Car Engines in boats, why dont you see more?

[Pennywizz6]

Ive noticed that the specs of comparable displacement engines from marine and onroad engines have quite a different spectrum. Ive noticed that a .21 hyper 8 from picco pumps out something like 2.6hp and 48,000rpm, and a .46 marine from OS only gets around something like 2.2hp and 28,000rpm? To me that jump could really speed up a boat especially 20,000 more rpm it seems a bit rediculous. I know that overheating may become a rising problem but you could easily do a mod for it. Is it mainly the torque needed to spin the propthat marine engines produce?

I think I remember saying boats are meant for acceleration, but when your going your going, and acceleration seems obsolete and the rpm makes it walk away. The reason im so curious is because on my future rigger I plan on building during those cold days of the winter I wanted to put in a pull start .21 hyper 8, cheap, quality and no need for a starter. But seeing nobody else run such an engine discourages me.

Phil <_< :huh:

 

[Joe_Knesek]

Ive noticed that the specs of comparable displacement engines from marine and onroad engines have quite a different spectrum. Ive noticed that a .21 hyper 8 from picco pumps out something like 2.6hp and 48,000rpm, and a .46 marine from OS only gets around something like 2.2hp and 28,000rpm?  To me that jump could really speed up a boat especially 20,000 more rpm it seems a bit rediculous. I know that overheating may become a rising problem but you could easily do a mod for it.  Is it mainly the torque needed to spin the propthat marine engines produce?
I think I remember saying boats are meant for acceleration, but when your going your going, and acceleration seems obsolete and the rpm makes it walk away. The reason im so curious is because on my future rigger I plan on building during those cold days of the winter I wanted to put in a pull start .21 hyper 8, cheap, quality and no need for a starter.  But seeing nobody else run such an engine discourages me.

Phil   <_<   :huh:

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Years ago, I ran a Paris Rex in a 20 mono. It turned tons of RPMs but it had so little torque that I had to run a smaller prop than everyone else. The lower RPM motors were faster.

 

[Lay26]

we got a very fast racer over here in namba dist 1 that runs a sppedmaster 21 with a ofna picco car motor, man i tell you it really runs. but like he tells me all the time it's not the motor you have to make it do what you want it to. he cleans up the wood(trophys) with that boat.

 

[TimD]

That and most rpm and power figures are not comparable unless they are from the same manufacturer and era. I think some just guess the figures to be honest.

Tim.

 

[Ron Olson]

That and most rpm and power figures are not comparable unless they are from the same manufacturer and era. I think some just guess the figures to be honest.
Tim.

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Tim, you've got a good point there. I've got a recent magazine around here somewhere, RC Driver I think, that had a great article on advertised engine HP and RPM claims, one of the best articles that I've ever read on the subject. A guy built a Dyno and did all of the testing himself on several of the popular .12 engines. Most were only putting out about HALF of their advertised HP but the RPM claims were closer but not by much. He did consistent tests with break-in time, the same fuel and tuned pipe system. He learned a lot about the engines while testing including how much of a difference that just a little change in carb settings made. Anyone that reads RCCA or some of the other car and truck rags may or may not have noticed lately that they aren't advertising their claims much, if any at all any more. If a company wants to make claims, tell us how you got those numbers; what Dyno, fuel, pipe, any corrections for altitude, etc. so that we know that you're not BS'ing the public.

 

[not2bright]

remember torque x rpm = h.p. but these boats need torque to pull the big props we run so in all reality hp doesnt mean squat unless the motor can make the torque to swing the big props

i probly dont make alot of sence but that is about the best i can do to explain things :blink: :blink:

 

[Pennywizz6]

Thats real interesting Ron, I have always been fishy about 2.6hp from a .21 engine. Theoreticly a 302 5.0l would produce like 3140hp! I know nitro content really boosts it compared to plain gas, but thats a pretty big number! I may be out of whack but whatever

Did it really say what to trust in that article? Its kinda a shame that companies would stretch the truth so far that its false advertising and nobody can be trusted.

But big name companies will test a certain engine hundreds of times and the biggest hp count will be the one that will appear in the ads. Maybe they broke it in so perfectly, had the airflow just right and the temperature for peak performance. You really will never know if its truthful and they guy that tested them was off or they really are stretching it, by half seems a bit much for tall tale telling.

So is it a bad idea to run buggy engines on a rigger? Should i just stick with marine engines? Im sure just about everybody here has more experiance than me so i better listen up

Phil :huh:

 

[TimD]

Novarossi marine engines are based on buggy engines.....

Just be wary of some of the car engines timing - some of them are pretty wild.

 

[TomMoorehouse]

i had an expensive RB .21 once..... never again! it never worked right..... i paid big bucks for it and sold it for a song :angry:

 

[not2bright]

wow tom every time engines get brought up you are always after RB. you must be pissed at them :unsure:

 

[TomMoorehouse]

hehehe $435 later..... yep!

 

[not2bright]

note to self: dont buy a RB engine

 

[Paul Pachmayer]

Hey Guys,

I'm not a nitro guy so bear with me here. What's wrong with spinning a smaller prop at a higher RPM to get speed your after? Right now I'm working on my SAW boats and my target RPM is in the 40 to 45K range. Prop sizes vary but V937 V940 and V942 seem to be the norm in many of the boats. A 12 cell 28" sport hydro I'm running is in the sub 6 second range turning a X637 at 41,500RPM.

Paul.

 

[izitbrokeyet?]

So is it a bad idea to run buggy engines on a rigger? Should i just stick with marine engines? Im sure just about everybody here has more experiance than me so i better listen up

yes.....most buggy motors are timed way down in the 70's for exhaust durations. You'ld be hard-pressed to ever get an Off-road motor to turn much over 20krpm.

there are some On-road motors that are very well suited to marine applications with some minor mods B) .......even better than most marine motors in my humble opinion.

 

[tracerbob]

I ran a CMB 21 car engine in a Sprintcat 21 a long time ago. It was a side exhaust but it the same kind of header setup as our modern day engines. Man that thing could go, with a smaller prop of course.

 

[Ron Olson]

With those of us building .12 powered boats, we don't have much of a choice in marine engines so we are going the air-cooled car/truck engine route. I've got 2 of the Fantoms and one Trinity/Picco, the T/P will outrun my higher HP and RPM rated engines any day of the week! Put those same engines into a truck and the Fantoms will kick the T/P's butt! I'm thinking that the difference in the power curve, where it's at that is making the difference and the timing numbers.

I'd like to know what the numbers are on the O.S.'s as they seem to do pretty well in the .12 'riggers that I've seen run.

 

[Jerry Wyss]

To "Echo" Lay26,,I too had an Ofna 4 port 21 engine in a Kyosho 8th scale 4wd

Baja rig many years ago. It was a Blast! I've often thought about using an engine

like that in a sport 20. The recoil start engines use a crank pin similar to what

our outboard engines require to turn the PTO for the Flex shaft. As a matter of fact

all the cranks I've been odering lately for my Thunder Tiger OB's is a Car pull

start Crank for the various .21 car engines. The Pull Start engines are probably

less desireable due to the slight amount of "Drag" on the engine as a part of the

pull start mechanics are always spinning with the engine. I had the Ofna that had

to be started with a starting box and it was a little "Brute" , and cost $109.

Jerry

 

[anthony_marquart]

Ron,

I just put a Trinity / Picco rear exhaust .15 in my firefighter and I have the same result. The T/P kicks the Fantom's _ss. Not only more speed from the same props but bigger props also.. No more pull start though... Lost that bit of convienence in trade for more power...

 

[Mark Anderson]

Most all of the 21 motors are based on car motors. Cars are where the r&d money is spent due to it being a much larger market.

Pull starters add drag and are notorious for leaking which will hurt power and make the engine a hassle to tune.

Other than looking ood the air cooled heads work great in boats. I ran one for years in a 20 canard that was very successfull.

Mark

 

[J Solinger]

I'm interested in .12 size riggers and was wondering if we could start a short list of engines that work and ones that don't. I was at the LHS the other day looking over the engine selection and didn't have a clue as to what to try. :blink: I've seen some good info already from this thread and would like to expand on it.