67 327 Dyno Results

[Mark L.]

Looking to understand how a 300 hp stock engine does on the dyno. If anyone has data can you share it? Thanks

[Chris H.]

Re: 67 327 Dyno Results

Hi Mark, just curious, are considering deviating from the totally stock setup? You know me, I’d at least go with a hydraulic roller.

[Chris H.]

Re: 67 327 Dyno Results

Having said that, I remember driving a ‘67 with a 300 hp motor and I really enjoyed it. Very smooth and civilized.

[Duke W.]

Re: 67 327 Dyno Results

As I've stated in the articles I've written about the Special 300 Horsepower 327 configuration, typical chassis dyno results for a Flint-built 327/300 with SAE air density correction are 190-195 RWHP at around 4500 and 270 lb-ft peak torque at around 3000 and its out of breath by 5000, which is before the 5300 redline. Using empirically derived conversion factors of 0.85 for driveline efficiency (including tires) and 0.89 net/gross ratio, the above rear wheel with SAE air density correction data converts to approximately 357 lb-ft SAE gross torque and 255 SAE gross horsepower, which uses "standard sea level atmosphere correction".

This "STD" air density correction yields about 4.5 percent higher numbers than "SAE" air density correction. The rest of the gross/net difference is due to front end accessory and exhaust back pressure loss. This 0.89 net/gross conversion is SPECIFIC to C2 small blocks because of their very low restriction exhaust system, which generates only 3 to 3.5 psi exhaust back pressure depending on configuration. A SHP big block develops about 6 psi making their net gross conversation no more than 0.85.

The significantly overrated advertised gross horsepower is typical of sixties vintage engines.

I received your test data yesterday and printed it out. As you are aware, the results are below expectation, and below the results of John McRae's Special 300 HP configuration test reported in the "Tale of Two Camshafts" article (The Corvette Restorer, Fall 2010) and Mark Hedberg's test from a little over a year ago reported in the following TDB thread. The McRae and Hedberg's tests were within about one percent across the board despite being done in different locations over a decade apart. In fact the Hedberg test was done on a Dynojet 224 chassis dyno which replaced the 248 model that was used for the McRae test, and the 224 operator assurred me that the results would be comparable. The following thread is a report and discussion of the Hedberg test:

https://www.forums.ncrs.org/showthre...ecial-camshaft

Using the above conversion factors to convert the Hedberg engine rear wheel data with SAE air density correction to "gross ratings" at the flywheel with STD air density correction, which is what was advertised back in the sixties, the Hedberg engine estimated gross torque of 371 lb-ft exceeds the OEM advertised 360 lb-ft value by about 3 percent. The 287 gross horsepower value is short of the 300 advertised value by about 4.5 percent, but 12.5 percent above the actual gross horsepower output of a Flint-built 327/300, which places the Special 300 HP configuration's peak power in the same ballpark as a Flint-built L-79 while developing significantly more torque/power in the lower half of the rev range and maintaining the OE 327/300's butter smooth 500 RPM idle speed.

As with any test that fails to meet expectations there is a reason, and it usually takes an investigation to find the reason(s). That's why I asked you in my reply to your email to call me in order to have an interactive and detailed conversation about the build and test, which will be the quickest way to ascertain the reason for the less than expected test results.

Duke

[Mark L.]

Re: 67 327 Dyno Results

Thanks Duke. So far I have been unable to find any gross hp and torque data from an engine dyno. Hopefully someone out there has run that test on a 300hp. I'll give you a call.

[Duke W.]

Re: 67 327 Dyno Results

I do have a lab dyno sheet, STD correction, for a purported "stock rebuild" 327/340. Peak gross torque was in the ballpark of the factory claim, but peak gross horsepower was only 295 @ 5500.

The owner asked me what happened to the other 45 HP, and I replied that it only existed in some marketing guy's dream.

Duke