150 Crossflow VS 150GT Crossflow

[LSaupe]

I have a 1984 150 V6 Johnson (J150TLCRD) which runs well, but I would like to bolt on some additional HP.

I picked up an Evinrude 150 GT powerhead (E150STLCOS).

Some questions, my understanding is that the blocks and pistons between these engines are the same. Is this correct?

Differences lie in the carburetors, reeds, heads and alternator circuit. Are there other differences?

The 150 GT powerhead has a bad hole, so I am planning on swapping over the carbs, reeds and heads. I don't need the additional alternator output.

What I find odd is that my straight 150 has a high speed timing value of 26 degrees BTC, but the intake cover on the GT calls for 34 degrees BTC? Does this sound right? If so, why so much difference? Does it make sense to increase the timing to 34 BTC on my straight 150 engine once I change over the heads, carbs and reeds (actually will be installing Boyesen reeds)?

Larry S.

[EMDSAPMGR]

The 1984 model year was unusual for the two 150 model types. This model year the actual blocks are different between the base 150 block and the 150S block. The 150S block is machined differently by the factory to have higher port timing (similar to the 2.6 that year) and has a higher rpm operating range, up to 5750 rpm, unike your base 150. The S models have the goodies. Larger throated carbs, different heads. The reeds/boxes are the same, so you don't need to pull the intake apart unless you decide to convert to composite reeds. If you do add the composites, you might as well add some older 200/235/2.6 intake filler blocks (322722-NLA)-they will add 5-8 hp. Some of the S models did run higher timing, 30 or better. That was as a result of the block porting, the heads and larger carbs which flow more fuel to cool the powerhead. If you just swap everything from the S engine to the base 150, it should work, however I'd be concerned about resetting the timing to 34 due to the block porting differenes. I'd probably leave the timing set where it is-(perhaps at 28.) I'd also run 92 octane fuel. The transfer of heads, carbs should improve your hp and performance, but the block will not breathe as well at high rpm's as the S block does. The other S differences are the vented 35 amp alternator system, the vented cowling with special cowling badging, stiffer lower engine mounts-which help with high speed steering. (You may want to consider transferring these mounts from the 150S mid section to your base 150, or transfer the base 150 powerhead to the 150S midsection.)

[LSaupe]

Thanks for the detailed reply. I messed up on the years a bit. The base 150 is an 84. The 150S is an 85. Not sure if that make a difference or not.

The case part number (on the BRP site) shows the 84 150 and 150S both as 0395017, but for 85 they show two case numbers for the 150S 0395729 (which is the same as used as the base 150 in 85), and also 0397381. The first is followed by 8510 and the second by 8520. Any idea what that designates?

I see a "150" stamped by my port #2 cylinder. Other than that I cant find the case part number on it. Where could I look to find this?

The S engine has one scuffed cylinder (starboard center - easy overbore), maybe it makes more sense to rebuild this S engine complete and drop it on. Suprisingly the S engine already had the intake stuffers installed.

I only have the S power head, but my current mid section does have both solid uppers and lower (old Land and Sea units).

[Riverratt]

Larry if you can swing it build the 150 Gt and try to get all you can out of and keep your 150 stock motor as a back up. The good thing about the crossflows are the pistons are not expensive. If you start transfering parts from one to the other trying to squeeze performance out of it and can soon end up with 2 blocks blown up and nothing to go boating with.

[EMDSAPMGR]

You are correct, both the 84 cases show the same part number. Guess I did not have my first cup of coffee this am...My guess is that the same holds true for the 85 blocks-probably identical, with same porting. Likely the 84 and 85 are direct replacements. My guess is that midyear 1985 they made a minor casting change to the block and had to take out another part number for it. Close observation on any V6 block will show that hp stamping from the factory machine shop. (See the pic.) That is the indication of the porting specs the machinist used when it was drilled. You may also find relevant information on the casting plug on the top of the block. (see pic of an 85 150S) Some years have the serial and model, though they seemed to discontinue this in the later 80's. If your block has the intake stuffers, you are ahead of the game. They don't show them for 84 and in 85, they were only on the 185, 185 and 235. That 150S block has more in common with the 175 than a 150, maybe that's why the stuffers are there. I am now puzzled as to why the 84 sales brochure would show the higher rpm operating range for the 150S, considering the porting is the same as a base 150. With larger carbs, I know it will breathe well up to 5800...