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

I first stumbled across that chart when I was fooling around with an Austin Healy Sprite I had for auto crossing. It is a 1098 .030 over. So call it 1100 cc it has a shaved and ported mini cooper head and cooper S intake with headers. It sports 2 h6's at 1 1/2 in. I believe it making about 70hp up a bit from stock 56. I had also given some thought to putting a pair of 2 lnchers from a TR6 3 liter car on my bored 235 (3.75 l) Plymouth engine but settled on two stock carters. Chassis dyno shows 127 rear wheel HP at 3280 rpm with some other mods but stock can. I like the tuneability of the SU's but didn't have the fabricating skills to do the intake. I would think two one into three setups with a balance tube would be fine. And yes there is a ported vacuum source on the carbs. But remember your signal will only be half of what the single carb provide cuz each of the 2 carbs is only pulling 50% of the total air flow.

 

All the SUs have provisions for ported vacuum under every carb, so maybe I just do that. Plumb in all 3 to the distributor.

 

If you were building an all out racing engine where top speed was the only consideration I would say use the 3 carbs.
For a street engine where drivability and economy are as important as top speed going slightly undersize on the carbs is a good idea, particularly with stock head and cam.

The engine you outlined actually sounds too mild for 2 carbs and would probably work better on 1. But if you add a cam and split manifold or header then 2 carbs should be about right.

Here is a thought. Why not build a log manifold with room for 3 carbs and run the 2 you have with a block off plate in the middle. Then try it out. If you find yourself with the throttle to the floor running as fast as you can go and wishing for more, and you still have a high reading on the vacuum gauge, buy another carburetor.

 

That make perfectly good sense in my little head!

That has to be tried out, ASAP.

 

On that subject, this is an intake for Volvo B18 & B20, the 1.8/2.0l 4 cylinder little brother of the 3l six you got your carbs from. Origin unknown, but it allows the use of either one or two 1 3/4" SU carbs.

 

Yes, and that is from a B20B, B18D looked different

This is the desires B18D separated cast Alu intake


This is the B30A intake

 

Something to consider:

You already have a factory installation of side-draft carbs on the 235 to use as a pattern. The 1953 and 1954 Corvette used THREE Carter type YH carbs. My guess is three were used because of the intake port configuration on the 235 cylinder head. I don't ever remember anyone ever stating the Corvette 235 was over-carbed.

Doing a bit of comparison: the H6 SU carbs have a throttle bore of 1 3/4 and the YH only 1 1/2; however, without actually flowing the carburetors, I would guess that the 1 1/2 inch YH flows more than the 1 3/4 inch SU (the bridge acts as a restriction). And while I really like SU carbs (I even have the capability of machining different metering needles), they simply are not as sophisticated as the Carter YH. OK, all you SU enthusiast can start throwing rocks; they won't hurt

So if you can fabricate an intake as good as the Corvette intake, three of the 1 3/4 inch SU's could probably be made to function quite well.

I understand your "build on a shoestring", however, take a peek at the second line in my signature! The metering needles in the SU are pretty specific. How does the peak RPM of the Volvo compare to that of the 235?

But in the long run, we can beat the subject to death in pixels, but the only way you will know for sure is to try!

Jon.

 

Some one say Corvette intake......just happen to have one...... I have more pics if interested if your looking to fab one up.......

Sent from my QTASUN1 using The H.A.M.B. mobile app

 

Sent from my QTASUN1 using The H.A.M.B. mobile app

 

I agree that 3 carbs are the answer but under the circumstances the twin carb setup should work well, and have practical advantages for regular driving.

The Corvette was a pretty mild engine. Stock 235 with mild cam later used in the 261, high compression, 3 carbs and dual exhausts. If you get a reground cam and split manifold or header, the 3 carbs should work fine. The duals will work too. The extra carb will help make more power but mostly at higher speeds which may or may not be of interest.

1953 Chev engines - all 235 six cylinder - basic manual trans engine, solid lifters, 7:1 compression, 108HP. Powerglide engine, hydraulic lifters, 7.5:1, 115HP. Corvette engine, hotter cam, 3 carbs, dual exhaust, 8:1 150HP

235 cu in = 3.8 liters. So, substantially bigger than the Volvo 3 liter but not to the point of being ridiculous.

 

I agree with you post, and I understand the part about the 235 being bigger, but it's only making 108 hp, where the Volvo makes 130hp in base trim and 165hp with injection. Engines still be the same. And at a wider powerband.

To me that tells me the carbs being more uniformly spaced, makes a major difference in fuel deliver.

But I been going back and forth in my head, about 2 or 3 carbs.
And the blocked 3 carb manifold makes good sense to me

 

I hope to pull manifold soon.
And start doing measurement for flanges.

Would it be blasphemy to paint the engine either Volvo red or Ferguson grey.

 

Paint it whatever color makes you happy. Stock engines were gray.

 

Hi, volvobrynk! Just saw your thread here. Love the idea of SU sidedraught carbs on a 235. Whether you use a Corvette intake or fabricate your own......

* The 3 siamese inlet port design of the 235 head lends itself to 3 sidedraught carbs. That will be the more efficient way to go due to equal fuel distribution and a straight shot into the intake ports. By all means, use a Corvette intake if you can locate a good one. GM engineers spent a great deal of time designing this intake and it is very efficient for what you propose.

* The GM intake is sized for triple carbs having 1-1/2" throttle bores. Use 3 SUs having same throttle bore dimensions. Alternately, you could use 3 Mikuni HS-38 motorcycle carbs.

* 2 carb intake will not be as efficient on this engine due to abrupt changes in direction of flow path, but you could use a pair of 2" SUs.
3 x 1.5" = same cross sectional area as 2 X 1.837". So you would need to step up to a pair of HS8s, as a pair of HS6s would begin to choke flow over 3,800 RPMs.

* Yes, connect ported vacuum lines of all 3 carbs together and connect your ported distributor vacuum to that.

* Yes, run good air cleaners with adequate flow capacity so air is filtered and flow and metering of carbs are not adversely affected.

Hope this helps,

Harry

 

You make a good point.

I'm not gonna run a homemade intake, corvettes is out of my price range.

I initially thought of two because I've seen em run 2 downdraft carbs. And thought that would be the good setup for a stock engine.

And the fact that I had em. I got a 235 carb that have been broken of the intake, missing one mount hole, and I got a carb of a 261 that has been left in the rain. That further motivated me to do a cab change.
And the very fact that a single carb on a long six just never been the performer that the engine deserves.

But thanks for the help.

 

Volvobrynk, on an otherwise stock engine, the pair of SUs might work for you. Jetting is the mystery. You will be breaking new ground there. I would suggest trying them as they are now jetted and see how they work for you. And if you need to rejet them, you can work that out after you have the engine running.

If you want to do this without spending huge sums of money building a new manifold from scratch, you can make some mild steel carburettor mounting flanges 1/4" to 3/8" thick for your SU carbs and either weld or braze them to your original iron intake and use a drill to open the throttle bore holes in the side of your intake. Just make a steel blanking plate for the original carb mounting flange and seal that off.

Good luck with your SU carbs,

Harry

 

Just remember that you may have to change the dashpot springs before changing the needles when you're setting up your SU carbs. If the piston goes to the top of it's travel before you've got your pedal to the metal, the motor will run weak - a stronger spring (the different SU springs are colour marked with paint) will improve, or with the correct spring, fix that. If the motor runs rich whatever under power, the dashpot spring is probably too strong and is preventing the piston from rising and admitting more air.

Many people have let themselves get into the situation where they're continually changing needle profiles on SU carbs and the motor doesn't seem to respond. This has lead to SU carbs being declared to be difficult or impossible to tune, but in these cases, the Dashpot spring being unsuitable is usually the culprit.

Carb setup really needs to be done on a rolling road dyno, as revving the car up on your driveway won't show what's happening when the motor is under load.

As a "quick and dirty" fix to see what's going on under load on SU carbs, I've taped an L shaped strip of tin (use double sided tape and a cut up baked bean can) to the front of the piston base so that the base of the letter "L" pokes through the carb intake, and the upright of the "L" comes level with the top of the dashpot. Make this letter "L" shape too large for the carb to actually swallow if the tape comes unstuck. Now, as long as you can drive your car with no hood, you can see the carb piston movement under load.

Edit: BTW, I think a pair of HIF44s should be plenty big enough, the 3 litre Austin Westminster from the early '60s made 110 BHP on a pair of 1 1/2" (IIRC) SU carbs

 

I been working on my transmission, for the same car, so I made no progress on the intake.

My latest idea might be a little wonky at best, but I would like to hear some advice on this, before I make up my mind.

I got three carbs in my stash, that is a matching set of 3 Solex 44 PA1 downdraft carbs, that's 1.73 inch bore, with a 1.25 inch Venturi.

It's surpose to flow ballpark off 200 CFM, can be a little more depending of year. Some sources say 210 CFM.

Will this be more fitting for a stock 235?

Or should I just spend more money on a third SU HIF6?

 

This is the carb in question

 

the 4.2 Jag ( 258 cu in ) engine made 170 hp on 2 x 2 inch SU carbs, ( HS or HD8 ) 215 cu in Olds, Buick Pontiac when used in Rover cars used 1 3/4 inch SU carbs x2 to make in the region of about 160 hp in the UK, I would have thought the pair of Volvo carbs you have ought to work just fine.

Kev

 

Volvobrynk, I think you are following my champ car build thread, but you mentioned you like the 300 Ford and if you haven't seen this 2 x SU intake I made here are some more pics. I plan on two HS-6s.
If that is not enough I'll build an intake for three SUs.
Or five.
Or six.

 

Any more comments about the 3x Solex 44pa1?

 

Volvobrynk, if you go with the downdraught Solex 44pai carbs on an unmodified Chevy 235 inline 6, 2 carbs are all that you need. I have used 3 of the Weber 34 ICH carbs with 29mm chokes (main venturi) on a modified 250 inline 6 but with the larger 31.75mm venturi size of the Solex, I would suggest staying with a pair of them. If you want to use your original iron intake manifold, weld or braze 2 carb base plates to it evenly spaced between the 3 port openings and blank off the original center carb mount with a blanking plate.

Beautiful work, Frenchtown Flyer! Love the dual SU intake!

Best regards,

Harry

 

update
The HS3s pictured have been replaced by two Mikuni copies, roughly equivalent to HS6s. These Mikunis were used on a Datsun 240 / 260 Z. Although originally fitted to a smaller engine. The Zs revved to a higher speed than my 300s so the airflow should be about right at 4500, my engine's sweet spot.

Volvobrynk, Did the 235 get done and driven? Any updates?