What the @#$% is an RV CAM anyway??

"Years ago I had a 440 that ended up with that new 'multipiece' cam It was 1/8, 1/4, 3/4, all rolled into 'several.' "

Many moons ago I ground a 324 Olds cam for a customer that was to be a display cam
in his parts department. It had 8 different grinds on it ranging from stock to all out top fuel.
Needless to say it got a lot of comments and sold lots of cams...Several people wanted to buy it and install it....That never happened but would have been interesting.

 

I used to have a 1970 Winnebago with a 300 Ford 6 I used to haul my vintage dirt track car around. After a couple of years of fighting this thing, something (probably a broken ring) went, and after putting in a quart of oil every 50 miles, we finally got home with the back of the RV COVERED in oil. Anyway, my buddy rebuilt the engine (typical ring 'n valve job) and it ran pretty well for 6 or 700 miles when things started to go sour. Turned out, the guy who did the valve job botched something with the valve rotators which caused them all to burn. I pulled the head and had it redone (thanks Gordy). In the meantime, I found a good deal on a new Sig Erson RV grind cam from Dale Wilch. I put this in with new lifters and a properly redone head, and I couldn't believe the difference. I remember coming home from the Fairmont race track on Hiway 60 south of Mankato, and going right around a friend of mine who had the same kind of a race car on a trailer behind a motorhome with a 440 chrysler in it. Best thing, it got 12 MPG pulling the car on the trailer. Foolishly, I got rid of it when I had a chance to buy a low mile RV with a 360 Dodge. That got 12 MPG as well (empty). Pulling the trailer, we were lucky to get 6. After that, I have always had a soft spot in my heart for "RV cams".

 

Back in probably '58 I went to the Montgomery catalog store in my little home town and went through the catalog for a cam for my '55 Chevy. They had two listed a 3/4 race and a full race cam. I got the "full race" one. It was an excellent cam with about the same dimensions of a '56 225 hp Corvette cam. Was just right for that 265 with 3 two bbls on it ..

 

an RV cam is what most of us would be running if we knew how to pick out cams. but what fun is a decent idle and smooth powerful acceleration when you can impress your friends with a cam so radical your mill won't idle or make power till 3k?

 

Maybe that explains why my 40 with its SBC and Crane "RV" type cam will cruise at 3000-3300 RPM (3:70 rear) and still get 21 MPG!!

 

A combination of earlier comments. RV cams are designed for low end torque. In the performance area there was only cams that were fairly "big". In the late 70s Popular Hot Rodding started Project Econoperformer, a 70 Monte. They put on parts that they expected to increase performance & milage. They had pretty good results, impressive gains in MPG & ETs, & that paved the way for things like the previously mentioned SP2P & milder grind cams.

 

ok guys I've got a question about this RV cam deal. I've got a 1964 283 in my 32. I haven't run it yet. it was given to me by a friend who told me it is bored 30 over, has an RV cam in it with 461 or 462 heads on it with 2.02/1.6 valves and roller rockers. my question is are the camel humps too much head for the RV cam in a 283?? I dno't know what it has for pistons so compression is also an unknown!

 

When I had the 392 in my International truck rebuilt (back before I knew anything about engines) they did a mild port and polish, gasket matched the heads, and put in what they called a Schneider "262 RV cam." Motor is very torquey and has a bit of a lumpy idle.

 

Here's where generic labeling gets confusing.

What would be a stock cam in a 350 would be like an RV cam for a 283. What would be an RV cam for a 350 would be akin to a steet performance cam for a 283. So what does it really have????

Doesn't matter, no worries on the heads in either case. Good luck!

 

Cam duration determines rpm range the engine works at...how does engine displacement matter?

 

Engine displacement speaks directly to intake vacuum levels as the duration varies. Or am I misunderstanding something fundamental here???

 

This was my concern regarding the heads and cam choice. from what I had read, the RV cams have a very low RPM range say 3-4k rpm max. everything i had read on the hamb says the 283 with bigger heads, valves really needs to wind out. I understand that 99.99% of these generic cam specs are given out based on a 350 and i have read that you should "bump up the rpm range suggested" when used in a smaller displacement engine.

i am running this in my 32 with a 39 ford 3spd and 3.78 banjo rear.

 

Shit! I remember those days

 

Exactly the smaller the CID the "Bigger" the cam behaves. Most SBC cams are ground for the 350. Some catalogs break it out for you with how a cam will work in a 283/307 & how it would or wouldn't work in a 383/400.

 

Engine displacement speaks directly to vacuum levels if the load is the same on both engines.

I don't understand how displacement could affect the rpm range that an engine makes power aside from how the ports and valves are sized etc.

Either you are misunderstanding something fundamental, or I am....and I'm not putting any money on it either way. I do know that I always disregard displacement when selecting cams, and my engines tend to do what I expect.

 

I believe there is more to a cam than simply the duration. The LSA has as much effect on rpm as any other aspect. NO, not try to start an argument on camshaft design.
IC engines are little more than fancy air pumps, and thus sensitive to valve timing; cam specs for a 400 inch will behave differently in a 300 ci unit.
This is evident in every cam catalogue. Pick your favorite camshaft brand and you will likely see a mild profile listed for a 440/460/454 that becomes a street performance profile for a 383/390/400 than then becomes a hot street-strip profile for a 318/302/307.


.

 

If valve size matters, wouldn't how long or how far the valve is open also matter? And to some extent, isn't duration tied to lift due to how the lobe has to be shaped?

Maybe the difference in our wavelength is because I'm using SBC as an example, and when looking at "RV" type engines there's a lot of flow similarity between the heads used on 283s and 350s.

If the heads are truly scaled to displacement, ala comparing a 350 to a 454, I start to see where you're coming from.

 

RV?
http://www.youtube.com/watch?v=TqLG7bVA-dk

Sorry, I couldn't resist!

 

DING!DING!DING!!!!!

"...We have a winner! Johnny,tell him what his prize pack consists of..."

 

isn't the powerband of a cam when the engine RPM matches the resonant frequency of that vacuum signal?? wouldn't that vacuum signal change size and speed with displacement??

this is just a wag....

 

When I got my truck last summer, people would ask "Has it got a cam in it?"

Yes I would say. (But I didn't tell them the bad idle was due to the carb, that needed work.)

They always had a look of satisfaction and would say stuff like "I thought so" or "you can tell".

That is also when my engine became 'variable displacement'. It is just a SBC is a truck, but everybody wants to know "what size is it?" sometimes almost asking in a whisper.... 283 makes 'em smile, 302or 327 they get excited, 400 the go "Ooooh."

305, they say, "ya gonna swap that out?"


David

 

RV cam is like many said a generic term for a small cam. Perfect for your grandma to drive. Great for towing and low speed engines. Terrible for performance.

Get some cojones and put a real performance cam in there.

 

Sorry, I beg to differ. Drop by the cam section at Herbert. I've used Chet's grinds for a lot of motors. There are stock style cams with slightly more lift and maybe a pinch or duration for a mild build. There are Truck & RV cams for even more lift and duration.

Think about how a truck (same motor in an RV - real truck, not pick-up) usually runs. It spends most of its time between 2500 and 4500 hauling a big load and holding gears for a while on any grade. RVs do the same. So usually, it's a cam optimized for factory induction and iron exhaust and pretty good engine speed. It is not a race cam, but it won't idle around all day like Caddy. Gas engine trucks don't spend much time idling. RV cams are good ones to build a tow or boat motor with. They are also good if you are rebuilding with all stock parts. They idle a bit rough and make good MID RANGE power.

 

That's a bit of the wrong way of thinking,

I/e, a .500 lift, 220 (at .050) duration cam on a 300 cubic inch motor, versus a 500 cubic in motor, will behave in two totaly differnt ways, on the smaller engine, you'll have way less idle vacuum (less on the 300, moreon the 500), probably some low end loss of power on the small engine, on the bigger inch engine you'll still have plenty of idle vacuum (due to the volume-read as cubic inches- that the engine can suck in, plus the idle quality of the big inch engine-read as "lump-ity-lump" vs the small engine, will be a world of difference.

Ofcourse, if you came up with a 500inch engine with 1.5 inch intake valves, your results will vary

 

O, BTW, RVOffRoad cams, as are what many as descrbed before, something that give good/better low-end, and midrange power/torque, than a stock grond cam.

Kinda plain and simple.

Heck, I'll bet a weeks paycheck(although I'm unemployed right now) that if you bght 5 "3/4 cams"...back in the day, from different venders, thay'd all be a different grind....as would Cam, COMP, Lunati, etc, all have different RV cams in the modern era.

 

rv cams pull really nice at low to mid rpm range but they drop off like a cliff. these grinds keep drivability up meaning less time rolling in new plugs.

 

I agree with you..

 

It wasnt a unicycle.

 

People who say 'it has a cam' or 'it has a stall convertor' usually say this to hide their ignorance about what specs their stuff actually has.

To me an 'RV-cam' sounds like the most boring cam in the book.