Dyno Results for 67 327/300 HP AC Vette

[Kirk M.]

Hey Everyone,

I posted this over on the Forum, but thought those who might have missed it there would enjoy seeing it here.

I drove my 67 327/300 HP convertible down to the Corvette Museum for the Caravan 09. Once there, I decided to Dyno my car for fun. Check out the pic and results.

Here are some things the dyno guys said:

1. The guy who ran the car on the dyno said it was the first C2 that he had dynoed that had a perfectly callibrated Speedo and Tach. He said most have at least one out of wack and many have both messed up.

2. I was told the car ran very strong and very smooth.

3. I was told the Air:Gas mix was almost perfect.

4. Only 157 hp at the rear wheels. That seems awfully low to me.

5. The dyno guy used a "factor" to multiply the rear wheel horse power and estimate the hp at the engine. The factor was 0.28 X 157 = 44 hp + 157 = 201 hp at the engine. Again seems low compared to its rated 300 hp.

Chime in and let me know what you think. Sure a lot different than the posted 300 horses at the block!

Kirk

[Steven B.]

Re: Dyno Results for 67 327/300 HP AC Vette

Kirk, it is hard to determine with the info. Were the numbers SAE Corrected? Observed, etc.? What were the conditions such as temps, is the engine 100% stock, how many miles or hpours on the engine, etc.? Remember HP calcs changed from '67.

Steve

[Kirk M.]

Re: Dyno Results for 67 327/300 HP AC Vette

Look at the printed information at the top of the summary sheet pic. It has all the temp and SAE info.

Completely stock 327/300 HP engine
87,000+ miles (assume it's not 1,087,000)

My car has PS, PB and AC. I know the PS and AC add additional front end loading to the engine.

Air cleaner lid was on.

Stock Holley 3810 carb and stock 2" exhaust (which is all repro new in the past year).

Car is an original 2-speed Powerglide Automatic.

Bias Ply tires.


Kirk

[Duke W.]

Re: Dyno Results for 67 327/300 HP AC Vette

A good OE 327/300 with a manual trans and base frontend accessories (coolant pump, alternator, and clutch fan only) should make about 190 SAE corrected RWHP in the range of 4000-4500 revs (with the power curve "falling off the cliff" at about 5000), and any good OE 327 with close to the OE compression ratio (which is typically 0.5 less than advertised) should make 270-280 lb-ft with 90 percent at 2000 for the 327/300 and near 80 percent at 2000 for SHP/FI engines except those with a 30-30 cam, which are worse.

The higher the specific output of the engine, the higher in the rev range that peak torque is achieved. An OE 327/300 will achieve peak torque at about 3000 and in the range of 3500-4500 for the various SHP/FI 327s, and the various Flint-built SHP/FI 327s should be in the range of 220-240 SAE corrected RWHP in the 5000-6000 RPM range. These benchmarks assume that there is sufficient external cooling to keep the fan clutch from tightening!

Using a driveline efficiency of 0.85 (in fourth gear) 190 SAE corrected RWHP is about 225 SAE net horsepower at the crankshaft and at least 320 lb-ft. Based on my library of both lab dyno tests and chassis dyno tests with similarly configured engines, the net/gross ratio is about 0.89. This applies to small blocks with 2.5" manifold/exhaust pipes, so my estimate of the true gross ratings of this engine are about 260 HP and about 360 lb-ft, Note that the SAE gross torque is reasonably honest, but the SAE gross horsepower rating is highly inflated, which was typical in the sixties.

The reasons your engine fell short of the above benchmark could be due to one or more of the following reasons.

1. Powerglide results in lower driveline efficiency; 0.80 is typically used for automatics.

2. If insufficient external cooling is available to avoid fan clutch tightening, the fan may cut peak torque about 15 lb-ft and reduce peak power by about 10-15.

3. Two inch manfolds/pipes reduce the net/gross ratio, but I have no data to estimate it.

4. If the engine was rebuilt with "low compression" peak torque and power will be down 5-10 percent from the typical as-built by Flint CR.

5. A malfunctioning or non-optimized spark advance map.

6. Tires: Bias plys have greater friction loss than radials and any tire will absorb more power as pressure is lowered. To get good dyno numbers, run the maximum cold pressure placarded on the sidewall.

I have no thoughts on why your low speed torque is so poor - only about 74 percent at 2000. Usually there is a torque spike at low revs on automatics due to converter multiplication, and since I see no downshift I assume the pulls were made in Low.

A couple of years ago one of my "327 LT-1" configurations was tested on a chassis dyno in 90 degree heat with no external fans. So the clutch fan was "locked and screaming". It made (SAE corrrected) 268 lb-ft at 4500 (with 80 percent at 2000 and 90 percent at 2500) and 278 horsepower at 6500. If there had been sufficient external cooling to keep the fan clutch from tightening it would have been closer to 280 lb-ft and 290 horsepower - nearly double your number!

All other things unchanged, "head massaging" will usually achieve closer to the advertised gross power ratings without any impact on the low speed torque or idle characteristics. That's why I recommend head massaging as the first performance modification to make to any vintage Corvette engine. You get more power and extend the useable rev range without any impact on visual appearance or normal driving characteristics - just noticeably more top end power and revs.

When you plan a test on a Dynojet chassis dyno, bring a diskette or blank CD and ask the operator to write the test files out to the output device and give them to you. If they have email, they can be attached to an email. The raw test files are small - only a few kilobytes.

Then download and install the free WinPep7 viewing software from the Dynojet Web site. Now you can load the test files into the "Dyno Tests" folder that installing WinPep7 creates in the root directory and manipulate, view, and print the graphs on your own computer using various scales, test parameters, smoothing, correction factors, etc, and you can share the files with others.

Don't challenge any ricers at stoplights!

Duke

[Kirk M.]

Re: Dyno Results for 67 327/300 HP AC Vette

Thanks Duke,

Still trying to digest all you wrote.

The car was placed on the dyno, out in gear and run, so it had to have shifted into 2nd at some point. Not sure were on the run graph though.

Don't really know if the engine block itself was "worked on" before I got the car, so I can't comment on that.

They definitely had large external fans cooling the front of the car.


Kirk