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Car: Nissan Patrol, TB42E, 4.2L Straight 6 Petrol with home made Turbo setup, Water to air Intercooler, Nistune Ecu
So tuning a customers car today, He originally said to tune to 14psi... Finished all the low load stuff and went to do a power run but noticed the boost reaching close to 15psi with no sign of leveling off (Internally gated and straight to the actuator)
Talked to the customer and told him where I was at. I did a test of the actuator and it seemed to be about a 18-20psi spring. He said go ahead and just tune it to whatever the spring pressure is... Not knowing these motors or what they can handle told him Ill be as careful as possible but no responsibility taken if it goes pop..
So pull all the timing in the mid to top end down to 5 degree's and do a run. Reaches 18psi, was Really rich.. Anyway get the fueling to where I want it (about 11.8:1) makes 180rwhp then try adding abit of timing, 8 degree's made 200rwhp and 10 degrees made 225rwhp but had to cut the run short as was quite heavy pinging in the top end so pulled it back to 5 degree's to have abit of safety as well.
Told him he would be better off with a different actuator and keeping the boost alot lower (14psi) and running more timing and likely make the same if not more power...
Does less boost but more timing put more or less stress on the engine and make more or less power? or does it work out to be the same and x amount of cylinder pressure will make x amount of power no matter if your making that pressure with more boost or more advance? I would have thought less boost with more advance would be more efficient??
Even tho this is a N/A motor with a turbo bolted on the stock compression is only 8.3:1 It seems like a very small amount of advance for it to start pinging? Would it have to do with it having a N/A cam designed for low down torque? Peak power is at 4000rpm...
Does having such low advance damage the engine at all? IE would the EGT's be getting extremely hot and could it Damage Valves or anything else?
When the Timing was retarded it made 18psi of boost, I noticed that when I advanced the timing the boost actually dropped to 16psi. Is this because with the retarded timing it would be burning longer into the exhaust stroke and be providing more energy to the turbo?
Thanks All, Look forward to your input.
Hey Clint, I'll address your questions below:
1. The power an engine makes is dependent on cylinder pressure so to a degree it doesn't really matter what combination of boost and timing you use to achieve that cylinder pressure from the perspective of the engine internals. However more boost and less timing will end up working the turbo harder, resulting in more heat in the intake charge and higher exhaust back pressure. These could be considered a negative.
2. Compression is an important consideration when it comes down to the engines ability to suppress knock, however there are other considerations too such as the combustion chamber design and cam timing/profile which will effect the dynamic compression ratio. You will also find that some combustion chambers promote fast burn characteristics which don't require so much ignition timing to reach MBT.
3. Your concerns are founded - Retarding the timing will increase EGT. It's hard though to put a number on the timing that is safe or reasonable and some of this will also depend on usage. For example in a street car this isn't usually much of an issue because it's hard to really stay at WOT for long. If you are tuning it for track use (unlikely I'm guessing in a Patrol) then this is more of a concern. Either way the only accurate way of knowing is to measure EGT. I personally wouldn't be happy with the timing being retarded to 5 degrees though. This to me points to a set up issue that needs to be addressed - Turbo size, boost, compression or fuel.
4. The turbo is driven by exhaust energy and this comes in the form of both heat and mass flow. As you retard the timing the EGT increases and hence this tends to drive the turbo harder resulting in more boost. It's an ugly situation that I see on some cars where the wastegate can't keep up and this results in boost creeping up at high rpm. Often this requires timing to be pulled at the same high rpm to avoid knock which hence increases EGT and causes more boost - The situation just snow balls and gets worse.
I think your assessment of the situation is valid. Drop the boost down a little and you will probably make the same power you are seeing with more boost and retarded timing. This will be better for the turbo system and the engine.