Drive ratio
 

How can you tell if your Bravo is a 1.5/1 or a 1.36/1 drive? My boat had a supercharged 502 in it and now it has a NA 468 making 450 hp and it wont turn over 4400 rpm with a 25 p mirage. Everyone is saying I should be able to easily turn over 5,000 with this combo. So I was thinking making the ratios in the drive are different. There are no numbers on the drive anywhere to tell. Is it possible to tell the drive ratio without tearing the drive apart?

Normally it would be on the upper part of your drive like this.

What boat is this package in? To spin a 25 @ 5000 should put you around 73-75 mph. What is your top end goal? If possible, find your serial number and contact mercury, or your local merc shop.

I called Mercury and gave them my serial number. They told me what gear ratio I had.

There is no serial # on the side of the drive. There is a serial # on the outer transom assembly. My boat is 24 Python and I have a aritcle where one of these boats came from the factory with a supercharged 454 and a 1.36 drive. I know my prop has had some work done to it as the tips have been cut down so I don't think I would call it a true Mirage 25p. I was going to try my buddies bravo 26 and 23 mirage + this weekend but I didn't get a chance.

The 26 Bravo 1 will lower your rpm even further. What is your gps speed with the 25 @ 4400rpm.

What HP and speed did you have with the supercharged motor? I owned a 24' Python w/ stock 502 MPI B1 1.5 gears. It would run 72 gps.

What does the new motor have in it? And did you use a dyno. That way you can tell excatly where your power curve is.

The reason I ask is becasue 2 weeks ago I dropped in a new motor. Only saw 4,900 rpms. After much research figured out my cam was degreeded in wrong. So I removed the motor and reset the cam ICL to where it should be. I was 5 degrees off which makes a huge difference lost all bottom end power and moved the power curve up so high I couldnt get over the hump. Not to mention the water reversion problemn.

The motor is a 468 with a custom Bob Madera cam in it. It made 451 hp and 511 ft/lbs torque at 5200. My GPS speed at 4400 was 61 mph.

Hmm. Something is surely not right. If your drive is a 1.5, then your slip is good. 12%, and you should see low 70's @ 5200, and that seems about right for the setup. If your drive is indeed a 1.36, your slip is 21%, and that is somewhat high. You mention that the prop has had work done, so a non labbed Mirage+ could maybe be a good baseline prop. Before ripping the motor apart, I would try a 23" and 25" M+ and see what happens. In best case, you might just be over prop'd, and a 23" on a 1.36 should be close. Alternatively a 22" and 24" B1 prop could also be good starters. What is you x-dim?

Ps. Ignore the 72-75 @ 5000 rpms in my earlier post. More like 70+. Typing when tired I guess.

I will try my buddies 23 mirage +, hopefully this weekend. The x dimension is set at factory levels. I didn't change it when I redid the transom. I was hoping to get 75 out of this combo. I guess theres no way to determine the drive ratio without tearing the drive apart?

If all the stickers are gone and no serial you can pull top cover and count the number of teeth on the gear.
Go on mercruiserparts . Com and enter the seriAl numbe you have of transom and see what pops up. If it's all stock should lead you in right direction. I had a python and to have a 1.36 it would be an earlier one.

Pulling the top cap as poker suggested is a good easy way for sure. I still think you should try the M+ 23". If you have a 1.36 and the power, speed should be 73-74 mph. If that is the case, get Bblades to lab it for you. Then 76-77+ would not be out of the way. Again that is only, AND only if you can get to 73-74 or so with a non labbed prop. If the 23" is way to easy to spin, then the next step is of course the 25. As pointed out, you need to find out if it is your prop that is the problem. Regarding tearing the motor apart. That was more in response to an earlier post, about wrong cam install. If you can't spin the 23" higher, then you have a motor issue. So try the prop, count your teeth, and go from there.

Let us know how it goes.

I checked the drive and it is a 1.5-1 drive. I found the issue why the motor will only turn up to 4400 rpm. When we dynoed the motor we had the timing set at 36 degrees. I had to pull the distributor due to oil leaking around the locking collar to put some silicone on it to stop it from leaking. I marked the distributor to make sure I put it back in the correct spot. We checked the timing this weekend and it was 39 instead of 36 and right after we turned it down the motor started a terrible tapping/knocking sound. I tore the motor down and had dropped a exhaust valve seat that destroyed 4 pistons. Now I am back to rebuilding the motor with new pistons, rings, bearings, and heads. This motor only had 2.7 hrs on it but it was my fault for not checking the timing immediately after I pulled the distributor.

Wow, sorry to hear:eek: Hopefully you'll get it sorted out, and get a good boating season anyway.

fwiw. I have an 89 272sr1 with bravo's and 25p @ 4600 its going 65mph on the wish o meter lol

Huh!???

:point:

the op was trying to figure out if he has 1.5 drives or not, so i figured Id post that to help

oh i see what happened, i posted before i read the whole thread LOL oops!