RPMS WAY TO HIGH on 19 pitch???

[Kenny1970]

I have a quick question on what prop pitch I should use.
I have a 1972 Chrysler 120 HP on a 1971 Thunderbird Pacemaker 16 foot.
It came with a 13 by 17 on it and the prop spun at 5600 rpm.I had it re-hubed and tried again.I had a super hole shot and hit Rpms super fast and did about 28 to 30 mph with the rpm over 6500 rpm.I moved it down to 5500 and it only did 24 to 26 mph.So now I went to a 13-1/8x19 prop and still get a great hole shot but the max rpms are 6200 at 36 to 37 mph. At 5500 to 5600 rpm it does 31 to 32 mph.
Should I still go to a higher pitch and if so where would I find one for a 35 year old Chrysler?
Thanks in advance.
Kenny

 

[steelespike]

Re: RPMS WAY TO HIGH on 19 pitch???

The motor developes its hp at 5,250 I'm not an expert but I'm guessing you shouldn't run it any faster than5,650.You could surely go up to a 21 pitch.
This would put you at 5,800 or 5,900 a 23 would be about 5,600. You may want to confirm your tach is accurate before any more tinkering.
Assuming tach is accurate the 23 would deliver impressive speed but may eat up some hole shot.Finding a prop may be a good trick.There is a very slim chance early force props might fit.You might ask the chrusler guys about fit.