Thoughts on carb conversions (Holley 350 vs. 500)

[Anonymous]

I'm seeing a lot of mention of swapping Holley 350cfm to 500cfm 2bbl carbs. Different folks think different things about the pro's and con's. Here's another thought that may be a fresh idea, or may be old news:

Has anyone given thought to adapting a Holley 480cfm 4bbl with vaccum secondaries? It would require fabrication to mount the 4bbl, but might be worthwhile.

Based on my search for a bigger carb on my old 302-equipped Falcon (before they lifted the CA smog restrictions on the '69's) it seemed to me that the Holley 500cfm 2bbl had two huge mains and no secondary. I was advised that it would be a Bad Idea<tm> to do this swap since the carb would feed way too much fuel at low RPM. The upper end performance gains would be good, but at the expense of low end power and fuel economy.

Enter the 4bbl- The mains feed the right amount of fuel for economy driving, and the secondaries deliver that added punch when opening it up. I'd think it would work the same on the Inlines. The 480cfm should deliver plenty of flow for those engines that need it.

Am I totally daffed? Or is the fabrication work just too much of a pain in the butt to worry about trying?

Relatively uneducated guess, but it's food for thought.

--mikey

 

[Anlushac11]

8)

If I ever get my Stang done sometime this decade it will have a 450cfm Holley 4bbl. I know some of the guys are going to use Holley 390cfm 4bbls.

 

[Anlushac11]

If you mean adapting a 4V to a small 6 log head that's really a waste of time and money! If you mean a big 6 or an Oz 250 2v head on a small 6 then the small 4V will work great.

With the turd head it's just like trying to stuff 10 pounds of crap in a 5 pound bag!

8) NOOO

I have a Oz 250 head. Would be a bit daft trying to mount a 4bbl over that ity bity hole in the log.

 

[Anonymous]

Yah- what he just said. Was musing about the oz 250-2v head and carbs for it.

don't have the head yet, but i love to scheme about these things.

Just thinking that the 4bbl may be worthwhile since it's (in theory) easier to tune for the whole throttle range with the mains and the secondaries. In practice, who knows? i like the idea about a 390 4bbl. didn't remember them coming that small. might be great for 200 motor w/ oz head.

--mikey

 

[Anonymous]

I would be concerned that a 4 barrel on a 2v manifold would not have nearly enough volume (depth or width) were the carb exits into the inlet for even dispersion of the fuel into the runners creating accelerated wear of the engine as a result.

 

[Anonymous]

Another thing that is often forgotten with biggers carbs etc is the need for room for a bigger filter to flow more cfm. I stumbled across an article that recommend about 5cfm for every square inch of filter paper.
I have a foam 6 3/8 by 3 1/2 on the way and it is only big enough to flow about 320 cfm successfully if 5 is to be taken as a bit of a guide. Some of the filter sizes and recommendations fall no where near this, it must be like trying to suck gravel through a straw at high rpm.

 

[xctasy]

First of all. Holley 4 bbls are a cool idea. Just look at this discussion way back. http://fordsix.com/forum/viewtopic.php?t=1518

The 390 and 600 cfm vac secondary 4-bbl Holleys had smaller primary bores than the 500 cfm 2-bbl. The 600 is an easiler carb to tune, but the 390 is able to work well on any thing from a 2 liter Pinto to a 454!

The idea is to heavily dampen the secondary circuit. Sure, it gives a bigger dead spot when the last half of the 4-bbl carb opens, but there is the plus that you'll spend more time on the (smaller) primaries.
My thinking is that any increase in plenumb area is a minus. I'd say the stock 2V intake is plenty big, and the picture of the 4 venturi version lookes okay by me!

I'm going to post the venturi sizes of all the Holley carbs I know of. There is a critical gas speed, and flow rate. Seams to me there is a match up with poor drivability and low gas speed, but there is also a bunch of different booster venturi and carb venturi information that causes interesting things to the behaviour of big inch 2-bbl sixes.

 

[Anonymous]

well this was the fight i had to do out when i re did my 300. I bought the clifford aluminum single plane intake and thier dual 33" headers, so i knew which ever carb i whent whith the motor was going to use it. I ended up going whith the 500cfm holley 2bbl becouse it was more availiable cheaper and gives more immediate power. And whith me mud racing the immediate power all throught the revs is what i needed.

 

[Anonymous]

Execute, you may be right but there is a great difference between the inlet manaifolds made for a four ballelr to suit the crossflow and the 2V manifold. I realised with mine that the four barrels two main venturys are going to be to close to some runners and not close enough to others. This would not matter as much if there was the same depth and volume in this area as the manifolds designed for the four barrel.

 

[Anonymous]

Ive gotta admit that that picture of the 4 barrel 2V does look good (does seem to have enough height). Is the carb fed by the two back ones most of the time?

 

[Anonymous]

If it involves modifying an existing manifold, is it possible to set things up so that the carb is rotated 90 degrees to get better distribution from the mains (and secondaries)? It would take some fancy throttle linkage in order to work, but maybe it could be done by converting to a cable-linkage(?)

And Xecute- if you can post the ideal venturi size, etc. numbers for an OZ 2V head, that would be really cool.

Is the Falcon 6 motor handbook a good resource for such calculations?

--mikey

 

[Anonymous]

My nine by two inch filter is 28 inches around the outside.My six 3/8
inch is 20 inches around the circumferencece. 5 cfm for every square inch equals 280 cfm not enough for my 500 holley to flow 350 cfm of air. My new 6 3/8 by 3 1/2 is actually closer to 350 cfm (not 320 as in above) and should be ok.
K&N say that their filters can flow up to twice as much as a standard paper filter in some conditions.
Strange that Ive heard it recommended that the first thing to do for a cheap performance increase is to change to a better larger filter. Its often the last thing done, if at all.

 

[xctasy]

Overview: Tim, look at these facts. As I told my mate Wayne with his 2V Cortina TE, he'd needed to get an lpg snorkle for an Impco CA 300 adaptor, and link that to a remote air clearner like an EFI...if he wanted the bonnet to shut properly!. There are quite a few old LP Gas snorkles for the Bendix WW, or Holley carbs, but its all about making it fit. The cross-flow is significantly easier than the non-cross flow. Or do the dirty, and convert the intake for cool air induction, a hood scoop, that kind of thing. Good thing is that the 6.375" by 3.5" foam air cleaner flows enough to get peak power at 4725 rpm, if you do the math!.

If you use the latest conical EFI air filters for K&N, you can have a very small air cleaner. Have a look at what Citroen, Peugeot, and Renault used to do. A remote air cleaner could sit on the LHS of the engine...there's heaps of space there with no exhast! Back on topic....

A good quality paper air filter with no steel mesh has a minimum size that is calculated by this formula:-

A, the area= (cubic inch displacement*rpm @ maximum power) all divided by 20 900.

A foam air filters' minimum size is calculated by this formula:-

A, the area= (cubic inch displacement*rpm @ maximum power) all divided by 18 870.

For K&N filter, you can have 22 % less surface area and still get the same flow. The formula for A (area) is:-

A, the area= (cubic inch displacement*rpm @ maximum power) all divided by 25 500.

For a 250 reving to 3500 rpm, this is 41.9 square inches. In practice, an Aussie 1V had (H=2.047", OD=10.0",ID=7.675"), an effective area of 56.46 square inches.
An Aussie 2V (H=1.535", OD=10",ID=7.675"), an effective area of 40.37square inches.

NOTE: It is my personal understanding that the 250 2V wouldn't package into a US Mustang with the stock 2100 Motorcraft/Autolite 2-bbl, and there is no room for an effective air cleaner. The size of the 2V air cleaner was compromised by the depth of the engine, and lack hood space. An engineering decision. How many 2-bbl US 250's on this forum of 29 000 people? None!

The way to calculate the effective area (AFH) of an existing air cleaner is to take the diameter and multiply iy by the effective height. The Effective height is the total height minus 1/4 to 3/8ths of an inch.

The formula for the minimum air filter diameter is therefore:-

(A/AFH) all divided by 3.142

For K&N filter, you can have 22 % less surface area and still get the same flow. The formula for A (area) is:-

A, the area= (cubic inch displacement*rpm @ maximum power) all divided by 25 500.

So a hot 2V, reving to a maximum power at 4500 rpm with a good paper element, will need 53.828 sq in, or , with a 39 mm (1.535") height 2v air cleaner, whic has an effective height of 1.285", you'd need 13.3 inches of diameter (339 mm) for good performance.

If it was a foam element, it would have to be 59.618 sq in, or, with that same 1.285", you'd need 14.7" (375 mm).


If it was an K&N, will need 44.118 sq in, or , with a 39 mm (1.535") height 2v air cleaner, which has an effective height of 1.285", you'd need 10.9 inches of diameter (278 mm)for good performance.

Further inane babblings....For our antipodean cars down in Aussie/NZ. We have the following sizes, care of the Ryco Manual of 2000, or check link http://fordsix.com/forum/viewtopic.php?t=5662:-

A37 60-61 144 Falcon (H=2.205", OD=9.685",ID=7.913")
A55, 62-69 144-170-188-200-221 Falcon (H=2.205", OD=9.685",ID=7.913")
A217(1-bbl) 70-76 200/250 tall block Falcon/Cortina (H=2.047", OD=10.0",ID=7.675")
A224(2-bbl) 70-74 250 2V tall block Falcon (H=1.535", OD=10",ID=7.675")
A391 Dodge Truck Air Cleaner used for Impco LPG carb like mine (H=2.835", OD=10", ID 7.675").

US Ones that have simliar dimensions are :-
A37 No interchange for US, but early slant six Chrysler may fit (H=2.205", OD=9.685",ID=7.913")
A55, Ramber,Studebaker, Canadain Fords (H=2.205", OD=9.685",ID=7.913") A217, no inter change(1-bbl) 70-76 200/250 tall block Falcon/Cortina (H=2.047", OD=10.0",ID=7.675")
A224 no inter-change (H=1.535", OD=10",ID=7.675")
A391 Dodge Truck Air Cleaner used for Impco LPG carb like mine (H=2.835", OD=10", ID 7.675").

 

[Anonymous]

Thanks for the info
Cant say for the TE but I have the flat 4 bonnet on mine and the 2V although higher than the Iron head crossflow (at the manifold) does allow enough room for a redline adaptor plate (bit over 10 mm) and a nine by two inch air cleaner. I have about 10mm + clearance to the bonnet and have turned the base of the air cleaner upside down and modified it slightly so that it now sits lower than before. It still seals well and the top stops it from moving.
I have had it rubbing on the bonnet previously but is good now. I am going to cut a hole in the bonnet for the new one with a small bonnet scoop.
Regards Tim

 

[Anonymous]

Execute
I looked at an original 2V one I have last night and it only has a bit over about an inch of actual paper and an outer and an inner paper. Must be fairly restrictive Id imagine.

 

[xctasy]

There is a good list of Holley carbs further on, which I've transfered below.

I got a little carried away, and ended up with all of Holleys pre 1988 listings, along with some special Barry Grant, 3-bbl and 650 cfm 2-bbl carbs which were realeased for racing.

 

[Anonymous]

Gah! Tried to post and got dropped. Right before the "Submit" button. Why don't we have a "resist" button, anyway?

Thanks for the info Xecute.

So, what constitutes a "long duration cam?"

I'm looking at a 264D-1 grind from AzCoupe. Is this agressive enough to give problems with a Holley 350?

Any general carb recommendations for the above cam, OZ 250-2V head, 6-2 headers/dual exhaust, electronic ignition with vacuum advance.

I'm thinking a 2-bbl with primary and secondary. Maybe a Weber 38/38 or Holley 5200. I'm going to leave behind the idea of a 4-bbl for now. Idea flow exceeds cash flow.

Eventually, I'm thinking of trying to design and fabricate a multi-port EFI system to run off a Mega-squirt. U have acess to some good tools. I just need to learn how to design the system- runner length, runner area, injector size and location, flow rates & velocity, etc. Long term plan. Carbs are the short term.

--mikey

 

[Mustangaroo]

Mikey,
Depends how much head work you have done but I'm using a Holley 500 2V on my OZ head and it runs great, very good grunt down low and great top end as well, I had to change from the stock #63 jets to #71 to keep it from running lean. The Holley 5200 is a nice carb for great MPG but not for more power!

 

[MandarinaRacing]

So, what constitutes a "long duration cam?"

Anything over 225 deg @ 0.050 is considered a long duration cam...

Alex

 

[xctasy]

The 44 carby Chronicles. All this is my opinion, hearsay, even, but it is based on feedback form people who have writen into publications like Australian and English Street Machine, Australian Wheels Magazine, Hot Rod, Popular Hod Rodding, Car Craft etc. In the fuzzy logic I work with, I've come up with these ideas on gas=flow and the Holley carb.

Theres been a lot of talk about "if my Ford Six will handle a bigger carb". Well, here's something which may help you if you are planning on a bigger Holley, possibly with more barrels.

I've done some research and found that the problem with big cams and carbs isn't the total CFM, but is in fact related to the throttle to venturi ratio, and the relative size of the primary barrels. If it has one, and the primary side of a 2-bbl or 4-bbl carb is sized small enough to suit the engines part throttle use, then the only other thing that will rain on your parade is the signal created by the shape of the carburetors venturi.

Here's the wrap. If you have a throttle area of more than 1.25 times the venturi area, you will have hassles running a long duration cam. This is because the fuel air mix fails to atomise properly due to the reversion waves, or pulses, from the intake valve. The fuel metering then gets screwed up, and the engine will back fire through the carb. In instances like this there are three options:-

1, Add more intake area or height to the intake manifold.

2, If you can back off on cam timing, do so.

3, The easiest alteration is to skim back the venturi area, so that the throttle area on the primary side is 1.06 to 1.15 times the venturi area. In other words, take the throttle diameter, divide it by 1.15 for a start, and then see if you can't fly cut the internal venturi without breaking into the carby body. If you do, just build it up with JB Weld, Epoxy, or Devcon filler, and smooth off. The jetting will need to be altered, but you will remove the propensity for spit back.

There will be situations where where the intake manifold is wrong, and nothing will fix this. Generally, if intake manifold area is about 50% of the total capacity of the engine, with no inlet tract much larger than the diameter of the throttle, then that will be a way of stopping reversion waves travelling back up to the venturi area of the carb. If it is smaller than this, the pulses can be deadened by reducing the venturi area.

Any why, heres the info to back it all up:-

Note
A. |No| is the line number of the chart,
B. |number|, the series model, not the part number.
C. |CFM| the cubic feet per minute quoted at whaever flow drop
D. |Pri B"| is the Primary throttle bore diameter in inches
E. |Pri V"| is the Primary venturi bore diameter in inches
F. |VentASQ| is the square inches of primary venturi area
G. |Signal|, the amount of intrusion of the venturi relative to the throttle diameter. Higher the %, higher the signal.
H. |Sec B"| is the secondary throttle bore diameter in inches
I. |Sec V"| is the secondary venturi bore diameter in inches
J. |Total V AREA| is the all up venturi area in the carb, primary plus secondary.
K. |Air SPD| is the actual flow speed at the cfm supplied. Maximum power happens at 200 to 300 ft/sec, so if someone has a flow rate of 488 ft/sec, then its not going to produce easy power there, and the cfm is likely to be optimistic
L. |PriBHP| is the maximum net power at 1.5"Hg for the primary ciruit
M.|Total BHP| is the maximum net power at 1.5"Hg

No|Number|CFM|Type-|Pri B"---|Pri V"-|VentASQ"|Signal%|Sec B"---|Sec V"--|Total V AREA|Air SPD--|PriBHP-|TotalBHP-| 01|#2110-|200-|1-bbl|1.4375-|1.3125|1.353“---|09.5-----|----------|---------|1.353“-------|355FT/sec|102bhp|102bhp| 02|#5200-|230-|2-bbl|1.2800-|1.0400|0.849â€￾---|23.1-----|1.4375-|1.0625----|1.736|318FT/sec|043bhp|102bhp| 03|#5210-|255-|2-bbl|1.2500-|1.0300|0.833â€￾---|21.4-----|1.6875-|1.2800----|2.120â€￾-----|289FT/sec|050bhp|113bhp| 04|#5200-|280-|2-bbl|1.2800-|1.0400|0.849â€￾---|23.1-----|1.4375-|1.0625----|1.736“-----|387FT/sec|061bhp|124bhp| 05|#6520-|280-|2-bbl|1.2800-|1.0400|0.849â€￾---|23.1-----|1.4375-|1.0625----|1.736------|387FT/sec|061bhp|124bhp| 06|#2110-|300-|1-bbl|1.4375-|1.3125|1.353"---|09.5-----|---------|------------|1.353------|532FT/sec|153bhp|153bhp| 07|#4150-|340-|2-bbl|1.4375-|1.0625--|1.7730-|35.3-|1.4375-|1.0625-|3.547--|~230ft/sec|106|213|
08|#2305-|350|2-bbl-|1.5000--|1.1875--|1.1075-|26.3-|1.500--|1.1875-|2.205--|~379ft/sec|84--|168|
09|#2300-|355|2-bbl-|1.5000--|1.1875--|2.2150-|26.3-|---------|---------|2.215--|~385ft/sec|-----|170|
10|#4150-|370|4-bbl-|1.43750-|1.0625--|1.7730-|35.3-|1.4375|1.06250-|3.547-|~250ft/sec|116|231|
11|#4150/60|390|4-bbl-|1.4375-|1.0625-|1.7730-|43.7-|1.4375|1.06250-|3.547-|~264ft/sec|122|244|
12|#4160-|450|4-bbl-|1.5000--|1.0938--|1.8979-|37.1-|1.5000|1.0938--|3.5310| ~306ft/sec|141|281|
13|#4360-|450|2-bbl-|1.3750--|1.0625--|1.7730-|29.4-|1.4375|1.1875--|3.988--|~270ft/sec|133|281|
14|#4160-|465|2-bbl-|1.5000--|1.0938--|1.8790-|37.1-|1.500-|1.0938--|3.759-|~297ft/sec|146|291|
15|#2300-|500|2-bbl-|1.6875--|1.3750--|2.9700-|22.7-|--------|----------|2.9700-|~404ft/sec|----|221|
16|#2305-|500|2-bbl-|1.6875--|1.3750--|1.4850-|22.7-|1.6875|1.3750-|1.4850-|~404ft/sec|111|221|
17*|2300-|500|2-bbl-|1.750--|1.3750--|2.9700-|27.3-|--------|----------|2.9700-|~404ft/sec|----|221|
18|#4160-|550|4-bbl-|1.5000--|1.1875--|2.2150|26.5-|1.5000-|1.2500-|4.6690-|~283ft/sec|168|344|
19|#4150/60|600|4-bbl-|1.5625--|1.25000--|2.4540|25.0-|1.5625-|1.3125-|5.1600-|~279ft/sec|183|375|
20|#4180-|600|4-bbl-|1.5625--|1.2500--|2.4540|25.0-|1.5625-|1.3125-|5.1600-|~279ft/sec|183|375|
21|#4010-|600|4-bbl-|1.5625--|1.2500--|2.4540|25.0-|1.5625-|1.3125-|5.1600-|~279ft/sec|183|375|
22|#2300-|650|2-bbl-|1.7500--|1.4375--|3.2460|21.7-|---------|---------|3.2460-|~481ft/sec|-----|288|
23|#4011-|650|4-bbl-|1.3750--|1.1560--|2.0990|18.9-|2.000--|1.3750-|5.069--|~308ft/sec|185|406|
24|#4165-|650|4-bbl-|1.3750--|1.1560--|2.0990|18.9-|2.000--|1.3750-|5.069--|~308ft/sec|185|406|
25|#4160-|660|4-bbl-|1.6875-|1.2500--|2.4540|35.0-|1.6875-|1.2500-|5.160---|~307ft/sec|-----|413|
26*|4160-|700|4-bbl-|1.6875-|1.5625--|3.8350|08.0-|1.6875-|1.5625-|7.670---|~219ft/sec|219|438|
27|#4150-|700|4-bbl-|1.6875-|1.3125--|2.7060|28.6-|1.6875-|1.3750-|5.676---|~296ft/sec|214|438|
28|#4150-|725|4-bbl-|1.6875-|1.3125--|2.7060|28.6-|1.6875-|1.3750-|5.676---|~307ft/sec|221|453|
29|#4150-|750|4-bbl-|1.6875-|1.3750--|2.9700|22.7-|1.6875-|1.3750-|6.216---|~290ft/sec|229|469|
30|#4010-|750|4-bbl-|1.6875-|1.3750--|2.9700|22.7-|1.6875-|1.3750-|6.216---|~290ft/sec|229|469|
31|#4150-|780|4-bbl-|1.6875-|1.3750--|2.9700|22.7-|1.6875-|1.3750-|6.216--|~301ft/sec|238|488|
32|#4011-|800|4-bbl-|1.3750-|1.1560--|2.0990|21.7-|2.000--|1.71875|6.739--|~285ft/sec|201|500||
33|#4150-|830|4-bbl-|1.6875-|1.5625--|3.8350|08.0-|1.6875-|1.5625--|7.670--|~260ft/sec|260|519|
34|#4150-|850|4-bbl-|1.7500-|1.5625--|3.8350|12.0-|1.750--|1.5625--|7.670--|~266ft/sec|265|531|
35|#4150-|855|4-bbl-|1.7500-|1.5625--|3.8350|12.0-|1.750--|1.5625--|7.670--|~268ft/sec|267|534|
36|#3160-|950|3-bbl-|1.7500-|1.5625--|3.8350|12.0-|1.75 x 3.625|1.5625 x 3.4375|8.682|263ft/sec|297|594|
37|#4150-|950|4-bbl-|1.7500-|1.5625--|3.8350|12.0-|1.750--|1.5625--|7.670--|~297ft/sec|297|594|
38|#4500-|1050|4-bbl-|2.000-|1.6875--|4.4731|18.5-|2.000--|1.6875--|8.946--|~282ft/sec|328|656|
39|#4500-|1150|4-bbl-|2.000-|1.8125--|5.1603|10.3-|2.000--|1.8125--|10.3206|~267ft/sec|360|719|
40|#4500-|1150|4-bbl-|2.080-|1.8125--|5.1603|14.8-|2.080--|1.8125--|10.3206|~267ft/sec|360|719|
41|#4500-|1150|4-bbl-|2.100-|1.8125--|5.1603|15.9-|2.100--|1.8125--|10.3206|~267ft/sec|360|719|
42|#4500-|1150|4-bbl-|2.130-|1.8125--|5.1603|17.5-|2.130--|1.8125--|10.3206|~267ft/sec|360|719|
43|#4500-|1150|4-bbl-|2.160-|1.8125--|5.1603|19.2-|2.160--|1.8125--|10.3206|~267ft/sec|360|719|
44|#4500-|1150|4-bbl-|2.190-|1.8125--|5.1603|20.8-|2.190--|1.8125--|10.3206|~267ft/sec|360|719|

Check with http://www.panteraclub.com/docs/carb.doc for all the gossip on all 4-barrel and even 3-barrel US carbs, including Holleys