Are you saying 15psi intake manifold pressure or 15psi of turbo outlet pressure. It makes difference. Also have you calibrated or compared the map sensor to ensure 15 is really 15psi and not 13 or 14psi for example.
15 at 15 is what everybody uses, very common. It is why I took the time to explain more exact values and process. I already knew you had this timing in mind because it is a typical copy cat. It is wrong for that engine because it is pushing highest brake torque which is not what you want if the goal is reliability. If you dyno the car depending on weight you may find that 11 to 12 works as good as 14*~ at 15.5 to 16psi, without spikes it shall be less than 2 or 3% difference. The difference will be at 14 or 15* is on the verge of some issues and with a slight change in load or temperature or fuel quality the engine may suffer inaudible knock which assuming you have factory pistons will deteriorate them eventually causing a fracture. Years is negligible it is miles and time spent at WOT that matters. The stock engine can reach 200,000 miles with 600rwhp using minimum timing with good air filtration practice and low lift cam to protect lifters and careful monitoring of oil temperature (you need an idea of piston cooling and temperature) and EGT. But when you play near MBT or highest brake torque timing , the engine is no longer reliability biased. Instead you are only trying to save fuel by improving BSFC and squeak out a tiny bit more torque 2 maybe 3% usually. It also may create perturbations or spikes in the dyno curve which leads to higher than realistic output maximums which misleading for people who have not had experience measuring combustion pressure with a transducer to see the spike which causes the jagged dyno curve. It also depends on sampling rate and acceleration rate of the roller.
In any case. I simply want the best for you. The highest mileage. All I am saying is this: Take the car to a chassis dyno. If the vehicle is around 3000lbs put it in 1:1 gear and perform a couple wot pulls. One with 11 or 12* and one with 14 or 15* and compare them. The 11 or 12* run should be within 2 maybe 3% of the other run and the curve will be smoother (Use smoothing=0) indicating you have smoothed and calmed the pressure spikes of combustion. The peak will be lower because spikes are reduced in magnitude. The overall curve shape improved will still indicate reasonable EGT (fuel burning more completely in the cylinder still).
If I am wrong then the torque will drop off massively and the curve will not smooth out. If that is the case show me these details and I will help pay your dyno time. I've tuned a thousand turbo engines and believe this or not, the 2jz and sr20 and RB engine series uses the same timing per power
isplacement ratios as the LS engine you have because the combustion chamber is modernized the same way for all engines. The more efficient the engine the less timing it will need. For example small block chevrolet is 36* btdc naturally aspirated common but LS/RB/SR/2J engines are near 24* sometimes 22* naturally aspirated for the peak cylinder pressure. So if you have actually done proper chamber work to the engine and truly improved upon an already great design then it will use LESS timing than it did previously. Otherwise you have actually made it worse and reduced the efficiency and it needs more timing than it should.
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Originally Posted by blindsquirrel
