crate motor
Senior Member
Joined: Jul 2005
Posts: 2,105
From: Central North Carolina
Hey guys, its not that they mis-rate them, although some small operations do seem to over rate their engines slightly.
The issue is that crate engines aren't rated so you can directly compare to other ratings. There are really three HP ratings you have to consider:
1 - what you get on an engine dyno: engine is on a test stand alone. Generally it is dumping its exhaust into a set of test stand headers and directly into straight pipes with not mufflers or cats, and breathing through a filter 5 inch intake duct, and has not accessories it is running except the water pump, and it is getting nice cold air from outside and has gobs of sool water for cooling.
2 - manufacturers rating in the car (what they advertise for the car) rated anymore with full mufflers, cats, accersorries, the car's air filter rather than the engine dyno's air duct, etc.
3 - RWHP, all that really matters, testedon a Dynojet of Mustang dyno usually, the Mustang generally giving a 5% lower rating.
A typical "385 HP" crate engine will measure somewhere about 385 on a test stand, would be equivalent to something of about 350 in the car, and would give about 310-315 at the rear wheels.
As another, not crate example, the supercharged C5R engine I had built for my 'vette did: 1) 833 on a engine test stand when new after running 8 hours at near idle being broken in on the bench, 2) I'd estimate 785 if a manufacturer had rated it in the car with cats and mufflers but of course I have no way to actually know, but with the AC and all, that is my guess, and 3) measured 704 RWHP with mufflers and cats, 740 without.
The issue is that crate engines aren't rated so you can directly compare to other ratings. There are really three HP ratings you have to consider:
1 - what you get on an engine dyno: engine is on a test stand alone. Generally it is dumping its exhaust into a set of test stand headers and directly into straight pipes with not mufflers or cats, and breathing through a filter 5 inch intake duct, and has not accessories it is running except the water pump, and it is getting nice cold air from outside and has gobs of sool water for cooling.
2 - manufacturers rating in the car (what they advertise for the car) rated anymore with full mufflers, cats, accersorries, the car's air filter rather than the engine dyno's air duct, etc.
3 - RWHP, all that really matters, testedon a Dynojet of Mustang dyno usually, the Mustang generally giving a 5% lower rating.
A typical "385 HP" crate engine will measure somewhere about 385 on a test stand, would be equivalent to something of about 350 in the car, and would give about 310-315 at the rear wheels.
As another, not crate example, the supercharged C5R engine I had built for my 'vette did: 1) 833 on a engine test stand when new after running 8 hours at near idle being broken in on the bench, 2) I'd estimate 785 if a manufacturer had rated it in the car with cats and mufflers but of course I have no way to actually know, but with the AC and all, that is my guess, and 3) measured 704 RWHP with mufflers and cats, 740 without.
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