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Timing vs Boost for making power with road tuning

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As the title states, what makes more power with an increase of single increments, such as adding a degree advance or one psi. This car will be tuned on the street, so finding MBT will not be focused on much. Many tuners have the different philosophies when making power. Other add more boost vs timing, and vice versa. From general knowledge I've gained, boost increase creates less heat compared to timing?? Car in question is a 2004 wrx sti with the 2.5l, with built bottom and top end. Turbo is a custom garret blend which is the GT3586, which is roughly a 75lb/min. Injectors are 1,400cc and a hard wired walbro 450. I'm pretty sure I won't reach my target boost of ~30psi, which is why I hard wired my pump and plan on 50psi base. I kind of strayed off topic, but with the understanding I won't reach my boost target due to my injectors, am I better off running low to mid 20 psi and a greater advance?

When I tune I look at what the car can hold in terms of TQ. My car can do 350 TQ before things start to get weak or break. So what I do is start by having a base line timing map like Andre talks about in his video. Then start the boost at 15 - 20psi and watch the TQ climb. The formula for HP = TQ*RPM / 5252. You might want to ask around on and see what others have done in terms of max TQ on the build you have. Then you can get a good idea on your timing map and boost you will be around.


My own philosophy has always been to run a little more boost and a little less timing. The reason i do this is because there are a variety of ever changing aspects to combustion that can influence the knock threshold of the engine (ECT and IAT are just two examples). While we can compensate the ignition timing based on these parameters, often it can be difficult to thoroughly tune the comp tables on the dyno to cover every likely scenario you could expect on the road and track.

If your engine is knock limited and you're running very close to the edge of detonation, it doesn't take much to push you over the edge. I prefer to keep a wider margin to the knock threshold and run an extra 1-2 psi if you want more power. I find this results in a wider safety margin for a given power level rather than tuning the timing to the absolute edge on a lower boost setting.

I just saw this interesting post.

Concerning knock Andre explained well, because knock preventive strategy are difficult to calibrate and a bit simple on aftermarket ECU.

Other important aspects are linked to the torque rise gradient and engine reliability.

Before MBT add more ignition timing will give immediate torque, reduce EGT, reduce BSFC, but add ignition timing has significant effect on maximum cylinder pressure.

Add boost will give more torque but only when you achieve the boost target. So in case of a complete full load, result will be same, but in case of a quick WOT demand at 3500rpm for example, time to reach the maximum torque will depend of if you use boost or ignition timing to make your torque...

Add boost also increase max cylinder pressure but torque gain/maximum cylinder pressure increase ratio is higher.

There are other aspect of cylinder pressure but more difficult to approach.

Boost also increase EGT.

If your engine is very knock limited you will have no choice that make boost.

If the engine is no knock limited, on road it is very difficult because, first, you can pass over the MBT point adding ignition timing, and you can generate high cylinder pressure which is destructive for an engine.

My explanation is a bit simplistic but this compromise is a big item that tuners don't really deal with, main reason is that a complete instrumented engine is very expensive.