1966 SS 327 cam? - Impala Tech
Performance Our High Performance Area

  • 2 Post By Big Dave
LinkBack Thread Tools
post #1 of 8 (permalink) Old 04-05-2020, 04:27 PM Thread Starter
Join Date: Jan 2020
Posts: 12
1966 SS 327 cam?

I have a 66 SS 327/2 speed, has been bored .030 over and has a mild 350/350 cam. Wondering if I could go to a more rougher idling cam or larger cam without having to change much in the heads/. And knowing probably will have to put a larger TQ converter in.
Thanks for help.. Kenny W.
Have a blessed one!
Kwilk1734 is offline  
Sponsored Links
post #2 of 8 (permalink) Old 04-05-2020, 06:35 PM
Join Date: Jan 2006
Posts: 13,023
That " rougher idling cam or larger cam" is the sound of lost power. It is the sound your engine makes as it struggles to stay running with the intake valve off it's seat. It is the sound of lost compression which is free horse power.

A Race car has a " rougher idling cam or larger cam" because it never idles. Never pulls away from a stop light either. In fact it only operates at one engine speed and that is wide open. You can try to drive around for a bit at wide open throttle. Dropping the transmission into drive from neutral at every green light; even if there is a cop sitting next to you. Not a great idea on the street, but every one thinks that rough idle means horsepower, and it does at the race track.

But on the street it costs you power you need to accelerate without the drama or a ticket associated with spinning your tires to get the car rolling. That added duration is on a race cam to allow the motor the time it needs to fill a cylinder with air at 6,800 RPM. This is because air is a fluid (a compressible fluid unlike water), but it flows like water at high speeds. It takes time for air to get into and out of a cylinder past the valves. You don't have a lot of time at high RPM to do this which is why they leave the valve open to allow the cylinder to fill even the the piston is rising trying to compress the fresh fuel/air charge (hard to do with an open valve). Instead at slow engine speed it pushes the fresh fuel/air charge back into the intake manifold pressurizing it. This makes the carb think the manifold vacuum has dropped so it dumps in more fuel than the motor can burn (ever notice how your eyes water and burn around a race car?).

If all you want is noise instead of power go to the bottom of the page for your cam choice. Just read the foot notes about requiring domed pistons to get back some of the compression you are giving away with a long duration cam. And the need for a steeper (higher numbered rear gear) to get your race car rolling off the line because it has lost bottom end power. or as you noted a higher than stock stall speed on your torque converter, so your motor won't stall at idle because it has no power at idle.

There is a reason the Z/28 only came with a manual (no torque converter stall issue) and 4.10 rear gears from the factory. It was because of the duration on the 30/30 Duntov cam that was installed in this factory made TransAm race car.

Big Dave
japete92 and 65_&_67_Impala like this.
Big Dave is online now  
post #3 of 8 (permalink) Old 04-05-2020, 07:38 PM
Senior Member
Join Date: Mar 2008
Location: Moneta, VA
Posts: 941
I always liked the 375 HP Solid Lifter Cam.

If you have the original '66 327, you already have the small Double Hump Heads.

-Parting Out over 75 '58 to '73 Full Size Chevy Cars-


-National Impala Association
-Vintage Chevrolet Club of America
62BillT is offline  
post #4 of 8 (permalink) Old 04-05-2020, 09:26 PM
Join Date: Aug 2008
Location: Miamisburg, Oh.
Posts: 3,348
Blog Entries: 15
Since you're running the Powerglide behind a 327, in a big ol' Impala I'm gonna assume you're not after power numbers since the Powerglide is quite literally like taking off in second gear.

Depending up on what kind of $$$ you're wanting or able to spend, if you are trying to keep it on the minimal then one limiting factor is your stock factory rocker studs. IIRC the stock heads should only be used up to around .480" lift. You could safely go higher if you had a shop put in screw-in studs of course.
The second concern is piston-to-valve clearance which obviously isn't something most folks can take a flyer on. Guess wrong and parts get destroyed.

So, all those caveats aside, you can get that lumpy note by choosing a cam with around 106-108, maybe 110 lobe separation angle.

Check out the line of Thumper cams from Comp Cams. Their specs should be in the ballpark of what you want.

Similarly, the *Net* Duration for a 327, to get the sound you want, will probably be around 224 - 236 degrees of duration.

I had a Comp Cam 244/292 cam with .507" lift in a 327 for a long time (with double-hump 461X heads and screw in studs) but that was with the Crane bleed-down lifters. Even with those bleeding off around 8-10 degrees at idle, it sounded sooo Good!!

One other option you have is to buy a set of 1.6 ratio rocker arms. Easy to do but just a small bump in effective cam numbers.

BA. is offline  
post #5 of 8 (permalink) Old 04-06-2020, 03:22 PM
Join Date: Jan 2006
Posts: 13,023
None of these cams are sold as service parts anymore by Chevrolet. Lunati, CompCams, Erikson, Isky, and CamDynamics all sell a reproduction grind: but none of them actually use the factory grind profile as it is old and crusty (especially those without a split overlap and difference in intake and exhaust lifts). No one wantsa stock cam but I included it for comparison purposes. Many offer these as hydraulic rollers and they even offer the 30/30 as a flat tappet hydraulic.

If you want noise like was said above look to the Thumper and VooDoo cams as they put the added duration on the exhaust side so the cylinders blow down faster (great for noise ) and the intake closes sooner to build compression to make power on the street. These cams are all about noise as you will never win a race with these grinds. But then you will never win a race with a street car racing a trailered race car anyway, so you are limitd to TO or grudge matches.

275/300 horsepower 327 Flat Tappet Hydraulic (stock) cam specs:
•Valve Lift:0.399" Intake /0.399" Exhaust
•Duration @.050" Lift: 187 Intake / 187 Exhaust
•Intake Centerlne: 114
•Lobe Separation: 116
•RPM Range Idle-4,600

350 horse 327 L79 (Chevelle-Chevy II part # 3863151) Flat Tappet Hydraulic cam specs:
•Valve Lift:0.447" Intake /0.447" Exhaust
•Duration @.050" Lift: 229 Intake / 236 Exhaust
•Intake Centerlne: 114
•Lobe Separation: 112
•RPM Range: Idle - 6,200

350 horse 350 Z/28-LT-1 (Part # 3896962) Flat Tappet Hydraulic cam specs:
•Valve Lift:0.468" Intake /0.462" Exhaust
•Duration @.050" Lift: 229 Intake / 236 Exhaust
•Intake Centerlne: 114
•Lobe Separation: 112
•RPM Range: Idle - 6,200

1961-'69 350 horsepower 327 Corvette and 1967-'69 290 horsepower 302 Z/28 (Part Number 3849346) Duntov 30/30 Solid Flat Tappet Cam Specs:
•Valve Lift:0.485" Intake /0.485" Exhaust
•Duration @.050" Lift: 254 Intake / 254 Exhaust
•Intake Centerlne: 114
•Lobe Separation: 108
•RPM Range: 2,400 - 8,600

Big Dave
Big Dave is online now  
post #6 of 8 (permalink) Old 04-07-2020, 02:05 AM
Senior Member
Join Date: Apr 2013
Location: Canada
Posts: 364
Actually, GM still sells the 3896962 cam if you do happen to decide you like that one.
Darth is offline  
post #7 of 8 (permalink) Old 09-02-2020, 07:43 AM
Join Date: Aug 2020
Location: Tampa, FL
Posts: 47
For how much do they sell the 3896962 cam nowadays? I don't quite remember the price.
Brandon Hendricks is offline  
post #8 of 8 (permalink) Old 09-02-2020, 10:25 AM
Join Date: Jan 2014
Location: CenTex
Posts: 39
65_&_67_Impala is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Impala Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome