Are the horsepower and torque ratings on GM crate motors corrected? I just had an engine built and dynoed and wanted to know how it compared to some popular GM engines ( zz4, 350 HO Etc).

 

They're usually dyno corrected flywheel HP. It's easy to fudge numbers to make any engine look like it has more power than it will actually put out. Once it's in your car, don't expect to see anywhere near the rated HP.

Even on a chassis dyno, numbers don't mean much except for tuning. Bragging that you have a xxx HP car from a dyno pull doesn't mean you can get all that power to the ground to move the vehicle.

The only number that shows real results is the MPH from a 1/4 mile run but only if you know the actual vehicle's race weight (car, driver, fuel etc). It's an easy formula to calculate how much power is required to move a specific weight a specific distance in a specific time. ET depends too much on traction but MPH will stay relatively constant if you hook up or spin off the line.

 

I know that the numbers will be lower once installed in my car. I was pretty happy with my numbers but wanted to know how they stacked up to something like a GM zz4 w/ fast burn heads etc.. My engine (355) ended up pulling 382hp@5100 and 430 ft/lb @4500.

The engine builder showed me some of the tricks to enhance Dyno numbers. He showed me a device ( I don't recall what it was called) but it's hooked to a hole in the valve cover and basically equalizes, by sucking air out of the cylinder, pressure in the cylinder so that the piston will have less resistance ( He didn't have it hooked up for my run)

It also did this on 20 - 50 oil and 87 Octane gas timing was 38 degrees CR is 9.1:1, but I'm getting off topic thanks again for the answer.

 

GM crate motors are rated at SAE horsepower. That's a more stingy spec than the standard temperature and pressure numbers you usually read in the magazines. It also means with the specified carb, air cleaner, accessories and full exhaust- but not much word on which of those items are spec'ed for a crate motor.

In short, GMs crate motor ratings are fairly "real world". Not going to see that much power to the rear wheels, of course, but at the flywheel they don't usually disappoint.

 

I agree with the "real world" HP numbers as stated above. Numerous shops have dyno'd stock GM crate motors only to find they make 10 to 20 percent more power on an engine dyno. However, by the time you add accessories and other power robbing components the power will be reduced. The new LS3 crate motor is rated at 430 hp but makes near 490 on an engine dyno. I am pretty convinced that GM crate motor power ratings are accurate for "worst case scenario." They still sell the old LS1 rated at 350 hp when we all know that isn't true.

 

Which cam, heads and intake did you use to get 382 hp at 5100 and 430 tq at 4500?