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Discussion Starter #1 (Edited)
I am looking at getting a carb and I was looking at a Holley 670 street avenger.

I got to checking the specs and I am confused. The ventrui and throtle plate bores on the avenger 670 are the same as a 1850 600 vac.

If the 600 is dry flow tested at 600 cfm how can the same ventruies and bores wet flow at 70 cfm more? I thought that wet flow testing would always show a lower more realistic flow.

According to one resource I found on the net, wet flow is typically 8% to 16% less than dry flow. If I factor my 3310 750 vac (dry flow) by say 11%, I get 670 cfm wet flow. If this is correct, then buying a 670 avenger because my 3310 750 vac is too large would be pointless.
 

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Technical Support Barry Grant
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Wet Vs. Dry Flow

It's not a fair comparision number since most manufactures won't test their carburetors at the same vacuum rating both wet, and dry.

Dry ratings are not a good comparision since they do not give you any valid data to compare.

Wet ratings are only valid if your engine is pulling the same amount of vacuum at W.O.T. as the vacuum being used in the test.

These type of test numbers are realistically only valid when comparing carburetors by the same manufacture that have been tested in the same manor.
 

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Discussion Starter #4
So, does this mean that the Holley 670 avenger (670 cfm wet flow) and the 600 (600 cfm dry flow) which have the same size ventruies and bores would flow about the same if they were both tested the same way and at the same pressure?

What I am really trying to do is find out the true flow of the 670 avenger compared to a 3310 750 or a 1850 600.
 

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Technical Support Barry Grant
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Litdave said:
So, does this mean that the Holley 670 avenger (670 cfm wet flow) and the 600 (600 cfm dry flow) which have the same size ventruies and bores would flow about the same if they were both tested the same way and at the same pressure?

Given the same testing procedure, and A/F ratio they should be the same on a flow bench.


What I am really trying to do is find out the true flow of the 670 avenger compared to a 3310 750 or a 1850 600.
Not really a good question... The real question would be what they would flow on your specific combination. Since an engine is an air pump it is going to flow the same CFM regardless of what size carburetor you are using (Unless you restrict it) so the real question is which one is going to work best on your application.
 

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Discussion Starter #6
Correction:

I just talked to Holley and they said ALL of their carbs are wet flow rated. I thought Holley rated their carbs (except avengers) on dry flow. They said the reason the 670 flows more than the 600 (with the same bores) is because they have a different style booster.

Tech @ BG, I know you are a Barry Grant tech person and I really appreciate your help on Holley carbs.

I have a ZZ4 engine in a daily driver with a 750 Holley. It runs fairly good but I thought downsizing the carb a little bit would help throtle response and not really effect total power. I have decided that a 650 vac secondary carb would be a good choice.

I am just trying to make sure before I spend $300+ that I am comparing apples to apples and really getting the right size carb. But, if they are all wet flow rated, then comparring Holley 600, 670, 750 or Demon 625 or 650 seems pretty straight forward.
 

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Technical Support Barry Grant
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I have a ZZ4 engine in a daily driver with a 750 Holley. It runs fairly good but I thought downsizing the carb a little bit would help throtle response and not really effect total power. I have decided that a 650 vac secondary carb would be a good choice.

650's run really well on these engines. Our 650 Speed Demon actually produces more horsepower on the average than a 750 Holley on the ZZ4 engines.

I am just trying to make sure before I spend $300+ that I am comparing apples to apples and really getting the right size carb. But, if they are all wet flow rated, then comparring Holley 600, 670, 750 or Demon 625 or 650 seems pretty straight forward. [/B][/QUOTE]

Still not a fair comparison when going from one manufacture to another, plus a flow bench number is still not going to be a fair comparison to what the air pump of an engine is going to do.
 

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Discussion Starter #8
OK, I give up. How do I make an educated guess on which carb to get?

I currently have a Holley 750 vac and thought that a carb that is approximately 100 cfm smaller would be better.
 

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Technical Support Barry Grant
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Realistically you'd need to speak with the Manufacture that you are planning on working with. The size that one manufacture may recommend may not be the same as one that another manufacture would recommend.

We build specifically calibrated carburetors for the GMPP Crate engines. On the ZZ4 we use a 650 Speed Demon.
 

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Hey Tech at BG.

I was thingking about getting one of those Holley annular booster carbs. They come in 750, 830, and 850 models. Which one would you suggest for my engine?

SBC 404 11:1
Sportsman II heads fully ported
234 @.050 .520" 114o lobe sep.
16 initial
RPM Air gap intake
 

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Technical Support Barry Grant
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Not being one of my carburetors, and knowing how they are calibrated I couldn't recommend one of theirs.

I would want to know more information about the combination to determine which one of our carburetors would work best for. You're most likely looking at something in the 750 range.
 
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