Cam selection beyond 1 800 cam help

[John Scott]

After buying off the shelf varieties for years, then moving up to custom grinds recommended by a cam techie sitting behind a phone, I shutting up and letting my builder do his thing. I've given all the vehicle specs, rpms, and everything I've read about cams lately. His advice is: "I choose a cam grind after I'm done with the heads and have the flow #s. That way I can taylor the cam right down to the lobe profile for a specific application." By his experience we know it will be at or slightly above .600 with duration in the mid high 240s. Also surprising is the size of the intake valve. He knows what works up here. Lift, duration, and even lobe profiles are taylored to the engine, components, and its application. I could never guess which lobe to choose, and only have basic idea of the rest of the specs. The other racers seem pleased with the results. I guess this is why he's doing the dirty work and I'm saving my pennies like crazy..

JS

[Guest RON JONES]

Sounds good!

[grumpyvette]

John Scott

I was hopeing more people would post on this,... theres three ways to look at that,

(1) if your willing to let someone with more that your present experience level make the choices for your engine thats not a bad plan(thats basically what your doing when you call cam company for advise anyway)

(2)learn enough about the subject to be able to make valid choices yourself, now this will take time and effort that you may not want to be involved in but it adds greatly to your understanding of what and how your engine works and will allow you to adjust the characteristics of that engine your building.(what I do now)

(3)or do what I did for years, list all your parts after doing research to make sure everything matches the displacement,gearing,rpm range,and intended use of your engine,call at least 6 cam companys and ask for the lift and opening and closeing points @.050 lift of the cam they suggest, average those figures and buy the cam from what ever company that has the cam that most closely matches the average figures or have a cam ground that closely matches those figures from your favorite manufacturer (usually not as expensive as you may think)but in most cases an off the shelf cam is available for most combos,(BTW its always better to go for slightly less lift and duration than slightly more than the average if you must compromise slightly)

[pparaska]

Cam choice - now there's a topic!

 

I agree that a builder that's done alot of winning cars for the racing style you are after is a good starting point.

 

But I've always been one to wonder how/why things work, and the issue of how to get air/fuel to flow in and out of an IC engine is very interesting to me - so I've done a bit of reading.

 

What's really enticing to me is the idea of fast opening and closing ramps. Especially when you have to deal with streetable compression ratios, short stroke (like my 327), etc. The theories on dynamic pressure and the effect of Intake Valve Closing IVC point really make sense to me. I think .050" duration figures are only slightly useful, as a slow ramp cam with say 230 degrees duration at .050" lift will have a later IVC point than one with faster ramps (like a roller, or the Comp Cams extreme energy flat tappet grinds, for example), all things being equal (LSA, etc.)

 

A case in point: Comp Cams 270S Magnum solid lifter cam for the SBC. This cams specs are:

 

PN 12-222-4

Grind Number CS 270S-10

_________________Intake Exhaust

Valve Adjustment 0.022 0.022

Gross Valve Lift 0.468 0.468

Duration At 0.015 Tappet Lift 270 270

 

Valve Timing At 0.015

______Open Close

Intake 29 61

Exhaust 69 21

 

These Specs Are For The Cam Installed At 106 Intake CL

________________Intake Exhaust

Duration At 0.05 224 224

Lobe Lift ______0.312 0.312

Lobe Separation 110

 

Note that the cam has 270 deg of seat timing, 224 deg of .050 timing and has a IVC of 61 deg ATDC

 

Now look at another solid flat tappet cam, from the extreme line:

 

PN 12-677-4

Grind Number CS XS274S-10

________________Intake Exhaust

Valve Adjustment 0.016 0.016

Gross Valve Lift 0.501 0.51

Duration At 0.015 Tappet Lift 274 280

 

Valve Timing At 0.015

______Open Close

Intake 31 63

Exhaust 74 26

 

These Specs Are For The Cam Installed At 106 Intake CL

_________________Intake Exhaust

Duration At 0.05 236 242

Lobe Lift 0.334 0.34

Lobe Separation 110

 

Note that the open/close seat duration is 4 degrees more on this grind (intake), therefore the IVC is only 2 degrees later (63 vs 61). But notice that it has 12 degrees more 0.050" duration (236 vs 224). Yes, the overlap is a bit higher (57 vs 50 degrees), but I'm hoping the IVC being close will mean that there should still be decent idle vacuum.

 

I realize this is comparing a non-split duration cam with a split duration, so the waters are muddied (more overlap being a consequence). That wider exhaust timing will cause a bit of low speed mixture dilution, I suppose.

 

But one issue is that with the latter cam (12-677-4), the cranking pressure (dynamic pressure to some) only went down from 196 psia to 192.4 psia (for my 327 anyway), versus the 12-222-4. And that's totally a function of the IVC point.

 

I also wonder that if I don't use the advertised lash setting, but run both at 0.016" lash, will things be more different or more the same?

 

Wow, pretty far afield with this response. I guess what I'm trying to say is having experts help select stuff is good, but I like being an educated consumer. But my education is far from over on this topic and many to do with engine design/building.

[John Scott]

I've been planning my build for a long time. I already miss one of the finest rewards of all this nonsense, at least for me, DRIVING it. My goal is to build the nastiest street engine, broad torque band, high hp, I can within certain RPM(6000 under), pump gas, budget, and timeframe. If Grumpy's figures are close, then 489hp @ 5500, 501@4600 is coming pretty close to my goals.

Grumpy, I've gone route#3 on your post above. You've been a great help with your testing of a few cam choices, the last with input from my builder. I quote you..."BTW thats one of the best combos with a good wide torque band I've ever seen on a 383..." I can no longer count the phone calls to cam companys. I couldn't believe the difference from tech to tech and day to day. I read researched and averaged all the info I could get. I then spewed this all to my engine builder. He said I was in the ballpark, but here is what I've found on the dyno and the track...Our altitude, your head choice with the 383... There are some of the new profiles not even in the catalogs we're testing. I've had really good results using this with that and so on.. I'm fascinated by the subject, but theory and having dozens of engines built, dyno'd, raced, cant compete. The only job thig guy has had for 18 years is flowing heads and building race engines. I've had really good luck with the custom grinds, but to have a successful builder say, that would be OK, but I've found this will work better, is what I want to hear right now. His name goes on the valve covers. He wants you to have the fastest car at the track. Good advertising. Pete, I've always wondered what made things tick, I admire the way you dig way deeper than most would dare to go.

JS

[Guest Anonymous]

WOW, now this is a broad subject. I would say buy a couple of books, and look for similar dyno comarisons of your motor combination. You really need to decide exactly what you want this motor to do for you. The cam is going to tell the motor where to make power. (this is not a perfect statment, but is generally acurate) I am plannign a lot of highway cruzing, so I figured out my cruzing RPM and picked a cam that started to make a lot of tork at that RPM. This should let me stay in overdrive, and give me good power should someone want to play. I hope this helps.

[Kevin Shasteen]

Ahhhh, Camshafts-Camshafts-Camshafts(?)

 

I remember reading a Hotrod issue where they stated that everytime they do comprehensive write up on "Camshafts" that that specific month becomes the most purchased mag of the year.

 

I agree w/Pete & Grumpy on their suggestion in educating yourself on camshafts. At a time I found myself purchasing every mag, book/source I could find on camshafts in an attempt to learn how they work & exactly what it is they do.

 

The best purchase I feel I made (I made a lot of them-some not so good) was:

 

The Best of Hot Rod's "High Performance Camshafts" Volume 11, by Car Craft

 

What I liked about that book is that they gave dyno runs on each cam install. They alsy did cam comparisons on the same engine & w/the dyno runs they would tell you "With this larger cam-you now need better flowing heads." You could see the difference yourself & think about the very info you were reading till it made sence.

 

I probably read that book a couple dozen times before the lights began flickering on (& staying on). It was a struggle to learn but a delight once I figured them out...still learning but now I have a firm grasp on the subject.

 

Believe me, & the others that have stated so-the learning process wont occur over night; you have to make a sincere commitment to learn cams-I must have fallen asleep countless times w/that book on my head only to awaken w/a pool of drool on my cheek (ugly image I know) & to find out it was three in the morning & I had to get up shortly...but I persisted; and now I understand cams.

 

One thing I would caution; you mentioned you're tired of building eng's that dont finish a race...keep in mind that if the "Nastiest Street Engine" is what you're after then your, choice of .600 lift or mid .600 lift camshaft profile will be lifting your valves quite a bit. W/that profile you are definatly in/at the "Dedicated Dragster" territory. The more [max'd] out an engine...the quicker things will wear out & possible break.

 

If this is going to be a street engine-be sure to factor in durability/endurance & be realistic....seeing how your wallet is at stake here. Remember-even tho your engine builder knows engines...its not his money you'll be using when something breaks (PS: it's your money you'll be using to make a repair when something breaks). What I'm saying is this: just because something will work (per your engine builder) doesnt mean it will be long lasting(?) especially if you plan on getting on it hard...more often than not!

 

Good luck w/your engine & let us know how everthing turns out.

 

Kevin,

(Yea,Still an Inliner)

[grumpyvette]

BTW heres a FEW good rules to keep you out of trouble while picking sbc cams,THIS APPLIES TO 350CID AND LARGER ENGINES, SMALLER ENGINES REQUIRE LESS DURRATION.

 

(1) IF THE CAR IS EVER DRIVEN ON THE STREET AND IF THE DURRATION @.050 IS OVER 250 DEGS. ON THE INTAKE OR THE LIFT IS OVER .600 YOU PROBABLY HAVE SOMETHING WRONG WITH YOUR COMBO THAT YOUR TRYING TO COMPENSATE FOR.

(2)WHEN IN DOUBT GO WITH THE LOWER DURATION LOWER LIFT CAM.

(3)ROLLER CAMS ALMOST ALWAYS PRODUCE MORE TORQUE/POWER BUT ARE NOT NECESSARY IN A MILD

STREET CARS

(4)SOLID FLAT TAPPET CAMS GIVE YOU A GOOD RETURN ON POWER PER DOLLAR

(5) ALWAYS CHECK ALL CLEARANCES EVEN IF THE COMBO (SHOULD BE FINE)

(6)DAILY DRIVER CAMS SELDOM WORK WELL IF THE INTAKE DURATION EXCEEDS 234 DEGS @.050 OR .550 LIFT

(7) YOUR ALMOST ALWAYS BETTER OFF WITH A SINGLE PLANE VICTOR TYPE INTAKE IF THE CAM INTAKE DURRATION EXCEEDS 230 DEGS. @ .050

[John Scott]

Thanks, all, for the replies.

Grumpy, sounds like I'm still on track with my selection. I'm not going to exceed the .600 lift, by much, but as you said if over 600 lift your compensating for something wrong. Oxygen @ almost 5000ft! Other than that, solid roller design, not a daily driver, and using a Victor Jr. The cam companies I talked to seemed to all like a high .500 lift with the duration of 246/48. We're using a .600 or just slightly larger because we've found at our altitude the higher lift and slightly larger intake valves, when combined properly, give better overall results. Often we have a 20-25% loss in hp over sea level. I'm looking at the option of using CC pro magnum 1.52 AND 1.6 rockers as I have access to both and not a complete set of 16 of either. Cam will be custom ground accordingly, I'll post specs when its ordered, as well as corrected dyno results to see how I've done. Keep the tips coming!

JS