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Does someone have the time to explain to me in english(meaning so a beginer hot rod builder can understand) how everything coinsides with one another in the engine to figure out how to come up with a combination for a good hot rod engine for the street and track. Chevy 350
Thanks for your time I know that this is no two sentence. I have some of the understanding of the operation and role of the parts just not how to figure out what goes together.

Well, I'm no engine expert, but lets start here: An engine is essentially an air pump. The more efficiently you can move air in and out the more HP it will make. But there are limits, so everything must be balanced to work together.

An example would be taking a stock engine and putting a 1000 cfm carb on it. It would seem that since it passes more air it MUST be a better producer of HP. But we all know that isn't true, because the rest of the components are not set up to take advantage of that carb.

That is why the carb, heads, pistons, cam and exhaust system must be all tuned to one another so that no one component restricts the other parts from doing their intended job. Some companies, like Edelbrock, sell a line of matched parts (I think under the Performer series) that are tested and proven to compliment each other, and when put on as a system provide good performance gains.

Now we'll let the guys who really know motors tell us the straight scoop.

Don

You could go to the bookstore and get several books on engine building and performance. There is a lot of good, detailed info in them.

A good beginning book is "How to Build Max Performance Chevy Small Blocks on a Budget" by David Vizard. My copy has an additional label "How to Build Horsepower, Vol. 3" which has typical buildups with dyno runs. Vizard makes a good point about actual dyno testing various configurations. Vizard has other books on rebuilding various engines and I used the one on the Pinto 2000 to rebuild a family commuter car and found his pictures very helpful which made the book on the 350 more convincing.

Don Shillady
Retired Scientist/teen rodder

Here's what I like to do. Go to compcam.com and look for the camquest link and down load it. Get ready to spend a lot of time as it is very addictive, well for me it was. It is fun to use though.
First you need a block. If you already have one, check for nickel content, a 10 or 20 will be displayed under the timing chain cover any where in the number system, and will contain 2% nickle and 1% tin. Very good block. Then you have to make a whole bunch of decisions(this is where the camquest will come in to play) Do a whole bunch of research BEFORE you buy anything. Go to scat .com, visit eagles site for a good rotating assembly (cranck rods and pistons. I would recomend all forged parts so if you want to later you add any thing you want such as a blower, nitrous, highrise or any thing that would produce in excess of 500 HP GO BIG on the bottom end and you'll do great. Next have the block checked for cracks, again do your homework and find a GOOD machine shop that does race motors so they'll know what your intent is. I would deffinately deck it for a flat head surface. If you get this far you'll know as much as you need to about this procedure.
Good Luck

In simple terms, you could compare a couple different applications.

If you were building a race engine, designed to produce maximum power, you would want to have maximum compression that the fuel allows, and you would want to run it at maximum RPMs, so you would need to have massive ports, valves, manifold runners, a high lift long duration cam holding the valves open as long as possible, a huge carburetor to allow for max airflow, and and headers to try to clear the gasses as quickly as possible. If any of these restrict the air volumn, you get whipped by the guy in the next lane. Also other basic things are different. The spark plug has to fire a little sooner, since things are happening so fast. The engine needs more fuel for the amount of air, since you make more power if you burn more fuel. That fuel needs to be higher octane, since the cylinder pressure is much greater.

On the other end of the spectrum, you have low octane pump gas, an engine that needs to start under the worst conditions. It will be operated at low RPMs most of the time, must produce torque down low when the light turns green and you are coming off of idle conditions, and must get good mileage and be reliable. If any one part of this whole picture is too excessive, you lose lots of horsepower.

Some of the problems with the race motor in a street car are that the air is now flowing very slow through all of those big passages. The vaporized fuel will not stay vaporized, and the fuel mixture is far too rich for idle conditions. If it stays running at all it will be fouling spark plugs, stalling out, be very very weak at low RPMs. You also will not be able to run it on pump gas, and in a race motor the fuel mixture will explode from pressure, before the piston gets to the top of the cylinder, and the spark plug fires. This is called detonation, and destroys engines!

Just like the race motor, if your street engine has one element that does not work in sync with the others, it will not work the way you wanted it to.

The point of all of this is that you need the right combination of parts, to achieve everything working at the same RPM range, for your desired operating conditions. If you have one important element is too much.....or too little....the engine will lose power, or have problems.

You need to look at the weight of the car, the driveline type, gearing, tire diameter, what you will use the car for, engine size, fuel type, and other things, then try to design a combination that works to perfection under those conditions.

You are making a good choice in asking people who have "been there" and "done that". Those are the ones you want to take advise from.

In my experience, the single biggest snafu made by first time builders is choosing a cam that is too large for the rest of the combo.

The key is coordinating the intake valve closing point with the available static compression ratio. If you have a stock 350 Chevy that has a SCR of 8.5:1 and you install a cam that is meant for a motor with SCR of 11.0:1, the intake valve will close so late in the cycle that you won't build sufficient cylinder pressure to make good power. The late closing of the valve allows the piston to push some of the mixture that has just been drawn into the cylinder, back up the intake tract to confuse the venturi and cause a rough idle. This is called reversion. It contributes to insufficient power at low rpm's and results in insufficient manifold vacuum to operate accessories such as power brakes.

Dynamic compression ratio takes into account the rod length and intake closing point. Paying attention to DCR will result in the optimum cam/scr combination to make maximum cylinder pressure for the available fuel used.

I've been playing with my dyno software and can tell you that I have found that no matter the internal components used, the power can be choked off at the inlet and outlet points on the motor. I simulated a 350 with stock-type intake manifold and 1 1/2" headers. Changing to a Performer RPM manifold and 1 3/4" headers pickup up 55 ft/lbs of torque and 90 hp!!!!!!!

Another snafu is choosing heads that are too big for the cubic inches and rpm range of the motor. Ultimately, the cfm rating of the ports is the deciding factor. For instance, the L31 Vortecs (12558062 casting) look too small for a 355 at 170cc intake runner size. But when you look at the flow rating on the heads, they outflow anything made previously by Chevrolet, including the double hump F.I. heads that are so sought after by newbies who really don't know any better. You can source 'em from a boneyard off of '96 to '99 Chevy trucks (5700 Vortec motor). Look for a sawtooth design on the end of the heads. When looking for aftermarket heads for a street motor, a good rule of thumb is the cubic inches of your motor times 1/2 for the intake runner volume.

As was stated by others here, it's a balancing act to get everything working together toward a common goal based on available fuel and what you expect the combination to do.

I absolutely positively support the info from techinspector – the Vortec heads from Chevy trucks seem to be the best ever. I don’t know what kind of wrecking yard access you have, but these heads used to be fairly accessible for about $100-200 apiece. GM may still be able to get this part number for about $500 a pair. Private party will clean them up and sell them online for a lot more.
This Vortec head is an LT1 designed chamber. It has LT1 intake and exhaust ports with 1.94/1.50-inch valves. If you can in a good clean set (tight valves and springs), they perform well in their stock configuration. Everything that I have read shows they can easily produce 400HP with “off the shelf” Performer series manifold, cam and carb from Edelbrock. The casting number techinspector referenced is the only good one. 10239906 was also used for these truck motors and it doesn’t flow as well.
Key to remember is that this head definitely requires a Vortec specific intake manifold. Also, like a lot of Chevy heads, this one uses press in rocker arm studs (3/8”). Not necessarily bad, unless someone has reefed on them or you’re building a really monster spring/cam combination.
You also get to use the really cool center bolt valve covers.
Good luck on this project

I would recommend studying the dyno-tested engine combinations at the website below. They should give you a good idea about combinations and the hp and torque different heads and camshafts will produce on 350's and 383's. Anything over 500 hp will probably not have good street manners. I built my 383 based on Combination #15. It is a great street engine, but I would not want a bigger cam with an automatic transmission.

www.ryanscarpage.50megs.com/