4Bbl instead of 3X 1Barrels?.

[powerband]

For discussion input: I was thinking of the the Offy type modification of 3 intake port - OEM center and cyl's 1/2 - 5/6 bored ports on the intake runner.

> A simple plenum box "adapter" from 4Bbl flange to the Offy' three carb ports? .

> IF instead of three single carbs, a plenum box to the 3 ports arrangement with (say) a single moderate 2or4Bbl would have what general effects on engine operation in your opinion ?.

(... considering experimenting with an alternate to the Offy 3X1 I'm currently running Current 3X1 Offy' (250) runs well, had experimented with outers blocked and center fed with 2X1 adapter and Holley 350 CFM 2300 ran quite well.)





have fub

 

[bmbm40]

Sounds interesting, I think Exctasy detailed something like that a while back. Have you considered running the two outer carbs only, block off center? I keep thinking that would be a good setup with 2 h/w progressives off the Pinto as they are 235 cfm I read in the Falcon manual. Together 470 cfm opened up and some use the 500 cfm Holley so does'nt seem like to much cfm. I don't know if the carbs are easy to find, maybe in a Pinto junkyard. May need the large log head and larger exhaust valves, definately a big cam.

 

[bubba22349]

I like were you headed in your thoughts been kicking ideas over for my bracket racer on building a ram type manifold for a 300 like the tunnel rams built for V8's they worked great if you didn't mind cutting a hole in the hood. For my near stock 250 street car over all it's a good runner, but that seems to hit a wall around 68- 70 bad if you need to pass somebody. Have also wondered about setting up a pair of 2V carbs or maybe even 3 progressive Webers 2V's where the 3 primaries are on straight linkage. Also cutting either the side or top out of the log head besides the plenum being too small IMOP the ports are also too short. If you could incorporate some of the tunnel ram design and a bigger plenum into your 4V Idea think it could be a winner. Some time back there was a discussion on the 240 / 300 on plenum sizes were FTF recommended that.

"Plenum shape is of lesser importance. There are rules for designing a good street driven plenum, e.g. the plenum should overhang the end runners by about an inch; the plenum volume should be about 50% - 65% of the engine displacement; etc." FTF

 

[xctasy]

When Lincs 200 came up with a Sidewinder external ducting to the out log like this,

,

I knew I could put a 2-bbl on the log and get it flowing well enough for port EFI.

If you slapped a proper 4180 or 4160 600 cfm 4-bbl on the Offy, and had some tubes going to the outer four cylinders via the secondary circuit of that carb, you'd be making serious power.


So we take a late head like this


and slap a 4-bbl to 2-bbl adaptor on the 1-bbl adaptor, and then funnel the secondary 2-bbl out to the outher ports.



And here are the basics in alloy.

 

[powerband]

... reviving an old post open to some new conjecture, revived the plenum proof work and have a few pics to post. Not nearly as esthetic' as Xctacy's alloy works' , ... hopefully to test soon:

.







have fun

 

[powerband]

.. here's an update for any interest in performance carb options: finished the Offy tri-power to 2BBl plenum adapter and attempted test start with a known-decent running 7448 350 cfm 2300 Holley , the 250 ran fairly well even with whistling vacuum leaks at fasteners causing idle problems. Copper gaskets sealed vac' problem and swapped in 500 CFM 4412 2300 Holley. The idle jets now are very sensitive - a good vacuum indicator , stable idle down from WOT jabs to @ 1100 which is about same as the tri-power setup ( 272H cam). surprisingly ran well enough to rig up throttle and take a drive... - improved low to mid power but local roads don't easily permit high speed tests.

...really wasn't sure what effect the large plenum to Offy runners would have. Widely different opinions drove me to test this out. I was satisfied that drivability was demonstrably improved and there is no dreaded BOG snapping to WOT . The three Holley 1904's ran very well but I'm trying some options for better performance, early result similar overall drivability gives credit to the vintage Offy tri-power 1904's " street cred " ...

habe fun

 

[FalconSedanDelivery]

Cool

 

[powerband]

I drove a few hundred miles to Bennington car show in Vermont and a trip to the Green Mountains with Hi-rise plenum 500 CFM setup. Performance has better low end grunt and I barely crack throttle to maintain legal speeds. there is no bog or hesitation and idle is lumpy (272 cam) but stable at @ 800 with 4412's ported vac to dizzy (at @ 16 TDC initial timing).

...anxious to return to LV's 1/4 mile for the real test ...

with heavily modded Edelbrock air cleaner, throttle and fuel line finished:

. .

haev fun

 

[xctasy]

It's lovely. You've given birth to a Tunnel Ram i6 intake, Powerband. Just add another two 500 cfm carbs!

From viewtopic.php?f=5&t=31668

I found I could run the time honoured Weber Isolated runner details

http://img.photobucket.com/albums/v223/ ... ing_II.jpg

I'd done some rearranging to this. It produces the carb size in mm's via the LN function at 6, 8 and 10 000 rpm, so its out of range for the 3500 to 5000 rpm our stock sixes often do.

Back then, I was thinking only three 350or 500 cfm carbs, but you can do it with a mixture of 4-bbl and 2 bbl carbs. It would then becoem a tunnel ram intake!

Summary of my purpose then was .

1. I'm trying to bring Port on port, isolated runner 'pulse tuning' right down to our stock 252 , 256 and 264 cams used in 200 and 250 I6 Fords, and fill out the torque power and economy curves as much as possible with stock Holley 2300 series 350 or 500 cfm parts.

2. I'm defining ideal Holley carb sizes by use on existing 200 and 250 engines, and defining new so-called Y3.5, Y4 and Y4.5 values for 3500, 4000 and 4500 rpm based on the time honoured Weber Isolated runner venturi chart

Background absolutes.

1. The ideal engine capacity for 2300 series 350 and 500 cfm, or split 4500 1050 or 1150 Holleys on I6 engines is a natural log (Ln) function. The Ln function varies due to rpm at maximum power.

As listed above, the venturi sizes in mm's are listed

at Y6 (6 000 rpm) is 13.9 Ln(x)-48.9,
at Y8 (8 000 rpm) is 17.1 Ln(x)-59.6
and Y10 (10 000 rpm) is 17.9 Ln(x)-58.9

From http://forums.hybridz.org/showthread.php?p=680623, I followed a link, and found the formulae for 5000 rpm via use of a Weber Jetting program used for 1200 to 2400 cc 4-cyl engines. It confirms the Y6 and Y8 equations. For Y5, the formula is

Y5, (5000 rpm) is 12.5 Ln(x)-46.8

The carb tuning looks to be so sensitive that a venturi even a mm or 40 thou too big or too small can vary the power rpm by 200 rpm.

I'm aiming for a Y4 (4000 rpm) or even Y3.5 (3500rpm) target.

I am now summarizing that a 250 Falcon with a three #4412 500 carbs needs a cam which provides peak power at 5000 rpm.

A 200 Falcon six with three #7448 or 9117 350 cfm carbs needs a cam whch provides power at below 5000 rpm, possibly 4800 rpm.

A 250 Falcon six with three #7448 or 9117 350 cfm carbs should only need a cam which provides power to 3500 rpm to run in an optimized manner.

2. Since I have an engine block that can be built as a 200, 221, or 250, and a block which can take any Ford head, and any number of cams, I can test any engine configuration.

3. The time hounoured standard jetting of isolated runner engines with no power valve, is always 1/25 th of the venturi diameter. So a 350 will like a 48 jet, a 500 will like a 56 jet. Since one carb is working for only a third of an engine , a power valve may need to be two stage and the PVCR's have to be reduced from 53 or 62 thou down to perhaps 16 to 19 thou. Any of the commonly available two stage power valves will cover for the difference from open loop (11.5:1 , wide open throttle ) to close loop (14.7:1, cruise) conditions. This will allow an effective enrichment of 2 or 3 jet sizes whenever vaccum drops, but will do so in stages. With some science applied, a triple carb engine should lean cruise like an EFI champion.

 

[xctasy]

I'm using a 4-bbl 660 centre squirter workalike on mine, with a second 2-bbl 350 with Holley 500cfm base and 1.25" venturis and 1.6875" throttles on my 3.3. That makes six barrells like a set of three DCOE42 carbs with 32 mm venturis. The power band comes in at 4400 rpm on my 256 degree cammed car, and with 54 to 60 Holley jets, and no power valve, I'm sure I'll get 200 hp.

I have a planed head, 12.7:1 compression, and your set up is very close to mine.

Lets do some parallel work, I love the way your heading FORD.

 

[powerband]

Parallel work on maximizing/optimizing the small block six is what it's all about, it's encouraging to have members who can actually "do the math" prep on engine builds without their eyes rolling back in their heads. :roll:. My machinist is helpful but often have to ask for help with real-world applications.

'trying to comprehend how a 4Bbl and two 2Bbls isn't too much for a mild cam 200/3.3. @13:1 CR was mentioned... ?. I think it was explained in the previous post ... 8)

have fun

. . .

 

[Soldmy66]

Just a Monday AM quarterback idea, but - here goes -- it might work out well to have the top of the manifold removable, so that the inside of the manifold could be bolted to the adapter from inside the manold, and the top bolted to a lip inside th maifold - and then different manifold tops could be tried. I assume something like a valve cover (or other) gasket coud be modified to use between the manifold and its top.

 

[rbohm]

Parallel work on maximizing/optimizing the small block six is what it's all about, it's encouraging to have members who can actually "do the math" prep on engine builds without their eyes rolling back in their heads. :roll:. My machinist is helpful but often have to ask for help with real-world applications.

'trying to comprehend how a 4Bbl and two 2Bbls isn't too much for a mild cam 200/3.3. @13:1 CR was mentioned... ?. I think it was explained in the previous post ... 8)

sometimes a larger carb actually works better than a smaller carb and here is why;

it comes down to airspeed velocity through the carb. while you want good velocity, if the intake isnt designed with handle that higher velocity, the incoming air and fuel can actually bounce around and separate, and then you have problems with some cylinders being rich and others being lean. with a larger carb, the air velocity is actually slower, which means the air and fuel can turn the corner better and remain mixed better, thus providing a more consistent mixture in all cylinders.

 

[xctasy]

Parallel work on maximizing/optimizing the small block six is what it's all about.....

'trying to comprehend how a 4Bbl and two 2Bbls isn't too much for a mild cam 200/3.3. @13:1 CR was mentioned... ?. I think it was explained in the previous post ... 8)

Iits only one 4160 4-bbl 660cfm carb with 1:1 link and thats mated to just one extra throttle body on a same sized throttle and venturi version in 2305 2-bbl form, to create a kind of Lima EFI 2.3 4 cyl manifold but in six cylinderform.

See http://www.merkurencyclopedia.com/Idea_ ... index.html. Then look at this,
http://www.bo-port.com/images/uploads/Lower_Intake.JPG
then look at this
http://www.merkurencyclopedia.com/Idea_ ... ntake2.JPG

A 6-bbl intake top piece version of the 4 cylinder would look like this.



It would have extra runners for the outer intakes, but you get the idea


The issue is then just the total amout of chamber filling with the jets you use. Tunnel Ram V8's with dual 4224 pn Holley 4-bbl 660 centre squirters are some of the least efficient combinations around in terms of how much horspower you could get from eight 76 call size Holley jets, but they produce a sensational amount of top end power,even if they need plenty more revs or fuel compared to that idelized Weber chart. They new all this back in the 1930's and 40's, and by the 70's, the tunnel ram revolution allowed engines to zone in on peak power for drag racing. I mean, a dual qaud engine might be running 1.5 times the revs at peak power and then need 3 times the jetting to make the same hp as the Weber chart, but if its just a cam, manifold and jetting choice, then the Tunnel Ram is the way to go for our sixes. In a drag race, three 350 CFM carbs on a tunnel rammed log head would beat three DCOE 45's on a 2V style Aussie head. In the situation where a 480 cfm 4-bbl Classic Inlines engine might make 265 flywheel hp, and more with DCOE45's on, you may only need six 38 mm venturis and 5000 rpm to get that. With a tunnel ram, and six 30mm venturis from three stock 7448 Holley's you'd need 7500 rpm and 69 Holley jets to get well over 265 hp. But the point is, you'd get over 265 hp. easy. Its nothing to wack in a nice 310 degree cam, and still have it idle. If you went down in rev range, you'd go down in power to about 210 hp at 6000 rpm with a milder Clay Smith 274 cam. And Tunnel rams idle really nicely. And probably 190 hp with a 264 cam on a 200 at 5500 rpm.

On a 250, the peak rpm figure would drop, and you'd most likely make 210 hp with a 264 cam at about 4800 to 5000 rpm. I'm picking that would run three 350 cfm carbs with ease.


Some background to the math. Just 1.64 liters per minute used to make a 3 liter 1975 F1 engine make 500 hp , but on a tunnel ram, it will need 4.3 liters per minute and use three times the fuel to make less hp. Tunnel rams are not econo packages, but they are beter than the tri power offy and edelbrocks. I'd say you add 20 hp if you slapped your old 1904's on that height intake manifold.

With the above Dual Quad combo, even a little 327 small block will make 400 hp with one tunnel ram. Any time a tunnel ram is employed, they make 40 hp more over a the best 4-bbl intake manifold. The key is what happens in the intake port runner when its resonance tuned. Some of the kinds of tunnel rams vary lots, but in all cases, adding height and carb size works fine, even if the carb venturis are sligtly too small. In terms of carb venturi area to cubic inches, 33 cubic inches per square inch of venturi which used find on a typical small block Ford or Chevy with a set of 660 or 850 centre squirters is pretty darn useless according to the Weber chartsd, but having a 5 to 10 inch drop from the carb base to the intake valve makes up all the hp you'd loose on the idelised Weber charts above.

It's the same deal when Ford added the twin 4500 Dominators to the 1969 Boss Mustang, top end power went for a skyrocket, 550 hp wasn't uncommon, but it was on an engine with only 5 inches from the intake valve to the carb. Any time you raised the intake with a tunnel ram and smaller 660 or 850 cfm 4-bbls, the HP figures went up despite the smaller venturis. Back then and now, racers couldn't legally get a tunnel ram or long branch Traco or Moon style DCO/DCOE Weber cross ram into the engine bay, but when those old TransAm engines were allowed to use the Moon style cross ram quad DCO 50's on super sedans, the Boss 302 and Chevy 302's gained even more power on the best tunnel ram. So the summary is that if you add height and length, you can play around with sub optimal venturi sizes, and still get some unreal hp from some out of range venturi sizes.

The final measure of efficency is how little total cc per minute of jet you need to make hp. If you can get I hp for every 3.24 cc per miniute of jet, you will make a six 32 mm venturis require a 50 call size jet, and you could get produce 370 hp from just 1.2 liters of fuel per minute. If it was a tunnel ram with four sub optimal 350 CFM Holley 7448s with 1.1875"venturis, but a nice tall height, it could use three time as much fuel to make 350 hp with that manifold and the right cam.

Anyway, have fun and keep on with it. Your almost at the stage where you can just slap three DGEV38's with 27 mm venturis, or three 5200's with routed out 30 and 31 mm venturis, and get a super runnig engine. Tunnel rams are an American institution,and yours is the best I've ever seen for a small I6 anywhere in the world.