[TJS69]

Eric, I didn't want to steal someone elses post, so... You don't think the 282S will work with my estmated compression ratio of 10:1 huh ? What do you think of Crower's 00320 ? It is a 264/270 Duration with .458/.468 lift, with a lobe seperation of 112*. http://www.crower.com/misc/cam_spec/...00320&x=37&y=8

[Mr.Freeze]

the cams are uncomparable to comp cams, even with .050 numbers.
Comp uses .015" for there seat to seat numbers.
Crower and most of the rest of the industry use .006" for there seat to seat values.

A similar comp cam when measured at .006" to .006" would be a longer duration then what it appears to be on comp's advertised numbers.

If you suspect that a cam with with 282 duration from .015 to .015" will not work with the combo (although i think differently) then you should also think that a cam with less duration from a point measured lower on the cam base circle will also be too small for the DCR value that you're looking for.

Also i believe that DCR values are nothing to worry about, as DCR is a waste of time in considering wether a specific cam will work with a specific combo in a specific situation with x gas.
The Exact same combo could need different octane gas depending on what time of year it is (becuase it'll be hotter or colder, wetter or dyier).

If you're looking to use a specific fuel, then aim at a compression that will easily be capable of being used with it, then choose the cam that compiments your intended RPM range and work from there.
Big Compression values arent going to make alot of power if you overshoot your goals and the car ends up detonating all the time.

dont work backwards, choose an RPM range and work from there, not a compression ratio to work from.

[stingr69]

Guys,
If you call Comp, they will probably tell you 9.5 C/R is good. That is what they told me TJS69 is probably running about 9.6-9.8 C/R by my calc with iron heads. Sounds like a pretty good match to me.

Eric has empirical evidence that the 282S works well with 10.3 or so C/R in his combo because he ran it in his 383 and in a friends 327. Aluminum heads if I remember correctly.

The dynamic compression ratio recomended numbers are based on empirical evidence. It requires you to know actual seat-to-seat timing, not advertised duration. Actual seat-to-seat timing is the same regardless of who's name is on the box. These numbers are not always easy to obtain but they are required for the DCR to work. The recomendations are based on modern aftermarket lobe lift rates and typical pump gas. Local fuel availability matters too but without building the whole shebang up and trying it out($$$), DCR and other empirical evidence are all we got. They are not perfect, but should not be ignored as a tool used in cam selection.

More to the point, TJS69 already has a C/R, he is just looking for a cam.

Let us know what you decided and how you like it now.

-Mark.

[Mr.Freeze]

Originally posted by stingr69:
Actual seat-to-seat timing is the same regardless of who's name is on the box. These numbers are not always easy to obtain but they are required for the DCR to work.

Actual seat-to-seat is .006" to .006", in other words the industry standard...except for comp cams.


Also, keep in mind new style aluminum heads with up to date chambers are definetly going to be capable of more compression then Old style 461 Iron heads.

[ 09-21-2003, 09:39 AM: Message edited by: Mr.Freeze ]

[Eric68]

TJS69, what exactly is your combo? What kind of heads (iron/alum, chamber cc, intake cc, brand, etc), pistons (flat-top/dome/dish), deck height, head gasket thickness, converter, gear, etc.

Let's get a good idea exactly what you have and where you are going before we decide what works and what doesn't.

Mr Freeze, the DCR calculator is far from a waste of time. I've personally used it with good success and am currently running an 11.3:1 motor on pump gas because I picked a cam with the right timing events (with thoughtful input from some folks around here).

While is not a miracle-all-knowing-pefect-cam-selection-tool it is very usefull when picking a cam --- especially when you are already saddled with a long block with a given compression ratio. While IVC and static CR are the main factors that determine an engine's DCR, other cam timing events can be changed to help fit a particular RPM range necessitated by gears, stall, intended use, etc.

Also, I fully understand that most cam companies use different adv duration specs. Its not just Comp --- every company does it different with some using different measurement specs for the same lobe for opening and closing points! Look at an Isky cam card sometime or the specs on an old GM grind . . . My point is that how much change in IVC angle do you think .015" vs. .006" lift makes anyway? Not much IMO which still leaves the DCR program in the ball park --- especially if you take the specs into consideration and stay conservative for a cam that is a little tighter than spec'd or go more agressive on one that is longer than spec'd.

As for temperature etc, you make a good point, but I certainly wouldn't throw out a useful tool because it isn't 100% on the money under all circumstances. If you are worried about air temperature, you should also be worried about coolant temperature, quench height, combustion chamber shape, VE, etc., etc., etc.

[Mr.Freeze]

Really?
What is that calculator going to tell you? It's just another number to look at, doesnt do you any good, as to determining what will and wont work in your combo.

The industry standard (SAE) .006" doesnt include many aftermarket cam companies (my fault on that) i checked up on what crower/comp and crane are using, crane and crower use .020" while comp uses .015". None of these are actual seat to seat except the .006".

The amount of compression you're capable has as much to do with cam timing as it does anything else.
Chamber size/shape, dome size, valve pockets, pump gas used (pump gas ranges depending on the area its in some can only get 91, while others 94).

DCR calculation without a base to work from is a waste of time. What it may be useful for is if you already have a working combo that works with a specific DCR and you want to increase cam timing and maintain the DCR. Still the way in which you increase compression will effect how a specific gas will work with the combo.

Aim at an RPM range and work from there, do NOT work backwards, or you'll have a disappointment....with the compression you wanted.
'Nough said.

[Eric68]

OK if you want to use 9.5:1 for a "relatively small" street cam, what compression do I aim for if I want a "relatively medium" street cam? what size exactly is a medium street cam or a relatively small street cam for that matter? I'm not trying to be smart, just trying to point out that at some point you have to pick a cam and compression ratio --- and I'm all for making the two match, not necessarily running on the ragged edge.

. . . and I agree with your aproach BTW --- if you are building a motor from scratch that is the way to go, but there are lots of folks that cannot always afford to build one from scratch . . . there are lots of guys looking to swap a cam into their existing motors to "get a little bit more."

PS. Comp uses .015" tappet lift to rate their Magnum solid cams, but they actually use .006" tappet lift for their hyd FT cams and maybe even .020" for the tight lash solid cams. I think their idea is to try to compensate for lash with a diff spec for the solids. Crazy ain't it . . .

[Mr.Freeze]

Eric,
The reason for there low ramp grinds like the 268H (not xe) to use .006", is becuase they are actually Federal Mougal grinds, reboxed and sold as comp cams.

Comp makes the the magnum/extreme energy and the high po drag race cams, but they just rebox the little stuff.

I think we can agree to disagree on the DCR calculator, i think it has no purpose, but if you guys find a point to it, fair enough.

[TJS69]

Sorry guys, I didn't mean to start anything. I currently have an Ultradyne "Ultrastreet" cam in my 327 that I am not happy with, thus I do have a specific compression ratio that I do want to match. My combo is: 327 bored .040 over. Stock 461 iron heads only surfaced - not milled. I think the 9.8 CR is a good guess. TRW flat top pistons. The current cam is a single pattern with .460 lift and 270 Duration. I have a 600 CFM Edelbrock Carb and an RPM intake. My trans is a TPI 700r-4 auto with a 2000 rpm stall. for rear gears I currently have 4.11's but I am switching to 3.73's, that I have new in the box.

[thrasher]

Some people don't rely on the DCR at all.They pick a cam and let her rip.Then select the next cam based on the cranking compression.

[pdq67]

Mr. Freeze,

I didn't know that CC was reboxing cams b/c when I look at some of the major players in automotive valve train marketing through the years, (TRW, Speed Pro, Melling, Elgin, etc..), I never ran into a 268 grind like the CC 268HE unless it was maybe a General Kenetic grind??

Please elaborate and I might even ask UDHarold about this too since I think he might have ground the 268HE for them when he worked there way back when??

pdq67

[Mr.Freeze]

Where i work we often have a guy who is local to the area stop by the shop. He's the exporter for the east coast automotive industry, all the big players go through him. He knows, as he deals with the big names in the auto industry directly, and he's let me know what goes on as far as who uses what.
All the standard type grinds are made by a major cam company like melling or federal mogal, and comp and crane and a few others just rebox mark-up the prices.

[Eric68]

OK . . . with flat top pistons and a normal .040-.050 quench height your compression ratio should be closer to 9.5:1.

What didn't you like about the Ultradyne? Too small? If its the 270* Ultrastreet cam duration @ .050 is 219, lift is .460" on a 111* LSA.

With only a 2000 stall and an overdrive tranny I think you will want to keep your adv duration on the short side or the car will wind up being soft out of the hole. I would look for a dual pattern cam that has a short advertised intake duration (like 265 - 270*) to help low speed performance and agressive lobes to let her breath better up top. The dual pattern has a longer exhaust duration which will work better with the stock head's weak exhaust port.

PS. I like the Crower you mentioned for your application. DCR is 7.9:1 and the wider LSA should help down low - power band should be 2000 'ish to 6000+ in your 327 (if the heads let it go that high).

[Rubeng442]

Just a few facts I have learned about the High Energy line of cams:

1. UDHarold (Harold Brookshire) claims to have developed this line of cams for Comp Cams back in the late 70's early 80's.

2. They are an assymetrical lobe design with different ramps for the opening/closing sides.

3. They are NOT the same type of cam that is mass produced by Federal Mogul/Melling/etc. As far as I know none of the cookie-cutter cams are assymetrical or anywhere as agressive as a High Energy cam in design. The true "cookie-cutter" cams are the PAW/Edelbrock/Summit/Lunati Bracket Master II and many other "brands" which offer the same exact cams. They are not hard to distinguish.

Also from what I understand the .006 lift is at the valve, per SAE Specs, which with a 1.5 rocker arm ratio is the same as .004 at the valve, which is the way Crane specs their cams. Isky uses a very strange system and I do not know what Crower uses. Comp Cams uses .006 lobe lift which is .009 at the valve. Their lobes will spec out about 6 degrees larger at .004 than at .006, again according to Harold Brookshire.

The industry standard for Solid flat tappet and solid roller cams is .020 lobe lift. Comp Cams uses this standard on all their race profiles. They use .015 for all their "street" profiles such as the High Energy, Magnum and Extreme Energy solid flat tappet/solid rollers. Crane measures some of their "stret grinds" at .018, their race stuff at .020 like everyone else....

[Mr.Freeze]

Rebeng, Could you be possibly speaking of the extreme energy line of comp cams?