Technical 2xSU carburetors on a Chevy 235, 1954 Car engine.

Hey

I got me a Chevy 1954 235 cui prezzurized engine.

And I want to run dual carbs on it, and instead of going straight to EBay, and buy a 2x1 or 3x1 intake for it, including Strombergs.

It's so far a T54ZD engine, and it's as far as I know stock.
And for now I don't plan to throw a cam
in it.

I plan to build my own intake, because I got the tools and skills to do so.

And I plan to be "thrifty", with my thriftmaster.

Here comes the big question, I plan to run side draft 1-3/4" SU HIF6 (AUD466F) out of a Volvo, go figure [emoji6], they was on a B30 (3liter/181", 130hp) and then on an modified B20 (2lite/121", 140hp).

But now I plan to run them on a Chevy 235.
They should flow around 240 CFM.

Any advice on manifold design?
Should I run velocity stacks or aircleaners?
How does one dimensions Velocity stacks of it's the way to go?
Is 240CFMx2 in the ball park for a 235?


And what is HP, CR and torque on a 1954 235

 

SU is the best carb ever made. Chopper magazine ran dyno tests on all available carbs in 1974 and SU was the best overall performer. I still have the magazine and use them on my Harley and my Model A

 

And I save that picture, ^^^^
Because that is the most bitching banger around!
Only Ford motor I like better is Flathead and 300 I6!

You rock!

What are you running HS6?
Making what HP?

@manyolcars

 

from the Chevy engineering documentation, you can get it from the GM Heritage web page.



I expect the carbs will work pretty well for your application. But there are three intake ports, so you kind of want 3 carbs, with a small balance tube. Remember that carbs that only see one or two cylinders need to be bigger than carbs that see all the cylinders.

 

They should work great. As squirrel pointed out you have the problem of feeding 3 intake ports from 2 carbs, the usual solution is to make a log manifold. 3 short pipes off the head, a long horizontal pipe connecting them, then a couple of short pipes to the carbs. If you wanted to save work you could use a square tube and bolt the carbs directly onto it.

For winter driving you might want to weld a water tube to the bottom of the manifold, connected to the heater hose for better vaporizing of the fuel.

The 2 carbs may be too much for a stock motor. Consider doing a split exhaust manifold and duals, or even a header if you feel ambitious. Add a reground cam and you have a real nice, mild hop up for not too much money. If you have a friend with a lathe, lighten the flywheel for whippier acceleration (another old hot rod trick).

 

X2...
You need three SU carbs. Variable venturi carbs are really great when they are properly maintained.

 

One question I don't have the answer for, is what to do with the vacuum advance to the distributor? It is ported vacuum, connecting to the manifold will NOT work. Do the SUs have a provision for vacuum advance?

 

3 carbs would be nice but he only has 2. Lots of Chev sixes have run with 2 down draft carbs. I don't know why side drafts wouldn't work.

As for filters or velocity stacks I would use filters.

PS thousands of Jaguar sixes used 2 SUs.

 

There are lots of ways to do it, and a log manifold should work fine. The suggestion for 3 carbs is based on the idea that SUs seem to work well feeding two cylinders who's ports are right next to each other.

search google for pictures of SU intake manifolds, there was a wide variety of them made for production and aftermarket use. And lots of triple Jag intakes, too

 

On my son's sbc, we have one barrel of the Weber feeding one cylinder. The reasoning is, better response, even flow, and easier to tune.
I have run SUs, Bendix sidedrafts, and Webers, and they all run better when you are feeding one carb barrel per cylinder.
We drilled each runner and plumbed the lines into a single piece of 1" copper pipe, to provide the signal for the vacuum advance.

 

I built one of these manifolds about 10 years ago. Still isnt on my car. but anyhow, it takes 3 SU 6's to get enough CFM at WOT. they just run lean with 2 carbs no matter how you fatten them up. I spent a ton of time with a paper and pencil and bought all the SU books I could find. Dont take my word for it though. buy the books and read up on it so nobody can fill you full of shit with what they think should work. PM me and I can send you a photo of what I built.

 

Hell I ought to just sell you my manifold. 3 rebuilt and perfectly matched SU - 6s off a volvo complete with polished pot. Exhaust almost done. Putting bungs on right now for balance tubes.......

 

Not that I entirely sure, but the HS makes less CFM then the HIF.
I think it's 200 vs. 240.

440 is still enough, for a stock engine?
I believe Langdon runs 36/38 on them.

I'm just curious, the same SU HIF6 can feat a Volvo 181" with 130hp, and can support up to 190hp.

Although, if I was going for that much, I would go Weber/Dell'ortos.


Sent from my iPhone using H.A.M.B.

 

The books recommend carbs based on cubic inches and RPM and then recommend the number of carbs. I dont think there was a 6 cylinders that these carbs come on that has 2 carbs, but I could be wrong. And if it makes any RPM at all it will need 3. My mild 235 needed 3 carbs. I looked for 8's but didnt want to afford them. A 261 would need 3 SU -8s. Again dont take my word for it. Buy the books and read up. its interesting reading. I also think the 36/38's you refer to are down drafts. And from what I read there is not enough statistical difference between any of the versions of the SUs to make a difference. They all work. I chose HIF because it fit my car better

 

If 2 SU's didn't work on inline 6's there must thousands of 50-60's Jags/Austin Healy's still waiting to be sold. I have no idea what SU's they were.
Other than that, the 54 and earlier Chevs had shimmed mains and liked to leak out the rear. A PCV would help and pretty ez to do with log manifold. The 62 Chev had the last 235 and did have a PCV at least in California.
One of the fastest Chev 6's at Bonneville used 3 S&S super G's and looked great coming off the side with a 5* up mount.

 

You make perfect sense, and I would kick my self for not asking the question.

And FYI Volvo B30A 181" makes 130hp with 2 Stromberg, but some people run the SU in stead. I belive its a marked/skillset thing.

But it only made 130hp, that's 15 more then the B20B that does make 115 with the same carbs.



But the same engine B30E (FI) makes 168hp, with same cam and parts.
Only slightly bigger intake valve and Bosch D-jetronic.

 

If you are saying lots of Jags, Austin healeys etc had 2 Su's on them it might be good to check cubic inches and which carbs they had. If in fact they had 2 carbs I would be willing to bet they were SU 8s on a 6 cylinder with a lot less than 235 cubic inches that didnt turn a lot of RPMs. I know for a fact that anything with these cubic inches required 3 of at least size 6. 8s are better. Im not trying to start an argument. Just relaying what I discovered.

 

That 235 probably isn't going to turn 5Krpms...think about what you'll build it for...not sure how to compare, but mild 235's ran pretty well with the holley 390 on them, not the cool factor of multiple carbs, and I know that 4bbl and 2bbl, etc are rated different for cfms,but just something to think about

 

Care and feeding of SU carbs
http://www.sw-em.com/su_carbs.htm#SU

 

So referring to the above graph, 235 cu inches is slightly under 4000cc ( 4 litres), and the graph doesn't state whether it includes losses in efficiency, so the smallest set-up you could get away with would be 2 x 2 in, for an engine putting out 125 to 150 hp.

 

Thanks, man.

Just curious, what SU carb is this specific for.

I'm not trying to be a PITA here, but there is two 1-3/4" SU, the "Old" HS6 and the "New" HIF6.

And they flow differently, respectively 200 vs 240.

And I bet it makes a impact on the chart, or moves the scales so to speak.

In just curious how much impact that is.


EDIT
I see now it's for the HS6 carb.
Anybody got a similar for a HIF6?

 

This is a chart with HS6 vs HIF6.

 

I haven't played with them in some time, but here is a link that I think will provide the information you are looking for.

http://sucarb.co.uk/technical-carburetter-maintenance-settings-hif

Bob

 

Both Austin Healey and Jaguar DID use 2 SU carbs on some of their sixes. Successfully. In a previous life, I had several XK-120's with the 3.4 and 2 SU carbs.

No offense meant with my next statement:

If you are building your own intake, then plenum versus IR, port arrangement, runner size, etc. is probably MUCH more important than whether you will use 2 or 3 carbs, or if you will use HS or HIF carbs. Once the manifold design is finished, will be time to determine number, type, and size of carbs.

Here is a link to a web article done by a gentleman who posts under the username of panic that explains far better than I am able to do:

http://victorylibrary.com/mopar/intake-tech-c.htm

Jon.

 

Plym46 that was the chart I was trying to recall and explain. Thanks for posting.

 

Fair and valid point, but if I have the carbs, but they won't fit, I might as well swap the SU in for a different intake with carbs, that fit the engine.
But I'm willing to find an third used Volvo/SU HIF6.
But I just feared it would be to much carb for the power the engine delivers stock.
I have no plan to swap the cam, at least till I have test driven the car.
Whole build is on a shoestring.
I just got a broken carb I don't want to buy anything new unless it's brakes or tire department.

Will a 2 SU adapter to the log manifold be a waste of effort?

I just like the look of multi carb on a Stovebolt six.

Have you seen this chart



Wouldn't this put two HIF6 with in the ballpark of stock 235.

 

I would think it depends on the year of the 235. I know some of the rated HP numbers were not that accurate, but if memory serves me correctly a 54 - 235 stock had 109 HP. the later 61-62's were 140. The problem is if those numbers arent very accurate. hmmmm

 

Okay, so getting an extra carb would be better, and I'm prepared if I want to go with a better cam?

And it can be made two work that way, if I do balancing tube between all there holes in the head.

How big should said tubes be.

 

I kept the volvo manifolds from my HIF. My balance tube is just a bit smaller than that becvauase thats the closes size we could get. I think its 3/8 NPT. And yes, if you put a cam in it and change much you could easily bump the HP beyond the limits of dual carbs. But Im not a carb guy.