Pete Ruff's Cars & Bikes
1969 Corvette - High Performance Engine
|XK120M Jaguar||1965 Mustang 2+2||1969 Corvette||1986 Corvette||2001 Corvette Z06||2007 Corvette ZO6||The Workhorse|
The story of the High Performance Engine
After I bought the 1986 Corvette, I wanted to improve the 69 Vette's engine. The original 350/300 engine had 130,000 miles on it with no internal work done except for replacing the timing chain and gear after a section of nylon teeth on the timing gear broke off. In addition to being tired, the engine's 10.25:1 compression ratio made the gasoline available in the late eighties unsuitable. When up to normal operating temperature, the engine would ping badly under even a light load, with the best gasoline readily available.
I talked to the folks at Rigsby Crankshaft (now Sheldust) in Pacheco, CA about adding some performance to the engine. Art said if I wanted to build a stout, streetable motor, I should start with another block. The reason is that all Corvettes have the Vehicle Identification Number (VIN) stamped on the machined surface on front of the block. If I were to blueprint the stock motor, the numbers would be obliterated, lessening the value of the car to any serious Corvette enthusiast.
Since another block would be fairly easy and inexpensive to obtain, that was what I did. I wanted a "4 bolt main" block, because all Corvette motors had them, and while the additional strength was not absolutely necessary for the motor I was building, it was the right thing to do. I scrounged around the wrecks at Martinez Auto Dismantlers (now defunct) until I found a four bolt block in a Chevy van - with the same casting number as the original, 3970010, a real plus! One of the wrecking yard workers raised the van on a fork lift, and cut the motor mounts out with a "fire ax". The block dropped free and I was on my way.
The folks at Rigsby then did their magic:
While the block work was progressing, I was collecting the new parts I would need to complete the engine:
The heads and intake manifold went to Granny at Air Flow Technology, who did the head work using a flow bench. Granny did a 3 angle valve job, cleaned up the ports and matched the intake manifold ports to those in the head, to help the motor breathe. And breathe it does!
Once I had all the parts and the block was complete, I assembled the top-end of the motor and put it in the car.
Of course, it was not as easy as just saying it. For instance, the aluminum water pump was slightly longer than the old one, so I had to make a spacer to move the pulleys on the harmonic damper out enough for the fan belts to align. I fabricated the stainless steel tubing I used for the positive crankcase ventilation system, and for the fuel lines.
The cast magnesium valve covers had oil drip protrusions that interfered with the rocker arms, so I ground them all off.
I drove it about 1,000 miles and parked it for 13 years while I went out and played with CBX motorcycles.
13 years later, I began the process of getting the old boy back on the road. It runs much better now, but I had to clean the carb, because it had dirt in the needle & seat - fuel was dumping down the secondaries at idle. That fixed it - it doesn't run nearly as rich as it first did 13 years ago. At the same time, I also changed the 65 power valve to a 75 to see if that made a difference. I may go back to the original 65 so the power valve opens at a lower vacuum, perhaps giving a little better fuel mileage. In 2011 when I tore the carb apart in an attempt to determine the problem I was having with the engine cutting out, I installed the original 65 power valve. Here is a Link to a Holley Video explaining hows and whys of power valves.
In the spring of 2004, I put on new B.F.Goodrich Radial T/A tires - the old Goodyear Eagles had flatspotted pretty badly after sitting all those years - and had the seats redone with new covers and foam - they look and feel like new!
In 2005 I had the front suspension rebuilt with new bushings, ball
joints, tie-rod ends, idler arm, sway-bar bushings and links, and a new
I installed a Breakerless electronic ignition conversion kit in the distributor to eliminate the points and condenser. Link to One Wire Ignition Conversion Kit. Then I had the distributor checked for any issues, and the advance calibrated to the engine by Dave Westgate who does Corvette Mechanical Repairs 1953 thru 1982. It came out like this:
With an initial setting of 10° I now have 36° at the
recommended 3,200 rpm. The mechanical advance now begins sooner than
before and reaches
the maximum at a lower rpm. I have full vacuum
advance of 14° (at the crank) at idle, which the engine really likes.
These changes in the advance curve really made the engine stand up and perform
to its potential.
It's ready for show and go! I think the go part is nicely taken care of...
Photos of the engine swap and build
Early on in the planning process for this engine, I happened to read this article in Hot Rod magazine. Here was a relatively inexpensive way to build a brand new top-end on the block I would soon acquire. Based on the results of the dyno runs in the article, by building a similar engine, I would have a reliable, strong running Corvette engine.