Triumph Rat Motorcycle Forums banner

1 - 3 of 3 Posts

·
Registered
Joined
·
95 Posts
Discussion Starter #1
So today is going to be a tinker day. I am installing the header and crossover mid-pipe from a '96 trident, the lower water pipe off a '96 Speed Triple, the lower water hose off (I think) a Ford, and I think a set of one range hotter Bosch Platinum +2 plugs (The NGKs I have in there have just over 10K miles on them, time to swap them out anyway)

I've been thinking, though. I am pondering a bit of ignition advance. I did a little searching on here, and it seems that I could file the mount hole at a rate of .65mm/degree of advance. Factory Pro sells a +4 degree rotor for about $100 shipped. My questions are: How much advance would be useful? Reading here there seems to be some disagreement there, with a couple of posts saying +5 or more degrees would give good results. Thoughts?

Also, if my target advance was, say... +5 or +6 degrees, that would mean increasing the size of the mounting slot in the rotor by 3.25mm 3.9mm. At that measurement, I might wind up just cutting a new slot. Depends on how wide the existing slot is.

I guess the question is- what would be the maximum advance you folks think I could get away with before affecting "streetability" or hitting diminishing returns?

Merlyn

--Has a Dremel and is not afraid to use it!
 

·
Premium Member
Joined
·
6,462 Posts
I'm not sure which heat grade of plug you're thinking of exactly? But imo the NGK DPR8 grade is perfect & I really like the Iridium type.

As for ignition advance, without a TPS or MAP sensor to map advance for engine load, modifying the stock curve involves a performance trade off of low/mid rpm & throttle vs high rpm & throttle. At certain high throttle rpm ranges there is also a danger posed by detonation with too much advance. (Also a function of the Octane quality of the fuel.)

The att. T509 (885cc FI Speed Triple) engine load % (broadly throttle %) vs rpm map illustrates the above. Without the ability to map vs load, Triumph would have had to choose the lowest advance on each rpm line to ensure safety from detonation. But you can see that esp at lower throttle settings, the engine can operate at a higher efficiency - better part throttle response/power with more advance used.

Also take a look at the 100% load column. Notice how the advance dips sharply at 2400 rpm & 4000 rpm. Modern engines rely generally on a very well mixed & turbulent fuel/air mix in the cylinder to achieve fast burn rates - which require the minimum of spark advance. But this process is highly non linear & subject to 'chaos' maths. Burn will vary within a certain range from one engine cycle to the next even when all other parameters are constant. The only way to produce a properly accurate map for a given engine & fuelling is to test it point by point on a dynomometer with the combustion suitably instrumented, to determine this range. You can be sure Triumph selected those points of significantly lower advance to prevent detonation (which can result - usually does - in a blown engine).

Also att is the stock Tbird advance curve which I drew from a number of points I measured with a strobe light. You can take some comfort from the fact that it has a smoother WOT curve than the T509 ie less variation in detonation risk. Tho' there is a dip around 5500rpm. Although only Triumph know if it's there for best power, or to avoid detonation risk.

Notice that max rpm advance is much lower on the T509, a 108hp version of a T3 series engine very similar to ours. More power requires more fuel/air - a denser mixture which generally burns a bit faster, hence less advance needed.

So, to summarise, advancing ignition at all points is unlikely to give more power at WOT, & may well give less. A lot of advance risks detonation mainly at WOT. But it almost certainly will improve power/response/efficiency at part throttle, so some can be useful.
 

Attachments

·
Registered
Joined
·
95 Posts
Discussion Starter #3
I'm not sure which heat grade of plug you're thinking of exactly? But imo the NGK DPR8 grade is perfect & I really like the Iridium type.

As for ignition advance, without a TPS or MAP sensor to map advance for engine load, modifying the stock curve involves a performance trade off of low/mid rpm & throttle vs high rpm & throttle. At certain high throttle rpm ranges there is also a danger posed by detonation with too much advance. (Also a function of the Octane quality of the fuel.)

The att. T509 (885cc FI Speed Triple) engine load % (broadly throttle %) vs rpm map illustrates the above. Without the ability to map vs load, Triumph would have had to choose the lowest advance on each rpm line to ensure safety from detonation. But you can see that esp at lower throttle settings, the engine can operate at a higher efficiency - better part throttle response/power with more advance used.

Also take a look at the 100% load column. Notice how the advance dips sharply at 2400 rpm & 4000 rpm. Modern engines rely generally on a very well mixed & turbulent fuel/air mix in the cylinder to achieve fast burn rates - which require the minimum of spark advance. But this process is highly non linear & subject to 'chaos' maths. Burn will vary within a certain range from one engine cycle to the next even when all other parameters are constant. The only way to produce a properly accurate map for a given engine & fuelling is to test it point by point on a dynomometer with the combustion suitably instrumented, to determine this range. You can be sure Triumph selected those points of significantly lower advance to prevent detonation (which can result - usually does - in a blown engine).

Also att is the stock Tbird advance curve which I drew from a number of points I measured with a strobe light. You can take some comfort from the fact that it has a smoother WOT curve than the T509 ie less variation in detonation risk. Tho' there is a dip around 5500rpm. Although only Triumph know if it's there for best power, or to avoid detonation risk.

Notice that max rpm advance is much lower on the T509, a 108hp version of a T3 series engine very similar to ours. More power requires more fuel/air - a denser mixture which generally burns a bit faster, hence less advance needed.

So, to summarise, advancing ignition at all points is unlikely to give more power at WOT, & may well give less. A lot of advance risks detonation mainly at WOT. But it almost certainly will improve power/response/efficiency at part throttle, so some can be useful.
:: laugh :: Damn- I love your posts, IRLMike. They never fail to make me feel stupid, but I do love the amount of information I get in the process!

I think, since the +4 advance rotor is almost half of a new programmable ECU (which I am going to have to get pretty soon anyway), I'll just wait and get the ECU and rig up a TPS.

As for the plugs, since I went to the pods I am seeing a lot of buildup on my plugs. Chalky, kinda reminds me of calcium scale. It takes on exactly the same color as the rest of the ground strap, but I can chip it off to find untouched metal underneath. No pitting or other damage. I'm thinking with the DPR7's I'll see less accumulation. At $8 a plug change I can afford to experiment a little. Once I find the right plug, then I'll shell out the $8/plug for iridiums :: chuckle ::

Merlyn
 
1 - 3 of 3 Posts
Top