Got some numbers

[bspeth]

2500 lb load.6300 ft elevation. 4800 rpms.35 mph on gps. Still had a little throttle left but 48 is the limit for my 229 v6 with an R drive.What can I do to fine tune my prop to my engine?Current prop 15.25x15. Thanks

 

[steelespike]

It appears you have an odd ball; In my chart 84-90 I don't find a 6 cylinder 3.8 only the more usual 4.3 or less common 4 cylinder 3.7.
Do you know your gear ratio?Also I don't recall an R drive?

 

[bspeth]

I will find out the ratio,it a 1984 ser 6681735 drive 6683545. Fun Times told me it was 1.84/1 and that the drive model number is01847014. Thanks.

 

[steelespike]

The calculator indicate at 4800 and 35 slip is only about 5%. Possible but not likely.
I have a feeling the tach reads a little low.If we use 5000 slip is more usual at about 10%.
Assuming it is actually around 5000 you have room for a 17" pitch.to put you at about 4600.
Nothing carved in stone. One inch change usually nets 150 to 200 rpm.At that elevation I lean more toward 200.

 

[bspeth]

How can I change the formula for 45oo ft elevation?

 

[steelespike]

If I remember correctly power loss per 1,000 ft is about 3%.

 

[bspeth]

So I should go for a 17 still.If so I will look for a used AL one before going to SS.

 

[steelespike]

Actually your tach is suspect(reading low) you may want to verify your tach. Perhaps borrow a shop tach to compare.
On the back of the tach there is a selector switch.Note its position and operate it a few times to clean the contacts.

 

[bspeth]

Will do,i will get back to you when I get new numbers, after having done that and check the tach with a shop tach.