5SFE 4" underdrive alternator pulley

[N/A Camry Sleeper]

Spent last Friday night fabbing this pulley since I was bored and we didn't get a babysitter...took about 4 hours to get fitment and all the bugs worked out. For this I used 6061 aluminum, but I will never use this alloy again. It likes to load up on the surface of the cutting tools and make cutting a bit more labor intensive where 7075 aluminum will not do this. 7075 is 60% stronger and more brittle than 6061 Al and finish machines very nicely with the carbide tools used. HSS tooling provides excellent rough cuts...anyway, here's the finished product on the car:



The stock 5S alternator pulley is about a 2" diameter, so I figured that doubling the diameter wouldn't be so bad. Didn't spend a whole lot of time with the design, just wanted to see the feasibility of running a larger pulley on this motor.
The stock 5S pulley weighed 196 grams. The underdrive version weighs 199 grams. If I had used 7075 Al the pulley could have been thinner and had more lightening holes to get the weight down to ~135 grams or so.

Had to get a 46" belt which was a little small, but fit just fine with the alternator adjustment bolts. An 5K4550 (45.5") belt will also work:



I will drive this for a week - which means about 550 miles or so total distance travelled and see how it works. The process is completely reversible of course, but I'm thinking this will help gas mileage by a small fraction...can't wait to find out!

If this works well then I may be able to make a 5" or 6" alternator pulley for those interested. Cheers!

[Chris Crash]

This would slow down the alternator, reducing it's effectiveness, correct? I'm just curious why you didn't opt for a smaller pulley instead. But with the racing battery, you probably need much of a charge these days...

[N/A Camry Sleeper]

Yes, the larger pulley will slow down the charge rate. But the new job requires a lot of freeway driving which should be just fine. At 78 MPH the motor is turning at ~3000RPM, so with this pulley it will have the same power output as if it were turning at approx. 1500 RPM.

This is uncharted territory as far as I know - I want to see the limits of the charging system in all conditions and should it not work I can always go back to stock in about 5 minutes...

I did this mod mostly for reducing parasitic engine drag, but *hopefully* I can get a .25 to .5 MPG increase in mileage as well - only time will tell

[71Corolla]

I don't think your mileage will change at all. The alternator/regulator is a dynamic system, so the load on the engine will be essentially the same. There will be less friction because the alternator is turning slower, but I doubt it is observable as far as mileage goes. One good thing is the alternator will last longer. What might happen is if the voltage gets too low at slow engine speeds, you will have a weaker spark which will hurt mileage.

But I think it's really cool that you have the means to fabricate something like this. Will be very interested to know the effect it ends up having.

[N/A Camry Sleeper]

Good point - I had my doubts as to if running a bunch of accessories (lights, rear defogger, A/C, etc) would be any different since 100W is going to equal 100W no matter what speed the alternator is turning.

No real HP gain to be had, but possibly a small fraction of 1ft-lb torque increase? Also, having the alternator last longer is a good thing since it's 3 years old already - where does the time go?

Doesn't drive any differently and the idle is the same with all the accessories running; even with the Braille battery. Let's see what happens in the dead of January!

[RichieRichJP]

I have to agree with the others, but I gotta admit, I love your little projects. That makes me want to go outside, look at my Camry and offer up some suggestions. Wait, I already have a few in mind! Plus I'm no longer working on my Camry...

[N/A Camry Sleeper]

^Why not Rich?

There have been MANY people on this board this year who have dropped out of the Camry modding scene for one reason or another. I can think of 8 or 9 right now who spent literally thousands on their cars and no longer want to or can't continue what they started...it's a bit discouraging I must say.

What's worse is that there are fewer people who are beginning to mod/restore their cars to take the salty ones' places. I dunno, I guess some people grow up and out of the scene or lose interest or what have you, but I see it counterproductive to spend all that time and energy and NOT finish a project like that.

Anyway, I'm hijacking my own thread here, and any suggestions are welcome, you know that...

[curry.style]

Eager to see how this all works out. Working in a machine shop with lots of scrap 6061 aluminum alloy available on the cheap, I too have been thinking about having some underdrive pulleys made up. Also, an overdrive pulley for the supercharger. If your battery holds up well I may utilize one as well for my setup to free up that area for my charge piping from my air to air intercooler.

[N/A Camry Sleeper]

I think that's a great place to bring in air for the intake - but Toyota put the battery DEAD in the way! Oh well, that's why there's people like us that can get around stuff like that...

6061 and 6063 are the primary Al alloys that most aftermarket people use but 7075 is far better. It is more expensive, but you can make lighter parts from it because it's yield strength is at least 40% greater at room temperature than any 6000 series aluminum. Above 300-350*F aluminum turns too plastic to use for almost anything practical, unfortunately

The hardest part about making the pulleys was cutting the belt grooves. I'm not the most experienced machinist out there, but I have patience and a great love for making things so *eventually* it will get done lol

[RichieRichJP]

Originally Posted by N/A Camry Sleeper

^Why not Rich?

There have been MANY people on this board this year who have dropped out of the Camry modding scene for one reason or another. I can think of 8 or 9 right now who spent literally thousands on their cars and no longer want to or can't continue what they started...it's a bit discouraging I must say.

What's worse is that there are fewer people who are beginning to mod/restore their cars to take the salty ones' places. I dunno, I guess some people grow up and out of the scene or lose interest or what have you, but I see it counterproductive to spend all that time and energy and NOT finish a project like that.

That's exactly it. It is a waste of money in the end. It's just a hobby and as simple as one idiot driver can smash into you and take it all away from you. Plus you don't receive any return but self-gratitude from finishing a project.

[curry.style]

^And the gratitude of the rest of the modders out there for supplying the community with something new...