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Thread: 89 johnson gt 175
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06-08-2006, 07:25 PM #1Junior Member
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89 johnson gt 175
what kind of mods to get 200 hp out of it,
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06-08-2006, 09:08 PM #2
I think they make close to that anyway. You need the good XP/GT heads, reeds, filler blocks, and big carbs.
You will have to run super unleaded and set your timing back to 24 degree's.
The heads make a huge difference, I put them on my engine and picked up 6 mph with the above mentioned changes. To bad it lost a cylinder.
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06-09-2006, 02:55 AM #3
You need to find a set of early big bore 235 heads. You can use split hose for the intake stuffers... Is that what you meant LJ? The 175 should come with the fillers, along with the exhaust bubble or bell as I call it. It should have the big carbs, but the mid 80's carbs are better.
I run 125 cranking PSI with a 1980 235 (yours is a detuned of this model) V stacks, Gold flywheel with ONLY 93 or better octane... with 26 total advance at 4500 rpm on a test wheel.Last edited by Forkin' Crazy; 06-09-2006 at 03:01 AM.
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06-09-2006, 04:44 AM #46000 RPM
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The engine is basically a detuned 2.6. While the 175 does have the big carbs, it does not come with the filler blocks, part # 322722. They NLA but are around and a cheap and a great bolt-on perf. part. Compsite reeds were stock on the 2.6 and a good addition for any engine. You will pickup a little from both of these mods. Changing the heads to a set of 325638/639 should get you to the 200 you are after. You may need to rejet your carbs up slightly for them. With their addition, follow lockjaw's advice on fuel/timing. The exhaust tuning megaphone is different also, but probably hard to find and a pain to install.
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06-09-2006, 07:54 AM #5
Yes I was talking about the intake stuffers. I have an extra set, 40 bucks plus shipping and they are yours.
The GT175 doesn't come with them. I went up 2 sizes on the high speed jet and 4 on the mids, and richened the idle 5 sizes for the reeds. Those mods with the heads made a big difference especially in acceleration.
It would have been interesting to see what a non water logged boat would have seen as far as improvements, but the 6 mph I picked up sure was nice.
If you want to do that, I would start working on getting the jets, that is what took the longest for me, they are getting harder to find.
I have a GT175 with all the stuff done, but it has a dead cylinder, I might part it out, which would get you gone through carbs, properly jetted, at least where I said they were, reeds, filler blocks etc. I cannot vouch for the heads, I have to check the one with a down cylinder, but I have 2 good port side ones.
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06-09-2006, 11:41 AM #6
Seems like I hear an echo here.
There also seems to be a conflict of terms... stuffers or fillers.
When I say intake stuffers I am refering to the rubber pieces that go beside the reed cages.
The filler blocks I am refering to are in the exhaust chest and should be already there.
You can run what you want on the timing. 24 I would call conservative, but do what you feel comfortable with.
Composite reeds will do nothing measureable on top end horsepower.
racer is the one that told me about using the hose for the stuffers.. that might save you some $$$$. He is also the one recomending 26* timing.