OK let's talk about XB mods

[kllr bee]

I need to start by saying the mods I am offering are for 1996-2001 225/250 EFI,all 250XB,and 300 PRO MAX motors. Some of these mods will work on newer models but fuel delivery and computer configuration is different on them and will need to be done differently.

The 3 liter Mercury is one BAD MOTHER stock. But she loves to do more.
After the cowl mod which I have posted we will go into the engine.
The 250XB is by far the baddest block to work with seeing that it does not have exhaust relief slots like the 225 EFI and 300 Pro Max blocks but the mods I will talk about will work on all 3 liter applications.
The rotating assembly(crank,pistons,rings) are extremely durable on all 3 liters and will handle whatever you throw at it. So let's make some power.

#1 -You must do the heads. 300 heads(67 cc) work well and will bump compression to about 130 pounds on a 250XB(slightly less on a 225EFI), but getting the 250 heads cut to 61 cc will give you about 140 pounds of compression(MADEFI can cut your heads for about 170.00 a set). That's about the max you can do on pump gas(93 octane). FYI the 225 EFI heads cannot be cut enough to help much on compression. Simon does some nice heads with interchangable chambers but I haven't tried them.

#2 -The next thing is the computers. I have tried every combination and found that the 300 PRO MAX ignition(6450 rev limiter and most timing advance) and the 250XB fuel(best fuel curve) work excellent together and that is IT. Simon can also handle reprograming any stock 3 liter boxes.

#3 -I have had the intake manifold modified by cutting the divider between 1-2, 3-4, and 5-6 cylinders. This will hurt bottom end a little but in my opinion it helps on top end(Performance Plus Marine in Florence,AL did mine). One other bonus is that if you have an injector failure it will run lean but not dry on the affected cylinder. This is not a must but an injector failure is not pretty at all.

#4 -On the tuner. A 300 tuner has a 1 inch hole in the back side of the exhaust chest.If you run overhub prop it will help but in a through hub prop application it will hurt holeshot. I currently run a 250XS tuner and it seems to be similar to a stock 250XB tuner. I have not tried the Simon tuner but he has some real good ideas on the 3 liter now. Just don't cut the exhaust chest off. I did that once. It didn't help performance. Also my ears were ringing every time I ran the motor and the marine patrol HUNTED ME DOWN and hastled me everytime I went to the lake. Sounded like a top fuel dragster.

#5 -I have tried moving the crank position sensor. Don't waste your time. It doesn't work in my opinion.

#6 -I run Boyeson 2 stage carbon fiber reeds which I think are the same as the stock reeds on a 250XB/300 Pro Max. I have tried single stage carbon but did not have as good low to midrange punch. IF YOU HAVE A STOCK 225 EFI PLEASE REMOVE THE STOCK STEEL REEDS. They cannot handle the added stress that mods put on the motor.

#7 -On the spark plugs. Don't be fooled there is only one good plug for the 3 liter.Use Champion QL77CC ONLY.

#8 I have not done this but if you can get a lightened flywheel. In my opinion it will let the rotating mass spool up quicker. I will be doing it soon and will post results. Simon motorsports does this work also.

#9 -Get your TPS(throttle position sensor) set richer. Mine is at .102 at idle and .432 at wide open.This keeps the lean sneeze from happening at idle. Not good on reeds and rotating assembly that is pushing the envelope.

#10 -On a stock 225 EFI you will want to get 250XB/300 PRO MAX ignition ECU's. They transfer the ignition current at a higher voltage.

#11 -I have tried underdrive pulley on alternator. It will help with holeshot but on a fishing boat it cannot keep the battery up.

#12 -I believe in the oil injection system and continue to have mine in service. I think it inhances performance over premix from idle through midrange. Also only use premium plus oil and add fuel injection cleaner every 5 tanks of gas to keep the system clean.

#13 -Older 225/250 EFI motors that do not have the 4 butterfly intake will need to have the 4 butterfly upgrade to have adequate air to feed the increase in fuel added by the computer upgrades.

More to come when I think of it.
Richard

Modified by kllr bee at 3:40 AM 12/14/2009


Modified by kllr bee at 4:02 AM 12/14/2009

[heavybullet]

ql77pp is better than ql77cc with these mods imo its what 300x uses.

[EuropeanAM]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by heavybullet &raquo;</TD></TR><TR><TD CLASS="quote">ql77pp is better than ql77cc with these mods imo its what 300x uses.</TD></TR></TABLE>

Interesting point.... however, the QL77PP would be designed for use with the 300X fuel system and porting (which this modified engine does NOT have).

I would recommend ONLY the QL77CC.

Guys: Richard has spent a LOT of time, and a LOT of money working on and experimenting with these things. He's proven what "does and does not" work well, and has been very kind to share with us his experiences!

Richard: THANK YOU for your contribution, and for sharing!

[hdbass]

is the 2004 250 efi the same as a xb ???

[kllr bee]

Years ago I spent several hours on the phone with Mercury racing R&D guys and their firm belief was to run QL77CC plugs. They tried several plugs on water and on dyno and thoroughly convinced me that these were the plugs to use on the 3 liter. All I can say is use the plugs you feel comfortable using, just speaking from personal experiences.
As for the 2004 250 EFI. It is not the same motor as the motor I speak of. It uses the updraft intake with a single computer. Simon motorsports can reprogram your computer and offers a larger intake butterfly for your specific motor. You could do those 2 mods and have your heads cut and wake that motor up pretty good. Call Eric at Simon Motorsports , he is a very nice guy and is always willing to help out when he can.
Richard


Modified by kllr bee at 3:45 AM 12/14/2009

[esdbass]

Richard: I was wondering if you had tried using the Hydro Tec 3 L tuner and what were the results in comparison to the 250 XS tuner you are using?

[heavybullet]

i guess you need do a little more research

[kllr bee]

Personally I feel that Hydrotech is still learning the Mercury motors. I will wait till I see some more numbers before I hop on that boat. I want good tuner performance but I have learned by trial and HASTLE that a quieter motor gives you more fun time and less inspections. Also a 2 stroke needs a certain amount of backpressure to hold the intake fuel/air mixture in the combustion chamber. Remember that the exhaust and intake ports are open at the same time, needs to breathe out the same amount it breathes in. That's why tuners are mainly all the same length. In motocross the 2 strokes carry an exhaust valve that limits the exhaust with adjustable spring tension on the valve for low end and top end power. Things like this would be difficult at best to be incorporated into an outboard application. I could go on and on about this, just saying I am happy with current tuner. FOR NOW!!!!!
Richard

[esdbass]

Richard: Thank you for your reply so can you elaborate a little more on what tuners and what mods to the tuner you HAVE tried? I assume you have NOT run the Hydro Tec 3 L tuner yet?

[Oldgeezer]

Hi Richard. Thanks for taking the time to detail what you have found that works for XB mods. At one time, you had indicated that the heads should be cut to 61 CC and 59 CC respectively. Here is what you had previously indicated. "I use cnc cut 300 heads that are 59 cc port and 61 cc starboard.If you do a compression check you will find that the 3.0 liter has more compression on the starboard side.with the heads cut different everything balances out on all 6cylinders." Would you still recommend this or go with the 61CC on both starboard and port? Thanks again for all of the information.

[kllr bee]

On the 225/300 blocks those cuts did even up the compression. When I went to the XB block the motor had a knock. Went to both at 61 cc and it went away. Also on the XB the compression numbers were even on both banks.I think now 61 cc is about tha max for safe operation. One of those trial and error things.
As for the tuners, I have cut the tuner housing and horns off one(load as hell with alot of topend and no hole shot at all). I took a 300 tuner and tuner housing and made a 3 inch hole in the back/bottom of the tuner housing(outstanding sound but only fair hole shot). XB tuner and housing(quiet and good hole shot). 250XS tuner and housing( good hole shot and and a good tone running down the river). That's why I am running what I am. Never tried a hydrotech though.

This is what modding a motor is about. You try something and if it works you stick with it if not you go another route. I'm just trying to help by telling what has and has not worked for me.

Richard

[esdbass]

Richard: Thanks for the info. If you can get one of the Hydro Tec tuners to try I have not heard anyone say that on an EFI 3 L it hasn't been awesome. Kurt and Brent are both running one and that they are VERY happy with the results

[492slayer]

In regards to the plugs on the 3.0L EFI's, Eric Simon told me to run only the QL77CC plugs. They were designed for these particular motors

[biggerbass]

with the promax 300 ign computer being more aggressive...wouldn't you think that's why the 300s blow up more often then the 250xbs. just noticed it when kllbee mentioned it. or what is the real problem why the promax 300s blow abundantly???

looking to upgrade slightly on my 250xb, but don't want to compromise too much reliability.

I specialize in automotive EFI tuning on our in-house auto chassis dyno and with aggressive timing it cracks/melts pistons and/or valves. I've seen a few blown promax300s and pistons look like detonation caused it via aggressive timing. Thru the years maybe it kills the pistons. Could it be the 300 ign computer or is something else.

should i even think about using the 300ign computer on my xb?

[kllr bee]

The 300 ignition ECU does 2 things. It gives you 2 degees more timing and raises the limiter to 6450 instead of 6250 on XB. Most blown motors I see have had injector failures or oiler failure. How many 3 liters have you seen with multiple hole failures. This is what I would think detonation would cause. I build and regularly check my own motors and in over 7 years I have never had a problem with this setup. I do however rering and replace bearings every 3 years for reliability sake because I fish 1 to 3 times a week year round. Imagine this, what would your boat run if it gained 200 rpm's top end
Richard

[--20ccbullet--]

Richard: I have a 3 liter 225 Carb. motor, pre mix oil that lost #5 piston. I rulled out fuel injectors and oil failure. What do you think?

[EuropeanAM]

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by --20ccbullet-- &raquo;</TD></TR><TR><TD CLASS="quote">Richard: I have a 3 liter 225 Carb. motor, pre mix oil that lost #5 piston. I rulled out fuel injectors and oil failure. What do you think? </TD></TR></TABLE>

Welcome to BBC!

I'm not Richard... but I'll throw out a strong possibility for you!

Single-cylinder failures (especially the BOTTOM cylinder) that are not caused by oil or fuel delivery, can often be traced to TEMPERATURE related events/failures. Common possibilities include "lack of proper warm up" and/or a thermostat that is sticking open, and preventing that bank of cylinders from coming up to operating temperature.

Often referred to as "cold-seizure".

[kllr bee]

Other causes could be worn cylinder hooking a ring. How many hours on this motor. Broken reed would be a likely candidate also. I would check the reeds. If they are steel they can tear a motor up good. First thing I would recommend replacing on any motor. Carbon fiber reeds can be digested by a motor alot easier than steel.
Richard

[Down Under]

Richard,

Firstly, great info, i have gained lots from your posts over the past year or so - thankyou.

I have a 1996 225efi with:

PM heads
4 hole intake
MAD Reedplate
TDR reeds
Simon poppet diverter
And i took your advice and "Modded" my exhaust similar to that on the PM / X motor.
My question is - i have gained a mountain of holeshot and midrange, but topend appears to be no better, i have had the ign and fuel ECU changed, but i believe it was only to raise the limiter to 6750, this was done by Rapair.
Do i need more timing?
Could it be the TPI? -
what should i be setting this to, can you run me thorugh how to set it correctly?.

[Down Under]

Don,

Could you kindly PM me with a price to replace my TPI just incase mines found to be faulty.

I set in via timing light at the moment, -1 degree at idle, and about -14degrees at 3000rpm. Is this right?

After running the boat, come back tot he ramp and check it and it has maybe moved to +1 and -10 degrees.

Your thoughts / input are also very much appreciated.