Swap GT heads on Johnson 150

[denlou]

I have a 1986 Johnson 150 TLCDC and was wondering would I gain anything by swapping GT heads onto it ?

Thanks
Dennis

 

[denlou]

Re: Swap GT heads on Johnson 150

bump

 

[emdsapmgr]

Re: Swap GT heads on Johnson 150

Typically the GT/XP heads are higher compression than a stock 150. Along with larger carbs, the XP/GT engines made about 10% more hp than a normal run-of-the-mill 150, or close to 165 hp. Yes, they will swap. You may need to bump up the high speed jets a size or two if you see a significant compression increase. If you really want to bump the compression, check salvage yards for these heads: 1978/79 150-200 (about 110 lbs) or 1978/1979 235 (about 120 lbs) heads.

 

[Faztbullet]

Re: Swap GT heads on Johnson 150

was wondering would I gain anything by swapping GT heads onto it ?

Other than increased expense from jets and fuel usage ...maybe a 1-3 mph increase in top end speed depending on hull and setup.

 

[concept10]

Re: Swap GT heads on Johnson 150

I'm curious: Is there some downside to increasing your compression by changing your heads? I guess I'm skeptical on increasing compression on an older engine (because of unknowns).

 

[emdsapmgr]

Re: Swap GT heads on Johnson 150

You will need to run 91 octane fuel.

 

[denlou]

Re: Swap GT heads on Johnson 150

Thanks for the replies,
Having to use 91 octane is a deal killer, gas is expensive enough.
I had thought they might offer better efficiency and lower gas consumption.
Thanks again

Dennis

 

[emdsapmgr]

Re: Swap GT heads on Johnson 150

These crossflows were never known to be fuel efficient. The larger 235 hp V6 model was nicknamed the twothirstyfive-for a reason.