Thread: Convert a chev 283 to 307 or bigger

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There is nothing wrong with using a 283 as a cruiser motor, but if you have it in your head to make a ground pounder, you'd do well to begin with a larger motor, regardless of cost. The best street combination, in my opinion, would be something like this....

Inspect main bearing bores for round and parallel. If skewed, have machine shop correct by align hone process. Register the block on the main saddle and cut the block decks to 9.000" block deck height. The rebuilder pistons I would use are 0.020" shorter than stock, so we must shorten the block deck height to help tighten the squish. When we cut the block decks, we not only are able to set a tight squish, but we are guaranteeing that the heads will sit squarely on the block and that the intake manifold will sit squarely on the heads and seal up correctly.

Here are the +0.030" pistons, they are also available in +0.040" and +0.060"....I would use +0.060" if it were mine.
http://www.summitracing.com/parts/sl...make/chevrolet
Inspect connecting rods for cracks and for being round. If cracked, throw 'em over the fence. If out of round, have machine shop re-size to round. Inspect crankshaft for cracks and for journals being egg-shaped. If cracked, throw it over the fence. Have machine shop grind undersize to correct egg-shaped journals. If you have to buy rods, remember that the rod journals are 2.000", not 2.100".

Now, we have a block, a crank, 8 rods and 8 pistons. The pistons will sit down in the bore by 0.020" with the piston at top dead center, so we will use shim head gaskets to set the squish.....
http://www.summitracing.com/parts/mrg-1130g/overview/
0.020" piston deck height added to 0.018" head gasket thickness puts the squish at 0.038".

Most any of the Chevy 305 C.I.D. cylinder heads will work on this budget build, the best of which may be the casting number 14014416 from '80 to '85 305 HO. A standard Edelbrock Performer intake manifold mounting a 600 cfm 4-bbl would be my choice for gettin' the mixture into the motor. I would normally recommend a Performer RPM if the build is a 350 or larger motor, but this tiny little 292 motor needs less manifold volume, so I'd use the smaller manifold.....
http://www.summitracing.com/parts/edl-2101/overview/

Now, let's go through the numbers to determine static compression ratio based on a +0.060" overbore.....
(.7854) x 3.935 x 3.935 x 3 x 16.387 = 598 cc's in the cylinder.
(.7854) x 3.935 x 3.935 x .02 x 16.387 = 4 cc's in the piston deck height
58 cc's in the chamber
6 cc's in the piston crown
4 cc's in the head gasket

Add all values together and find 670 cc's total.
Subtract cylinder volume from total volume (670 less 598) = 72
Divide total volume by 72 (670 / 72) and find 9.30:1 static compression ratio, perfect for pump gas with iron heads and a tight squish.

Now, knowing the static compression ratio, we can intelligently choose a camshaft for the motor.
Although I will not use a flat tappet hydraulic camshaft myself any more, you may be up against a wall and be forced to use one if your finances are thin. If I were to spec a flat tappet cam for you, it would be this Crane unit. This cam will make an 8.48:1 dynamic compression ratio when used with the aforementioned 9.30:1 static compression ratio. Again, perfect for pump gas with iron heads and a tight squish.
http://www.summitracing.com/parts/cr...make/chevrolet
If you choose to go this route, use only genuine Crane lifters with this cam, not some fosdick offshore Chinesium units. Also use the valve springs that Crane recommends with this cam, Crane #99848-16. The hydraulic intensity of this cam is 56, a good compromise between too fast and too slow. (44 would be too fast and 70 would be too slow.)
And do not make the mistake of thinking that this little motor needs more camshaft than that. It doesn't.

If you want to pull out the stops and guarantee that you will never roach a cam lobe, step up to a hydraulic roller cam. Here would be my choice for you in that respect.....
http://www.summitracing.com/parts/hrs-110315-10
And again, use only genuine Howards hydraulic roller lifters with this cam. Talk with the tech guys at Howards for the proper part number of valve springs to use.
This cam will make an 8.34:1 dynamic compression ratio when used with the aforementioned 9.30:1 static compression ratio. And again, perfect for use with pump gas and iron heads and a tight squish. The hydraulic intensity of this cam is 53....again, a good compromise between too fast and too slow on the valve actuation. Use an aluminum thrust button on the front of the cam and set clearance between the button and the timing cover at ~0.010". Some fellows will tack weld a small sheet of 1/8" thick steel to the inside of the cover so that the cover will not "oilcan".

Finish off this motor with a good set of long-tube headers, 1 5/8" primaries. Construct an X or H pipe immediately after the collectors and use 2 1/4" pipe to the rear bumper. Use mufflers of your choice. Top the carb with a 14" x 3" or 14" x 4" air filter assembly so the motor can breathe. Don't terminate the pipes under the car, run them to the rear bumper of the car. Nothing sounds as awful as a ratty set of mufflers with pipes terminated under the car, with the sound resonating against the under sheet metal of the car. That can make you nuts in just a few minutes and you will not like driving the car anymore.

This little motor will like a looser torque converter and a numerically-larger rear gear set. I might be thinkin' a 10", 2500 stall converter, maybe something like this....
http://www.summitracing.com/parts/sum-g2700-1/overview/
and a 4.11 rear gear.

I would be envisioning an easy 300 hp with this build, just right for a tractable around-town driver, particularly in a lightweight car or truck with a loose converter and stiff gear.

P.S. If you decide to use a flat tappet hydraulic camshaft, please read through this tutorial a few times so that you don't get caught with your pants down.....
http://www.crankshaftcoalition.com/w...ips_and_tricks

Use this tutorial to nail down TDC so that you can time the motor with a light after you get it together.....
http://www.crankshaftcoalition.com/w...op_dead_center
I would use a stock GM HEI distributor and set the ignition timing at 12 degrees at the crank, with 24 degrees centrifugal advance in the weights, all in by 2800 rpm's. Use a Crane vacuum advance unit...
http://www.summitracing.com/parts/crn-99600-1
Try both ported vacuum and manifold vacuum and see what the motor likes best.

Valve adjustment.....
http://www.crankshaftcoalition.com/w...stment_SBC/BBC

I'd probably use an Edelbrock Performer 4-bbl carb with vacuum secondaries and might even be tempted to use one of the little 500 CFM units. Limit fuel pressure by the use of a premium fuel pressure regulator such as the one shown below to 4 3/4 to 5 psi at the carb inlet. More fuel pressure than that will not make more horsepower. What it will do is to overpower the needle and seat in the carb bowl and allow the fuel pump to blow raw fuel into the intake manifold, creating a tuning nightmare for you.
Here's the Owner's Manual to help you tune the carb.....
http://www.edelbrock.com/automotive/...ers_manual.pdf
http://www.summitracing.com/parts/hly-12-803/overview/

Let me say this one more time.....4 3/4 to 5 psi MAXIMUM at the carb inlet


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Hello Techinspector1 thank you for your wealth of information, you have given me plenty to work with.
Some of your terminology or lingo I'm still trying to work out, what is squish

Thanks Martycar

Originally Posted by martycar

Hello Techinspector1 thank you for your wealth of information, you have given me plenty to work with.
Some of your terminology or lingo I'm still trying to work out, what is squish
Thanks Martycar

It is desirable to have the piston come up very close the the underside of the cylinder head to "squish" the fuel/air mixture over into the combustion chamber, thereby mixing and homogenizing the mixture, eliminating rich and lean areas so that ALL the mixture gets lit off and burns at the same rate. The result is good detonation-resistance, fuel mileage and power. A builder needs to use a piston that has a nice, flat, generous squish area on the crown of the piston, so piston choice is critical.
Here's an example of a piston that you do not want to use. It has only a very thin band of flat piston area to mate with the underside of the head.....
http://hotrodenginetech.com/wp-conte...L92pistons.jpg
Here's an example of a piston with a generous flat area on the crown to facilitate a good squish. The squish plateau is on the left side of this piston in the photo.....
http://raybarton.com/parts/media/cat...street-flat.jp
Here's an example of a dished piston to lower the static compression ratio of a build. See the flat area on the left of the piston?
http://static.summitracing.com/globa...39632-8_ml.jpg
Think of squish as dropping a book flat down onto a table. You can visualize how the air is "squished" or "jetted" from between the book and the table. Some fellows will refer to this as quench, but I feel that squish is a better term to use.

On a small block Chevy, extensive research has proven that the ideal squish clearance measurement is between 0.035" and 0.045", so when engineering a build, that's what you should shoot for. You adjust that figure with the piston deck height (how far down in the bore the piston is when it is at top dead center) and the compressed head gasket thickness.
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