Crazy powerhead swap

[qnarkill]

Hi,
Does anybody have any idea if an johnson/evonrude 40 or 50hp powerhead would fit 30hp "chassis". Are they interchangable?

 

[jimmbo]

Welcome to iboats

What yrs are you talking about? There some where a 40 might fit a 30 of certain years, and also some 40s that might fit some 50s. But there are no 50s that will fit on a 30 Midsection

 

[909]

I think he's trying to live his life a quarter mile at a time.

 

[qnarkill]

Welcome to iboats

What yrs are you talking about? There some where a 40 might fit a 30 of certain years, and also some 40s that might fit some 50s. But there are no 50s that will fit on a 30 Midsection

2003 johnson with eletric start and choke. The doner can be chosen, havent bought anything yet. Just it needs to fit physically.

 

[qnarkill]

I think he's trying to live his life a quarter mile at a time.

We here have kilometers

 

[jimmbo]

At the Dragstrip near YEG Airport, they have a Quarter Mile Track, not a 402.336 Meter Track

If they shortened it to 400 Meters, Everybody's ETs would improve

 

[jimmbo]

2003 what? 30, 40, 50?

 

[qnarkill]

2003 what? 30, 40, 50?

Its 25 but has the 30 carb slapped to it. Hits 5700rpm alone driven but has issues planing with just 2 other persons on board on a alu-boat thats limited to max motor 30. Boat is perfect to my use otherwise. Im not really keen on adjusting propulse everytime i have family/company on it.

 

[jimmbo]

Put the 25 carb back on, it will probably work better overall. How are you placing the extra people in the boat? Try putting some of the Weight further Forward

To answer your Original Question, No 40 or 50 will bolt up to that Midsection, and even if it could, the Gearcase is not strong enough to handle the increase in Torque

 

[qnarkill]

Put the 25 carb back on, it will probably work better overall. How are you placing the extra people in the boat? Try putting some of the Weight further Forward

To answer your Original Question, No 40 or 50 will bolt up to that Midsection, and even if it could, the Gearcase is not strong enough to handle the increase in Torque

Unfortunately does not, all it does is limits max rpm to 5000 and is also just a smidge worse on lower rpm so no use other than fishnet weight.

Would 40 hp gearcase fit the midsection. Theres this guy selling whole motor for couple hundred.

 

[jimmbo]

No

You haven't made your 25 into a 30 by changing the Carb, the Crankcase is different between the 25 and 30(likely Porting)

What's wrong with the 40? if it id okay, buy it and use it

 

[racerone]

Nothing will fit your dreams.----This simply will not work !!

 

[qnarkill]

No

You haven't made your 25 into a 30 by changing the Carb, the Crankcase is different between the 25 and 30(likely Porting)

What's wrong with the 40? if it id okay, buy it and use it

Sorry the motor is exactly the same otherwise, looked up at the parts diagram and the change in rpm also was a proof.

40 is not legal to this boat, thats why obviously as allready mentioned.

 

[qnarkill]

Nothing will fit your dreams.----This simply will not work !!

Could you give arguments on why or is it just facts like jimbo here.

 

[racerone]

What you are dreaming of will not work !------Time for you to check some parts books to see if powerhead gaskets are the same.----Or crankshaft splines are the same.-----Or to be blunt , I would like some of the stuff you are smoking / drinking.

 

[jimmbo]

The Diagrams are the same, but try looking at Part Numbers. Your top end went up a bit, but the Low End Torque dropped, because of the Bigger, Incorrect Carb.
Just because the Engines have the same Displacement it doesn't mean that just a carb Carb change will upgrade to the Higher HP. Things like Porting and Exhaust Tuning come into play, as does Compression ratios. In the late 60s thru till the mid 70s. OMC had a 18/20 engine that they hopped up to a 25, by moving the location of the Wrist Pin on the Piston, this altered the Port Timing, and also reduced the Compression. Next the Head was replaced to one with a Smaller Combustion Chamber to restore Compression. Carb and Intake Manifold were changed, and the Reeds were slightly different.
Now a lot of Brainiacs figured that they could turn their 18/20 into a 25 by swapping the Head. What they did, was turn their motor into scrap, because the 25 head on a 18/20hp engine made too much compression, and Detonation destroyed the engine.

 

[qnarkill]

What you are dreaming of will not work !------Time for you to check some parts books to see if powerhead gaskets are the same.----Or crankshaft splines are the same.-----Or to be blunt , I would like some of the stuff you are smoking / drinking.

I asked for knowledge not guesses. Go troll some other topic.

 

[jimmbo]

I asked for knowledge not guesses. Go troll some other topic.

The guy you quoted above, has forgotten more about those engines than you will ever know.

 

[qnarkill]

The Diagrams are the same, but try looking at Part Numbers. Your top end went up a bit, but the Low End Torque dropped, because of the Bigger, Incorrect Carb.
Just because the Engines have the same Displacement it doesn't mean that just a carb Carb change will upgrade to the Higher HP. Things like Porting and Exhaust Tuning come into play, as does Compression ratios. In the late 60s thru till the mid 70s. OMC had a 18/20 engine that they hopped up to a 25, by moving the location of the Wrist Pin on the Piston, this altered the Port Timing, and also reduced the Compression. Next the Head was replaced to one with a Smaller Combustion Chamber to restore Compression. Carb and Intake Manifold were changed, and the Reeds were slightly different.
Now a lot of Brainiacs figured that they could turn their 18/20 into a 25 by swapping the Head. What they did, was turn their motor into scrap, because the 25 head on a 18/20hp engine made too much compression, and Detonation destroyed the engine.

The 25 is actually a 30 and the only difference in parts is the carb which has now being swapped, intake is same, reeds etc. Its completely different thing to swap head than just the carb so the analogy is unfortunately way off.

So you think the motor lost power since the boat couldnt plane onboard 3 person at all with 25 carb?

Please leave commenting if your knowledge is not adequite.

 

[qnarkill]

The guy you quoted above, has forgotten more about those engines than you will ever know.

Does not really seem so since he does not argument it. Saying do your own research isnt knowledge.