Changed my crossflow heads, standard to 135hp heads, Wauwwww

[JohnsonV4]

Motor is a 90hp 1991 crossflow. Standard carbs. Intake stuffers.
What a difference. Gained 5 psi cold pressure, but man, it gained 500 rmps on top.
With the same prop, from 6100 to 6600. Unbelievable.

Ok, cold starting is a little tough, but warmed up, she is turning 800rpms ok.

Just to let you guys know.
Best mod i did.
And these are not even the best heads around.

[olboatman]

Being my first OMC V4----- Are the 135 heads an upgrade for my 84 140. Gettin ready to go thru her in the spring. Thanks in advance for any info. Gary

[thornl01]

Hate to tell you, but neither of those heads are 135's

Must be early 140's.

135 's did not have coil mounting boss.

[1BadAction]

Being my first OMC V4----- Are the 135 heads an upgrade for my 84 140. Gettin ready to go thru her in the spring. Thanks in advance for any info. Gary

The 1973 135 heads are the ones you want. After that year the chambers are bigger and don't have as much compression.

[racer]

Heads pictured appear to be 115 not 135, the exhaust side is much wider on the 135 and would bump compression more than 5 psi. The pictured heads are very similar to later 140 heads. Also 135 heads did not have coil mounts.

[JohnsonV4]

Aha, the info on here is terrific. So these are 115 heads. I am a rookie concerning crossflows.
They labeled 326502/3
The gain in rpms is unbelievable.
I blueprinted this motor, clearing all the intake edges.
They do produce a lot more heat though.
They just spool so much better now, it is crazy.

[71V153]

They labeled 326502/3

Those are newer 140 heads. I have an '83 with the same part #(s).

Someone mentioned '73, but I think the '76's were the bad boys.

Fer sure hi-comp heads'll wake up any xflow. What kinda exhaust?

Can you post a pic?

[71V153]

Being my first OMC V4----- Are the 135 heads an upgrade for my 84 140. Gettin ready to go thru her in the spring. Thanks in advance for any info. Gary

Your 140 has hi-comp heads. If I'm not mistaken '84 was the year OMC upped from crank rated to prop rated hp. So y'oughta have most of the good stuff already.

Reed stuffers, bubble butt exhaust, bigger carbs/jets, etc.

[powerabout]

when the 140 went to prop rated it became a 115 and the comp was lowered yet again
Nothing went as well as the first 140 ( with its taller gear ratio as well )

[wired247]

Your 140 has hi-comp heads. If I'm not mistaken '84 was the year OMC upped from crank rated to prop rated hp. So y'oughta have most of the good stuff already.

Reed stuffers, bubble butt exhaust, bigger carbs/jets, etc.

84 was the last year of the 140. Following year got the lowered compression and slightly smaller carbs ( 1 3/8" to 1 3/16" ) and they called it a 115. . Intake stufffers were all over the place. Ive seen them in box stock early 80's 90 HP motors.

[EMDSAPMGR]

326503 heads first came out on the 1981 140. Decent heads, but the guys are correct- 73 135 heads (and later 74/75) are some of the highest production compression heads in the V4 crossflow family. Johnson, did you do any carb re-jetting when you switched to those 140 heads? Go to 92 octane fuel? Do anything with the timing?

[1BadAction]

the guys are correct- 73 135 heads (and later 74/75) are some of the highest production compression heads in the V4 crossflow family.

Exactly, my 73 135 had over 150 psi after a bone stock re-ring, and that was before it was even fired for the first time. The downfall is you can burn them down if you're not careful, even on 93. The throttle response is wicked, though.

[JohnsonV4]

Ok, Great.
So '83 140 heads.
And to answer Emdsapmgr: Timing is at 24. No jet change, standard 56's. Exhaust is completely standard for a 90hp from 1991. So, gonna watch the plugs carefully for any alu flakes.
But do you guys reccon i have to enlarger the mainjets. I choked it a few times on wot, and it did not go any faster with the extra fuel. So my feelings says i can keep it like this. Your opinions please?
Could not find bubble back exhaust on the www yet.
So, it just revved to the 6600, wind in the back, regarding the 6100 it previously did.

[EMDSAPMGR]

If it were mine, with the high compression heads, I'd be running 92 premium and increase the main jets slightly, testing the plugs as I went up. Start with one size larger. When you run it and you sense it is overfueling, then back down the jet size one size. DON'T REAM THE JETS OUT, go with new only. When the engine is jetted normally, and you push in on the choke, it should bog the engine slightly-that's the point of overfueling. Right now, it's still taking the extra fuel (no bogging,) so it's slightly lean at WOT. These engines love to run lean-make some of their best hp, but that's the problem- unless you check the plugs and piston crowns, as you say you will do.

[JohnsonV4]

Emdsapmgr,
being a mx-man, i don't get scared of 130psi values.
But yes, with choke it does not bog down, it does that mid-throttle only, so you could say i cld go up a notch with the jets.
Will monitor the plugs and pistons.
This is a run-about boat, used for touring/fishing. Won't see high rpms stretches of more than 20 seconds.
This is the combination.