Converting to carb questions
- Thread starter stangman8825
- Start date
Dean85GT
New Member
Dean85GT
New Member
I have a fresh rebuilt motor with 9.5:1 compression, slightly ported (on exhaust side) e5 heads, a trickflow cam, weiand stealth intake, and a holley 650cfm carb and my motor makes 270hp and 330tq. With a mechanical fan, stock headers, offroad x and stock 2.25inch tailpipes
A word of warning on EFI to carb swaps: don’t expect to pass emissions in any state that does comprehensive smog inspections, because it won’t happen. You won't get any more power from a carb than you will from EFI.
Doing the swap: You must know how to read electrical diagrams and wire circuits properly to do the swap. Don’t take shortcuts or cut corners in the fabrication of the electrical or mechanical assemblies. If you do NASCAR quality work, the car will look good, run good and be as reliable as a carb’d car can be. Take pride in a job done with excellence.
Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. Either go full EFI or use a tank/fuel pump/fuel lines out of an 84 or earlier Stang. Fabricating your own setup is possible but there are some snags to overcome.
Do not attempt to leave the EFI in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.
If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.
You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump.
You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.
While you are at the electrical part, you'll need a Durspark or similar ignition system. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Durspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information.
Doing the swap: You must know how to read electrical diagrams and wire circuits properly to do the swap. Don’t take shortcuts or cut corners in the fabrication of the electrical or mechanical assemblies. If you do NASCAR quality work, the car will look good, run good and be as reliable as a carb’d car can be. Take pride in a job done with excellence.
Do not use an EFI in tank fuel pump with a carb. You will never get the pressure/flow regulated properly. Either go full EFI or use a tank/fuel pump/fuel lines out of an 84 or earlier Stang. Fabricating your own setup is possible but there are some snags to overcome.
Do not attempt to leave the EFI in place in an attempt to control either the electric fuel pump or ignition. Doing so qualifies you for the “Road Kill Mechanics Award”.
If you try to use your current tank, you will need to pull the fuel pump out and fabricate a pickup tube & strainer sock to replace the fuel pump. Or you can have a sump fabricated and welded onto you existing tank. Many welding shops will not weld fuel tanks because of the dangers involved if the tank isn't purged properly.
You will need an external electric fuel pump unless you change the timing cover for one with the mechanical fuel pump mount on it. Rip all the EFI wiring out, and the computer controlled fuel pump won't work. You will need to add a relay & switch and wire in the existing inertia switch for an external low pressure electric fuel pump.
You will need to run some new fuel feed lines or braided hose. The 3/8" aluminum tubing works well, but you will need a flaring tool and bending springs to fabricate the lines. Braided hose is easy to run and route, but is much more expensive. It is about $3.50-$4.00 a foot plus the end fittings, which are $3-$4 each. Fabricating hose assembles can be difficult, but anyplace that makes hydraulic hoses can do it for you for an extra charge. See http://www.amazonhose.com for more information.
While you are at the electrical part, you'll need a Durspark or similar ignition system. The EFI ignition depends on the EFI sensors to advance the spark. Rip out the TPS and MAP/Baro sensors and the computer will have no idea of the proper ignition timing for best performance. Running a fixed timing setting is only for test purposes or for a race track only car. Don't try it on the street: the results will not be nearly as good as a properly setup Durspark or equal. Crane makes a really nice distributor for non-EFI applications. . See http://www.cranecams.com/index.php?show=browseParts&lvl=4&prt=127 for more information.
Stealth intake with a Holley 600 double pumper and you'll be set. Right now i'm running a Victor Jr intake and a 650dp but i'm going to have heads and a higher lift cam than the E over the winter so it'll all match up better.
Funny thing about the intake choice....i was running a Stealth before i got this Vic jr, and contrary to everything i've heard and know about single plane vs. duel plane intakes, the Vic Jr just runs a hell of a lot better on my car than the Stealth ever did. It pulls harder throughout the RPM range. The only thing i've noticed is that the responsiveness of the carb is a bit softer, but that can be corrected with tuning.
Funny thing about the intake choice....i was running a Stealth before i got this Vic jr, and contrary to everything i've heard and know about single plane vs. duel plane intakes, the Vic Jr just runs a hell of a lot better on my car than the Stealth ever did. It pulls harder throughout the RPM range. The only thing i've noticed is that the responsiveness of the carb is a bit softer, but that can be corrected with tuning.
1Bad88notch
New Member
The Edlebrock performer rpm is also a good intake too, as far as carb goes i wouldnt go no bigger than a 650cfm, for fuel pump a holley blue pump would work fine.
If i were you and i was converting to carb, i'd go with a mechanical pump for now untill you get serious with the power. To do that you'd need to swap out your timing cover for one of the older ones with the opening for the mechanical pump....you could just run an electric inline pump which might be easier for you.
It all comes down to airflow, pressure drop across the intake system and proper atomization of the fuel mixture.woodsy said:only a matter of time before jrichker came inAnd to state definatively that a carb wont make any more power than EFI is silly
And yes, I know your carburetor qualifications
Every carb ever made depends on a venturi to provide a pressure drop to pull fuel out of the float bowl. That venturi represents a restriction to airflow. There is no way to pull fuel out of the float bowl, atomize it properly and have a consistent linear flow without the pressure drop across the venturi. The pressure drop not only sucks fuel out of the float bowl, but it helps atomize the fuel. That atomization process is somewhat sloppy. Many times I have watched the fuel being pulled out of the main metering circuit in various streams of fine droplets (good) and large drops (not good). Liquid fuel does not disperse well to all cylinders. It is a fact of life, just like the passage of time. With a venturi, there is a pumping loss which causes a reduction in volumetric efficiency. Volumetric efficiency is measure of the ability to fill the cylinder with the maximum possible amount of air/fuel mixture. In a naturally aspirated engine, that is 100%.
EFI does not depend on a pressure drop to pull fuel into the intake or help atomize the fuel. The ventrui and associated restriction of the intake airflow is eliminated. Instead EFI measures either air pressure or airflow along with air temperature, water temperature, RPM, and throttle position to calculate the amount of fuel needed. The calculation is much more precise than the simple mechanical process of a pressure drop across a venturi. Since a pressure drop across a venturi is not part of an EFI system pressurized injection is needed. The injectors are capable of consistently breaking the fuel into tiny droplets that flash to vapor and distribute themselves evenly in the individual intake ports. Couple the precision of the air/fuel measurement along with timed, pressurized injection of the fuel directly into the intake port, and you have a superior system.
Look at the top 9 second or less fox bodied drag cars: all of them are EFI of one type or another. I have not seen a twin turbo carb car among the top contenders.
Why is EFI better?
Superior air/fuel mixture management
Better atomization
Less pressure drop between the outside atmosphere and the intake valve, resulting in higher volumetric efficiency.
If you can present an engineering viewpoint that demonstrates carbs as better performers than EFI, I would like to hear it.
89-notchback
New Member
Im going carb myself also, for me it's more of a money issue, Fuel injection just cost more, plus i know more about carbs than injection,plus i allready have all of the stuff, I think they both have there ups and downs, but i agree with Jrichker, you should have some knowledge of wiring to do the job right, and fuel injection is definatly where it's at if you have the cash. Oh heres a fast carbed car for Jrichker 
allthough it's not a ford http://www.procharger.com/chevy_nova.shtml 
allthough it's not a ford http://www.procharger.com/chevy_nova.shtml 
