dimented24x7

iTrader: (2)

alright... i was looking at holley's site today and saw that they claim that the 4bbl tbi unit actually has progressive linkages (if it doesnt then ill make it have progressive linkages). My thoughts on this are "great! only two of the injectors will be used when im crusing around so ill still have good throttle responce, fuel economy, and idle quality." Id really like to run this unit witht eh new setup i had in mind since the 4bbl unit by itself would be comprable in price to a good carb. How would i adress the issue of the progressive linkages? Id have to have only two of the injectors running at part throttle and then be able to bring the other two online when the extra two throttle blades begin to open. I was thinking of using an extra ecm with bare bones input to run the second set of injectors. I guess id have the primary ecm operate the first two injectors and tune it witht he other two injectors inactive and then use the secondary ecm to operate teh second set of injectors under high throttle load. Kinda like a carb with digital secondaries. Tuning would be a pita, though. What are your thaughts on this? I think it would be pretty damn cool to get a system like this going using off the shelf parts rather then blasting 1400-1500 dollars on holleys ecm witht eh tbi unit.

FRMULA88

FYI: The progressive TBI unit is designed for the Projection 4Di system the only thing progressive are the throttle blades, all four injectors still fire.

You tune the IV (injection volume) fuel map on the 4Di system based on MAP (manifold absolute pressure aka vacuum) and engine RPM. A fuel map tuned for economy/performance will look like a smooth "hill" with lower IV values at low loads and engine speed.

The progressive linkage helps with throttle responce... since the older design just opens all 4 blades at the same rate.

dimented24x7

iTrader: (2)

ive never had experience with the 4di systems but i never knew they jsut had the injectors keep dumping fuel in. Id still like to set one up in the way i mentioned previously. One of the things i dont like about having all the injectors firing at once is that at low rpms/loads the four high pph injectors will give way too much fuel then thats needed. I could use lower pph injectors but that kinda defeats teh purpous since id need more fuel at higher rpms and loads. Id like to possibly set it up as a sort of carb setup where it jsut behaves as a 2 bbl tbi to give good fuel economy and the second two injectors come in at higher loads. Id obviously modify the tbi as needed to do this but one of the things is how to syncronize the the injectors to the throttle blade openings. I wonder how feasible doing something like this might be.

seanof30306

iTrader: (4)

instead of making all those mods to the factory computer to run a 4bbl, would it make sense to go to an accell gen vii dfi computer, which has such awesome tunability?

in last months gm high tech performance, they did that to project magnum (a tpi car). they bought a harness from a place in california that split the factory computer off to control only the emissions controls and let the dfi computer handle engine management.

this would probably be overkill on a 305 or mild 350 tbi, but at some point, you just make too much horsepower for a 2bbl unit to handle.

the complete gen vii system with distributer runs around 3,200.00. i've been wondering about lower cost alternatives. would this be one?

dimented24x7

iTrader: (2)

wow... thats more then i paid for the whole car. I was looking to keep costs below 800 dollars... I know the dfi systems can do better but the cost is just too prohibitive. The other problem with the holley setup is itll be too much fuel under light load/ low map or what ever you wish to call it. Im planning on running a setup which would probably need more air then the 500 equivelent cfm that the bb tbi can give with a low rise dual plane intake with its small plenum volume.

steve8586iroc

I think before I went to all that trouble of trying to make the holley 4brl tbi work with the extra ecm, I would just buy a edelbrock or holley vacuum secondary carb. Your mgp might drop a little but you could forget about having to burn chips for the next year and still not having it work properly.

Steve

dimented24x7

iTrader: (2)

but that would be wussing out J/K I know it would be a ROYAL pain in the a@@ to tune, but, you have to admit, it would be a really trick setup if i ever got it to work. I probably wont use it, though... like you said, it would be a pain to try to get it to work.

FRMULA88

The method you are describing is nothing diffenent than a 4 barrel carb with vacuum or mechanical secondaries.
Smaller primaries are used for part throttle fuel economy, mash the pedal and the large secondaries kick in.

With electronic fuel injection this is not necessary since fuel delivery is regulated "electronicly"

Like I stated the fuel map (Injector Volume) regulates fuel delivery based on engine speed/load.

The 4 Barrel TBI was designed to work with the Projection system so as far as the HOLLEY ECM is concerned it knows it's firing four injectors, so if you only need 20#/hr fuel at 800 rpm it knows that each injector will deliver 5#/hr.

A 2 barrel system in the same scenario would need to deliver 10#/hr per injector.

A 8 injector system (Tuned port, Direct injection)
would deliver 2.5 #/hr.

JPrevost

Any of you doing source code yet?
If so, hit me up through PM because I'd LOVE to be kept updated on how you would go about doing what is spoken. Not saying it's impossible, just it's a LOT of work. A 4 barrel TBI with stock "min sync pulse widths" and async pulse widths thresholds are being met forcing the ecm to basically go loco and dumping fuel in like a top fueler with nitro . Adjusting these thresholds will let your ecm firing the injectors at VERY low opening rates and allow for a better idle. Stock calibration you'd almost be forced to run a >900rpm idle just to keep the car from stumbling/hickups.
Even with a 2 barrel TBI setup this becomes a problem, only it's not as extream since with 2 injectors (like formula88 said) they need to flow twice of much meaning while in sync mode the injectors will fire close but not exactly twice as much pulse width, but twice as often. I'm having this problem now but last evening a good friend of mine was tinkering with the setup and noticed low fuel pressure. We turned the screw in and the fuel pressure wasn't moving. Turns out we almost needed to bottom out the screw in the regulator just to get some decent fuel pressure. I'm going to take it apart today and see what's going on but I have a feeling the spring is sagging from all of the heat cycles and the natural frequency of the spring seems to not like to keep up with the walbro fuel pump . Anyways, I hooked up the vacuum up to the regulator and it works GREAT. Low fuel pressure at high vacuum (idle and decell) and high pressure under acceleration. Helps with pump shot a lot too as a side effect. Anyways, back on topic, without the regulator I'd have to run lots of pressure all the time and at idle speeds (750rpm) the car would hate me.

seanof30306

iTrader: (4)

the 3,200.00 i mentioned was the cost of the entire dfi system. you wouldn't need the entire system for this.

the problem with running a 4bbl injection system is that the stock computer is only designed to handle a 2bbl system.

to run a 4bbl, you need a computer to manage it. people on here have tried "patching" the factory computer, but i think i've only seen one person who was able to work it out.

i was suggesting using the dfi computer to control the 4bbl injector, and using the factory computer to control the emissions equipment to keep it legal. none of the aftermarket computers control emissions. the aftermarket ecms offer incredible tunability, though. much better than burning chips. depending on the cost and feasability of doing it, i think this would be a much better way.

i think the dfi computer is only 400, 500.00. not sure.

rather than a 4bbl tbi unit, however, i think there are better ways. once you get past the hp/cubic inch limits of a 2bbl tbi unit, i think you'd be much better off to go to a direct port injection system. they're a lot more efficient.

the main problems have been cost and legality. dfi and projection are incredibly expensive and they are legal for non-emissions vehicles only. the legality has been addressed recently with custom wiring harnesses that allow you to keep the factory computer to control the emissions equipment, but you're still looking at around 3,000.00 for a good aftermarket system.

a lot of people switch to tpi. while it does offer an improvement in hp and efficiency, it still has some of the same limitations as tbi ... specifically running out of power at higher rpms. addressing that with different runners and intake bases is really expensive. look at arizona speed and marine's or tpi specialties' websites. if you wanted to swap to a tpi setup to support an engine making too much hp and or having too many cubic inches for tbi, you're still looking at over 3,000.00

i'm going to mess with my 305 tbi for awhile. at some point, though, i want to swap to a 400 sbc that'll hopefully make over 400 hp. tbi won't support that. i think the best solution is a stealth ram tpi setup. the stealth ram is way cheaper than aftermatket tpi intakes and runners and offers much more power. you could get everything else you need (ecm, wiring harness, oxygen sensor, etc,) from a junkyard and do the entire swap for less than 1,500.00. the next step beyond that would be to add an aftermarket ecm like dfi for even more power and efficiency.

now i'm sure the carb guys are going to go crazy, but fuel injection is definitely the better way to go for power, economy and drivability. on this past weekend's horsepower tv, they swapped a carb out for a complete dfi setup on a 502 powered chevelle wagon and picked up over 40 hp out of the box! the strength of that system is it's tunability ... surely there was more there to be had.

RBob

iTrader: (1)

If you get the chance check out the newer Cmdr 950 system. With that ECM the secondary injectors can be enabled at a particular TPS setting. This way they stay off until the secondary blades start to open. I must say that holley seems to be responding with some interesting solutions.

RBob.

dimented24x7

iTrader: (2)

looks like holley beat me to it. Sure would be alot easier to buy the system then to make it myself.

RBob

iTrader: (1)

Well, the code change to do this is rather trivial. Just have the ECM check for the TPS to be greater then x%. Then use an external or internal driver board for the secondary injectors that the ECM then enables at the same time it cuts the BPW in half.

RBob.

dimented24x7

iTrader: (2)

how hard is it to program an ecm like, say a 7747? Im good at programming with c++ and similar languages but ive never had any experience with the ecms and the code that gm used to program them.

RBob

iTrader: (1)

No reason that you couldn't learn it. The fact that you have programming experience makes it all that much easier. There are some sticky's at the top of the DIY PROM board, 'patch method demo' and the 'source code' that have some good info in them. Grab the hac of the '8746 (diy-efi.org/gmecm or such) and the Motorola 68HC11 tech ref (from their web site) and see how it all looks. Moto assembly is straight forward (unlike Intel's).

RBob.

Pablo

iTrader: (1)

Im going to make a guess that the original poster does not fully grasp the basic notion of FI that was posted by FRMULA88 several times.

While there are some problems concerning syncronous and asyncronous injection and fuel map resolution etc which is just a problem with large injectors which is probably what RBOB is talking about it sounds to me like the original poster is assigning carburetor like traits to fuel injection.

I suggest you re read his posts a couple of times and then tackle the details once you go through the basics of chip programming

FRMULA88

Pablo,

Thanks for the compliment.

I tuned my map for WOT 1/4 mile performance so my IV values are a smooth "ramp", it does not take into account lower IV values based on MAP load, rather the IV values are constant across the MAP scale.

By doing this I am not taking advantage of the TBIs efficiency, since it is tuned more like a double pumper CARB, BUT the performance is great. It would be nice to pick-up a few more Miles per gallon but I built the car to race it.

dimented24x7

iTrader: (2)

An uneccesary comment IMO.

Actually, i do understand teh basic theory of efi. Thats the whole reason i thaught of this is because i want to only run two injectors at low map/rpm values so that my 350 will idle properly and get good fuel economy and yet still ahve good performance. Unlike formua88 i have to drive my car for more then a 1/4 mile at a time under various loads and speeds. I imagine that tuning at low rpms and loads, MAP or what have you with four injectors would be like trying to do needle point with a pile driver.
Thanks for the input RBob. Ill look into it. Even though its unlikely that ill run a 4bbl unit id still like to at least try and look into it rather then jsut admit defeat right off the bat.

FRMULA88

I drive it alot more than 1/4 mile at time, it is not however a daily driven vehicle. I just have not taken the time yet to fine tune the injection volume map.

With a ECM that is laptop tunable and with "Autochart" I can data log and use the analyze function which makes corrections to the IV map (add or subtract fuel)I can then apply these corrections to the fuel map send it to the ecm and data log some more. I just need to hook up the laptap and go for a drive. This would give me a very good "street" fuel map. I can only imagine that win ALDL does the same thing.

RBob

iTrader: (1)

Another alternative is what JP has mentioned: the vacuum referenced FPR. I am going to try it out myself. Right now I am running 2 BBC inj's at 16psi. At idle the PW is ~ 1.2 msec., and difficult to control. At an idle of 60KPa the VFPR will reduce the fuel pressure to 10.2 psi. This should have a positive effect on the idle PW.

Of course still take some time and look into learning the Motorola assembly. Being able to change the code in the ECM opens up a whole new world. The ECM is nothing more then a computer.

RBob.

dimented24x7

iTrader: (2)

i looked into sopme of the operation and programming of the motorolla processor. Its quite interesting. My uncle writes alot of assy. code for similar processors from motorolla for use in electronics so ill get in touch with him. He should be able to supply me with more liturature then ill ever need.

trumps2000

iTrader: (2)

Hey dimented, Were you able to get this to work?

Ronny

iTrader: (1)

I bet he went onto bigger and better things! That was 2003 remember.

It just seems to me a MPFI system run my the Port EBL ECU is a better idea. I believe it can be done economicly with an EFI Pro products manifold and LS TB unit.

trumps2000

iTrader: (2)

But Ronny this is the TBI forum!

I'm sure he's moved on to bigger and better things, but I'm interested in finding out how far he got. I'm putting together a TBI system with 4bbl and EBL, but as they've already found out, having all four injectors firing at idle is going to drown the motor at idle. I can get a progressive throttle body, but the EBL isn't setup to run it. I'm curous if Rbob is open to modify the code. If not I suppose I could design an inline module that would modify the 'secondary' injector pulse based on TPS position.