Holly carb recommendation for 1972, 413

[Moondowg]

Hello, I just bought a 1972 STARCRAFT Motorhome 22 Foot. It is on a Dodge M300 Chassis with a 413 Engine. I went to Pick it up in Central Pa about a 160 miles away. Needless to say I should have went with my first instinct, and had it towed home by a hauling company. But I attempted to go and get it with my son following me in my Dodge Ram. It broke down on the way home about half way. So I had to get it off the PA turnpike it was Half way between Bedford and Somerset. The Tow Truck cost me 820.00. The so called rebuilt carb finally quit at this point. Besides all of this we had a good time I got to spend time with my 35 year old son. OK enough about this adventure, the reason I am writing this is I gathered some information about this Carburetor which I would like to pass along. It is a Holley four Barrel. Carb # LIST 6231 this number is located on the outside of the choke throat. Rebuild Kit from Holley is Part # 3-119 about 33 bucks. Floats, Part # 116-1. about 10 bucks each. Vacuum secondary Diaphragm Part # 135-3 about 10 bucks. I decided to go with a new Holley # HLY-0-80457S. It is a 600 CFM with Electric Choke, The Tech at Holley said this would be the best one to replace it with. I also purchased a Chrysler Throttle Extension Lever for it recommended by the Holley Tech. And to make things easy a Tuning Book for the new Holley. I purchased this from Jegs the # is SA08. I hope this info will be of some use, Thanks, Dave.

[tiinytina]

AAA + RV or the Good Sam version of the same thing!  That tow bill was outrageous!
Tina

[Oz]

One can always say it's best to go with your first instincts.  However, a shakedown trip, one which a whole, enjoyable camping trip is on the line, isn't the best choice for one, so one can't say you made the wrong choice.

[ClydesdaleKevin]

Welcome to the group Dave!  Just double check that recommendation that the tech gave you...600cfm seems a little lean for a 413.  I had a 413 in my old 72 Futura, and I was told to go with a 650cfm minimum and it worked out great.

Kev

[Oz]

Correct, Kev.  600cfm would be optimum for a 318, 650 would be par for a balance of economy & power for a 413.  750cfm for a 440.

[Moondowg]

The 413-1 is rated at 265 HP @ 4000 RPM with 445 FP of Torque @ 2400 RPM. If you go to the Holley Website and Click on the Interactive Carb Selector And enter the 413-1 @ max RPM of 4000 it will tell you the CFM should be 390 CFM to 570 CFM.If you say the Max RPM is 4500 Then it will give you a CFM range between 570 and 670. If you have a Summit Racing Catalog they have a formula to use to get the Correct CFM. it is Cubic inches x Max RPM Divided by 3456, using this formula at 4000 RPM the CFM is 478 @ 4500 the CFM is 537 and @ 5000 it is 597. I would not think the Max RPM of this Old Engine Would  be over 5000.The original Holley Carb is a 600 CFM, that is why I chose this particular carb, the Holley HLY-0-80457S for my engine. Thanks, Dave.

[ClydesdaleKevin]

Okay then.  Just trying to let you know, that despite recommendations and charts, the 413 engine really does perform better in a motorhome with a 650 cfm carb.  The 413 is pulling a lot of weight despite its horsepower or listed RPM, and is geared very low in the rear end.  Mine had plenty of power, towing a fullsize Dodge van at the time, and got an average of 8mpg.

Kev

[Oz]

Did those charts indicate that the subject engine was meant to pull 5 ton or more vehicles?  Ummm... nope.

Charts and formulas are good for guidelines but don't forget one, very important thing... those formulas are meant for cars.... not RVs.

Those formulas with all the this times that plus blah, blah, blah doesn't convince me that when I replaced the 600 cfm with a 750, it doesn't run better and much stronger when I put my foot on the gas pedal, which it does.

Many of us have been down this road, so we're speaking from experience.  Years of it, from many actual users, not parts distributor charts meant for cars.  The consenus from actual application is that the 750 cfm is the option for peak performance and the 650 for economy.  A 600 cfm is for a 318, not a big block.  You can use the message search and confirm that this fact has already been well established.

Buy the 600 and you'll think it's ok because the carb you have now is shot.  Then, line up next to me on the highway and I'll smoke you like a cheap cigar!  When we hit a big, long hill, I'll still be increasing speed while you've got your foot stomped on the floor and you're barely holding 40mph.  Sound like I know what I'm talking about?  I do, because I've been there, done that. 

I'm sorry, but on behalf of all the members who previously contributed their recommendations on this based on experience, I have to give the 600 cfm a "thumbs down" as the best choice for the 413.

We are simply giving you the answers you need to make the best choice so you don't waste your money on getting the wrong thing and then wishing you would have listened to the people who really know in the first place.  That's why so many people rely on CWVRV to be their source of expertise.

[Moondowg]

I Just finished installing the Carb, new points, plugs and condenser. Took it out for a ride about 100 miles. It pulled up Penn View Mountain at 66 mph. Not bad for a 600 CFM Carb!

[Oz]

Not bad, but it still doesn't change the best choice.  The good thing is that your 22' is equipped with a 413 in the first place, which gives it a big plus over it's predecessor years which only had 318s, not the 600 cfm carb.  It's still a little weak.  Some D20 owners opted for the 440 and those things fly past anything, including me, because they are so much lighter, but they still run a 650 for optimum balanced of performance and economy.

Maybe only about 8 of us (out of over 500) know Penn Mountain.  Been up it at least 100 times (It's steep, for the most part, but not long at all).  Hit it doing 70 to start with and it's no problem gettig up with a lighter 22' and a big block.

[Moondowg]

The 600 CFM Carb Will give me better low end torque and better fuel economy, that is what  I was looking for. This particular Motorhome is only 8500 LBS. I have a camp on the Yough River about 25 miles from my home in Monroeville, Pa, that is where the Motor will be traveling most of the time. I apologize for Ruffling anyones feathers, Thanks, Dave.

[Oz]

Lighter is definitely better in that region, and the low-end torque helps get a good jump start going up and maintaining a decent speed.  Because of the terrain factor, gas mileage is at it's worst.

My rig is a bit heavier, being 24' and, when I had the 600cfm on, I almost always was towing a 17' bowrider boat too.  I'm sure that had a lot to do with slowing me down on the mountains as well.  But, once I got the 750cfm on, it was like I wasn't towing anything at all.  The 600cfm may have been adquate for regular use without towing, especially here, in south central PA where the "mountains" are more like big hills.  The big upside to the 600cfm was that I got a full 8 mpg over a 300 mile trip, even towing that boat through the mountains! 

Like using headers and selecting exhaust set-ups, carb choices vary greatly. 

Specific application and intended use and performance preferences play the biggest fine tuning point when selecting key components in obtaining the desired results.  50 cfm difference isn't much, that's for sure.  The 600cfm would be the minimum size choice, best for 22' or under in length and not towing.  650cfm is standard, and 750 gives the best power across the rpm range and heavier demands.  My 24' literally leaps off-the-line.  Not that I'll be entering it in the Vintage RV drag races any time soon, but it provides optimum performance for a heavier rig and towing.

All feedback is helpful in establishing what is best across a range of applications so that members who are contemplating making a change have a full spectrum of information to refer to and make the best choice for their use.

In the end, if you have selected the right carb for your application and performance preference, that's the most important thing!   

[ClydesdaleKevin]

No feathers ruffled at all Moondowg.  My 413 was pulling a LOT of weight, and in retrospect I should have went with a 750cfm...I wouldn't have been nearly as slow up the big hills!  But then, we fulltime it so our rig at the time was HEAVY, and pulling a fully loaded-with-all-our-crap fullsize van...lol!

Our rig now is a 77 Itasca, 27 feet, with a 454 engine, still towing the packed van, and we definately went with a 750 cfm. 

While you might have been better off with a 650 cfm, hopefully the 600 will work out for you just fine for your usage.

Happy RVing!

Kev

[RV Mech Tech]

Couple of things to remember here-  first, an internal combustion engine is nothing more than a big mechanical vacum pump with accessories ( fuel, ignition system etc.) added to it -  if either the intake or exhaust system are restricted then the 'pump' will no longer be efficient- (just ask the NASCAR boys about that one -restrictor plates under the carb!) - so if you have a certain displacement  you will have a range of cfm that's required  according to the requirements thats required of that engine in that application - for example take a 413 . put it in a car and you do not need a lot of torque/power  (in that order)  in that application- take that 413 and put it in a heavy duty application such as a motorhome then what is needed in terms of torque/power is altogether different - put that 413 in a full size utility vehicle and you will be lucky to see anything above 4000 rpm. - so everyone is correct in what they are saying here - Moondowg is happy with his 600, Mark is correct in saying that the full potential of the 413 is not being utilized with the 600, Kev is correct in relating his experience with his engine and carb, etc. - one other thing that nobody has mentioned yet - the most important item in an engine is the camshaft and camshaft timing determines everything - I used to work in a high-performance speed shop in the 70's and more than half of the customers who were building an engine did not have a clue how to determine the right camshaft- you can have two identical engines and two different camshafts installed in them- one will be a high-performance cam and require a minimum 650 cfm carb and the other will be a stock  engine that is meant for low end torque/power and requires a carb that has 600 cfm and anything larger will be a waste of money and gas- camshaft timing determines what cycle or stroke a particular cylinder is in regardless of piston position - a racing camshaft will allow more valve lag and leed to take advantage of more cylinder filling and emptying - this kind of engine will require a larger carb - these are only a couple of examples of different requirements for carbs with the same engine and don't forget different gearing in the transmission and rear axle - third - don't forget the introduction of emission equipment and that started to happen in California during the 60's and the rest of the USA and Canada during the 70's - a 413 made in the early 70's may have a different cam than one produced two years later along with lower compression, smaller valves,more emission equipment etc. so the carb requirement may be different between the years -  most truck and RV applications may be exempt during those years in lets say the eastern USA but make an RV  destined for the west coast (California) and you have a de-tuned internally, downsized same size cubic inch engine with a smaller carb- same block, different cylinder heads, same bore, different pistons and compression ratios, different cam timing etc. -  fourth - different types of carbs can be tuned to  supply fuel within a certain cfm and power range and the Holley is more versatile and tuneable than others - a 600 cfm carb can be tuned for a number of different applications - you can buy tuning kits for this such as different accelerator pump cams, different vacum secondary springs, adjustment on the accelerator pump, different jets and power valves etc. - and fine tune your carb to your engine- this is why the Holley website gives you an rpm 'range' for each cfm and provides you with the tuning tools that you need - and one final point - I don't know how many of the members know this but starting in the 1980's companies that manufactured timing chain sets started to put a 5 degree retard in the lower crankshaft gear for emission compliance ( the Feds were responsible for that one)  - this was supposed to reduced the pollution out the tailpipe but all it did was make the driver step on the gas more on account of the fact that the torque curve fell off considerably even at 5 degrees- this also has an affect on ignition and carburation - if your engine has never been touched  then you will have the stock original timing gears in it but buy a replacement stock timing gear set and that's what you get - the high-performance sets do not have this retarding of the timing- I first became aware of this on Chev engines - if you compare the crank gear on an early engine for a small or big block Chev engine you will see that the gear teeth are positioned slightly off between an original gear and new replacement stock gear in relation to the crankshaft keyway - this is one that the manufactures have had to comply with (Federal regulation) that they did not tell anyone about (and have been sneaking it past the public for years) - I have not had the chance to check on the Mopars or Fords yet so keep an eye out for this for anyone replacing timing gears - compare the old ones to the new.  Hm?