Car Engines in boats, why dont you see more?

[Bradley Ward]

Gday Gill im not familiar with that? Is it something that I could look up on line? I'd be keen to have a look at it! Thanks for the help

 

[Kez]

Maybe car engines have evolved in recent years but back in the 80s and 90s the car engines (Picco, OPS, Rossi etc) had the same piston/sleeve as the marine counterparts. The only difference was the heat sink head vs marine head.

 

[Christian Holmstedt]

At least for Off-Road car engines I can see why they are not used much as they are tuned to have a wider power band. Running an engine with a very narrow power band with high peak power off-road just doesn't work well. It's hard to drive and the car will be slow out of the corners.

On-Road engines might be different. They are in general more 'peaky' like Marine engines.

 

[Bradley Ward]

What creates a power band? The Pipe? I'm pretty new to marine engines so i don't know? As over looking simply the carbie side of things on car engines there doesn't seem much difference between on road or off road carbs!(i could be wrong?) And with Novarossi they don't build a whole lot of different carbs for every car engine!(i cannot even spot a difference between an on or off road carb) maybe the crankshaft timing is the only difference? (I would love a guru to tell me!) Then does running different thicknesses of shims re time an engine? Or only boost compression (I'm also unsure?) I may be going out on a limb here but I'm a firm believer that header length in combination with tuned pipe differences (be it car to boat pipes!) With a marine style carbie change and tuned appropriately to suit all the above changes! The deference between car and marine engines would be like trying to split a hair!!but any engine gurus on here i would love to hear from them! And chime in as until then I'm sticking to my story RPM between Novarossi car and marine engines is exactly the same!

 

[Christian Holmstedt]

The power band is controlled by the engine timings and the shape of the pipe.
A very simplified rule of thumb is that the higher exhaust timing (the longer it stays open) the higher up in the rpm range peak power can be found and a pipe with shallow angles gives a wider (but lower peak power) power band. The more power you want the more rpm you'll need the engine to turn... hence high port timing. That leads to compromised lower-mid range power.

It all works together.

There are (were) some really unusual exhaust port shapes on off-road engines. The RB C6 for example was a real monster. Good peak power but with a very nice wide mid-range power band. It had effectively 3 exhaust ports. Two small high timing ports on each side of the main port which was timed much lower.

As for carbs. I've head many say that a car carb doesn't work on a boat. Well, that's BS. it works just fine. However, many carbs for boats have very large ID to flow good at high rpm. So that might be where the 'car carbs don't work' come from. Car carbs usually have inserts to restrict the opening to gain drive ability and fuel economy. The largest was/is around 9mm.

The last point is that car engines are setup to run 30% Nitro at the most. That's because of the rules.

This is a huge but interesting topic but I'd go out on a limb to say that a on-road car engine will be easier to work with than an off-road type. When I raced 1/8 buggies I never spent much on engine and had the most fun with thee cheapest ThunderTiger and OS RG.... modded to hell, but I did run the OS V-Spec and RB C6.

 

[Christian Holmstedt]

But yes, I agree.

A car engine with good timings and a boat pipe and big carb + nitro will run great.

I'd love to test a car pipe on a boat engine.

 

[Bradley Ward]

Thanks for the information boys this all helps me! I will test a car pipe on a marine engine if you like! (If only for my own interests) i started out by buying OS carbs to run on Novarossi's only due to Novarossi's lack of Australian supply and no agent here in OZ at the time! Plus getti g ripped of for thousands by different RC boat guys in Australia left a **** taste in my mouth!(so 4/5years ago i just packed it all up and forgot about it!) Since being on this website it has restored my fauth in the RC boating community and ive proceeded to blow the dust off of some old items! I inclosed some pictures of some carbie's i have! Also a question if the marine engines have port changes done? Why is the part numbers exactly the same for marine and on road liner on the Novarossi website? (Im talking 21 Mito)

 

[Christian Holmstedt]

Also a question if the marine engines have port changes done? Why is the part numbers exactly the same for marine and on road liner on the Novarossi website? (Im talking 21 Mito)

Because they are the same and there is no difference between on-road/marine in that case...... I would guess.