The Stovebolt Site Forums The Shop Area The HiPo Shop One or two Carbs? Check the Vacuum?

I was told that before I add another Carb, that I should check to see how much vacuum it is pulling at, say, 50 mph.
I have a stock 235, with a Rot-chester Carb. But, I have an Edmunds 2 Carb Intake that I can put on the truck, IF it would give it a little more horsepower.
I want it to be a little stronger going up hills at 50 mph and not keep 'fading'.
Anyway, I was told it needs to pull about 2-3 inches at 50 or it would not help.
Is this the way to check?
Timmer

Timmer,

Interpreting vacuum readings is sort of a science. I am guessing that your source for this
information was indicating this test would be a
benchmark of your engines health.

I am not "vacuum wise", so I am not much help in regards to your specific question. If your engine is good condition, the two carburetors will give you a noticeable increase in power.

The vacuum test might be one way to check...but not the only way. If your rig starts and runs fine, doesn't burn a quart every 10 miles and can cruise down the road without laying down a smokescreen then it is probably a fine candidate for the two carb setup.


Stuart

I am guessing I could pull the motor, stick a mild cam in it while I am at it. I just didn't want to do all that, AND spend the extra bucks for another carb, IF I would not see any big difference.
Timmer

timmer - you could send that intake to me and i will break it in for you and tell you how it works!

Timmer,

I might be out to lunch on this theory, but I have always felt that the larger cam gave the engine the ability to breath better (longer), which opened the door for more carburetion. These two items go hand in hand!


Stuart

Timmer,

I think if you are loosing steam going up hills then a cam ground for low to mid-range torque would be most suitable. Large cams (lumpy idle) are typically used for high speed operation where the velocity of the incoming charge helps to fill the cylinder, ram effect.

As for the carb, is the truck starving for fuel? If not then more carb is not the awnser, too much carb has a detrimental effect on low-end performance.

What is the rear-end ratio? Maybe a change in gears is in order.

adding carbs to your engine can do 2 things,,over rich on fuel and slow dist timing,,if you can play with it enough and it is in good cond you could see some increase in power but it willnot be just a bolt on and go like hell...

i have a two carb set up with a nova 2.73 rearend and the dual set up does real well here in the midwest. i also have an s-10 5 speed and it pulls well in overdrive on mild hills, no slowing but you can tell. ron

Aw rite den. That's some good advice. I know I can do several things, but I just don't want to get radical. It's a new motor and the thought of pulling it to put a cam in it is not appealing. You know how it is, I got a set of Fenton Headers and that Edmunds Intake just sitting there on my shelf beggin' to be put on my truck.
Every thing you do affects something else, so now that the headers are in the equation, then there is dual exhaust, then how big of pipes, and flow master, or glass paks, etc.
Dang, I just didn't want to get this complicated, BUT I DO WANT TO GET IT RIGHT, without spending money on things that did not make a difference.
Timmer

Timmer,

As my momma used to say..Just Do It! You don't have to pull the engine to put the new cam in. The dual carb thing has been around since you know who was a kid..it works, right away! The Fentons are running a close second in the history books. They sound nice and you will feel the difference, right away.

Just do those two things, it isn't complicated. If you can do your own tax returns then this is a piece of cake. The fellow with the nose ring and Mohawk at the muffler shop will tell you in no uncertain terms the VERY best mufflers and pipes to put on your ride!

So, as my dear old dad used to say, "quite spittin on the handle and git to hoeing".

Stuart

go ahead and install and enjoy...A six will get very vocal with duals so pick a muffler that will give you the tone you want...

Timmer,
We've all been thru the thrash you are contemplating in one form or another. My 2 cents: If you have a stock rear say 4:11 go thru and check your valve timing and set stock to the year of your engine, check the book most are .006 and .013 hot if they are solid. If you are running say a 2:73 to 1 with a solid lifter cam pull a couple out of the setting this will move your power band up to better match your rear. Esample: (Cam Card .014 and .016 change to .012 and .014). If its running good move on and carefully pick your carbs, matched numbers are important. Strombergs are nice as are Zenith's but who can find them anymore. So you are stuck most likely with Rottenchester's. Rebuild them and match them up, follow the directions on this site or Inliners International as to drilling out the lead plugs and cutting springs. Get your self some smaller jets and play around with ground strap plug color.Then put on the intake and Fentons. Couple of things to think about here. Gasgets are nice but not necessary so long as your head surface and manifolds are square. I use high temp orange silicone with the intake rings, never had a problem on any engine. As far as exhaust pipe size, go smaller from the Fentons to the mufflers, then go 2+1/2 or larger from there back. This will help your gas mileage some in our hard times. Lots of information here and good people, pick their brains.

52pu - You talk about cutting the springs on the rochesters. I have seen the Inliner's tech tip on rochesters but have not heard about cutting springs. I assume you are talkeng about the springs under the power valve. Yes? Can you explain more?

Thanks
George

Because of the difference in distance between the carb and intake valves for middle and front or rear cylinders on these motors cylinders close to the carb could be running rich while those farthest away run lean.

One of the reasons for going dual carb is to achieve more consistent mixture across all six cylinders. Properly sized and tuned I would expect it to make more power and run up that hill a bit better. Might even get better mileage.

46forme:
Yes the inliners international site under tech tips and multiple rochesters; Easiest way to say it is follow their directions. You may have to collect a few rochesters at swap meets to get enough parts. Keep in mind with 2 1bbls your vacumn signal will be 1/2. Small carbs are the key. Play around and have fun.

46forme, you can get rebuilt carbs from auto zone for 100.00 i bought one 4 months ago and i have a daily driver and i am very satisfied with them. ron

46forme:
May I suggest another carb, look around for some Carter W1's. I see them all the time at swap meets around here in the carb piles. I don't pay more than 5-$10@. Turn the carb on the side and you will see W1. However they made many different varities, so look for an identical pair and get rebuild kits and match them up. They have a small venturi and good gas mileage. You will have to use a round file on the castiron base and widen up the holes to make them fit the 235 intakes.

OK, all sounds good, think I'll go ahead and make the leap.
Any suggestions on the cam?
Not looking to race here, just some good sound and better 'pick up'.
Timmer

Timmer,
Double carbs properly set up with the fentons will give you the extra umph you are looking for and also better gas mileage within reason, without going for another cam. You say its a new engine, keep the cam you got. Get this thing running on the 2 carbs before you even consider another cam. It will be an all together different engine I promise you. You'll also have to reset your timing. My experience is less timing vs more with 2x1 bbl carbs. Also reset your points to .015.

Sounds good to me.
I shoot for the twin carbs with the Fentons and dual exhaust.
I'll tweak that out first and see what I got before any other changes.
Thanks guys.
Timmer

Timmer - 52pu's comments concerning the W-1's is very good advice. You would want to use either the 483s or the 574s. These may be mixed or matched as the difference is basically the way Carter made the castings, not in the calibrations.

A couple of other comments: 52pu probably meant to say that the airflow through each carburetor will be half, not the vacuum. Vacuum will be reduced in each carb, but not half. The reduced airflow will cause a lower velocity in each carb, which will reduce the point of bleedover. This is an excellent reason for using the Carter W-1 carbs, as these carbs have a physical override on the power circuit; instead of the vacuum only system in the Rochesters.

And while slotting the throttle bodies is certainly an easy approach, and inexpensive; I prefer to take the intake to a good welder, have the existing holes heli-arced, and then redrill and retap. It costs more, but makes a much nicer appearing installation (MOO).

Jon.

If it's not too late, the absolutely best carb setup I've come accross for these engines is a 2 stage 2 barrel (like half a 4 barrel)used on some Vegas, Pintos and Chrysler K cars. Tom Langdon (Langdon's Stovebolt Parts) also sells rebuilt ones for about $65 I think. He also sells the adapters to bolt them onto a stock manifold. Even installing one of these will make a noticable difference in the engine. If the engine is in good condition it will probably accept 2 without a problem. The beauty of these carbs is that they have a small primary with a larger secondary. That gives you great fuel economy and still improves the overall performance. I have a pair of them on my 261 in a '50 pickup with a little cam an it hauls butt and still gets 20 + mpg. I also installed one of these carbs on a stock '62 Biscayne and it worked very well. Neither application required rejetting the carbs. They're great!

I personally prefer the Holley 1904. I'm running a pair on my 235 and the whoop the snot out of the Carters that I had on it first. Thay were cheaper and easier tp rebuild too. They use they same main jets as a 4bbl Holley so rejetting is easy. Mine came from a pair of I.H. 1 1/2 tons, but they also show up on GMC's and Mercury/Edsel
6 cylinders. Some of them even have a cool looking glass float bowl.

I just replaced an aged Rochester on my stock 235 with one of Tom Langdon's Holley/Weber progressive 2 bbls. He suggested the H/Weber 5200 (270cfm)($65) setup over the Carter/Weber ($85) that flows a little less and works better on a 2-1 intake. There is a bunch of info available on tuning and rejetting if you feel the need. I personally am looking for 20 mpg@65mph.

I was totally amazed at what a simple, inexpensive upgrade this actually was. I had tried the rebuilt route and couldn't find a rebuilt that had a decent throttle shaft and that was assembled properly. The H/W was $65.(with no core charge) the adaptor was $15. and the linkage was $35.00. The water-heated choke to 12v electric choke conversion was $12.00. He also sells a little paper filter breather for $35-45 bucks.

For less than the cost of a worn-out rebuilt I have a setup that runs as smooth as silk and for the first time I feel like my little 235 is responsive and operating efficiently. I've got some pics in my album that show the linkage and carb. This single progressive 2 bbl. will fill the bill until I recam and try out the C/W dual setup. At this moment I really feel that it can't get much simpler or less expensive than this upgrade.

more carbs look cooler... even if you block all but one off!!!

I say go for it.. worst case it doesnt work.