Holley Carb, AEM UEGO Questions?

[F8d2Blk]

I am trying to find the best a/f ratio for my carburetor. I think most know my setup. It is a VG30e with 2 barrell Holley Carb in my 510. I don't know the jet size as this will probably be what will fix all by swapping out jets but I am trying to just get this thing running safe enough for autox the next few weekends.

Alright this is kind of what is going on right now when I am at idle it is around
11.0. Which is rich, when I get on it full throttle it goes up to 13 range. And leans out some. On holley carbs you can't really adjust air/ fuel mixture at full throttle. You can only adjust at idle essentially.

Questions:
Would you advance or retard the timing to get the fuel to burn better?

It seems as if my setup is back asswards because I know the jets are to big, I am really getting around 12 mpg.
So I know I need smaller jets but essentially what should the car be reading
at idle, at partial throttle and full throttle?

Hopefully QD doesn't tell me I posted in the wrong forum.

[StraightSix]

As to what the engine should have for AFRs, I'm going to ask one question. Why would the AFR that is good for one engine be not good for another?

[quickdodge®]

Hopefully QD doesn't tell me I posted in the wrong forum.

Why would I say that? If you don't want to start anything, don't post dumbass shit. Take that shit somewhere else. Later, QD.

[NevrNufTorq]

it's late si i'm not getting into this but easy way is to pm turbodave or just call him at the shop....770 943 1968 :goodjob:

[F8d2Blk]

Why would I say that? If you don't want to start anything, don't post dumbass shit. Take that shit somewhere else. Later, QD.

It wasn't dumbass shit, it was more or less a partial joke but it is kind of in the wrong forum. But I posted here in hope of some people with Holley carb knowledge. :D

[EP3sAreFun]

AFR should be the same for every Gasoline drinking Naturally Aspirated engine right?

Idle around 14 and Full throttle around 13?

something like that anyways.... sorry i can tell you good AFRs for a turboed car for sure though lol

[StraightSix]

Let's the break this down into something more easily understood. An AFR is the Air/Fuel Ratio, right? And, lots of people, even ones without an engineering degree or any exposure to thermodynamics, know what the stoichiometric ratio should be. But, what does that mean?

The stoiciometric ratio is the ratio where the amount of air to the amount of fuel is correct. So, simply, a good AFR for an 800hp turbo whatever is going to be the same for a roughly 100hp Honda, or a 5hp lawn mower.

Adjusting timing to get won't really change anything. All you're doing there is changing when the volume of air is going to be entering and leaving the cylinder. It isn't going to solve the problem of getting too much fuel.

Rejet the carb first, then fine tune with timing. And, all this is assuming that the carb is the right size for the engine in the first place.

[EP3sAreFun]

Let's the break this down into something more easily understood. An AFR is the Air/Fuel Ratio, right? And, lots of people, even ones without an engineering degree or any exposure to thermodynamics, know what the stoichiometric ratio should be. But, what does that mean?

The stoiciometric ratio is the ratio where the amount of air to the amount of fuel is correct. So, simply, a good AFR for an 800hp turbo whatever is going to be the same for a roughly 100hp Honda, or a 5hp lawn mower.

Adjusting timing to get won't really change anything. All you're doing there is changing when the volume of air is going to be entering and leaving the cylinder. It isn't going to solve the problem of getting too much fuel.

Rejet the carb first, then fine tune with timing. And, all this is assuming that the carb is the right size for the engine in the first place.
Sorry man, thats not how AFRs work. a good turbo WOT could be 12:1 or 11:1 sometimes, where a non turbo car will be much leaner. i think the OP needs to find out what a good naturally aspirated AFR for idle and WOT is.

[green91]

afr for optimal fuel usage and afr for optimal power are often different. most performance related vehicles will run slightly rich to ward off spark knock, and can allow a little more advanced timing. I would imagine 14.5:1 - 14.9:1 at idle, and approx 13.1:1 - 13.5:1 would be close for WOT, N/A. obviously the best bet would be to put it on a dyno and also have a detonation detection device of some sort.


how about you tune any turbo car @ 10+psi at 14.7:1 and lets see how long before it detonates itself to pieces. I generally tune my cars to 11.5-12.0:1 afr in boost and 14.5:1 part throttle driving.

[EP3sAreFun]

afr for optimal fuel usage and afr for optimal power are often different. most performance related vehicles will run slightly rich to ward off spark knock, and can allow a little more advanced timing. I would imagine 14.5:1 - 14.9:1 at idle, and approx 13.1:1 - 13.5:1 would be close for WOT, N/A. obviously the best bet would be to put it on a dyno and also have a detonation detection device of some sort.
Good info right there

[green91]

Another thing to consider with carb'd engines is that there is one source of fuel delivery (carb at intake of the manifold), instead of having metered fuel dispersed at the intake ports. This often leads to uneven fuel distribution, typically inner cylinders would be slightly richer and the outer cylinders would be slightly leaner. A slightly rich fuel output helps to ensure that all cylinders have more reasonable EGTs, and also help prevent detonation on the outer cyls.

[StraightSix]

Sorry man, thats not how AFRs work.

Uh, yeah. It is. Air-Fuel Ratio is defined as the mass of air to the mass of fuel in a combustion process. This is something that is immutable. It is fact; pick up an text on thermodynamics and look it up.



a good turbo WOT could be 12:1 or 11:1 sometimes, where a non turbo car will be much leaner. i think the OP needs to find out what a good naturally aspirated AFR for idle and WOT is.

Now, let's actually think about this for a second. Knowing how an AFR is defined means that a 12:1 or 11:1 is really freaking rich. This is not good from the stand point of efficiency, or the chemical reaction of combustion. It's not good because not all of the fuel is being used.

It *is* good from the stand point of not blowing up a turbo charged engine. Too lean of a burn in that engine will cause combustion temperatures to rise; the excess fuel helps to keep combustion temps in the individual cylinders down. In a non-turbo charged application, combustion temps aren't as critical so the mixture can be leaned quite a bit.

[quickdodge®]

It wasn't dumbass shit, it was more or less a partial joke but it is kind of in the wrong forum. But I posted here in hope of some people with Holley carb knowledge. :D

I didn't know it to be a joke (partial or not). And I wasn't talking about your entire post being dumbass shit. Just your "joke." If you were joking, then my apologies. Later, QD.

[AE86Raptor]

If you're running gasoline, stoic is at about 14.7:1 for an N/A engine, which I would try to shoot for at idle. Other fuels have drastically different specs for stoic. At WOT, I'd aim around 13.5:1, any more and you would have black exhaust smoke (if you don't already). I run ~15:1 at idle and ~14.2 at cruise and ~13.5 at WOT.

[F8d2Blk]

All this is great info. I really appreciate it.
Yes the Holley Carb is actually to big for the application. But the actual manifold that is made I think restricts it some more too.
I should be closer to a 300-350cfm but the one I have is 500cfm
I did the formula but don't remember exactly what it should be but I know there are a number of people running the same setup with better gas mileage and performance is still decent.
www. vg30.com

So I finally have it sitting at 14+ at idle
Wide open throttle is anywhere from 12.5-13.5
Partial throttle is the problem it is really rich ranges from 15+ to over 17+ or when I let off the gas.

" IS THIS BAD?"

so I am guessing this is going back to big of jets. Although my chevy guy also gave some advice about changing a cam on the carb to allow the gas to come in later on.
So all was this morning until my fuel pump quit. Can't go anywhere now. Doh!

[AE86Raptor]

The higher the number the leaner it is. It could be alright, do you hear any detonating? How does it drive, any hesitation? When you let off the throttle I would imagine it would jump lean, and then stabilize to something slightly richer, unless it has a fuel cut-out system of some sort (I know most EFI cars have it, even my 86 model, but I'm not sure on carbed engines).

[F8d2Blk]

It hesitates and boggs some. When it hits those higher numbers and wants to die.

[AE86Raptor]

Another thing I forgot about was that you said that your pump went out. If the pump was weak that could have cause the motor to read lean. Get a new pump and start again. But the hesitation would cause those lean numbers.

[F8d2Blk]

Pump is fine, I accidently cut the line with a flap disc. I could of sworn I had everything pulled away. I was making a new ground in hopes to fix the tach and accidently cut the line.

[DirtyMechanic]

Uh, yeah. It is. Air-Fuel Ratio is defined as the mass of air to the mass of fuel in a combustion process. This is something that is immutable. It is fact; pick up an text on thermodynamics and look it up.




Now, let's actually think about this for a second. Knowing how an AFR is defined means that a 12:1 or 11:1 is really freaking rich. This is not good from the stand point of efficiency, or the chemical reaction of combustion. It's not good because not all of the fuel is being used.

It *is* good from the stand point of not blowing up a turbo charged engine. Too lean of a burn in that engine will cause combustion temperatures to rise; the excess fuel helps to keep combustion temps in the individual cylinders down. In a non-turbo charged application, combustion temps aren't as critical so the mixture can be leaned quite a bit.

I would ask you to stop trying to give advice about stuff you dont know about. but im sure you wont. but im going to try anyways. STOP TALKING!!! you have really no business talking about what A/F raitos should be.


afr for optimal fuel usage and afr for optimal power are often different. most performance related vehicles will run slightly rich to ward off spark knock, and can allow a little more advanced timing. I would imagine 14.5:1 - 14.9:1 at idle, and approx 13.1:1 - 13.5:1 would be close for WOT, N/A. obviously the best bet would be to put it on a dyno and also have a detonation detection device of some sort.


how about you tune any turbo car @ 10+psi at 14.7:1 and lets see how long before it detonates itself to pieces. I generally tune my cars to 11.5-12.0:1 afr in boost and 14.5:1 part throttle driving.+1


All this is great info. I really appreciate it.
Yes the Holley Carb is actually to big for the application. But the actual manifold that is made I think restricts it some more too.
I should be closer to a 300-350cfm but the one I have is 500cfm
I did the formula but don't remember exactly what it should be but I know there are a number of people running the same setup with better gas mileage and performance is still decent.
www. vg30.com

So I finally have it sitting at 14+ at idle
Wide open throttle is anywhere from 12.5-13.5
Partial throttle is the problem it is really rich ranges from 15+ to over 17+ or when I let off the gas.

" IS THIS BAD?"

so I am guessing this is going back to big of jets. Although my chevy guy also gave some advice about changing a cam on the carb to allow the gas to come in later on.
So all was this morning until my fuel pump quit. Can't go anywhere now. Doh! dont do anything. what you just said sounds right on. part throttle could be leaner and the off throttle could be richer. but other than that. your good. to help the wanting to die when you let off try riching the idle up ever so slightly. this will help the dieing part.

[StraightSix]

I would ask you to stop trying to give advice about stuff you dont know about. but im sure you wont. but im going to try anyways. STOP TALKING!!! you have really no business talking about what A/F raitos should be.


Really?? Tell me, please, exactly which portions of my post were in any way wrong. From where I'm sitting, you've made an empty accusation since you're unable to justify your opinion. Heaven forbid someone understands the theory behind why and how an engine runs. Perhaps my tone was a bit snide, but the facts remain; anyone who can read and knows a little math can very easily corroborate the information I've presented. So, until you can refute, intelligently, what I've presented don't criticize what I have to say.

[DirtyMechanic]

Really?? Tell me, please, exactly which portions of my post were in any way wrong. From where I'm sitting, you've made an empty accusation since you're unable to justify your opinion. Heaven forbid someone understands the theory behind why and how an engine runs. Perhaps my tone was a bit snide, but the facts remain; anyone who can read and knows a little math can very easily corroborate the information I've presented. So, until you can refute, intelligently, what I've presented don't criticize what I have to say.

stoic means nothing for modified car. and even for a stock car it still means really nothing. for a stock car thats usually where idle is. but idle usualy goes rich then lean so the cats can perform. and yes stoic is where air and fuel combusts to produce the least amount of emissions. but since it goes rich and lean the nox and co go up and down. now with a cat the nox and co are lowered due to the rich/lean change of idle. now for power you never ever use stoic for a tune other than idle.

power for n/a is usualy from the high 12s to the mid 13 a/f. it all depends on the engine and what the specific engine likes. which you will only know if you tune on a dyno to find out where the power is. now for boosted cars the a/f is usualy much richer for safety reasons. which are usualy form the 11s to the low 12s like i said depends on what the engine is and what it likes and where it makes power. but usually tuners go for a richer a/f to save the motor.

like one guy said before you tune a boosted car to a 14.7 stoic that motor will
1: not make any power
2: pop real quick
3: not run

even for a n/a motor 14.7 is not going to yeild you any power. just extremely high EGTs. so there i back up what i say. if you want talk more be my guest ive been in the aftermarket area on the tuning and building said for more than 3 years.:goodjob: may have heard of the shop. Forged Performance

[EP3sAreFun]

Uh, yeah. It is. Air-Fuel Ratio is defined as the mass of air to the mass of fuel in a combustion process.
You are correct. AFR is nothing more than a unit of comparison of Air to Fuel Vaporl


The stoiciometric ratio is the ratio where the amount of air to the amount of fuel is correct. So, simply, a good AFR for an 800hp turbo whatever is going to be the same for a roughly 100hp Honda, or a 5hp lawn mower.
But once again, this is completely wrong. what do you assume the correct AFR is? is it the point where it runs best? makes most power? or a combination of both? there is no easy answer. it depends on the application.

screw your book on thermodynamics. go read Wikipedia. http://en.wikipedia.org/wiki/Air-fuel_ratio


Knowing how an AFR is defined means that a 12:1 or 11:1 is really freaking rich. This is not good from the stand point of efficiency, or the chemical reaction of combustion. It's not good because not all of the fuel is being used.

12:1 is the correct AFR for my car @ 18psi with WOT. who gives a shit about efficiency when your trying to make 300hp and 400tqe

Don't give advice when your not sure whats going on. *shrug*

[EP3sAreFun]

StraightSix

Read this


A stoichiometric mixture unfortunately burns very hot and can damage engine components if the engine is placed under high load at this fuel air mixture. Due to the high temperatures at this mixture, detonation of the fuel air mix shortly after maximum cylinder pressure is possible under high load (referred to as knocking or pinging). Detonation can cause serious engine damage as the uncontrolled burning of the fuel air mix can create very high pressures in the cylinder. As a consequence stoichiometric mixtures are only used under light load conditions. For acceleration and high load conditions, a richer mixture (lower air-fuel ratio) is used to produce cooler combustion products and thereby prevent detonation and overheating of the cylinder head.

[DirtyMechanic]

dot dot dot

[NAMNORI]

dot dot dot

Oh no not the dot dot dot of doom!?!

[F8d2Blk]

Well I think the first thing I need to do is install this fpr that I have and put the stainless lines on. I think part of the problem is the pump isn't completely consistent. Plus when I thought I had it set the other day in warmer weather, no humidity it seemed fine. But on sunday, cooler temps and moisture it changed some. I am pretty sure I just need to richen it up some to stay consistent and not have to mess with it anymore. ;)

[StraightSix]

dot dot dot

I don't really need to say anything else. You guys pretty much proved my original point which I'll restate for the reading comprehension impaired. If one knows a "good" AFR for a particular engine, i.e N/A, turbo, E85, propane, et al., then one already knows the target AFR.

[DirtyMechanic]

I don't really need to say anything else. You guys pretty much proved my original point which I'll restate for the reading comprehension impaired. If one knows a "good" AFR for a particular engine, i.e N/A, turbo, E85, propane, et al., then one already knows the target AFR.but good sir you are incorrect on your definition of stoiciometric ratio. it is NOT and i quote "The stoiciometric ratio is the ratio where the amount of air to the amount of fuel is correct." stoici is 14.7 A/F for gasoline. so at 800hp 14.7, is NOT a good A/F more like mid/high 11s to low 12s A/F.

[EP3sAreFun]

I don't really need to say anything else. You guys pretty much proved my original point which I'll restate for the reading comprehension impaired. If one knows a "good" AFR for a particular engine, i.e N/A, turbo, E85, propane, et al., then one already knows the target AFR.

stoich for E85 is not 14.7 by the way.... its 9.765 :)

[StraightSix]

but good sir you are incorrect on your definition of stoiciometric ratio.

Yeah. I am. The stoichiometric ratio for gasoline *is* 14.7:1, and we can agree on that. Which means that for any gasoline powered engine, stoich will always be 14.7:1 regardless of application. Stoich isn't limited by the engine; it's limited by chemistry. Stoich will change if the atomic structure of the air of fuel changes.

Let's make sure we're all on the same page as far as what stoichiometric means. Stoichiometry involves the combination of reactants in a chemical reaction and the resultant products. The stoichiometric point is where all of the recants are "used" up in the reaction and are accounted for in the products. So, that means that for *any* given chemical reaction there is a stoichiometric ratio.

One can vary the amounts of the reactants, fuel and air in the case of an internal combustion engine, but that will result in a lean or rich condition. So, by chemistry, and termodynamics, even if a particular engine produces it's max power at a 12:1 AFR, the fact remains that this AFR is still a rich condition.

[StraightSix]

stoich for E85 is not 14.7 by the way.... its 9.765 :)

Super. But, it's based in chemistry and anything deviating from that 9.765:1 for an E85 engine will be either lean or rich, regardless of what the engine wants.

But, why is it different? Because the chemical components of the fuel are different than those for gasoline, so a slightly different oxidization reaction is taking place and then the stoichiometry changes and the math has been done again. It'll also result in different flame temperature, and the engine will want a higher compression ratio to work best with the fuel.

[EP3sAreFun]

Super. But, it's based in chemistry and anything deviating from that 9.765:1 for an E85 engine will be either lean or rich, regardless of what the engine wants.

But, why is it different? Because the chemical components of the fuel are different than those for gasoline, so a slightly different oxidization reaction is taking place and then the stoichiometry changes and the math has been done again. It'll also result in different flame temperature, and the engine will want a higher compression ratio to work best with the fuel.
oh, awsome fantastic. just making sure you knew.

[EP3sAreFun]

But really.... clearly you don't get it man.


"The stoiciometric ratio is the ratio where the amount of air to the amount of fuel is correct

This is from where all your problems are stemming from. An engine can be perfectly stoich and at the same time be running the wrong air fuel ratio for it's requirements.

Also, a car can be running the correct Air/fuel ratio and not be stoich.

okay? Savvy? Comprende? got it?

[DirtyMechanic]

Yeah. I am. The stoichiometric ratio for gasoline *is* 14.7:1, and we can agree on that. Which means that for any gasoline powered engine, stoich will always be 14.7:1 regardless of application. Stoich isn't limited by the engine; it's limited by chemistry. Stoich will change if the atomic structure of the air of fuel changes.

Let's make sure we're all on the same page as far as what stoichiometric means. Stoichiometry involves the combination of reactants in a chemical reaction and the resultant products. The stoichiometric point is where all of the recants are "used" up in the reaction and are accounted for in the products. So, that means that for *any* given chemical reaction there is a stoichiometric ratio.

One can vary the amounts of the reactants, fuel and air in the case of an internal combustion engine, but that will result in a lean or rich condition. So, by chemistry, and termodynamics, even if a particular engine produces it's max power at a 12:1 AFR, the fact remains that this AFR is still a rich condition. i would stop trying to back pedal. because you 14.7 is only good for idle. that i can say is correct. but for a power and to keep a engine together you need a much richer a/f which you say is incorrect because for a correct a/f it has to be stoici. which is not correct. every engine, even two engines with the same parts will need a completely different a/f, because no two engines are the same. but for the real world applications stoici is never really followed, well maybe sort of from the factory for idle. but even then its varies lean to rich for the cats to work.

[AE86Raptor]

...every engine, even two engines with the same parts will need a completely different a/f, because no two engines are the same...

+1

You got to it before I did. Stoic, at best, is a guideline for a stock engine A/F, whether you're running gasoline, methanol, ethanol, or CNG. For modified engines on the other hand, stoic is just a ratio/number since they are ran with a richer mixture and are tuned more aggressively and a wrong A/F ratio can easily destroy an engine. All stoic tells someone is complete combustion occurs at a certain ratio. It may or may not be optimal for the engine to run at stoic due to age, parts added or any other variable. Even engines that come from the factory will have different power ratings from one another and what will work for one may not work for the other. The point of monitoring your A/F ratio is to not blow up the engine and/or pistons and to make sure you getting enough fuel. The same goes for ignition timing. Some cars you may advance it 20+ degrees, but others you may only advance it 5 degrees before it detonates.

[DirtyMechanic]

also at idle 14.7 is a good a/f to have. going rich on a fresh motor can cause you to wash the cylinder walls and will make you re ring the motor. going to lean well... depending on compression could pit the piston and chip the rings. but usually 14.7 or slightly leaner is usually safer for a fresh motor so you dont wash the cylinders and have to re-ring so quick on a new motor.