401/425 cam

[kitabel]

and better reflects 'real world' operating conditions

Yes, it does. Your cranking cylinder pressure is lower due to only partial stroke capture. This condition persists, in some engines as high as 3,000 RPM, but in general the entire stroke is captured somewhat before the torque peak and oif course continuously from that point.
The static compression ratio is far more accurate at any speed that develops any power.

[64Nailhead]

kitabel,
I understand what you're describing. I've read about this alot. From what I've read and what I've figured out, this describes what most cam manufacturers are referring to when they list power bands for varying cam grinds, i.e. 'rpm power range 1500-4000' vs. 'rpm power range 2500-5500'.

I BELIEVE, emphasis on I believe, they are describing EXACTLY what you're saying in your last post.

Basically, I'm trying to pick the proper cam for my application without using the trial and error method. I'm hoping that the advice I get here will allow me to pick the right cam the first time.



The info in 'Doc's cheap tricks' is awesome. The info about the switch pitch trans, SuperTurbine 300 & 400 (correct), has gotten me thinking that modifying the 'switch pitch' shift mechanism in the trans is a way to run a more agressive cam (longer duration) without having to suffer with low end power loss, that is associated with more agressive cam grinds, when I don't want to. Correct me if I'm wrong, the basis for this modification is to allows for 2 different rpm operating ranges...right?

Please correct me if I've misinterpreted this!

[kitabel]

DCR effectively predicts torque at low speed (typically bad with a big cam, even if compression is raised), and knock resistance.
The DCR figures, like 8.5:1 can be obtained with many different combinations of static CR and intake closing, but they have very different low speed power and maximum power.
A big cam simply doesn't catch everything until it's turning faster.
Yes, the higher stall mode pretty much covers the soft low speed performance of a big cam, allows a clean idle in gear, etc. It's not exactly different ranges, because most of your stall speed is gone before the major power. I think of it as a way to run a high stall converter when you want to, and tighten it up during normal driving for better mileage and lower fluid temp.

[wkillgs]

Basically, I'm trying to pick the proper cam for my application without using the trial and error method.

I've done lots of cam comparisons using the Dyno 2003 software.
There's a free download here...scroll down to the 'Software' section:
http://loco4fomoco.com/video.html

It may not be 100% accurate, but it's great for doing comparisons.
Here's an example plotting 4 cams on a stock 401...
-stock cam
-Poston NH400
-Comp cam in Erik's build
-TA413-401 cam

Basically, you'll find the bigger cams make more power at higher rpm's, but lose torque below 4000 rpm...for a given Static CR, say, 10:1.

[wkillgs]

Yes, the higher stall mode pretty much covers the soft low speed performance of a big cam.

I'll put it a slightly different way, and say the higher stall IGNORES the soft low speed performance of a big cam. At 3000 rpm stall speed, you just bypass the low rpms.

[wkillgs]

The DCR figures, like 8.5:1 can be obtained with many different combinations of static CR and intake closing,

Some rough calculations put a stock cam with 9.75 static CR near 8.5 DCR.
To maintain that same 8.5 DCR....
Poston NH400 cam would need static CR at 10.0
Erik's Comp cam would need static CR at 10.2.
The bigger TA413-401 cam would need a static CR at 10.7

Kitabel...I'm thinking these 4 combos would perform similarily at 3-4000 rpm cruise, but the bigger combos would kick but at WOT and 5000+ rpm

[64Nailhead]

Thanks for the help. I have some more checking to do, piston to valve clearance and determine what head gasket thickness will be, but you guys have sent me in the right direction.

But, onto the next item in 'Doc's cheap tricks' that caught my attention. He mentions that nailheads like big cfm carbs. For a 401/425, how big is big and how big is too big? 600, 650, 750, 850?

Thanks again for any input.

[wkillgs]

Stock Carter AFB was 625 cfm. Most guys recommend at least 750 cfm.

Found some great camshaft info on the CompCams site. They have a 'Master Lobe Catalog' that lists specs for the lobes used on their cams.
Lobes range from their basic 'High Energy' series, to the ultra-fast ramp 'Xtreme Energy' and 'XFI' series. Fast-ramp designs offer better performance, but are harder on the valvetrain components, some upgrades may be necessary.

Valve-piston clearance.... Isky cams uses a term 'VOTC' which means 'valve opening at top dead center' as a guideline for determining adequate v-p clearance.
CompCams also lists a 'Tappet lift @ TDC' spec.
I feel this is a great guideline to determine what cams MIGHT fit without v-p clearance issues.
-My stock '66 401 cam has VOTC of about 0.030".
-The Poston NH400 cam I installed is 0.050".....
V-P clearance with stock 0.045" deck clearance, 0.007" off the heads, and a steel 0.015" head gasket was in the 0.090- 0.110" range. Pretty safe. Adding Tom's roller rockers reduced v-p clearance about 0.020"
- The Isky cam i put in another engine has VOTC of 0.085-0.090".
Pistons had to be cut, even with a 0.040" head gasket.

With that said, a CompCam lobe with 'Tappet Lift at TDC' (110degree) around 0.050" should work on a stock block. 'Might' be able to go 0.060-0.065" with a thick 0.040" head gasket.

Opinions on this theory appreciated!

[telriv]

On the '51 Henry J we got away with .020" of V-P clearance all last & this season. The good thing is that the piston is moving AWAY from the valve. This happens in our engine at about 5* ATDC. The exhaust has plenty of clearance. When you advance the cam it makes the clearances even tighter. We have the J's at 4* advanced. If we retarded it to say "Straight" up we would have MORE clearance on the intake & less on the exhaust.

[64Nailhead]

Walt,
I've been reading several threads ab0ut carb size. From what I've read it seems that I almost can't go too big. I'm relativley sure that I'll use an 800-800+ CFM Edelbrock or Holley due price, parts availabilty and tuneability.

What do you, or others, view as 'safe' valve to piston clearance in a street/strip application? I assume that .060" is minumum and .090" being better, but I could definitely use some schooling on this.

I've also been reading several threads about cams, and after reading some of them, I end up somewhat more unsure of what to do than prior to reading them. I will keep reading and I think I'm gonna call Comp Cam and TA Performance and see what words of wisdom they offer.
Thanks for all the help.