Rated HP vs. Dyno HP???
 

Does anyone have any idea what kind of horsepower these merc engines actually produce? I have read some threads that say these engines are actually a lot lower HP than what they state. I have a set of 1989 454/420HP , are they really 420 hp from the factory?

Re: Rated HP vs. Dyno HP???
 

As far as I know, all of Mercs' horsepower numbers are lower than their engines actually produce. I guess they do this to cover themselves. If you were to put one of their motors on a dyno and get less power than they sell it as, I would think you would have a valid law suit.

Re: Rated HP vs. Dyno HP???
 

Tyler Crocket in one of the builds he did on a stock 98 502. He dyno'd it before the build and it only made 393hp.

http://www.hotboat.net/members/artic.../BOLT-ON_s.htm

Re: Rated HP vs. Dyno HP???
 

Russ

Re: Rated HP vs. Dyno HP???
 

Russ Let me try this again... I assume this was a 502/502 merc engine?

Re: Rated HP vs. Dyno HP???
 

Our federal Gov. allows OEM's a variable of +/- 10% on production engines. I have not seen this in writing, I have tried to find it, but my info comes from a couple of reliable sources. Bob, RMbuilder, due to his extensive background working in or for GM, may be able to shed some light on this.

Chris

Re: Rated HP vs. Dyno HP???
 

I beleave it was a 502 mag. From Merc it was rated at 415HP.

Re: Rated HP vs. Dyno HP???
 

393 HP is 5% low, but there could be that much variation from dyno to dyno, let alone from operator to operator and run to run. Statistics is a b*tch. Your 420s are great engines. If compression and tune is good, you make that much HP.

Re: Rated HP vs. Dyno HP???
 

Thanks for the info...although I was hoping I had like 300hp and that explained why I only go 60mph.

Re: Rated HP vs. Dyno HP???
 

formula377

What boat are your 420's pushing? I have the same problem with my resin bucket 357.

Re: Rated HP vs. Dyno HP???
 

502 Magnum "Carb" engines were rated for 390 hp at the propshaft.
502 EFI is 415 hp at the propshaft.

Re: Rated HP vs. Dyno HP???
 

Hmmm well there is a reason that we think alike... 89' 357 SR1
Although it has aftermarket Fuel injection with MPI. Not too many other perf mods. It does have a new interior, dash and gages.
This gave me 4 MPH on GPS...of course I did not have gps before the gage changes...hahaha

Re: Rated HP vs. Dyno HP???
 

i have always heard that merc motors exceed their rating's,a good example is the efi 525,they say it is really close in speed to a 575. As far as dyno operators trying to make good print and sell their services in a magazine article,i don't trust their before #'s,it looks ALOT better to say all their mods gave someone 80 hp than 50 or 60,just my .02,Smitty

Re: Rated HP vs. Dyno HP???
 

Formula 377

Gotta love bolt on hp. That interior looks choice. Like the white out. Did you remove the windshield and regel coat the dash? I really updates the boat!
I freshened up the 420's in my 86' 357 kamma I thinks the cams added somewhere around 15-20 hp will see if I can break the 60 mph barrier. Maybe with some interior mods I can really turn some speed(haha)
Anyway nice looking boat.
Josh

Re: Rated HP vs. Dyno HP???
 

remember horse power is not measured on the dyno, it is a calculated number by an equation!!!! So one dyno may vary from another

Re: Rated HP vs. Dyno HP???
 

Ok Just explain the "Kamma" to me??? and yes I removed the winsheild along with every nut bolt gage and even found a bikini under the dash too! Thanks for the comments, even after all the time it took to do it I know it was worth it, but always nice to hear it too. Got any shots of your 357?

Marc

Re: Rated HP vs. Dyno HP???
 

JBonz,

Torque is measured on a dyno.
RPM is measured on a calibrated tachometer.

HP is torque multiplied by engine speed.
So if you got a good tach and are bolted to a dyno, you CAN accurately measure HP on it.

NOW, each dyno is located at a different altitude.
Ambient temperatures, cooling capacity of the system, and steady state response time can also vary from dyno to dyno.

All dynos have the capability to approximate what the HP would be if "corrected" to sea level altitude, a set temperature, and humidity of the intake/ambient air.

Hydraulic BRAKE dynos can measure STEADY STATE power which is more accurate than the INERTIAL dynos that measure the acceleration of a weighted roller (these are usually used on wheel-driven machines: the DYNOJET dyno is an example of an inertial dyno).

Bottom line is that most dynos vary a bit from each other as far as the results you'll get, but if operated with care, a brake dyno is considered to be fairly consistent.

Re: Rated HP vs. Dyno HP???
 

Put a Stellings Ext. box on it and one of my ON-BOARD-DYNO units and then you can measure real time TQ and HP while you drive!