GM TBI on my 1970 360 duster

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dusterbd13

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ive been messing with GM TBI in 80's chevy trucks for a while now. Which means I have a bunch of spare parts and tuning equipment for these things. I almost have enough to build a complete system, if the inventory in my head matches my inventory on the shelf.

reason im looking at this is that im currently running an 850 double pumper that has been heavily modified. No choke, different air bleeds and idle passages, etc. I have problems with this carb, and have been seriously debating swapping it for an 800 CFM AVS from Edlebrock. at 400 bucks, i can probably build a TBI system for less, and have better drivability and economy to boot.

a few questions while i ponder this conversion:
1. Fuel lines. im currently running the stock 318 fuel lines size. i think its 3/16. might be wrong. i have no return line. Stock 70 tank and pickup. what do i do about the lines? is there a pickup that has a return line already built in, and then i can bend up a 5/16 feed line?
2. the car lays down 427 horse at the wheels. should i use the biggest throttle body i can get my hands on, or shoudl i go with a little smaller to keep air velocity and throttle response?
3. ignition. Currently im running an MSD box and rev limiter setup from an 80's winston cup car. Stock electronic distributor. The GM ECM can control the timing as well, so it would be stupid not to use it. any idea how to do this with a chrysler distributor?
4. should I? the car is built as a sleeper. looks all but stock at first glance. Very clean and uncluttered underhood and everywhere elso. Im worried that if i convert to EFI, all the extra wires and sensors will be a dead giveaway and ugly to boot. it aso only gets driving a couple of thousand miles a year. Mostly because it drives so bad.

anyway, goive me your thoughts.
Michael
 
1. I think the fuel lines are too small to feed your existing combo, with a killer carb or not. I would look at the non braided push style hose from Aeroquip, Russells, or Earls. The non braided stuff is still rated plenty high for what you are doing, is relatively inexpensive, and you should only need a few fittings to make it all happen. Is there an aftermarket pump for TBI that will support the HP you are making, or do you need to go to a high pressure pump and regulate down. I am thinking #2 is the better way to go
2. The biggest TBI for OE came on the 454 chevy. I would think it to be the best option, to feed 400HP. I concern it might be too small?
3. No idea on ingnition
4. Have you looked at finding or using one of the Holley Projection units? They had 2 and 4 bbl units, and both of these used a standard square bore pattern, as opposed to GM's 3 bolt triangle pattern. I would think the 4bbl unit would be far better for airflow and fuel supply capabilities, and all would contribute to stock appearance underhood.

Used Holley Projection on ebay, 182.50 currently
http://cgi.ebay.com/ebaymotors/Holl...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
 
the small block TBI was rated at 490 CFM stock, and the big block at 645.

with some mods and such, you can realistically pick up about 40-50 CFM over stock.

The pump is a concern, but it doesnt have to be large. TBI systems dont require a bunch of fuel pressure, just volume.
the best option would be runnig a bigger than needed pump, and an adjustable FPR at the TBI.

are the lines too small? ihave not noticed any starvation issues on the street, but havent had it at the track yet so...
you can onl;y run so hard on back roads.

ive thought about 4BBL pro-jection briefly. i dont know it, dont have any parts for it, and havent ever spent any time researching it. so thats why it hasnt really been an option. If i could run it with a GM ECM, and use GM sensors, i might do it.

the three bolt flange really sint a problem. If i wanted to spend money, guys make adapters. If i dont, i make my own out of oak or something.

Michael
 
Hi Mike, I was over here looking for a 318 stroker thread referenced on Moparts. I stumbled across your question, and I enjoy EFI discussions, so I joined so I could share my .02. Some other guys have responded while I’ve typed this, so some stuff is redundant. Oh, well.

The GM TBI is, IMHO, the best OEM system for low-cost retrofitting. There is a lot of performance tweaking that can be done to it and it is well-documented on the ‘net if you dig around (although some of the CFM ratings on the TBs things don’t always match up). Regardless of what TB units you use, you will most likely need to modify it for more airflow and also play with fuel pressure to get the right flowrate on fuel. These 2 items are done outside of the ECM’s realm of awareness and allow you to tweak a proper AF based on the MAP pressure the ECM sees (the controller only handles pulsewidth, so more pressure = more fuel).

1. ‘Standard’ Mopar fuel line size was 5/16, should be what you have. I have seen some fuel pickups with built-in return fittings, so see if one’s available for you’re a-body. I’m a C-body guy so I don’t know all the A-B-E parts that are out there. Try Paddockparts.com or Year One.
2. For your HP level a 454 TB unit is the minimum, and it still might not be enough. A 305/350 TB will NOT flow enough air or fuel in stock config. There are modified 305/350TBs out there, but I think a 454 is a safer bet (and it may still need to be modified for more airflow).
305/350 TB has 1 11/16” bores, a 454 has 2” bores. According to the calculator on the Megasquirt website, a stock 454 TB is good for just under 300 hp (I think GMs 454s were rated at 270hp net?).
http://www.megamanual.com/v22manual/minj.htm#throttle

Based on crude calculations, you need approx 106 lb/hr injectors for 425 hp. But you have that at the wheels, so you need even larger injectors. Early 454 TBs have 90lb injectors run at 12-13 PSI, and that is the TBI unit you will need to start with. Late 454 TBs have smaller injectors run at 30 PSI to give the same flowrate, and you can’t raise the pressure on these injectors high enough to feed your needs. I would recommend an early 454 TB with the 90 lb injectors, then change the regulator spring to the late-unit 30 PSI spring. This should get those injectors to about 136 lb each, and should be enough for around 450 hp.

If you can’t find a late 454 30-lb return spring, you could put an adjustable regulator in the return line or modify your existing regulator. This is fairly straightforward and is noted in some of the links at the end.

You should get a spreadbore intake to run a 454 TBI, the blades are too wide for a standard square 4-V plenum area. There is a Trans-Dapt plate that nicely installs one in the larger rear section of the plenum. You could make one (as I have done in the past) but it is SO much nicer to buy it and start bolting stuff on (place a value on your time!).

Here’s a guy that modifies TBI units:
eBay Store - Xtremefi GM TBI V6 5.0 5.7L 7.4L BBC, LT1 LT4 52mm 54mm 58mm LT-1


3. I don’t have good info on the distributor, but look for the ‘DUI’ distributor, which uses an HEI module, it might be what you need. Generally-speaking, ECU-controlled timing can be a huge benefit, but if the GM ECU will still operate properly with no feedback on ignition you could simplify things by staying with what you have. However, if the GM strategies monitor ignition activity, and it sees activity different from what it is commanding, it may go into a limp-mode?
4. TBI is undoubtedly the most stock-looking EFI setup to meet your visual goals. Yes, you need to add sensors and wiring, but these can be integrated tastefully if you put the effort in. Trying to throw a GM pickup harness as-is into the Mopar engine bay will surely be ugly. Plan on shortening and extending wires as needed and putting new loom on it at a minimum. No, you can’t completely hide it, but you can make it blend in somewhat and look nice.


Here is one thing that could be an issue:
It sounds like you have a large-size cam, possibly with a lot of reversion. Your engine’s Volumetric Efficiency will surely differ from a mild, small-cam TBI engine, so there may be some ‘holes’ or flatspots when the GM power curve is not parallel to yours. Meaning, if your engine simply made 50% hp more than the GM, your power curves are proportional, so just flow more air and crank the fuel pressure up appropriately and the ECM maps work fine. However, if your engine comes on strong at 3000RPM, very few OEM EFI maps will fuel properly for that. If you have the ability to hack the GM ECU and change tables this is not a big issue. Also, a vacuum-referenced FPR could help out a little (it is explained in one of the links below).


EFI is not really cost-effective for a limited-use car of only a few thousand miles/year, but I truly believe once you get it installed and the bugs worked out you’ll want to drive your car much more often!



http://dynamicefi.com/4-INJUpgrade.php
http://marine-performance-parts.com/gmtbiperformance.aspx
http://dynamicefi.com/EBL_Flash.php
http://members.shaw.ca/betterthanyoutoo/how-to/fpr/fpr.htm
http://www.strokerengine.com/TBIkit.html
http://dynamicefi.com/EBL_Drawings.php
http://dynamicefi.com/TBI_Fueling.php
http://home.earthlink.net/~jcgebhart/msindex.html
 
fury fan said:
Hi Mike, I was over here looking for a 318 stroker thread referenced on Moparts. I stumbled across your question, and I enjoy EFI discussions, so I joined so I could share my .02. Some other guys have responded while I’ve typed this, so some stuff is redundant. Oh, well.

The GM TBI is, IMHO, the best OEM system for low-cost retrofitting. There is a lot of performance tweaking that can be done to it and it is well-documented on the ‘net if you dig around (although some of the CFM ratings on the TBs things don’t always match up). Regardless of what TB units you use, you will most likely need to modify it for more airflow and also play with fuel pressure to get the right flowrate on fuel. These 2 items are done outside of the ECM’s realm of awareness and allow you to tweak a proper AF based on the MAP pressure the ECM sees (the controller only handles pulsewidth, so more pressure = more fuel).

1. ‘Standard’ Mopar fuel line size was 5/16, should be what you have. I have seen some fuel pickups with built-in return fittings, so see if one’s available for you’re a-body. I’m a C-body guy so I don’t know all the A-B-E parts that are out there. Try Paddockparts.com or Year One.
2. For your HP level a 454 TB unit is the minimum, and it still might not be enough. A 305/350 TB will NOT flow enough air or fuel in stock config. There are modified 305/350TBs out there, but I think a 454 is a safer bet (and it may still need to be modified for more airflow).
305/350 TB has 1 11/16” bores, a 454 has 2” bores. According to the calculator on the Megasquirt website, a stock 454 TB is good for just under 300 hp (I think GMs 454s were rated at 270hp net?).
http://www.megamanual.com/v22manual/minj.htm#throttle

Based on crude calculations, you need approx 106 lb/hr injectors for 425 hp. But you have that at the wheels, so you need even larger injectors. Early 454 TBs have 90lb injectors run at 12-13 PSI, and that is the TBI unit you will need to start with. Late 454 TBs have smaller injectors run at 30 PSI to give the same flowrate, and you can’t raise the pressure on these injectors high enough to feed your needs. I would recommend an early 454 TB with the 90 lb injectors, then change the regulator spring to the late-unit 30 PSI spring. This should get those injectors to about 136 lb each, and should be enough for around 450 hp.

If you can’t find a late 454 30-lb return spring, you could put an adjustable regulator in the return line or modify your existing regulator. This is fairly straightforward and is noted in some of the links at the end.

You should get a spreadbore intake to run a 454 TBI, the blades are too wide for a standard square 4-V plenum area. There is a Trans-Dapt plate that nicely installs one in the larger rear section of the plenum. You could make one (as I have done in the past) but it is SO much nicer to buy it and start bolting stuff on (place a value on your time!).

Here’s a guy that modifies TBI units:
eBay Store - Xtremefi GM TBI V6 5.0 5.7L 7.4L BBC, LT1 LT4 52mm 54mm 58mm LT-1


3. I don’t have good info on the distributor, but look for the ‘DUI’ distributor, which uses an HEI module, it might be what you need. Generally-speaking, ECU-controlled timing can be a huge benefit, but if the GM ECU will still operate properly with no feedback on ignition you could simplify things by staying with what you have. However, if the GM strategies monitor ignition activity, and it sees activity different from what it is commanding, it may go into a limp-mode?
4. TBI is undoubtedly the most stock-looking EFI setup to meet your visual goals. Yes, you need to add sensors and wiring, but these can be integrated tastefully if you put the effort in. Trying to throw a GM pickup harness as-is into the Mopar engine bay will surely be ugly. Plan on shortening and extending wires as needed and putting new loom on it at a minimum. No, you can’t completely hide it, but you can make it blend in somewhat and look nice.


Here is one thing that could be an issue:
It sounds like you have a large-size cam, possibly with a lot of reversion. Your engine’s Volumetric Efficiency will surely differ from a mild, small-cam TBI engine, so there may be some ‘holes’ or flatspots when the GM power curve is not parallel to yours. Meaning, if your engine simply made 50% hp more than the GM, your power curves are proportional, so just flow more air and crank the fuel pressure up appropriately and the ECM maps work fine. However, if your engine comes on strong at 3000RPM, very few OEM EFI maps will fuel properly for that. If you have the ability to hack the GM ECU and change tables this is not a big issue. Also, a vacuum-referenced FPR could help out a little (it is explained in one of the links below).


EFI is not really cost-effective for a limited-use car of only a few thousand miles/year, but I truly believe once you get it installed and the bugs worked out you’ll want to drive your car much more often!



http://dynamicefi.com/4-INJUpgrade.php
http://marine-performance-parts.com/gmtbiperformance.aspx
http://dynamicefi.com/EBL_Flash.php
http://members.shaw.ca/betterthanyoutoo/how-to/fpr/fpr.htm
http://www.strokerengine.com/TBIkit.html
http://dynamicefi.com/EBL_Drawings.php
http://dynamicefi.com/TBI_Fueling.php
http://home.earthlink.net/~jcgebhart/msindex.html
Click to expand...


That is one helluva a first post!!!:cheers:
 
Now, this is funny. I had a GM TBI on my '70 360 Duster about 8 or 9 years ago. I wasn't able to sort out all of the issues before my EFI guru left town. We figured out after the fact, that most of my issues came from using a lean-burn distributor. We had also set up a dual TBI on a 350 in a '72 Chevelle using a truck ECM.
I'll try to post some more info later(when I'm not at work).
 
dusterbd13 said:
2. the car lays down 427 horse at the wheels. should i use the biggest throttle body i can get my hands on, or shoudl i go with a little smaller to keep air velocity and throttle response?
Click to expand...

You're not going to find a TBI that's too big in a junkyard. I've seen motors that put 200 hp to the wheels get starved for air with a stock 350 throttle body. It would ruin the sleeper effect, but I doubt two 350 TBIs on a dual quad manifold would be too much for this motor.

I presume you've got some way of hacking the stock ECU? A speed density computer that's used to a truck motor that revs to 4,000 RPM is not going to know what to do on a high winding screamer, so you're going to have to teach it.

3. ignition. Currently im running an MSD box and rev limiter setup from an 80's winston cup car. Stock electronic distributor. The GM ECM can control the timing as well, so it would be stupid not to use it. any idea how to do this with a chrysler distributor?
Click to expand...

Lean Burn distributor + 7 or 8 pin HEI module. I have this combination on my Dart. Note that the engine will run if the pick-up is wired backwards, but timing will be all over the place. I'd keep the MSD box though.

4. should I? the car is built as a sleeper. looks all but stock at first glance. Very clean and uncluttered underhood and everywhere elso. Im worried that if i convert to EFI, all the extra wires and sensors will be a dead giveaway and ugly to boot. it aso only gets driving a couple of thousand miles a year. Mostly because it drives so bad.

anyway, goive me your thoughts.
Michael
Click to expand...

What good is a car with a mean sucker punch if you can't take it out and find suckers to punch? It sure sounds as if it needs some better tuning, whatever option you chose.
 
I have a 670 holley projection system forsale.Almost 2 complete units,actually.If you are interested,please pm me,ill take 350.00 plus shipping for them.

340.jpg


342.jpg


343.jpg
 
thanks for the distributor info.

as far as the ECM and tuning of it, that is actually the least of my worries. I have been burning custom tunes and datalogging for a little while on my FSP prepped s10. actually about to do a SFI and DIS swap to it, which will require a LOT of computer hacking.

Any ideas on how to plumb the return to the tank?

Also, the 454 tbi setup, though hard to find, would be the minimum of the way to go. still would be a little undersized, even after spacingthe injector pod, knife edging the blads and shaft, and unshrouding. but the statement was made that it will hit the squarebore intake. which is bad.

a fella mentioned a little ways back that he had a setup on his car like this. can i see some more info?

Im still really debating this. i know that the eddy carb will be easier, quicker, and more in line with the sleeper image. but i just cant get the EFI idea out of my head.

either which way, this holley has to go. im sick of it. never liked holleys in the first place, and this one is the last staw for me. anyone wanna trade for a 750-800 eddy?

Michael
 
With the lower cfm ratings, these sound like they might be nice for a dual quad setup. What kind of issues would one encounter when trying to run 2 of them?
 
prblems:

synching the throttle shafts together accurately.
injector driver in the ECM may not be able to support the load of the 4 injectors. may have premature failure.
tuning.
gattintg theIAC and MAP sensors to read accurately.

should be pretty easy to sort out these issues, except for the injector driver.
 
You cain’t be havin’ no trubbles wit a Holley, Holleys is best! Joking aside, the 750 AFB Eddy has a bad reputation, I’ve seen some discussions on Moparts about it. I have a 750 myself that makes me hate my car – another reason I’m working on EFI.

See if there’s an A-body sending unit that already has a return fitting in it, visit Paddockparts or YearOne. Also visit this thread, there’s some info on the return fitting possibilities.
http://www.cbodydrydock.com/forum_viewtopic.php?6.89276

If you can hack the GM ECU, you’re a couple steps ahead already. One of the links I posted earlier is for a source for running 2 TBI units from 1 GM ECU. Could run a 4-V Holley TBI that way, too. Holley’s system was known for less-than-ideal ECUs, and their TBI parts are proprietary, so parts aren’t as easily found like for GM TBs.

Here’s a layout of the throttle bores. Red is Carter AVS, yellow is a smallblock GM TBI, blue is a Dodge Magnum V8 TB unit (which has 2” bores like a 454 unit). Shows that these are not real friendly with a squarebore plenum.
plenumoverlay.jpg
 
why not rotate the TBI so the bores are in the corners of the manifold? if were making an adapter, shouldnt be too hard. the 2.8 s10's had em skewed like that as well.

wanna reference the threads on moparts for me? id like to see those. might help me make up my mind.
 
Sorry for the delayed reply, for some reason my subscription didn't notify me. ???

I considered turning a TBI on an angle as you suggested, but you'd have to route the throttle cable to match, which might require a large radius in the cable, and would probably require a cable for throttle kickdown (rod linkage would probably be a PITA to make work).

The bigger problem, IMHO, is that you now have fuel/air mix aimed toward one side of the manifold, and aimed toward a plenum wall. I think that's asking for wierd tuning trouble there.

For the 750 Eddy issues:
The Moparts board will now only let you search back thru 1-year maximum, so it's becoming a lost hope to get info out of there. The threads are still there and supposedly a websearch can find them, though.

Here's are 2 I saved links to:
http://board.moparts.org/ubbthreads...nswer&Thread=5191306&partnumber=1&postmarker=
http://board.moparts.org/ubbthreads...nswer&Thread=5428740&partnumber=1&postmarker=
 
The return is easy - I just drilled the side of the tank and put in a bulkhead fitting with a gasket. You can also do this to the sending unit or filler neck, probably easier.
 
Oklacarcollecto said:
I kept passing these up because of what looks like a return line.

Another picture.
Click to expand...
I bought one that looks just like oklacarcollecto for my Dart. It was ~$60 from 1A Auto about 6 mo.s ago via ebay. I have seen for ~$45. since. The outlet measures 3/8" OD and return 1/4" OD. Return is probably for emissions, but should work. Projection specs <4 psi return drop. On my 65 Newport, I drilled my sender and installed a fitting and O-ring as MadScientistMike suggests. No need to molest your tank and much safer.

Don't focus on fuel pump pressures. They are positive displacement pumps. Max pressure is where you motor stalls. The external Ford type ca 1990's works for either throttle body (~20 psi) or EFI (~60 psi). Many manufacturers, similar look. I got a new one off ebay for ~$25 recently. Listed for V8 Mustang. Auto Parts usually sell for ~$80 w/ lifetime warranty. You need a 3/8" line to the pump inlet, then 5/16" is OK for most, maybe not for >500 Hp. Projection says to mount near the tank, but I moved to the engine bay so easier to replace on the road (carry a spare), and no issues. You'll know if it cavitates. Even when running fine it makes noise so mount w/ rubber isolators if a driver car.
 
dusterbd13 said:
thanks for the distributor info.

as far as the ECM and tuning of it, that is actually the least of my worries. I have been burning custom tunes and datalogging for a little while on my FSP prepped s10. actually about to do a SFI and DIS swap to it, which will require a LOT of computer hacking.

Any ideas on how to plumb the return to the tank?

Also, the 454 tbi setup, though hard to find, would be the minimum of the way to go. still would be a little undersized, even after spacingthe injector pod, knife edging the blads and shaft, and unshrouding. but the statement was made that it will hit the squarebore intake. which is bad.

a fella mentioned a little ways back that he had a setup on his car like this. can i see some more info?

Im still really debating this. i know that the eddy carb will be easier, quicker, and more in line with the sleeper image. but i just cant get the EFI idea out of my head.

either which way, this holley has to go. im sick of it. never liked holleys in the first place, and this one is the last staw for me. anyone wanna trade for a 750-800 eddy?

Michael
Click to expand...

I'm going the Bone Yard path. I have a TBI, wiring harness, computer from a 90 GMC. I know that the E-Prom will need reprogrammed.

What systems for data logging and programming do you use?
 
i use tunerproRT for datalogging and editing. also use a burn2 for chip burning. right now, i have neither working properly....


if you google tunerproRT, look for the new version5. it has some autotune stuff written intop it. whole lot easier.....
 
did you change the dist? can a pertronics feed the gm module
 
pertronics wont feed the module. youll have to get a setup like the GM's installed. somewhere i fould some info, onece.
 
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