273 Rocker on 340

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I'm running the Isky ductile iron rockers on my bracket 408 with a Comp roller cam that has gross lift of .690 intake and .660 exhaust and have no problems.
 
Did it on several cars. As far back as 1974.Big thing to look for is valve spring clearance as performance springs may be larger diameter compared to the spindly 273 spring. We would grind some from the back of each rocker to clear the retainer and spring. Easy to do. 318-340-360. They work well,along with the stock 273 ball and cup push rods.
We ran the Crane Hyd with a .490 lift and the Mopar Performance purple shaft .508
 
I ran them on race cars 50 years ago with up to 550/570 Lift.
They clear 1.47 spring with no grinding. Do not get crazy on the
grinder as they tend to crack pretty easy around oil hole.

Another issue is that the interference adjuster tended to loosen every
10/20 runs. I spot faced the rockers and put a nut style adjusted on them.

There are better cast rockers on the market now.

Watch them closely for excessive wear.
 
I AM running 273 adjustable rockers on my 340 with solid lifters.

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I have a set on a 340 and they work fine. No grinding. Small cam/springs.

I also have a set of Comp Cams Magnum rockers (not 5.9/5.2 Magnum) on a 318. They were $600 more than the 273’s.

That’s a good looking cam. I have always liked my cams in that neighborhood. My 73 Duster has a 222 @.050, my D100 has a 226, and 70 ‘cuda has a 228 @ .050.
 
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Been decades now but it was so fun to go to a "Junk Yard" and find a 273 with the adjustable OEM rockers. Remove them and get them cheap.
 
Nice cam specs, I ran something like that in my 11.3/1 alloy-headed 367, and I absolutely loved it. I was very sad when it dropped lobes.
I've been eyeing this cam but thinking maybe 108 centerline? Also maybe going solid. Expert I'm not.
340, 10 over KB pistons, 160 cranking pressure 10:1 Comp (I believe), Eddy heads, RPM intake, 750 ABS carb, Stock manifolds 2 1/2" Exhaust, 4 spd., 323 rear gear, 235/60/15 tire. Street car with some weekend highway cruising.
Also eyeing this one.
Howards Cams 718001-09 Howards Cams Rattler Camshafts | Summit Racing
 
I cannot remember. Have we discussed that your shafts are installed incorrectly? The notch on the end shoulf face down and to the rear on the passenger's side and down and to the front on the driver's side. Both of yours appear incorrect. It's important to get them right.
Yes that’s one of the problems we identified from this build. I have a new set from Rocket and they will be installed correctly. Thanks
 
Yes that’s one of the problems we identified from this build. I have a new set from Rocket and they will be installed correctly. Thanks
I thought we had pointed that out for you, I could not remember for sure.
 
I can guarantee you that you will have to grind on your 273 rockers to get them to work with Edelbrock sized springs. First hand experience here.
Yep. I should have used Beehives!

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Before grinding, I would verify the rocker shafts don't need relocating.
 
I would verify the rocker shafts don't need relocating
Something else I ran into - called B3 or whatever the relocation guy is, and found out you need to do that before you torque the heads down because you have to clearance the pushrod holes. I had already installed mine so I just went with it. He didn't seem put out by it, either from a usability or wasting time with a looky-loo standpoint. We were on the phone for probably 10-15 minutes. Seemed like a good guy. Also, he advised 0.030 clearance between the spring and rocker, so I used a piece of welding wire as a go/no-go gauge
 
I've been eyeing this cam but thinking maybe 108 centerline? Also maybe going solid. Expert I'm not.
340, 10 over KB pistons, 160 cranking pressure 10:1 Comp (I believe), Eddy heads, RPM intake, 750 ABS carb, Stock manifolds 2 1/2" Exhaust, 4 spd., 323 rear gear, 235/60/15 tire. Street car with some weekend highway cruising.
Also eyeing this one.
Howards Cams 718001-09 Howards Cams Rattler Camshafts | Summit Racing

Which cam?

Howards Cams 710461-10 Howards Cams Hydraulic Flat Tappet Camshafts | Summit Racing
Specs of 273/277/110, 226/230 @050, and lifts of .525/.531
or
Howards Cams 718001-09 Howards Cams Rattler Camshafts | Summit Racing
specs of 281/289/109, 227/235 @050, lifts of .480/.488
IMO;
running just 160 psi with the alloy heads, would be a gross unfairness to them, as would running less lift than at least what the Edelbrock springs are capable of.

As to the 718001 cam;
Installed with an Ica of 68* the V/P ratio is predicted to be 126, about the same as a 5.2 Magnum, which is what it's gonna feel like under say 3000.rpm, so, yur gonna need to slip the clutch to get moving. and at just 105* power stroke, it will suck gas. But, it will make great power at about 5100, which with 3.23s/ your tires, is 46mph in First/87 in Second, and so you'll probably want more rear gear; like 4.10s and those will not like cruising in Direct at 65=3300
Whereas;
As to the 710461 cam;
Installed with an Ica of 64*, the V/P is predicted to be 137 which is getting torquey, the 3.23s can stay. and at 111* of power-stroke, she will use a lot less gas. This cam may power peak a few rpm sooner, but the advertised specs make it out to be a tad over one camsize smaller, increasing your Dynamic compression ratio from 8.08 to 8.37
But the good news is that this smaller Advertised spec cam, together with the longer Power-stroke, means that you could advance that cam to in at 61*, which would get you a CCP of 178psi, and a V/P of 145, with a Dcr of 8.54, and the Powerstroke ends up at 108* still better than the the 105 of the larger cam.
However;
IMO
this is a band-aid for not having enough Scr; 10.5 is NOT ENOUGH for either of these to optimize the cam install.
> the smaller ca wants 11/1, and
> the larger wants 11.4/1
In both cases installed at ~split-overlap,
the Pressure is predicted to be ~183psi, and
the Dcr is predicted to be 8.75.
But, whereas the bigger cam is predicted to make a V/P of 140, the smaller is predicted to make 145, obviously a 10% stronger bottom end.

Now, V/P is very important to a clutch car, on the street. The more you are able to run, the stronger the low-rpm will be. And with just 3.23s, your engine will not get to the torque until say 3300rpm which is 30mph, in First gear. So, you need all you can get.
Then, to get from a true 10.5, to 11/1, with a swept of 696cc, will require the total compression chamber volume be decreased from 73.3cc, to 69.6cc, which is just 3.66cc; but to run 11/1, you really need your Quench to be in the window of about, .028 to .045 and it is not advisable to run in the window of .050 to .080. So in your particular case with open chamber heads, this may not be possible.

IMO
between these two cams, I would run the "smaller" one, straight up to maybe 2 or 3 degrees retarded, at a higher pressure, with a tight quench. I think it may make very similar power than the bigger one, without the torque loss at lower rpm. I would run it with hydros and .5 turn preload.
 
My .557 lift purpleshaft cammed 70 340 was built with 273 rockers on the X heads - I seem to recall some minor machining was done by my engine builder but it's been 40 years
 
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