ok gang,
here it is. i have been trying to keep this clear here and through AIM conversations with several people. chips are a very good thing, but you still need the basic base lines of fuel pressure and initial timing to make any chip work properly.
every new combo will require a little bit of tuning to run perfectly, but the first step is not to run out and get a chip.
any tiem a bigger cam is used or higher ratio rockers are installed you will need to increase you initial timing and add fuel accordingly to supply the new rpm range of the motor.
anytime a greater air flow device is installed(open element, ported TB, after market manifold) there will need to be an increase in fuel pressure or volume(volume=larger injectors).
to get any new combo to idle cleanly or sometimes to just get the car started you will need to get the base timing close and the fuel pressure so that when you pull the plugs out after it idles for a few mins they will look clean, almost white with a slight brown tinge. the only thing that will prevent this from being possible is if the cam is large enough that it requires a faster idle speed than the stock chip is programmed for(which is 550rpm i believe) at which point you should just be able to crack the throttle far enough to ge tht ecar to idle there and then set these parameters.
also you have to remeber to set you TPS and IAC correctly once you get your new chip, especially if it includes a change in idle speed. if you leave the blades where they were to idle the car at 550 it will not be able to idle at say 700rpm properly, it will likely surge as it tries to support the idle.
i know that a properly burned chip is the only way to get everything out of any combo, but it is not a legitimate first step nor can it take the place of the basics of how an engine works.
i am glad a lot of people are getting into ecm tuning, but don't overlook the simple solution on the way to the high tech solution.

later
tim

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91 Camaro RS-LO3,Auto
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The problem with an eprom is that it too has it's limits. For example, there are two tables that control the VE (fuel) curve. One is an "adder" that is dependant on RPM only. The other is dependant on MAP pressure. If you match up rpm for rpm in both tables you can NOT go over 100. Stock totals up to I think 95 in some MAP values around 3200rpm and up! This is where you NEED to tune your fuel pressure. I don't know why people think more air is all they need...IT ISN'T!!! You need more fuel too! The advantage of eproms is that you can adjust the fire rate of the injectors without messing with fuel pressure! The easy "real time" way to adjust is with fuel pressure.
For people that can't afford eprom burning and have many bolt ons....INCREASE FUEL PRESSURE!
About the timing....eprom is the ONLY way to do it. You can't disable EGR mechanically and if you just put a check valve in place the ecm with think it's got a working EGR. The problem with this is that you're ecm WILL increase timing a few degrees, this is a bad thing if you don't have a functioning EGR. You'll probably end up getting knock with some pump gas and this will hurt your performance more than you've gained by disabling EGR.
Tim, you have alum heads and this is why you can get away with the extra added timing. If you had iron heads I'll garantee you wouldn't be advancing stock timing much more than 6 base.
As you can see there are some things you just can't do easily without effecting something else equally important.
The timing and fuel pressure is GREAT for the average Lo3 bolt on guy but understand that an eprom can control all of that and if it can't it can at least compensate .
Good point Tim, now for anybody that hasn't done an adjustable fuel pressure regulator....DO IT, it's FREE (minus cost for new gasket kit).

------------------
, Jon (350 TBI!)
91 Red My website

[This message has been edited by JPrevost (edited October 08, 2001).]

 

thanks jon,
i can get about 3 more degrees out of the aluminum heads because of how they dissapate heat energy. i was running about 10.5 after i put on the heads and rockers and could go all the wya to 12 on good gas. some of that timing is because of the increased cam duration created by the 1.6 rockers and some is from the aluminum. i believe it to be about a half and half thing.
base timing is a tricky thing in our cars. teh ecm controls all advance of timing but it only goes forward from what it believes to be 0degrees. if you increase the timing it doesn't really know that, it just happily thinks it is still at 0. so by changing the timing a little you have now effectively changed the base, initial(base+idle advance in the ecm), total timing(how far it will go ahead), and absolute timing(how far it can advance before knock occurs).
that is why timing shoudl always be a little at a time thing when adjusted mechanically. if you have astock chip or a mild off the shelf chip(like what they sell from summit or jeg's) you can pull the old advance until it pings then back up 2 degrees just because the advance curves are so mild that you are not going to get ahead of the engine that way. if you are getting a custom chip burned you will want to get the car so it can start and idle and then tell the person doing the chip how many degrees that starting points at so they can avoid going too far.

later
tim

------------------
91 Camaro RS-LO3,Auto
New Times Coming Soon!
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you're off on several things guys, I dont have much time to go into detail right now but really, there are no limits with what you can do when programming, ve tables are only a small part of the equation at WOT, bpw, WOT afr , and several other parameters play a huge part. The long and short of it is you shouldnt HAVe to go to 100% on the ve tables when everything is set up correctly. If you do thats a sign of something wrong

Trying to tune an efi engine by conventional means is like trying to drive on an ice skating rink, youll go nowhere fast and will probably even start working against yourself. Theres alot more to it (and less in a sense) than it seems. Timing tables arent one dimensional for instance and there is much to be said about a timing curve, total and base are but a small part of the equation, (base a smaller part since you could pretty much have the dist in a number of places and it wouldnt make much difference if you programmed the chip for it)

gotta run
Pablo

 

i can see that there is a lot that a chip can do. but i can't agree with your comment about tunign mechanically though. i have used only mechanical means to get a 14.2 out of my stock cam. if it was really so far off base why when i data logged did the engine never hithte knock sensor and stayed in the barely rich area through 3 gears at WOT.
even calmap(accel's DFI software) says that the base program will get the engine started and a reasonable idle shoudl be found with fuel pressure and checking the base timing. you need a solid base line no matter what the chip is capable of.
the only thing that can really keep a simple fuel injection system like ours from being drivable by mechanical means is if the cam is too large to support idle at the 550rpm that the stock program places it.
my car always idled like glass and got 25mpg on the highway, that is a very good state of tune, and that was all mechanical on the stock chip.
i know my case can't speak for every combo, but you can't discount what the correct fuel pressure and base timing will do for the performance of any engine.

later
tim

------------------
91 Camaro RS-LO3,Auto
New Times Coming Soon!
Check Out The East Coast F-Body Nationals Home Page
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My MAFB.ORG Home Page
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DSI Racing Home Page
www.geocities.com/foff667

 

Pablo, I highly doubt that most of us have the resources and experience to tune a GM ecm for a crazy engine. Tim's is mild, hell, he's got a stock Lo3 cam!!!! That is why, Tim, I think you have a smooth idle, not because of your other stuff.
As for no limits...of course they're aren't any real limits in theory but in practice there are lots of personal limits like money and time. You could in theory support a 600+hp engine with the 8746 ecm, but you would need some large injectors because even they don't keep firing, they have a physical limit. Same as parts of the ecm. Unless you have gobs of time on your hads you won't be able to adjust for some things. Heck, even the timing can only go so far and you need to revamp a lot of the constants JUST to allow for more timing! I'm just saying there are some things eproms can do that fuel pressure and base timing won't let you do. Like set air fuel ratios or enable highway mode. Tim, you have to understand that you've done a lot of mods and look at the idle! It's smooth, yes, but that's because of the cam and expensive heads, not because of fuel pressure.
Tim, you're running with a functional EGR right?

------------------
, Jon (350 TBI!)
91 Red My website

 

egr is disabled on mine.
i understand where the limits of the mechanical are in a car like ours, believe me over the years i have crossed them enough times
i jusat think that you can do the basic power my way and get the ultimate power using both. if the basics are right it will be easier to tune the ecm because you will be starting from closer.

later
tim


------------------
91 Camaro RS-LO3,Auto
New Times Coming Soon!
Check Out The East Coast F-Body Nationals Home Page
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Ok Tim, I'm going to see what PSI and base timing will do after swapping in the LT4 cam. Do you have any suggestions for how much to bump up the timing and fuel pressure.

------------------
91 RS 5.0 TBI....LT4 cam....Edelbrock TES headers .. 3" exhaust ...Dynomax muffler...5spd... 3.08...underdrive pulleys...cold air K&N flat bottom breather...strut tower brace...6-point rollbar...sub-frame connectors...Koni shocks and struts...16" Black GTA wheels...Autometer guages...custom chip...Grant steering wheel...a/c delete...smog delete...rear seat delete...ultimate TBI mods...afpr...36mm front and 25mm rear swaybars with poly bushings... The peanut is dead!!!!

 

you will want to bump the timing until it smooths out a little, you should be able to see the motor calm down. that cam is gonna need a raised idle most likely. so setting it may be a little tricky.
you'll hafta rev it until it is out of warm up loop and see if it will even try to idle onits own. if it cannot sustain an idle on its own or if it won't even stay startedyou may have to crack the throttle just a little bit to get things started.
if you have to hold th ethrottle open to keep it alive, figure out how low it can go before it dies. you should be able to get an idea of how much fuel it wants by how much is going in to keep it alive. if it won't idle below 1000rpm then you will need to put some timing in to help it out.
you will also be able to sort of see the amount of fuel going in, once you get it so that it can idle down toward 700rpm or so(which i think it shoudl have enough vacuum to do) you will want to put it in gear and make sure it can run under a slight load. then you can start to slowly drive around just to get a baseline of what the engine wants.
this will give you a start of what the motor wants. i really think the first thing the chip will need to do is raise the idle, i think it will hafta be around 700-750 to idle and drive good, a very big pump shot, and need a strong advance curve, that is a big cam for a 305.

later
tim


------------------
91 Camaro RS-LO3,Auto
New Times Coming Soon!
Check Out The East Coast F-Body Nationals Home Page
www.geocities.com/njspeeder
My MAFB.ORG Home Page
www.mycar.net/mafb/registry/detail.cfm?id=299
DSI Racing Home Page
www.geocities.com/foff667

 

Thanks for the reply Tim. I probably was not clear on what I wanted to do. I have had the cam in since Sunday and it cranks great, idles great and overall runs great. I had the chip set to idle at 750 already and have had zero idle problems. I had the base timing set at 2 stock and now with the cam it's set at 4. The scanner reads knock only in 5th gear at cruise up hills 70 to 80 mph. (which it did stock also). No knock in any other gear or at WOT. It cruises with a BLM of 125. I need to figure out WOT tuning fuel and a timing for max performance. It feels like a stronger motor just with the cam change. I'll bet it does pick it up with heads and intake changes! See Ya

 

After thinking about it since everything else seems to be working correctly I think that adding more fuel and timing with the chip for WOT is what I should be adding after doing some plug cuts. Just some thoughts before changing heads and intake which will be more tuning.

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91 RS 5.0 TBI....LT4 cam....Edelbrock headers....3"Dynomax exhaust....5spd.... 3.08.....Ultimate tbi....afpr...