Re: Cams

[Darwin <65Val@xxxxxxxxx>]

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""Sorry to go on so long""


Don,dont EVER say that. I love your emails as feel I'm getting a great 
education and insight into building high performance motors from someone 
who's really "been there,done that". I've saved almost all your messages in 
a special folder and refer to it if I ever need the info. I thank you very 
much for your knowledge and your willingness to share it with us.

Darwin/Victoria BC/Canada
'65 Cdn.Val.Cust.100 'vert
Slant 6/factory 4 speed

----- Original Message ----- 
From: "Don Dulmage" <big-d@xxxxxxxxxxxx>
To: <1962to1965mopars@xxxxxxxxxx>
Sent: Saturday, December 03, 2005 5:22 PM
Subject: Cams


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It is true i like Racer b s cams but only becase hey really really work. 
Putting all that aside here is what i found out in my years of playing and 
testing BB Mopars.

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
[Non-text portions of this message have been removed]

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Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
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bOyW3N.