KyleDallas

Chevrolet Factory Cam Specs with GM part numbers
Part # Lifter..duration @ .050 In/ex--Lift in/ex....centerline.....factory eng.

3849346 Mech - 254/254 - .484/.484 - 114 - 327 365HP& Z-28 302
3863151 Hyd. - 221/221--.447/.447-114 - 327-350HP, L79
3896929 Hyd. - 195/202 - .390/.410 - 112 - 327 300 HP
3896962 Hyd. - 222/222 - .450/.460 - 114 - 350 L-46, L-82
3927140 Mech - 257/269 - .493/.512 - 112 - Off Road
3965754 Mech - 262/273 - .488/.509 - 112 - 2nd design road race, short track
3972178 ?
3972182 Mech - 242/254 - .459/.485 - 116 - 70 LT1 360 & 370HP, 71 LT 330 HP
10134334 Roller - 235/235 - .480/.480 - 114 - 350ZZZ and ZZ2 Crate Motor
10185071 Roller - 208/221 - .474/.474 - 112 - 350 345, ZZ3&4 Crate Motor
10224241 Roller - - 92-94 GenII, LT1, 350
10243779 Roller - - 94-96 Gen II, L99 265 V-8
12353914 Hyd. - 180/194 - .378/.401 - - GM Crane Lo speed Hi torque
12353915 Hyd. - 194/204 - .401/.423 - 104 - GM Crane street
12353916 Hyd. - 204/214 - .423/.446 - 110 - GM Crane 305-350 street legal 50 states
12353917 Hyd. - 204/214 - .420/.441 - 112 - GM Crane nan-emissions vehicles & off road
12353918 Hyd. - 214/224 - .442/.465 - 112 - GM Crane marine & off road
12353923 Hyd. - 224/234 - .465/.448 - 114 - GM Crane off road
12364050 ?
12364051 ?
12364052 ?
12364053 ?
12364054 ?
12370845 Roller - 214/224 - .488/.509 - 112 - Off Road, lobe for mech fuel pump
12370846 Roller - 222/230 - .509/.528 - 112 - Off Road, lobe for mech fuel pump
12370847 Roller - 232/242 - .539/.558 - 112 - Off Road, lobe for mech fuel pump
12551142 Roller - 203/210 - .476/.480 - 115.5 - 96 350 LT4 w1.6 roller rockers
12551705 Roller - 201/208 - .447/.459 - 112 - 95-96 Gen II, LT1, w center dowel pin
14088843 Hyd. - 202/206 - .403/.415 - 115 - 305 HO, 83-86
14093643 Roller - 202/206 - .403/.415 - 115 - 87 350 Corvette, IROC Camaro
24502476 Hyd. - 121/220 - .435/.460 - 112.5 - 350 300 crate motor
24502586 Roller - 218/228 - .525/.525 - - 96 LT4 H.O.T. crate motor, use with 1.6 roller rockers
NA........ Roller - 202/210 - .472/.478 - 111 - 97 Gen III LS1 Corvette 350 uses 1.7 roller rockers

KyleDallas

If you have others... or would like to post Big Block specs.. Have at it-

63 340HP

Can you find the actual timing (the equivalent of a cam card)?

Intake and Exhaust timing at 0.050" lift (and 0.006" and 0.015" lift to compare with other cam grinders & the "blueprint" grinders)?

Intake and Exhaust timing at lash point (for Mechanical cams)?

Intake and exhaust POML?
Intake closing point BTDC?

Finding this information may prove challenging, and rewarding (blueprints and full specifications for some GM cams are out there, but I have never found found them on the net).

Thanks

KyleDallas

I don't have those details, Ed... some of the cam makers have details
like those on their websites... but I wouldn't know where to get those facts on GM Factory cams. I suppose if one of the cam makers was making
a true reproduction part you might be able to exume that info from them
.... but, there might still be a tad of difference between their reproduction
and the factory cams.

One of our more GM savy members might know...

KyleDallas

** Remember, you can alter the total lift of these cams by changing
the ratio of your rocker arms... the factory rocker arms are 1.5 ratio
arms.

Changing to 1.6 or 1.7 ratio arms will provide you with more lift.

To see how much more lift.... divide the cam's lift by 1.5... then
multiply that answer by (1.6 or 1.7) (the new ratio) to obtain the
new total lift numbers.

This rocker modification, for example, would allow you to run
the duration of a L-82 cam.... with the lift of a Duntov....lots of options.
It is also something you could do if you wanted a little more power
from a hydraulic cam without having to step up to a solid lifter cam
and perform the adjustments that come with running a solid lifter cam. Check with your machinist to prevent any clearance or rubbing
issues... also check and make sure you don't need new pushrod
lengths with the altered rockers.

Dicecal

I saw some roller tiped rockers that Ecklers sells, but they only have a 1.52 ratio. They claim another 10 HP or so. I saw some 1.6 on Comp cams website and they claim 15-30 HP increase. Anyone have any actual experience with these and can say these claims are true? Also, will these rockers (1.52 or 1.6) fit under the stock SHP small block valve covers? (Alum Finned ones)

Kensmith

Most if not all roller rocker arms need the tall valve covers.

C64BOB

What you get for a power increase depends on the cam they're being put above. In my experience 15 HP is about all you can expect if the motor's healthy to start with (less power to start with less increase it's a percentage thing). The tall roller adjusting nuts is usually what fouls the valve covers. With the right nuts they'll fit all the early Chevy factory valve covers. If cast in drippers are in the valve covers (like LT1covers) they've got to be removed. If you're using a LT1 cam use 1.6 (or bigger if you can find them) rockers on the intake. That wimpy lobe needs help.

Hitch

The Comp Cams Roller tip, Magnum and Pro Magnums have no problem clearing under stock finned valve covers. I've had all of them on my motor and have yet to have a problem. I've used the thick valve cover gaskets just for the extra clearance but it was not needed.
Dave




Then I believe this is a pic of 65TRush's set up under stock covers

Kensmith

Be careful, those are not stock heads in the photos. Some may fit while others will not. Check with someone who has done this if you have stock heads.

Dicecal

http://www.ecklers.com/product.asp?p...dept%5Fid=1211

These are the rockers I was refering to, steel roller tipped rockers comp cam magnums. They do not have the tall studs, just nuts like stock rockers.

aworks

AFR and Dart heads have raised rails. In other words where the valve cover bolts on they are .5 higher than stock GM heads. Thats why roller rockers will fit under stock valve covers when using aftermarket heads. Most will not clear with stock heads. Sometimes double gaskets work or just buy spacers.

66BlkBB

^^^^^^^^^^^^^^^^^^^^^^^^^^

I can't verify or deny the HP gain from the roller tip rockers but I have a set of the Comp Cam units on the 427 in the vette and on a 327 in my 32. I put them in just to ease up the wear as much as possible on the valve train. They do fit under the stock valve covers. I had stock covers on both engines when I put them in.

Steve

Dicecal

Thanks Steve, Nice car!

JohnZ

Either HOT ROD or CAR CRAFT had an article on a series of back-to-back dyno tests about a year or so ago on the same engine with four different cams and combinations of 1.5 and 1.6 ratio rockers to answer that perennial question, and their conclusion after all the testing was done was that changing from 1.5 to 1.6 rockers wasn't worth the money and effort in real-world driving.

Kensmith

I read that article, they did a ton of tests with all the dyno readouts. Was not significant enough to spend the bucks!

knight37128

It is not the roller rockers but the nuts that have clearance issues.

Yes you can make them fit.

Shaft rockers are better.

KyleDallas

The increase in power that results from increased lift.... caused by
either a cam swap or a rocker arm change will be partially determined by how well your heads flow at certain lifts....... this is why I ranted a few weeks back on how great the Dart Iron Eagle Platinum heads were.

Unlike the old days when you just kind of guessed at a heads performance.... today, most of the aftermarket head manufacturers list their head flow in cfm at various lifts... usually between .200 lift to .700 lift ..... most of the street cams for the SBC have a lift in the .400 lift range as you can see above....

I would agree with John on the limited benefits of increased lift on heads like the Double Humps.... but on Heads like AFR Eliminators, Dart Iron Eagle Platinums, GM Performance Parts Vortec Bowties, GM Performance Parts Fast Burns, Trick Flows, Canfields, Stock L-31 Vortecs, RHS Vortecs, and any of the altered angle 18 degree-etc. heads available..... lift equals a good return on your investment of a
new cam or rockers that put your lift into the heads "flow sweet spot".

I will make a statement that may make some a little miffed... but
there isn't anyone today,who is serious about performance,that doesn't
look at the lift vs. flow data of the heads they are using..... If you don't know what your heads flow at certain lifts then how can you even
remotely gauge the performance potential of the motor you are trying
to build??..... you can't.... and if you are using old heads that flow
the same baisic cfm at .400 and .500... then, yes, there's not too much to be gained by extra lift. ...... the main reason some 350's struggle
to make 400 hp and others easily top 500hp is headflow and lift.... via cam and/or rocker ratio.

For example... let's look at the headflow on the old 64cc chamber Chevy '492 casting with 2.02/1.60 valves.. vs. some of the heads I've mentioned. Notice the 492 casting flow cfm in the .400 to .500 range..which is where alot of the SBC GM cams above put lift.. (.410 to .480 lift) .8 cfm difference from .400 lift to .500 lift...and only 11cfm difference in flow between .400 and .600 lift.... with the 492's the extra lift is pretty much wasted.

HEAD.................Portsize..lift/cfm@ .300.......400.......500.......600....
GM492/2.02..........157/62...........173/125..198/137..206/141..209/141
-------------------------------------------------------------------
L31 Vortec #885....170/61...........190/129..227/140..239/147..229/151
---------------------------------------------------------------------
AFR Comp190's......190/xx...........201/157..243/180..264/195..276/208
--------------------------------------------------------------------
Dart Platinum IE....200/xx............194/158..242/198..274/208..283/214
--------------------------------------------------------------------
Bowtie Vtec185....185/xx.............182/xx...223/xx....251/xx....240/xx


Look at the Dart Iron Eagle Platinum 200cc port heads..they start off
flowing 44cfm more at .400 lift than the '492s and you gain 33cfm more
if you increase lift to .600. If these lift numbers scare you because
you are used to SBC lift numbers.... do a little cross-training and go
look at the lift numbers the LS engine guys are running in their aftermarket cams... .500 to .650.. you just have to have a valvetrain
built to handle it.

The general rule of thumb is to look at the lift numbers of your cams
peak lift...and the lift numbers of the group just below (where your
cam will place your lift while it is off the seat the majority of the time)
So if you had a .510 total lift cam... you would look at the heads
flow at .400 lift and .500 lift to get a rough idea of what your heads
will be flowing a majority of the time.

Notice on the L31 Vortec heads and the Bowtie Vortec 185cc's how
flow drops down at .600.... but on the AFR Comp 190's and Dart Platinum 200's it keeps climbing. Something to consider when deciding
on a cam.... or revising lift with different rockers.

Here's what a 520hp 350 looks like:
http://airflowresearch.com/articles/article054/A-P1.htm

the 520hp engine has....
1. Good flow number heads
2. A cam that takes advantage of that flow
3. A good Demon carburetor and spacer
4. A good Edelbrock intake..

I believe you could replicate that motor using your stock block
and have about 170 more horsepower than a ZZ4 for about the
same money.

KyleDallas

You can get 1.6's in the stock style stamped steel rockers I believe... I know I have seen them in some dirt track motors... Midwest Motorsports or Smiley's would probably have some.... they cater to the dirt track crowd...... where the claimer motor guys make HP on the cheap.

Unless you are going to go well over .500 lift.. I wouldn't worry about
fancy rockers... just get'em in your desired ratio.... roller tips are a
good compromise between a stock and a full roller rocker.... for about
$100 give or take....

These PRW rockers are good quality and are similar to the Comp
Pro Magnums... but cost $100 plus less...



CNC Motorsports has them for about $180.00

here is PRW's website.....
http://www.performanceracingwarehous...p-rockers.html
PRW has some nice roller tipped rockers also
Scorpion Performance makes rockers in the 1.7 ratio...

A Rocker ratio change is also a way to cheat the cost of going to
a roller cam and still getting into the .500 to .550 lift range with a
plain hydraulic cam with streetable duration.

KyleDallas

Here is a practical application for the use of different rockers on
a 327/350hp L-79.

You are surfing Ebay and notice a set of Vortec L31 #885 heads
with a Buy it Now price of $300.00 complete with valves, rockers,
etc. .....
You buy the heads and order a set of 1.7 ratio rockers... you leave
your L-79 cam intact... but instead of giving you .447/.447 lift...
you are now getting .506/.506 lift... making the most of your head
flow while not digging into the block. L31's go for $300 to $350 a
pair pretty routinely.

If you wanted to step up a little over the L31's... you could
order the 185cc Bowtie Vortecs for $554 a pair bare from GM Performance Parts Direct.... or the Dart IE Platinums 200cc port for $660.00 a pair bare from Competition Products.... and use the same
rocker ratio trick with your stock L-79 cam.

Intake flow for 492's with stock 1.5's
198cfm at .400 lift

Intake for L31's with 1.7 rockers
239cfm at .500 lift

Intake for Bowite Vortec 185cc with 1.7's
251cfm at .500 lift

Intake for Dart IE Platinum 200cc with 1.7's
274cfm at .500 lift

all figures using the stock L-79 cam...