Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-14-2012, 01:43 PM   #11
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[quote=Incommando;120454]I wasn't trashing on the Holley just noting that it can be made better, especially for serious off-camber stuff and climbing/descending angles. I swapped an intake and a 390 onto a 231-powered Skyhawk and it really helped. As you know the 231 is the direct descendant of the 225. But that is a completely different app and intended usage.

There are dozens of sites with tips for improving a Holley for off-road. The 390 usually isn't mentioned but the same principles should apply. Just one example:

Offroad tricks for Holley 4 barrel carbs | ClassicBroncos.com Tech Articles

The mod most often mentioned is the vent tube.

Incom,

Hey, no problem.....the beauty of these forums is Opinions.

I can only testify to my own experience with the Holley 390 cfm. If it had been or was an issue it would have long ago found its way into the garbage can.

And thanks for the reference material. I did do that crossover vent Mod years back.

Ultimately , use,acceptance & performance of any part usually boils down to simply , just who's turning the wrenches.
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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-15-2012, 02:49 PM   #12
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I have used all of the above on different motors of different sizes with good results but mathematically speaking a 225 ci motor at 4500 rpm at 83% volumetric eff. (typical of oem combos) it would require 243 cfm at even 100% it still only requires 292 cfm. If it were cammed to run 7500 you would be at 405 at 83% and 488 at 100% v.e.

 

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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-15-2012, 09:28 PM   #13
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Quote:
Originally Posted by Tinman22 View Post
I have used all of the above on different motors of different sizes with good results but mathematically speaking a 225 ci motor at 4500 rpm at 83% volumetric eff. (typical of oem combos) it would require 243 cfm at even 100% it still only requires 292 cfm. If it were cammed to run 7500 you would be at 405 at 83% and 488 at 100% v.e.
Tinman good points,

We know that in order to calculate true Volumetric Efficiency which is the actual amount of air the engine ingests compared to the theoretical maximum trapped per cycle one must first know what the Mass air flow volume is for any given cylinder.

Knowing at a minimum the swept volume , flow numbers on the cylinder heads, manifold,carburetor,exhaust system and air density would also be needed to even closely make a theoretical calculation at Wide open throttle.

In regards to the carburetors mentioned above the only known is the published Flow numbers of each carburetor at "Wide open throttle" and since none of these would normally see "WOT" for any length of time the comparisons given may be of no consequence.

 

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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-15-2012, 10:04 PM   #14
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Tinman22 and tarry99 you two blow me away with your knowledge
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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-16-2012, 02:19 AM   #15
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Lots of great info here!

Honestly im not a big fan of holleys, never been able to get em to work for me and dont like the design. Dad wants me to go with a spreadbore 500-650 cfm edelbrock, but from all your info that sounds like way too big

 

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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-16-2012, 02:52 AM   #16
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Quote:
Originally Posted by sweet66monza View Post
Lots of great info here!

Honestly im not a big fan of holleys, never been able to get em to work for me and dont like the design. Dad wants me to go with a spreadbore 500-650 cfm edelbrock, but from all your info that sounds like way too big
Monza,

Nothing truly is going to be perfect,and we all know there are plenty of choices out there. That 500-650 CFM is probably a larger than needed carb for that old 225 Odd-Fire in it's stock form.
But having said that your going to have to work on something to get it to your own personal liking so pick something you like and go to work.

 

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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-16-2012, 03:15 AM   #17
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The dirty little secret of a vacuum secondary carb is that it is rated by maximum air flow at WOT. However, the engine will only draw the CFM that it needs when opening the secondaries. The problem is that on most of these carbs the stock settings for the jetting/needles/whatever allows a higher fuel flow in the larger CFM carbs than a small engine can handle and they generally have a more aggressive tune via accelerator cam profiles and springs to allow the secondaries to open sooner and to squirt more fuel as well as flow more air. On a highly tunable carb like a Holley you can usually customize the carb to meet your engines fuel flow needs. Ever notice that GM used a 750 CFM Q-jet on basically every application? 307? 750 cfm. 403? 750 CFM. 455? 750 CFM. Some apps had an 800 CFM rating but for the most part most everything that had a 4v q-jet carb used a 750 CFM version for a couple of decades. Although a Q-jet has mechanical secondaries they are technically controlled via air flow, not throttle postion, and act like vacuum secondaries. They "custom tailor" themselves to the air flow needs of the engine in the same manner as the other vacuum secondaries.

By starting with a smaller max air flow CFM rated carb you are probably getting closer to the right "out of the box tune" for a smaller engine. But the main point is that as long as you can restrict fuel flow on both the primary circuit and the secondaries to a usable amount the max air flow CFM rating really is not very important on a tunable vacuum secondary carb. As the 390 has been used on tons of V6's succesfully it would seem that the stock tune of the primary jets is close to on the money for that app and that even if your engine will not draw 390 CFM at WOT it is not an issue as 390 CFM is not being forced into the cylinder, only the required CFM is being drawn in.

 

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Default Re: What is the best 4bbl carb for oddfire 225 V6? 

Old 07-16-2012, 02:37 PM   #18
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Quote:
Originally Posted by Incommando View Post
The dirty little secret of a vacuum secondary carb is that it is rated by maximum air flow at WOT. However, the engine will only draw the CFM that it needs when opening the secondaries. The problem is that on most of these carbs the stock settings for the jetting/needles/whatever allows a higher fuel flow in the larger CFM carbs than a small engine can handle and they generally have a more aggressive tune via accelerator cam profiles and springs to allow the secondaries to open sooner and to squirt more fuel as well as flow more air. On a highly tunable carb like a Holley you can usually customize the carb to meet your engines fuel flow needs. Ever notice that GM used a 750 CFM Q-jet on basically every application? 307? 750 cfm. 403? 750 CFM. 455? 750 CFM. Some apps had an 800 CFM rating but for the most part most everything that had a 4v q-jet carb used a 750 CFM version for a couple of decades. Although a Q-jet has mechanical secondaries they are technically controlled via air flow, not throttle postion, and act like vacuum secondaries. They "custom tailor" themselves to the air flow needs of the engine in the same manner as the other vacuum secondaries.

By starting with a smaller max air flow CFM rated carb you are probably getting closer to the right "out of the box tune" for a smaller engine. But the main point is that as long as you can restrict fuel flow on both the primary circuit and the secondaries to a usable amount the max air flow CFM rating really is not very important on a tunable vacuum secondary carb. As the 390 has been used on tons of V6's succesfully it would seem that the stock tune of the primary jets is close to on the money for that app and that even if your engine will not draw 390 CFM at WOT it is not an issue as 390 CFM is not being forced into the cylinder, only the required CFM is being drawn in.
Incom: Right, Right, & Right ....all Good points and precisely the point I was making earlier regarding WOT...
First off both the 2 barrel 2100 & the 4 barrel 4160 have primaries that are if not the same sized are very close to each other at I believe 1.562" each?
So no matter how you get there 2 barrel versus 4 your only getting what the engine requires via the CFM ingested air flow. DONE!
And If you don't mind playing with the Carb I still like the ability to custom tune the 4160 with all the aftermarket tuning parts available from Holley Performance. Just my Opinion!

 

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