Theoretical Tuning Question

[IJ.]

Given a hard limit on Octane which approach will make more power

Higher boost with less advance

Lower boost with more advance?

[stevieturbo]

Only way to know is by testing....far too many other variables come into play. Not least, the amount of power you are after for a given engine size.

[IJ.]

Theoretical.....

There are 2 variables

Boost
Timing

Octane is set assume tuned to a safe level re detonation.

[stevieturbo]

So turbocharger, exhaust design, camshaft, cylinder head flow, intake design, intercooling, compression ratio etc etc arent variables ?


There is no simple answer.

[PeteS]

Hi guys,
Everybody is correct with what they are saying,

From my relatively low experiance I have observed the following.
For a given set hardware/fuel combination, you would test the results of boost verses ign timing.
Personally, I tune to say 1 bar boost on the engine, maximise power with fuel and ign adjustment,
then add say 2 PSI boost and tune ign and fuel, add 2 more PSI tune to suit and so on.
What happens with most common systems is that you get to a point where adding the extra 2 PSI doesnt make much more power, its at that point that you have basically maximised the given set up. A lot of factors cause the fall off in power, including intercooler size etc however the most common reason is exhaust back pressure.
So even if you try to make more boost, which you can, it effectively doesnt make it through the engine due to the ever increasing back pressure in the exhaust system, you read it on the MAP sensor but it doesnt do anything for the power. The only cure for that is larger exhaust housing/turbine etc, but then of course you run into lag issues, it goes on and on as I am sure you all know.

So in short I spose, you should always tune to gain the most power using ign timing at the lowest boost possible. This keeps the backpressure lower which is therefore overall more efficient for the engine to produce power.

Unfortunately this method while the best for making maximum power is fraught with the danger of detonation, especially when using pump fuel.

[IJ.]

Thanks Pete for a constructive answer.
(Used this method recently)

It seems the guys are overthinking the question.

I didn't come here to argue or cause a problem just to ask a simple question.

ie: Juggling ONLY the 2 variables outlined what would yield more power.

Good point on the back pressure V's improvement per PSI, I've noticed this on the dyno.

[Ben-S]

There is no answer to your question. If you were to ask "how do you tune timing/boost" the answer would be simple but your question cannot be answered in theory or otherwise. On a restricted car with a high compression ratio obviously low boost high timing is the answer on a drag car with 8:1 compression and a huge turbo the opposite is true. Deciding how much boost to run is pretty simple and has already been explained but each combination of parts is going to have a different ideal "boost to timing ratio" so like we have already stated you cannot just wish away the other variables.

If power is your only goal you will run as much boost as you can without having to drop timing so low that you lose power which could be 5psi on one car and 50psi on another depending on your fuel, turbo, compression ratio, cams etc.

[stevieturbo]

So you want to play with only boost and compression.


Have you discovered an easy way to adjust the compression ratio, without stripping engine parts ?

You hadnt considered EGBP, or plenty of other variables already mentioned. There is no simple answer to your question...except maybe....


High boost and high CR will yield more power....as long as it doesnt blow up, and it remains efficient based on the other components used in the system. Is that the mega simple answer you want ?

[Ben-S]

I understand your question perfectly but you are looking for an answer to a different question. The question Pete answered is how do you determine how much boost to run.

Assuming no other changes you might end up with 2psi and 30* of timing being the best possible combination or 50psi and 8* of timing. There will always be an optimal combination of timing and boost for a given setup but it cannot be generalized like you are suggesting.

You do not have to change any components with timing or boost but you do have to have components to make boost and have timing and depending on what those components are currently (no changes) the optimal timing and boost will be different.

[JamieA]

Ok, I hve just edited the thread down to remove the unneccesary posts. The question is reasonable, as are the answers. Please just keep the responses about the topic, nothing more.