****DISCLAIMER: I am not an expert, and am CERTAINLY not looking for an answer to a question.****
My intention is to inspire some thought and discussion about a very important engine component. Please read my entire post before responding.********
Thanks!!
ps, I left(mostly) the actual diameters and list numbers out because it was simply to labor intensive for a post that may or may not take off.
I have been spending a considerable amount of time trying to learn as much as possible about Holley carbs,
and picking the right one. My research has been pretty limited, but I think its helping.
My recent hang up has been on the cfm ratings holley provides for their carbs. I have been taking a closer look at venturi and throttle bore sizing as opposed to cfm ratings. With this in mind the 950HP "should" flow less air at a certain depression than an 850 because the 850(4781) has larger venturi's and
throttle bores than the 950. Taking it a step further, a 750 4500 series carb will have 1-11/16
venturi's and 2" throttle bores. This is way larger than the 850, and yet is rated at 100 cfm less.
Now I am sure boosters will have some effect on airflow, but not hundreds of cfm's.
So i am forced to conclude that there are two things happening. Holley uses cfm ratings as a marketing
ploy, and thus other carb manufacturers follow suit. By keeping us in the dark as much as possible
they can sell us a new carb instead of making the one we have work. The second thing is that cfm ratings are
not quite what we are "led" to believe. A cfm rating might actually be the carbs intended flow usage?
In other words the carb is configured or calibrated to operate well at the listed flow rating.
Although its speculation on my part, and probably painfully obvious to some, it just seems Holley
does not want us to figure this stuff out on our own. Further from talking to Holley on recent occasions
they have been kind of condescending and will answer some questions but don't like to expand on why
the answer is what it is. I notice Mikuni, Kehin(spelling) and some other moto carbs don't mention cfm ratings
anywhere. They simply go by size, ie. 34mm, 35mm...
So my theory is that the difference in many Holley carbs is more the size of the restrictions in the metering
blocks,differences in air bleeds, and boosters then it is venturi diameters. Again this is not a revolutionary thought, but it tells
me that configuration is more important that sizing. Holley would
prefer I buy another carb than understand exactly what is happening with my fuel curve. If you have the
experience and knowledge to change restrictions and bleeds to make a venturi dimension work well with a specific
engine combination. You'll have found that you can tailor a large bore carb to meter fuel effectivly
at a lower than rated flow level. Like a 1150 dominator on a car Holley would suggest a 750 for.
The 750, 1050, 1150, and so on, Dominator series carbs all share the exact same venturi and throttle bore diameters. Thats a big difference, further illustrating my point that calibration is everything in carbs. Precisely why aftermarket carb companies show increased succes past selling shiny parts. Custom calibration is where its at.
In Summation:
Selecting the right carb is more about selecting the right calibrations than it is actual size. Carb companies do not want you to know this, and sell carbs as a direct result.
The 1000HP has the same venturi and throttle bore dimensions as the regular 850, the 950 HP shares the 750 baseplate, and slightly larger venturis. If you were to need a good 850, I'd buy the 1000 HP just to have the adjustability. If you are not into tuning that much, the 850 would be a better choice.
My intention is to inspire some thought and discussion about a very important engine component. Please read my entire post before responding.********
Thanks!!
ps, I left(mostly) the actual diameters and list numbers out because it was simply to labor intensive for a post that may or may not take off.
I have been spending a considerable amount of time trying to learn as much as possible about Holley carbs,
and picking the right one. My research has been pretty limited, but I think its helping.
My recent hang up has been on the cfm ratings holley provides for their carbs. I have been taking a closer look at venturi and throttle bore sizing as opposed to cfm ratings. With this in mind the 950HP "should" flow less air at a certain depression than an 850 because the 850(4781) has larger venturi's and
throttle bores than the 950. Taking it a step further, a 750 4500 series carb will have 1-11/16
venturi's and 2" throttle bores. This is way larger than the 850, and yet is rated at 100 cfm less.
Now I am sure boosters will have some effect on airflow, but not hundreds of cfm's.
So i am forced to conclude that there are two things happening. Holley uses cfm ratings as a marketing
ploy, and thus other carb manufacturers follow suit. By keeping us in the dark as much as possible
they can sell us a new carb instead of making the one we have work. The second thing is that cfm ratings are
not quite what we are "led" to believe. A cfm rating might actually be the carbs intended flow usage?
In other words the carb is configured or calibrated to operate well at the listed flow rating.
Although its speculation on my part, and probably painfully obvious to some, it just seems Holley
does not want us to figure this stuff out on our own. Further from talking to Holley on recent occasions
they have been kind of condescending and will answer some questions but don't like to expand on why
the answer is what it is. I notice Mikuni, Kehin(spelling) and some other moto carbs don't mention cfm ratings
anywhere. They simply go by size, ie. 34mm, 35mm...
So my theory is that the difference in many Holley carbs is more the size of the restrictions in the metering
blocks,differences in air bleeds, and boosters then it is venturi diameters. Again this is not a revolutionary thought, but it tells
me that configuration is more important that sizing. Holley would
prefer I buy another carb than understand exactly what is happening with my fuel curve. If you have the
experience and knowledge to change restrictions and bleeds to make a venturi dimension work well with a specific
engine combination. You'll have found that you can tailor a large bore carb to meter fuel effectivly
at a lower than rated flow level. Like a 1150 dominator on a car Holley would suggest a 750 for.
The 750, 1050, 1150, and so on, Dominator series carbs all share the exact same venturi and throttle bore diameters. Thats a big difference, further illustrating my point that calibration is everything in carbs. Precisely why aftermarket carb companies show increased succes past selling shiny parts. Custom calibration is where its at.
In Summation:
Selecting the right carb is more about selecting the right calibrations than it is actual size. Carb companies do not want you to know this, and sell carbs as a direct result.
The 1000HP has the same venturi and throttle bore dimensions as the regular 850, the 950 HP shares the 750 baseplate, and slightly larger venturis. If you were to need a good 850, I'd buy the 1000 HP just to have the adjustability. If you are not into tuning that much, the 850 would be a better choice.