[nadzerin]

So I'm having the same debate that thousands before me have had: flash or piggyback. I've read the posts on here discussing this very question. And it contains some very insightful information.

But I'd like to know: what exactly is in a flash? Like for a generic mail-in flash from Dynoflash for example (say for a car with only TBE, MBC, and 255lph fuel pump)- exactly what maps are being changed and exactly what values are being changed and by how much? I'm guessing fuel injector maps are changed and probably ignition maps as well - but there are probably several different fuel maps and ignition maps, and of course many different RPM/Engine Load points within these maps. Before I buy a flash, I'd like to know what I'm getting and not just have some dyno sheet that says I gained 20hp. I'd like to know where exactly that 20hp came from. With a piggyback, you know where your hp came from.

So do you gurus have any insight on this? Thanks in advance.

 

[turbolarry]

I know for sure the timing is changed. A while back I tuned a dynoflashed Evo with a S-AFC on top for fine tuning. According to the logger the timing is set at 5* between 3000-5000 RPM's, than advances and peaks at 17* at 7000 RPM's. I know it's set because when the car ran with straight 100 octane it failed to raise any of the above timing numbers like the normal ECU does. I can't say what else is changed because I only use my little logger.

 

[nadzerin]

I know for sure the timing is changed. A while back I tuned a dynoflashed Evo with a S-AFC on top for fine tuning. According to the logger the timing is set at 5* between 3000-5000 RPM's, than advances and peaks at 17* at 7000 RPM's. I know it's set because when the car ran with straight 100 octane it failed to raise any of the above timing numbers like the normal ECU does. I can't say what else is changed because I only use my little logger.

So only 5* between 3000 and 5000 RPM? That sounds pretty low, right? But I guess they need to have a margin of safety? Looking at some of your SAFC tuning logs on here 17 seems a little low too (I think Warrtalon was getting 22*-23* on one of his logs). But I guess again, they need safety. Was the log you saw on a car with a MBC holding 19-20 psi all the way to 7000?

How about fuel on the flash? Is it richened or leaned out and where in the RPM band? Looking at your SAFC tuning logs again, if I understand them correctly, it looks like you guys try and lean it out up top to get more timing (make the ecu think less air, so less fuel, so more timing). Does the flash do the same thing? Also, looking at the log of the stock RS in your "tuning guide" it shows O2 to be 0.93 - 0.95 up top (around 6000). But yet when Warrtalon leaned it out up top to get his timing, it seems as if his O2 did not change (stayed at 0.93). How did he get it like that? Sorry, I'm not real familiar with the SAFC. (I'm referencing the logs in his post entitled "Turbolarry - tuning advice"). In the log of the stock RS it seems as if A/F is pretty "good" up top around 6000 ("good" as in not too rich not too lean). I thought evos were tuned rich from the factory for safety? Is that a true statement? If so, where in the RPM band are they tuned rich?

Anyways, sorry for all the nubbish questions. Thanks for any answers you guys may have. As you can see, I need some knowledge dropped on me!

 

[Warrtalon]

Ok, let's start over.

Stock tune:

Starts out very lean (12.5:1) right where we hit peak boost in the mid 3000s, then by 5200rpm it's back into the 11s. After 5200, it starts to decline steadily to about 6000rpm where it falls off a cliff into the 9s. Every form of tuning removes this incredibly richness by removing fuel. With an SAFC, removing fuel indirectly causes timing to be added, but you don't have direct control over it, so you get what you get. Sometimes, you get too much timing, and it causes knock even if your AFRs aren't too lean. The other problem is that you can't reduce the lean state in the low RPMs without ADDING FUEL. When adding fuel on the SAFC, this causes the ECU to use less aggressive timing maps, so even if you get the AFRs down where they should be, you lose out on timing - catch 22.

What a flash does is it has direct control of timing AND fuel, so you get a less lean peak boost area and mid-range, but with very good timing. On my new logs with a flash, I get no less than 7-8* timing through the entire low-end/mid-range from where the turbo spools to about 5000rpm, which is when it starts steadily climbing. I peak around 20* at 7000rpm on pump gas, but as high as 24* on race gas (and now alky). Back when I had the SAFC, my timing would drop to 0 and sometimes -1 at 3800rpm, because it was unavoidable without upgraded injectors or higher octane, both of which allow you to REMOVE fuel at this rpm without blowing the engine.

On the top end, the flash removes a ton of fuel to get you from the 9s to the low-to-mid 11s, but it keeps timing in check without advancing too far. The end result is a very strong torque kick that turns into a very smooth and linear powerband that continues to climb until 6800rpm or so before falling off (cam-dependent).

 

[Nuked]

When using race gas without turning up boost there would be relatively no gain right? What I mean is say you are tuned for 93, get maximum timing on set boost, then the extra octane would not increase timing without an increase in boost as well? I understand that it would be more safe with the race gas, but from power output would it be the same at same tune/boost as 93?

 

[Warrtalon]

When using race gas without turning up boost there would be relatively no gain right? What I mean is say you are tuned for 93, get maximum timing on set boost, then the extra octane would not increase timing without an increase in boost as well? I understand that it would be more safe with the race gas, but from power output would it be the same at same tune/boost as 93?

Without turning up the boost, there will be no gain, and perhaps even a LOSS IN POWER DUE TO BEING MORE RICH unless you are tuned so close to the edge that there is slight knock suppression and timing retardation occurring, in which case the higher octane would provide its own knock suppression without the ECU having to dial back timing. Basically, if you're tuned well without being on the edge, then you will have absolutely no gains from race gas unless you turn up the boost. If you add race gas and crank the boost 2-3psi, then you will definitely gain power, although it won't quite be optimized in terms of tuning.

For anyone racing without a means of self-tuning, I recommend only using unleaded race gas (100-104oct), because it won't make you run rich and won't mess with your o2 sensors.

 

[nadzerin]

Ok, let's start over.

Stock tune:

Starts out very lean (12.5:1) right where we hit peak boost in the mid 3000s, then by 5200rpm it's back into the 11s. After 5200, it starts to decline steadily to about 6000rpm where it falls off a cliff into the 9s. Every form of tuning removes this incredibly richness by removing fuel. With an SAFC, removing fuel indirectly causes timing to be added, but you don't have direct control over it, so you get what you get. Sometimes, you get too much timing, and it causes knock even if your AFRs aren't too lean. The other problem is that you can't reduce the lean state in the low RPMs without ADDING FUEL. When adding fuel on the SAFC, this causes the ECU to use less aggressive timing maps, so even if you get the AFRs down where they should be, you lose out on timing - catch 22.

What a flash does is it has direct control of timing AND fuel, so you get a less lean peak boost area and mid-range, but with very good timing. On my new logs with a flash, I get no less than 7-8* timing through the entire low-end/mid-range from where the turbo spools to about 5000rpm, which is when it starts steadily climbing. I peak around 20* at 7000rpm on pump gas, but as high as 24* on race gas (and now alky). Back when I had the SAFC, my timing would drop to 0 and sometimes -1 at 3800rpm, because it was unavoidable without upgraded injectors or higher octane, both of which allow you to REMOVE fuel at this rpm without blowing the engine.

On the top end, the flash removes a ton of fuel to get you from the 9s to the low-to-mid 11s, but it keeps timing in check without advancing too far. The end result is a very strong torque kick that turns into a very smooth and linear powerband that continues to climb until 6800rpm or so before falling off (cam-dependent).

Exactly what I was looking for. Thanks, WT. That answers all my questions (for now). :thumb: