Too little timing?

Hey guys, I have a simple question that might seem dumb for some people but I figured, might as well ask cause I am bamboozled.

Can running too little timing actually hurt and engine. For example i've been tuning a 1.5jzvvti for the past years. 6266 on 26-27 ish psi of boost, professional drift car, puts down around 750whp. Built 2jz bottom, ported 1jzgtevvti head, cams, intake manifold, 2200cc injectors, the whole shabang. Running on e98 racefuel. Car runs in the 0.75-0.77 lambda in WOT. I've set the timing to be around 7 btdc at around 3.8k rpm and it goes up from there to 8 by 4k and up to around 12-13 at 8000rpm. Would that seem okay to you guys? ( I know for a fact I could go higher than that, i've pushed it to like 18 before but it kinda seems to stop making significantly more power beyond 16 ish) but i've been told numerous time that ''i'm too conservative on the timing and that I should run upwards of 20'' and that would kill engines, head gaskets and such. That kinda seems alot to me for a car making over 700whp that stays on the limiter for like 40 seconds.

I've also been told (by some random dudes) that for a reason i'm actually unable to explain logically ( although I might be wrong, I've been wrong more times than I've been right, as does everyone that tunes), that too little timing raises IAT by quite a bit.

Would that seem okayish? Thanks!

Salut Martin,

I'm not super familiar with tuning JZs, but I'll pitch in some ideas.

So, the only reason I think that IAT could increase with running retarded timing is that the engine will need more boost to make the same power. If it's so retarded, boost would increase (acting as small Anti-Lag), and the turbo could work harder and possibly fall out of is maximum efficiency range which would create heat. (This is only a theory and I might be wrong, don't quote me on that!) I'm curious what the others will have to say!

To be honest, I've stop chasing timing numbers, and I give what the engine wants. As long as you are at MBT without knock, why give it more? Also, when you are too far from MBT, adding 2 degrees will results in a big jump in power (with less boost sometimes), the closer to MBT you are, the less effect adding timing have. If your base timing is set, and you have check for timing drift with increasing RPM with a timing light, well it is what it is.

If you would be running less boost with more timing (without knock, obviously), would it make the same power? If the answer is yes, then I would decrease boost and add timing.

Have you check a log to see how hot are the IAT?

Frank

Thoughts and discussion points, rather than confirmed facts.

The fuel/air mix in the cylinder has x energy, adjusting the timing will alter the balance of pressure increase before and after TDC that uses that energy.

Assuming no detonation, too far advanced will reduce net torque because it increases "negative" torque and reduced "positive" torque because the combustion pressure increase is too early. It will also increase the heat rejection into the cooling system and into the piston crowns, the latter may be a concern. It will also increase maximum cylinder pressures around TDC, and stress the head gasket seal, studs/bolts, etc, the most.

Retarded isn't any better, because while the "negative" torque is reduced because the pressure build up is reduced, the pressure increase is also too late to apply the greatest overal pressure at the right points in the piston travel. In this case there is more thermal energy being passed through the exhaust into the turbocharger turbine - this can result in overheated, even dropped, exhaust valves and excessive manifolt and turbocharger turbine temperatures, possibly to the point of softening or melting the blades. The other affect of the excess energy being passed into the turbine is that it will drive the compressor harder/faster, which will increase potential boost.

Getting back to the charge side, while the increased boost from the over-driven turbo' impellor may seem like a good thing, the negative aspects are the increased boost will increase the temperature of the compressed air and so still be hotter after passing through the charge cooler into the manifold/plenum and will be seen as an increase in boost pressure but, as pressure does not always mean increased air mass, that may not mean more potential power.

So, retarded ignition > reduced torque, increased ex' pressure, hotter exhaust valve and manifold > increased turbine speed, hotter running turbine, hotter housing > more boost > increased intake temperature, possible lower mass density > retarded ignition > ...

In your position, I'd look at getting the best timing for torque/power expecting a reduction in boost as the overall efficiency is going to be improved. If you haven't already done so, I'd suggest getting a temperature sensor to monitor the exhaust gas temperature and check that against the turbo' manufacturer's max' operating temperature, then consider adjusting the fuelling to suit what the engine actually wants in balance with timing refinements.

The bottom line is you are looking for the maximum torque/power from the engine assembly (engine, turbo', coolers, etc) and so chasing arbitary numbers like "boost", "timing", "lambda", isn't really of any importance - EGT and spark plug heat ranges would normally be considered much more important.

Oh, what others are running for timing, etc, should only be considered a rough guide - it's VERY unlikely any of the others are running exactly the same combination as you are, so what works for them is unlikely to work for you - if you find 16 degrees gives best torque, there is no reason to try 20 - and many reasons not to - just because it worked for them.

I have compared your ignition numbers with mine 1.5jz running on 93 octane pump gas with MMA aditive and they are very conservative indeed considering you are using e98.

As Gord said too much ignition retard will cause too high exhaust gas temperatures that will overheat exhaust valves and raise overall temperature under the hood.