RomRaider

Just an update: I'm currently tuning my car in on modded stock injectors, and I'm transitioning to E85. That has influenced my method of tuning some. The fact that I will be scaling my injectors somewhat close to stock values (I will end up scaling my inejctors to 600 cc).

So far, I have changed the injector latency, and that gets me in the ballpark with the AFR's. My AFR's still dance around, and I don't like that, and I think that has to do with the gross tuning that the latency values give you.

I suppose what I'm getting at is that I don't think choosing either latency OR maf scaling is the finally solution. I can see arguements for both. And I think I'm going to arrive at using both of them.

Its obvious that when dealing with short pulsewidths, that there is "new" restriction in the injector. It used to be the cap. Now, its probably the space between the armature and the bobbin bore. This is causing some non-linearity in the flow of the injector and the response time (latency) of the injector. This is the arguement for latency.

But, this non-linearity is only apparent at low pulsewidths (low flows), and with modifying the latency, the ECU seems to have difficulty maintaining AFR's when in closed loop with the o2 sensor. This is a good arguement for MAF scaling.

Well, as time passes and I continue to try to dial in my modded injectors, I'm more and more in agreement with you gabedude. Tweaking the latency and tip-in got me in the right ranges, but I had difficulty getting rock solid AFR's.

I have abandoned the latency method and gone to the MAF scaling method. I believe this will prove to be a better overall method. I'm not done yet, but I think you are right...

I did the same comparison a while back. It's really interesting. The JDM STI map that utilizes pinks is scaled to 552 IIRC and the USDM WRX 420. That's roughly 31% larger. The latency is untouched.

Here's a comparison of tip-in enrichment (sorry for the old defs, point still stands): pink line = USDM 2.0L WRX. yellow line = JDM STI. Teal line = percentage difference.



The interesting thing is the JDM STI's MAF scaling table. Since both cars use a 65mm MAF, a comparison can be done: Pink = USDM 2.0L WRX. Yellow = JDM STI. Teal = percentage difference. Notice how Subaru "skews" the lower end on the JDM STI? This is exactly what we aim to correct with latency adjustments... the low "tail" of the total AF correction.



From my own personal experience, I've used this method on all "pinks" equipped cars. They run great. I'm thinking about applying the same logic to the next set of larger injectors and see what happens.

Nice graphs Ben.

heh, didn't mean to steal your thunder, I just had these laying around from a while ago when I did the same comparison. I just haven't had the stones to abandon my latency method. It's like a warm safety blanket!

The Legacy GT changed from 520 cc injectors to 550 cc injectors. The MAF scaling was changed but from what I can tell, the change to scaling was to correct some errors in the original MAF scaling. And, the changes to the MAF scaling are not enough to account for differences in latency.

The latency was increased a constant 0.09 ms between 11.50 volts and 16.50 volts. I have no idea about the change at 6.50 and 9.00 volts. Those really low voltage ranges may be used for other reasons such as trying to start a car with a near dead battery situation.

They have the same model (part #) topfeeds?

If so that is interesting.

The 2006 Spec B uses the STi side feed injectors. The 2007 Spec B uses blue top feed injectors which are supposedly the same as the JDM pinks.

The 2006 and 2007 injectors are not comparable. They are different but so is the latency. I just wanted to point out that Subaru doesn't always correct latency using MAF scaling.

My opinion is to adjust latency so that the MAF scaling is as close as possible to actual. Or at least comparable to the original stock tune. This is to prevent distortion of the load value. Also, if the adjustment to the MAF is too great then there can be fueling issues in the lower left corner of the fueling maps (high rpm, low load).

The blue topfeeds are not pinks. Pinks are of the same design as the light blue WRX topfeeds. They use the same latency. Latency as defined by Subaru mappings match the "type" of injector. Your 2007 topfeeds in your example match the scaler and latency settings for an 06-07 WRX and an 07 STI because they are the same injector. There are differences in the MAF scaling however between the STI and the WRX.

So what I am referring to is that the "pinks" or "light blue" 750CC topfeeds I have have the same real world latency as across the board for that "type".

I thought the premise of the argument here was that Subaru does NOT use real world latencies and that they fake it by adjusting the MAF scale.

In the 06 Spec B and 07 Spec B, they use the exact same intake.

The STi and older WRX use a different intake.

No the argument is to match as close as possible the latency to the type of injector using that type of injector's latency values. They are all the same across the board for the type. There are two types of topfeeds you can get from DW. 550's and 750's are the older types (pinks, light blue WRX injectors) and 650's and 850's are the dark blue topfeeds (550.67 CC 06+ WRX and 07 STI+ topfeeds). Whether or not Subaru is using real world values for latency is not what I am referring to here.

However, I see your point, Even on my car with this method and the DW 750's running 02-05 WRX (or JDM v8) latency, I can get +8% total correction when I rev the engine in the B range vs letting the AC do the loading where it goes to -8%. I need a tad more latency, but the values are really close.

I decided to do a test yesterday. So I drove to work and decided to try the Injector tab on the RR logger. It came up with a scaler that was a bit too lean and latency that had an offset of -0.05 MS. I ran applied the latency, then drove home, and got an offset of +0.05, so it is back to 02-05 WRX latency values (the same as JDM v7 and v8 STIs as the pinks are the same type of injector).

So now my MAF is scaled pretty well. I have my conservative tune on there with no meth yet (hooking it up this week). Peak boost hits about 19 PSI and tapers to 17 at redline at my 550 ft altitude (mapped for 20 peak).

Hopefully the Meth will add around 40-50 WHP. I'll be happy then... Maybe...

Those numbers will go up when it gets cold, it was 72 and humid this morning.

That looks good Gabe. Is that a stock turbo or 20G on 93 octane? I'd like to see the secondary axis on your chart showing the AFR scale.

I have compared JDM pinks to the Spec-B's top-feeds, as we recently did a FP Green/FMIC/Aquamist/EWG setup on a 2008 Spec-B, and the injectors are cosmetically very different. I'd venture to say the coils are probably different, too.

Since Deatschwerks is located in my home town, and friends of mine, we've had this conversation a lot. One of the big influencing factors on mapped latency is not just a function of the injector coil, but the overall electrical system of the vehicle. We've kicked around the idea of hooking up DW's equipment to various cars, but never got around to it. I almost wonder if Subaru takes this into effect with mapped latency.

Yeah the 06+ WRX topfeed (darkblues) have a smaller coil body. That is why latency is different. I have seen no difference in latency vs rom type, etc. If the injector is of the same type, latency is always the same in the rom.

BTW, yeah TD05 8CM^2 20G under 20 PSI peak running 11 degrees at peak TQ and 20 at redline 11:1 AFR. Very conservative tune. I had less power under the curve on my VF43 pushed to the max, but like 5 more peak hp. This is definitely faster though.

Sweet!

I had a 7cm 20G/FMIC on my previous 2005 STI, and I had it tuned by MZM way back in the day. If I recall I was only running 19 degrees advance at redline on 91 octane, very similar to yours.

Area under the HP curve is monstrous on the 20G compared to stock, even with a small peak gain. I was wompin' on stock turbo STIs!