Curtis73 (Forum Supporter) said:
bentwrench said:
In reply to Tom1200 :
I can guarantee it would run better with a proper EFI...
I can promise you that is not always the case. For most of the 90s and early 2000s, carbs were still crushing aftermarket EFI and many factory EFI setups.
This is like saying that all IKEA furniture will be good quality. Since a huge variable is how it's assembled, that's a big if. EFI can be wonderful if you have the knowledge to tune it right and fix all the bugs. Both systems have benefits and drawbacks, but neither one is intrinsically superior in every way. A properly tuned carb will beat a roughly-tuned EFI just as easily as a properly tuned EFI will beat a poorly tuned carb.
But to say that properly tuned EFI will always beat a properly tuned carb is just not really accurate.
I'm sorry to pile on Curtis, trust me I mean no disrespect.
The gas part is the same. A carb has a mechanical squirter while Injector squirts the same amount of gas.
The difference is the manifold. Air has mass. Stick your arm out the window on the freeway if you doubt it;-)
Look at EFI manifolds. Much longer for more power over a wider range. You can't do that with a carb. Because the gas will fall out of the airstream. P
No disrespect inferred. I agree with the air mass in the manifold, I'm simply saying that it doesn't always have the affect of being better/worse, especially when you use that additional mass/velocity to your advantage with a carb'd intake. Using the velocity/inertia of that heavy intake charge can have notable affects on VE.
You see the reduced mass as a benefit. I see it as a drawback depending on how each one is tuned.
EFI manifolds can be short or long, really depends on what you're trying to do. You can have carb manifolds with long runners, I remember some Mopars that had a carb on either side of a long runner crossover manifold. Can't remember for the life of me what it's actually called but
I have built efi manifolds that have really short runners... though efi with ITBs usually have the same runner lengths as carbs due to having the same packaging constraints. You can have side drafts with really long horns and the carbs close to the heads, no problem.
Paul_VR6 (Forum Supporter) said:
frenchyd said:I can still tune a Hilborn style mechanical Fuel Injection. Vintage racing allows mechanical fuel Injection. And yes it's better than carbs.
I have the exact opposite opinion. I have had good success on WOT or NOT type cars, but transitions generally are a lot better on EFI and *gasp* carbs. On road race setups it probably depends a lot on setup/driver/goals for how well it works. Also seems to work better on setups that have a relatively flat torque curve where you are wanting to use it. One of my favorite little projects is to add sensors/logging to mechanical and carbd cars to tune them. After looking at it you can see what "feels good" vs what's "actually good" if you want to take economy, etc, into account.
Mechanical fuel injection is definitely more difficult to tune then carbs or efi and a a carb that's not running well will run better then a mechanical injection that's not running well. Mechanical injection is still used lots on sprint,super modified and midget racing. Used to be used in street cars but most went back to carbs as they had similar performance with much easier maintenance etc.
Is there a 2 barrel carb that is Qjet simple ?
maybe a 2 barrel progressive but not a Holley Weber that I could never get to run right ,
Thanks
Tom1200
UltraDork
4/29/22 11:32 a.m.
I also think the type of carb matters a lot; I went to Keihin FCR Flat slides almost 20 years ago and they are far and above a better carb than anything else. Also slide valve carbs flow more by virtue of not having a throttle shaft down the center of the carb impeeding the flow.
californiamilleghia said:
Is there a 2 barrel carb that is Qjet simple ?
maybe a 2 barrel progressive but not a Holley Weber that I could never get to run right ,
Thanks
Probably gm Rochester 2 barrel carbs. In oval racing holleys 350 and 500 cfm carbs are very common. Gm actually used Holley 2 barrel carbs for the 427 tri power corvettes. 2 Holley 500s and a 350 Holley center carb.
In reply to MotorsportsGordon :
And then they realized that an 850cfm Q-jet flowed the same without the horrible mixture distribution issues of a 3x2 manifold 
I've played with carbs one time and it was enough to make me not want to do it again... And yet I suddenly find myself asking this question in earnest:
The lawnmower carb'd 40mpg SBF video shows him basically adding an IACV plumbed in after a rich-running carb to have it automatically meter in additional air to accurately hit his target AFR's as conditions change... So wouldn't that type of system largely address the main argument against carbs while keeping the electronics and hardware changes to a minimum compared to an EFI conversion?
JBinMD
New Reader
4/29/22 3:08 p.m.
SKJSS (formerly Klayfish) said:
I didn't want to hijack the thread Robbie started, so I'll create one here. I recently picked up a '77 Corvette. Such a cool story...I got it from the family of the original owner. It was her mothers' daily driver when new. Mom got into track days, and so did daughter. They ran it together. When mom decided to hang up her racing shoes, daughter and her husband took the car. It's lived as a track day special since. Race suspension, aluminum radiator, heated up 350, 4spd (original). It's was running HPDE with Chin at Sebring....some people here may have seen it. Anyway, daughter sold it to me so that she can finance her own daughter running karts.
The car is so cool. It's a worked over 350 with a carb on it (don't recall the carb specs). It needs a good tuning, as it had just been rebuilt and quickly put back on before they sold it to me. Before I go down that path of having the carb tuned (I have no idea how to do it), considering converting it to fuel injection. Obviously, lots of "pros" and few "cons". I just don't know much about that. Without buying some made in Taiwan special, what would be the most cost effictive and efficient way to convert the car?
Didn't the mid 90's GenII LT1 engines come with sequential port injection? It seems like that might be the cheap/easy way to convert it to fuel injection, but I am honestly not familiar enough with the different GM small blocks to know what their differences are or which parts swap between them.
californiamilleghia said:
Is there a 2 barrel carb that is Qjet simple ?
maybe a 2 barrel progressive but not a Holley Weber that I could never get to run right ,
Thanks
The Rochester DualJet is basically the primary side of a Qjet. The Holley Weber two stage two barrel is a good carb. However, it came in a gazillion different configurations for different applications and can be pretty far away from a bolt on.
MotorsportsGordon said:
Paul_VR6 (Forum Supporter) said:
frenchyd said:I can still tune a Hilborn style mechanical Fuel Injection. Vintage racing allows mechanical fuel Injection. And yes it's better than carbs.
I have the exact opposite opinion. I have had good success on WOT or NOT type cars, but transitions generally are a lot better on EFI and *gasp* carbs. On road race setups it probably depends a lot on setup/driver/goals for how well it works. Also seems to work better on setups that have a relatively flat torque curve where you are wanting to use it. One of my favorite little projects is to add sensors/logging to mechanical and carbd cars to tune them. After looking at it you can see what "feels good" vs what's "actually good" if you want to take economy, etc, into account.
Mechanical fuel injection is definitely more difficult to tune then carbs or efi and a a carb that's not running well will run better then a mechanical injection that's not running well. Mechanical injection is still used lots on sprint,super modified and midget racing. Used to be used in street cars but most went back to carbs as they had similar performance with much easier maintenance etc.
Mechanical injection works best when the cam is working in the range designed.
In other words don't over cam the engine. I could put a real serious camshaft because I knew how to keep the car in that tight RPM range where it worked. That was the purpose of the Saenz dog ring gear box. Because the gears inside the box could be quickly swapped for different sets, it was straight forward to have the right gear for every corner. The owner really should have had an automatic.
I used the Kinsler Dial a jet and the last 4 jets were for the different air density's I forecast. I'd stand in the pits and signal him up or down based on what the air density was.
The first position was for starting. Throttle wide open, turn on the ignition, turn on the fuel pump. as soon as the holding tank filled, hit the starter. ( you could hear the pump strain when tank was full) Explosive start.
You'd pre-lube the engine with everything off until oil pressure pegged. Then go through the starting ritual. But it started on the "key"
Driven5 said:
I've played with carbs one time and it was enough to make me not want to do it again... And yet I suddenly find myself asking this question in earnest:
The lawnmower carb'd 40mpg SBF video shows him basically adding an IACV plumbed in after a rich-running carb to have it automatically meter in additional air to accurately hit his target AFR's as conditions change... So wouldn't that type of system largely address the main argument against carbs while keeping the electronics and hardware changes to a minimum compared to an EFI conversion?
Stick the valve on the air bleeds, and congratulations! You have reinvented the computer controlled carb.
JBinMD said:
SKJSS (formerly Klayfish) said:
I didn't want to hijack the thread Robbie started, so I'll create one here. I recently picked up a '77 Corvette. Such a cool story...I got it from the family of the original owner. It was her mothers' daily driver when new. Mom got into track days, and so did daughter. They ran it together. When mom decided to hang up her racing shoes, daughter and her husband took the car. It's lived as a track day special since. Race suspension, aluminum radiator, heated up 350, 4spd (original). It's was running HPDE with Chin at Sebring....some people here may have seen it. Anyway, daughter sold it to me so that she can finance her own daughter running karts.
The car is so cool. It's a worked over 350 with a carb on it (don't recall the carb specs). It needs a good tuning, as it had just been rebuilt and quickly put back on before they sold it to me. Before I go down that path of having the carb tuned (I have no idea how to do it), considering converting it to fuel injection. Obviously, lots of "pros" and few "cons". I just don't know much about that. Without buying some made in Taiwan special, what would be the most cost effictive and efficient way to convert the car?
Didn't the mid 90's GenII LT1 engines come with sequential port injection? It seems like that might be the cheap/easy way to convert it to fuel injection, but I am honestly not familiar enough with the different GM small blocks to know what their differences are or which parts swap between them.
The only things that swap between LT1 and SBC are... um... some cranks? Maybe rods and pistons? Perhaps some cylinder head parts? Even the exhaust manifolds are not intetchangeable without a lot of work.
The LT1 had a cam position sensor built into the distributor. That was the Opti part of Optispark. The distributor was driven off of the front of the camshaft, along with the water pump. Because of this, you can't bung an LT1 timing cover on an SBC - the shape is way different. And I don't think an SBC water pump would clear the distributor. And you could not use the LT1 water pump because the block does not have provisions for coolant return (dry intake manifold).
Easier and better to use an LS1 computer.
Caperix
New Reader
4/29/22 6:24 p.m.
I have not tried to run an early small block off ls electronics but dynamic efi makes some good tuning solutions for the tpi engines. That is the setup I am using in my 70's small block converted to efi. The hardest part is plumbing in the oil pressure switch.
APEowner said:
californiamilleghia said:
Is there a 2 barrel carb that is Qjet simple ?
maybe a 2 barrel progressive but not a Holley Weber that I could never get to run right ,
Thanks
The Rochester DualJet is basically the primary side of a Qjet. The Holley Weber two stage two barrel is a good carb. However, it came in a gazillion different configurations for different applications and can be pretty far away from a bolt on.
Correct. A dual-jet is like taking the primary side (the front half) of a Qjet and making it slightly bigger. They also did a Varajet which is like taking the left or right half of a Qjet so you have a single primary and a large secondary.
Varajets are rated anywhere from 375-400 cfm. Dual jets are either 270 or 350 cfm depending on the size of the throttle plates. They are referred to as "big plate" and "small plate." That isn't apples to apples, though. 4bbl carbs are rated at 1.5"h2o pressure drop. 2bbl carbs are rated at 3" drop.
I also think that all Varajets were post-computer, meaning they have an electric "flutter" valve that PWM's the primary circuit to control mixture. You can't just pull the plug, they require an ECM to control it.
JBinMD said:
SKJSS (formerly Klayfish) said:
I didn't want to hijack the thread Robbie started, so I'll create one here. I recently picked up a '77 Corvette. Such a cool story...I got it from the family of the original owner. It was her mothers' daily driver when new. Mom got into track days, and so did daughter. They ran it together. When mom decided to hang up her racing shoes, daughter and her husband took the car. It's lived as a track day special since. Race suspension, aluminum radiator, heated up 350, 4spd (original). It's was running HPDE with Chin at Sebring....some people here may have seen it. Anyway, daughter sold it to me so that she can finance her own daughter running karts.
The car is so cool. It's a worked over 350 with a carb on it (don't recall the carb specs). It needs a good tuning, as it had just been rebuilt and quickly put back on before they sold it to me. Before I go down that path of having the carb tuned (I have no idea how to do it), considering converting it to fuel injection. Obviously, lots of "pros" and few "cons". I just don't know much about that. Without buying some made in Taiwan special, what would be the most cost effictive and efficient way to convert the car?
Didn't the mid 90's GenII LT1 engines come with sequential port injection? It seems like that might be the cheap/easy way to convert it to fuel injection, but I am honestly not familiar enough with the different GM small blocks to know what their differences are or which parts swap between them.
As has been mentioned, no swappy. The LT1 shares the rotating assembly with an SBC. The blocks and heads are darn close but they revised the coolant passages and raised the intake and exhaust ports so swappin ain't easy. Still, with a wee bit of TIG, an LT1 EFI setup stuffed into bungs on an SBC intake wouldn't be terribly hard.
Driven5 said:
Pete. (l33t FS) said:
Driven5 said:
I've played with carbs one time and it was enough to make me not want to do it again... And yet I suddenly find myself asking this question in earnest:
The lawnmower carb'd 40mpg SBF video shows him basically adding an IACV plumbed in after a rich-running carb to have it automatically meter in additional air to accurately hit his target AFR's as conditions change... So wouldn't that type of system largely address the main argument against carbs while keeping the electronics and hardware changes to a minimum compared to an EFI conversion?
Stick the valve on the air bleeds, and congratulations! You have reinvented the computer controlled carb.
And the drawback is?...
None as far as I am concerned. They were only used on tiny cam no-compression 80s engines, and they had wires and stuff on them, so therefore "bad" I suppose.
I don't think an 80's electronic feedback carb is anywhere nearly as effective as the lawnmower carb + IAC setup. I'm really curious how well that setup performs when he puts the 390cfm Holley back on the car.
That car is crying out for an overdrive transmission like a T5 and some other tweaks.
If you can get good mileage out of an air bleed and a rich carb, you should be able to hit the same thing using other methods where you have good fuel control. There is no free lunch.
In reply to Paul_VR6 (Forum Supporter) :
Not necessarily, if you can get the same precision with a carb. Generally speaking a carb will always be able to get better fuel economy and make more peak power because the atomization is so much better.
In reply to Pete. (l33t FS) :
The challenge is getting precise enough control across a wide enough range of conditions. If you can't get things precise enough, you can easily lose more than the better atomization gains you.
