The Holley "Trick Kit" literally

NoMoore

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May 26, 2006
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****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.
 

LS6 Tommy

MalibuRacing Junkie
May 15, 2004
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Booster size does indeed have a lot to do with flow. You'd be suprised. if one booster only restricts 25 cfm more than another, that's 100 CFM right there at WOT. Booster location matters, too. IIRC, even though it is considered to be a "higher" performance setup, a carb with downleg boosters will flow less than one with straight boosters in the same carb body because the booster is in a smaller diameter part of the venturii, so less air gets by it. That's also why a downleg is generally considered to be more sensitive.

My carb guy is specing out an HP 1000 for my 454, only he wants annular boosters to make sure he gets good atomization to make up for the idiosyncrasies of my stock LS6 intake. He tells me it will not be oversized because of the restriction of the annular boosters.



Tommy
 

Goob

Top Fueler
Jun 6, 2003
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All you would have to do is place a 750 Dominator next to an 1150 Dominator to see what Tommy was saying.....

The Dominator carburetors were developed by Holley in conjunction with the Phord factory engineers to solve fuel distribution problems in the FE Series NASCAR engines, by moving the throttle bores away from each other, and spread them out over the plenum area.


Some drag racer saw one of them deals and it was on..... 8)
 

CutlassRacer

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Dec 18, 2004
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Great topic!!

I think it would be really neat for someone to test some of your theories on an actual flow bench to see what different boosters do to the flow. Like Tommy said, booster location would also be something that needs to be experimented with. I would kinda doubt that there is a major conspiracy on Holleys part, but it would still be interesting to find out exactly what is going on.

I have always been under the impression that the cfm rating on a carb was figured out (by Holley of course) as a measurement of the amount of dry air that flowed through the carb at a given amount of vacuum under the carb.

There are so many things that can affect the cfm of the carb that may not be listed in the dimensions of the carb. Carbs work off of a venturi effect, so minor differences (how the bore is tapered, size of the bore, venturi style, venturi placement, throttle blade size) I would certainly think could make a huge difference in the total cfm that the carb can flow. Like Tommy said, take what happens in one bore, multply it by 4 and you can see that minor differences can add up quickly.

So who has a flow bench and alot of free time that wants to figure this out for us :)
 

NoMoore

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Thread starter
May 26, 2006
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With the 4500 750, I guess they have boosters that are shped like upside down mushrooms, which covers a good bit of the venturi.

I have a similar but much more humble thread going on speed talk. Here is a quote worth reading. It is the ONLY flow data I have seen yet, but I am still hunting.
I have a carb flow setup for my SF 600 bench. I do flow test lots of carbs. The Demon carbs flow quite a bit MORE thaN THEY are rated at. The Holley 950 is a real joke. I hear people raving about it all the time. On the dyno, it is the SAME as a 750. and on the flow bench, it is around 15 to 20 CFM better than a 750. An 850 flows more and gets around 25 more HP than the socalled 950.The Demon 850 will flowup around 1020 cfm dry. By the way, Holleys rated flow is wet, so my test setup says to deduct 8 percent forr the wet flow loss.Just a little insite on carb flow numbers.
JOE SHERMAN RACING ENGINES
 

NoMoore

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Thread starter
May 26, 2006
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On the venturi shape, it is very possible that the shape has a huge effect. Case in point, Holley will use the same drill for more than one jet size, flow is altered by the length of the hole and the taper before the hole.
 

Goob

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Jun 6, 2003
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Supposedly jets are stamped with the "size" by their actual flow, not the size of the orifice......that is how they come up with the "H" jets as well, but you are correct, the entry/exit radii and length of the orifice do account for the flow available.
 

NoMoore

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Thread starter
May 26, 2006
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Here is a pretty good source for parts, and booster installation tools.
http://www.blp.com/default.asp


I am interested in spending some tome learning about booster positioning and the actually restriction sizes in metering blocks by part number.

Do any of you have any info on this?
 

Goob

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Jun 6, 2003
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BLP RULES!! on small parts and tools, I need a booster tool myself to fix my 850 that progressively got worse on the throttle hit to the point that the engine would nearly die.....I think I have a well tube that has fallen loose in my secondary metering block, and it also has a loose booster.

I'm leery of playing with emulsion holes in the metering blocks or high speed air bleeds without the aid of dyno time and EGT's for all 8 cylinders.

Some of the carb modifiers do very little to the out of the box Holleys they sell as "custom", some of the others actually do some work, and you'll never know which is best without lining up about $40K worth of carburetors and trying them on a durable dyno mule. Even if you did that then put the carb on a car and went to run it, the results could vary from what you saw on the dyno.

For what we do, I think the out of the box Holley carbs and a touch of tuning are as good as you get.
BG's carbs are tunable, but at 3 times the cost of a Holley for the bleeds and small parts.

Consider the replaceable booster multi-cfm rated carbs he sells.

If you're not looking for performance improvements of thousandths of a second or running an endurance engine setup, it's not worth the trouble or expense, I just jet it fat, run it cool, and let it eat......

I do know this though, the top NAPCAR engine builders own their own carburetors that will pass tech, and they have a freaking heart attack when one of them gets damaged in a wreck. The engine builder moves on to some other team, his notes and carbs go with him.

Good circle track racers think nothing of having $3500-$4000 in their carburetor.

For me, shoe polish is cheaper.
 

Goob

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Jun 6, 2003
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Indianapolis
booster positioning and the actually restriction sizes in metering blocks by part number.

Do any of you have any info on this?

Forgot to answer that. :roll:

No, but I'm always looking......I saw a carb shop site a while back that was interesting, I need to look and see if I can recall it.
 

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