93 OMC 302 COBRA issue

[Twistedwake]

Hello I’m in need of some help. I cracked my motor last winter I guessed I’m not sure how but none the less. I have recently bought a 74 model 302 mercruser motor and I over hauled it and converted it over to a OMC motor I have used the same out drive I have always had. Same prop it is a 14 1/4 x 21. The issue is my last motor at WOT I was running about 5300 RPM’s my new motor a WOT will only run 3200RPM’s and also takes forever to plane out. With people in the boat I have moved weight around but it didn’t help I have to put everyone on the front of the boat to Finley ge lt it to plane out. But my last motor was kinda the same about planing out. What should I do? I’m sure that the WOT range is 5000 to 5300 RPM’s

 

[Scott Danforth]

way to many changes from the 93 motor to the 74 motor. compression ratio, heads, cam, you lost about 35-45hp by using a 1974 motor vs getting a proper 1993 mix of parts

your 1974 motor was 188hp rated at the crank
your 1993 motor was 215hp rated at the prop

 

[Twistedwake]

So am I looking at the propper RPM’s that this motor should run. 3200 rpms is what this motor should run if so I’m good with that and I’m good with the top speed it runs great it just doesn’t plane out fast enough what can I do

 

[Scott Danforth]

motor should run much higher RPM. however since your down on power you will have to drop your prop pitch down to get your RPM's back up.

 

[Twistedwake]

Thanks any recommendation on what size prop and should I go 3 plaid or 4 blade. Also I’m having trouble when I start trimming my motor up I start to porpoise real bad so I have to keep it trimmed down.

on a side note what would you all recommend on me doing to gain some more HP.

 

[Scott Danforth]

.

on a side note what would you all recommend on me doing to gain some more HP.

with the existing motor you have? depends on what you have for pistons as that may be the limiting factory, however better heads (many of the late 80's and early 90's ford 5.0's had GT40 heads. better cam to make use of the heads. the 93 would have used the 351 cam (hence the different firing order)

what did you do when you "overhauled it" as you stated in post #1?

best way for more power is to unbolt the 302 and bolt in a 351