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Alternator Drag, Tech links

396 Views 16 Replies 5 Participants Last post by  steves280

"Any electronic ignition system, whether it be CD or inductive (HEI) will run optimally with an alternator. The more input voltage you put into an ignition, the more output you get out of it. As mentioned in Myth 2, HEI systems only draw 2 to 3 amps off the battery. CD systems draw between 6 and 10 amps off the battery. An alternator will keep the battery and the ignition to their optimum the entire race. Remember, an alternator only draws less than 1 hp (another myth is that alternators rob too much horsepower)!"

So by "killing" the alternator you free up less than 1HP of drag and by doing so kill ~ 20% of the avalible voltage to the ignition system best case. Of course this means the ignition system will be much weaker and will cause MORE than 1HP of power loss. One more internet myth busted...

BTW circle track is probably the best tech, no BS magazine out there that I've seen. Looks like some killer free info at their site.


Nice article explaining why "area under the curve" is more important than peak HP numbers.


Lots of good reading there....
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bed time story for me, im too worn out of installing a bunch of junk today...lets see..

2. clutch cylinders/bleed clutch; it works
3. heater hoses
4. passenger side wiring harness
5. filled engine with oil
6. filled tranny with Redline <-PAIN
7. installed brand new spedo cable
8. installed my cool "Z" shift knob <-hehe
9. rolled car back and forth and tested clutch<-grabs way to fast....needs adjustment...
10. ate McDonalds for the 10th time in a row
11. checked my oil pan with RTV, NO LEAKS SUCKERS
12. messed with EFI harness trying to figure out best way to hook it up and look good at the same time
13. cleaned up
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I disagree with the notion that an alternator only draws 1 HP and I have dyno results from just a week ago to prove it. I did dyno runs with and without the electric cooling fan, which is just a 10 amp draw.
With the fan on, I lost 5 HP. Made reruns to verify that there was no glitch.

and how much did you loose when you reconnected the engine-driven fan and ran it like that?

the alternator normally only runs for charging. I don't know of anyone who runs a fan during a drag pass.

EVERYONE runs the ignition, though, which is the only draw you will have. And the point he was making is that the reduced voltage that you get by turning off the alternator looses MORE power due to ignition misfiring and decreased performance, than if you leave the alternator connected.

Subtleties exist here that actually require people to think. That's why the arguments go on forever and ever and ever...

I knew this would start---I warned him...

Here we go again...
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Bubbles? Who cares what you did today?

Seems to me that the input difference of 12V verses 13V when charging is not going to change the engine power at all. As long as the ignition system is rated for 12V and the plugs fire, I cannot see where it would make a difference.

I would assume that it if DID make a difference, then drag racers would pull the voltage regulator aor just just run a 24V battery w/o alternator.

uh, dude, THEY DO!

serious dragracers run a 16V battery, and in some cases a special battery with a 12V post and a 16V post to connect the ignition.

12 V is NOT enough juice to run a competition ignition system. Saying otherwise reveals gross ignorance on serious racing, and on ignition system performance.

So FYI, they DO run a bigger battery. Not 24 V, but 16V, as the terminal voltage will never dip below design 12V specification of 13.8 even at the end of a run while on full draw.
Ah! So if you're not cheating, you're not winning?
Hmmm... 16V batteries, eh?

Post Edited (Oct 22, 11:58am)
perhaps steves280 cares what i did today? actually, now its last night, but how about just shutting up hybrid. if you dont have anything to say thats nice, keep your stupid childish comments to yourself.
actually steves, that was really interesting, and i understood it all! thanks a lot for the read!
Well bubbles, start your OWN thread then, maybe call it "status" or something and anyone that is interested about it at that time will open it? That's the way it's supposed to work so we can read posts by topic...

Thanks for understanding,

I didn't have time on the dyno to swap the fan from electric to belt driven. The electric fan is mounted behind the rad so it has to be removed since it interferes with the belt driven fan blade.

Would have been interesting to see though.
well hybrid, you used to complain about some of the threads i was starting just to show the progress, so i thought i would half way highjack steves thread, but i did state in the beginning that i was intrested in reading this, but it was going to be a bedtime reading for me becuase i was tired...then i went in to explain why i was so tired.
Maybe it makes a difference at very high RPMs? But then that's what the racers will be pulling so it would give a very slight edge?
Of course when you load up an alternator it draws more power. With "racing loads" (which should be nothing but the ignition and fuel system) there -is- less than 1HP being used. I hope people don't have 200W Amps with subs, cooling fans etc running while they race? And if you have the fans running while in line with no alternator, you easily risk dragging the voltage down lower than even 12V before your run. Seen this happen to a buddy who runs slalom stuff.

Given the alternator output is 14.5V not 13V (go check your's) that's 20% less voltage for the ignition that at 12V static.

I'm not even going to get into the whole electric fan thing, the people who make these claims never seem to have the "time to test it". It's easy enough to go to the dyno with a belt fan (with a working fan clutch) and just remove the fan to see if it is really a problem. It's hard to imagine that a disengaged fan that you can easily stop with a piece of newspaper is causing a HP loss.

BTW try killing the alternator next dyno run (with only a "race" load on the car) and see how much "power" you gain.
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Yea, who needs another horsepower by just flippng a switch. No one would do that :)
Show Me...

One Rule that stipulates what voltage battery you must run in your vehicle to be legal for ANY class.
Show me one...
Yea, who needs another horsepower by just flippng a switch. No one would do that :)

You really are this clueless aren't you?

Turn off the alternator and you LOSE horsepower. The less than 1HP you gain costs far more thwe 1HP loss in engine output from the weaker ignition.
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