beermanpete Posted March 11, 2011 Share Posted March 11, 2011 I have been wanting to install a smaller alternator in my 240Z for a while now. After reaserching the subject all I came up with was articles on swapping in higher output alternators. I am using my car for time trial events and hope to get into racing as well. I rarely drive the car on the street and have removed the heater, wipers, horn, and such to reduce the weight of the car. Since I do not need to run lights, fans, and the like I decided I might be able to save a few pounds by using a smaller alternator. After some thought I remembered that one of the motorcycles I use to own had a belt drive alternator, so I bought a used alternator and managed to fit it to the Z engine. The donor motorcycle is a 1987 Kawasaki Ninka 750. The alternator is rated for about 25 amps output which should be plenty to run the breaker point ingition and Holley fuel pump. The Ninja alternator in an internal regulalator type and weights in at about 6 pounds. The stock alternator and regulator weight in at 11.5 pounds yeilding a weight reduction of 5.5 pounds. The Ninja alternator used a micro-V belt so I will have to make a new pulley which is ok since I am not sure about the gear ratio needed for the new alternator. To get the new pulley aligned with the crank pulley I started by mounting the new alternator to a spare engine. The stock 240Z alternator mounts worked well with minimal mods. I had to grind a small ridge off of the front of the lower mount to clear the new alternator because the mounting ear is shorter that the stock alternator. I also increased the thread size for the pivot bolt from M8 to M10 because the Ninja alternator uses the M10 screw. The stock upper mounting/adjusting bracket needed to be flatened and shortend. I used one of the water pump mounting bolts to attach the engine end of the bracket which helped align the radius of the alternator end of the bracket to the smaller alternator. A few pieces of new hardware were requied. A M8 x 100 mm screw is need to attach the upper bracket to the engine. I had to shorten it a little bit so a 95 mm screw should work if it is available. The lower mounting (pivot) bolt is M10 x 40 mm. A M8 x 45 mm is used to attach the upper bracket to the alternator. The new alternator has an adjusting slot in it and so does the adjusting bracket, so I will use fender washers on both sides. An M8 x 45 mm bolt and nut hold it together. I had to make a small flat spot on one side of the rear washer due to the short mounting ear. The end result looks good. It is very rigid and should work out well. Now I need to make the pulley and figure out what length the belt needs to be. Quote Link to comment Share on other sites More sharing options...
Racer Z Posted March 11, 2011 Share Posted March 11, 2011 I have been wanting to install a smaller alternator in my 240Z for a while now. The correct term would be, "our 240Z", little brother. Our Dad made us this new pulley to fit the alternator. Beerman drew up the plans and Dad turned it on his lathe. We have not yet fit it to the alternator. We don't yet even know at what RPM range the Ninja alternator wants to spin at. This is an experimental size, about 4 5/8 inches diameter. We can turn this one smaller or make a bigger pulley as needed. Once we get the size for RPM correct we can shave certain areas to lighten it and drill a few holes in it for air flow cooling. Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted March 11, 2011 Share Posted March 11, 2011 Couple things I can think of right off. One the Kawa Alt is made to spin faster than the Z engine, so a smaller pully might be a better idea. Kawa cycles rev easilly in the 3-8Krpm range, so I'd expect this alt to be happy there. A smaller pully will turn faster, but the resistance should stay about the same. What size was the stock pully? If you're at the point where every Lb is making a difference, then have you pulled out everything else like the horns and headlights? Quote Link to comment Share on other sites More sharing options...
Racer Z Posted March 12, 2011 Share Posted March 12, 2011 The stock Kaw pulley was pretty tiny, but we don't know what size the drive pulley was in the Kaw motor. Yes, we have stripped the car of all non-essentials.... it is a dedicated track car. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted March 12, 2011 Author Share Posted March 12, 2011 Couple things I can think of right off. One the Kawa Alt is made to spin faster than the Z engine, so a smaller pully might be a better idea. Kawa cycles rev easilly in the 3-8Krpm range, so I'd expect this alt to be happy there. A smaller pully will turn faster, but the resistance should stay about the same. What size was the stock pully? If you're at the point where every Lb is making a difference, then have you pulled out everything else like the horns and headlights? The original pulley is about 1.75" in diameter. The engine this alternator came from redlines at 11K RPM as I recall. What I don't know is the drive ratio. The info I have found indicates most car alternators run at about twice engine speed and output rated current at about 2500 engine RPM. The Ninja alternator is essentially the same, just smaller. The new pulley is the same diameter as the water pump pulley which should run the alternator about 20% faster than the engine. This means at race speeds the new alternator will be running between 4800 and 7200 RPM. If the output is low due to running too slow I will reduce the diameter of the pulley. I left the center section full thickness for this purpose. After I get this sorted out I will thin the center section of the pulley to lighten it and make it look nicer. The only electrical loads remaing in the car are the ignition, fuel pump, electric cooling fan, brake lights, and head lights. The car is really not driven around town. we left the lights on so we could get away with short test drives around the block if needed. On the track the ignition and fuel pump are the only steady loads and are about 10 amps combined. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted April 4, 2011 Author Share Posted April 4, 2011 We finally got the new pulley on and a v-belt that fits. The belt size is Gates 7360. The length (circumference) is 36 - 5/8". So for it looks like it will work ok. The only snag is the space between the pulley and the mounting bolts. The pulley is large enough to overhang the bolts. The space is a bit too small, especially at the upper mount, so I thinned the bolt head a bit and reomved the washers. I think the mounting is good enough to run the engine long enough to test the alternator output to assess the pulley size. If the alternator needs to be sped up the pulley will get smaller and the bolt clearance problem might go away. If the pulley size stays as it is I will have to figure out how to improve the mounting so it will be suitable for regular service. It will be a few weeks before the car is ready to run and we can test the alternator. Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted April 4, 2011 Share Posted April 4, 2011 Hmm your bolt clearance issues could be solved by using an adjustable bracket similar to the Z32 bracket. Screw type. Also aluminum to save weight. How'd the Pully work out? Quote Link to comment Share on other sites More sharing options...
beermanpete Posted April 5, 2011 Author Share Posted April 5, 2011 Hmm your bolt clearance issues could be solved by using an adjustable bracket similar to the Z32 bracket. Screw type. Also aluminum to save weight. How'd the Pully work out? The screw type adjuster is nice. So far what we have thought about is using an aluminum braket with a PEM nut at the alternator end. The screw can go in from the back side. There is a short slot in the aleternator so it will have some adjustment, but not very much. Luckily the braket is flat so it will be easy to make a new one. We hope to eventually make an aluminum lower mount at some point to replace the original heavy cat iron part. The pulley seems ok so far. The groove is aligned nicely with the crank pulley and water pump pully. The only issue we found so far is he bolt clearance. After we get the wiring back in the car and run it we will know if the pully diameter is correct or not. Quote Link to comment Share on other sites More sharing options...
Racer Z Posted April 5, 2011 Share Posted April 5, 2011 If the adjustable looks similar to this, it will only aggravate our bolt clearance issue. I also suspect this adjustable bracket is heavier than the stock bracket. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted September 10, 2011 Author Share Posted September 10, 2011 We finally got the car back together and running. The new alternator works well and has adequate output. The ammeter indicates a charge rate of about 15 amps when above 2000 RPM. At idle (900 RPM) the ammeter indicates a discharge of about 10 amps so the total alternator output is about 25 amps as expected. The break-even point is around 1500 RPM. It seems the pulley diameter is ok and could actually be a little larger. We plan to drive the car at Willowsprings in couple of weeks. This will be the real test. After Willow we will finalize the upper bracket and possilby thin the center section of the pulley. Quote Link to comment Share on other sites More sharing options...
240zip Posted October 14, 2011 Share Posted October 14, 2011 does the smaller alternator result in less drag on the motor and thus a measurable increase in HP? Is the weight difference significant? Quote Link to comment Share on other sites More sharing options...
Racer Z Posted October 14, 2011 Share Posted October 14, 2011 does the smaller alternator result in less drag on the motor and thus a measurable increase in HP? Is the weight difference significant? Having discussed this in great detail with my brother, Beer Man Pete, the deciding factor for us was the weight. In my research, I decided that most alternators have the same drag, unless they're advertised as being "low drag". The only low-drag units I could find put out gobs of power and were even larger and heavier than our stock unit. It would seem logical though, that part of the drag would be based on the amperage output at run-time. That is to say that there is more drag with the headlights on than off. So, once the battery is fully recharged after starting, most alternators would have the same amount of drag. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted October 15, 2011 Author Share Posted October 15, 2011 does the smaller alternator result in less drag on the motor and thus a measurable increase in HP? Is the weight difference significant? The motorcycle alternator is physically smaller and lighter so the pole piece (moving part) is smaller in diameter and lighter. This should reduce the inertial drag somewhat in the same manner that lightening the flywheel does. We are running it half the speed of the original alternator, further reducing drag. Since this alternator is from a 1987 motorcycle it is newer than the original alternator from the Zs and might have some newer design features that improve efficiency somewhat. Quote Link to comment Share on other sites More sharing options...
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