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Run_em_Hard
04-09-2007, 08:14 AM
Is there a quick way to check your ratio? Bravo 1 with IMCO gears.

RiverToysJas
04-09-2007, 08:19 AM
In theory......if you can see the coupler, you can turn the prop and see how many times the coupler goes around. One and a half, one and a third....etc.... I think it'll work....but I just pulled that out of my butt so who knows. :)
RTJas :D

ToMorrow44
04-09-2007, 03:47 PM
Give us some info on your boat (motor, drive, speed, prop size, etc) and I bet we can figure it out.
-Tom

BDMar
04-09-2007, 04:07 PM
Just a little FYI.... Imco as well as everyone that builds a Bravo l uses Mercury gears. If they are XR gears the ratio is changed in the lower so you cant just remove the top cap and count the teeth. Remove the spark plugs, mark the damper, have someone rotate the engine by hand keeping good count while you count the propeller revolutions. I would rotate the engine exactly 10 times then compare that with the propeller rotations. The most common ratios for XR gears are 1.50:1 and 1.35:1. Standard Bravo l ratios are 1.50:1 and 1.36:1.

Run_em_Hard
04-09-2007, 07:57 PM
Just a little FYI.... Imco as well as everyone that builds a Bravo l uses Mercury gears. If they are XR gears the ratio is changed in the lower so you cant just remove the top cap and count the teeth. Remove the spark plugs, mark the damper, have someone rotate the engine by hand keeping good count while you count the propeller revolutions. I would rotate the engine exactly 10 times then compare that with the propeller rotations. The most common ratios for XR gears are 1.50:1 and 1.35:1. Standard Bravo l ratios are 1.50:1 and 1.36:1.
I will have to give this a shot this weekend.

Run_em_Hard
04-09-2007, 08:01 PM
I put a new outdrive on this past winter the the guy I bought it from said it was 1.5 gears. I am having a hard time hitting my RPM's. The motor is running sweet, just not getting all the way there.

uselessgrant
04-09-2007, 08:39 PM
seems to me that the ratio on a bravo 1 is stamped on it somewhere on top. not sure where though

Racey
04-09-2007, 09:36 PM
What size prop and how fast do you run, the Gear ratios are all Under-Drive, usually 1.36's run 22-24 pitch in 4 blade, 1.5's run up to 30 pitch, these are for 75-85 mph boats, Generally speaking of course.

BDMar
04-10-2007, 02:08 PM
seems to me that the ratio on a bravo 1 is stamped on it somewhere on top. not sure where though
That is true, however he mentioned that the gears have been changed.....

shockwaveharry
04-10-2007, 02:32 PM
Try plugging your numbers into a prop slip calculator like the one on BAM Marine's site. If you know your prop pitch, top speed and at what rpm's it happens, it should be apparent when you plug in different gear ratios. For example, if you're going 70mph at 5000rpm's and spinning a 24 pitch prop, you probably have 1.5's. If you're prop is a 22 with the same speed and rpm, than you probably have 1.35's.
It's not the surest way, but at least you won't get your hands dirty.

Run_em_Hard
04-11-2007, 04:37 AM
Well I used to run 5600 rpm with a 23 rev 4 up to 75ish @ 5k+ foot.
Now I am only able to hit 4500 rpm with same prop and elevation but my gps was being tempermental so I don't have a speed. I am betting that it has the 1:36 gears. How hard are they to change and how expensive?

RiverToysJas
04-11-2007, 06:51 AM
How much horsepower are you running? What drive did you have before?
RTJas :D

BDMar
04-11-2007, 07:31 AM
Well I used to run 5600 rpm with a 23 rev 4 up to 75ish @ 5k+ foot.
Now I am only able to hit 4500 rpm with same prop and elevation but my gps was being tempermental so I don't have a speed. I am betting that it has the 1:36 gears. How hard are they to change and how expensive?
Going from 1.50:1 to 1.36:1 wont drop 1100rpm's.
The expense depends on if it was modified to accept XR gears or not. The XR gear ratio is changed in the lower and the standard Bravo l is changed in the upper. Take off the top cap and look at the gears. Bravo l has helical cut (angled) steel gears and XR gears are straight forged gears. The pinion on an XR will have 16 teeth and Bravo l will have 27 teeth for 1.50 and 1.36. They are very easy to tell the difference.
Feel free to call me and I can help you figure it out.
626-443-3721
Brian

Run_em_Hard
04-11-2007, 08:36 AM
I do run a vortech and I have the correct pulley on. I used to run about 9 psi and now I am only seeing 5. Remember this is at 5k+ elevation. Could that also play a factor in the 1100 rpm drop?

BDMar
04-11-2007, 09:12 AM
I do run a vortech and I have the correct pulley on. I used to run about 9 psi and now I am only seeing 5. Remember this is at 5k+ elevation. Could that also play a factor in the 1100 rpm drop?
Your post #11 said the only change you made was the sterndrive? Also verify that the tach is not wrong. You said the GPS was not working. Are you sure the speed is off? 1100 RPM loss will be a lot slower. Do you remember what the boost would have been before, when everything was running good, at 4500? Is 5 about right or is it low? Trying to figure if it is the engine or drive ratio.... The taller gear will drop the RPM's more with a Vortech than it would a normally aspirated engine.
At this point you need to verify the gear ratio.

Run_em_Hard
04-11-2007, 09:27 AM
Your post #11 said the only change you made was the sterndrive? Also verify that the tach is not wrong. You said the GPS was not working. Are you sure the speed is off? 1100 RPM loss will be a lot slower. Do you remember what the boost would have been before, when everything was running good, at 4500? Is 5 about right or is it low? Trying to figure if it is the engine or drive ratio.... The taller gear will drop the RPM's more with a Vortech than it would a normally aspirated engine.
At this point you need to verify the gear ratio.
I will get and check my ratio soon...everything seems to point to that in my opinion. The motor is just runnin so sweet right now.

Run_em_Hard
04-18-2007, 06:25 PM
Bump...just checked ratio, 1.26's:eek:
What is my best option at this point? Gears are expensive:(