Ways to increase horsepower in a two stroke V6 240 EFI

[Ladiesman]

Ok,
I've been scouring the forum for ways to improve my engine's performance but came up empty handed :ack:. I recently bought an 01' Challenger 1800 with low compression in 2 cylinders. I figured since I am going to rebuild this whole thing It would be a great time to port and polish or something. I do not know anything about 2stroke motors and not sure where power can be made . If any of you have done some power increasing mods to a Mercury V6 240 EFI I would like to know what can be done. I can't even google search with much result..

 

[Dr Honda]

You were searching wrong. (sort of) Search for Mercury outboard performance. Your 240 is basically the same as any of the 2.5L Merc outboard powerheads. Theres guys that run these engines up to 10,000 RPM, and are putting out a lot of power.

The quickest way to bump the power is to take a few thou off the heads, and run the static compression up to 140 psi.

BUT..............................

The issue with trying run the power up too much is... it's hard to harness that with the pump. You can get to a point where you just can't process the water. When it's on an outboard... you can just put on more prop.

 

[Ladiesman]

The quickest way to bump the power is to take a few thou off the heads, and run the static compression up to 140 psi.

gotcha, makes alof of sense there

The issue with trying run the power up too much is... it's hard to harness that with the pump. You can get to a point where you just can't process the water. When it's on an outboard... you can just put on more prop.

I found ONE aftermarket impeller blade SOLAS....which im guessing only is a little more different.

Is there interchangeability with larger boats with bigger pumps ? ETC

Stroker cranks ? Turbos ?

What is the MAX compression ratio or PSI this block can handle ?

It seems like not many people bother to max the HP out of these motors

 

[snikwad003]

No turbo on 2 stroke but they like nitrous

 

[Ladiesman]

No turbo on 2 stroke but they like nitrous

why no turbo ? tuning ?

 

[Dr Honda]

why no turbo ? tuning ?

Despite what anyone will try to say....... A 2-stroke doesn't really benefit from a turbo.

To start... A "Standard" 2-stroke works by pressurizing the air/fuel in the case... and when the bypass ports open... that pressure pushes the air/fuel into the combustion chamber.


1) when you force feed it... you can run the case pressure to the point where you just push the seals out. Also... since the the back side of the piston is pressurizing the case... you are just putting more resistance on the piston on the down stroke. (loss of power)

2) When the piston is all the way down... the bypass and the exhaust ports are all open at the same time. If you force feed it... you never really add pressure to the combustion chamber because of that. AND... you are just going to blow raw fuel out the exhaust.

3) A 2-stroke REALLY BENEFITS from a properly shaped expansion chamber. (think about a 2-stroke dirt bike pipe) Unfortunately, on this engine... its vey hard to get access to each exhaust port. (but it can be done) If you want to hang 6 tuned pipes on this engine... you could see a +100 hp jump in power. BUT... this engine was designed to be a reliable engine... so the exhaust is all channeled into a manifold, and into a general chamber.

Anyway... trying to add a turbo to this will totally remove the advantages of the expansion system.


If you google 2-strokes, and turbos... guys have done it... and they claim HP gains. BUT... if it was just properly tuned, with a good pipe... they would have made the same power without the crap, and wasted fuel


As far as "Using a bigger pump"... there isn't a bigger sportjet pump. But, if you made an extra 50 hp... you would want to start with having your impeller re-pitched.

 

[Dr Honda]

FYI... look at my screen name. I'm a HUGE fan of turbos... but they DO NOT work on 2-strokes. (but they are fun on a Honda)

 

[snikwad003]

This is what you need

 

[Dr Honda]

This is what you needView attachment 36062

YES !!!!!!!!!!! :cheers:



I'm guessing that's 400~450 HP worth of happy Mercury power.

 

[snikwad003]

Its a 10,000rpm mid 80's evenrude that made its way into a volvo amazon with a tube chassis in sweeden called rudezon. Its on youtube but i cant find it on a dyno or making a pass. Sounds vicious revving with that cammed out v8 idle, with no cam!

 

[snikwad003]

https://youtu.be/lRKeuHyI0lw i think tis is the same motor with out the expansion chambers

 

[biffdotorg]

It seems like not many people bother to max the HP out of these motors

Believe me, I love to mess with my toys and get as much out of them as possible, but the toys that the family enjoys, I will take reliability over performance any day. Especially when a well running Merc 240 performs so well in these boats.

We have a limited number of days/weekends each summer. And I fear each season of the day my 240 will bail and I will have to consider what to replace it with. Until then, it performs like a champ. Anytime I can get my 20ft X20 up to 53mph on GPS, it is performing well. Anytime I can load it up with 4 adults and pull two 2-person tubes with two teenagers on each, it is performing.

Sure, It would always be cool to make this boat pop out of the water quicker, or top out higher, but I have no real complaints yet. Other than my pump may be in need of a sleeve soon someday. I will deal with that when my performance drops.

Get your engine in a good running condition and report back the results. You may be surprised that it is all you need in stock form.

Good luck,

 

[Ladiesman]

So i took my motor out finally luckily only one cylinder looks like this... you can see the rings through the piston here...hmm next step?