[DeTomaso] Comp Cams Kit

[Daniel C Jones]

> I thought Dan normally recommended a 109 LSA for his 'pet' cams?

No, I do not specify a single LSA for different engines.
What's best for an in-line valve Windsor is not necessarily what's
best for a canted valve Cleveland.  Furthermore, 2V and 4V heads
have different optimal LSA's due to the difference in valve sizes.
What I do is calculate the "optimal" LSA based upon David Vizard's
guidelines.  To do this, I need as a minimum:

 bore diameter (in inches)
 crankshaft stroke (in inches)
 intake valve diameter (in inches)
 compression ratio
 canted or inline valve heads
 desired RPM range
 rocker ratio
 type of lifter (roller or flat, hydraulic or solid)
 desired idle characteristics
 exhaust system characteristics

I've worked up a bunch of cams for people on this list and most of
them are different from each other.  For a more detailed explanation,
see the post attached below.  Also, the current issue of Popular Hot
Rodding has another test of LSA on a 4.6L Ford SOHC engine.

> Dan, it was my typo...here are your suggested cam specs for my motor...
> I'm off by 1 degree on the LSA...your suggestion was the Reed
> Cam that you specd, probably the same Mikes using....
> 228/232 degrees @ 0.050" lift (280/284 @ 0.006"), 0.588"/0.588" lift,
> 107 LSA, 68 degrees overlap, installed in the engine on a 104 intake
> centerline, Reed Cams # 535-TM280HR-284HR-107A."

That's not the cam Mike is using.  That's the cam we are using on
the 351C dyno mule.  I offered that up as an example since your
short block is similar to ours.  Due to the tight LSA of 107 degrees,
I only recommend that cam if you run a very efficient exhaust.
Stock Ansa mufflers or Euro GTS mufflers (gutted or not) won't
cut it with that cam.  Narrow LSA cams need minimimal back pressure,
otherwise they won't run well at lower RPM and will have a poor
idle.  If you have  restrictive exhaust, I'd opt for a wider LSA.

> Yes, I am running 1970 4V quenched heads (not sure if they have been
> cut) with .030 over forged speed pro flat top pistons.

Did we settle on what sort of lifter you want?  You may have told
me already but I'm helping several people with their engines and
from behind my monitor, you all look alike :-)

> turns out their custom grinds are only done from the "lobe design
> patterns" they have in their system, which are plentiful.

Yes.  Cams with identical specs can behave very differently depending
upon the lobe shape.  Life expectancy can also vary widely.

> Summit has the best price for the kits about $30 less than Comp Cams
> price...

Alex Denysenko at moneymakerracing.com can usually beat Summit on
Ford Comp Cams kits and can do custom grinds.

> When ordering from Summit or Comp Cams you have to give a core number
> (32-000-5 for a Cleveland)

There are several different cores (flat or roller tappet, solid or
hydraulic) for a Cleveland.  Be aware that some grinds can some cores.
For instance, a street profile can not be ground on a Comp steel
roller core because the difference in profile shapes is so different
it will break through the heat treatment.  Instead Comp uses an
austempered ductile iron core for it's hydraulic roller and some
street solid roller profiles.

> It may be easier in the long run to order #535-TM280HR-284HR-107A from
> Reed Cams and source all the parts separately. At least you know your
> getting a cam that works.

Unfortunately, Reed may be a victim of the weak economy.  It appears
that Reed may be out of business or temporarily shut down (phones and
website down) .  Reed had good products and when you called, you talked
to someone who knew what they were doing.  Even more startling is they
would take notes from their customers and put it in their database so
they could help other customers avoid mistakes.

> Dan recommended a custom ground Bullet cam for my application.
> He provided Bullet's Master List part number and all the specs.
> I called Bullet expecting a custom ground to be more expensive than
> an off the shelf cam and a long wait. Bullet told me they do not stock
> any ground cams. They carry cam blanks and take the orders during the
> day and grind the cams at night. No additional cost for a custom grind.
> They ground my cam that night and shipped it the next day.

Yup.  Bullet is very good at that.  Their Master Lobe List calls out
the lobe type:

 The first letter is either "C" for a conventional shaped nose
 on the lobe, or "D" for a dwell nose. Dwell lobes are often
 used when there is a lift rule, such as NHRA stock classes.
 Dwell lobes are usually not well suited for higher RPM applications.

 The second letter is either "R" (RPM) for lobes suited for higher
 RPM applications or motors with numerically high rocker ratios,
 or "T" (Torque)for lobes suited for lower RPM or motors with
 numerically low rocker ratios.

 The third letter is either "S" for symmetrical lobes (opening
 and closing ramps the same), or "A" for asymmetrical lobes
 (opening and closing ramps different). Asymmetrical lobes usually
 have a slower closing rate to help prevent valve bounce.

However, I've only had experience with their flat tappet Cleveland cams.
I'm not sure what they offer for roller tappets.

> Funny what you said about the tech people at Comp Cams...I must have gotten
> one of the lesser informed... the guy I talked to on Tuesday said "you
> probably don't want to go over 6000 rpms because Cleveland heads don't
> breath".

Sadly, all too common.

Dan Jones

Lobe separation or lobe centerline angle (LCA) is the angle between the
intake and exhaust lobes.  On a single cam engine, it's ground into the
cam core itself.  Cam duration and lCA combine to form the total amount
of overlap (i.e. the time the intake and exhaust valves are open
simultaneously).  More overlap means a rougher idle and poorer low end
response due to reversion of the exhaust charge into the intake plenum
as well as loss of dynamic compression ratio.  For a given overlap, there
is an ideal split between duration and lobe separation.

David Vizard has published a couple of articles in the hot rod magazines
with guidelines for specifying cams.  The guidelines are distilled from a
much more sophisticated software progam that Vizard developed, based upon
theoretical considerations and also upon literally thousands of dyno tests.
In "Be the Camshaft Expert" (July 2006 issue of Popular Hot Rodding),
Vizard presents his rules of thumb for selecting cam specs based upon what
he's learned in developing the cam selection program.  The program was
reportedly 18 years in the making and used data from thousands of dyno
tests.  In the article, Vizard presents graphs of CID/Inch per cylinder of
valve diameter versus ideal LCA.  The graphs are for inline valve heads and
engines between 9 and 11:1 compression ratio.  If canted valve heads are
used, the ideal LCA is 2 degrees less.  The optimal LCA is also adjusted
for compression ratios outside the assumed range.  Once ideal LCA is known,
you pick your desired overlap via application:

 1. Street towing       10 to 40 degrees
 2. Regular street      30 to 60 degrees
 3. Street Performance  50 to 75 degrees
 4. Street/Strip        70 to 90 degrees
 5. Amateur Race        85 to 100 degrees
 6. Professional Race   95 to 115 degrees

This serves to set the RPM range.  Where you fall in the overlap range is a
function of valve size per cubic inch.  Big valves on a 302 use the low end,
a 350 with typical size valves use the mid-point, big inch small block or big
block, use the right hand side.  Once LCA and overlap are known, duration
falls out of the equation.  Lift is determined by the intake valve diameter.
For other than race application, the ideal lift may be excessive so the
suggestion is to use a lift consistent with your reliability goal.  Vizard
also suggests the rocker ratio on exhaust is best kept 0.1 to 0.2 of a ratio
lower than the intake ratio.  He states that the exhaust is less sensitive to
valve acceleration than the intake but is sensitive to duration.  If an
existing cam's LCA is too wide, higher ratio rockers may increase output.
For rocker ratios between 1.5 to 1.9, each 0.1 ratio increase on the intake,
the LCA needs to be spread by 0.75 to 1.  Another point raised is that, for
most V8's with reasonable heads, the ability to raise low speed torque with
compression increase holds to around 285 to 290 degrees (at lash point) of
cam duration.  After that, drop off is faster than an increase in compression
can recover.

In the "Be the Camshaft Expert" article, Vizard presented the results of a
LCA test:

 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album15/LCA_comparison.jpg.html

Ideal LCA for that engine was 108 degrees.  Narrowing to 105 degrees made
similar power but had noticeably worse idle and low speed characteristics.
Widening to 111 degrees lost power.

At low speed, lots of overlap is bad as it hurts low end but overlap
helps as the RPM increases.  To a degree, you can offset overlap with
static compression.  In another article ("Compression Comprehension")
about running up to 12:1 compression on pump gas, Vizard presented the
results of a compression test:

 http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album10/album15/CR_vs_low_speed_output.jpg.html

"When used in conjunction with a bigger cam, increased compression can
 work wonders for the entire curve. When a 265-degree cam (gray curve)
 was substituted for a 285-degree cam (blue curve), a substantial drop
 in low-speed output was seen. Raising the CR from 9:1 to 12:1 recovered
 almost all the lost low end and gave a further increase in top-end
 output"

I wrote a little program based upon the article.  I know for a fact that
Vizard's cam selection software uses much more detailed information including
head flow data, port and runner dimensions, even things like desired idle
vacuum levels.  However, based upon my limited experience, the simplified
program seems to give pretty reasonable trends.  As a starting point, you
could do worse.  For larger valves like the 351C-4V, the theoretical lift
where flow tapers off is quite large.  However, for small valve heads,
like my little Rover/Buick aluminum V8, the maximum lift is reasonable.
Vizard's article notes this and says to use whatever lift you can tolerate
for the application.  Jim Sams has run Vizard's full up program and notes
that it doesn't tell you what ramp rates you need.  According to Jim,
Vizard's suggestion is similar to the lift one: "Use the most aggressive
ramp you can tolerate for your application."

As a test, I ran the simplified program for my Buick/Rover stroker project.
The results are pretty much in line with what experience suggests works
well.  On Buick 215 and Rover 3.5L engines, a LCA of 111 or 112 degrees with
around 0.5" lift works well (assuming normally aspirated, no nitrous).  On
a stroker like mine with ported Buick 300 heads, tighter lobe centers (108
degrees) and a bit more lift (up to 0.550") work well.  That's right in line
with what Vizard's simplified cam selection method predicts.  BTW, when
stroking an engine (assuming the cam timing was optimal to begin with and
keeping all other variables constant), Vizard suggests tightening the LCA up
by a degree for something like every 16 cubic inches increase in displacement.
That will lead to very tight lobe centers which may not be acceptable for
certain applications.  A mass-air EFI 5.0L might not be too happy with 106
degree lobe centers, for instance.  Vizard's full-up program allows you to
specify idle vacuum to get around problems like that but the simplified
program doesn't have that sort of flexibility.

The required inputs for the simplified program are:

 bore diameter (in inches)
 crankshaft stroke (in inches)
 intake valve diameter (in inches)
 compression ratio
 canted or inline valve heads
 desired overlap range:
   1. Street towing       10 to 40 degrees
   2. Regular street      30 to 60 degrees
   3. Street Performance  50 to 75 degrees
   4. Street/Strip        70 to 90 degrees
   5. Amateur Race        85 to 100 degrees

I use this program as a starting point for my Dynomation engine simulation
program.  One thing to be aware of is that narrow lobe separation angles
require an efficient exhaust (minimal backpressure).  If you have a bunch
of backpressure, it will hurt a narrow lobe separation angle engine more
than a wide one.