Martin Jay and I had no problems setting the advance as per my post in http://www.tr-register.co.uk/forums/index.php?showtopic=28937 . Remember early drivers used to adjust their timing whilst on the move, sans strobes Andy Edited April 22, 2011 by 67_gt6 Quote Link to post Share on other sites
sidescreen Posted April 23, 2011 Author Report Share Posted April 23, 2011 Thank you all for your contributions ! I will give it a go at 8deg BTDC to start and see how it goes. Have a nice weekend - Raymond Quote Link to post Share on other sites
TR Man Posted April 23, 2011 Report Share Posted April 23, 2011 Hi Guys, Just a question about advance timing, seems to be a bit confusing for me. The manual is telling us it must be 4 degrees static or 10 degrees with a running engine with about 850/1000 rpm. These figures are based on "old" petrol with an octane number of 80. But how much would it be in your opinion with our modern 98 fuels....? Looking forward to your answers ! Regards - Raymond Dear Raymond, We just started and tuned our reconditioned fast road engine with Weber Carbs last night and the ignition timing was 14 degrees TDC at 1000 revs. This gave a very smooth running engine with an 800 rpm 'tick over' no over-heating, nice exhaust temperatures and no 'funnies' when ignition was turned off. Regards, Martin Quote Link to post Share on other sites
Peter Cobbold Posted April 23, 2011 Report Share Posted April 23, 2011 Fuel octane has no effect on flame speed. Detonation is the 'end-gas', usually near the exhaust valve exploding, and high octane deters this by virtue of the flame chemistry. Detonation is promoted by high compression so as most TRs have been modified with skimmed heads and/or re-bores/over-bore liners/hot cams etc there is no longer a standard advance setting. That said a 10 degree (crank) spread in ignition timing will have a low percentage effect on power, say 1-2%: timing is not that critical. But in the search for the last percent of power timing should be such that peak pressure occurs around 16deg ATDC. We have no means of measuring that so the method is to set the timimg up at peak torque rpm - say 3000- until the engine starts to detonate and then back off a degree. Then you are near 'klimep'. Heat build-up in the combustion chamber during wot running can promote detonation. So an engine that is set up at klimep during brief rolling road session might detonate at sustained high speed and load (eg up a long motorway hill). And that detonation will be inaudible. So klimep tuning is not without risk. Quote Link to post Share on other sites
Ashley James Posted April 23, 2011 Report Share Posted April 23, 2011 I don't know if it's the same all around the country, but we have two rolling roads nearby, one of which is very good at sorting out old cars, so if yours has had all sorts of modifications and you want to make sure you're getting the most possible power and that nothing is set in a way that might cause damage, it's well worth the expense. A friend modified his VW Beetle for trialing, he fitted different rockers to increase lift, double carburettors and a special exhaust. It didn't make a huge different until it went on a rolling road. They found him another 25bhp, so it can be worth it. I believe it cost him about £200. Ash Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.