1973 351C 164hp/4000rpm ?

[tawod]

why 164hp power for 351c 2v is given for 4000 rpm? Is there a dyno diagram for this engine somewhere? Is that real horsepower at the engine or at the wheels? someone must have explained it before. I tried to find this information on the forum but I couldn't.
If anyone could help ??

 

[Ron Tanzi]

As far as I know there are no dyno diagrams. The horsepower ratings at the time were measured @ the flywheel. You have to take into account that as of 1972 and thereafter all horsepower was calculated by the SAE net system as opposed to the pre-72 gross method. IE: the engine output was measured with all accessories installed IE: exhaust system, air filter, alternator, water pump as it would be installed in the vehicle. As an example the the 351 Cleveland 2V was rated at 250 horsepower in 1971 and 166 in 1972. The 1973 model year was the first year of EGR, 8:1 compression and the wide spread use of electronic spark timing controls. All of these changes hurt engine output. In 1972 the cam timing was ******** 4 degrees (at least on the CJ cams) as well. It is unclear if the 2V engines had suffered the same 4 degree cam timing ******.

Ron

 

[Duncan Mach72]

As Ron has expressed, it may be lower than you would expect. On the other hand I would think that no matter how restricted the engine is, by compression etc, it will make more hp at 5000 or 5500rpm than 4000. So it may not be the whole truth.

 

[mrgmhale]

Attached is a PDF file showing two different dyno runs on our 73 Mach 1. The original 302 had been replaced by the prior owner with a 1994 351W (not C) that was built for moderate street strip performance. The combustion chamber compression ratio is only 9.5:1 to allow it to run on the low octane ethanol free gasoline out here (90 octane). The ignition timing is set at the stock 6 degrees BTDC, although those engine do not begin to wake up until we set them for 12 degrees BTDC. If we had better fuel I would be nudging the timing up a bit more. After the rebuild it reportedly pulled 360 HP at the crankshaft, with its alternator and cooling fan connected (not power steering). After we purchased the Mach 1 (a few years after the 351 was swapped in) I decided to do a dyno pull at the rear wheels just to see where it would dial in at. Showing just over 220HP at around 78 MPH (just under 4,870 RPM in third gear with the C4 and 3.5:1 rear axle gear ratio) was a little disappointing, as it is generally said we can expect a 15-20% HP loss through a drivetrain as "average". I would have anticipated a rear wheel HP closer to 288 HP or so. I did find the horsepower and torque bands on the chart (attached) to be interesting, pretty flat before tapering off once the HP peaks.

The Mach 1 itself runs great, and with the C4 in it on the 1-2 upshift at Wide Open Throttle, close to 55 MPH, the rear tires would break loose with some tire burn and some tire noise (series of chirpings). I have not taken it to a quarter mile strip to see where it clocks in, yet. Perhaps this coming Summer I will do it on a lark. Meanwhile, the C4 was replaced with an AOD. The 1st & 2nd gear ratios on the AOD are fairly close to the C4 1st & 2nd gear ratios. The AOD 3rd gear is a direct drive 1:1 ratio, like the C4 3rd gear was. The AOD 4th (OverDrive) gear ratio is 0.7:1. I have not done any WOT runs with the AOD yet, just because I am not really that much of a street romper nowadays. I am more into some fun cruising in a vehicle that can deliver some spirited performance. I can tell the engine had plenty of power to overcome the air resistance art higher speeds, so the AOD brings a higher top end to the party, as well as a reduced engine RPM at highway speeds, while preserving pretty much the same 1st and 2nd gear ratios of the prior C4. The AOD was a good move.

Anyway, FWIW the dyno runs for the 73 Mach 1 is attached if you are interested in where the torque band is, and the horsepower.