ATM/Holley verses Carter 625 AFB

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Newbomb Turk said:
If you want the science behind it you’ll have to call Mark Whitener at Lightning Racing Carbs and ask him.
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I was there (MotorsportVillage) when Bruce was explaining it way back when.

Newbomb Turk said:
So with 20-22 holes, no flow loss and a huge signal gain these boosters make it so you can use a bigger carb not lose any flow. Of course, with booster gain like that atomization goes through the roof.
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You're starting to sound like Troy Patterson now. So its still a Holley with an annular discharge booster and its got more holes? Got it.
 
You dyno guys can explain to me if I'm looking at an AFR calculated off the fuel consumption and a measured or assumed airflow, or from an WBO2.

I ask because these my takeaway from the graphs:
1. This engine will keep increasing power until at least 5100 rpm
2. The Carter didn't loose or gain anything. The engine was given a different air fuel ratio and responded accordingly.
There may be more potential in on the higher flowing carb, but we compare the higher flows with the same AFR.


The other thing that may be a little different is the depression. And this engine might like more manifold vacuum or a little less depending on things like the distribution. The engine with a TR vs. a dual plane on it should (in theory) have pretty good distribution and so be fine with less vacuum which is a potential advantage of a 'higher flowing' carb.
twocents-gif.gif
 
Hysteric said:
I was there (MotorsportVillage) when Bruce was explaining it way back when.


You're starting to sound like Troy Patterson now. So its still a Holley with an annular discharge booster and its got more holes? Got it.
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So you picked one thing I said and ran with it. Got it. BTW, if you have the link to what Shrinker said I’d love to read it. All that MV stuff is near impossible to find any more.
 
Mattax said:
You dyno guys can explain to me if I'm looking at an AFR calculated off the fuel consumption and a measured or assumed airflow, or from an WBO2.

I ask because these my takeaway from the graphs:
1. This engine will keep increasing power until at least 5100 rpm
2. The Carter didn't loose or gain anything. The engine was given a different air fuel ratio and responded accordingly.
There may be more potential in on the higher flowing carb, but we compare the higher flows with the same AFR.


The other thing that may be a little different is the depression. And this engine might like more manifold vacuum or a little less depending on things like the distribution. The engine with a TR vs. a dual plane on it should (in theory) have pretty good distribution and so be fine with less vacuum which is a potential advantage of a 'higher flowing' carb.
View attachment 1716208407
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Those AFR’s are from my O2 sensors. I’ll put the air hat on it next time and get more numbers, but it won’t be on the same intake manifold. It will be a Holley Street Dominator and then a Strip Dominator.

If I’m following what you are asking, then yes the AFR should be the same between any carbs being tested. My carb is pretty fat down low, so I’m sure that hurt torque below peak. And, it may be a skosh lean at the top but for some reason with these O2 sensors it may like 13:1 or a bit more.

Even if I lean the Carter out to get it to 13:1 it won’t make 37 horsepower more.

Edit: the intake is a performer RPM. Distribution is GARBAGE like it always is with a dual plane intake.
 
The Holley makes more power on the dyno and is good for 2 tenths at the track over an AFB
 
Newbomb Turk said:
So you picked one thing I said and ran with it. Got it. BTW, if you have the link to what Shrinker said I’d love to read it. All that MV stuff is near impossible to find any more.
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I'll add, that if you or anyone has more than was captured vy the WayBackMachine, we can recreate it in a couple places so it doesn't get lost again.
 
Mattax said:
You dyno guys can explain to me if I'm looking at an AFR calculated off the fuel consumption and a measured or assumed airflow, or from an WBO2.

I ask because these my takeaway from the graphs:
1. This engine will keep increasing power until at least 5100 rpm
2. The Carter didn't loose or gain anything. The engine was given a different air fuel ratio and responded accordingly.
There may be more potential in on the higher flowing carb, but we compare the higher flows with the same AFR.


The other thing that may be a little different is the depression. And this engine might like more manifold vacuum or a little less depending on things like the distribution. The engine with a TR vs. a dual plane on it should (in theory) have pretty good distribution and so be fine with less vacuum which is a potential advantage of a 'higher flowing' carb.
View attachment 1716208407
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Great Post^^^

Lots of very good observations!
 
Newbomb Turk said:
My carb is pretty fat down low, so I’m sure that hurt torque below peak.
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It could have hurt the entire pull because it was pretty consistant.

Some time back I started a thread sharing an overlay between rich pulls, different carbs. The power was similar.
But changing the jets on the smaller carb made a huge difference in power.
Mattax said:
Here's how much was gained by changing jets.
70,74 to 66, 72
View attachment 1715473374
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For the bigger Franken carb, I don't have a back to back comparison, because there changes to exhaust and timing, and then corrected the AFR drift in the secondaries.
 
Mattax said:
It could have hurt the entire pull because it was pretty consistant.

Some time back I started a thread sharing an overlay between rich pulls, different carbs. The power was similar.
But changing the jets on the smaller carb made a huge difference in power.


For the bigger Franken carb, I don't have a back to back comparison, because there changes to exhaust and timing, and then corrected the AFR drift in the secondaries.
Click to expand...


Once I get some baseline tests done I’ll put the Carter back on and fatten it up a bit. As long as I can find my Carter jets.
 
Newbomb Turk said:
So you picked one thing I said and ran with it. Got it. BTW, if you have the link to what Shrinker said I’d love to read it. All that MV stuff is near impossible to find any more.
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I'm just stating the obvious which you haven't figured out yet. A carb will only flow what the engine demands irrespective of what size you put on it. Here's what Bruce had to say about annular boosters:

The more holes the more air to fuel interaction. But having said that the double step design of a dogleg has fuel all the way around the circumference of the booster so what the heck. Each to his own. If you start playing with more holes and big or small drops you will find that some engines need fat drops some need fine drops. It depends upon the heat and dispersion in the cylinder. Cylinders with high heat or exhaust retention make more power with fat drops. Been there, done that, proved that many many times. You have to learn how to balance the speed of vaporization and where it occurs in every engine. They are all different.

The conversation that was had was why one carb (Dominator) better suited one engine over another. What its comes down to is droplet size and suitability to the engine design.

Go look at a Dambest carb and see what he's doing.

No link sorry.
 
Hysteric said:
I'm just stating the obvious which you haven't figured out yet. A carb will only flow what the engine demands irrespective of what size you put on it. Here's what Bruce had to say about annular boosters:

The more holes the more air to fuel interaction. But having said that the double step design of a dogleg has fuel all the way around the circumference of the booster so what the heck. Each to his own. If you start playing with more holes and big or small drops you will find that some engines need fat drops some need fine drops. It depends upon the heat and dispersion in the cylinder. Cylinders with high heat or exhaust retention make more power with fat drops. Been there, done that, proved that many many times. You have to learn how to balance the speed of vaporization and where it occurs in every engine. They are all different.

The conversation that was had was why one carb (Dominator) better suited one engine over another. What its comes down to is droplet size and suitability to the engine design.

Go look at a Dambest carb and see what he's doing.

No link sorry.
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LOL, I understand that the carb only flows what the engine wants. But you can reduce pumping losses with a bigger carb.

And that’s why the boosters matter. I can get the atomization I want and still reduce pumping losses.

You also have to consider the fuel we get here is not the same as the fuel you get down there. Not even close.
 
Newbomb Turk said:
Build the best you can, send it here and I’ll test it.

In fact, the next time I run the engine I’ll put the air hat on it and we can see what the air flow says.

Did you forget the 340 came with an AVS that had a similar flow rating?

And it is apples to apples because like I said, a swap from a 625 to a 750 is a regular occurrence.

I’m not doing an 1850 Holley test because they are door stops at best, right along with the AFB.
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Don't forget too, the 71 340 came with either an 800 or 850 Thermoquad. I don't remember which.
 
Newbomb Turk said:
It will be a Holley Street Dominator and then a Strip Dominator.
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The AFB doesn't play well with a decent cam and a single plane off idle and a mash of the go peddle.
Don't know if your dyno will show that on a slow even pull.
 
Here let me show you again:

https://www.motortrend.com/news/how-to-pick-the-best-carburetor-for-a-street-strip-car/

Imagine running quickest with a 650 DP on 425 CI with all those pumping losses......and 5.5 inches of vacuum at WOT. Greg Kuchel had no problem making stupid power with just an old 750.

Fuel is a hydrocarbon. Every fuel is different dependent on what the fuel chemist choses to use in his blend. What doesn't change is the chemistry and process of combustion.

While you obsess about airflow you miss the most important fact about an Internal Combustion Engine......COMBUSTION!
 
Hysteric said:
Every fuel is different dependent on what the fuel chemist choses to use in his blend. What doesn't change is the chemistry and process of combustion.
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But the combustion process can be different, and that's why the chemical reaction can end up with different percentages of the various exhaust products.
That was one of Shrinker's points. One set of combustion chambers, compression, heat in the walls, etc and distribution may prefer larger drops or smaller drops for best power. As extreme examples we know from the restricted carb classes that its possible to build engines that make power with high manifold vacuum at WOT. A TR will be at the other extreme.
 
RustyRatRod said:
Yeah, they take some time to dial in.
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It’s not so much that, because I love doing that work. But getting it to fit correctly on these manifolds is the chore.

I don’t want to carve up the manifolds, and I’ve already tested a couple of the adapters and they suck.
 
Mattax said:
But the combustion process can be different,
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The process is the same but the constituents produced can be different different. Bruce spoke about "burn styles" now go and think about that one for a while :lol:If you look at what Greg wrote here he stated quite clearly that it was about energy management. Why, because there are many factors that affect vaporization (liquids don't burn gasses do) and where it happens. To give you an example Bruce changed the camshaft on his engine going larger (From memory a local prostock class) and that changed the vacuum generated most likely at the valve curtain diminishing the vaporization rate so to fix it he had to build smaller carbs to get that back what he lost to make the same power.

Its how you manage the energy imputation to the fuel and where that dictates the quality of the burn. It can be done in many place and messed up in many places......

Bruce developed his own platform to be able to adjust droplet sizes and that lead him to certain conclusions by being able to change the burn that took place which would also manifest itself on the plug. That's why he advocated reading plugs not wide bands. The chemistry produced whether its a high CO or CO2 burn manifests itself on the plug.

What fuel you use is Irrelevant ultimately as the process is the same you have to convert the liquid to a gas to burn it to release the energy to the piston and crank. The better the burn the less time it requires. The energy required for different fuels is what differs.

Newbomb Turk said:
No. It is a Carter 625 Competition AFB so the primaries and secondaries aren’t the same size.
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Which Carter? The earlier original carter 625 or the Federal Mogul produced carbs with different calibrations?
 
Hysteric said:
The process is the same but the constituents produced can be different different. Bruce spoke about "burn styles" now go and think about that one for a while :lol:If you look at what Greg wrote here he stated quite clearly that it was about energy management. Why, because there are many factors that affect vaporization (liquids don't burn gasses do) and where it happens. To give you an example Bruce changed the camshaft on his engine going larger (From memory a local prostock class) and that changed the vacuum generated most likely at the valve curtain diminishing the vaporization rate so to fix it he had to build smaller carbs to get that back what he lost to make the same power.

Its how you manage the energy imputation to the fuel and where that dictates the quality of the burn. It can be done in many place and messed up in many places......

Bruce developed his own platform to be able to adjust droplet sizes and that lead him to certain conclusions by being able to change the burn that took place which would also manifest itself on the plug. That's why he advocated reading plugs not wide bands. The chemistry produced whether its a high CO or CO2 burn manifests itself on the plug.

What fuel you use is Irrelevant ultimately as the process is the same you have to convert the liquid to a gas to burn it to release the energy to the piston and crank. The better the burn the less time it requires. The energy required for different fuels is what differs.


Which Carter? The earlier original carter 625 or the Federal Mogul produced carbs with different calibrations?
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I’ll look when I go to the shop tomorrow but I’m pretty sure it’s not a FM but a genuine Carter piece.
 
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