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Old 10-27-2005, 08:54 PM   #1
moby4dick
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Default What is a "safe" tune?

Obviously a NOOB question...

What makes a safe tune versus aggressive tune?

Would limiting boost pressure be a part of this? As an aside, what maximum boost would you be running before having problems with leaks through gaskets?

Thanks,

MB
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Old 10-27-2005, 09:28 PM   #2
ahains
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A safe tune generally refers to making some concessions in total power output to reduce some negative aspects of power production.

The main negative aspects I believe are detonation and the overall amount of heat you are putting into the engine and exhaust system.

Typically under boost you cannot run the most optimal timing advance for max power production, so you have to limit yourself to where you are seeing no detonation, or low levels of detonation.
If you tune for minor detonation on occassion, you will go a bit faster but be less safe.

For boost levels, folks often run less than maximum boost at high RPM because that amount of air is really pushing the stock turbo. This causes a lot of heat. If your valves are super hot, you have a greater chance of detonation.

Additionally, a tuner may back off from the limits a bit on the dyno in anticipation that your gas may sometimes be a bit lower quality (in terms of detonation resistance), your intercooler may be less efficient (from heatsoak, bent fins, hot weather, or whatever), etc.

Some folks enjoy datalogging everyday and keeping their car tuned to the ragged edge for the conditions, perhaps with the smallest amount of detonation. I would definitely call this an aggressive tune.

Another aspect is air/fuel ratio. A very safe tune may target 11.5/1 AFR, whereas an aggressive tune may target max power at target 12.5/1 AFR. Once again, this may theoretically be fine on the dyno but later cause problems when it is hot out or you have substandard gas.

HTH!
Adrian
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Old 10-27-2005, 09:49 PM   #3
PDXTuning
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A safe tune is a balance of fueling, timing, and boost. The point of a safe tune is to deliver solid power with a map that will not fall out of that balance point in as many different conditions as possible. That means if you take the car up in altitude, run it on a hot day, cold day, with 4 600lb people in it up a hill with the AC on the car will remain safe. Finally, knowing if that last HP is worth it is part of a good tune. You can always make a little more power, the question is should you. If you put in that extra degree of timing it may make 2 more HP, but then it may detonate easier on the road.

Some people think that running less boost is safer than running more boost. You can make a tune with higher boost safer than one with lower boost. A good tuner knows how to setup your car so that you have cushion before hitting a condition that could cause detonation or some other engine endangering condition.

A good tune is just a balance of AFR, timing, and boost.

The points that Adrian made above are all good points, I just thought I would add a bit more.

Jarrad
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Old 10-27-2005, 10:14 PM   #4
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Quote:
Originally Posted by PDXTuning
A safe tune is a balance of fueling, timing, and boost. The point of a safe tune is to deliver solid power with a map that will not fall out of that balance point in as many different conditions as possible. That means if you take the car up in altitude, run it on a hot day, cold day, with 4 600lb people in it up a hill with the AC on the car will remain safe. Finally, knowing if that last HP is worth it is part of a good tune. You can always make a little more power, the question is should you. If you put in that extra degree of timing it may make 2 more HP, but then it may detonate easier on the road.

Some people think that running less boost is safer than running more boost. You can make a tune with higher boost safer than one with lower boost. A good tuner knows how to setup your car so that you have cushion before hitting a condition that could cause detonation or some other engine endangering condition.

A good tune is just a balance of AFR, timing, and boost.

The points that Adrian made above are all good points, I just thought I would add a bit more.

Jarrad
In regards to my question about boost, then is there a maximum "safe" level of boost? Is it dependent at all on the turbo?

As a tuner, are there accessories/upgrades you would have found helpful, other than being sure there's adequate fuel delivery?

MB
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Old 10-27-2005, 10:42 PM   #5
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Theres people running 24psi + on stock blocks, so....

Other items would be a wideband O2 meter, and a knock light.
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Old 10-28-2005, 08:53 AM   #6
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Quote:
Originally Posted by moby4dick
In regards to my question about boost, then is there a maximum "safe" level of boost? Is it dependent at all on the turbo?
it's quite dependent on the turbo. turbo compressors have an efficiency rating which indicates how much of the energy of the compressor is used to actually increase density rather than just increase pressure. the link between those two parameters is temperature. so running a turbo inefficiently will cause a higher outlet temp for a given outlet pressure.

different turbos are designed for different purposes. for example, my wife's saab 9-3 uses a fairly high compression motor with a low pressure turbo. this allows for good throttle response while "off boost" and still reaps some of the benefits of higher power output while on the highway. that turbo would need to be optimized for a lower pressure ratio (ie the difference between inlet and outlet pressures) since that is the way it is run. iirc it never produces more than 10psi of boost.

trying to squeeze 20psi out of that turbo is probably a lost cause. could it do it? sure. is it a good idea? most certainly not.

as jarrad pointed out, boost doesn't kill motors... detonation kills almost all of them. (if you are an exceptional tuner and really pushing the envelope you will actually run up against the mechanical limits of the bottom end.. ie, bent rods. this occurs around 400whp on the ej205 block. that's a bit over 500 crank horsepower, which is a LOT of power... more than double OEM output.)

keeping your motor together then pretty much depends on avoiding detonation. running a turbo inefficiently will create a hot outlet temp, as i've described above, and unless you're taking some definite steps to combat that (ie, water/alcohol injection, bigass intercooler, etc) that hot outlet temp will find it's way into the combustion chamber. that is not the way to make power--in fact it's setting the stage for detonation.

having said all of that, i should point out that i did run 20psi on the oem turbo all last winter. my motor is still tight and strong. i did the tuning myself, but i had the right tools (good ems, wideband, egt, detcans), and during the winter here in new england it gets pretty cold. cold temps are very good to intercooled turbo cars for two reasons: a) colder inlet air is more dense, and turbos run more efficiently on dense air, and b) colder ambient air makes the intercooler more efficient (part of its ability to transfer heat from charge air to ambient air depends on the difference in temperature between the two). in the summer i had to turn it down to 18psi for those very reasons.

hth
ken
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Old 10-29-2005, 05:54 AM   #7
AZScoobie
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To me a safe tune is a tune that never knocks under any conditions. A tune that can take WOT runs at high speed without high EGT and a tune that you can load the car down and not have any issue. This typicaly means much, much lower power. Every car I tune gets a min of two maps. One that is for max power but not on the ragged edge and a Safer tune.

Clark
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Old 10-29-2005, 07:14 AM   #8
ride5000
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Quote:
Originally Posted by AZScoobie
To me a safe tune is a tune that never knocks under any conditions. A tune that can take WOT runs at high speed without high EGT and a tune that you can load the car down and not have any issue. This typicaly means much, much lower power. Every car I tune gets a min of two maps. One that is for max power but not on the ragged edge and a Safer tune.

Clark
and to go along with what clark has said, it's obvious that a DIY tune (like my own) can be much more aggressive if only for the fact that i can dial it back IF it knocks, or IF it gets high egts, or IF it has issues with very high loads.

a vendor selling a tune has to be much more proactive, and therefore has to leave a little more margin off the top. i would do things exactly the same way if i were selling my services and putting engines other than my own at risk.

ken
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Old 10-29-2005, 09:50 AM   #9
ahains
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If you intend to tune yourself and are relatively new, you may want to mimic the cobb stage 1 map if you are looking for a safe tune. You can definitely tune more aggressively than their off the map tune, but if you don't really know what you are doing it may be a good place to start.
Their map notes for stage 1 are here:
http://www.cobbtuning.com/wrx/access...2091%20oct.txt

I'm not positive, but I thought they lowered their boost target some as you approach redline. Maybe I'm totally wrong on that. It's not mentioned in the map notes.

-Adrian
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