ProRacing DynoSim - Dyno Testing With A Computer

The software predicts more horsepower but less torque. The cam in my engine provides a ton of low-end torque. My engine also makes power at a lower rpm and should have less stress at lower rpm. I think I got lucky with this cam because it pulls really strong coming off the turns.

Now I'll explore some of the custom engine features of the DynoSim software to see if we can get it to agree with the measured data more closely. First, under the Short-Block section, my engine has a 0.040-inch overbore, which makes it slightly more than 383 ci. The type is still Chevy 383, but I click on the bore space and enter 4.04 inches. It computes the total volume as 384.6 ci. I don't see much change in performance. Under Cylinder Heads, I had selected Wedge/Fully Ported, Large Valves with 2.02-inch and 1.6-inch valves. If I click on Airflow, it tells me the flow data the program is using. It shows an intake flow of 285 cfm. I know my heads aren't that good. I try to generate some data more like I would expect my heads to flow, and the program takes whatever I put in, but it is hard to guess what the flow is at all valve lifts. I then load Wedge/Pocket Porting, Large Valves and look at the new data. It peaks at 261 cfm, and I decide to use that data. The horsepower is down to about 590 now.

Next, I look at compression. I click on the CR Calculation button, which allows me to input custom data necessary to calculate the compression ratio. Using the dome piston version, it throws me a curve I'm not expecting. It asks for Piston Down From TDC data. Thinking it's asking for deck clearance, I put in 0.020 inch, but it does not accept that. I discover that the program is looking for measured cylinder volume above the piston with the piston set down in the cylinder enough to get the piston dome below the block deck. This would be an accurate method of determining the piston dome size, valve relief size, and deck clearance all at the same time. But it requires having the short-block on an engine stand and putting a measured amount of liquid in the cylinder similar to how you would check the head combustion chamber volume. Not desiring to tear down a working engine, I opt to stick with the 12.5 compression ratio that the pistons are stated to produce.

Under Induction, my carburetor is really a 950-cfm Holley, so I type in this data. This produces maybe 2 more horsepower. My manifold is a Victor Jr. with gasket matching, but I don't know if that qualifies as Single-Plane, High-Flow or not. Standard flow kills about 10 hp. Torque doesn't change much. I choose to go with the Standard Flow. Under Exhaust, I select Large-Tube Headers Open Exhaust. This picks up horsepower a little but makes it flat to a higher rpm. This appears desirable if you have an engine that will withstand 8,000-9,000 rpm. I don't trust mine at that rpm, so I will stick with the small tube headers.

Next is the camshaft selection. I had selected a Drag Racing/Circle Track profile. The data looks a little radical for my engine. The Dual Purpose Street/Track profile picks the torque up to over 550 with a loss of about 15 hp. This is closer to what my engine does. The program has a Cam Manager button, and I find the cam card on my cam, so I click on that. This gives a screen with lots of spaces to input cam data. This is mostly over my head, but a cam grinder could try all sorts of grinds to get a particular performance. I input my cam data to the best of my ability. Some of the data does not match exactly, partly because I have duration data at 0.010 lift, and the program is looking for data "off-seat." It appears close enough.

To exit the Cam Manager screen, I find by experimentation that I have to press Enter on the keyboard to get back to the main program. Now the power and torque curves are looking similar to my measured data. The curves appear narrowband, but I think it's because I cannot stretch out the horizontal rpm scale like I'm used to doing.