difference between chrysler 70hp and 90 hp

[lucas_chrysler_1]

i have a 1973 chrysler 70hp with no mods. i was wondering what the difference is between it and a 85hp or 90 hp. if it was just carb jetting, or if there were porting differences? or any easy power mods. this motor is in a 14 foot sidewinder thanks.

 

[Frank Acampora]

Re: difference between chrysler 70hp and 90 hp



Lucas: The differences are many. The 70 is ported differently, has different carbs, and a different lower unit. To increase it to a 90 you would need to disassemble the engine and port it, use the 1 5/16 diameter (instead of the 1 3/16 it has now) venturi carbs, and install a 2 to 1 ratio lower unit.

If you are going to go to the trouble of porting it, you might as well go all the way and have an engine that delivers an HONEST 90 HP at the prop.

The second two photos are of an experimental engine I have not yet completed or tested. Fourth and fifth are of engines in use. First is the ported three cylinder engine.

 

[lucas_chrysler_1]

Re: difference between chrysler 70hp and 90 hp

just wondering, i was gunna put a set of 85 force carbs i have onto my 70, but put the 70's jets intot he 85 carbs for bigger barrel on them but i wont be over fueling, this motor runs sweet and starts as soon an the starter hits the flywheel so i dont want to fool around with it to much, i got lots of other motors for that, il upload a pic of boat and motor in action, i havent gps'd it but i am the exact same speed as my friends sidewinder who has gps'd his at 52mph with a 4 blade 21 stainless chopper, on a 1988 60hp evinrude. and i have a force 1 piece 2:1 lower unit on mine.

 

[lucas_chrysler_1]

Re: difference between chrysler 70hp and 90 hp

is that some home made loop charging goin on there?

 

[Frank Acampora]

Re: difference between chrysler 70hp and 90 hp



Do not switch jets between the carbs. These carbs are jetted for a specific airflow and vented for a specific jet size. If the 70 jets are smaller (some are, some are not--it varies with carb model) then the 85 carbs will run lean at full throttle and possibly damage the pistons. Use the 85 carbs as-is. You won't pick up a lot but there should be some small increase in speed with the lesser restriction of the 1 5/16 venturi over the 1 3/16 venturi you have on now.

No, it is not loop charging. I am simply trying to copy the crossflow system used on the twin carb Chrysler 60 and 65 shown in these photos.