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carb to EFI conversion questions

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Old 06-12-2008, 01:22 AM   #1
SmallBlockFloyd
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Default carb to EFI conversion questions

Hi guys, i am just curious how many of you all have done a carbed to EFI conversion(1971 mustang). I am thinkin about doing an EFI conversion on my 351c, for the tunability&mileage gains. I was mainly curious with how you all routed your fuel return line. I was thinking about just using a high pressure line from the fuel return on the FPR, and run it back to the tank, add a nipple on the top of the tank, and just let it pour back into the tank by itself.

I just wanted to hear how everyone else did it, and any info, tips or what not to do'es. Did you use an intank fuel pump, or anexternal inline pump? Thanks guys, I appreciate the help.
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Old 06-12-2008, 02:19 AM   #2
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Default RE: carb to EFI conversion questions

check out jamesw pagehes got the simple fuel setup. you will need to get a 351w efi dist and 5.0 mass air computer setup and you can get an intake and power elbow etc from coast high performance.
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Old 06-12-2008, 04:43 AM   #3
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Default RE: carb to EFI conversion questions

Heres jamesw site http://www.midnightdsigns.com/james/
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Old 06-12-2008, 09:56 AM   #4
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Default RE: carb to EFI conversion questions

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ORIGINAL: rmodel65

check out jamesw pagehes got the simple fuel setup. you will need to get a 351w efi dist and 5.0 mass air computer setup and you can get an intake and power elbow etc from coast high performance.
Will a 351w dizzy fit a 351c? You may be looking at a custom setup because I don't think the windsor based kits will work for his engine. If it is just a fuel line routing questions then James W's site is a great source of info.
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Old 06-12-2008, 10:37 AM   #5
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Default RE: carb to EFI conversion questions

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ORIGINAL: SmallBlockFloyd

Hi guys, i am just curious how many of you all have done a carbed to EFI conversion(1971 mustang). I am thinkin about doing an EFI conversion on my 351c, for the tunability&mileage gains. I was mainly curious with how you all routed your fuel return line. I was thinking about just using a high pressure line from the fuel return on the FPR, and run it back to the tank, add a nipple on the top of the tank, and just let it pour back into the tank by itself.

I just wanted to hear how everyone else did it, and any info, tips or what not to do"es. Did you use an intank fuel pump, or anexternal inline pump? Thanks guys, I appreciate the help.
Different car, but I"ve been through it. I added the high pressure supply line to the fuel rails but used the OE carb hard steel supply line for the return. Rather than plumb it directly back into the tank, I tapped it into the filler pipe below the unleaded-only restriction (1979 car).

There is a little more to getting a successful fuel delivery system when you"re starting with a carbed tank and running an external EFI pump. EFI does not have anything comparable to the carburetor fuel bowl(s), and can easily hiccup/stumble/run rough/quit if the high pressure pump loses suction even briefly.

There isn"t much baffling in older fuel tanks, so slosh away from the fuel pickup under acceleration/braking/cornering needs to be addressed (note that this effect still matters even if you use a submerged EFI pump installation).

Anyway, I used a low pressure Holley pump and a regulator to feed an intermediate tank that holds a bit more than a quart and whose level is controlled by a Holley float bowl. This intermediate tank is relatively deep but narrow, and the EFI HP pump draws from that. Fuel slosh becomes a non-issue as long as the LP pump can do better than just keep up with the HP pump. I did get a fuel delivery stumble once - during a long sweeper toward the end of an autocrossrun when I let the fuel level get down to about 3 gallons in a flattish 18 gallon tank (fuel apparently sloshed away from the LP pump pickup for a long enough time that the HP pump managed to empty the intermediate tank). In more normal driving, I can drain the main tank down to about 1 gallon.

You should probably use an inertia switch to shut off the fuel pump(s) so that they do not continue to pump fuel out of a ruptured line should the car be involved in an accident.


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Old 06-12-2008, 12:49 PM   #6
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Default RE: carb to EFI conversion questions

The 351w efi distr does not work. I need to get a 460 TFI distr, and change the gear to a 351c gear. it fits just fine then. I was thinking about just dropping the tank, putting two new lines on it, one replacin the bent steel fuel line, and another to the top of the tank, to be a simple return. There should be enough pressure in the return line from the rails, to push the fuel up the line, allowing it to 'dribble/pour' back into the tank. I hadn't considered the baffles. I need to drop the tank, and clean it out anyways. It's old enough to merrit it. I may just put in an aeromotive baffled sump, and use that for feed/return aswell. If I went with a baffled sump, i don't imagine I would need a smaller supply pump intake, but i don't know.

If so, I may just get a cell, and strap that up underneath the car instead. I am mostly concerned with fuel line supply, along with injectors. I don't know what # i should run. I know the 5.0 runs on 19#'s, but I am running a 351c. I was thinking 24-30# injectors, which ever i could get the easiest. The next issue is, what angle should i place them at? I was giong to use an aluminum single plane intake, and then weld up a 'plenum' with a 65-75mm TB(again pending on avail/price). Does anyone have a recommended angle? Most injectors aim towards the valves, for cold start ability, and so forth so on. I plan on running megasquirt, which the way i understand is I will not be required to run a MAF, since it has all sorts of programming, along with an internal MAP sensor. So, I will just be running like IAC/IAT/CLT/TPS/o2 sensors.

Thanks for the help. I appreciate it guys.
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Old 06-12-2008, 12:55 PM   #7
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Default RE: carb to EFI conversion questions

Quote:
ORIGINAL: 68EFIvert

Quote:
ORIGINAL: rmodel65

check out jamesw page hes got the simple fuel setup. you will need to get a 351w efi dist and 5.0 mass air computer setup and you can get an intake and power elbow etc from coast high performance.
Will a 351w dizzy fit a 351c? You may be looking at a custom setup because I don't think the windsor based kits will work for his engine. If it is just a fuel line routing questions then James W's site is a great source of info.


The best option is to get a distributor from an EFI 460. This drops right in. The second best option is to use the distributor from an EFI 351W and change the gear to a 351C gear.

http://www.detomaso.nu/~thomast/efi/ you can do the swap with factory mass air parts the fuel lines are the biggest problems, then the intake in this link they used a 351w intake and modified it slightly

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Old 06-12-2008, 01:18 PM   #8
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Default RE: carb to EFI conversion questions

Yeah, I am not using a 351w intake. I am going to use a single plane carbed intake, and just tap it, then weld in injector bungs. it fits, flows almost as well, cheaper than buying efi intakes, and modifying them, then end up having seating issues with it mating to the heads/block. Just my opinion. The fuel lines are the only trouble i have atm. And I have it almost figured all out. now comes the paying for it :-p.
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Old 06-12-2008, 01:27 PM   #9
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Default RE: carb to EFI conversion questions

yeah i dont know how much this runs but heres a link thye have 351c intakes too http://www.coasthigh.com/Fuel%20Injection/spyder.htm
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Old 06-12-2008, 01:53 PM   #10
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Default RE: carb to EFI conversion questions

There's a formula for sizing injectors based on estimates of BSFC, HP, cylinder count, and (usually) an 80% or so duty cycle. But don't go too big, as injectors don't always work very well at very short pulse widths (< 1ms).

Don't worry about having enough pressure to push the bypassed fuel back to the tank. Worry about having large enough return tubing so that you won't get back pressure at the fuel rails when most of the fuel is being bypassed. I think if that happens, you run over-rich because the FPR can't reduce fuel rail pressure that's due to a restriction that is downstream of the FPR.

You'll still want as deep and narrow of a baffled sump as you can safely fit, and unless ALL of your hard driving is in a straight lineor you NEVER let the fuel level drop below some point (that you usually find out the hard way) a rear mounted sump will not be the answer. Consider that the combination of low fuel level plus either braking or cornering would keep fuel from refilling the sump and would run you into the same situation I got that once at auto-X, where the HP EFI pump still momentarily lost its suction.


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Old 06-12-2008, 04:52 PM   #11
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Default RE: carb to EFI conversion questions

Yeah. I was actually thinking of running a sump with a LP fuel pump intank, feeding to a fuel filter, then to a 1/4-1/2 gallon 'resivior' tank, that would then be fed to the HP fuel pump. That way, I should be able to effectively negate the effects of heavy braking/corning, and not feeding the injectors. I was also going to run a baffled sump, just for the benefit of the doubt.

As for the injector sizing formula, you mentioned 'BSFC'. I do not understand that abreviation. Could you elaborate please? I don't want to go too big, as I was thinking 24-30# injectors, 30 being the biggest I would go. I am staying n/a and fairly stock. I am planning to put a torquey cam in it, with 1800-5000 rpm range or so, giving me plenty of room to romp, while still being in the middle of the power band, while cruising down the highway *3.25's + .78 overdrive* should put me right at about 2500-2600 rpm's to turn 75 mph. I think 24# injectors will do just fine. I am to understand, that high impedance 24# injectors from ford would be 'blue tops'?

Thank you guys for all of your help, thoughts and insightful experience.
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Old 06-12-2008, 05:02 PM   #12
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Default RE: carb to EFI conversion questions

Well, double post time. I googled a injector size guide, and found a webpage that gave estimated calculations, based on simple numbers, such as power lvl, cylinders, et cetera. I plan on making about 325-350 horses with the cleveland, so it was sitting right around 28# injectors. So, I guess I should grab a pair of 30# injectors, and use those? I would run 24#'s but based on that chart, they should only be good to support about 310-320 ponies at the wheels. I don't want to max out my injectors, as that is bad on the entire system.

Anyone have any recomendations? Sorry for the double post, but thanks for all the help.
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Old 06-12-2008, 05:44 PM   #13
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Default RE: carb to EFI conversion questions

idk all the exact standards for injectors and the power levels but if your gonna start gathering swap parts, look for a lincoln mark 8 they have 24lb injectors from the factory
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Old 06-12-2008, 08:01 PM   #14
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Default RE: carb to EFI conversion questions

Alright, what colour are they, so i can compair the advertised # of injector to the colour of the top?
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Old 06-12-2008, 08:28 PM   #15
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Default RE: carb to EFI conversion questions

blue also efi 460 come with 24lbs iirc
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Old 06-13-2008, 06:04 AM   #16
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Default RE: carb to EFI conversion questions

Quote:
ORIGINAL: SmallBlockFloyd

Yeah. I was actually thinking of running a sump with a LP fuel pump intank, feeding to a fuel filter, then to a 1/4-1/2 gallon 'resivior' tank, that would then be fed to the HP fuel pump. That way, I should be able to effectively negate the effects of heavy braking/corning, and not feeding the injectors. I was also going to run a baffled sump, just for the benefit of the doubt.

As for the injector sizing formula, you mentioned 'BSFC'. I do not understand that abreviation. Could you elaborate please? I don't want to go too big, as I was thinking 24-30# injectors, 30 being the biggest I would go. I am staying n/a and fairly stock. I am planning to put a torquey cam in it, with 1800-5000 rpm range or so, giving me plenty of room to romp, while still being in the middle of the power band, while cruising down the highway *3.25's + .78 overdrive* should put me right at about 2500-2600 rpm's to turn 75 mph. I think 24# injectors will do just fine. I am to understand, that high impedance 24# injectors from ford would be 'blue tops'?

Thank you guys for all of your help, thoughts and insightful experience.
"BSFC" is Brake Specific Fuel Consumption, and is given in units of lbs per HP per hour. It's a measure of engine efficiency. Typical values might be 0.5 foraverage normally aspirated engines and 0.6-ish for forced induction. Injector sized should also give the pressure that the flow rate is associated with. If you're borderline between two injector sizes, go with the smaller and bump the fuel pressure up a little. IOW, an injector rated at 30# at 40 psi will flow almost 32 at 45 psi. The pump can handle long-term a little more than the 43-ish that I recall was common, but don't go overboard on that either.

I *think* the injectors that came with the Accel SuperRam on my 350 SBC are 30# and no, I don't think you'd want to go any bigger than that either. I went through all that math even though my calibration software had a "get started" routine that gave you a fuel map that was good for . . . getting the engine to start and run. I even called the tech line about the injector numbers, but it's been 10 years or so since then and I don't remember them off the top of my head. Fresh, that engine was probably upper 300's for HP and torque, so maybe it was aimed just a little higher on the rpm scale than what you're looking at. 10.2:1, AFR 190cc heads, hydraulic roller cam with mid two-teens intake duration and 0.5" lift if that helps.

I also think you can build an EFI engine up a little differently than a carbed motor. The EFI is so much better at the low rpm's that you don't have to compromise quite as much up top to still have good idle and off-idle behavior. You just can't get too wild with the cam unless you're running Alpha-N (I think that's what it's called).


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Old 06-13-2008, 06:38 AM   #17
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Default RE: carb to EFI conversion questions

If you are going to use a Mega Squirt, then why not a low impadence say in a #42? Will the MS not support these? Sumitt sells sumps thatcan be installed in an old style tank. You will need some good wellding skills, but these seem to work well (unless you get smacked in the rearend). Adequate fuel delivery is a must also, so the proper fuel pump size is an absolute. Like Norm says, you can get some serious HP out of one of these and it will remain very mild mannered.Heres how I done mine.
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Old 06-13-2008, 01:00 PM   #18
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Default RE: carb to EFI conversion questions

(horsepower * BSFC) / (# of injectors * duty cycle) = lb/hr injectors needed. duty cycle is usually 80% or .8 and BSFC for a typical n/a engine is around .5, if it's tuned really well, with an efficient engine, then .45ish. for a Cleveland with stock heads etc .5 BSFC if tuned right is a good value to use.
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Old 06-14-2008, 12:55 AM   #19
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Default RE: carb to EFI conversion questions

Thanks for all the help guys. I figured up a bit. I am going to run 24# blue tops from a 460, and I am going to run a sump, with an inline low pressure pump, then a fuel filter which is feeding to a 'swirl pot', or 'accumulation tank', that i am going to bolt/screw to the pass. fender skirt(wheel well), with four -8an nipples on it. the swirl pot is going to be 8"tall,6wide,4thick, and after figuring it will be 3.8x5.8x7.3 for the fuel return nipple, it will hold aprox 7/10th's of a gallon of gas.

The reason being it will have more than plenty fuel to feed the injectors, incase of a 'slosh' away from the mild pump. After the swirl pot, I am going to run a high pressure pump (55psi, yeah it's high but I couldn't find any pumps i liked around 40-45psi, so i will detune this one down to about 45-50psi) and should be good. I don't want to run 42# injectors because they are too big. i couldn't even use them. Megasquirt can run both high and low impedance, but I couldn't find anything i was satisfied with. I /could/ buy up two 'sets' of 'green tops' from the 2.3T cars(30# low imp. injectors), but i decided that with what I was running at the time being, 24# would be fine, and I can always step up injectors very easily.

I know the 'swirl pot' is a bit 'big', but i am using it to prevent vapor locking the system aswell, as it drains back to the filler neck onthe tank, which i am installing a T on. Then the drain back from the fuel rails will drain into the swirl pot i have, until it hits the 'overflow' height, and drains back into the tank. I just need to setup both pumps on a relay and setup a 'kill switch' so if there is a collision it will shut itself off. Then, I just need to get everything. The biggest pita is going to be getting everything set up and i just get this feeling that building my own fuel/spark maps for the cleveland are going to be a blast... a blast right into angryville...

Thank's for all the help and recommendations, James.
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Old 06-14-2008, 12:55 AM
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