scottyMIz Posted July 17, 2001 Share Posted July 17, 2001 I asked this question before but i can't remember who i talked with but they told me the stock zxt computer automatically adjusts the timing when more boost is given but i forgot to ask if you get higher if it still adjusts the timing or if it only goes so far and stops.He also said it only adjusts up to 4k.So i'm going to give my baby a couple more pounds do i have to retard it at all?I'm going to take the boost up to14 lbs or so.this isn't a timing question but when my boost gets up high it drops just a bit like it will go to 11# then after it stays there like i'm building speed it will drop to 10# my guess is the pop off valve anyone think the same or different?Thanks to everyone on this site you guys have been so helpful before hopefully you can help again. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 17, 2001 Share Posted July 17, 2001 I don't believe the stock computer adjusts timing for boost, because there is no boost sensor to measure boost. However, I don't know how the computers are programmed, and it may be possible to deduce boost in software given the air temperature and airflow measurements. However, I have a somewhat low expectation of these cheap and dirty ECUs and I doubt the stock computer at stock boost levels even needs to retard timing. My 0.02, FWIW. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 17, 2001 Share Posted July 17, 2001 Also, let me add that if you are boosting to 14 psi, definitely retard the initial timing back from the 20 BTDC. If you have a good intercooler, you may be able to advance it back, once you feel there is no danger of detonation. You will know if your pop-off is limiting your boost, as it will hiss or flutter when you hit its limit. You may also have too much exhaust restriction if you are peaking boost early, and it's dropping off at higher RPMs -- either from a stock exhaust and turbo or plugged cat. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted July 17, 2001 Author Share Posted July 17, 2001 Thanks sleeper i didn't explain good what i ment to say was it senses knock in the engine and retards the timing.The exhaust i have is twice pipes i have a feeling it is restrictive but it does spool up fast.My ic is a big one i couldn't tell you how efficent it is i think it's off of a volvo but i'm not sure.What kind of system are you running from the sopulds of it you never used a stock ecu.Is your programmable? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 17, 2001 Share Posted July 17, 2001 Actually, I ran the stock ECU for a while, and recently switched to a Z31 ('87ZXT) ECU. I've finally got all the bugs out of it, but I still can't run the knock sensor - the ECU stores a sensor error. I'm thinking it may be the noisy inline 6 motor? As soon as I can get a cheap (used) 300zx knock sensor, I will try again. By trade, I am an electrical engineer, and I have some knowledge of machine code. That's why I went with the 300zx computer, as I intend to dis-assemble the code and reprogram it, just like Jim Wolf does, only cheaper. By no means am I the end-all to turbo knowledge, as I have yet to install an intercooler in my Z and run high boost, however I am well studied, and I think I have a reasonable practical knowledge on the subject having troubleshot my system going on 4 years now. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted July 18, 2001 Author Share Posted July 18, 2001 I'm no rocket scientist either but i make due.By trade i'm a radio installer like cop radios and radios for farmers,truckers all that stuff i try to stay away from cb's they suck the band is just a crappy band.I use to be a mechanic for a ford dealership so i know cars.I've done alot of jobs so every where i work i pick stuff up.I'm glad you have helped me or else i would have killed my engine already.I haven't had any problems with my ecu yet it has worked great so far.I'm at about 12 psi now and it runs great no knocks yet i think i'll need that hybrid turbo sooner that i thought. I bought the book from motor sport maximum boost and it is a great book but i don't understand all the stuff in it i'll have to read it a coupl more times before i understand it all. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 18, 2001 Share Posted July 18, 2001 Scotty... From your description, it sounded like you were saying that when you first see boost, you get around 14psi, then as you stay in the throttle and the RPM rises, the boost drops off to round 11psi. Is that what you were trying to say? Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted July 18, 2001 Author Share Posted July 18, 2001 Tim it goes to about 11# then drops to 10# when the rpm goes up.If i have a good ic do i need to retard the timing.I have it hitting about 14psi now and i hear no knocking.In first how much pressure can the turbo produce?How much can the stock turbo produce max?I have my dial a boost open all the way now and i get about 14 lbs max.I think i need to adjust the afm too richen it up alittle what do you guys think.Man that thing hauls ass with that much boost. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 18, 2001 Share Posted July 18, 2001 Okay - if I'm understanding this correctly, it goes to 14psi, then drops to 11, then to 10. Is that right? If so, then I think that you may have already found the limit of how much boost the stock turbo can supply. The turbo can make 14psi at lower RPM, because it requires less airflow to make boost at low RPM. As the revs rise, the airflow out of the turbo doesn't, so the boost pressure drops. At 14psi, you really should be doing something to augment the fuel flow. Tweaking the AFM won't do it - the injectors simply aren't big enough to flow that much fuel at the stock fuel pressure. You will either need to go to bigger fuel injectors, or a rising rate FPR if you intend to run that much boost. Also, you will most likely need a fuel pump that is capable of delivering enough fuel at the required pressures. This is especially true if you use the rising rate FPR, since it will need to raise the fuel pressures to around 80-90psi when you are under full boost. The stock turbo fuel pump has an internal pressure relief valve that opens at 65psi, as I recall. The stock n/a pump opens at 55psi. Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted July 18, 2001 Share Posted July 18, 2001 I want to help! I know for a fact that a stock t3 can generate 17psi of boost and have seen articles were they were run up in the 26psi range. I think most any turbo can produce alot of boost, but whether it can use it or it has any effeciecy at that level is a different story. When you have problems with boost dropping back off that is usually caused by excessive back pressure. A few years back when I ran the stock downpipe, 2.5" exhaust and chambered muffler I had the same pressure. The exhaust could not physically flow enough and then because the exhaust backpressure built up it caused the boost to lower. The 1st thing I did was remove the chambered muffler and the problem was immediately solved. If you can measure the backpressure that would give you the answer to what I am proposing. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted July 18, 2001 Author Share Posted July 18, 2001 The exhaust i'm running it the twice pipes and i think it is restricting it some.And tim it doesn't drop from 14lbs to 10 it just drops about a lb in any gear for example in first it will run 11 lbs then drop back to 10 and in second it will run 14 then drop back to 13 and stays that way thru the gears.How much does the stock turbo produce max in first?I was wondering to see if i did something wrong.The fuel pump i have is an after market one mine blew out a few months ago and i had a high pressure one ordered before i had the turbo in the car.I think i'll change the exhaust when i can get the money.What injectors do you suggest?I plan to run 20 to 25 lbs of boost when it's all said and done so i'd like to get something i won't have to replace twice.What would happen if i took the fuel pressure regulator right off?Or am i going to have to get an adjustable one?Thanks for the help so far i'm learning Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted July 18, 2001 Author Share Posted July 18, 2001 oh ya how do you measure back pressure if your not rich to afford the expensive tools to do it? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 18, 2001 Share Posted July 18, 2001 I don't know of many people that actually try to measure the backpressure. Try disconnecting the exhaust and run it that way, then you will know if it's the backpressure, or the stock turbo is just running out of steam. James: You are probably right about the stock turbo being capable of 17 psi, so it's probably exhaust restriction limiting his boost. However, I don't believe a stock turbo is capable of putting out 20+ psi you are claiming at any useful flow rate, even a T3 super 60. Just by looking at the T3 flow maps, 20+ psi is very high up the chart, any flow you manage to get out would be so hot the air would be useless. The T3 compressor cannot flow enough air on the L28 past about 3000-3500 RPM without overspinning the turbo (150,000 RPM) at 22 psi let alone 26 psi. You are caught between the surge limit and the maximum turbine speed. Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 18, 2001 Share Posted July 18, 2001 Expensive tools? A pressure port welded into the downpipe and a pressure gauge is all you need. I used a steel -4AN fitting in the downpipe, and ran some steel tubing a foot or two to get it away from the heat, and connected the pressure gauge to a fitting that I placed at the end of the steel tubing. You can kind of see it in this picture, the tubing goes to a fitting mounted on a small plate at the back of the intake manifold. It's capped off in this picture. Quote Link to comment Share on other sites More sharing options...
240Z Turbo Posted July 18, 2001 Share Posted July 18, 2001 Here is a pic of the pressure port before the turbo. The bottom tube is the pressure port and the top thingy is the EGT probe. Quote Link to comment Share on other sites More sharing options...
scottyMIz Posted July 18, 2001 Author Share Posted July 18, 2001 Thanks guys i'm going to change the exhaust next what do you suggest?I was thinking 3" pipe but what kind of muffler or should i even run a muffler?Michigan has no emission standards so i'm free to do as i please.Does anyone know if the turbo will make the same boost in any gear or does it work it's way up as the gear gets higher? Quote Link to comment Share on other sites More sharing options...
Sean 83ZXT Posted July 19, 2001 Share Posted July 19, 2001 I had a custom DP made a while back ($$$!) and I'm gonna run a Dynomax Bullet Race Muffler. Why? The cost is merely $36 from Summit! What I'll do is have the muff right off the DP, if that proves too loud I'll run another one at the end of a 3" mandrel bent system. Also when I went from full stock exhaust to just the DP spool up decreased immensly and it scares any honda away. (and some V8's!) Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted July 19, 2001 Share Posted July 19, 2001 One of the people that James knows that ran the stocker at 17# boost is me. Having a free-flowing exhaust starting from the wastegate was key in reducing backpressure and therefore heat buildup in the turbo. Whatever volume the t3 was moving at 17# was probably extremely hot but that is where an efficient I/C and proper fueling and timing help contribute to the engine making HP at that level. 111mph trapspeed and a gain of 27mph in the 2nd half is certainly proof I was still making good HP. Having said all of that, I would not recommend folks go that route. Spend the $400 to upgrade the t3 or more $$$ for a full-up t3/t04. You will be extremely happy and surprised at the difference. Remember, the best turbo exhaust is no exhaust. Quote Link to comment Share on other sites More sharing options...
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