EFI or carb
04-07-2011, 04:07 PM
#23
http://www.carcraft.com/techarticles...ion/index.html
Found this gives alot of good points for both. I dont care either way i like fuel injection and i can tune a carb.
Found this gives alot of good points for both. I dont care either way i like fuel injection and i can tune a carb.
04-07-2011, 05:48 PM
#24
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
Ok, so you can quote someone in a book who makes a series of generalized statements, but has no scientific data or explanation to back it up. Saying that EFI has better control over fuel curves is 1 thing, but saying HOW it does that is another thing entirely. And that makes his statements true because why? Even engineers are wrong, and arguably they are wrong much of the time and can't allow their egos to let them admit that they're wrong. I work in the engineering field with engineers, who sometimes are wrong more often than they're right. Designers(who are mostly not engineers) are the ones who do much of the actual designing, because what the engineer tells them to design while great on paper, doesn't always work in the real world.
Automotive engineers are arguably some of the worst in that regard. How many decades were they ignoring performance engine builders and producing engines that generated terrible power levels and got terrible mileage in order to clean up emissions? Only to, decades later, build production engines like high performance engines(the way performance engine builders told them to in the first place), and lo and behold the power and mileage got way better, and they produced low emissions.
You have to be careful when you listen to engineers sometimes, since "dumb engineer" jokes aren't necessarily without warrant. Many of them spend more time in a lab or an office than they do actually building and testing. It's one thing to believe something is true because you read it in a textbook, it's another to actually go out and test those theories and find out what works and what doesn't. And in that regard, in high end racing applications that have different induction systems tested(carb vs EFI), the carb setups make better power more often than the EFI setups. Based on that data alone there's obviously something going on that's causing carbs to make more power.
While some of what was stated is accurate, such as manifold distribution and dry flow manifold design(which has advantages and disadvantages), some of it is outright wrong. Carbureted engines have been proven to be FAR more detonation resistant than EFI engines, for the reasons I stated in my previous post. Wet flow manifolds plus the Joule-Thomson effect, combined with better fuel distribution, means carbureted engines are far less likely to detonate under the same conditions, tune and on the same engine.
Some of what he states is just plain not accurate. Like I stated, the emulsion system in a carburetor is there to account for changes in load and rpm to deliver the proper amount of fuel. Air and fuel both flow through the system, air is less dense and more reactive than fuel in that circuit. But properly sizing and locating the emulsion, jetting and air bleeds, along with venturi size and booster design, you can develop a carburetor that delivers the proper AFR over the entire range of load and rpm.
Carbs can be run with blowers just fine, and actually run FAR better with blowers than EFI, again because of the wet flow manifold design. Blower carbs are properly calibrated to account for the additional air flow, and because the fuel in the manifold absorbs heat energy, it acts like an evaporative cooler(because it is). In fact, blow-through carb blower engines can on the same engine and with the same fuel octane, run similar boost pressures WITHOUT an intercooler, than the same engine with EFI can run WITH an intercooler. The fuel flowing through the manifold alone generates a similar adiabatic efficiency for cooling the incoming charge that an air-water intercooler can. And carb'd blower engines with intercoolers can run ungodly amounts of boost on pump fuel. If you don't believe me, go read on ProCharger's site, they list the boost pressure vs compression ratio you can run for a given octane. And they clearly state carb'd engines being able to safely run HIGHER boost levels WITHOUT intercooling that EFI can WITH intercooling. http://www.procharger.com/faq.shtml#5 But hey, they only build superchargers used on some of the fastest blower cars on the planet, so what do they know.
Of course, properly setting up a carb'd blower engine is another matter entirely, and is much less forgiving.
As far as fuel slosh affecting carburetors, that depends on how the carb is set up. There are floats and baffles available for carbs to account for g forces under high loading conditions. So that's not an issue.
And this.....
"The biggest compromise here [carburetors] is that, other than at idle where the mixture screws have enough authority to change things, we are locked to one flow ratio of air to fuel for the primary circuit and one ratio for the secondary circuit, if so equipped. This means tuning a carburetor often boils down to a compromise of desired air/fuel ratios between cruise, light throttle, and wide open throttle. With crude adjustments at best to control transition and no real way to adjust for nonlinear performance across a wide RPM range, there is room for improvement. Additionally, since actual fuel flow is proportional to air velocity in the venturi rather than actual air mass flow, air/fuel ratios can change slightly with changes in ambient conditions. The term 'good enough' works for many racers, but leaves a lot to be desired on a daily driven car expecting good economy and emissions. (19-20)"
...and this statement....it makes me want to slap my forehead with an anvil. Does this guy know anything about how a carburetor works or how airflow affects fuel flow AT ALL?
First of all, fuel flow is NOT proportional to air flow in the venturi, that's why carburetors HAVE air bleeds and emulsion(invented by Stromberg a century ago), because fuel flow is ENTIRELY non linear and non proportional. Fuel flow is actually EXPONENTIAL to air flow, in other words as air flow through the venturi increases linearly, fuel flow increases EXPONENTIALLY, NOT proportionally. The purpose of the air bleeds an emulsion, is in working with main fuel well levels, to introduce air into the main fuel supply to lean out the fuel mix under increasing air flows as well as to reduce booster signal to prevent over fueling under increasing air flow. THAT'S the real guts inside a carburetor. The combination of jetting, main well sizing, fuel level, emulsion size and placement, air bleed sizing, venturi sizing and booster design and placement, all work together to ensure proper fuel flow for the given level or air flow across all ranges of rpm, load and throttle.
Now, since carb's do respond to air flow VELOCITY and not necessarily mass, yes, AFR can change some with differing atmospheric conditions. But not as much as people think. That air flow generates pressure in the booster....atmospheric pressure on the fuel in the bowl and on the air bleeds pushes fuel through the main circuit and air through the emulsion circuit. So a carb is really just responding to changes in PRESSURE and not necessarily air flow velocity(which generates that pressure). The nature of the emulsion system and boosters will determine how much the carb is effected by changing atmospheric conditions. But again, remember that engines don't really respond to fueling changes of as much as 3-5%....so while the AFR may change somewhat, it's unlikely to be enough to matter.
My setup generally changes by about 0.5 AFR at most across 4,000ft of elevation change. So if I'm 12.5:1 at WOT and 6k rpm at high altitude, at ~ sea level it's 13:1. It's unlikely there's more than 1% power gains to be had by recalibrating. On a competitive race car it can matter, so you'd want to rejet, but on a street car it doesn't.
EFI has it's advantages and disadvantages. Carburetion has it's advantages and disadvantages. But most of what people believe about both is the same old information that people have been accepting as gospel truth for decades. So what if it's in a book by some guy? So what if that's what "all the engineers" say.
Remember too that the greatest scientific minds of the world all agreed for centuries that the world was flat, the sun revolved around the Earth, and big rocks fell faster than small rocks. Everyone believed it to be true, everyone KNEW it to be true. And anyone who disagreed with them was laughed at and called crazy. But it turns out those crazy guys were correct. Because they did something that everyone else didn't....they actually went out and TESTED those theories. They gathered data and looked at the evidence.
Automotive engineers are arguably some of the worst in that regard. How many decades were they ignoring performance engine builders and producing engines that generated terrible power levels and got terrible mileage in order to clean up emissions? Only to, decades later, build production engines like high performance engines(the way performance engine builders told them to in the first place), and lo and behold the power and mileage got way better, and they produced low emissions.
You have to be careful when you listen to engineers sometimes, since "dumb engineer" jokes aren't necessarily without warrant. Many of them spend more time in a lab or an office than they do actually building and testing. It's one thing to believe something is true because you read it in a textbook, it's another to actually go out and test those theories and find out what works and what doesn't. And in that regard, in high end racing applications that have different induction systems tested(carb vs EFI), the carb setups make better power more often than the EFI setups. Based on that data alone there's obviously something going on that's causing carbs to make more power.
While some of what was stated is accurate, such as manifold distribution and dry flow manifold design(which has advantages and disadvantages), some of it is outright wrong. Carbureted engines have been proven to be FAR more detonation resistant than EFI engines, for the reasons I stated in my previous post. Wet flow manifolds plus the Joule-Thomson effect, combined with better fuel distribution, means carbureted engines are far less likely to detonate under the same conditions, tune and on the same engine.
Some of what he states is just plain not accurate. Like I stated, the emulsion system in a carburetor is there to account for changes in load and rpm to deliver the proper amount of fuel. Air and fuel both flow through the system, air is less dense and more reactive than fuel in that circuit. But properly sizing and locating the emulsion, jetting and air bleeds, along with venturi size and booster design, you can develop a carburetor that delivers the proper AFR over the entire range of load and rpm.
Carbs can be run with blowers just fine, and actually run FAR better with blowers than EFI, again because of the wet flow manifold design. Blower carbs are properly calibrated to account for the additional air flow, and because the fuel in the manifold absorbs heat energy, it acts like an evaporative cooler(because it is). In fact, blow-through carb blower engines can on the same engine and with the same fuel octane, run similar boost pressures WITHOUT an intercooler, than the same engine with EFI can run WITH an intercooler. The fuel flowing through the manifold alone generates a similar adiabatic efficiency for cooling the incoming charge that an air-water intercooler can. And carb'd blower engines with intercoolers can run ungodly amounts of boost on pump fuel. If you don't believe me, go read on ProCharger's site, they list the boost pressure vs compression ratio you can run for a given octane. And they clearly state carb'd engines being able to safely run HIGHER boost levels WITHOUT intercooling that EFI can WITH intercooling. http://www.procharger.com/faq.shtml#5 But hey, they only build superchargers used on some of the fastest blower cars on the planet, so what do they know.
Of course, properly setting up a carb'd blower engine is another matter entirely, and is much less forgiving.
As far as fuel slosh affecting carburetors, that depends on how the carb is set up. There are floats and baffles available for carbs to account for g forces under high loading conditions. So that's not an issue.
And this.....
"The biggest compromise here [carburetors] is that, other than at idle where the mixture screws have enough authority to change things, we are locked to one flow ratio of air to fuel for the primary circuit and one ratio for the secondary circuit, if so equipped. This means tuning a carburetor often boils down to a compromise of desired air/fuel ratios between cruise, light throttle, and wide open throttle. With crude adjustments at best to control transition and no real way to adjust for nonlinear performance across a wide RPM range, there is room for improvement. Additionally, since actual fuel flow is proportional to air velocity in the venturi rather than actual air mass flow, air/fuel ratios can change slightly with changes in ambient conditions. The term 'good enough' works for many racers, but leaves a lot to be desired on a daily driven car expecting good economy and emissions. (19-20)"
...and this statement....it makes me want to slap my forehead with an anvil. Does this guy know anything about how a carburetor works or how airflow affects fuel flow AT ALL?
First of all, fuel flow is NOT proportional to air flow in the venturi, that's why carburetors HAVE air bleeds and emulsion(invented by Stromberg a century ago), because fuel flow is ENTIRELY non linear and non proportional. Fuel flow is actually EXPONENTIAL to air flow, in other words as air flow through the venturi increases linearly, fuel flow increases EXPONENTIALLY, NOT proportionally. The purpose of the air bleeds an emulsion, is in working with main fuel well levels, to introduce air into the main fuel supply to lean out the fuel mix under increasing air flows as well as to reduce booster signal to prevent over fueling under increasing air flow. THAT'S the real guts inside a carburetor. The combination of jetting, main well sizing, fuel level, emulsion size and placement, air bleed sizing, venturi sizing and booster design and placement, all work together to ensure proper fuel flow for the given level or air flow across all ranges of rpm, load and throttle.
Now, since carb's do respond to air flow VELOCITY and not necessarily mass, yes, AFR can change some with differing atmospheric conditions. But not as much as people think. That air flow generates pressure in the booster....atmospheric pressure on the fuel in the bowl and on the air bleeds pushes fuel through the main circuit and air through the emulsion circuit. So a carb is really just responding to changes in PRESSURE and not necessarily air flow velocity(which generates that pressure). The nature of the emulsion system and boosters will determine how much the carb is effected by changing atmospheric conditions. But again, remember that engines don't really respond to fueling changes of as much as 3-5%....so while the AFR may change somewhat, it's unlikely to be enough to matter.
My setup generally changes by about 0.5 AFR at most across 4,000ft of elevation change. So if I'm 12.5:1 at WOT and 6k rpm at high altitude, at ~ sea level it's 13:1. It's unlikely there's more than 1% power gains to be had by recalibrating. On a competitive race car it can matter, so you'd want to rejet, but on a street car it doesn't.
EFI has it's advantages and disadvantages. Carburetion has it's advantages and disadvantages. But most of what people believe about both is the same old information that people have been accepting as gospel truth for decades. So what if it's in a book by some guy? So what if that's what "all the engineers" say.
Remember too that the greatest scientific minds of the world all agreed for centuries that the world was flat, the sun revolved around the Earth, and big rocks fell faster than small rocks. Everyone believed it to be true, everyone KNEW it to be true. And anyone who disagreed with them was laughed at and called crazy. But it turns out those crazy guys were correct. Because they did something that everyone else didn't....they actually went out and TESTED those theories. They gathered data and looked at the evidence.
04-07-2011, 06:58 PM
#25
4th Gear Member
Join Date: Feb 2006
Location: So. Cal,the O.C.
Posts: 1,538
Even engineers are wrong, and arguably they are wrong much of the time and can't allow their egos to let them admit that they're wrong. I work in the engineering field with engineers, who sometimes are wrong more often than they're right. Designers(who are mostly not engineers) are the ones who do much of the actual designing, because what the engineer tells them to design while great on paper, doesn't always work in the real world.
You have to be careful when you listen to engineers sometimes, since "dumb engineer" jokes aren't necessarily without warrant. Many of them spend more time in a lab or an office than they do actually building and testing. It's one thing to believe something is true because you read it in a textbook, it's another to actually go out and test those theories and find out what works and what doesn't.
You have to be careful when you listen to engineers sometimes, since "dumb engineer" jokes aren't necessarily without warrant. Many of them spend more time in a lab or an office than they do actually building and testing. It's one thing to believe something is true because you read it in a textbook, it's another to actually go out and test those theories and find out what works and what doesn't.
04-07-2011, 07:59 PM
#26
6th Gear Member
Join Date: Aug 2007
Location: Elk Grove, CA
Posts: 5,896
This thread amuses me
67m302, one thing I think you're discounting when talking about carbs is the level of carb most people are using. Most people pick up a base level Edelbrock or Holley carb, tweak it a little, and leave it at that. No annular boosters, no adjustable air bleeds, just a basic carb in basic form. Yes, everything you've done with your carb makes it superior to EFI in most regards, but that's far more than most people running carbs are going to go through. It requires lots of time, knowledge, and money. Conversely, I can go yank the mass-air EFI system off a fox body and make a working fuel injection system for well under $500. And unlike a carb, it won't require any tuning. Fire it up, let it 'learn' for a bit, and you're good to go.
Personally, I'd love to have your carb. But lacking that, a cheap 5.0 mass-air fuel system is a perfectly acceptable substitute, IMO.
67m302, one thing I think you're discounting when talking about carbs is the level of carb most people are using. Most people pick up a base level Edelbrock or Holley carb, tweak it a little, and leave it at that. No annular boosters, no adjustable air bleeds, just a basic carb in basic form. Yes, everything you've done with your carb makes it superior to EFI in most regards, but that's far more than most people running carbs are going to go through. It requires lots of time, knowledge, and money. Conversely, I can go yank the mass-air EFI system off a fox body and make a working fuel injection system for well under $500. And unlike a carb, it won't require any tuning. Fire it up, let it 'learn' for a bit, and you're good to go.
Personally, I'd love to have your carb. But lacking that, a cheap 5.0 mass-air fuel system is a perfectly acceptable substitute, IMO.
04-07-2011, 08:34 PM
#28
2nd Gear Member
Thread Starter
Join Date: Jan 2011
Location: NC
Posts: 341
If you do any changes or upgrades later I think the carb. is easier/cheaper to change (jets, etc.) or replace. If you make changes with EFI you get to a point where you have to change injectors, MAF,etc. gets more involved and $. It mostly comes down to preference. Can you give an example of the Edel. packages that are suggested for carb. vs. EFI that you're looking at?
Jon
Jon
Cam Style Hydraulic roller tappet
Basic Operating RPM Range 1,500-6,500
Intake Duration at 050 inch Lift 227
Exhaust Duration at 050 inch Lift 234
Duration at 050 inch Lift 227 int./234 exh.
Advertised Intake Duration 298
Advertised Exhaust Duration 302
Advertised Duration 298 int./302 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.520 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.520 in.
Valve Lift with Factory Rocker Arm Ratio 0.520 int./0.520 exh.
Lobe Separation (degrees) 112
Cylinder Head Material Aluminum
Combustion Chamber Volume (cc) 60
CNC-Machined Combustion Chamber No
Intake Runner Volume (cc) 170cc
Exhaust Runner Volume (cc) 60cc
CNC-Machined Intake Runner No
CNC-Machined Exhaust Runner No
Intake Port Location Standard
Exhaust Port Shape Square
Exhaust Port Location Standard
Intake Valves Included Yes
Intake Valve Diameter (in) 1.900 in.
Exhaust Valves Included Yes
Exhaust Valve Diameter (in) 1.600 in.
Brand Edelbrock
Manufacturer's Part Number 7121
Intake Style Dual plane
Basic Operating RPM Range 1,500-6,500
This is the EFI set-up:
Performer 5.0/5.8L Heads
Direct bolt-on heads for 1982-95 5.0L and 5.8L V8s
Torque improved more than 80 ft/lbs. over stock on a 1993 5.8L engine when these heads were combined with the Edelbrock Total Power Package
These heads accept 1982-95 5.0L V8 pedestal mount rocker arms and valvetrain
Cylinder Head Specifications
Combustion chamber volume 60cc
Intake runner volume 170cc
Exhaust runner volume 60cc
Intake valve diameter 1.90" & 2.02"
Exhaust valve diameter 1.60"
Valve stem diameter 11/32"
Valve guides Manganese bronze
Deck thickness 5/8"
Valve spring diameter 1.46"
Valve spring maximum lift .575"
Rocker stud N/A
Guideplate N/A
Pushrod diameter 5/16"
Valve angle 20°
Exhaust port location Stock
Spark plug fitment 14mm x 3/4 reach, gasket seat
Made In USA
#2122
Cam
RPM RANGE: Idle-5500
Duration at 0.006" Lift: Intake: 270° Exhaust: 280°
Duration at 0.050" Lift: Intake: 204° Exhaust: 214°
Lift at Cam: Intake: 0.280" Exhaust: 0.295"
Lift at Valve: Intake: 0.448" Exhaust: 0.472"
Timing at 0.050" lift: Open Close
Intake: 5° ATDC 29° ABDC
Exhaust: 44° BBDC 10° BTDC
Centerlines: Lobe Separation - 112° Intake Centerline - 107°
04-07-2011, 08:38 PM
#29
2nd Gear Member
Thread Starter
Join Date: Jan 2011
Location: NC
Posts: 341
For driving i love fuel injection, doing this to my 67 yes it get spendy if you want everything now, but its the same as upgrading a fox body and alot of the performance parts for foxs are cheap and everyone has them. I have a few buddys with fuel injection in their classics and i have driven them and i like it. I say go fuel injection and throw a 2000 dollar foxbody supercharger and you have a pretty quick set up. You should be able to run the heads and cam with a tune. Only expensive thing i ran into with fuel injection was the intake if you want a good aftermarket one, otherwise i think i have 200 into all the parts for the swap.
Thanks
Last edited by Dennis Marks; 04-07-2011 at 10:08 PM.
04-07-2011, 08:54 PM
#30
2nd Gear Member
Thread Starter
Join Date: Jan 2011
Location: NC
Posts: 341
Actually, an EFI system will outperform a carburator at every point in the RPM/torque curve except one. A carbed engine is designed and tuned for peak HP or torque at a single given load/RPM, thus at any speed/load other than that one point it is not optimally tuned. (For example, at any load above peak torque you actually gain power by leaning out the mixture slightly, something that is impossible with a carb unless you can change the jets while the car is going down the drag strip.) The advantage to an EFI system is that the mixture can be adjusted for any given RPM and load to provide optimimum torque, fuel economy, emissions, etc. EFI cars have much flatter torque curves, which is why they are better for daily drivers/cruisers. If you combine this with distributorless ignition (which you can't on a 5.0/302) you can also adjust spark timing precisely at different RPM/load points as well. That's why cars like the 2011 GT get heaps of flat-torque curve power from a 5.0 motor, have a smooth idle, and great mileage too (the vict helps too!).
Very good points. Long story short this is basically a new engine which functions perfectly as it is.
Another advantage is that with factory-type EFI intakes the runners are all the same length (or close) which means that each cylinder is 'tuned' to make the same power at all RPMs. With a conventional carb intake the runner lengths usually aren't the same, which means the cylinders with shorter runners are making more power in the upper RPM range and the cylinders with longer runners are making more power in the lower RPM range. However, the different-length runners in a carbed intake tend to flatten the torque curve somewhat, though it does so by reducing power and efficiency across the board.
The biggest advantage to EFI in a daily driver/cruiser - click the key and it starts in any weather, can't flood it, burns clean, and gets great mileage.
Your heads shouldn't be an issue with EFI but your cam might not be ideal. EFI engines and intakes usually prefer slightly different cam grinds than carbs, but probably not enough to worry about.
Granted, factory EFI doesn't look as 'classic' but personally, after seeing the umteenth vintage Mustang with a carbed small block at a car show or cruise-in, I like seeing an EFI conversion. To me it says the owner appreciates classics but recognizes that newer technology can improve the old girls, but that's just personal preference (like carb or EFI).
Very good points. Long story short this is basically a new engine which functions perfectly as it is.
Another advantage is that with factory-type EFI intakes the runners are all the same length (or close) which means that each cylinder is 'tuned' to make the same power at all RPMs. With a conventional carb intake the runner lengths usually aren't the same, which means the cylinders with shorter runners are making more power in the upper RPM range and the cylinders with longer runners are making more power in the lower RPM range. However, the different-length runners in a carbed intake tend to flatten the torque curve somewhat, though it does so by reducing power and efficiency across the board.
The biggest advantage to EFI in a daily driver/cruiser - click the key and it starts in any weather, can't flood it, burns clean, and gets great mileage.
Your heads shouldn't be an issue with EFI but your cam might not be ideal. EFI engines and intakes usually prefer slightly different cam grinds than carbs, but probably not enough to worry about.
Granted, factory EFI doesn't look as 'classic' but personally, after seeing the umteenth vintage Mustang with a carbed small block at a car show or cruise-in, I like seeing an EFI conversion. To me it says the owner appreciates classics but recognizes that newer technology can improve the old girls, but that's just personal preference (like carb or EFI).