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BLM? 304-vs-345

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  • Guest's Avatar
    Guest replied
    305 injectors

    I have done some 350's with the 305 injectors and have found the same thing. Runs good in closed loop but needs work in open loop. Soemtimes it is just easier

    I very seldom touch the VE2 table. When I do it is mostly in the upper RPM ranges where the VE1 table has left off.

    The reason you see sensitivity in the lower RPM ranges is because you are working between two cells that are close together and it also only takes a little bit of pulse width to make a big change. How does the saying go; do the math.

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  • Eagle-Mark
    You guys sure seem like your enjoying this chip programming but for me I just don't have time or the will to get into this right now, maybe someday?

    So I opted for the easy route and I am getting my chip from AFI.

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  • Bill usn-1
    You make some very good points for those guys starting to do it on their own.
    I have accumulated a few different ECM's with all the systems I have bought. A couple being the 8746 which if I did my homework right is a car version of the 7747 but it looks to have an ACT input. So I think, as you say... the guys in the mountains in CO may be better off with this ECM. Though tuning support again is a little limited compared to the 7747.

    To follow what you were saying about the BPW, I noticed the ASDU bin to be the most sensitive to changes in the BLM at the 600-1000 RPM if you adjust the BPW away from factory.
    To make the tuning easier I just went with the 350 injectors when I use the ASDU file and keep the BPW at factory setting.
    I tried to adjust it for the 305 injectors and as I adjusted the closed loop towards 128 it would really start to stumble in open loop..
    I found most fine tuning can just be done with the VE1 table and not even need to adjust the VE2.
    Of course I am still learning to walk when it comes to these chips!!!!!!
    There is so much going on at the same time.

    Then of course it all has to be tweaked again after you play with the timing!!!!

    Are we having fun yet?????

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  • Guest's Avatar
    Guest replied

    Bill is correct about the Base pulse width calculation of the motor. It uses a combination of the cu. in. of one cylinder and the flow of the injectors to determine the base pulse width value.

    Now that being said I wish it was that easy. For the most part that is true, however even Chevy uses the same base pulse width value for three different size injectors. The base # is calculated from 61# injectors; they used 61, 65 and 69 pound injectors though with their units. What they have done is played with their fuel curves (VE tables) to provide the proper fueling. They have spent a long time on them and so you may have to also. Technically you should be able to plug the # in and the VE table defines the engine; it isn't always used that way though. Many times it is a combination of both.

    Do remeber that all GM ECM's have an adaptive feature to them. This allows the ECM to "learn" what your fuel shift is at the various speed load points. For the most part if it is not off to far this feature can account for a fair amount of "stack-up" in a system. The issue with the 7747 is the processing speed of the computer; slow compared to today's units and even some of the other units used in that time frame.

    The best ECM to actually use to provide all of the fast processing speed functions is the 93 - 95 truck ECM's that had the electronic transmissions. These units had a faster processor because of the transmission and have much more capability to them. They are however a lot more difficult to program and there is not a lot of info available for them. This then brings most back to the 7747 for its ease of use and programming.

    One more thing for all of you techies making your own chips. Be carful about how you use your BLM and INT functions with software. Most engine calibrations are put together from the factory at a known constant air and coolant temperature; this being 100 degrees ACT and 200 degrees ECT. (Air Charge Temp and Engine Coolant Temp). For modern day engines and most of the MPFI systems they are equipped with an ACT sensor that adjusts the air charge calculation based upon the air temperature. With the 7747 there is not an air temperature sensor so the calculation is stricktly based on ECT, RPM, MAP and BP (barometric pressure). So this being said this is what you need to be careful of.

    When you are trying to tune be very aware of what the ambient conditions are with regard to temperature and humidity. When the temperature that you are running in is within the 70 - 80 degree range then your BLM should be providng you a fairly accurate account of what your stackups are. Look for consistency within the cells as opposed to actual #'s that you are getting. For instance if you are running in 40 degree weather that is very humid your BLM will learn out more than running in say 70 degree weather on a very nice day. As long as you have consistency from cell to cell you are fine and have tuned it well. If on the other hand you see one cell that is always off then that is an area that you will want to take a look at.

    Go for consistency before you go for actaul #'s.

    The opposite is also true, when you are running in very warm temperatures the BLM will be adding more fuel than when it is cold outside. But again consistency is more important than actual #'s. The unit should go from high to low depending on the conditions, that is why you use a closed loop system and let it work.

    For this reason when we build a system for known conditions like all dessert running or high altitude cold running we use the late 80's Camaro and Caprice TBI system which uses an ACT sensor. This way we have one other input that is trying to make our mass calculation more accurate. We have several snow cats that have our systems on them that run up to 12,000 ft. in -40 degree weather sometimes. Do the math, thin air + real cold, another input makes it work a lot easier.

    Sorry if I have been to long or too technical but these are some good things to remember when tuning your own chips.

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  • Binderman
    Bill What can I say but WOW!! That was deep!

    You mentioned that there was two 100 dollar options as far as obtaining the proper chip/combination for my 304. I am not one to back down from any challenge and have never let anyone else work on my vehicles so will have to save up my coins and get the burner you mentioned and start on the zantac!! Did you buy your eraser or make it?

    Will the laptop info optained and a little more reading on the way things work be enough to tune my own or do I need some other source of info on the subject, like a book? If so can you or anyone recommend a good one as vaction is coming up and there will be lots of time for reading!!!!!!!!!!!!!!!!

    You mentioned three FI-ed scouts you are working on, is one black and white with no flex in suspension at all LOL. If so what major differences are there between its chip and your trail scout because the Ruff scout has a few engine goodies doesnt it? How much difference does the extras make in tuning one properly for it? Tougher or about the average of the others?

    Time you finish the three you are working on now then tune up the chip for the motor home conversion you will need a case of Zantac!!

    I did not put the whole o2 sensor/18mm spark plug thing together some time ago when i needed to clean up the threads on a bung I removed a faulty sensor from when I bought the tap to do it with. It was a double ended spark plug thread chaser. Thanks for the wake up on the anti fouler use for bung!!! This I can do!

    What would I do without the internet? Probly get the sleep I need!! Thanks Bill

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  • Bill usn-1
    Well guys there is the easy answer and the hard answer.
    (AFI correct me if I get off course)

    The easy answer is that with a baseline chip you can just input the new cubic inch and injector flow ratings into a formula and come up with a new BPW for the chip( it a little more involved but nothing hard). So in "theory"
    since the design of the motors are basically the same you could just apply the new data to the 345 chip and use it for the 304.

    Now the fine print...............................

    Will it work?
    Sure it will run. just like a stock 305 chevy chip will run your 304.
    Will it be optimized to your motor?
    I have burned between 75 and 100 chips for the 3 scouts I am doing right now. I try different things to see just what the motors like. Most of the time is spent on the timing curves. adding a couple degrees here and there. The fuel is the easier of the 2 to get close.

    All 3 scouts are driven regularly. they all run good, they all start right up and drive. So do I need to do anything else to them......
    Sure....We are always looking for free horse power.

    The question is ...what do you guys want to do?
    Just drop in a chip and be done or play with it in your spare time and really try to learn what makes it tick?

    One takes 2 minutes and the other is quite a while(days, weeks, months)
    When I did my first one it was just to look for something a little more up to date than a carb. I wanted to do it myself and I wanted to learn FI. And I wanted to stop the flooding and burping of the carb on the trail. It tends to break things.

    Even if you don't want to learn a lot about the FI system, you will still need to make the ALDL cable and hook up a laptop to it so your fuel MAP can be tuned to your motor.
    Whoever does your chip will need the data.

    Right now I do about 1 chip a night when I'm tuning.
    I go for a long drive(30-45 min), aquire the data I need, come back to the house, adjust the tables in the BIN file(30-60 min), burn the chip(10 min if I don't have to erase) then go for another run and see how it does.
    I learn something new about the BIN data everytime I play with them. There is a lot that happens in that little 4K file to run one of these motors!!!

    You guys decide what you want to do and I will help all I can.
    If you want an easy way than I think AFI said he will do a chip for $100 and will work with you to get it right. Thats a good deal!
    I spent that on my burner. Of course he does not include the lost hours of sleep or the cost of zantac for the heartburn caused from the stress, but I would say it is a fair trade.


    An easy O2 bung is to use an 18mm spark plug anti fouler from the help section in your part store. Just cut it in half, drill the hole in your pipe and weld it in!!!!! You do have a cut off wheel for your grinder...right????


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  • Binderman
    Sandracer Thanks for the info about the o2 bung. That is cheap enough no reason to look eslewhere. I forgot about Summit. We both run automatics so we should be able to get by with about the same chip i would think?? Still pretty deep subject for my small brain to soak up. I will be happy if mine just runs when finished, but I am like many, there is always room for improvement but much studying is needed to figure out what needs to be adjusted. I feel I am riding others shirt tails on this whole thing at this point. Everyone has been able to attribute something to the conversion so far and all I do is ask for help. Thanks again guys!!!

    The "IH FI Bum" aka Binderman

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  • Guest's Avatar
    Guest replied
    I'd imagine that Jegs has the O2 bungs. I just looked at the Summit site and they list 4 of them. They offer ones from Holley, Hooker, and Tesla in addition to a store brand ranging from $4.99 to $12.99.

    I'm anxiously awaiting responses on your 304 vs. 345 question as I'm working on a TBI for the 304, as well.

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  • Binderman
    started a topic BLM? 304-vs-345

    BLM? 304-vs-345

    I will keep this short and to the point. Will my 304 perform as well on the same custom burned chips as the 345? I was looking at Bills blm photos and reading up on the whole blm thing and it got me to thinking about my little 304 as most are running a 345. I know Bill has been working on his chip burning daily for his 345's. There was a guy that said he burned about 400 different chips before he got his right on the AFI site. So I am kinda at a loss as what I should do about the chip thing. Should i study it more and learn/buy the stuff to burn my own or just stick with one for 345? Thanks to all that have spent many hours on this so far. Bill how many hours do you have in your chip alone right now? Thanks again guys!!!!

    P.s Where do i get a bung for o2 sensor. My Jegs catalog is over ten years old and has not one.