When I get my profec b spec 2 in on wednesday I want to turn up the boost I am currently at 10-11psi (crapy mbc). Now I have read on here before that about 15psi is where you realy should start to retard timing to prevent detonation. I know that the ecu advances timing and then starts to retard it as you get knock from the knock sensor but how much timing must be retarded at which boost levels? I can check timing with my cousins x-ray tool but I am not sure what to look for while tuning. Now why at 15psi of boost should you have to retard timing if you have good a/f # like .88volts? I do not understand why timing is an issue as long as you have plenty of fuel and a good a/f mix. What are some bad timing numbers to see under boost? Can someone please explain this to me.
Patrick
96 GS
14.14 @ 96.5 mph on 8psi 8 Nov.02
HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

we have members here running almost 20psi with no timing being pulled.

Yeah, I was running 18 the other day with a totally stock ignition. Hook up a datalogger and get to your desired boost level and see how much advance your getting. Around 15 digrees should be fine. When you get into the higher boost levels you need to be sure to hit WOT so that the ecu will retard your timing or your gonna have some problems. I like keep my eye on the EGT gauge and play with the pedal to get some advance below 10 psi, but after that you gotta add a lot of gas or run at WOT. keep it lean and run at WOT.

Thats what I was thinking. I thought that as long as you had the fuel you should not have to worry about detonation. So at WOT if I see 15deg. or less, good a/f, and good egt's it does not mater how much boost I run correct? So basicaly if you have to retard timing it would be because you might not be getting enough fuel? Sounds good to me and what I was thinking. Thanks guys
Patrick
96 GS
14.14 @ 96.5 mph on 8psi 8 Nov.02
HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

Originally posted by mitsudsr
Thats what I was thinking. I thought that as long as you had the fuel you should not have to worry about detonation. So at WOT if I see 15deg. or less, good a/f, and good egt's it does not mater how much boost I run correct? So basicaly if you have to retard timing it would be because you might not be getting enough fuel? Sounds good to me and what I was thinking. Thanks guys Patrick 96 GS 14.14 @ 96.5 mph on 8psi 8 Nov.02 HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

That's not 100% correct though. At some point the boost pressure will be enough that 15 degrees of advance would be a problem. Is that 20 psi or 25 psi? Who knows, I just didn't want you to think that you could run 30psi as long as you have enough fuel, because that may not be true. The other thing to consider is the octane of the fuel. Is that board member running 20psi on race gas or pump gas? There is a big difference because the extra octane helps keep the car from detnoating where it otherwise might due to timing. I would bet if you ran 20psi on pump gas without retarding timing things would be a little harry. I have not yet done that myself so I am not speaking from personal experience, just the conventional wisdom I have come by through the years. Also that 0.88 volts, is that your O2 voltage? I wouldn't say that 0.88 is rich, if I'm not mistaken that's a little lean. I run 18psi and my O2 reading is 0.98 volts. 0.88 might not be lean on 10-11psi but on 16 it would be. If I remember correctly even at 8psi I was shooting for 0.93 volts.

I think so long as you don't get ANY knock, you don't need to pull any timing. That's how other turbocharged people tune and how I follow suit.

Chris (Murix) often makes the point that there really isn't any magic 15 psi or 20 psi threshold where you can't boost over. Just monitor your tuning at a given psi, with a datalogger and make sure everything's in check. If your timing is getting pulled due to fuel, outside temperature, or excessive psi, then at that level, you should probably pull back. I've run about 20 psi before, and my timing is in complete check without it being pulled at all. From that, I think it's fair to assume, there's no knock and no need to retard timing.

Well I run 93 octane all the time and would not go over say 17-18psi boost if this fuel setup can even handle that. So I would boost say 17psi on the street and then use 110octane at the track and try to boost say 20-21psi. This sounds reasonable to me but I am still learning and am very capable of making mistakes. This spring I am going to have it wide band dyno tuned to be safe at 17-18psi. Then ask them if they think there is enough room to make the 20-21psi with 110oct. And my a/f is at like 9-9.6v because I wanted to be safe too. A friend of mine just finshed reading a book on a/f and he told me that it said that .88v is the optimal number, this may not apply to us however because we have forced induction. Also by me having the s20g would that effect my timing at all because I know that at 17psi I am making more power than a s16g at 17 psi? May be a stupid question but I always want to be safe and not sorry, I blew my motor once and never want to do it again. Thanks alot
Patrick
96 GS
14.14 @ 96.5 mph on 8psi 8 Nov.02
HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

Yeah Jason that's what I was trying to say. I would think there has to be some point that it will start knocking, like I said nobody knows what it is, so you have to keep a good eye on it at higher boost levels, as long as your not getting knock you should be ok.