1988 88SPL vs 1973 Merc 150 Inline 6

[sycamore]

I currently have a 1988 88SPL on a 20' Sea Ark Jon Boat and it runs well, about 41 MPH with a 19 pitch SS prop. I do have at my disposal a 1973 Merc 150 (my dads, it is in good shape). I know the lower unit on my 88SPL is 2:1, does anyone know what the ratio is on the 150 Merc? Engine displacement on the 88 is about 97 in^2, and I think 99 on the Merc, so not much difference there. I think the Merc is rated at the crank and the 88SPL at the prop, so I may not gain as much as it seems. Does anyone have a preference or any comments? I could probably pull a higher pitch prop, but I am not sure of the lower unit gearing on the Merc.

 

[Laddies]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

If thats a well designed hull that Mercury will run the butt off that rude!

 

[sycamore]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

The hull is 1/8" aluminum, rated for 130 HP in basic version, 140 HP in dressed up heavy version.

 

[walleyehed]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Your 88spl is 99 cube...

 

[ledgefinder]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

First, with the 19" prop, you're not getting all you can from the 88. You're not letting it rev enough. Try an 17" when you get a chance - should come out of the hole better, and get you a couple more miles per hour.<br /><br />Second, the 150 is equivalent to the post-1986 Merc 115(virtually same port timing per Sam Tellig).<br /><br />In general, I'd agree with Laddies (older equivalent HP Mercs stomp on the OMCs). However, IMHO that only applies up until 1986. tThe OMC V4s from 1986 on up are stout, per HP rating (the 88 is roughly same as pre-1986 115hp). Further, the Merc 150 is pretty highly-tuned, and unless mechanically solid (clean carbs, tuned right, etc.) is nowhere near as reliable as an 88. I doubt any larger outboard has a better reputation than the 88.

 

[ledgefinder]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

I think all the Merc tower 6's are 2:1.

 

[Dhadley]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

I guess I missed the part about what rpms youre capable of with the V4 and the 19" prop. Assuming the Sea Ark is an aluminum hull, the 19 sounds like a good place to start.

 

[jimmbo]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Most inline 6s were 2:1, however some the pre 1973 115hp were 1.78:1. The 1973 150 was 2:1. Rev range for a 1973 150hp was 4800-5800. The porting on this engine is more radical than the later 115s. While it does idle nice and smoothly, it does tend to be a little eratic between 2000 and 4000 rpm. Once it hits 4000 things will happen fast, it will pull hard to 6000 rpm.

 

[WillyBWright]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

And it never developed 150Hp ... ever! On it's best day 135 would be about max. 150Hp? BAH!!! Wimpiest 150 ever built! Nonetheless, that boat isn't rated for 150. It makes these arguments kinda pointless, doesn't it?

 

[phatmanmike]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

88hp is more reliable, by leaps and bounds<br />150 merc, or almost ANY inline 6 merc, will blow the doors off that damned V4<br /><br /><br />im almost in the same boat. i HAD a 1976 inline 6 1150 merc and now i just bought a 1976 115hp v4 johnson<br /><br />same boat, same weight, same everything. gimme about a month or soo and ill tell you what the reaL DIFFERences are.<br /><br />i know the inline merc sucked down fuel like no tomorow. well see how the v4 does.<br /><br />i do know one thing, the inline merc had a "coolness" factor no OMC could touch!!!!!

 

[reeldutch]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

try to replace the pistons in a i6 and then replace them in a v4 then come back and tell me wich is the coolest moter.<br />the i6 90hp that i have doesnt need tstats probebly thats why it guzzels gas.<br /><br />reeldutch

 

[sycamore]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Thanks for all the input. I think I'll hold off on the swap until "myoutboards" does his comparison. In 1986 I melted the top of piston #3 on the Merc 150. We put an oversized in #3 and new rings on everything else. I agree the Merc idles better than the 88SPL, I would also say it starts easier, I also agree that there is more roughness between 2000-4000 RPM and that at full throttle it would empty a 6 gallon tank in 15 minutes. My 88 SPL runs a long time on 6 gallons. I grew up on phantom black, I guess that's why I'm considering going back. (Sorry, couldn't resist.) I know there is more power there, I guess the only way I'd know how much is to put a couple more holes in the transom. I will run the 88SPL with my new tach this spring to make sure I'm getting everything out of it. Dhadley is correct that I should make sure that I have the RPM's.

 

[Laddies]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Willy Just Be Wrong Again

 

[walleyehed]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

I grew up on phantom black,

I'm sorry to hear that....<br />Now, I know the merc is rated at the crank, and the jonny at the prop, but the jonny wasn't all that far off when rated at the crank as compared to the prop now.<br />Both manufacturers had a "few" engines that were WAY out of spec on the 10% rule and were required to de-tune or re-rate. One of the first was the Johnson GT 150, alot of years ago...merc got their hands slapped with the 2.5L(a specific model of the 2.5L) just a couple of years ago because they wouldn't set a specific HP for the engine...that engine isn't even built any longer for the fact it was so dirty emission-wise.<br />Bla bla bla....<br />That V4 will do a much better job over-all, than that merc was ever capable of, it's been proven over and over.

 

[Dhadley]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Hummm...guess all those bad-ax in lines were hiding when we raced the V4 cf. The IL6's we raced aginst (beat) never showed me anything. <br /><br />And an in line idling on 4 sure isnt smooth. V4's are way smoother.

 

[ledgefinder]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Now we could REALLY light it up:<br /><br />"Difference between Evinrude & Johnson? When they come off the assembly line, if it starts on the first try, they paint it blue. Otherwise, white."<br /><br />- told by "a crusty old fart" who even a hurricanse couldn't put out of business

 

[jimmbo]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

The inlines didn't have t-stats cause they didn't need them. On outboards that have em, the T-stats only control the water temp at idle speeds, pressure valves open and allow more water to flow at speeds above idle. The reason for stats was to keep the engine block warmer to prevent fuel from condensing and puddling in the intake manifold. Inline Mercs didn't have an external manifold for the reeds. The carbs were bolted right on the crankcase and the reeds were on the bearing blocks. This method seemed to have less need to control engine temp at idle speeds. As for idling smoothness, my inline 6s even idled smoother firing only on 5 holes than any V4s myself or my father owned, even when they were firing on all 4

 

[Walker]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

I though Kiekhaefer was just being a wise-*** when he put the reeds in there.

 

[walleyehed]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

jimmbo, will the I6 idle continuously at 400-450 RPM for hours????

 

[jimmbo]

Re: 1988 88SPL vs 1973 Merc 150 Inline 6

Heck no! It makes for a very tiny crankcase which helps create higher compression in the crankcase thereby making the transfer of air/fuel to the combustion chamber a little more efficent than an engine which has a larger crankcase due to the reeds being on a manifold and a passage between them. The difference is small, but I'm sure it is one of the many reasons Kiekhaefer was able to pull lots of power out of relatively small engines