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| CFM question https://www.slantsix.org/forum/viewtopic.php?t=6820 |
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| Author: | Slanted73 [ Fri Sep 05, 2003 9:43 pm ] |
| Post subject: | CFM question |
Kermit Lucas's topic had me wondering now. What is the CFM rating for a stock Holley 1920? And, if I chose to use multiple 1920's.... can they be detuned (that the proper term here?) to get the desired overall CFM? |
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| Author: | Dennis Weaver [ Fri Sep 05, 2003 10:07 pm ] |
| Post subject: | |
That's a good question. I know 2 barrels are rated at 3.0" vac drop and four barrels @ 1.5", but what are 1 barrels measured at? I would suppose you could look at multiple singles as either 2, 3(?!), or 4 barrels, depending on how many you plan to attempt to use... I would just compare venturi area or carb bore size and equate it to a similar 2 or 4 barrel in terms of CFM flow. "DW" |
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| Author: | Eric W [ Fri Sep 05, 2003 10:43 pm ] |
| Post subject: | |
I've read the 1920's are rated around 190 CFM. Don't know the methode of measuring....The Holley 1945's are around 205 CFM. |
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| Author: | DusterIdiot [ Fri Sep 05, 2003 10:45 pm ] |
| Post subject: | It was in one of them there books... |
One of the Holley books and I think it was retouched in a Carter book as well like Dennis said that 4 barrels have the 1.5" (Hg)drop and 1 and 2 barrels are rated at 3.0" (Hg) drop (for those who've ever stared wide eyed at an OEM Holley 3 barrel on an early 60's Ford Truck...those get the same drop as a 4 barrel since it uses 1 main oval rear throttle plate instead of two smaller round ones...). I've heard the Holley 1920 and 1945 are rated at 175-180 cfm since they have a pretty huge bore for a 1 barrel. There's a guy in town that used to run the dual one barrel setup 5 years back on his valiant and he said it wasn't much more fun than the Super six, but his gas mileage was worse (I think some more 'tune' time and linkage solving might have helped that...) -D.Idiot |
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| Author: | Dennis Weaver [ Fri Sep 05, 2003 10:57 pm ] |
| Post subject: | |
I dunno, I think a 1920 holley isn't much more than a sorta-controlled fuel drip... My mileage improved after going from a 1920 one-barrel to a BBD two-barrel on my Duster. I don't say that just 'cause I hate holleys. The 1920 on Kermit (my Valiant, not to be confused with Kermit, the message board member  ) has kind of endeared itself to me...  "DW" |
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| Author: | Kermit Lucas [ Fri Sep 05, 2003 11:22 pm ] |
| Post subject: | |
" I dunno, I think a 1920 holley isn't much more than a sorta-controlled fuel drip... " I think Holleys are all like that. I remember friends in sea-level Houston buying a new Holley and having to drop a jet size or two for a stock engine. "The 1920 on Kermit (my Valiant, not to be confused with Kermit, the message board member ) has kind of endeared itself to me... " It ain't easy being green! |
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| Author: | Dennis Weaver [ Fri Sep 05, 2003 11:30 pm ] |
| Post subject: | |
HEY! You killed KENNY! You $%)*&*&! Kartmann |
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| Author: | Slanted73 [ Sun Sep 07, 2003 11:32 am ] |
| Post subject: | thanks for the replies |
I have been working on an aluminum intake manifold design for too long now and it never occured to me to look at the CFM of a Holley 1920. I was planning on either 3 or 6 carbs. 3 is plain enough, but I guess that leaves me around 540 CFM. The 6 carb setup was to use the second row of 3 kicking in at half throttle. Unless I can bring the CFM down to reasonable levels, I guess I have to stick with 3 carbs and some tweeking. Are there other 1 barrel carbs better suited, maybe off a smaller engine? |
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| Author: | Pierre [ Sun Sep 07, 2003 12:13 pm ] |
| Post subject: | |
All carbs, holley 1920 or not, are (somewhat) controlled fuel drippers..... |
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| Author: | Dennis Weaver [ Sun Sep 07, 2003 10:01 pm ] |
| Post subject: | |
The better ones atomize the fuel into nice, tiny droplets... "DW" |
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| Author: | Dennis Weaver [ Sun Sep 07, 2003 10:07 pm ] |
| Post subject: | Re: thanks for the replies |
Quote: I have been working on an aluminum intake manifold design for too long now and it never occured to me to look at the CFM of a Holley 1920. I was planning on either 3 or 6 carbs. 3 is plain enough, but I guess that leaves me around 540 CFM. The 6 carb setup was to use the second row of 3 kicking in at half throttle. Unless I can bring the CFM down to reasonable levels, I guess I have to stick with 3 carbs and some tweeking. Are there other 1 barrel carbs better suited, maybe off a smaller engine?
Not necessarily. Do we know what vac drop the supposed 185-190CFM 1920 rating was measured at? I'm sure that's not @ 1.5" Hg like a four barrel. I don't have one in my hand, but I'd want to know the 1920 carb bore size, just for a starting point. Then I'd do my estimating from there. I'd bet three 1920's is more like in the 300-400 CFM range with all three carbs installed and measured @ 1.5" vac drop."DW" |
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| Author: | Pierre [ Sun Sep 07, 2003 10:07 pm ] |
| Post subject: | |
If you want atomized you should see the spray pattern of fuel comin out of my throttle body injectors
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| Author: | Dennis Weaver [ Mon Sep 08, 2003 12:29 am ] |
| Post subject: | |
Hey, injection is the way to go, I've never said otherwise. For us non-techno guys, carbs are still the simple solution. I had thought about injecting my six going back years, but decided I really didn't feel like developing that sort of expertise. Still, I'm keeping my '88 truck TB injected because it's already set up that way, even though I'm going to put in an off-the-wall engine combo. I just think a TB injected 400 CI polyspherical small block will be interesting and torquey Of course you know as well as I that MP injection is the ultimate way to go on any motor and makes TBI look like some cheesy stone-age stuff..."DW" |
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| Author: | Slanted73 [ Mon Sep 08, 2003 7:13 am ] |
| Post subject: | carbs vs injection; carb bore |
I agree on injection being the best thing, but for me, I'm looking for something of my own. I'm aiming for different and original. When the day comes where I am ata car show and the hood is raised, I want people to say - what the &$*#! is that? The , when they ask if it actually runs, I want to be able to start it up and drive home. I don't know where you measure carb bore. If it is the bottom oopening where the butterfly is, I think it was 1 1/2" to 1 9/16" diameter. Perhaps turning in the mixture needles/screws would make it possible to run all six? |
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| Author: | Slant Cecil [ Mon Sep 08, 2003 7:43 am ] |
| Post subject: | |
Holley's conversion factor for converting 2 barrel to 4 barrel flow is ---CFM devided by 1.414. I don't know how accurate this is. The #4412 500 cfm 2 barrel is half of a #4779 750 cfm 4 barrel. If flowed at the 4 barrel 1.5", cfm should be 375. The 1.414 factor says it's 354 cfm. The #4412 500 cfm rating must be rounded up as are all carb ratings. How can the performance AFBs and Holleys always have cfms of 500, 600, 650, 700, 750? Nice and even #s. Another way to judge carb cfms is to compare throttle bore and venturi size. The flaw in this method are not all boosters are the same size and shape. Take half of a #4412 500 cfm Holley. 1 barrel will be 250 cfm. The 1920 1 barrel from a 225 slant six has the same throttle bore of 1 11/16" and the venturi is only 1/16" smaller, 1 5/16" vs 1 3/8". If the 1920 is 180 cfm, does the 1/16" smaller venturi account for 70 cfm? Probably not, the 1920 booster has to be more restrictive. I was told the only difference between a 500 cfm and 600 cfm Eldebrock/Carter AFB was the booster size, same throttle bore and venturii. The bigger booster in the 500 would reduce the cfm but make the carb more responsive by giving a stronger signal. I don't have a Carter resource book, can anyone verify the 500 and 600 throttle bores and venturii? Cecil |
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