Has anyone here ran the Duntov 3030?

http://www.carcraft.com/techarticles/116_0403_camshaft_basic/viewall.html

 

I thought 30-30 should have been the overlap degrees as I could not understand why so much clearence was needed? Fords did around .020 and any others I adjusted for people were no where close to .030 but of course back then was like 45 years ago so memory fades and storys grow.....

 

Actually they ran best around .026/.026 cold. They ere set .030/.030 running hot because the ramps were so log you had to use a very precise routine to be sure ou weren't on the clearance ramps.

""30-30" SOLID LIFTER CAM VALVE
ADJUSTMENT
By John Hinckley and Duke Williams
The traditional method of adjusting valves one or more cylinders
at a time with each cylinder at TDC is fine for hydraulics and for most
solid-lifter cams, but NOT for the factory "30-30" solid-lifter cam used
in '64-'65 L-76 327/365 Corvette engines (and in '67-'69 Camaro
302/290 Z/28 engines); this cam has VERY long clearance ramps
that are .020" high, and at TDC for any cylinder, both the intake and
exhaust valve for that cylinder are still on their ramps, NOT on the
cam's base circle, which is why the Service Manual for all cars so
equipped says specifically to set them "hot and running"
.
There is, however, a better way to adjust the valves with a "30-
30" - you can set them "cold and not running" by setting the intakes at
90 degrees ATDC and the exhausts at 90 degrees BTDC - so the
lifters are on the base circle, not on the ramps. This has been
confirmed with cam lift/crank-angle diagrams, and I've done mine this
way - results in a nice mechanical "singing" sound, no "clacking", it
runs better, sounds better, idle is more stable, and throttle response
is improved. Several other Z/28 owners have followed this procedure
as well since we developed it, and all of them have seen the same
positive results.

Set them cold at .026"/.026". The actual measured (stamped
rocker arm) ratio at the lash points is actually about 1.37:1 (not the
design 1.5:1, which is a max lift measurement), so the clearance
ramp, which is exactly .020" high on the lobe, is all taken up at .0274"
clearance; .030" clearance with the valve closed is too loose - the
ramp ends/begins before the .030"clearance is taken up, resulting in
the valve being lifted off and returned to the seat at greater than ramp
velocity. This will contribute to valve seat recession, and can cause
valve bounce at the seats at high revs - it will also be noisy. You can adjust two valves at each 90-degree rotation point, starting
at #1 TDC, turning the crank 90 degrees at a time seven times
(measure and mark your balancer first at 90-degree intervals from
TDC). Removing the plugs simplifies rotating the crank, but you were
going to change them anyway, right? Proceed as follows:

TDC #1 - 8E, 2I
90 deg. - 4E, 1I
180 deg. - 3E, 8I
270 deg. - 6E, 4I
0 - 5E, 3I
90 deg. - 7E, 6I
180 deg. - 2E, 5I
270 deg. - 1E, 7I

Start at TDC #1, then rotate 90 degrees at a time, setting at .026"
cold. If you like, you can then go back after you're done to each
cylinder's TDC position and check clearance on that cylinder's two
valves, and you'll find that they've closed up to .024", indicating that
both valves are still on the ramps at TDC, as I pointed out in the
beginning.

This progressive procedure will ensure that you are on the base
circle on ANY OEM Chevrolet cam for adjustment, and the factoryrecommended clearance on other OEM Chevrolet small-block solidlifter cams should be factored as well by the 1.37:1-vs.-1.5:1 ratio
difference at the lash point and rounded-down to the next-nearest
thousandth or two to ensure that the valves are picked up and seated
at ramp velocity
.
What about the original “097” Duntov (used from late ’56 to
’63)? The “097” Duntov was designed for .012”/.018” clearance with
1.5:1 rocker arms, but in 1963 the intake clearance was revised to
.008”, and this was also recommended in Corvette News back in the
late 50’s for “weekend competition events”; the tighter intake
clearance gave a bit more effective inlet duration. Factoring the
original .012”/.018” by the 1.37/1.50 rocker ratio correction yields
.01096”/.01644, call it .010”/.016”, so if you’re already running the
.008” intake clearance, it shouldn’t be tightened any further.

 

Is this thread still going?

 

Great info, Hoop. It should keep the thoughtful man from heading down the wrong path in most applications.

 

Yeah throw the Z28 air cleaner on the carburetor, slam the hood and we're out of here!
Whoooops! Now you have to replace the air cleaner and hood you just messed up.

I regress. I had to do some research to refresh my 46 year old recollection. I had the low profile on the wrong end of the stack. I also had the CFM rating wrong on the LIST 2818-1 carburetor and the CFM switched around on the other two carburetors.

The Corvette with the L76/L79 engine option is notorious for the narrow margin of clearance between the carburetor and the hood.



If you replace the stock LIST 2818-1 carburetor rated at 600 CFM with a LIST 4053 carburetor rated at 780 CFM or a LIST 3310 carburetor rated at 750 CFM and retain the stock air cleaner then the engine will loose performance. The problem is the design of the air cleaner assembly. 1) air cleaner element flow rate. 2) channeling of the air flow into the carburetor air horn. It appears as though GM matched the carburetor to the air cleaner rather than matching the air cleaner to the carburetor.


______Z28 air cleaner element___________L76/L79 air cleaner element

If you Google > C2 Corvette hood clearance < then you will find unbelievable stories about the air cleaner lid being 1/2" above the choke air horn or people milling an 1" off of the intake manifold just to mention a few. The purist will never admit that GM cobbled up the L76/L79 induction system, but those who want horsepower can't get rid of the LIST 2818-1 carburetor fast enough.

Was the Rochester FI really that great? Ten horsepower says no and after the manifold and carburetor upgrade John was never out ran by a FI'd Corvette. Perhaps GM was hiding that by using the 'truck carburetor'.

OK guys, as hoop98 pointed out this thread is damn near a year old. The OP more than likely made his decision some 130 post ago. Let's start a new thread. Any suggestion for what we could argue about?

McGurk

 

Hey mcGurk, instead of arguing let's explore Booster Signal for High CFM carbs to improve low RPM fuel metering?

I think you have some good info to share on that topic?

 

Not really. I just got lucky when one of the performance car magazines published an article written by the late Paul Blevins. All I had to do was read, follow the instructions, make the reamer and hope like hell I didn't screw up when I cut the carbs. I went to work in a machine shop at the age of 13 so the hardest part for me was reading.

Further more if you was to hand me a carburetor from this era then I would look like a monkey with a Rubix Cube

McGurk

 

I was wondering if anyone had played much with 2G boosters. I know they do for CFM in Oval tracking restricted classes. Someone was asking about running he GTO tripower carbs on a 283 and that got me to thinking about boosters or venturi clusters that might work the best.

Mmmmm uh McGurk, there are no carburetors from this era

This seems to be a good start.


Paul Blevins Article

About 1/2 way down the page.

 

With the wide box, rear gear, and the car not being that heavy (this combo suggests you will be wringing it's neck from time to time?)......I'd run a bit more cam than the 30-30 (Factory Chevy cams leaned more towards duration than lift for spring life and that hurts bottom end power a little) and a 600 or 650 double pumper carb. Don't be scared of solids. If everything's OK they do NOT require frequent adjusting. The Chrysler 225 slant 6 I believe are ALL solid lifter motors and people rarely if ever adjust those for 1000's of miles. I've got a pretty rowdy small block that I haven't adjusted in 4 yrs. When I checked them a few months ago they were within .001-.002 of where they were supposed to be. I like the Comp 282S for your combo. 236 @ .050 and .495 lift. Decent idle (almost smoother than you'd expect), and broad torque range. Oh, and at .022-.022 lash, it's a bit noisier (to me) than the 30-30 (30-30's quieter than you'd think for that big lash)

 

VERY important^^^^^^^^^

 

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