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350 Horsepower 350 engine buildup
Build a potent rodent without trick parts
By Cole Quinnell
Since Chevrolet introduced the 283 horsepower 283 in 1957, there has been a certain magic about building an engine that produces 1 horsepower per cubic inch of displacement. Today there are plenty of go-fast parts to help you build much more power than that, but speed costs: How fast can you afford to go?
We decided to take a step back to see if we could meet the goals of old with an engine build-up that didn’t use expensive or hard-to-find parts – an engine that anyone could build with the same components we used and make the same power. And no trick parts means no high prices.
The groundwork
The key to this engine was to build a simple power plant using ordinary parts to make good horsepower at an affordable price. Even at the expense of insulting some of our more informed and affluent readers, we wanted to build an engine that anyone, anywhere with nearly any budget could duplicate. People’s opinions of ordinary and affordable differ greatly, so it was necessary to lay the following groundwork.
The quick rundown starts with the short block. We wanted to use a 350 chevrolet because rebuildable cores are cheap and easy to find. It was also easier to reach our goal of 350 horsepower starting with this displacement rather than a 327 or smaller engine. We didn’t need a 4 bolt main block or a steel crank, which made it even easier to find an engine core. And, of course, the engine would have to run on pump gas.
Even though it would have been easier to accomplish our objectives with aftermarket cylinder heads, we wanted to show that it is possible to make power with stock, open chamber heads that have not been ported. No die grinders allowed, no alloy heads and no hard to find factory heads. Even with prices as affordable as they are on aftermarket heads, we wanted to bolt on a set of mid 70’s “smog heads” that can be found anywhere in the country for free or cheap. The money that we invested in reconditioning and upgrading the heads was still less than if we had bought a set of aftermarket aluminum heads.
The no trick parts rules continued up the engine to mandate a flat tappet hydraulic camshaft, a single four barrel carburetor and a compression ratio that would run on the street. No single part in this engine should invoke visa revoking convulsions
The fear
So far it sounds like we are setting off to build a 320 horsepower engine, right ? That thought crossed our minds, too, and we were often reminded of this fear when talking to people about building the engine and selecting the parts and the machine work that we hoped would make the difference between failure and victory. And that is what this article is really about. If you look at the list of parts we used for this engine, there is only a few items that might not be on any mild performance engine. So, the key was proper parts selection and machine work and maximizing the power potential wherever possible. Even as the engine was being broken in on Flowmaster’s dyno, though, we didn’t have a clue whether we would really reach our goal of horsepower per cubic inch or not.
The key elements
We know that many of you will look to see what cam, intake and carburetor we used and believe that’s all the information you’ll need to build an engine that makes at least as much power as we produced. Wrong. These components were pertinent to the power we made, but things such as machine work, piston choice and reducing power robbing practices throughout the engine are just as important. In the combustion chamber, there were two elements that we wanted to change for our benefit: quench and compression. Quench refers to how the piston top and the combustion chamber of the head work together to squeeze and position the air/fuel mixture before the spark plug ignites it. The better the quench, the more power the engine will make. Without changing cylinder heads and in order to use the most common head gasket, which is .038 – inch thick when compressed, we improved the quench by decking the block to locate the top of the pistons closer to the heads. This also raised compression, which is another way of improving power. The compression that you can use in a street engine is limited by detonation, but you can get away with more compression if the cylinder’s qunch is good and the cam shaft has adequate duration to allow cylinder pressure to escape at lower rpm.
Power thieves in an engine are primarily oil-related. The first culprit is the oil pump. Oil pumps require power to rotate, and high-volume or high pressure pumps require more power. An accepted rule in street performance and race engine building is that an engine requires 10 psi of oil pressure per 1000rpm. So, an oil pump that can produce 60 psi would be more sufficient for this engine. Anymore and the oil pump is wasting horsepower that the engine is producing. The next suspect is oil splashing on the crank as it rotates. It’s hard to believe that a fluid can have any effect on the crank and rods as they spin at higher rpm, but it does.
We’re also convinced that the quality of the machine work our engine received had a significant impact on the power it produced. From items as important as proper cylinder wall honing for sizing and piston-ring friction, to easily overlooked details such as smoothing the transition from seat to port when valve seats are increased in opening-size for larger valves, good machine work is worth paying for.
Now it sounds as though we have totally discredited the cam, intake and carb, which is not the case. These parts were all selected to also maximize power and are essential to reach the horsepower and torque levels that we did. But, these parts can be more effectively used if the above-mentioned details are attended to.
The Power Players
To make sure that any of you can duplicate this engine and get excellent results on all parts we used, we worked with Jeg’s High Performance. The company carries every part we used, with the exception of those that are available from your local GM dealership, and offers very competitive prices on everything. The service and speed with which the parts arrived was also excellent, and we would even recommend that our shop there. The machine work that we have already spoken so highly of was performed by Jim Grubbs, Pete Christensen and Todd Roselund at Jim Grubbs Motorsports. Details on the quality work that this shop does can be found in Chapter 3 of this magazine.
The rebuildable engine we used came from Memory Lane, a Southern Californian salvage yard for hotrodders and specialty old car enthusiasts. It will also ship used parts anywhere in the country, so you can even get your core from the same source we did.
Finally, the dyno tests were performed by Kevin McCelland and John Wilson at Flowmaster on a super flow dynometer. In addition to being highly qualified dyno operators, the pair was a great help in tuning the engine, swapping parts for comparison and tying up loose ends in general.
The Reality
It can done, and we did it. We made our goal with a few horsepower to spare ans surprisingly enough, also made excellent torque throughout the rpm range! What’s even better is that literally everything we did you will read about here. There are no secrets, and were even a couple of goof-ups. Our mouse motor turned out even better than original expectations and didn’t compromise our no-trick parts rules.
