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Old 06-19-2003, 05:52 PM   #1
zoomfactor
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03 WRX
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Default Attn: Tuners - What is the relationship between timing advance & HP?

Is there a formula that defines the relationship between timing advance and its affect on horsepower? What is the effect of 5, 10, or even 15 degrees of advance?

I understand the engine dynamics behind advanced/retarded timing. I'm trying to get a handle on the actual impact that timing advance has -- as measured in HP. (i.e, is it significant?)

Any tuners out there?
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Old 06-20-2003, 01:26 AM   #2
thng
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There is no formula that I am aware of. There are way too many variables involved. Different head configurations. Different piston configurations. 4 valve, 2 valve, 3 valve, 5 valve....etc. If there were such a formula there wouldn't be any parts houses selling all these competing products.

It's adjust timing to the point of detonation and then back off. You can do that safely with an NA motor but not so with a turbo motor. With a turbo motor you can do what manufacturers do and measure combustion pressure with a scope. For stock applications I remember one Ford engineer saying that they normally target maximum pressure to occur at 12 degrees after TDC. Maybe other manufacturers follow that number and maybe not. I would imagine that it's the same with turbo motors in pure stock form.

For competetive purposes you want to have the pressure peak as close to ATDC as possible. The policy at TRD at the time was to try and be within one degree of detonation at all times. The original map was established at sea level. Now ship the motor to Pikes Peak and figure out how to deal with that.

The final number will be different for every compression/boost/octane/barometer reading/throttle angle and so on. The risks here are the usual. Being so close to TDC there's little room for mistakes, changes in quality of fuel, malfunction in boost control...the list can go on endlessly.

There are some relationships that exist for timing vs head design. Like, you don't need much advance when you use a 4-valve head pentroof chamber design with a centrally located plug. The subaru appears to have this design. If you look at the chamber and draw a line dissecting the chamber in the direction of the crank axis or at 90 degrees to it you will see that one side mirrors the other.

There is never anything easy about wanting more horsepower. There is no one product you can buy that will answer every current generation car owner's dream of getting max horsepower. You could with $$$$ by buying the car that has the power you want already in it. But on a budjet? No way.

That's my guess.
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