Cam selection for Mopars

[Ghoste]

I ripped this off from the Dodge Coronet Registry site.  I didn't write it and I don't take credit for it.  It was written by Don Dulmage.

Biggest problem is getting enough duration. We are conditioned to being overcautious because we are constantly reading Chevy stuff and we some how get ingrained in our mind that it applys to BB mopars too. But not necesarily.
First if you are buying a cam you want a grind that is Mopar Specific meaning it has actually been designed and tested on a Mopar . Most cams are designed on a 350 chev and then transferred to everything else in manufacture.

The Comp cam extreme energy series are specifically designed to take advantage of the Mopars large lifter diameter (904) so even though I prefer the Racer brown they are good cams for these engines.

Secondly when you modify a set of IRON heads you discover that valve lifts over 540 (Dvorak says even 530) cause a reduction in flow. (You can port the head differently so this is not the case but the end flow figure will be no higher that when you do it properly so you have gained nothing. In other words if you can get 275 cfm 2@540 or 275 cfm @600 you still have only 275 cfm so other than spending more for valve springs for the extra lift you are in exactly the same place)
So assuming you want the lift to be no more than 540 you need to decide on the duration. Every degree of duration produces a specific number of rpms. That is what duration does. It controls the engine speed available.
Too much will kill torque and to lttle will limit engine speed. this is where it get tricky. To get a 440 to run strong to 6150 we need approx 253 deg at .050 duration in an hydraulic (About 268 in a solid cam)
When we look for a cam with that much duration it is hard to find one with 540 lift or less. Racer brown had this figured out years ago but the rest are just catching on now. That is why we really like the ST-H-42. It is an absolutley BRUTAL cam that suits these engines really really well. (because it was designed for them) Sig Erson used to make a cam with 525 lift and 310 adv duration which was pretty close at the 050 mark but when Mallory and them got in bed together they stopped making it. Both these cams require really good tuning skills but power is unbelievable.
Comp has been working lately in this same vien .
So what about if I have too much diration I will loose torque thingy you ask?
Well the BB mopar 440 has about the second highest stock torque rating of any of the engines. If you had any more you probably couldnt stick it to the ground anyway so it is a non-issue. Even with these big cams and more we were backing the cams off (retarding ) a few degrees to get rid of some of the monster toque we were generating. So bottom line is with this particular engine it is not a relevant issue. With a 383 or 400 it would of course be much more important.
When you go to Alum heads like Indys or Edddys the 540 lift limit goes away and you can run as big a number as you have guts and gold for (Pick your cam lift to match the cylinder head fow rating. See whare the highest point is (ie like peak flow at 650 lift would use an hydraulic cam of 650 lift (A solid would need more because its lift is given at .000: lash so it would need a cam with more lift minus the lash to arrive at the same figure.
For instance a solid cam for a head with peak flow at 650 lift would need a cam with 678 lift - .028" valve lash = 650 lift. (Some cams are rated at 020 as well. Check the specs before you buy.
This is the type of thing that no one ever tells us which is why I wrote the articles I did in the first place that turned into the book.
We ran, in the course of a few years, some 23 cams. Racer Brown Cams matched the one cam exactly (but was much easier on the valve train so we still like it best) and beat all the rest. That is why i prefer his STX 20 for instance.
How do you find out what duration you need? You start by keeping a log book of every cam you run and its peak power (often RPM trough the traps in a properly set up car.) You have to be honest as well. If you BS yourself your results are meaningless. After awhile you get a feeling for what the motor wants. I use 25.34 RPM for every deg @050 myself for Hydraulic cams and 25.35 for Solids because they need extra ramps to accel and decel the valve lifter that a hydraulic does not need in the same fashion.
This has worked very well for me and for others I have given it to. Even some Ford racers have used it with excellant results.
Dont expect the cam guy on the phone to understand this . It comes about by lots of trial and error but never the less it works. Understanding how much lift you need and how much duration you require will get you to above average performance from seemily mundane parts in a big hurry.
The next secret is to match the cam to the compression ratio.
No compression takes place until the intake valve closes at the early stage of the beginning of the compression stroke. That leaves less distance of piston travel or compression stroke to build pressure but the longer we hold the valve open at the bottom of the intake stroke and into the beginning of the compression stroke the more cylinder filling at higher RPM we have (to a point , everything has its limits. )The only way to get the cylinder pressure back where we want it is to use a piston of a higher compression ratio or reduce clyinder head combustion chamber volumes. That is why you can ran engine with 10 or even 10.5 compression ratio on the street on pump gas with a big cam.
the 10 or 10.5 ratio is a strictly mechanical rating and assumes the valves are all closed at the BDC (bottom) of the intake stroke and the beginning of the compression stroke and that is how the ratio is determined. In fact especially with a prefiomance cam they are not and compression does not take place till the intake valve is fully colosed. By that time the piston is already moving up the bore , all be it slowly , so the distance of the ACTUAL or REAL compression stroke will be somewhat less than the 3.75 stroke (say only 3.70" for instance) that we would normaly use to caculate it. and cylinder pressure at the end of the compression stroke would be reduced.
IE I once tested this for a local fellow. We took a stock 327 mouse and measured the compression. It was 135# on my gauge. We installed a 350 Hp chevy grind in the motor and measured it again. It was now between 95 to 97 #. He would need to raise the compression by 30 to 35 # to get it back where it should be. Because of a whole host of other factors too long to go into right now he would need to raise te ratio about 15 to 18 % . The factory by the way did this when they built the 350 Hp engine. The subject is kinda complicated but not too bad of you just go one step at a time.
Anyway. These are some of the major factors ueed for cam picking for max bang for your buck. (While i have not personally run one I have raced against cars with the Mopar 533 hydraulic grond and have come to believe it is also a very good cam.
The vast majoriity though offered to us are just pure crap and were desgned and tested for a 350 mouse and nothin else.
This stuff is much easier to explain with a blackboard and a few chairs that with a keyboard. Sorry to go on so long.
Don
Author of
Return to Deutschland (True Adventure)
Old Reliable (Mopar)
http://stores.ebay.ca/Don-Dulmage-Enterprises

[Ghoste]

He did issue a correction on his forumla:

should have said

"I use 25.34@050 for hydraulics and 23.54@050 for solids."

Also I probably should have said a little further down

"The next secret is to match the compression ratio to the cam ."

instead of the other way around. Sorry for any confusion
Don

Really wasnt an article, more of a reply to a post of a question.

[max]

uh, yeah.

there seems to still be alot of old tech in those paragraphs. there are alot of cam companies that are steering towards large lifts and short duration along with wide LSA and a faster ramp speed.

compression can be increased or decreased slightly depending on how the cam is  installed either by advanced or retarded.

i'm considered old school i like a mild lift with mild duration and a narrow LSA. 

[Ghoste]

I think he was talking less about the right and wrong of the theory behind it and more about understanding how the different specs relate to each other.  At least that's what I get out of it.

[max]

I think he was talking less about the right and wrong of the theory behind it and more about understanding how the different specs relate to each other.   At least that's what I get out of it.

now that you mention it, i can see that.
i must be getting old things just aren't what they seem anymore

atleast someone took the time to type it all out instead of using one liners and not explaining whats behind it.

cams are and always will be on the top of the confusion ladder, what works great for one combo will work just the oppisite in another and there might only be the slightest differeance between the two.

[firefighter3931]

Most of that information is old and long before descent flowing heads were available. With a small head you need to overcam to make power. Racer Brown Cams are ancient and the profiles are 30+ years old. They are not very street friendly with lots of seat timing and low lifts....at least compared to the modern grinds that are readily available. A lot of the bigger Racer Brown cams are ground on tight LSA's with big overlap numbers. These types of cams are designed to be run on open headers and don't like to be capped up with exhaust....making them a poor choice for a street application.

A good example of this is the recent tweaking of Vegas Mike's e-headed 440. He was running the MP590 which is an old racer Brown grind and the motor hated it. The cam was swapped for a modern profile Comp grind and it made more power everywhere. At 3600 rpm the Comp cam was making an additional 130ftlbs of torque....that's a huge difference. Here's a graph with the two dyno runs overlayed against each other : The red lines are the 590 mp cam and the black lines are the Comp fast rate grind. The streetability comparison between these 2 cams is night and day...the 590 barely idles at 1200 rpm while the Comp has a nice 850 rpm lope.

Ron

PS. Here's the thread in case you guys didn't see it:

http://www.dodgecharger.com/forum/index.php/topic,6000.0.html

[Ghoste]

That's kind of eye opening.  If someone were to write a similar cam choice for Mopars thing but pertaining to todays world, that might be helpful.

[11sails]

sorry guys but i would put my money on don dulmage. i"m sure he would tell you that the .590 MP cam is wrong. anything over .540 lift with stock style heads is no good. don builds a 440 that dynos between 530 and 550 hp without the big buck aluminum heads ect...

[Steve P.]

These types of cams are designed to be run on open headers and don't like to be capped up with exhaust....making them a poor choice for a street application.

A good example of this is the recent tweaking of Vegas Mike's e-headed 440. He was running the MP590 which is an old racer Brown grind and the motor hated it. The cam was swapped for a modern profile Comp grind and it made more power everywhere. At 3600 rpm the Comp cam was making an additional 130ftlbs of torque....that's a huge difference. Here's a graph with the two dyno runs overlayed against each other : The red lines are the 590 mp cam and the black lines are the Comp fast rate grind. The streetability comparison between these 2 cams is night and day...the 590 barely idles at 1200 rpm while the Comp has a nice 850 rpm lope.

Ron

PS. Here's the thread in case you guys didn't see it:

http://www.dodgecharger.com/forum/index.php/topic,6000.0.html

You took the words right out of my mouth.....   As I was reading this I was wondering if you had read it allready...

[Ghoste]

Say Ron, that cam of mine would fall into that uncapped category too, no?

[Steve P.]

sorry guys but i would put my money on don dulmage. i"m sure he would tell you that the .590 MP cam is wrong. anything over .540 lift with stock style heads is no good. don builds a 440 that dynos between 530 and 550 hp without the big buck aluminum heads ect...

VegasMike's motor is NOT and WAS NOT built with STOCK STYLE HEADS.. They are E-heads with Hooker S-Comps.  Once it was capped up, it cramped up!!!!!  This is what Firefighter was saying..

You know, I love Cragar S/S wheels. Some people HATE pizza!!

[firefighter3931]

sorry guys but i would put my money on don dulmage. i"m sure he would tell you that the .590 MP cam is wrong. anything over .540 lift with stock style heads is no good. don builds a 440 that dynos between 530 and 550 hp without the big buck aluminum heads ect...

The 590 isn't a bad cam in the "right" application....but it's no street cam with closed exhaust. It needs 11.5 + compression to make it effective and that takes the engine out of the "pump gas" category. Don builds good motors, no doubt....but how streetable are they. Do they idle at 850 rpm and run on premium ul with closed exhaust....don't think so.

That gets back to the point i made earlier about overcamming to compensate poor/average flowing heads....it works but streetability in terms of fuel and idle quality are compromised. 

Ron

[firefighter3931]

Say Ron, that cam of mine would fall into that uncapped category too, no?

The 484 is fine on a closed exhaust system with headers. The cutoff is 108lsa for capped exhaust....anything tighter doesn't like to be restricted. The 590 is a 106lsa  

Ron

[Ghoste]

Thanks.  I ask because my car always sees quite a difference with the headers opened and I've always figured that was just an indication that I have an exhaust that's too restrictive.  Then I saw that little blurb and with my other wrong camshaft issues, I just thought that might be another one.

[firefighter3931]

Thanks.   I ask because my car always sees quite a difference with the headers opened and I've always figured that was just an indication that I have an exhaust that's too restrictive.   Then I saw that little blurb and with my other wrong camshaft issues, I just thought that might be another one.

Usually if the exhaust is too restrictive, the car will get quicker when opened up. I don't know what you're running for pipes/mufflers but if it's 2.25 in compression bent then it's probably too restrictive. The header primary tube diameter & collector diameter largely influence the engine's powerband....but restrictive headpipes will also hurt HP #'s.

Ron

[Ghoste]

Yeah, it's the standard 2.25 compression bent.

[MOPARHOUND!]

I ripped this off from the Dodge Coronet Registry site.  I didn't write it and I don't take credit for it.  It was written by Don Dulmage.

Secondly when you modify a set of IRON heads you discover that valve lifts over 540 (Dvorak says even 530) cause a reduction in flow. (You can port the head differently so this is not the case but the end flow figure will be no higher that when you do it properly so you have gained nothing. In other words if you can get 275 cfm 2@540 or 275 cfm @600 you still have only 275 cfm so other than spending more for valve springs for the extra lift you are in exactly the same place)
So assuming you want the lift to be no more than 540 you need to decide on the duration.

The theory I subscribe to disagrees with this.

Lifting the valve slightly beyond the "peak flow lift" will allow the engine to see the peak number twice, once on the way up the cam lobe and once going down the cam lobe, and thus for a longer duration than just lifting the valve to hit the "peak flow lift" number once.   

In other words, oversimplified, keep the door at the wide open point as along as possible, versus swinging the door wide open just for an instant. 

Yet put another way, theoretically speaking, if I can get 275 cfm at .600" and at .540", I will have maximum flow for the duration the valve hits .540" lift on the upside clear to the lobe's peak, and then on the lobe's downside until the valve passes .540" again on the way to the valve seat.

Comments welcome.

[Ghoste]

I'm probably not the one to comment, but wouldn't the overkill be simply a case of running too much cam?  You'd hit the peak number twice but also use duration to get lift you can't use?

[Chryco Psycho]

if the heads are ported correctly you will not find peak flow my production heads have flow tested as still marginally gaining at .700 lift

[Ghoste]

Meaning it's almost impossible to overcam if the ports are right.  So where does the stock port guy who just wants a cam upgrade fit into this?

[firefighter3931]

The theory I subscribe to disagrees with this.

Lifting the valve slightly beyond the "peak flow lift" will allow the engine to see the peak number twice, once on the way up the cam lobe and once going down the cam lobe, and thus for a longer duration than just lifting the valve to hit the "peak flow lift" number once.   

In other words, oversimplified, keep the door at the wide open point as along as possible, versus swinging the door wide open just for an instant. 

Yet put another way, theoretically speaking, if I can get 275 cfm at .600" and at .540", I will have maximum flow for the duration the valve hits .540" lift on the upside clear to the lobe's peak, and then on the lobe's downside until the valve passes .540" again on the way to the valve seat.

Comments welcome.

In theory, your theory is sound  The only problem i see with it is the intangible cylinder head flow at higher lifts. If the heads stall at say .520 lift and you're opening the valve to .600 then it will work as long as the port doesn't go into turbulance. This is often the case with unported or poorly ported heads. When the port reaches critical velocity it can actually show a reduction in flow....which will result in a power loss. I suppose a head that reaches peak flow and holds it w/o going turbulant would be a good match for this type of overcamming. There is power to be found by opening the valve sooner and keeping it open longer.

Ron


Ps. A head such as Neil described will work with a big cam. Nice work on the porting Neil ! 

[Chryco Psycho]

thanks , I was surprised when we flowed the heads , I figured it had to stall somewhere