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Maximum CFM question for a 3.7 Liter 225 Super Six
https://slantsix.org/forum/viewtopic.php?t=56176		 Page 2 of 3
Author:  Rick Covalt [ Fri Sep 12, 2014 1:25 pm ]
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Since you describe yourself as a novice the Holley is probably not as easy to get tuned in. Plus from others experience they claim constant changes needed to keep it running optimally. So make friends with someone who knows how to adjust them. If you purchase a new Holley for $450 it will likely cost you some more $$ to get it running correctly.

Remember, even with a 4 barrel carb you are not running on all 4 unless you have it wide open. I would not have any fear of running a 500 Edelbrock on a stock motor, and have done it a couple times. Someone else can speak to the Holleys. I only run Edelbrocks.
Author:  Hatchworx [ Fri Sep 12, 2014 2:32 pm ]
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Rick ... I have prior experience with Edelbrocks and love them for their simplicity. This is the carb I want to run on the Offy intake. What say you?

http://www.summitracing.com/parts/edl-1801
Author:  sandy in BC [ Fri Sep 12, 2014 3:01 pm ]
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The best money and time you can spend will be to get it running right in stock Super 6 form.

A four barrel wont fix a bad advance curve or adjust valves.
Author:  Rick Covalt [ Fri Sep 12, 2014 4:05 pm ]
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Quote:
A four barrel wont fix a bad advance curve or adjust valves.
What Sandy is saying is true! If you put on a new Weber you should be able to get that sorted out 1st. It is no use to spend $400 on another carb if the carb is not the issue to start with.

It sounds like you are in a rush, and that makes things worse. But I would take my time and do some more research into what you really have as far as the cam is concerned. Then make sure your distributor curve, valves adjustment ...etc is correct. Then figure out how to adjust the Weber. Someone on here should be able to help you with that. Or search the internet for adjustment advice.

Rick
Author:  sandy in BC [ Fri Sep 12, 2014 5:51 pm ]
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The same stuff that makes a Weber run bad ,,,,,will make a Holley run bad.\


If you are in a hurry it will cost you double.

I never did run a 4 barrel on a slant....by the time it ran well enough for a 4 barrel I had more power than I needed.
Author:  Hatchworx [ Fri Sep 12, 2014 11:02 pm ]
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Here's my issue with the Weber. Two of the good trustworthy and knowledgeable carb tuners and rebuilders in my town and circle of car buddies won't touch the things. But I finally found one older gentlemen who specialized in Webers because in the 1970's he raced B210 Datsuns.

On a side note, those little Datsun race cars are amazingly fast when properly built out for racing. Anyway, at one point two years ago, I printed out a build chart from Slantsix.org where many of the kind fellows on this site had experimented with various jetting and finally found the right combination.

I then ordered the new jet kit from Weber and paid the Weber specialist to rejet my carb based on specifications I got from this fine website. The fist set up from the Weber factory was crap. Totally bog and no power at all in low RPM ranges. The original set-up would not open up and show power until at least 65 to 70 MPH.

After the rejetting job, no change. Well a little change. Still total bog and power loss at low RPM and a noticeable power increase sooner now at around 50-MPH but nothing amazing or impressive. And even worse, going up grates or hills at over 85-MPH, my car bogs and loses torque and drops 10 to 15 MPH almost instantly.

So, I have experimented and dumped time and money into that Weber for over two years and I hate it. Absolutely hate it. But keep in mind that I highly respect all of you here on the board and I am merely looking for power. Look, my former 1986 lean burn B-150 Van which weighed well over two times what my Dart weighs had a tiny single barrel and would burn the tires from a dead stop. It had great power. Even when loaded and climbing grates.

But my Dart is like a boat anchor with shiny rallie wheels on it. I just want a fun, peppy car. And I feel like I am never going to achieve my goal. And my confusion is that I have 50% of mechanics telling me to put on a 4-Barrel. But of this percentage of 4-Barrel enthusiasts, half of them say do not exceed 390-CFM and other say I can go as high as 600-CFM. Then there's the 50% that swear by 2-Barrels with most of them suggesting OEM BBD Carters and the others suggesting Webers. With a tiny percentage referring Holley's 350-CFM Performance Racing 2-Barrel Carb.

Can you see why I am confused? It just seems to me that every configuration I have tried with the Weber, it always bogs at low RPM and it bogs from being too lean. And at highest RPM wide open at over 85-MPH, it feels like there is plenty of headroom left to go but not enough gas output at the highest RPM range as well. Which is where secondaries on a 4-Barrel would really kick in and benefit overall top interstate speed.

Can someone explain in simple language from both sides of the argument why they prefer a 4-Barrel and why the other side of the debte prefers a 2-Barrel?
Author:  wjajr [ Sat Sep 13, 2014 3:47 am ]
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Which model and size Webber are you struggling with?
Author:  emsvitil [ Sat Sep 13, 2014 4:14 am ]
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Sounds like insufficient fuel flow...........

Clogged up fuel filter, clogged up fuel sock in tank, restriction in fuel line.....
Author:  Rick Covalt [ Sat Sep 13, 2014 1:52 pm ]
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Quote:
my former 1986 lean burn B-150 Van which weighed well over two times what my Dart weighs had a tiny single barrel and would burn the tires from a dead stop. It had great power.
If that statement is correct then you have more troubles than bolting on a carburetor is going to help.

You feel like your confused with the information you are being given, and much of that will go away after you decide what you really want to do, and what you already have on this car.

What cam is in this car? What size valves are in the head? Do you know the C.R. Is it stock exhaust wise? Can you find out the answer to these questions. If not, then I would say you probably need to assume that the motor has near stock everything in it and then just put a 2 barrel BBD on it and go.

But before I did any carb changes I would do some of the things already mentioned. I would adjust the valves, check the timing, make sure the advance is working and how much it is. I would pull the plugs, check the gap, and what color are they? If it is really running that lean, there should be some indication of it on the plugs. Run a compression check, and make sure that it is not running out of fuel. That is a good start.

You can run plenty fast on the street with a 2 barrel. Just as a reference, my race car was acting up and had a bad flutter when the 4 barrel opened up at the last race I attended. I disconnected the secondary linkage on the carb and the flutter went totally away. Funnier than that is that I actually went faster on the 2 barrel than I did running the 4 barrel the night before. My car has Enginebuilder valves, .473 lift cam, headers, and 3.91 gears...etc

Check some stuff and report back. You'll be glad you did.

Rick
Author:  Jerame_c [ Sun Sep 14, 2014 10:16 pm ]
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Get the offy. even if you put a 2bbl adapter plate on it it has a better plenum setup than any of the stock manifolds (and is a lot lighter).
Do you have a vacuum gauge setup?
I would suggest setting one up even if you just run a tube through the window. If you floor it and it drops to almost no vacuum then you have too much carb for your cam/valves/exhaust.

Based on what Im hearing my first guess would be timing.

If you eventually go to a 390 holley find a copy of the slant six racing manual and it has all the carburetor settings for that carb on a slant.
Author:  Joshie225 [ Sat Sep 20, 2014 5:12 pm ]
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To be blunt; the reason you're having trouble is you don't appear to have a solid background on the fundamentals of engine performance and are therefore relying on the opinions of others. Read David Vizard's book Performance With Economy. It's full of good information on theory and practice.

Tune up the Dart. Make sure the valves and timing are set properly. Make sure the mechanical and vacuum advance mechanisms works well. Check the fuel delivery volume.

If you have the stock 1 7/8" noodle of an exhaust system then you're a good candidate for an exhaust upgrade. Your van had 2 1/4" exhaust if memory serves.

If you still want more power after doing the above then you are entering the realm of internal engine work as you really do need to raise the compression ratio before you consider a cam change or most other modificaion.
Author:  kesteb [ Sat Sep 20, 2014 8:56 pm ]
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Are you running a fuel regulator? A Weber can't handle more the 3.5 psi of fuel pressure. A stock \6 fuel pumps put out around 4.5psi of pressure.
Author:  patrickhenryhague [ Sat Nov 01, 2014 11:31 pm ]
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It sounds like you got lost in the beginning. The factory 2 barrel set up works quite well they put about 10,000 hours of jetting and research in to the system to make sure it worked well.
Like some suggested start at the beginning, plugs, wires. distrubtor cap, points, condenser, timing, and valve adjustment. Use a vacuum gauge it can inform you if your timing is off, bad valves or valve adjustment, setting your idle, vacum leaks and other conditions inside the engine.
A lot of people are going to be upset with this one go back to the original ignition system and start over make sure it is running correctly with the stock equipment! Then start with modifications the BBD carb is a good one if it is all "original" not some rebuild remember the factory is right in this case. Take care of the tuning with the stock stuff first it works.
The Webber, the 390 Holley, a 500 cfm Edlebrok the all work well. Again take care of the tuning first with the "stock stuff" there is no perfect carb set out of a box. The best thing that you had in that direction was the factory BBD set up it gave you a factory base line to start with. The Edlebrock manifold is a good buy. As for all the carb's you have listed I've used one time or the other they are all good but I had all the other problem solved before I started making carb changes. As for larger carbs than the one's listed DON'T. These are fairly simple to set up.
Author:  Doctor Dodge [ Sun Nov 02, 2014 7:20 am ]
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A internal combustion engine needs a certain amount of air / fuel to turn a certain RPM. (basic "air pump" math)
A 225 needs 326 cfm of "air" to support 5000 RPM and 391 cfm to turn 6000 RPM.

So the question now becomes: can my stock engine turn 5000 RPM... even with the bigger carb?
Answer: No... because of the stock cam.
OK... let's get a bigger cam along with the bigger carb...
Sounds reasonable but bigger cams need more static compression in order to keep the cylinder pressure where you want it. (DCR)

OK, let's mill the head / block to jack-up the compression.
That works... but now that cam needs different distributor timing advance to make the cam work to the needed RPM.

So... make one big change and be ready to many others changes to get the system to work well again or keep your change(s) small, so they do not have major impact the current system.
DD
Author:  Serj22 [ Sun Nov 02, 2014 7:23 am ]
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IF you're running the weber 38/38 now, I'd say that on top of it being expensive, you likely bought the Chinese one instead of the real Spanish production.

I spent $300 on my Weber for my Supersix and it ran so beautifully. There was never hesitation or bog. It was jetted to match the Jeep inline. I never opened it or did anything, just bolt on and go. It ran way better than the 1920 and single bbl intake that was on there previously.

Also 390cfm is more than a stock slant should be spinning i think. That would "technically" allow for 5k RPM if you do the math. That's with 100% volumetric efficeincy though.

The 32/36 is a 240 cfm carb if you have that one, and the 38/38 is (supposedly) a 390, but I believe according to weber it's a 300. I'm not sure on that one. Also if you have the 32/36 it's sychronus so the large barrel is open at lower speeds, and then the other barrel opens later.

Also if you're worried about it being "fun" or peppy, the problem has nothing to do with the motor, and everything to do with that freeway gear rear end. You will never take off quick from a stop light with it. And if you really want fun, put a turbo on it.
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