what is up with this compression 200gt

[dannyman3]

i have a 1990 200 gt i going to rebuild is the compression in all 6 cyl,s are 70 psi that seams low to me but they are all the same has me stumped it runs good this winter im gonna rebuild it how can i turn it in to a 250 what do i need will the carbs and all that stuff work can i bore stroke it to make something great also what do i do to get lot more compression i wont it to out run my buddys merc lol

 

[coolguy147]

Re: what do ineed to do to make 250hp

Re: what do ineed to do to make 250hp

on the compression we suggest a good decarb it will surely raise the psi.


ur better of buying a 250hp motor then trying to get 50hp out of ur outboard

 

[kenmyfam]

Re: what do ineed to do to make 250hp

Re: what do ineed to do to make 250hp

Get a 250hp outboard. That will get you the extra HP.
Regarding the compression, try checking it with a different gauge. All gauges are not created equal in my experience. The fact that all the readings are the same is a good sign.
My feelings on "tuning" a 2 stroke motor for a 25% increase in HP from original specs is that even if possible you will lose a whole lot in reliability and durability. Not a good idea if you are stranded on the water somewhere. There again your buddy may tow you in after you have outrun him.

 

[dannyman3]

what is up with this compression 200gt

i have a 1990 200 gt that all 6 cyl,s are 70 psi ive done decarb ive soaked cyl,s marvin oil nothing changed it runs good its on a 20 ft heavy boat runs 64mph turns 6100 rpms ive seen other johnson motors with this low compression deal whats up does anyone have info hard to bleave all are bad and same psi runs good other than gas hog hope someone has info on this ive asked everone and nothing surley someone knows something

 

[ezeke]

Re: what do ineed to do to make 250hp

Re: what do ineed to do to make 250hp

If you want to take the time to read the many excellent threads with performance advice on the 200HP looper motors, go to advanced search, enter "200* Looper" and search for the user name "Dhadley".

 

[itsaboattime]

Re: what is up with this compression 200gt

I have had compression guages give false readings before. I would try a different guage. let us know what u find.

If it pushes the boat that fast, turning those RPMs, I would believe the compression is good.

 

[kenmyfam]

Re: what is up with this compression 200gt

With those performance figures I would invest in a second compression gauge of a different make to compare.

 

[Faztbullet]

Re: what do ineed to do to make 250hp

Re: what do ineed to do to make 250hp

It can be done with your block but the 93 and newer blocks are better as they are fingerported. My Junkrude started as a 1999 200/225 engine block. I had all sleeves removed and I die grinded out the casting and flashing in the intake transfer ports and smoothed the transitions as the castings suck at lining up to sleeves. Had new sleeves installed and exhaust ports raised to 225 HO spec's, water mod's done to block, no exhaust relief holes, running a set of trued 1987 2.7 heads
with water passages modified for 3.0, 1989 300hp carb bodys and throttle plates, 1990 200hp throttle plates to make it idle, 30 idle jet ,22 midrange,drilled out and tapped vent bowl to 1/4 -20 and installed jet drilled to 104 size to richen midrange cruise and 81D high speed jets, CDI all digital ignition system,20ft Javlin DC, lighting gearcase,14 inch set back jack plate,Dyson 28pitch prop, 5800 rpm GPS @73.8mph full load, best run empty 81.3mph GPS. Thinking about going to Brucattos fuel injection for the loopers as gas is killing me(89 octane). You will spend around $ 2800-3500 to have done right,but if you got a "pig" hull you are just throwning money away.
To go fast you need (1)$$$$(2) Performance hull (3) HP (4) Setup and tuning of engine to hull

 

[Faztbullet]

Re: what is up with this compression 200gt

You aint going to get much more as its the heads that give it low compression. The 92 and back had bigger cc chamber thus low static(cranking) compression, the compression will increase as engine runs to around 90-100psi. The new heads are close to same cc but all combustion is sort of aimed to center of piston. Below are pic's of newer and older head as you have.(new ones are first 3 pic old one are last 2)

 

[freddyray21]

Re: what do ineed to do to make 250hp

Re: what do ineed to do to make 250hp

I would check with another gauge as indicated. Not sure on that motor, but some of the motors are low compression motors so yours may be fine. If it is running fine then leave it be is my motto. If you want 250 it will be cheaper and easier to buy a 250.

 

[freddyray21]

Re: what is up with this compression 200gt

it's not good to run two different threads on basically the same subject.

 

[tashasdaddy]

Re: what is up with this compression 200gt

i have merged you threads, it waste valuable to of helpers to have two theards.

 

[JB]

Re: what is up with this compression 200gt

Those big V6s often test at 60-70psi when there is nothing wrong with them. Your engine is not broke, don't fix it.