Flathead Intakes

I'll post my Y-intake tomorrow.My mill will also have the generator running on top of the intake,so,I can't see how you can run both generator on that place & a dual 2bbl intake aswell?!
I'm going for period-correct,all the parts on my '39 will be pre-'55.
You people in the states have it easy,trust me.Sweet mills you guys do run there.I'll be the first guy in South Africa running a flathead in a hotrod,can you believe that!?

 

First one I had was a Jack Henry, two into the original manifold. who knows if it made a difference or not. There were not many dual manifolds around at that time.

the trouble is that when you stick that on the manifold,you have already made changes to the engine and you really don't know whether it was the adapter , the cam or the heads.

LOL

You just use what is available and what you can afford. If you can't afford one, get some pipe and build it!

traderjack

 

Feeding both carbs into the same 2 bbl. opening is more restrictive than separate mounts.
However: the vacuum demand at each venturi is reduced by 50%. This means that:
1. the CFM of each carb is reduced (you're not getting 155 from a 97 any more)
2. the total CFM supplied to the engine goes up
3. pumping loss is reduced

I did some math, and a 239" motor turning 5,000 RPM and 70% efficient, using a single Stromberg 97, draws 3.05 psi of vacuum - it's not big enough (duh). If you use 2 of them the restriction drops to .76 psi - which is about the rated pressure drop for modern 4 bbl. carbs (.74", which is safe).
Pumping loss is reduced by 8.5% - a very nice drop.

A thought as to why progressive works better: the primary carb "sees" the same vacuum conditions it would if it were alone, so low speed response and jetting are fairly predictable - the vacuum only drops when the second carb opens.

 

1 - The CFM of each carb remains the same.
2 - The total CFM AVAILABLE to the engine goes up, the engine will only draw whatever it is capable of

 

1 - No.
2 - No.

 

1 - Yes
2 - Yes

We can do this all day.

1 - Bolting on four 1000 CFM carbs does not change the fact that they're 1000 CFM carbs. Carbs are rated at a specific flow (varies by 2bbl or 4bbl) - just because you can't pull that flow through them does not negate their "official" rating.
2 - There is 4000 CFM available to the above engine now, but it's doubtful the engine can use all that CFM based on the nominal displacement of a street engine.

 

"Bolting on four 1000 CFM carbs does not change the fact that they're 1000 CFM carbs."

Ummm... yes, it does. The rate is entirely dependent on the engine vacuum. The 1000 is rated (like all 4 bbl.s) at 1.5" Hg.
If it were on an engine large enough to pull 10" of vacuum, the carb would flow 2582 CFM.
If the engine is so small that it can only draw .5" (just barely running - the low limit of venturi function in conventional carbs) the flow drops to 577 CFM.
With the engine off (no vacuum), a 1000 CFM carb flows 0.

"Carbs are rated at a specific flow (varies by 2bbl or 4bbl) - just because you can't pull that flow through them does not negate their "official" rating."

Wrong again. What's missing here is that you simply don't understand how a carburetor works. Rather than just repeat your mistake, again, again - why don't you do some research?

 

Re: "2 - The total CFM AVAILABLE to the engine goes up, the engine will only draw whatever it is capable of"

Let me back up a bit.
That statement has some merit, because if engine demand is low the flow through the carb drops.
It's got a limit though - if the demand is low enough to drop the vacuum at the venturi to less than 1" Hg the carb begins behaving badly, poor response, needs a big pump shot and rich jetting. If it goes below .5", fuel flow at anything less than WOT is irregular and can't be adjusted out.
However, it's important to distinguish this from vacuum-operated secondaries and CV carbs, where the opening itself automatically adjusts to engine demand.

Still confused? Don't be - it's a complex subject, I've been doing this for over 40 years. Read my article (unless you already read it when it appeared in "MoPar Action"): http://victorylibrary.com/mopar/intake-tech.htm

 

I do believe we're arguing semantics. You admit that the carb is flowed at 1000 CFM at 1.5" Hg. The fact the engine cannot draw that is irrelevant & does not change the carb RATING at all. A Holley 1850 is still 600 CFM even if I bolt it to my 3.5HP Briggs & Stratton. Will it be an effective fuel metering device on that engine? Nope.

I'm not confused - it's quite obvious what's going on here. I suggest you go look up the word 'obtuse' - we're done here.

 

I agree, in that I have no interest in explaining this to any greater degree.
It's not semantics, it's physics and it's not subject to opinions.

 

For me, it's what I could afford, and I think it looks damn cool. It's traditional, as the old ads from the mags show.

FOR ME, it's not all about performance. It's going to be about simplicity, ease of tune, and fun. I'll probably not even run the second carb, probably block it off. Won't have to deal with dual power valves, etc. I'll make a linkage that looks like it's being used, connect a fuel line, etc.

But it'll look really cool, and run fine on the one carb.

Don't care if you don't like it. Ain't your car.

Pete

 

My purpose is not (NOT) to show how smart I am - why should you care?

It's, instead, to supply information that allows people to make their own successful choices before spending time and money.

There are 2 general rules to follow so your project works:
A. ask someone who knows, and do what he says.
Problem #1 with this is that everyone thinks he knows. The very popular "I have a nice car, therefore any statement I make about how it works is correct" is an example. Trust me - there are winning race cars out there that would be even faster if the owner knew what he was doing. Almost every winning car before 1970 was based on ideas we would properly laugh at today.
Problem #2 with this is the common tendency to listen to several people (who don't entirely agree), and to believe that "taking the best of both" is a good plan. It's not. The buffet method ("I'll take this from here, and that from there") of selecting speed equipment is a big mistake.

B. learn the subject yourself - start by reading Vizard (easy - he explains it in practical terms), Bell, Smith, and Blair (if you can stay awake!). It's taken me 40 years - don't expect to learn it in 10 minutes.