Engine Dyno vs. Boat
 

Ok, here's the thing. Let's say you have your engine dyno'd and the peak hp happens at, say, 5650 rpm. You really don't want to turn it 5650 in the boat, you want to turn no more than 5200. Do you go to a different cam to bring the peak hp down in the rpm range? Or do you just prop it to turn 5200 in the boat, knowing that you're below the peak hp and probably loading the crap out of the crank? Just a hypothetical question, as just about everyone knows I run stock 330 motors in my tub of a Searay. I'd just like to get differing opinions. Thanks.

why the hell would you build and engine for an application other that yours? knowing it? then dyno the engine, then change the engine configuration? ....i really don't understand???

hp=rpm*tq/5252....play with the #'s yourself.

and yes i have had to change cam timing IN THE BOAT after making a prop change to get optimal performance...could this have been done on the dyno?..yes

additional ?'s????

Regards,
Joseph Allen Skrocki
Engineering Technologist - Phase III Dynamometer Lab
ATNPC Box 38, 35500 Plymouth Rd., Livonia, MI 48150
Phone: (734) 52-35339 Text Pager:(734) 651-2028
Email: [email protected]

To answer your question, if you had for some reason made a poor cam choice for your application I would prob change the cam 5650 to 5200 is a pretty big change and for the price of a new cam/instalation the change would probably be worth it

ursus not sure if i understand???..maybe i do??

the cam for 5600 rpm engine will be very different than a 5200 cam...thus it requires additional spring...thus more heat!...decreased valveterain life.

the dyno is a tool to test and validate what will be used for the application...

i guess i'm still lost to what is the question??

Well as I understood it crazyhorse asked what would you do if you had an engine cammed so peak hp was at 5650 but you wanted to run it at 5200 max, would you leave it and prop it for 5200 or change the cam. I would change the cam.


Perhaps I misunderstood his question, maybe he can clarify correct me if I am wrong :(

Audacity,

I think he's just throwing out a hypothetical question... In fact, I've had the exact thing happen to me. Comp says cam was supposed to peak at 5500, ran dyno up to 5750 rpm and hp still never peaked. Yes, the cam was degreed in, I checked all the cam lobes for seperation, centerline, etc to verify it wasn't a grinding screw up. In the boat could only get 5200 rpm. Started to look for fuel delivery prob.

One issue I see, and correct me if I'm wrong, a dyno works by lightening the load on an engine to let it rev to the next level...in a boat, however, the load is constantly increasing with the hydrodynamics and drag. Seems like apples and oranges to me...

Zack:)

maybe the engine was built prior by someone else and you got it that way?? well if i got it for free then yes change the came and other surrounding componets...if i had to pay $$$ for it,,,for get...how do ya like that answer.


ursus....hey i need to buy you a drink :D

make it a double you got a deal :D

"a dyno works by lightening the load on an engine to let it rev to the next level"....INCORRECT...off with your head!LOL:D

Zack there are a lot of missing facts here...i was not runing the dyna....have no idea what the engine data specs are...what cfm carb are you running...what were the dyno #'s...corrected and NOT corrected!

have at this.....i dailed in a bike to 110 hp on the dyna...to X top speed....at brainerd (fastest corner 1 in north america) we miss calculated the drag CF or frontal area at that speed...guess what we never pulled the top end # we wanted...thus changed cam timing (not gearing) only pulled to 100 on the dyna and our top end # was 15mph higher.

the bottom line is people mess with things and make them slower, or a lot less reliable...i perfer both....

Thanks for the comments guys. Keep 'em coming. This scenario did present itself on KAAMA's engines early this year, as well as SuperV's. I think KAAMA decided to make a cam change while SuperV can (and does occasionally) turn his to 5600. Personally, I think I'd prop SuperV's to turn 5300. I think that would give him a little higher cruise speed, which is what he mostly does now that his wife and young son are with him most of the time. Audacity, I appreciate all your comments, but please understand most of us don't have your background experience. Any chance you might be coming over to the west coast near Holland/ Grand Haven/ Muskegon this year?