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Old 01-19-2007, 04:52 PM   #1
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Default Boost, Timing, KR and You!

I've been answering a lot of questions lately regarding KR and boost. Usually its something like this:

I have 1 to 2 degrees of KR with my 3.4 pulley can I put a 3.2 pulley on with higher octaine (race gas).

or

I have a 3.4 and see 2-3 degress of KR, if I put PEMS/Headers on my car can I put a 3.2 on it.

1) Boost is not an indication of power, boost represents the amount of pressure in the manifold. Boost is negative vacuum or positive pressure.

2) A motor will make more power with less boost than another motor with more boost if it is processing more air. A cammed car with a 3.4 will make more power with 6lb of boost than a stock motor with a 3.0 pulley and 15lb of boost. Why is this? Boost creates heat, heat creates detonation, detonation causes the computer to retard timing (KR). Too much boost heats the cyilnders up very quickly and if you can't get that hot air out it will never dissipate. You can either allow the motor to process the air quicker (cam, headers, rockers, heads, etc...) allowing the hot air to get out quicker and help cool things down or you can add octane. Higher octane fuel resists detonation and is harder to burn. It also makes less power unless oxygenated (most race fuels over 100 octane).

3) Our PCMs have adaptable learning. A healthy knock free car with stock programming will command up 15 degrees of timing at WOT. However, most of us are not running healthy knock free car as even from the factory KR is present. Two tables exist in the PCM, a high octane table and a low octane table. The max WOT timing is 15 in the high octane table while in the low octane table it may be 3. As the car learns your driving style, octane choices, etc.. it will position the timing somewhere between these two tables moving your max timing to a place where you see little to no knock.

Consider the following:

Car 1 has a 3.2 pulley, rockers. PEMs and 91 octane. It makes 14psi of boost and it sees no knock but has a max timing of 8 degrees due to the car learning overtime that at 8 degrees it has no knock.

Car 2 has a 3.4 pulley, rockers, headers and 94 octane. It makes 8psi of boost and It sees no knock but has a max timing of 15 degrees due to the car learning that even at max timing it sees no knock.

Which car makes more power? Consider that each degree of timing can be as much as 2-3 WHEEL horsepower. Car 1 should either add octane or move up in pulley size and understand that it can take the computer some time to learn and advance timing to gain power.

My car makes 25 more wheel horsepower by adding 5 degrees of timing which I can do safely by adding race gas. In fact, the sweet spot in timing for these cars is about 24 although that is head gasket roasting territory especially without an intercooler. 18-20 is a great place to be on a street car and doing whatever mods to your car to allow you to run 18-20 degrees of timing on pump gas (93-94 octane) should be the goal to make good safe power even it means running larger pulleys.

I will probably be fleshing this out and editing it somewhat for a while but I figure it may answer a bunch of questions for some people.
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Old 01-19-2007, 04:57 PM   #2
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Good info. I'm stickying this.
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Old 01-20-2007, 01:17 AM   #3
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You answerd all my Questions, Todd.
Thank you!
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Old 01-20-2007, 05:10 AM   #4
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Very informative post. Just what we needed IMO.

Some people just don't understand sometimes that smaller pulley is not always better. If you can add timing on these cars it helps out a lot. I run 23 degrees of timing daily and my car LOVES it, it runs very strong.
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Old 01-20-2007, 08:59 PM   #5
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That'* why I have pullied back up to a 3.4" with the Gen V.

When I race with the water injection for cooling I will go smaller.

Last year when I ran with the 2.9" pulley I didn't pull any KR and the timing was around 19 with the water injection.

Shawn, you have knocked the water injection in many previous posts but I am a believer if you are not.
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Old 01-30-2007, 12:59 PM   #6
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I give up...What is KR?
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Old 01-30-2007, 01:07 PM   #7
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Quote:
Originally Posted by wolfpackcpl
I give up...What is KR?
Knock Retard, when the PCM detects detonation (knock) via the knock sensors it will retard timing to reduce cylinder temps until the knock goes away. It will do this before you ever hear the audible pinging normally associated with detonation.
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Old 01-30-2007, 03:24 PM   #8
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OK...now that is really great info and answers a ton of questions.

You do realize of course, that it will raise even more questions, lol.

Example: You say that our stock PCMs allow max 15 degrees timing at WOT on high octane. Yet you suggest that we try for 18-20*. The assumption is that we would have to get a performance PCM to do that, correct?

Of course all this applies most specifically to the boosted engines. What are the best methods to achieve max safe power on pump gas for the odd NA crowd? Obviously, there first needs to be the basic breathing mods, like PEMS/Headers, ported TB, CAI, maybe ported LIM, etc. Then what? Lifters, cam, rockers, heads???
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Old 01-30-2007, 03:31 PM   #9
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Quote:
Originally Posted by lash
You say that our stock PCMs allow max 15 degrees timing at WOT on high octane. Yet you suggest that we try for 18-20*. The assumption is that we would have to get a performance PCM to do that, correct?
Correct

Quote:
Originally Posted by lash
Of course all this applies most specifically to the boosted engines. What are the best methods to achieve max safe power on pump gas for the odd NA crowd? Obviously, there first needs to be the basic breathing mods, like PEMS/Headers, ported TB, CAI, maybe ported LIM, etc. Then what? Lifters, cam, rockers, heads???
Timing is not nearly as important (or power inducing) in an N/A setup as it is in a boosted setup. We have taken timing as high as 30 degrees in an N/A car with really no power incrase. N/A already has increased timing from the factory and simply doesnt benefit from advancement like boosted cars do.
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Old 01-30-2007, 03:35 PM   #10
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Ahhhhh...

Also good to know.

An excellent thread, Todd!!

I'm glad it'* stickied.
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