The Stovebolt Site Forums The Shop Area Engine Shop 3 two-barrels on a 235???

Was perusing the Clifford catalog today, and happened across an IR style intake for the Chevy 235 / 261. Manifold is drilled for (3) three 500 CFM Holley carbs!!!

I realize that using an IR intake throws the normal CFM figures out the window (still think three 500's is too much); but has anyone tried the Clifford three carb intake? Clifford part number is C4750.

You guys that like "eye candy", I think that, with appropriately sized carburetors, this thing would attract a LOT of attention at shows; and with appropriately sized carbs, should show a significant increase in performance.

What are appropriately sized carbs? Don't know, would require some mathematical calculations to get a starting point.

Jon

Is there still a Clifford catalogue? I'd like to thumb through one.

After highschool, I was in a car club with a guy that had a 53 Chev coup with a 270 GMC engine mounting five (5) Stromberg 97 carbs on a ram-log manifold and tube headers. It had a hot cam and was "built to the hilt." He won a lot of grudge-match money street racing. 57 Chevs with a 283 power pack were no match at all. How many CFM does a Stromberg 97 flow?

The boys over on the H.A.M.B. say the Stromberg EE-1 marked "97" flows 150 CFM.

I have never found a flow rating in my Stromberg literature.

I don't know if there is a current Clifford catalog; but I have several older ones.

https://www.thecarburetorshop.com/Carbshop_lit_speed-catalogues.htm#CliffordResearch

Jon

For those interested, here is the main web page for Clifford 6=8 site. I see pages with products listed for Chevy 235/261 and GMC 270/302, but neither showed a 3 carb intake set up. Could be the web site hasn't been updated if there is a newer catalog out???

Back when I was building "claimer" engines for the Street Stock division at Nashville Fairgrounds Speedway, we were required to run a single Holley 7448- - - -350 CFM 2 barrel. It was the local track's version of restrictor plate racing since the carb was a pretty effective way of limiting the cost of building engines. High dollar cams, cylinder heads, intake manifolds, and other "go fast" stuff made no sense if the engines couldn't breathe. A 355 cubic inch Chevy V8 would max out around 6100 RPM- - - -no matter what camshaft, compression ratio, or gear ratio we ran. The carb simply couldn't flow enough air to run any faster. A stovebolt cylinder head serves the same purpose- - - -no matter what kind, or how many carburetors somebody hangs onto the thing, the ports, valve size, and combustion chamber design will be the limiting factor. The laws of physics are not "suggestions"- - - - -no matter how creative the ad writer gets with his claims!
Jerry

What is an "IR" intake in this context?

There were several Clifford 3 Carb manifolds at the Moultrie Swap Meet this past weekend. I saw a couple for $225.00. Just wasn't interested.


PS: These were "Log" type...

Individual runner as opposed to plenum type.

I found the manifold in a 1974 catalog; I have no clue as to if it is still available. Generally, everything for which I think I need is no longer available, and I have to find used versions.

Jerry - not arguing for more air, just "better" air

Jon.

In theory, a 235 at 5000 RPM could flow 340 CFM- - - - -assuming 100% volumetric efficiency. That figure only exists in the land of unicorns and Santa Claus. Why would anyone think 1500 CFM's worth of carburetors would be a good idea?

I’m intrigued. Love to know what you’re thinking in terms of “better air.” Better distribution to each cylinder?

Also - curious what you’d calc as the right size carb for this “IR” application.

I am beginning to wish I had not started this thread

After seeing the intake in the catalog, I was curious if anyone had tried it.

If I owned a 235 or a 261, and could find one of the intakes, I would try it; but I have a wider selection of carburetors to play with than most who will read this thread.

JW - you guessed correctly on better distribution.

Now as to a size GUESTIMATE:

I will bow to Jerry's expertise on a maximum RPM (and Jerry, as I previously posted, I think three 500 Holleys are way too much), and thus use 5000 for the calculations.

For a 235, I would TRY 2-barrel carbs of approximately 225 CFM; for a 261, those of about 250 CFM. Should be able to find various size Stromberg WW's to try.

And where do these numbers come from??? Well, did you ever hear of an ouija board? I would have used my crystal ball, but I dropped it!

Actually, most are familiar with the CFM "equation" that CFM = (CID x RPM) / 3456.

But the above is not the complete "equation".

The above is more or less accurate for 4-cycle multiple cylinder engines WITH A LEAST 4 CYLINDERS. As most folks are concerned with either a 6 or an 8 this equation generally applies.

For engines with less than 4 cylinders, the equation is modified as: CFM = [(4/N) x (CID x RPM) ] / 3456 where N is the number of cylinders.

When dealing with the IR design, while one is still dealing with a 6 cylinder; for the purposes of calculating carburetor size, one is dealing with three 2-cylinder engines.

Thus the 235 may be thought of as three 78 CID 2-cylinders, whereas the 261 as three 87 CID 2-cylinders.

Plugging in the numbers (again, using Jerry's 5000 RPM)

For the 235 we have CFM = (4/2) x (78 x 5000) / 3456 is equal to 225 for each carb

For the 261 we have CFM = (4/2) x (87 x 5000) / 3456 is equal to 252 for each carb

PS: Clifford also makes single 4-barrel intakes.

Jon

Three Harley Davidson Mikuni side draft carbs and some aluminum conduit would be a lot simpler, and MUCH less expensive! They're "constant depression" slide type carbs with a vacuum diaphragm, and they adjust the venturi size and mixture to the volume of fuel and air the engine demands over a wide range of RPM and throttle openings.
Jerry

I use a slightly different method of calculating CFM- - - - -since it takes two turns of the engine to get a 4 stroke cycle on all the cylinders, I plug in cubic inch displacement times 1/2 the desired RPM- - - -which gives "cubic inches per minute". Divide by 1728 (cubic inches in a cubic foot) to get "theoretical" CFM. For a more realistic guesstimate, use 90% of that number to account for less-than-complete cylinder scavenging on the exhaust stroke.

Example- - - - -
350 cubic inch Chevy V8
6K RPM

350 X 3000 = 1,050,000 cubic inches per minute, or 608 CFM theoretical volume

608 X 0.9 = 547 CFM- - - - -now- - - -why does somebody need a 750 CFM carburetor (or bigger) on that engine?

Jerry

This is exactly why a spread bore 4 bbl. is so effective on the V8, small primary bores for great idle and mid-range drivability with repeatable crisp performance. Vacuum actuated secondary with large bores will allow the amount of air/fuel that the engine is capable of inhaling. Even though the Rochester/Carter Q-Jet was rated at 700 - 750 CFM for the small block and a stock big block Q-Jet was rated for 800 CFM, they would flow only the cubic feet of what the engine could flow.

The big secondary throttle plates on the QJ are actually mechanically opened, but there are two "fail safe" modes incorporated into the design. When the choke is applied, even a little bit, the secondaries are blocked shut with a mechanical lockout. Once the engine is up to normal temp and the choke is released, a spring loaded air valve prevents too much flow through the secondaries. The Pontiac 230 cubic inch overhead cam engine actually came equipped with a QJ carb! Some of the Rochester 4G square base 4 barrel carbs back in the 1950s also used spring loaded secondary air valves.
Jerry

My apologies to everyone, seems I need to start reading with a magnifying glass.

There was quite a list of applications.

But reading the fine print, I find that the manifolds were designed for three Holley 500 CFM 2-barrels EXCEPT for the Chevy 6's which were drilled for single barrel carbs.

Makes a LOT more sense!

I guess no one has tried this, or they would have corrected my initial post.

For those who like eye candy that actually works; this manifold with APPROPRIATE single barrel carbs should work well.

Again, my apologies for starting the thread with incorrect information in the first place.

Jon

I doubt this is individual runner, but it wouldn’t take much to make it that way:

Home made intake

Interesting choice to have the carbs mounted 90 degrees out of phase with the center one. But the way the outer carbs are biased to the center, makes me think it might actually fit in an AD truck.

Perhaps a good starting point for a sufficiently motivated person (not me) to do some three carb experimentation.

(Not my item, just linked for discussion purposes)

That one's a home-brewed application- - - -look closely at the picture and the brass welds that attach the outboard flanges can be seen. Carbs for the WW II or early 1950s flathead Jeep 4 cylinder engine might be a good choice to run on something like that. The engine would still be WAAAAYYYY overcarbureted, but not nearly so much as with three 216 carbs or something similar.
Jerry

That one is definitely a home-brew kludge. Unless there's block off plates in between the carbs (can't be seen in the pictures,) it would probably run better with the two outboard carbs blocked off below them and run just as dummy non-functional carbs.

Oh I fully realize it’s home brew and ugly as sin. But it wouldn’t take much to make it a decent starting point for a test manifold.

If anyone has one of the Clifford C4750 intakes that is available, I would be interested. This thing sufficiently intrigues me to build even though I don't have an engine to put it on. Bet if I built the unit, I could find a volunteer to test it for me.

Jon

I would take one for the team, Jon…

If the secondary carbs were linked progressively, I bet it would be a lot of fun. The brazing even looks proficient, Farmer John knew how to rock a hot wrench. That home brew tri-power is the soul of hot rodding.

So….some were kicking around the idea of using 3 side draft carbs the other day. Jerry has mentioned the Mikuni thing a few times.

I stumbled upon a local FB listing for some Zenith-Stromberg 175 CD. Which sent me down a rabbit hole trying to figure out which cars used them. Looks like most British stud…Jags and Mags.

I know nothing about side draft carbs and even less about British-application side draft carbs. Would three of these be a candidate for a 235/261?

Here’s an eBay link just for reference:

https://www.ebay.com/itm/1268273874...r=&widget_ver=artemis&media=COPY

JW51, those look just like the carbs on a Sunbeam Alpine I had for a while. https://photos.app.goo.gl/CYHTHohaoakkH9ns8

My daughter had a Triumph Spitfire with one of those carbs on it, back when she was in high school (She's a grandma now). As I remember, it was a pretty good carb, although I had to rebuild it once. It's in the same category as the old S-U "constant depression" design, where a sliding piston tries to maintain the same manifold vacuum at all cruise throttle settings by sliding a piston up and down to change the size of the venturi, with a needle valve attached to it for mixture control. The difference is how the piston gets moved- - - -the carb in the ad, as well as the Harley Davidson carb I mentioned use a rubber diaphragm to move the piston. The old S-U just had a close-fitting piston in an aluminum cylinder- - - -no diaphragm. The Brit engine S-U carb mechanics interpreted "constant depression" as their state of mind when they tried to keep the things synchronized!
Jerry

It has been a long time since I played with any of the S.U. / British Stromberg CD series carbs; but memory tells me lots of folks removed the CD's to replace them with the earlier S.U.'s.

Jon

Older thread from the HAMB on this topic.

https://www.jalopyjournal.com/forum/threads/stromberg-175-cd-sidedraft-carbs-on-a-six.615320/

Jack made a couple of different versions of the tri manifold. For the 235/261, the first versions were actually steel fabricated. I have only seen photos. I have never seen one in person as they are very very rare. I am going to have to dig up my old Clifford catalogs and look for this unit as I do not remember seeing a cast aluminum version for the 235/261. Keep in mind that at one time there was still an NHRA class for the 235 and 261 so anyone running that class was trying to extract every ounce of power they could. Clifford sold some really large camshafts for these motors. I owned one that I had purchased new in the late 80s from Jack when he was still alive and running the business, right up until I had it reground last year after I realized it was way too big. Never even used it. Realized as an older guy that the head simply could not support the cam. But it was strictly a race motor approach, and probably because customers were asking for this stuff, he made it. As a young man, I was in the bigger must certainly be better mode so I might have been right in that wheelhouse had I had the money to get the cam and the tripower manifold, lol.

On the other hand, Clifford did make a ram IR type cast aluminum intake for the 230/250/292 motors. I own one but have not built a motor to use it on yet. I have to double check but my memory is that the manifold was drilled for the large base Rochester 2 bbl. But I also remember talking with a guy who was running one and said the Rochester 2bbls on that manifold were too small and that most ran Holley 500s. Keep in mind that the 2bbl cfm is determined using a different mercury factor then the 4bbls 1.5 vs. 3.0 so if you are comparing a 4bbl cfm with the 2bbl cfm, you have to do a little math.

If you want to compare the CFM rating of a 2 BBL to that of a 4 BBL multiply the 2 BBL rating by 0.707. So a 500 cfm 2bbl flows 353.5 which is not really that much on an IR manifold.

The only Clifford Aluminum Ram Tri power I ever saw that ran three Rochester 2bbs was on a race pickup truck. But he had a plenum box made to bolt to the Clifford IR to create a plenum. That intake set up ended up on Jim Tinsmith's "Mild Bunch" altered. I have a photo of the manifold on the truck so when I get home I will post it.

Man-a-Fre also made a tripower intake for a late model chevy. Originally for a Pontiac but fit the chevy. Had tiny cast sort of plenum that proved too small and so lots had issues getting them to run correctly on a race motor

www.youtube.com/watch?v=EySvHVl93Qk

Dos Palmos also made a terrific tripower intake with big ports that connected the runners with each other with rubber hoses. Very rare but that intake ran really good with three holleys. Rarely seen.

Here is a home made intake with three 500 holleys on a 292. Not a ram intake, similar in design to the Dos Palmos with the large tubes connecting the runners, but well done just the same.

www.youtube.com/watch?v=4Uw9GcsuLp0

The head on a 230-292 will support that kind of HP, not so much with the 216-261.

Calculating the theoretical CFM at various RPM ranges (assuming 100% volumetric efficiency which is impossible) can be a real education. Most people stick their fingers in their ears and chant "LALALALALALA!- - - -I CAN'T HEAR YOU" when I point out that the laws of physics aren't suggestions! A 235 at 5000 RPM can only flow 408 CFM- - - - -and that's assuming there's no friction losses in the ports. Now- - - - - -tell me why it's going to need around 600+ CFM of carburetion- - - - -I'll wait patiently!
Jerry

It seems that three Harley EVO carburetors would be about the right size for a 235. Three EVO engines are about 240 cubic inches. Just looking at possible setup.

I've been preaching that idea for at least the past three years, and getting ridiculed every time I mention it. I've offered to donate free runtime on my dyno to anyone who thinks his ridiculously overcarbureted engine will show some kind of dramatic improvement in horsepower or torque, and all I ever hear is crickets. Like the old Sun Electric Company slogan that they put on all their test equipment- - - - -"We Test- - - -Not Guess!"
Jerry

Taking a 350 cfm Holley, calculating to be apples to apples with a 4bbl, it’s 247.45. Two would be 494.90, so pretty close. 600 4bbl, yes, too big. 450 4bbl, pretty close.

We were required to run a Holley 7448 (350 CFM) in the "street stock" racing class I built engines for about 20 years ago. A 355 cubic inch small block Chevy will run an absolute maximum RPM of 6100 on that carb before the venturis restrict the airflow enough to prevent any more speed- - - -regardless of the gear ratio, cam, exhaust system, or head modifications. At one time, I had a hundred hours or more of dyno time documented on that setup, trying to wring a few more RPMs and faster lap times out of it. That "350 CFM" carb was flowing 627 CFM at that speed- - - - -it just couldn't do it at the manifold vacuum Holley specified. My engines would turn 6500-7K, but they couldn't pass a detailed tech inspection. Fortunately, the tech crew was too dumb to catch how I was cheating- - - - -they even confiscated my carbs frequently- - - -and I'd take a brand new one out of the box and run the same lap times with it.
Jerry

An air bleed?

I was looking at those carbs the other day just to get an idea what you were envisioning.

The manifold fabrication would be easy peasy. One thing I couldn’t quite get my head around was throttle linkage. I’m sure there’s a way to do it. But would take some figuring.

There is an outfit online that sells a 3 to 1 throttle cable. That might be the most expedient way to handle it.

I have heard that the traditional 3 carb manifolds (such as Offy) interfere with the firewall and/or fender brace in AD trucks. And looking in the engine bay, would agree that is probably true.

Here’s a goofy idea that might minimize the amount of custom fab work a guy would have to do to run three carbs in a 47-55 truck. It’s a pretty half-baked idea, feel free to shoot holes in it.

Take a 3 carb manifolds (use Offy just to picture it). Flip it upside down. Run three UPDRAFT carbs. There were at least a few updraft carbs that had an accelerator pump type of system. Trick would be finding ones the right SIZE.

It would be ugly as sin unless you did some custom milling of the exhaust heat provision which would be facing up. Clearance with a stock manifold might be a problem, too. Might force you into headers.

Yep- - - - -I had a few sneaky ways to bypass the carburetor and give the engine more air. The engine wouldn't idle- - - -way too lean- - - -but it was easy to jet the carb rich enough to compensate for the air leaks at speed. One trick was to drill holes in the bottom of the intake runners so they could suck up air out of the crankcase. Of course, we also used a little oil that way, but locating the holes as high as possible on the manifold plenum helped. Some guys put flat washers between the carb base and the intake, but the tech guys learned to use a feeler gauge and catch that trick. My engines had to have the intake manifold removed to find my modifications, and that didn't happen very often.

A bellcrank and heim joints can link three of those Harley carbs together, and if the heim joints have turnbuckle type threads the synchronization is pretty simple.
Jerry

Smokey would be proud.