boost versus timing

not sure if this is the correct sub-forum, but the moderator can move it to the correct one if needed

general scenerio we tend to see: normal pump gas (low quality), stock/forge build engine, average compression (8.2- 9.0), medium turbo td04 - td05 range, all supporting mods (fmic, managment/piggyback, etc)

anyways, is there a preference for any one over the other....it seems some persons like to quote "big" boost numbers, but run pretty retarded timing at those levels. would it be better to run less boost and more timing in such cases?

the above turbo range is efficient usually between 14 - 23psi, will this play a part in the need to want to run more boost and less timing?---to keep in the efficieny range of the turbo

just something that crossed my mind a while now,,,after doing some research, reading the forums and listening to people

any comments are welcomed
 

AdamB

Member +
You will definitely have to take into account the turbo's efficiency. From what I've seen power is made all through temperature, the less temp, the more ignition timing can be run.

But like you say, some people tend to run for a low compression ratio engine and boost it through the roof. I think it depends on what the car is intended for. Me personally if its a drag car then low compression and big boost, with lots of ignition timing, makes the car more aggressive and helps with what your trying to achieve. But if running a street car or a circuit racer, I prefer to see a higher compression engine with less boost. I would always try to run the turbo in and around its optimum point in the flow map, and select the chosen fuel to determine what CR to go with.

The question is really, do you want more MPG, greater powerband, better off boost response with a high CR engine. Or do you want massive boost and an aggressive setup?

Obviously it would depend on the engine being run as well, I'm sure a 5E could go to a lower CR without anyone noticing much whilst driving and yet gaining that little more boost or ignition advance since its a greater capacity with more torque.
 

GP82

Member +
In any setup the optimum fuel curve and timing is dialled in for the target boost pressure so the car performs at it's best.

When boost pressure is raised to maximise the turbo with normal pump gas, there will be a tendency for knock to occur which will melt pistons and rings.

Therefore you have to make the timing map more conservative so knock does not occur for the higher boost. This is why you see a high boost motor with timing pulled out so that it can survive.

You gain more power per pound of boost, so it is a trade off for the C/R and timing map for the motor.
 

Rev

Member +
I guess tuning is an art but what ive heard 2 timings are attained 1 for max torque ( relates to max boost ) and 1 for max power.

1 Peak boost relates to turbo type if tuned for timing properly you should have very good max torque occuring at at peak boost and where the turbo reaches max efficiency so temperature is controlled. ( no det allowed )
2 After peak Boost you are heading towards peak power you add timing up to peak power but avoid too much timing at highest revs. ( no det allowed )

There is rich det and lean det to consider as said above Temperature must be controlled and so must knock . This is where cr and fuel type and afr help. I have read when knock occurs and the ecu pulls timing this can add heat so if you are already at max heat due to boost level or turbo blowing hot, knock can trigger heat that may cause pre ignition that melts your engine.

I would add knowing the intake temp/ turbo limits is important at what boost is the turbo out temp ( or intercooler out ) triggering pre ignition for your setup . eg. 4e with FMIC stock ep82 pistons if your ambient temp is below eg. 25deg C this may typically be 18psi but on a
40deg C hot day you may want to run 15psi at wot to be safer.
 
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very interesting view so far...i know ther eis so much talk around, it can get a bit confusing sometimes
i guess its a trade off on each engine, which as rightfully said above can be further influenced by many variables - ambient temps, gas, CR, etc

just sometimes seems like people like to say proud out loud "i run 1000psi (but with 100 degrees retarded timing--which they dont say out loud)" to sound impressive, when the same relative power could be made at "700psi (but with 5 degrees advance---which again is not usually said out loud)" ...lol

also, tuners have different styles so that must be taken into consideration too
 

AdamB

Member +
I think you only need to take a look at the boosted Honda's imo. A stock Honda b18 at what 160bhp? Slap a turbo on it and at no more than 10psi boost pressure they can make like 350hp. High compression motor with like 9.5:1 CR, pump gas and they are able to push 200% above stock power.
 
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