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Old 05-22-2008, 06:44 AM
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camshaft mistake!

For my 305 chevy Caprice wagon 2 bbl 1978 that I am currently rebuilding, a friend bought for me the wrong camshaft.
But I wonder if I could use it.
He took the sealed Power CS 673, which covers the 76-80 GM truck applications, which seems to deliver for trucks: 140 HP at 3800rpm, and 235ft/lbs@2000rpm, instead of the Sealed Power CS711 which gives: 145hp at 3800rpm and 245ft/lbs@2400 rpm torque for cars.
What would be the inconvenients or advantages using that truck camshaft on my car in terms of driving and fuel economy?
Thank you again.

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Old 05-22-2008, 08:40 AM
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it would be nice if you could give us cam specs. duration, lift, lsa.

a good sealed power cam for your application would be a KC-274.
(194/203 at 0.050",112 LSA)
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Old 05-22-2008, 09:44 AM
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I only have a few specs from the 78 stock camshaft, and nothing for the new (wrong) CS673 I have.
Stock camshaftI have:
journal diameter: 1.8682- 1.8692
Lobe lift:
Intake .2217
Exhaust .2315
Camshaft end play: .003- .008
That's all I have for the moment!
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Old 05-23-2008, 03:30 AM
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Here are the specs I found for both camshafts:
CS 711: Duration at .050" 178 int, 194 Exh, Lobe separation 108
CS 673: Duration at .050" 189 int, 202 Exh, Lobe separation 109
So if someone can say if the 673 will do it without changing the springs, and what will be the results, mainly at highway speeds and the fuel economy it will make, it will be great!
Thanks.
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Old 05-23-2008, 07:10 AM
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The 673 looks like a good cam for small block in search of mpg and low rpm torque. I think the 673 should work well with cr between 7.5 and 8.5:1, and gears in the 2.50 to 3.08 range. And would work well with stock exhaust and stock heads. Plus it will have much better top end than the 711. That 711 is a very weak cam.

The 673 is about the same cam that I recommended that you to get. But I actually like the 673 better for your engine. The narrower 109 lsa will help build cylinder pressure and help the stock intake port breath better.

I bet you can run stock spring with that cam, since I doubt the lift would be more that 0.420" with that cam and it will not make power past 4800 rpm. I'm guessing your 305 will make 200hp with that cam even with stock exhaust.

If you are looking for mpg. Use a stock 4bbl intake and a Q-jet. Small tube headers would also help but make extra noise. I would also run 2-1/4 exhaust with dynomax super turbos and a x-pipe. With the above mods (headers, exhaust, carb) you could expect 225hp and an extra 2 mpg on the highway.
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Old 05-23-2008, 09:36 AM
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Thank you very much for your sharp answer. I begin to think it wil will be better to install the 673!
I do hope the springs will be the same, usually GM doesn't change springs between so close engines, but I will check (if you have an idea where...). One thing I know is that on books they usually put umbrella rotators even on intake springs for truck applications. I don't think it's necessary to do so.
I live in France, and here such an old car is authorized on roads without catalyst, so even without headers it will work fine.
At the end of my job this should do a good an simple wagon to use that maybe can haul easier.
Meanwhile, this year 305 is 2bbl equiped and I plan in the future to install a Quadrajet I have on the shelves. One thig at a time!
Thank you again.
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Old 05-23-2008, 11:44 AM
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Required spring force is a function of rpm and valve lift and cam lift rate. I'm sure your stock springs will work fine with that mild cam.

I have run cams with 20 degrees more duration and up to 5500 rpm with stock springs without any issues.

The trick for flat tappet cam durability is it run as little spring as possible. This is especially true for todays motor oil which are low on antiwear additives for emission reasons.

You can change the springs later if you have valve float at higher rpms. Just make sure the valve spring has enough travel for the lift of the cam.
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Old 05-23-2008, 01:22 PM
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Ok, I checked different head components ref over 2 suppliers:
Valves, Rockers, lifters are similar, exhaust and intake springs are the same on the 78 wagon, but they use a different ref just for the 78 truck intake springs, and the same ref for the exhaust ones. I wonder why .
I also noticed different valve seats insert ref between them, maybe they put heavy duty valve seats on trucks.
Anyway this drive me little by little to a yes doing the job instead of buying the cs711.
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Old 05-26-2008, 01:07 PM
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OK, another strange problem.
Before installing that sealed power cs 673, I just proceeded to a check between my worn out GM original cam and this new one.
I was surprised to find that the lobe lift was bigger on the old one than on the new cs 673.
Does anyone can give me an explaination?
I don't feel safe installing that 673, there's maybe an error of package!
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Old 05-26-2008, 02:11 PM
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The part number is usually stamped into the back of the camshaft, along with the manufacturer brand name. Check to see if the CS673 is boxed wrong, or if the camshaft was changed in your 305 already.

It's quite possible a rebuilt engine has been put in your car sometime in the last 40 years. Then there is another thought I have that the rebuilt engine could be a 350.
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Old 05-26-2008, 02:38 PM
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First off, let me say that when I answer a question on this board, I try to explain it in very simple terms and perhaps go overboard so that the younger enthusiasts who perhaps have less experience at these things can understand what's going on. All of us began at zero knowledge and I'm sure there are some of those individuals reading this.

In checking cam lobe lift, let's establish some references so that we're all on the same page. If you hold the cam up and sight through the longitudinal axis of it like you were looking through a telescope and hold the tallest part of the lobe in the "up" position, you can imagine that point on the lobe as the "North" position on a compass. Halfway around the lobe, at the bottom of the lobe where it is the shortest, we might imagine as the "South" position on a compass. To the left would be West and to the right would be East.

Now, when comparing two cams, always measure each cam on the exact same lobe one cam to the other. Reason is, if the cam is ground on a "split pattern" or "dual pattern", then the intake lobe is ground differently from the exhaust lobe. Usually, the exhaust lobe will have more duration and lift than the intake lobe on cams for a street motor or moderate race motor.

Another thing to consider, one cam to another, is that the base circle diameter may be a little different based on who ground the cam and whether or not one of them was ground on a reduced base circle in order to work in a special application such as using a 3.750" Chevy 400 crankshaft in a Chevy 350 block. Most times, there is interference between the rod bolt head and the camshaft lobe on one or more positions of the cam, so some of the manufacturers will grind the cam on a smaller base circle in order for the rods to clear at the cam lobes. When using a reduced base circle cam, longer pushrods must be used to make up the difference in the "stack" height from the base circle of the cam to the rocker arm. Grinding the cam on a reduced base circle does not necessarily mean the cam has less lift than a similar cam ground on a full base circle. It's the DIFFERENCE between the base circle and the peak of the lobe that determines the lift of the cam lobe.

Now, back to regularly scheduled programming.....

Using your dial caliper or micrometer, measure the north-south dimension on front lobe nearest the drive pin. Write it down. Now, measure the east-west dimension of the same lobe. Write it down under the north-south dimension. Subtract. Now, you have the lobe lift at the cam. Multiply that figure times the rocker arm ratio to find theoretical valve lift of that particular lobe. If you measure each lobe in this manner and keep a running tally on another sheet of paper, you'll be able to make sense of the cam when you're through.

Last edited by techinspector1; 05-26-2008 at 02:43 PM.
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Old 05-26-2008, 03:48 PM
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So, thanks for your suggestion.
First, the engine I am working on is the original one and had never been opened I am the third owner of the car.
About the number stamped on the camshaft, none are similar to the sealed power commercial reference, cs673. I found: 113220 and 371030 USA and 1539. I even checked on the federal mogul site to find theme, but no way.
Second I took the lobe dimensions in the good way, like your North, south East West exemple and did the difference to find the cam lift figures.
I also understand that the pushrod length play an important action in the lift value figures, but the # I found in parts catalogs for them is similar between both engines (truck or car).
As I live in France here you have my metric figures about valve lifttaken from exhaust and intake cam lobes)
Old worn out GM Car cam lift: exh 6.9, Int 6.9
CS 673 Truck new: exh 7.1, Int 6.2
GM Car theorical Chilton shop manual figures: exh 6.6, Int 6.3
I don't have the best micrometer, so these figures can vary a little, but the very strange figures are for me those from the GM worn out one should I beleive these Chilton's figures?
Now I plan to reorder a basic CS 711 for my 305 but I take much time checking that cs 673 because shipping over here is rather expensive, more than the cost of the part.
Thank you for your help.
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