ThisIsLivin

Just when I was getting ready to pull the credit card out. LOL

SabrToothSqrl

Score one for the guys with "only" 300 HP. Like me also thankfully I have 2 lol

boatnt

I don't know guys to each his own, if you look at the specs of the steel SEI uses it's just as good or better Steel than merc uses, also plenty of guys have put those lowers on big heavy older cigarettes will great success,

SEI has been building Alphas for over 20 years and bravo lowers for over 10 years now and they have a pretty good track record, I would assume they did their homework before they started offering Bravos because I don't think they're new to this game

Brad Christy

Boatnt,

The toolmaker in me needs to inform you that hard is not the same as strong. It's actually quite the opposite, typically, specific alloy properties aside. There is always an optimum balance between hard and strong where longevity is maximized for a given application. I have no idea what alloy steel either company are using for their gears, but, generally speaking, past a certain hardness, the increase in hardness may very well be the very contributing factor to the SEI gears disintegrating.

Does anybody know the alloys in question? I have a world class heat treating company right here in my back yard (so to speak). I can call them and pick their brains for their vast wisdom on the subject. They will likely not advise on allow selection, but they can definitely tell you what you're going to get from a given allow and a given process.

Thanks. Brad.
(937)545-8991

ThisIsLivin

Talking to George at AADS, he said the Merc gears are only case hardened 1040. He was looking to make his own gears, I recommended 8620 or S7. 8620 is used in die making for it's ability to take a pounding for long periods of time. It's also used for making the bolt in an AR's. I would cryo it and nitride it and you will be breaking cases, not gears.

Brad Christy

ThisIsLivin,

S7 would not be a good candidate for our application. While it has very good shock resisting properties, it does not get particularly hard; right around 54-57Rc. Gears, under the load we put them through, would wear out, and get very sloppy, fairly quickly.

8620 is an excellent choice. A good case hardening should yield a 60+ Rc, at a minimum of .030" deep, and a very strong/tough interior. 8620 is a good candidate for this.

4140 annealed would also be a strong consideration. I'd think that 4140, forged to near-net, through hardened to 50-52 RC, case hardened as above, then finish ground, would likely yield a forever gear, short of some other calamity. It would also be an expensive gear.

The problem we run into is that we like the quiet operation of spiral bevel gears, which tend to have rather thin cross sections, particularly at the outer ends of the gear teeth, right where they lose the collaborative support of neighboring teeth. This is why the XR gears are straight-toothed gears. But straight cut gears don't mesh and unmesh as smoothly as spiral tooth gears, which is why they are noisy and parasitic. Everything is a compromise.

Thanks. Brad.
(937)545-8991

boatnt

Oh yeah, understand that Harder steel is priddle, I don't know SEI specs versus Merc, all I know Mercs been having gear problems forever so they haven't figured out either,

For the record, there is plenty of people that have used SEI drives with great results. Arctic is the only one that had problems with the gears so let's not condemn the whole company.

Brad Christy

Boatnt,

Not in the least. Just pointing out a potential flaw in the logic that was being tossed out.

I think the majority of Merc's problems stem from the fact that people fail to understand that, just because they CAN, doesn't mean they SHOULD. It's pretty easy to "bolt on" HP, if one has the coin and/or the gumption. So, people do. My boat is a prime example. A 496HO with an M1 ProCharger is advertised at 615HP, and that's without the Whipple stage II tune. Even if it falls short of that expectation, I'm pretty sure we are still well above Merc's advertised 450HP limit of the Bravo1, which I'm fairly certain is bone stock. I'd guess that, if we had an actual supercharger, that delivered good low-RPM torque, we'd have scattered that outdrive long ago. I'd say, with the number of drives out there, the vast majority of which are behind stock engines that are perfectly reliable, they have a tremendously success product. It's only us tweakers who think it's a Merc problem, rather than one we've created for ourselves.

I, for one, am glad to see SEI making a go at forcing Merc to improve their product line. And the more people buy from them, the more Merc will be inclined to address that competition. At the very least, we'll have an option, should Merc up and decide to drop the I/O market altogether.

Thanks. Brad.
(937)545-8991

ThisIsLivin

Good point, it's like when I added a 150 shot of nitrous to my 77 Trans Am back in the day. The T10 didn't like that very much and by the time I polished off the first bottle the T10 was making noise and died shortly after that.

cheech

On down the line is right, easy to power up and then break everything after that.
Just a hunch, if someone has enough (OVER) power to have issues with an authentic Mercury Bravo, they'll have issues with the SEI's also.
Mercury doesn't suggest the regular Bravo on anything over 350HP. That's without some air time to shock load it, long runs at high rpm.

Mercury has addressed weak Bravos.