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is port height diffrent between a 150 vs 175 and 200 2.4Merc?

roadkill636

roadkill636

Member
After much searching im still at a loss of what makes the diffrent hp in a 150 175 and 200 hp Mercury 2.4L motor. Some say carbs and tuner but others say tuner wont do anything and carbs are basicky the same if the same W series. So what makes the diirent hp on these XR4 motors. Whats needed to get my 150 up to 200?
1988 Mariner Mag 2 2.4 L steel bore.150
 
The ports are different. Little higher on the 200. Exhaust chest is a little more open on the 200. Tuner is different. Carbs are different in as much as the jetting is different. 2 strokes are weird about their carbs and jetting and freeing up exhaust restrictions will lean things out. You can have the block decked and mill a corresponding amount from the pistons which effectively raises the ports and raises the power band. Depends how handy you are and if you have machinist friends. Or you can get in there and hand port the block as it is a steel sleeve motor which gives you some advantage over the 200 chrome bore PITA motors. That and a 200 tuner, mill the heads to 30-31 CC's, hand massage the exhaust chest a bit . Or you can bite the bullet and send it over to Rucks where you can get all the porting you need for around $600. If you have vertical reeds you need to shatcan those and the God awful vertical reed front end and pick up at least a 5 petal horizontal front half.


Its not just bolt ons

That or buy a 2.5 200 powerhead.
 
wired said:
The ports are different. Little higher on the 200. Exhaust chest is a little more open on the 200. Tuner is different. Carbs are different in as much as the jetting is different. 2 strokes are weird about their carbs and jetting and freeing up exhaust restrictions will lean things out. You can have the block decked and mill a corresponding amount from the pistons which effectively raises the ports and raises the power band. Depends how handy you are and if you have machinist friends. Or you can get in there and hand port the block as it is a steel sleeve motor which gives you some advantage over the 200 chrome bore PITA motors. That and a 200 tuner, mill the heads to 30-31 CC's, hand massage the exhaust chest a bit . Or you can bite the bullet and send it over to Rucks where you can get all the porting you need for around $600. If you have vertical reeds you need to shatcan those and the God awful vertical reed front end and pick up at least a 5 petal horizontal front hal

Its not just bolt ons

That or buy a 2.5 200 powerhead.
Click to expand...

Please tell me more, I am very interested to learn the difference in these motors. So its porting, jetting, exhaust, and reeds?
 
Lower ports in the 150. Vertical reeds on the XR4 that really arent conducive to making good power. The front half would need to get changed out to make real power. Same reed blocks on both. Some people prefer fiber reeds. I do but they really only make a difference at idle.

Jetting is going to be on a case by case basis and depends on the carbs. Some people will tell you to put 200 carbs on there which sort of makes sense as the carbs MAY have larger venturi if they are the right model but the jetting will be all wrong and it will be all wrong no matter what you do if you start doing other mods. You probably have to rejet if you do mods to the motor and you do that by checking the wash pattern on the pistons or the color of the plug insulator or electrode line. The 150 carbs will work most times just fine if rejetted to the motors needs.

The XR4 is still a piston port motor. Its more difficult to get it souped up than a similar 2.5 but with a little porting or port relocation and some higher compression, proper jetting, and shorter tuner you can do all right. Depends on how far you want to get into it.
 
Never understood what the logic was behind the vertical front. Maybe it created a vortex when having to change direction but think that would help anyway since air and fuel goes through the crank case.
 
Vertical reed front ends are one of those things that whenever I see one I think..."what the hell were they thinking?". I think it was a velocity concept. Works well at low RPM's but falls on its face later on. I get the same feeling when I see the reed cages in an inline. I guess any goofy idea will work but sometimes the straightforward approach works better for making big power.
 
I got me a horizonal front half and 7 peddle reeds and big bore wh5 or 20 carbs comming in the mail any day now. Im hearing that the 5 reeds mite be better . But I got this whole package at a great price. Its off an 80-81 2.4 225
 
I dont know. I hear the 5 petal reeds are better for low end power but I run 7 petal carson reeds in 280 cages and I'm up on plane in about 15 feet even with a 26 pitch chopper and going 60 MPH before I can look down.

Make sure you pull the locator pins from your block where it meets up with the front half.
 
Got the front half and carbs in the mail and the carbs turn out to be WH 20 ..... and 7 pedle reeds and cages and set the front half of the block onto my block and even snuged up the 6 big block bolts and no binding what so ever. But the carbs have .072 mains in them .. so I think I will be lookn for something a bit bigger to start out with. Anybody got some .080 or .088 or anywhere inbetween ya want to sell me?
 
The. Arbs I got are the large bore WH 20 and 7 peddle reeds and front half. I mocked up the fro t half with the locator pins IN and everything still spun very freely. Its going on a 750# Hydrostream Viking and with all the folks telling me diffrent ideas about using a 5 vs 7 peddle set up im leaning twards my 7 that I already have. Because this boat isnt going to be used for holeshot or pulling skiers. Hope im not dissapointed.
And the tuner is 8"-9" long
And I mis measured the ports. They are 1.650"
 
I see that 7 petal is bad on the bottom end thing thrown around a lot. Pretty much a bunch of crap IMHO. Better idea is to use a lower pitch prop like a 21-23 when pulling a skier and prop up when going fast. I have an EXTREMELY strong bottom end with my 2.5 7 petal motor.
 
Well.... after many weeks of grinding on the ports in the basement a few minutes at a time I finally have the intake ports at 1.52 and the exhaust and boosts at 2.12 hopefully it will put down some ponys to the prop.
 
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