Cam shaft question

[pflaming]

Some change the camshaft when 'souping up' an engine. What does that replacement cam do and what is the result? It obviously changes the amount of time a valve is open/closed. Does that then allow more air to enter the cylinder and thus a bigger 'explosion' which gives more power? Does that then give better MPG?

 

[Robert Horne]

More or less power does not always make more mpg. Have the right amount of power for your vehicle is

what is important. My old chevy truck with a small v8, 180hp, got 27mpg on a 400 mile trip, where as my newer

Chevy truck with a small v8,230hp, got 20 mpg on the same trip.

[austinsailor]

Let's hope you don't have an "explosion", big or small. That would be spark knock, and can destroy an engine pretty quickly.  In reality, a burn without an explosion is the goal, and you go to a higher octane fuel to avoid explosions.

 

Just a fine point.

 

Gene

[james curl]

It helps increase the torque if the grind is designed to increase torque.  With the long stroke engines to increase the rpm to gain horsepower does not gain you much, but with more torque you can now run a higher gear ratio rear end thus reducing the rpms required for modern highway speeds.  If you are content to run 50 mph top speed for extended periods of time then you would not gain much with a reground cam.

[Don Coatney]

Did you do any research or try google?

 

http://www.crankshaftcoalition.com/wiki/How_to_choose_a_camshaft

[austinsailor]

James, you missed the most important thing about the reground cam - It sounds so cool!

 

 

Gene

[greg g]

most re profiling of cams focus on lift, and duration.  Other considerations are timing and overlap.  Most factory cams for passenger cars are a compromise to get fuel economy, smooth operation, and street power needs.  Most regrinds sacrifice smoothness, and operating flexibility for mor HP achieved at a higher RPM.  Remember the old terms 3/4 race and full race?  maybe sounded great and provided good burnouts but erratic street driving experience.  Most race cams are designed to operate at Wide open throttle, How much time does your car or truck spend at WOT in actual use. I would thing a cam ground to provide optimum conditions between 1500 and 3000 rpms would provide the best results for actual driving.  Hmmm might that be the stock cam???

Edited January 16, 2014 by greg g

[pflaming]

Greg: So in different terms, "Don't mess with mother nature"?

[martybose]

Greg: So in different terms, "Don't mess with mother nature"?

Not really.  The OEM cam might be fine with the single one-barrel carb and log exhaust manifold, but if you are going to add carburation or open up the exhaust to a set of duals you might have an opportunity to increase the available power beyond what could be done with the OEM components.  Plus, as Austinsailor put it, it can sound nice!

 

Marty

[greg g]

Just a caution. You see cars running around that run like crap, most folks seem to go with the bigger is better scheme of things.  You see over carbureted. over cammed, and over exhausted cars running around, and not running good, and not driving good, making lots of noise and being visually impressive but nearly impossible to drive.  Just encouraging moderation.  Look at what you have, decide what you want, a driver or a race car, and then build it to those specs.  I raced mostly stock cars when I Ice raced.  A bit more timing, some slightly bigger jets and an opened up exhaust.  car ran well performed well and finished every race I entered, while the highly modified cars, fell out allot with mechanical problems half way through a race, or half way through a season, and much of their extra power was wasted making more ice chips in stead of more speed.

[martybose]

Greg's point is well-made.  My first attempt at a multi-carb setup on my 230 was two 97's on an Offy manifold, and it ran like crap.  It either ran well at cruise but knocked at full throttle or it ran great at full throttle and wouldn't idle.

 

The second attempt was a pair of Carter-Webers on an Edmunds manifold, and that setup works really well at any speed.

 

Marty

[pflaming]

Thanks fellas for the dialogue. I like dependability and simplicity and a stock cam will suit me just fine, yet is it nice to be a little more 'in the know'. 

[greg g]

If you need a lumpy idle, retard the timing and introduce a vacuum leak.

[Don Coatney]

If you need a lumpy idle, retard the timing and introduce a vacuum leak.

Or pull out the choke cable.

[austinsailor]

Greg's point is well-made.  My first attempt at a multi-carb setup on my 230 was two 97's on an Offy manifold, and it ran like crap.  It either ran well at cruise but knocked at full throttle or it ran great at full throttle and wouldn't idle.

 

The second attempt was a pair of Carter-Webers on an Edmunds manifold, and that setup works really well at any speed.

 

Marty

This is really good news. I have an Edmunds dual 2bbl for my 251, with 2 progressive carter webers and a very lumpy cam. I still have to assemble the whole thing. It sounds like it has a chance of being a good ride.

 

Gene

[Scruffy49]

You need to be careful with torque cam grinds as well...

 

My 49 truck's "pasture pal" is a 69 D100-128, with an RV cammed 318, an RV shift kit equipped 727 automatic, and 3.55 rear end gears. It will launch like a top fuel car, to and including frame/body twist. Right up to 55 or 60 mph, where it falls flat on its face and runs out of top end power. If I can get traction, it will pull a 378 Peterbilt coffin box or KW W900 stand up sleeper tractor trailer cab w/o breaking a sweat. But it can't do it fast...

 

A basically bone stock small L6, is not a good candidate for a reground cam profile. A basically stone stock big L6 isn't much better. If you go through the port/gasket matching processes, mill the head and/or swap for an aluminum version, decent overbore, good 3 or 5 angle valve job, headers, dual carb intake, etc... a cam swap would make sense, maybe. It is still an L6, they don't have the best flow dynamics, well, honestly, their flow dynamics are pretty poor. Very inefficient design, and relieving the block in the valve pockets doesn't help much...  We built a 1941 or 46 Pontiac engine to the max when I was in college, gained 12 horsepower, 1/2 a mph on the top end, at great expense and a shortened service life (you think Mopar stuff is hard to find, try old Buick, Olds, Pontiac L6 stuff).

 

Save your coin for a rear axle upgrade.

[austinsailor]

I don't think Scuffy's remarks were directed at me, but more general in nature.  But I'll comment that I've matched the ports, ported it, have it at about 9 to 1 compression and a set of tube headers for it.  It should push my '42 Plymouth 2 door just fine, if I ever get time to assemble the whole mess!

 

Gene

[Scruffy49]

I don't think Scuffy's remarks were directed at me, but more general in nature.  But I'll comment that I've matched the ports, ported it, have it at about 9 to 1 compression and a set of tube headers for it.  It should push my '42 Plymouth 2 door just fine, if I ever get time to assemble the whole mess!

 

Gene

 

Yep, just in general. So many people put RV grinds in trucks that don't need them, and hot cams in engines that can't take full advantage of the new profile... That old D100-128 powertrain is almost indestructible, the combo of RV cam and RV shift kit in the transmission keep the speeds pretty much uselessly low. I did use it to tow a horse trailer cross country in Mar/Apr 2011, and the bed was about 1/2 full at the time. Never could break 60mph indicated (if the speedometer felt like behaving at that).

 

I'm "okay" with the power output of the 230 we picked up for the 49 B1B-108. I honestly don't expect the truck to ever see city use, other than cruise in nights. I'll upgrade to a more modern rear axle assembly that takes common parts and has better gearing, but it still won't see the north side of 60-65mph, ever. I'd just like to keep the rpms down a bit, and have easy to get locally brakes.

 

If I wanted Ancient Blue to be fast, I'd run C4 or C5 Corvette suspension parts and a big block V8. I'll be more than happy to just get to drive it under its own power again before it goes to my brother's daughters.

Edited January 19, 2014 by Scruffy49

[pflaming]

"Some change the camshaft when 'souping up' an engine. What does that replacement cam do and what is the result? It obviously changes the amount of time a valve is open/closed. Does that then allow more air to enter the cylinder and thus a bigger 'explosion' which gives more power? Does that then give better MPG?"

 

The statements above are my original query. So a couple of simplified answers are: no more power just transfered power in a different area of the RPMS a the expense of something else. Better MPG, probably not. 

 

These answers are not the best benefits of this thread for me. The discourse was a good one for me. I learned things not written in the manuals nor shown on U Tube videos. Google, i.e., the net is our friend and very helpful but  discussions like this one  reveals the innuendos. As a result the learning curve keeps rising. 

 

ps: I did not know that some valves are domed, some flat and why there are as they are; did not know that the crank shafts make TWO revolutions to activate the twelve valves; did not know that cubic inches is not measured by the size of the block, but rather by the length of the piston stroke so the cu in is determined in the cylinders and how they work. Those are three things I learned from this thread. 

 

My thanks to those who participated. 

[Don Coatney]

I have only seen one engine where the block was relieved as pictured below. I was told this engine was used on a circle racer but I do not know how well it did. It is my opinion that the relief cuts would do more harm than good due to the loss of compression ratio.

 

[wayfarer]

There are two reasons for re-grinding a cam: repair of a well worn lobe/lobes and the opportunity to actually make a little more power without making sacrifices in daily driving.

The comment about using a 3/4 or full race cam is off the mark in this day and age, as there is no such thing...possibly with the exception of some old time grinds for a ford v-8 flathead...and the name was applied to what ever the grinder wanted to apply it to. There were few if any standards, only bragging rights.

 

Re-profiling a stock shaft, for any IC engine, simply offers the opportunity to tailor the cam to the engine that you have and the job that you want it to do. The cam supplied by the factory is nothing more that a comprimise of a thousand requirements.

 

Reusing a stock cam, (without regrinding, even if back to near stock numbers) is a mistake simply from a wear and tear view as you cannot expect the well used cam lobes to be even remotely similar to one another.

 

Your money your choice.

[DJ194950]

The one topic I have never seen has been did the factory ever change the cam profiles over the years - car, trucks, industrial, per years made and obviously the application?

 

Is that info avail. anywhere?

 

Simply my curiousity asking for general interest at this time.

 

I used parts from a car engine and  forklift mopar flat motors to put together my 50 car motor. Car was 53?, forklift motor in a 60's  forklift  from military '47 according to the #'s? 230ci. I don't remember which cam I used as both motor parts were scattered in the garage at the same time! Used the best looking one but both were usable. MY BAD!

 

My car runs strong with plenty of torque as do most, So?

 

Probably no answer to that particular cam question now!

 

Any info would be interesting tho.

 

Thanks,

 

Doug

[knuckleharley]

Some change the camshaft when 'souping up' an engine. What does that replacement cam do and what is the result? It obviously changes the amount of time a valve is open/closed. Does that then allow more air to enter the cylinder and thus a bigger 'explosion' which gives more power? Does that then give better MPG?

Depends on the grind,the intake,gear ratio,tire diameter,timing,compression,and maybe the phase of the moon.

 

Generally speaking,there are 3 types of cam grinds. One is what is called a RV grind,which is basically a very low RPM cam that works best with small valves because it is designed to build torque instead of HP.

 

Next up would be what I guess can best be called the typical factory cam. Designed to idle smoothly,and to produce an acceptable amount of hp,torque,and fuel mileage,with the emphasis usually on smoothness and fuel mileage.

 

Then come the high-performance cam grinds,and their purpose is to build horsepower. They go all the way from mild performance boosts over stock,to OH MY GOD! For anything above a moderate increase in duration and lift they need bigger valves and generally benefit greatly from polishing and matching the exhaust ports to help exit the gases quickly. If you plan on getting very radical in a street engine you MUST boost compression to 10 to 1 or higher or all you are doing is wasting money and gas. With today's gas,10 to 1 means a electronic ignition like a MSD to control spark. If you are serious about it,spend the bucks for a roller cam and lifters.

 

Now,backing up,a RV cam generally improves fuel mileage. Dual 1 brl carbs and split exhaust manifolds or headers can also improve fuel mileage while increasing horsepower and torque. Gas mileage starts to go to hell rapidly about the time you hit what used to be called a "3/4 race cam" back in the 50's. Gas mileage is all downhill from there.  So are budgets as you start to buy stuff like forged pistons, rods and cranks to try to keep it alive. Not only because of the engine,but because by then you are running lower gears,and hammering the hell out of it every chance you get.

 

One thing I recommend for any engine rebuild on a car you are going to keep and drive is engine balancing. A total win-win situation.  Better fuel mileage,better power,and it will last longer to boot. A engine balance along with a moderate cam and carburetor  can be fun,sound nice,and give good (better than stock) gas mileage for a daily driver.

 

My opinions only,and your actual mileage may vary.

Edited January 20, 2014 by knuckleharley

[knuckleharley]

"Some change the camshaft when 'souping up' an engine. What does that replacement cam do and what is the result? It obviously changes the amount of time a valve is open/closed. Does that then allow more air to enter the cylinder and thus a bigger 'explosion' which gives more power? Does that then give better MPG?"

 

"ps: I did not know that some valves are domed, some flat and why there are as they are;"

 

That's pistons,not valves. Or at least I have never seen a valve that didn't have a flat face.

 

"did not know that cubic inches is not measured by the size of the block, but rather by the length of the piston stroke so the cu in is determined in the cylinders and how they work."

 

It's not. Cubic inches are determined by the size of the bore AND the stroke.

 

Even then there are some tricks for performance that alter performance without changing displacement. For example,I have a balanced and blueprinted 412 Chevy small block (400 small block with a .060 overbore) that runs custom Keith Black pistons with piston pins moved so I can use the 5 chevy 350 "long rods" instead of the 400 rods that are shorter. This is supposed to improve mid-range torque over what is made with the standard 400 rods,plus forged 350 rods are easier to find and cheaper to buy. Cheap enough it made up for the cost of the custom pistons.

 

BTW,this is the engine I am planning on replacing the tired 305 in my P-15 coupe with. I put it together to run in a 39 Ford on the street,but then the engine in my GM 1 ton van that I used to pull trailers with at the time took a dump,so I put in it the van instead. I had only put about 20k miles on the van with the new engine and trans when I junked it out so I decided to keep the engine and use it in the Plymouth.

 

BTW,unless you are one of the luckiest people on the planet or somebody famous,you can almost never sell a high performance engine for even a fraction of the money you put in it. Take that as a word of warning. Plan on using whatever it is you build for a long time,or reconsider how and what you are doing.

[knuckleharley]

 

"The comment about using a 3/4 or full race cam is off the mark in this day and age, as there is no such thing...possibly with the exception of some old time grinds for a ford v-8 flathead...and the name was applied to what ever the grinder wanted to apply it to. There were few if any standards, only bragging rights."

 

Custom cam grinders like Delta Cams can weld up and grind your cam to any profile you want. IIRC,they have records of what the old "3/4" and "full race" grinds were from popular cam grinders like Isky back in the 50's and 60's,and can duplicate them.  So it is possible to call cam regrinding companies and tell them ,"I want a 3/4 grind cam for a 46 DeSoto" and get one of the old grinds. As you said,the whole "3/4" and "full race" are arbitrary measurements,though. For example,Clay Smith was turning up 7,000 RPM's in flathead 6 Fords back in the late 40's,and I think most of us even today will cringe even thinking about that one. I have to believe there were many,many "full race" flathead 6 cylinder Fords out there back then turning considerably slower RPM's than that one.

 

"Re-profiling a stock shaft, for any IC engine, simply offers the opportunity to tailor the cam to the engine that you have and the job that you want it to do. The cam supplied by the factory is nothing more that a comprimise of a thousand requirements.

 

Reusing a stock cam, (without regrinding, even if back to near stock numbers) is a mistake simply from a wear and tear view as you cannot expect the well used cam lobes to be even remotely similar to one another."

 

I couldn't agree more. Make sure you add hardened valve seats,new valve springs,and new lifters while you are at it.