PlayinPossum

I have a 1998 312 Formula with T-454 mags. I had 28 pitch props and the max rpms was around 4300+/-. I have changed the props to 26 pitch and can only run around 4500+/- rpms. The speeds was about the same on both. I have purchased this boat about 5 weeks ago and the dealer told me at the time of purchase it should run about 5000 +/- rpms but now he has no ideals. The engines run strong up to this point. Is this normal? Can someone give me some ideals to try. Thanks.

blue thunder

I would hunt down some 25p mirage non plus props. Should spin you to 5000rpm base on the numbers you listed with the 26p and 28p. I'd guess a speed of 63-65mph. What were you getting for mph with the 4 bladers (assuming they were)?

BT

Jan

Sounds like he has 1:36 gears in the drive??? Maybe the boat had big motors at one time and the bravo gear ratios were changed.

Friend has a 312 with 454 mag efi's. Ran in the low 70's new, runs in the mid 80's with wipples. Not sure about what props he is running.


Jan

PlayinPossum

Thanks for the information from all of ya'll. The dealer has told me after the fact that the previous owner had new heavy duty drives put on the boat and the ratio was change from 1:6 to 1:5. The problem is I had purchased the boat from a dealer in CA and I live in north TX where the boat is now. Is there a quick check for the ratio or will I just have to go into the drives to find out? Thanks to all.