what is the diffrence in powerheads

basspirate

Petty Officer 2nd Class
Joined
Apr 26, 2009
Messages
124
i have a 2000 johnson 130 that i might have to put a new powerhead on at the end of the season. compression is a little low. i was thinking about putting a 135 powerhead on to gain a little horsepower but i noticed that the part number is exactly the same for both the 130 and 135 powerhead. i know that on a car the blocks may be the same but horsepower is gained through different pistons and crankshafts. my question is if the powerheads are the same model number how does the engine gain its extra horsepower?
 
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