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Old 03-26-2002, 11:12 AM
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Post All a matter of timing with BBC and an EFI?

I'm kinda new around here, and Roy's been helping me on getting this beast set up, but I hate to keep bugging him for everything so I thought I'd spread around a little of the joy.... :p

The Beast is an 86 Suburban 1/2 ton 4WD. Power is from a GMPP 454HO (425HP@5250, 500FT-LB@3250, hyd roller cam with Lift: .510" I, 540" E. and Duration @ .050: 211 I, 230 E., has rectangular port heads and 2.19" intake valves and 1.88" exhaust valves with 118cc open combust. chambers and 8.75 compression). I've also added Hooker super comp headers and custom 2.5" dual exhaust with H-pipe.

To top it all off, I added an Holley Comnader 950 multi point fuel injection kit w/30LB injectors.

With the EFI I'm using a computer controlled HEI distributor. I have to set the timing from a laptop based on load (vacuum/MAP sensor) vs. RPM. Nothing but total timing is involved (no vac advance) since the computer controls it.

With Roy's help, I've gotten my timing at idle set up to 22 or so. Idle is pretty smooth, vacuum is around 17-18. The question(s) I've got are how to set the timing for the high load vs. "cruise" or light in town driving. So far I've used 40 as the max advance. But I'm afraid I need a lesson on various ways and reasons to vary timing for economy vs. performance.

1. How fast should I advance the timing for just light in-town driving around? (economy)
2. How should I change that for harder or WOT acceleration? Advance faster or slower? As high or retarded a bit? (performance)
3. For maximum fuel economy (only getting 7-8mpg in town right now), how should the advance go and how far?
4. If my highway cruise RPM is 2400 rpm, do I want all timing in by then, and if so, what is the performance result when you punch it to pass someone on the hightway? Shouldn't there always be some advance left for performance reasons when you need fairly quick response (like passing)?

I apologize for the length of this, but I think I'm getting real close on finalizing the "normal" EFI setup and want to make sure I'm doing the best I can with it all. Then I'll tackle the WOT fuel map settings. Anybody willing to try and explain this timing stuff to this old timer? I'm too used to just turning the distributir to get it where I wanted it, and this EFI stuff is new.

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Old 03-26-2002, 06:00 PM
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Boy am I jealous, that sounds like quite the truck. Sounds like you have everything close to perfect but remember your old fashioned distributor worked pretty good for what it was. Here are some of my recommendations;

1) Get all your advance in as soon as the engine can take it without pinging, 40 degrees is a lot so I would just try getting it in sooner if it doesn't ping under light throttle. Maybe try reducing it to 32-36 if it pings with all the advance coming in at 2400 rpm. Maybe reduce your initial a little also, it is a bit high and will make the engine run hotter with no HP gain, I'm kind of amazed it doesn't ping at that amount now? 16-18 initial worked good on my old 454. My rule of thumb is all advance should be in at cruise RPM or normal highway speed for optimum economy. Too much advance is just as bad as to little.

2) You should dial in a little timing retard for WOT, how much will depend on what works best for your setup. 8-12 degrees to start is what I used on my Fords by adjusting the vacuum advance using the old vacuum canisters and changing the washer/shims. I would use more retard if getting the advance in early caused it to ping, this setup gets you the most torque at all rpm's. Hopefully your computer can be adjusted to give different retard levels depending on vacuum not just on throttle plate angle.

3)For economy and power, advance should be all in as quickly as the engine can handle it, keep in mind too much total advance can make your exhaust temps go sky high and will actually rob you of power. I inspect the plugs carefully with a 10X manifier to look for overheating signs, going colder on the plugs to compensate works on the track but will kill your engine on the street. This is how exhaust valves get burnt.

4)I think the above answers this question.

One last thing, my numbers are a little rusty as I have not had a BBC for a number of years. There are so many factors that affect the actual numbers that I recommend you take a friend and your laptop to a nice quiet corner of the world and do some experimentation. Let a stop watch be your guide. I can't think of a better way to spend an afternoon come to think of it.

Some of the other members can give you their timing setups so you can compare apples to apples. The basics of timing have not changed with computers so remember, timing all in as soon as possible without pinging, total timing is dependant on combustion chamber shape and flame speeds (thats why Dodges are different than Fords and Chevy's), initial timing is interrelated to total timing and the two go hand in hand. Try less initial with more advance and vise versa your engine might like either one.

As always let the stop watch be the judge and check your plugs often while testing to look for detonation (little aluminum balls adhering to the porcelin). After you have the timing dialed in you can work on plug heat range or just use a copper core plug, they are pretty forgiving assuming your timing is not excessive.

When I do plug chops I use a new set of the standard heat range Champion plug (non copper)and do one full throttle blast in top gear from a low rpm and kill the ignition at redline. When I pull the plugs I check to see if the nickel plating is burnt off halfway down the side electrode, if so you have her darned close assuming no detonation and the mixture is good.

No doubt it can get complicated with a brand new setup when one thing affects the others so make sure you work on one thing at a time, do the mixture/jetting first, then the timing/retard, then the plugs. This is just the way I do it I am sure everyone has their own technique.

[ March 26, 2002: Message edited by: 4 Jaw Chuck ]</p>
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Old 03-28-2002, 08:13 AM
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Thanks for the info, Chuck, and for taking the time to post such a detailed response. And thanks as well for the compliment! Naturally, I have a couple of follow-up questions.... (Surprised?) NOT!

To answer one of your questions/hopes: Yes, the timing grid is based on the load (MAP sensor/vacuum) at various RPMs. So I definitely can increase the timing faster as RPM increases at light load and advance it at a slower rate for WOT like conditions (it is not based on the throttle position, only vacuum and RPM).

I haven't gotten this motor to ping yet, so I'll dial in a little more advance by 2400 RPM or so. Hopefully I'll hear it under the light throttle like you mentioned. I'll pull and check a couple of plug ceramics for the little balls, too. Never heard of that one. That's the indicator that I'm in detonation and have it advanced too far, right?

I've currently got it idling at 950-1000, and at that level the 22 initial is what got the most vaccuum and smoothest idle. You really think I should drop it to 18 or so? Even if it gets rough on the idle? It may still be a fuel map related problem, but it seems to have more initial power at the 22 setting. I'll try it lower to confirm that though. One problem I'm seeing is the timing and fuel maps have to be changed together. If I decrease the timing I end up having not enough fuel according to the O2 sensor. Increasing the timing seems to use less fuel (more efficient?).

If getting all the advance in as early as possible (normal cruise rpm) gives both better performance and economy, why do all the "factory" set-ups and distributors not do this? Their stupidity?

I've got an easy way to measure 0-60 performance, just using the on ramps of the highways around here. Not too hard to find one where I can stop and then punch it to get that measurement, so I'll give it a shot and see what happens. Again, THANKS!
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Old 03-28-2002, 05:57 PM
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Vernw, sounds like lots of fun adjusting all those things together. One thing that you might consider buying/borrowing is a type k thermocouple to help you tune, I have found mine to be invaluable for tuning carburated cars. Mine has two inputs so I can check each bank at the same time. What I have done before is loosen the headers on both sides and then slip my thermocouple wire in behind the gasket so it hangs into the port. You can check each cylinder this way, but you soon find the one that runs lean and that is the one you tune to.

Temps for tuning 4 cycle piston engines should never exceed 1600 degrees F with 1250-1450 a good compromise for the street. Rotary engines are around 1900-2100.

The big problem is that fuel injection systems use an O2 sensor for mixture adjustment and 0.5 volts is the chemically correct ratio of 14.7 to 1. this is the best ratio for keeping catalytic converters working at their optimum but not necessarily the best for economy. 12.5 to 1 is near the best for power so the O2 sensor is ignored during full throttle blasts and your fuel map is executed exactly how you program it.

The numbers I mentioned earlier may very well be completely wrong for your motor and I would take them with a grain of salt. If she wants more timing I say keep giving her more untils she says enough. Your experience is unique to your automobile and I doubt anyone will have a blanket answer unless they have the exact same thing under the hood.

Another thing during your tuning is see how low you can get that idle, you should be able to get 600 rpm out of it and I would tune/time to get it lower. Getting a low steady idle is a sign the engine is operating at optimum mixture and timing. If she idles (loping with that cam) at 500 rpm give the throttle a good WOT snap and see how it responds, there should be a slight hesitation and then a full banshee run up to full revs. Upon release of the throttle it should not drop so bad that it seems it will stall. These are all tuning clues I use for carburated engines so although yours is injected the behaviour should be the same. This idle speed is just for tuning not day to day driving.

Reducing the timing will certainly cause your engine to need more fuel, that is normal. You might not feel a change in acceleration by reducing timing but I bet you will see it on a watch. More fuel means more torque and ramping the timing up as quickly as the motor can handle it builds torque quickly. It is a delicate balance to be sure and some experimentation will be necessary. Don't be afraid to try some wacky combinations it is the only way to learn.

I remember my 69 mustang, I had an Autolite four barrel on it and an assortment of jets I had pirated from the junkyard ranging from 47-62. The engine had a .490 lift 290 duration cam with lightly ported heads and headers. I tried every jet size and then changed timing to suit and by the seat of the pants method it seemed the leaner (closer to 47) I went the quicker it revved. Sounded good until I timed it over a quarter mile and found that the richer jets gave me a better time up to size 58, after that there was no gain. I ended up timing it to suit and found that the car ran cooler with less variation due to outside temperature changes and also started easier with less sensitivity to being hot started. For regular driving I ended up going leaner to a 56 so the mileage was acceptable, that car got close to 20 MPG in that state and ran low thirteen quarters with the stock 3.0 to 1 axle, not bad I thought.

One thing you must remember about factory timing is they must reduce emissions equally for all pollutants, retarding timing is one of the only ways to reduce the NOX emissions. The other way is exhaust dilution through an EGR valve arrangement. High NOX levels are produced when combustion chamber temps are at their highest, just what you want for best power. To bad you can't have low NOX levels and high combustion temps together, we wouldn't need a catalytic converter.

Thankfully as evil polluting hot rodders we could not care less about a pollutant that cuases use to detune our engines so we time and jet and tune differently. Quick and fast is what we want and no damn politician is going to tell us how to tune our automobiles.

I know this sound like a lot of work but trust me you will gain a whole new understanding of internal combustion and how everything interelates, it is like looking at a new puzzle in the box and figuring out what the picture is by seeing only one piece. After doing this job you will be able to do it like a Nascar professional and you will be able to have a whiff of the exhaust and listen to the idle rump and tell if she has to much fuel or timing.

I wish you luck in your tuning endeavour and please feel free to come and ask any question no matter how silly you think it may sound, everyone on this forum would be more than happy to help you out. I only wish I could play with your FI system so I could learn more about them myself, please keep us updated with your findings I would love to know/learn what you find out.

P.S. When doing your tuning runs make sure you do it scientifically and are comparing apples to apples on the same day. I normally take a car to a straight level stretch of highway out in the middle of nowhere and bring my tools etc. with me. Early in the morning is best because you can watch how everything changes as the sun warms things up, being able to do most of your tuning with a laptop inside the truck is certainly a bonus. Do rolling starts in a higher gear if she wants to break the tires loose on you.

I only wish I could be there with you keeping the beer cold and holding the watch, my wife can't understand the attraction of this facet of the hobby Ha Ha!!!
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Old 03-29-2002, 12:00 PM
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I agree with ya on the nasty hot rod polluters we all seem to be. To hell with the politicos. I figure I'm doing my bit for cleaner air by getting rid of that old oil burner and having an EFI unit I can tune lean if they ever implement checks here just north of Dallas. :-)

Man, I wish we were closer together as well, I could sure use the help! As it is, I'll keep experimenting and messing it up then backtracking and starting over. Sigh.

The exhaust port temp checks sounds like a good idea. To avoid having to unbolt the headers, how much good or accurate would it be to use one of the laser temp guns to read it? These headers are NOT ceramic coated, so would they be pretty close to the gas temp after idling for 10 minutes or so?

From what I've learned talking to Roy Newton, I suspect part of my tuning problem lies in the long tube headers and how far away from the exhaust port that puts the O2 sensor. I moved it upstream to the point where the pipes all come together (front of the collector), but I suspect it is cooling off too much for an accurate reading.

The reason I think that is: I get a hell of a lot better throttle response and sense of power out of the engine when I set it strictly for open loop instead of letting the O2 sensore adjust the fuels levels. In open loop I seem to stay in the .75-.85 O2 voltage range and it runs pretty damn well. Turn on the O2 sensore and it drops some. Even get faltering "tip-in" throttle initial response. I've got a set of individual tube header blankets, but haven't installed them because I'll probably have to pull the engine or drop the headers to get enough room to be able to put them on. But if I installed them, it seems to me that would help keep the exhaust temps up to the O2 sensor. Seem reasonable to you?

Just out of curiousity, since 12.5 ratio is best for power, any idea approximately what O2 sensor voltage that would equate to?

I'll also see if I can get the idle slower and stay fairly smooth. Guess I'll have to try lower initial timing as well. Personally, if I could get the damn O2 controlling to work like I think it's supposed to, and get double digit mileage, I'd probably just leave it alone. Seems like I've been doing this forever (almost 2 yrs now), although I feel like I'm closer than I've ever been. Oh well, onward and upward, right?

Thanks for your time on all this!

--- Vern
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Old 03-29-2002, 07:31 PM
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Vernw, one thing I know is that that O2 sensor will cause you never ending grief especially with the hot cam etc. on your engine. Keeping them hot is a never ending problem with high overlap camshafts.

One thing I thought of after posting before was is it possible to run open loop with only the map being the guide? If in open loop the timing could still be contolled while the MAF and altitude sensor did their adjustment to the map it might solve your problem? Many older non-MAF type injection systems worked very well once the map was tuned for that engine set-up. That O2 sensor is there for one thing and that is to keep a catalytic converter functioning at it's best. You should be able to pick up some good fuel economy gains at part throttle by tuning to a leaner mixture under part throttle if this scheme would work.

Maybe it is possible to reduce the effect of the O2 sensor on the map by changing some muliplier or something? Maybe fooling the computer with a 0.5 volt fake voltage input could do this for you too? Making a simple circuit that could be wired into your electrical system would be easy and you could have a switch that would function like a choke, on for closed loop engine warmed up and off for cold engine start? Would fool the computer into following the map without adjustment. I would try this as a last resort however.

12.5 to 1 mixtures would completely cool off the O2 sensor. Ultra lean mixtures will do the same believe it or not. Something like anything above 17 to 1 is lean enough to cool off the sensor also, even though lean part throttle cruise could be acceptable at this mixture strength.

So try the reduced timing and more fuel and see how she runs, let us know how it works out.

[ March 29, 2002: Message edited by: 4 Jaw Chuck ]</p>
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Old 04-01-2002, 01:46 PM
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Chuck - yes I can run in open loop. Except this is a MAP based system, so running in open loop does not get any adjustments to the main fuel map except temperature compensation. There is no MAF sensor. Ignoring the O2 sensor means only the fuel map is used for fuel delivery. The timing map still works regardless since it is MAP and RPM based. Luckily I can still control the warmup fuel additions even w/o the O2 sensor, I just have to put in the amount manually to add for different temps as it warms up. Luckily I don't have to do the wirong work around you mentioned.

Do you think using the header blankets (individual tube asbestos wraps) would keep the exhaust hot enough for the O2 to work pretty well, or do you think its a lost cause with this cam? I didn't think the cam was all that hot...

Thanks for all your advice on this, I'll let you know how it all works out - as soon as I figure it out myself &lt;grin&gt;
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Old 04-01-2002, 02:45 PM
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Exhaust blankets are great for keeping the headers hot and actually add a little power if you have to big of a primary tube but.....

Those blankets keep the headers red hot and the plain mild steel in inexpensive headers will soon heat crack, stainless headers seem to handle it OK, although it does shorten their life somewhat. It would certainly help with keeping your O2 sensor hot. The blankets that surround the headers as a group are better than the individual wrap type in my opinion, and the nice side effect is the under hood temps are reduced as well, noise too.

Might be a good idea to ignore the O2 sensor altogether by unplugging it and spend your time getting your map dialed in. Once you have the sensor out of the loop and it's constant adjustments not screwing up things you will have a easier time dialing your combo in. After everything is working like a charm you might find that you don't want the O2 sensor at all unless the MAN wants to emission check your truck if and when that becomes mandatory.

This reminds me of a dream I've had where I pull into an emissions depot and detune the cam, fuel system, exhaust etc. all through a laptop sitting on the seat. After my car passes the test I pull out and then reload the performance program and the testing guy standing in the bay looks up as my car turns from a whisper quiet granny mobile into something more akin to a nascar stocker with the attendant rumpy idle and I wave by by.
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Old 01-19-2003, 04:59 PM
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I have purchased a commander 950 for my 454. The base maps are not even close was yours
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Old 01-19-2003, 05:53 PM
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Vern, 4 Jaw, this is great stuff for a fledgling Fuelie. I have the Edelbrock Pro Flo system installed on my 383 but have not fired it up. I have been trying to get a mobile muffler guy to come to the shop to run the exhaust system and put in the 02 bung. I'm running Sanderstrom Cast headers so I should be able to get it close to the fire. Had I not read your posts, I would have had him put it further down stream so it would be easier to change out. Hope to see more of this thread.

Trees
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Old 01-19-2003, 06:01 PM
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Also just reviewed some curves on Spark Advance vs RPM at different throttle settings. The wide open throttle spark advance settings are almost as 4 Jaw suggested in his first post. I also have curves showing differences between long and short duration cams and the long duration curves also match 4 Jaws inputs.

Trees
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Old 01-20-2003, 07:32 AM
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Nope, they aren't even close. They've started emissions testng here, so I'm back to trying to tune the beast in again. Which 454 have you got? We may "need to talk", hopefully we can both help each other out here!
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Old 01-20-2003, 07:35 AM
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TREES - please tell me more about these spark vs. rpm curves you've got, it may be "just what I need".....
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Old 01-20-2003, 04:26 PM
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Vern, I just sent you an email with some curves attached. My phone number is included, cause the quality is suspect so I will have to give you the numbers that correspond with the different curves.

Trees
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