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Johnson 90 to 140 conversion.

Bill/Wired,

Is there a down side to putting the 140 heads on my 88 Special?

The motor is aging (1994) I just don't want to add the straw that breaks it's back. Ya know!?

Thanks.

HD
 
hotdaddy27 said:
Bill/Wired,

Is there a down side to putting the 140 heads on my 88 Special?

The motor is aging (1994) I just don't want to add the straw that breaks it's back. Ya know!?

Thanks.

HD
Click to expand...


You'd need premium gas . Probably not but its insurance more than anything else. $3 more a tankful. I did pick up 2 MPH with the 140 heads. Lot snappier on the lower end too.
 
wired said:
You'd need premium gas . Probably not but its insurance more than anything else. $3 more a tankful. I did pick up 2 MPH with the 140 heads. Lot snappier on the lower end too.
Click to expand...

Doesn't sound like much of a down side!

If I had to guess, it sounds like you got a solid 5-10HP out of the mod to gain that much on the top end (where it is the hardest to gain). I am more concerned with the low end, so I am happy to hear that it was a "lot snappier"!

Thanks again.

HD
 
Well the compression will always make it snappier, and unless you gain 4 or 500 rpm you didn't gain any top end, but, anytime you make a big gain down low, just go up 2" of pitch and use the gain you made correctly
 
I refer back to this thread often, so I figured I would bring it up front.

Update: I sold the "88 Special" and now have a 1995 "90" and also picked up a 1979 "115" with the bubble back exhaust.

I am not sure how interchangable these units are, but my plan right now is to leave the "90" on my deck boat and work on the 140 over the winter.

Does anyone know what the compression should be on a 1979 Johnson 115?

Also, will the 1979 powerhead bolt on to the 1995 mid section?

Thanks.

HD
 
The 79 motor will bolt on the 95 mid section.


Your compression will be determined by the condition of the motor. 130 ish for a good one.
 
wired said:
The 79 motor will bolt on the 95 mid section.


Your compression will be determined by the condition of the motor. 130 ish for a good one.
Click to expand...

Bill Gohr said:
you cannot just drop a 79 on a 95, while the base gasket is the same the drive shafts and crankshaft lengths are different and that will cause issues, the cranks and the shafts must stay together
Click to expand...


This is good info!

Let me give you the big picture...

I have a complete 1979 "115", but it does not have power trim. So based on the above, I can use my "115" power head on my "90" mid w/ power trim and use the l/u from my "115".

Basically, I would just be swapping the mids.

Does that make sense?

Thanks.

HD
 
So besides the tighter heads, is there anything else I need to convert the "115" to a "140"?

It has the bubble back exhaust already.

The "115" is a 1979 block.

Thanks.

HD
 
I plan on using "140" head #s 328624-1 and 329745. I think they are from the 1986/1987 era.

Any thoughts?

Thanks.

HD
 
well those arent 140 head numbers, and we didnt have a 115 with the bubble on it in 79 so, what is it you have? what are the head numbers,
 
Bill Gohr said:
well those arent 140 head numbers, and we didnt have a 115 with the bubble on it in 79 so, what is it you have? what are the head numbers,
Click to expand...

This could be interesting...

The head numbers on my motor are 320370 and same with -1 (I think)?

It definitely has the bubble exhaust. I will take some pics when I get home.

The head numbers I listed were some that I found for sale...they aren't 140?

Got any of the real "tight" 135 heads laying around from the mid 70's Bill?

Thanks.
 
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