88 xp150

[jdramsey]

I have a 1988 XP150 on a 19' Norris Craft and was wanting to know if there were any cheap mods that could be done to get more power out of those motors?

[EMDSAPMGR]

This XP version of the 150 already has some significant improvements from the factory. It is equipped with decent high compression heads, and large carbs. You can tweak it by adding some bolt-on parts. The early small bore 235 heads will add about 10# compression. A set of intake filler blocks 322722 will add 5-8 hp, but like the 235 heads, are NLA and hard to find. A set of compsite reeds will improve idling and midrange, maybe even add 100 rpm on top. If you want to tear it down, you can square the intake and exhaust ports, effectively increasing the rpm breathing capability/range on top end. Adding the 235 bubble back exhaust is a machine shop job. If this engine has the plastic carb bowls, I'd replace them soon-with the older aluminum ones. They are not structurally rigid and will warp with age. If they warp, they can leak gas-worse they can cause internal air leaks which can cause the engine to run lean.

[jdramsey]

Thanks for the info. I may just end up buying an older Mercury or Yamaha. It seems like I can find parts alot easier for these motors than the Evinrude.

[ChrisCarsonMarine]

we have the filler blocks,glass reeds ,and aluminum carbs,although i personally worry about the carbs,just dont overtighten the bowls,better go up 2 jet sizes on the mains....keep it,it's a great motor,chris

[jdramsey]

If i went with the filler blocks, reeds and carbs, what kind of numbers should I expect out of the motor?

[ChrisCarsonMarine]

It would be poor judgement on my part to forecast hp gains but acceleration and midrange should be greatly improved with reeds,filler blocks and a little more compression.The carb change was not for performance,but design improvement,I think.You may see topend gains as well,some do some don't,but either way you'll get there noticeably faster,chris

[jdramsey]

Right now the low to mid range is pretty good, its the top end that seems to be lacking. It has a 24 mercury prop and turning 5300. Haven't gotten a GPS reading on it, but it feels to be in the mid 60's. Is there anyway to gain some compression without putting new heads/having them milled? I'd like to get this boat into the mid 70's, do you think this is expecting to much?

[wrechin2]

Problem with the heads are combustion chamber designs (shapes). I have heard of people taking off .050 and being ok. You can measure clearance with .100 solder by placing in the spark plug hole far enough to the side to be about 3/4 across the piston ( left and right) and rotate the engine. (do each side to determine the least side) This will smash the solder, then you measure it and this will determine squish band. (clearance between head and piston) .040 is the least you want. I have milled heads and simply bolted on without head gaskets and rotated to see if they hit. If not I mill off .003 then test again. The .053 head gasket will raise it up past the "SAFE" .040 clearance mark. Compression is the best bang for your buck. But goes with jetting changes and 93 octane fuel.


Cudo's Chris!!! I love the fact you didn't take a "GUESS" what the increases should be. But that there will be a increase.

[jdramsey]

If I have the heads milled, and the other things that were mentioned done, will that effect the reliability of the engine?

[ChrisCarsonMarine]

jd,your motor uses the same crank,rods,pistons,and lower unit as any crossflow v6 up to the old 235hp.It is way overbuilt,and just about bullet proof if it is in good condition.You can extract plenty more hp without stressing it,just dont overtime it,or run too lean,chris

[wrechin2]

Too high of timing is it's enemy. I like 24* even though they were 30* from factory.... Reliability is how you treat it. If every time you run it is on the floor for miles on end, even on a stock engine, it will eventually take its toll. Just because you have the power don't mean you have to use it. I have had modified engines last for years with no problems, but they were ran smart.

[jdramsey]

Thanks for the info. So I guess I need to start looking for heads or modifying mine? Chris, can you do this work in your shop?

[ChrisCarsonMarine]

anything you would like,give a call tomorrow 305 394 3354,chris

[wrechin2]

Make sure you get a set of reeds from Chris also.... Don't kill your engine over a broken reed!!!!

[jdramsey]

Reeds are the first thing I plan on doing. I'm almost positive the engine is bone stock and hopefully they will help smooth out the idling. One more thing, what RPM's should this motor be turning?

[wrechin2]

It has a 5800 RPM limiter. Anything up to there is fine.

[stratos179]

Do you still carry the xp150 intake fillers and reeds? if so could you call text or email me [email protected] 843 934 9825

[mn808gade]

the plastic carb bowls were supercieded(?) june 2012 to orig. style alum. same part number,same price.intermedit jets have to be changed to the other style,theres a explanition sheet packed with the part.i have changed four motors over to alum bowls this summer.dealers have info on jet changes.-th

[ChrisCarsonMarine]

We stock he reeds and stuffers,Chris

[EMDSAPMGR]

That engine in stock form will make good hp up to 5700, 5800. At that point the way the porting is-you run out of breating capability. You could port the intake and exhaust ports to change the operating range to make it higher.-maybe up to 5900 or 6000 with a stock flywheel. I'd be looking for a set of the old 1979 small bore 235 high compression heads. Theywill really wake up the engine. 323872/873. Compression should get up to around 120+. You would have to dial back the timing-30 degrees is too much with those heads.

[stratos179]

That engine in stock form will make good hp up to 5700, 5800. At that point the way the porting is-you run out of breating capability. You could port the intake and exhaust ports to change the operating range to make it higher.-maybe up to 5900 or 6000 with a stock flywheel. I'd be looking for a set of the old 1979 small bore 235 high compression heads. Theywill really wake up the engine. 323872/873. Compression should get up to around 120+. You would have to dial back the timing-30 degrees is too much with those heads.[/QUOTE]

Good to finally hear there are still guys out there squeezing some hp out of these old cross flows. I've looked [almost] everywhere and can't find a whole lot of info on them. I have a 1986 xp150 on the back of a 1986 Stratos 179fs. It is not the lightest bass boat out there but it flies for what it is. swinging a turbo 24-c at 65 by gps last saturday. I'm assuming that's about all it's got but not sure what rpm's were. Forgot to look at the tach! Currently no jack plate and I'll measure the prop shaft to pad soon. I have a cmc manual 6" jackplate ready to go on and just installed a th marine hotfoot and cable. Really looking forward to getting the boat in the water again. I've heard 85# on all cylinders is good right? All were within 2.5# of 85. Let me know if there is anything you would recommend. I'm all ears as this is my 3rd boat and first that really hauls. It ain't no 80 mph but its fun as heck. Thanks for all yalls time. I'd also like to know some prices on reeds and stuffers if you got em chris. Thanks.

[ChrisCarsonMarine]

Reeds,stuffers,shipping to you...140.00,thanks,Chris

[EMDSAPMGR]

268079Make sure you optimize your setup. Get the engine as high on the transom as you can without running out of water pressure. Run a hi-rake stainless prop. You can modify the lower unit to run it higher. One simple way is to fill the top hole of the 4 water inlet holes.

[stratos179]

268079Make sure you optimize your setup. Get the engine as high on the transom as you can without running out of water pressure. Run a hi-rake stainless prop. You can modify the lower unit to run it higher. One simple way is to fill the top hole of the 4 water inlet holes.

I am in the process of jacking up the motor. i had not heard of filling the top holes. how is the best way to do that? i am always amazed at the knowledge on here. i have building small block chevy engines for a few years with my dad but never a boat motor. i am now addicted to the adrenaline and would like to someday be a part of the 100 club! (mph) but for now the goal is 70. thanks again.

[EMDSAPMGR]

Look for a product called Marine Tex.

[stratos179]

Look for a product called Marine Tex.

Ok i can get some marine tex easily. You just cover the top holes. its open inside lime a plenum right? just tryin to figure out y covering top hole helps water pressure. does it just minimize chance of sucking in air?

[58Evinrude]

That's right.

[bruzercomp81]

That engine in stock form will make good hp up to 5700, 5800. At that point the way the porting is-you run out of breating capability. You could port the intake and exhaust ports to change the operating range to make it higher.-maybe up to 5900 or 6000 with a stock flywheel. I'd be looking for a set of the old 1979 small bore 235 high compression heads. Theywill really wake up the engine. 323872/873. Compression should get up to around 120+. You would have to dial back the timing-30 degrees is too much with those heads.

Would you have to run race gas on a flat back crossflow with 120+ lbs compression though?