Thread: SBC cam question

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Originally Posted by jerry clayton

36 sedan-footnote #2 on that cam says that requires machining on cylinder heads----------I said fix guides/seals/springs!!!!!!!
You said dual quads block hugger headers---I said go bigger or dual quads
You said block hugger headers---they are shorter than 36"? I said shorter headers-------


Kind of similar ????????????

WOW!, that is exactly what you said! Touche'

I'm checking out of this one until the op comes back----------

Relax fellas! I appreciate the fact that all of you gave your input. I am no no stranger to building engines...just simply wanted to know a good cam setup for a hot street car/occasional runs at the strip to see what it does. I still have to check the gears and measure the header tubes...it came with basically everything to run...just want it to run so i can move it. i dont mind taking it apart over the winter and doing it right. Just dont want issues with it running for the time being. I will take a complete inventory on all specs and get back with you. I'm not going anywhere....

Buick---welcome back on a Sat morning----you will probably go down in history as the new guy that got twp people banned after only 2 posts------------

Originally Posted by jerry clayton

Buick---welcome back on a Sat morning----you will probably go down in history as the new guy that got twp people banned after only 2 posts------------

It wasn't his fault

Originally Posted by 80buickregal

I have a gen 1 stock block...Dart iron eagle heads 64cc chambers 200cc runners (max .520 lift springs) 2.02/1.60. Weiand stealth intake.what would be a good cam for the street? From what i am told the car was pretty radical before the bottom end blew out..cannot talk to the former owner about what cam he ran in it. Also have 1.5 full rockers and a demon 650 carb. It does have a stall in it as well although im not sure what rpm so I'll probably replace it. So i'd like an idea as far as a good sized stall as well. Thanks!

Because cylinder pressure is dependent on static compression ratio and the intake closing point of the camshaft, we cannot intelligently choose a camshaft for a motor until we know the actual static compression ratio. Since you state that the car was "pretty radical", I would think that the builder used flat top pistons to arrive at a static compression ratio of 10.2:1 to 10.3:1 with the 64cc heads. I would also guess that the previous owner could not prevent the motor from detonating on pump gas, possibly because of a "too wide" squish dimension.

We are all limited in our builds by one thing or another. In this case, with a street motor, it is the static compression ratio that you can use with iron heads and still use pump gas without detonation. Most of us would agree that with currently available fuels, we should limit SCR to around 9.5:1 with iron heads and 10.5:1 with aluminum heads. If, as I suspect, your motor is 10.2:1 to 10.3:1, you could be faced with a motor that could be a problem for you in street guise on pump gas.

So, before I would go suggesting a camshaft grind for you, I would want to see inside the motor, take measurements and figure the SCR. The motor may require a piston change to reduce SCR down to ~9.5:1 for use with iron heads, so nail down the SCR before you begin trying to choose a grind that will work for you.

The Iron Eagle heads are not the end-all heads for a hot rod motor, even at 200cc runners on a 350. In my opinion, I'd rather use heads with more efficient, smaller volume intake runners to keep velocity up and pack the cylinders a little better on a run-of-the-mill street motor. 99% of the time in street driving, you will need good power from just over idle (wherever the converter stalls) to about 3500 rpm's, so use heads that flow well and pack the cylinders well at the lower range of rpm's. It's torque that moves the car around, not horsepower, so on a street motor, build for torque. Exhaust flow on the Eagles is a little lame also, so I would use a camshaft with a dual pattern, favoring the exhaust side with more duration and lift. Actually, if I were to build a 350 today, I would begin with Pro-Filer 195cc aluminum heads, whether on a 350 or a 383.

It only took me a couple of engine purchases as a young man, to figure out that I could do it better myself. So, every hot rod motor I have used over the past 40-50 years has been built by me from all separate parts that I chose to work together toward a certain goal. You might also come to this conclusion before you're through with this hunk.

Since you stated that you could work on this motor over the winter, why not disassemble it and document the parts that were used to build it so that you can come to an intelligent decision about what parts you want to use in it. You might even find something really stupid, like pop-up pistons or aluminum rods.

Once you have the motor disassembled, have your favorite machine shop to check the validity of the main bearing bore for all holes being round and parallel with each other. If not, correct via align-honing the bores. Then, chuck the block up on the main saddle and cut the block decks to square according to the stack of parts and head gasket thickness you will use. Once the block is square, the heads will sit on the block squarely and the intake manifold will sit on the heads squarely and the motor will have a much better chance of sealing itself up upon final assembly. At the same time, you can engineer the squish to prevent detonation with pump gas. 0.035" to 0.045" is the generally-accepted range for squish in a small block Chevy. For instance, if your stack of parts was 9.000", you might cut the block decks to 9.000" block deck height (zero deck) and use a 0.039" to 0.041" head gasket thickness to set the squish figure. You have iron heads now, but who knows, you might opt for some aluminum heads in the future and you'd already be set up for them, with the thicker composition gasket that the aluminum head manufacturers call for.

Now, in order to find the static compression ratio, you will need 5 values, cylinder cc's, combustion chamber cc's, piston deck height cc's, piston crown cc's and head gasket cc's. Let's put a trial combination together so you know how to do it.....we'll figure a 350 with 0.030" overbore, 64cc heads, zero deck (so, no piston deck height figures to include), 6cc piston crown, and this gasket....
http://www.summitracing.com/parts/fe...make/chevrolet
with its 9.1 cc's of volume....

.7854 x 4.03 x 4.03 x 3.48 x 16.387 = 727.4 cc's in the cylinder
64 cc's in the combustion chamber
9.1 cc's in the head gasket
6 cc's in the piston crown
zero in the piston deck height
Total cc's 806.5
Subtract cylinder cc's from total cc's (806.5 less 727.4) and find 79.1 cc's
Divide total cc's by 79.1 (806.5 / 79.1) and find 10.2:1 static compression ratio with a 0.041" squish.

This same formula works for any motor you will build. If the piston is down in the bore a little, figure the cc's for piston deck height just the same as you did for the cylinder cc's. For instance, let's say the piston deck height is 0.020" (twenty thousandths of an inch)......
.7854 x 4.03 x 4.03 x .020 x 16.387 = 4.2 cc's
You would add the 4.2 to the other 4 values that you had and figure it like I showed above.

Now, let me add some food for thought here.....
Using a flat tappet camshaft is a really bad idea in today's world. Oil manufacturers have eliminated extreme pressure lubricants from off-the-shelf motor oils due to pressure from the federal government and the new car manufacturers. So, us hot rodders can do one of two things, add the EP lubes to our oil or use a roller tappet camshaft that does not need EP lubricants. Honestly, the days of flat tappet cams has come and gone. They are technology from the last century and no longer fit into the scheme of things. These cockroach "extreme grinds" don't help any either. Back when cams were ground with long opening and closing ramps, the cam and lifter had half a chance of survival, but with today's attitude of "yank it open and slam it closed", life expectancy is reduced......and they're noisy as hell. Here is a tutorial that I originally wrote and that has been edited by a number of my peers over the years. I think you'll find it interesting.....
http://www.crankshaftcoalition.com/w...ips_and_tricks

Here's one I wrote to help first-timers get an idea of what range of cam to use with what static compression ratio. The information was gleaned from the Crane Cams Master Catalog.....
http://www.crankshaftcoalition.com/w..._compatibility

Speaking of Crane, old Harvey Crane had a pretty good mind and came up with an idea about how quickly or how slowly the cam lobe lifted the tappet. His research was labeled "HYDRAULIC INTENSITY. You can see an example of it by subtracting the 0.050" duration from the advertised duration. Let's say, for instance, that the 0.050" is 230 and the advertised is 290. The difference, or hydraulic intensity, is 60 degrees, 30 degrees on the opening flank and 30 degrees on the closing flank, assuming a symetrically-ground lobe. Years ago, cams were ground with a hydraulic intensity of around 75-80. Some of today's cams are ground with a HI of less than 50 (Comp Cams Extreme Energy grinds), yanking the valve open and slamming it shut. It's not actually like slamming, the valve must be seated on its seat rather gently, but the effort of yanking the valve open and closed puts additional stress on the valvetrain, over a lobe with a milder HI. Today's world dictates a HI range of roughly 52 to 62 for longevity of the valvetrain and being efficient in operation. Harvey Crane used an HI of 62 on most of the cams he ground in the last century.

Here's another area that you should pay attention to, the validity of the harmonic damper inertia ring where top dead center is cut into the ring.....
http://www.crankshaftcoalition.com/w...op_dead_center
Without validating the damper and coordinating it with the timing cover tab, you cannot intelligently time the motor with a light.

Another point that gets a lot of attention on these forums is valve adjustment. Here's the way I do it.....
http://www.crankshaftcoalition.com/w...stment_SBC/BBC

Any questions?

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Build a clock.. That's funny....I like that!!!