Converting to carb questions

[Modular2v]

if you want to buy a stealth let me PM me. . . i have one with less than 1000 miles on it i will sell to you!

 

[Modular2v]

It all comes down to airflow, pressure drop across the intake system and proper atomization of the fuel mixture.

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.

are you sure about that?

 

[jrichker]

are you sure about that?

Show me the record, I learn new stuff all the time. None of the sub 9 second SBF contenders that I have seen written about in MM&FF are carb cars.

 

[85_SS_302_Coupe]

Show me the record, I learn new stuff all the time. None of the sub 9 second SBF contenders that I have seen written about in MM&FF are carb cars.

There was a guy with a Fairmont running 9s with a turbo/carb hat...if fuel injection were so superior then Top Fuel/Funnycar would have gone that route by now wouldn't they? Or NASCAR? I'm not saying EFI isn't better in a lot of ways but you sort of made it out to be useless when compared to EFI.

 

[Modular2v]

Show me the record, I learn new stuff all the time. None of the sub 9 second SBF contenders that I have seen written about in MM&FF are carb cars.

I know some carb 306s running 9s all motor

 

[jrichker]

There was a guy with a Fairmont running 9s with a turbo/carb hat...if fuel injection were so superior then Top Fuel/Funnycar would have gone that route by now wouldn't they? Or NASCAR? I'm not saying EFI isn't better in a lot of ways but you sort of made it out to be useless when compared to EFI.

The last time I looked, the top fuel dragsters were running Hilborn fuel injection. NASCAR rules strickly define what goes into a race car. I am not familar with them, so it may be possible that EFI is excluded by the rule book.

Thes are some very interesting comments, but we are highjacking this guy's thread. Maybe a "Carb compared to EFI" thread would be a better use of time and attact more input. I will be glad to post my views in a new thread if you or someone else will start it.

 

[Modular2v]

fuel injection actually is used in top fuel, but it is direct port into the cylinders with NITRO

 

[1Bad88notch]

this is starting to look like another thread on the pros & cons of carb vs. EFI. The guy is just asking whats the best carb and intake for his setup.

 

[85_SS_302_Coupe]

I didn't want it to be a vs. thread, i just thought it was notable to defend what i felt was bashing it a little which might have swayed his move to carb. Truth is, if it was so useless compared to EFI then nobody would use it anymore. It's cheaper and it works if you know how to use it. Sorry if i lead all that to a hijacking...

 

[EMW150]

It all comes down to airflow, pressure drop across the intake system and proper atomization of the fuel mixture.

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.

I disagree. A properly built carbed setup will make more power than EFI. Look at the NMRA and the big weight penalties for running a carb. My theory is, while you may think the atomization process is sloppy, it's somewhat the opposite. The finer the fuel droplets, the better and more powerful the burn. EFI fires a spray directly before it enters the cylinder having very little time to mix with the incoming air. A carb however draws fuel from the bowl by air, through the long runners of the intake while the whole time it's mixing with incoming air and the mixture is getting finer droplets and more air creating a more powerful burn. Sorry for the hijack.

Check this out: http://www.pro-system.com/scoop92102.html

 

[Carb'dCobra]

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.

I know I'm kind of behind but just to reenforce his point. I left my Holley electric pump in because I was lazy and didn't want to have to pull my ps pump off. If you really want to keep your electric pump, you'll have to wire it yourself, that includes relays, fuses, etc, and run your own fuel lines ( I ran mine from the quick disconnects by the pass. side fenderwell). Also you'll need a carburetor fuel press. regulator (anywhere from 1-15lbs). I run mine around 7-8lbs but then again I'm on a highly modified motor with a 750cfm carb. Most likely your not an idiot like me and you like to keep your gas for a while, so I'd run a Holley 600-650 (at most)/vacuum secondary carb (no power valves, jets, etc./very easy to set up and very streetable) and at about 4.5-5lbs.

But of course the easiest way is to use the tank and lines from an 84 or earlier fox chassis and use a mechanical pump.

No matter what you do, it's still a 5.0 and it'll still rock some s***.
Good luck.

 

[emeraldcoupe]

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

are those rear wheel numbers? i'm building the same exact engine except i'm using a set of ported 70 351w heads. i'd be plenty happy with those numbers.

 

[Dean85GT]

No thats what the motor makes at the flywheel

 

[Modular2v]

are those rear wheel numbers? i'm building the same exact engine except i'm using a set of ported 70 351w heads. i'd be plenty happy with those numbers.

Your car will be making about 25 more hp with those heads over a set of e5s!

 

[stangman8825]

so if I use the older style timing cover and a mechanical fuel pump...what do i need to do with the tank?

And does my E cam have the lobe to run the fuel pump?

 

[EMW150]

so if I use the older style timing cover and a mechanical fuel pump...what do i need to do with the tank?

And does my E cam have the lobe to run the fuel pump?

You could install a pickup from an '85 carbed model in the tank or you may be able to modify the origional pickup I'm not sure. Also you need an eccentric that bolts on the cam gear of the timing set and don't forget the longer cam dowel pin.

 

[90_Red_LX]

The last time I looked, the top fuel dragsters were running Hilborn fuel injection. NASCAR rules strickly define what goes into a race car. I am not familar with them, so it may be possible that EFI is excluded by the rule book.

Thes are some very interesting comments, but we are highjacking this guy's thread. Maybe a "Carb compared to EFI" thread would be a better use of time and attact more input. I will be glad to post my views in a new thread if you or someone else will start it.

Again you hit it on the head jrichker. Nascar rules dicate mandantory use of a carburetor. Also they require iron blocks, and pushrod engines. Every single one of those teams would rejoice if EFI was allowed. So much more control of whats going into the motor. And you can bet your ass if they opened up aluminum blocks, efi, and some other rules chevy will sure as hell run the ls1, and if they open up OHC motors the 4v ford will sure as hell be there. Why the hell you think they still run 350 chevys, 351W fords, and w/e the hell mopar is?

 

[85_SS_302_Coupe]

Again you hit it on the head jrichker. Nascar rules dicate mandantory use of a carburetor. Also they require iron blocks, and pushrod engines. Every single one of those teams would rejoice if EFI was allowed. So much more control of whats going into the motor. And you can bet your ass if they opened up aluminum blocks, efi, and some other rules chevy will sure as hell run the ls1, and if they open up OHC motors the 4v ford will sure as hell be there. Why the hell you think they still run 350 chevys, 351W fords, and w/e the hell mopar is?

I'm no huge NASCAR nut, but i believe they all run a 358ci block....don't quote me but i believe so.