back to basics

[rsk_wannabe]

Since I have been driving the DSM again this past week (need to change valve cover gaskets on Subie), I have been pondering how to get rid of WOT smokescreen that I experience sometimes. Here is what I notice.

Car IMO runs terrific. I drive it 250+ highway miles/day, averaging about 28 mpg. Since there is hardly any traffic on my route, I do have the opportunity to go for a few WOT blasts when the mood hits. I have a logger but am too lazy to tune and seriously think that fine tuning is so dependent on temps that trying to get the car running perfectly all the time is not practical. So the current SOTP tune indicates that the car is running fairly well.

If I hit the gas gradually all the way to WOT, car accelerates nicely and I do not see any smoke. Normally this will be in 5th gear (obviously only for a few seconds) and I will hardly go over 4K rpm. If I floor it suddenly, however, I will see a James Bond-esque smokescreen for a few seconds (seems much longer). If I happen to downshift to fourth gear and floor it, even more so. A quick upshift to 5th and the smoke dissipates.

Most know what I have, but here is a quick run down of pertinent information: Evo 16G unported/not clipped; 550s; old skool 5 knob AFC, 1G hacked MAS; running about 20lbs boost on AVC-D. No I have not performed a boost leak test. Here are the questions:

1. I know that the newer S-AFCs have hi low settings. Is this better for the air count based instead of load based vehicles? In other words, does this style AFC allow different settings per RPM depending on whether you go WOT quickly or gradually?

2. Someone mentioned that a boost leak causes smoke. I guess I see some logic since some air may be escaping prior to reaching combustion and after it is counted. Therefore, you may run rich thus causing black smoke. But does that explain why I only see smoke on floored WOT and not during gradual WOT?

3. Is having the hacked 1G a cause of the smoke at floored WOT? Thinking about this as a possible answer though leads me to think I should be lean if anything, i.e. MAF is already not counting all the air and when you floor WOT, even more air comes in faster and not counted. Will using 2G MAS (once I learn how to solder properly) cure the issue?

Thanks in advance for any information. As I said, I am perfectly content with how the car is running, but with four hours of commute time, your mind starts to ponder all sorts of mysteries of life. For a die hard DSMer, figuring out smokey WOT blasts is one of those perplexities that confounds and causes one to lose sleep.

[blcknspo0ln]

1. An SAFC/SAFC2 uses HI and LO settings to adjust by user designated throttle points. Example, MY old SAFC2 setup was 30%/80%. Of course we're concerned with WOT so my SAFC2 would correct for my HI settings once I was over 80% throttle position. So, gradual or not, it will only correct for when TP is at a selected state.

* Just thought about it, but an SAFC2 does sort of compensate for gradual to WOT via the TPS. From what I've seen it calculates how much fuel you want to take out based on TPS and your selected HI settings at a particular RPM. Example, HI is set at -40%@3500 and TH point is 80%, but you're at 2500 rpm @ 50% throttle (LO is seti at -20). Instead of taking out -20% because you're out of hte 30% region and you're not just in the HI setting, it will take out -30%.

2. I've had tremendous boost leaks (system only holding 4 psi) and never put a black screen out..

3. I suspect your 1g MAF for the same reasons you do.

[rsk_wannabe]

^^ Thanks. When I get a chance to put in the 2g mas, I will report back on our hypotheses. Sounds good to me though.

[TurboMike]

So basically you only get the smoke during high boost (if you slowly accellerate not smoke, if you floor it you get smoke).

What color is the smoke? Black is unburnt fuel (very rich), blue is oil (old and dirty) and white can be coolant or oil (fresh and clean). Any coolant loss?

I'd say if the smoke looks blue or white possibly your turbo seals are going and you're burning at oil only during high boost (have you checked your shaft play lately?) or only burning enough at high boost to see the smoke.

If the smoke is black I'd look at a bad tune or a boost leak.

If I were you I'd get unlazy and get your logger hooked up to see how rich you are while you get this smoke. Or if you wana be lazy dont do anything and wait until something breaks. :)

[rsk_wannabe]

Of course the other option would be to simply not gun it and keep enjoying the acceptable performance that comes from highway cruising. 8)

The smoke seems black, hence unburned fuel, certainly not white (no coolant loss). To be honest, can not distinguish blue smoke from black smoke as I look through my rear view mirror going 80mph. Chances are that there probably is a boost leak somewhere and the fact that it only pops up when I floor it, may mean that the leak does not manifest itself unless there is a sudden large burst of air working its way into the system. Other than changing UIC/LIC connections and some hoses used to connect to the AVC-D, I am still using the original 15 year old vacuum hoses.

Maybe I am just getting old or disinterested... But connecting the logger and pretending to get the car in a "better" state of tune that can be accomplished on the 5 rpm point limited 1G AFC with the first and last points (800rpm and 7200 rpm) hardly ever in use does not seem worth it. I have tried my tuning abilities over the years and am just a little hesitant on leaning out a car to get the optimal power level for a given set of mods. Also, the two Greddy EGTs I purchased have failed and I would prefer to simply keep it rich, if anything, until I get a wideband. As stated before, IMHO tuning adjustments at this level simply have to accept some indiosyncracies since even changing outside temperatures and/or switching gas brands can affect the car's performance in some aspects.

I am now at about 45K miles on this personally rebuilt motor (wiseco-eagle combo, with ARP hardware) and overall I am happy that the car is still kicking. I was able to change out my valve cover gaskets on the Subie on Saturday so that DD will be back in use again. Trying to keep four cars running (the other three being daily drivers) is a bit of a balancing act so efforts for the DSM are always a "whenever I have a spare moment" priority.

I do appreciate the advice and will report back the results as experienced. If I pass the DSM to my oldest who will turn 16 this April maybe he will have more motivation to fix the little niggling aspects. As always, thanks to the DSM experts as I can always get a prompt, concise and accurate answer to any question under the sun.

[atc250r]

Pop the hose off of the turbo outlet and see if its oily. If it is then you're probably having some issues with the turbo seals.

John