Performance Boats Forum banner

1 - 20 of 33 Posts

·
Retired Air Force
Joined
·
940 Posts
Discussion Starter #1
Are there any worthy gains to be had by fitting a cut out switch to the alternator, de-energizing it to remove the load during a race?
 

·
Spiral out
Joined
·
1,545 Posts
Are there any worthy gains to be had by fitting a cut out switch to the alternator, de-energizing it to remove the load during a race?
Not really.......The mechanical act of turning the pulley/armature is still there....which is where most of the load comes from.
 

·
Registered
Joined
·
4,318 Posts
So making amps is free? I guess you have never hooked jumper cables to a dead battery from a running engine and heard it drag rpm down? Used to be rule of thumb was alt. took about 5hp to run
depending on how much work you re asking it to do. V-belt uses more hp than serp. belt. Starting a race with a fully charged battery
helps. Running an ignition on anything less than full charge voltage might cause a problem. The only performance gain would only be at wot.
The first problem you will run into is how to turn an alternator off at wot. Going to need some kind of throttle switch to control a relay that will cover the max output of the alt. I'm going to take a wild guess and say any performance gains would be somewhere in the minuscule category.
I'm thinking best results would be found with using a serp. belt, smaller crank/larger alt. pulley OR an alt with output rating just high enough to cover system load.......although i think your time might be better spent making sure your tune is spot on.....or maybe going on a diet. lol

Or just buy a 16 volt battery and special charger, ditch that evil power sucking alternator and pulleys and belt.....just make sure you remember to charge it between races:wink2:
 

·
steelcomp was here
Joined
·
26,515 Posts
So making amps is free? I guess you have never hooked jumper cables to a dead battery from a running engine and heard it drag rpm down? Used to be rule of thumb was alt. took about 5hp to run
depending on how much work you re asking it to do. V-belt uses more hp than serp. belt. Starting a race with a fully charged battery
helps. Running an ignition on anything less than full charge voltage might cause a problem. The only performance gain would only be at wot.
The first problem you will run into is how to turn an alternator off at wot. Going to need some kind of throttle switch to control a relay that will cover the max output of the alt. I'm going to take a wild guess and say any performance gains would be somewhere in the minuscule category.
I'm thinking best results would be found with using a serp. belt, smaller crank/larger alt. pulley OR an alt with output rating just high enough to cover system load.......although i think your time might be better spent making sure your tune is spot on.....or maybe going on a diet. lol

Or just buy a 16 volt battery and special charger, ditch that evil power sucking alternator and pulleys and belt.....just make sure you remember to charge it between races:wink2:
I'm pretty sure all you have to do is kill the 12v supply to the alt., not worry about it's max output. Simple toggle switch could do that before a pass, or micro switch on the carb, or rpm window switch in the igntion if you have one. Really no load on the voltage going into the alternator.
Everything else, I agree with.
 

·
Resident Ford Nut
Joined
·
10,075 Posts
Not really.......The mechanical act of turning the pulley/armature is still there....which is where most of the load comes from.
Oh I don't think so. Have you ever had an alternator spun up and tested? when they aren't charging they just spin freely when you stop spinning them. When they are charging and you stop spinning them they can damn near lock up and stop spinning.


S CP :wink2:
 

·
Registered
Joined
·
2,034 Posts
Right... same old dead horse... let's keep beating it.
"start a race with a fully charged battery" Define that. How many volts? How many years old is the "fully charged battery?" How many rounds have you run that day on said "fully charged battery?" Do you have an electric fuel pump? Any other loads other than ignition?
Sure, put in a 16v battery.
Fuck it. Keep beating.
If you are running a PE boat, you should just charge the battery before you leave the house.. or 6 second cove class. All will be fine.
Wags
 

·
steelcomp was here
Joined
·
26,515 Posts
Right... same old dead horse... let's keep beating it.
"start a race with a fully charged battery" Define that. How many volts? How many years old is the "fully charged battery?" How many rounds have you run that day on said "fully charged battery?" Do you have an electric fuel pump? Any other loads other than ignition?
Sure, put in a 16v battery.
Fuck it. Keep beating.
If you are running a PE boat, you should just charge the battery before you leave the house.. or 6 second cove class. All will be fine.
Wags
Dang, Wags...not racing this weekend? Little grumpy? ;)
 

·
Registered
Joined
·
46 Posts
Seems like it might be worth trying. Keep the switch on up until you run a pass so the battery is fully charged. Then you could test your results with and without.
 

·
Registered
Joined
·
5,853 Posts
When I took my alternator in to have it disassembled, I ask the Alternator guy about how much power an alternator uses. This is what he told me. He said his alternator tester uses a three horsepower electric motor to drive the alternators and that it will handle all sizes of alternators except the very largest used on some new cars. I think that is somewhere around 150 - 200 amps.

In his opinion, using the alternator is a plus factor because your ignition is based on the voltage supplied to it and multiplied. The alternator puts out 14 volts as compared to the 11.5 to 12.5 volts from a battery and when the ignition takes its power along with an electric fuel pump and gauges, there is a large difference in the voltage to the spark plugs.

Keep in mind the 3 horsepower electric motor tester is more than enough to handle most alternators we normally run. When the alternator has charged the battery, it essentially shuts down on its own and uses virtually-0- power.
I plan to keep my alternator.
 

·
Registered
Joined
·
4,318 Posts
I'm pretty sure all you have to do is kill the 12v supply to the alt., not worry about it's max output. Simple toggle switch could do that before a pass, or micro switch on the carb, or rpm window switch in the igntion if you have one. Really no load on the voltage going into the alternator.
Everything else, I agree with.
Brown trigger wire on a gm alt? Going to have a hard time turning mine off....i don't have that wire:wink2:
Trigger wire just kicks alt on




I've been running one for years. I haven't seen a performance disadvantage yet. Mine is a standard GM 100 amp that is spun 1:1 with the engine. Have never had a dead bateery. Total MSD igntion.
Tim
Might have had an almost dead and never knew it. Ye old 100 amp alt. turns into discharge without sufficient rpm to do any work.


Humpty grumpty.:wink2:
"Fully charged' in my little world anyway, would indicate a battery that has been charged to the point where it no longer accept an appreciable amount of current. All the work that the alternator does and the power it consumes is limited to whatever load the rest of the electrical system puts on it.

100 amp alt will consume the same hp as a 50 amp if the battery is fully charged and the rest of the system only uses 20 amps.
A 100 amp alternator achieves that rating at something like 3000 engine rpm overdriven 300%.....Same alt driven @ 1:1 might take 9000 rpm to make that rating.
Bigger alt pulley and 100 amp alt. might be good for a few hp as long as the battery is full....run that puppy 1:1...make a couple passes through the channel with the tunes bumping hard...back out on the lake for a hard run and now the alt gets to replace all the current that was used when the system was using more than alt output.....and it's probably using more hp to do it....

Any which way it is set up i can't see it involving more than 10 hp....whatever hp a 100 amp might use to charge a dead battery and maintain system voltage....i can't see it using more than 10.....race application, fully charged battery...might be worth 2 hp....20% of that might be v-belt drag..i bet serp. belt is half that.

And yep, i run over sized alt pulley on my deal and i need to make best use of every hp i make...cause it's not that many:wink2:
But the only reason that pulley is on there is because it's the easiest way to keep the belt on past 6500.....Actually..now that i think of it..i might have already tested the alt/no alt theory...been doing some testing.....best rpm so far was 6750....and the belt was still on after that run....been running 6600- 6700..except for with them muffs that rex sells...thing wouldn't even spin 6k

Cheater way is to just run the belt loose...belt that is tight enough will be when you can't turn alt. pulley by hand....Alt output is limited and so is the power it can suck....or spend the 250 and buy a 16 volt...it will keep system voltage up till it's almost dead...long past cranking motor over.

Years ago i built a 750 honda chopper.....10 'C' sized ni-cads stuffed in frame tube for the battery...kick start...ran discharge below 1100 rpm 1300 with headlight on..points ignition, nothing else electrical...brake light on rear brake only...never had a problem as long as i avoided cruising state street...save 8lbs...confused a lot of people:wink2:
 

·
Distinguished Member
Joined
·
5,772 Posts
Are there any worthy gains to be had by fitting a cut out switch to the alternator, de-energizing it to remove the load during a race?
Tim, you'll get as many opinions as there are people that post. Yes, the alternator "drag" uses HP, but not enough that you'd measure it even on a track (at least in a boat). However, if you're running a MSD and a bunch of other electrical stuff, you'll defintely lose HP if your system voltage drops low enough. IMHO, an alternator is a "must have" with a MSD style igniton.
On the flip side, if you run a mag (the prefered ignition of REAL racing engines ;) ), mechanical fuel pump & gauges, there's no reason to even have an alternator in the boat...
 

·
Spiral out
Joined
·
1,545 Posts
Oh I don't think so. Have you ever had an alternator spun up and tested? when they aren't charging they just spin freely when you stop spinning them. When they are charging and you stop spinning them they can damn near lock up and stop spinning.


S CP :wink2:
Sooooo, Are you providing voltage/amps to a coil on a race boat........MS's boat.

Or are you providing voltage/amps to your blender, a/c unit, navigation/depth finder screen, gps unit, radar boom, cooling fan, TV, refrigerator and raw water pump on your race boat.

Lets talk LOADS here.;)
 

·
Registered
Joined
·
4,318 Posts
Tim, you'll get as many opinions as there are people that post. Yes, the alternator "drag" uses HP, but not enough that you'd measure it even on a track (at least in a boat). However, if you're running a MSD and a bunch of other electrical stuff, you'll defintely lose HP if your system voltage drops low enough. IMHO, an alternator is a "must have" with a MSD style igniton.
On the flip side, if you run a mag (the prefered ignition of REAL racing engines ;) ), mechanical fuel pump & gauges, there's no reason to even have an alternator in the boat...
And that too!:))THumbsUp lol..........although a mag isn't free electricity either.


On the other hand...if you have a geo metro with AC you will find the throttle activated compressor cut of switch a necessity if you wish to keep up with traffic on most any inclined surface :wink2:
 

·
Registered
Joined
·
47 Posts
Alternator for tuning -

I need to slow my boat down about 5 hundreths of a second, one hundred rpm on the rev-limiter is about 15 hundreths. Wonder if a one wire alternator with a tght v-belt would do the trick?? I think I will try it at Marble Falls next weekend! - Any thoughts?? -
 

·
Spiral out
Joined
·
1,545 Posts
I need to slow my boat down about 5 hundreths of a second, one hundred rpm on the rev-limiter is about 15 hundreths. Wonder if a one wire alternator with a tght v-belt would do the trick?? I think I will try it at Marble Falls next weekend! - Any thoughts?? -
Place 8 gallons of E85 in the side tank that you are not pulling from......that should do the trick.:)bulb
 

·
steelcomp was here
Joined
·
26,515 Posts
Sooooo, Are you providing voltage/amps to a coil on a race boat........MS's boat.

Or are you providing voltage/amps to your blender, a/c unit, navigation/depth finder screen, gps unit, radar boom, cooling fan, TV, refrigerator and raw water pump on your race boat.

Lets talk LOADS here.;)
I think you provide the battery when it drops below a certrain voltage.
 
1 - 20 of 33 Posts
Top