gnosez Posted May 16, 2002 Share Posted May 16, 2002 What should my A/F ratio for my 3.0L SU driven Z be at, at 3000 rpm. I seem to remember thay like to run a like rich. Is this right?? Quote Link to comment Share on other sites More sharing options...
gnosez Posted May 18, 2002 Author Share Posted May 18, 2002 I got the answer, from Dave Rebello, thanks for all the responses. And I'm keeping the info to myself.... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 18, 2002 Share Posted May 18, 2002 3L240, If any one here knew the answer, they would have shared it. Most, if not all of the guys on this board will go out of there way to help. Hope you will be able to help someone with the information you have come up with. Mark Quote Link to comment Share on other sites More sharing options...
gnosez Posted May 18, 2002 Author Share Posted May 18, 2002 I just not in a good mood at the moment..maybe cause it snowed today here in Boston!@$#% Its' hard not to think that someone has an O2 sensor installed and took readings, but here's what I have from Dave Rebello: 13.5:1 @ 1/2 throttle and 12.5:1 @WOT. My A/F meter gives me a reading in mv and I can see that one carb is slightly richer than the other (or is it that one is slightly leaner?). Anyway, I couldn't get to WOT as there was traffic out last night so I had to settle for readings at 110mph which were @12.7:1. Half throttle seems to be more or less on track. I have velcroed the small meters to the passenger side kick panel for normal usage (I don't need to look down when I should be looking ahead)and they come with about 6' of cable so I can take them off the panel and see them when needed (like during a tune-up or a dyno run). I made up a small box with velcro for this situation. Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted May 19, 2002 Share Posted May 19, 2002 What O2s are you using? If they're a stock style O2 I wouldn't rely too heavily on the readins as stock style O2s are usually only very sensitive in the 14.7:1 range. FJOINC.COM (think that's it) sells some VERY nice ones that are W/B. The DIY-WB guys also have a setup that's cheaper. I can probably direct you to a good deal on the FJO stuff if that's of interest to you. Some of them will even do datalogging! Quote Link to comment Share on other sites More sharing options...
gnosez Posted May 19, 2002 Author Share Posted May 19, 2002 System overload!!! Hey, the only chip I got in my 72 is the one in the MSD box, so datalogging is way too much on the modern side for me. I've got one wire Toyota O2 sensors in there now, with one per SU bank. Can you talk me thru what it is your suggesting..thanks Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 20, 2002 Share Posted May 20, 2002 He's talking wide band 02 sensor, which means it has a operating range of 0-5v's I believe, narrow band (standard 02 sensor used by nearly every standard production passenger cars) have a range of 0-1v meaning the wideband has a much great resolution due to the increased scale by five fold. On a modern fuel injected car, a wideband offers lots of advantages because it can read a wider range, and react to subtle changes in A/F mixture and make adjustments much finer and faster than the narrow band. On a carb'ed car, I don't think I'd worry about a wide band o2 sensor because carbs so crudely meter fuel that its not worth the expense IMHO. If you have 1 of them on each set of cylinders for a carbed car IMHO you have a good enough setup to get the carbs as close as one can get with carbs. Because of the courseness of tuning from one jet to another (or even the courseness of the SU needle valve) its either going to be rich, richer or lean, not like EFI where it can be varied much closer. Also since its only used for monitering, the expensive wide band outside of being more accurate is somewhat wasted as it can't change anything in a carb. For my wallet, 3-400.00 vs 22.00 at Kragen for a universal 02 sensor is a no brainer for me. If I had injection and could get a good deal, by all means, I'd get the wideband. Just an opinion from someone with a thin wallet. Regards, Lone Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted May 20, 2002 Share Posted May 20, 2002 Yup, WideBand. They've gotten much cheaper too! OEM passenger cars are starting to use them and as a result the cost of the sensors has fallen. The FJO setup with a digital display (actual A/F ratio) runs about $600. The Techedge DIY-WB unit is significantly less expensive. The $22 sensors are pretty rough and in the case of some of them are useless much on either side of Stoich. Stoich is great for emissions NOT for power. Stoich is 14.7:1 and good power is made closer to 12:1 or even richer if running forced induction. The OEM units are inaccurate enough that factory ECUs will not read them at WOT. Can't speak to how rough a carb adjustment is but with multiple side draft carbs it's got to be finer than a big honking Holley! Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted May 20, 2002 Share Posted May 20, 2002 It may be better on side drafts, I can tell you that watching the Holley go through its circuits is rather funny as its about as crude and pouring fuel down the intake out of a can. Even the idle is noticably rough for no apparent reason outside of the pulses of the V8 cause the idle circuit to kinda shoot pulses of gas through the intake as each piston pairs or whatever it is draws the vacuum to suck the fuel out of the manifold. Couple that with the uneven mixtures from the manifold itself gives a great excuse to change to fuel injection. Watching the meter in the heat is funny two, in the morning my jettings great, by afternoon in the heats its all wacky. Soon as I can swing it (which will be a bit now) I'm F.I. bound, no question about it. To much is made about how much tuning is needed for F.I. with a laptop and all that, when many of our setups (not the huge cam guys) wouldn't need much more than a stock ICU IMHO. Carb guys, get used to it, its a bit pricey but once you drive a FI car you'll never go back, wish I could afford it now. Regards, Lone Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 20, 2002 Share Posted May 20, 2002 I found out that with 0v-1v O2 sensor. car runs best with A/F meter all the way rich in part throttle and around lamba in wot. I could lean some more but my plugs look almost lean. Quote Link to comment Share on other sites More sharing options...
gnosez Posted May 20, 2002 Author Share Posted May 20, 2002 I believe I now understand the difference and why with a SU driven car don't need to overly worry about complete lack of accuracy a cheap O2 sensor will give me. "Get it close enough to race" approach seems to be about right. Right now the intakes are out of the car as I noticed a slight crack in the back unit just below the bolt hole. Hey, I wanted to replace all those little water hoses anyway. Out it came this morning and into the shop. Just got a call form the shop saying that cracking isn't 1 inch long it's 4"!! Since Nissan only has front intakes, it gets welded up and I'll polish it next weekend. Then I'll re-adjust my SUs with my inaccurate O2 sensors. Thanks again... Quote Link to comment Share on other sites More sharing options...
johnc Posted May 20, 2002 Share Posted May 20, 2002 Dave gave you some very conservative numbers regarding a/f ratio. If you can control it you should run 13.5/1 at WOT and 14/1 at any part throttle. Running a car rich hurts power. Quote Link to comment Share on other sites More sharing options...
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