Good point.

As the boost pressure is increased, the effective compression is raised and the limits of the fuel become the limiting factor. When this occurs, one has to retard the ignition timing to such a degree that it's defeating the potential for additional power.

Therefore, one can boast about running XX psi on 93 oct with a retarded spark curve, but in actuality he won't be doing as well as someone with the very same setup, running a bit less boost and a more realistic spark curve. A/F also bears some influence, and something along the lines of 11.5:1 is more forgiving than senselessly lean mixtures.

As to where this point of diminishing returns lies, it varies depending on the overall setup, so there is no 'one size fits all'.

 

A very true statement, from my past experience with the stock turbo no matter how high you set it (<24psi) it will level off to around 20psi up top regardless. Considering how rich some of these cars are tuned all that initial spike does is allow you to hold slightly more boost in the midrange which does make a positive difference in the feel of the car.

 

That's a nice log, dryad. Again, it doesn't follow suit with what Precision was saying, since they said they are able to run higher boost with less aggressive timing. Your timing is JUST like mine, but then again, I notice that you are letting it go rich at the top. Can you verify that you are making more power by having higher boost/timing while running rich as opposed to running a nicer AFR with less boost? That is the big question, because I incur knock when running more than 21psi with 11.5-11.7 AFRs and equivalent timing as you. I could richen it up to low 11s and high 10s while running a bit more boost, but that defeats the purpose I thought...

The other problem is I'm looking for stock turbo references, although I realize the WR is a stock-like turbo. Regardless, I will patiently await your 4th gear log later this week with the MAFT.

 

Ted, this is the crux of my entire argument/statement/inquiry. This is how I understand it, so I'm trying to figure out if running 23-24psi on 93oct with a tune that allows it is better than a more aggressive tune at 21psi. I'm also trying to figure out how 23psi can be considered conservative on pump gas with the STOCK turbo.

 

The only way you will get a definitive answer to this question is to conduct road tests with adequate data logging, or to conduct dyno tests using an Eddy Current dyno (e.g. Mustang or Dyno Dynamics). You can't use a Dynojet because it cannot give real world loading, which will unquestionably influence the outcome.

 

23 PSI is NOT conservative on 93 octane. That statement is completely false, IMO. It is possible to run but DEFINITELY not conservative. I believe Precision is exaggerating on the CONSERVATIVE comment.

EDIT: I guess it depends on your definition of conservative. If conservative in your dictionary means, "approaching the limits of a certain situation, but not at the edge YET". Then I guess it could be conservative.

Brian

 

I wont have a MAP column anymore since that is being used by the maftpro so all you can do is trust me that I will pull 23 or very very close to there. My afrs are usually set a little to the conservative side, but I could go leaner. Hopefully the 60 degree weather can hold out for a few more days before the boost gets turned down because of the cold. If you want me to run 11.5 more than willing to try it at that. Ill try and get a few different logs with more timing on lower boost say 21 and less timing on higher boost. Ill come back with the logs and the butt dyno report.

 

All of that would be great to see. I guess the problem then becomes the fact that we don't know which one makes more power. We will be able to see the timing and AFRs, but we will have no idea which one is better.

If you have a way to easily save the settings from each method, it would be nice to see how each setup does on the dyno and how each one does at the track. That's a lot of work, but if you ever get around to it, the results would be invaluable...

 

you were only only able to run 21 psi because of your SAFC. Yhe AFC alters MAF signals and that is what the ECU uses to determine it load. You were running in different load points where the timing advance was to great. An aggressive tune on a SAFC will cause knock much sooner because the high timing advance. You will most likely need a custom flash to change your timing table so you can make 23psi not knock. BTW I can run up 25PSI without knock on 93 octane. Onc of the runs at CFT was at 25PSI and it did over 370 and no signs of knock.

 

Bob told me it was ok to splice into the cables of the MAFTpro to get MAP working again in UTEC. Might want to try that.

 

Why didn't you leave it there? What was the problem?

Also, it has been confirmed recently that the CFT reads abnormally high (not just my opinion anymore), but that's another conversation. Even so, that's a lot of power at 25psi on pump. Not sure why most everyone else is unable to do this. Were you able to do that before the MAFT, or does that not really have any bearing on this?

 

I have run 23 psi/93 Octane on my car for over a year now. The only time I had the ECU pull timing is on really hot days, doing a highway pull in 4th gear.

On the timing vs boost question, my personal opinion is that it is better to run less boost/more timing upon initial boost, and then run as much boost as possible (with less timing) in the upper rpms.

This opinion is based on the information I was able to glean off the many tunes my Evo has gone through. My current setup makes more power on initial spool if I back off the boost to 21 psi and run more timing and then clearly makes more power up top with more boost (23 psi). However, I am not sure how that will translate to a stock turbo, since I am running a 3071, which can hold 23 psi all the way to redline...

l8r)

 

Does he realize you are on the stock turbo? I run 22 psi in the mid range droping to 20 by redline(as read by a reliable map sensor in my AEM EMS) for a couple years.... but my mechanical boost guage was reading 24 psi down to 22 during that time. In reality I was running 22 psi but someone relying on my mechanical guage would have told you I was running much higher than that.

Now, on my GT35R setup I was running 23 psi on pump gas (25 on the guage) before I put in the alcohol injection system with no troubles.... but it gives a much cooler air charge than the stock turbo.

Also, you are on the stock FMIC aren't you? No way in hell I would run more than 21 psi on pump gas with stock turbo and stock FMIC.

Also, boost gauges are much like dyno's.... they all read different for the same car, same day. Your gauge could be reading lower for the same boost level than the guages he is normally using. The map sensors used with the AEM EMS (and most industrial applications) read lower them most mechanical boost gauges on the same car.

Keith

 

Yes, I'm pretty sure he knows I'm on the stock turbo, and yes, I have the stock FMIC. Just as you say no way in hell you'd run more than 21psi on pump gas, they are saying that 23psi on pump with the stock turbo is conservative. It could have something to do with gauges reading differently, but fwiw, I'm referring to boost as it reads on a mechanical gauge...I'm using both the factory Mitsu gauge and an aftermarket Autometer.

 

i'm tending to agree with precisions style of tuning from my experience with my own EVO, and from my experience tuning other cars.

On my previous tune I was able to crack 300 whp on the gruppe-s dyno with peak boost @ 20 psi tapering to approimately 17 psi at redline as verified on the sensor from the dyno. This was with the a/f between 11.5-11.8 and a fully optimized ignition curve for MBT (maximum brake torque).

On the street, datalogs showed high noise activity on the AEM at in the 6k range, and after checking the plugs, while they showed no physical damage... they showed some signs of too much ign timing for 91 octane.

Lowering the ignition timing, and richening the mixture to an 11.0 quieted the knock sensor significantly, but now my car felt significantly slower than before.

Now I've raised the boost so that my stock MR gauge goes a little past 1.5 tapering to 1.3 at redline. I have verified that my stock gauge read higher than actual, but cannot determine my actual boost since I'm running the MAF still with my AEM.

The car feels faster but still not as fast as it was with less boost and a fully optimized ignition curve, so i raised my timing to near the midway between my fully optimized setting, and my obviously over conservative timing.

Now the car feels as fast if not faster than it felt when I left the dyno, with a lot less knock sensor noise. This is on 91 octane. I need to go back to the dyno to see exactly how much power I'm making to see if it can be pushed further.

While ignition timing on these cars does pick up significant power, I do not recommend tuning a turbocharged car to MBT with pump gas. This brings you very close to the knock limit and different weather conditions and load conditions can cause knock that previously wasn't there. It is also possible to knock on 91 octane before MBT is even reached. The only true way to verify what's going on is by starting a tuning session with fresh plugs and checking the porcelan for deposits between runs, the knock sensor while useful, is not the be all and end all for knowing what goes on in the engine.