FrontEngineDragsters.Org Forum
Technical => Spud Miller's Cave => Topic started by: Mister_Fitz on October 05, 2014, 11:12:19 AM
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I run a n/a alcohol injected 350" sbc in my FED. Best et so far is 8.41sec 159.5mph. Planing to do some upgrades this winter to be able to go faster. My goal is a 7 sec run, which might be hard...
I have a Mallory SprintMag I, which never have been recharged during the 4 years I have raced with it.doing about 10-20 passes each year.
Engine is running good and feels strong. Can I expect any power gains if I have the mag recharged?
Or should I get a bigger mag? SuperMag IV would be nice since they do not need to be recharged.
Will a bigger mag help me make more power? Or will it just increase the losses since it takes more power to drive?
What mag is the best for my application?
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A Sprintmag is fairly comparable to a Vertex magneto except that it makes a little more current and voltage at the plug due to the external coil. You might notice a little power gain from recharging if the mag is way down on output. I'd be most concerned with reliability if you've not had anything done to it in that many years. Since mags generate ozone inside the cap, things can rust up pretty quickly depending on what climate you're in. Having it serviced every other year means it'll run its best and have plenty of poop. Your Sprintmag can be upgraded to a Sprintmag+ which makes about 3 amps (7 amps measured like a Pro-Mag) and that would have a rare earth magnet in it.
The best thing about the Sprintmag is that it's a "constant duty" mag. You can run it all day and it won't get too hot and hurt itself.
A Super-Mag IV would work great but they're bigger in diameter. Not sure if space is an issue. The power to drive them isn't going to be noticeably more than the Sprintmags. You probably wouldn't see a gain in HP for your application. A little nitro or a supercharger and you would. If you're drag racing, then a Super-Mag would be great for you. Anything bigger than a Super-Mag III gets too hot to run for a long time. Lake boats, hot rods or circle track guys need to stick with a Sprintmag or a Super-Mag II. A III will be ok if it's out in the breeze.
The good news is the lower drive for your Sprintmag will also work on any Super-Mag if you decided to go that route. The coil would work too. You'd just need the generator and be up and running.
For your application, I'd say the best mag is one that's "paid for" :) If you plan improvements in the future that would require more mag, upgrading to a Super-Mag at some point would be a good plan. Until then, your Sprintmag oughta work great with a little love.
Spud
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I'm not familiar with the mag lingo.... what does it mean 'recharging' a mag??
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I'm not familiar with the mag lingo.... what does it mean 'recharging' a mag??
Many old magnetos use a ferrite based magnet. As the mag is used, the magnets slowly lose their magnetism. Sometimes they can lose as much as half their power. If a guy welds on his chassis, sometimes it can totally demagnetize the magnet if the mag is left on the car during the welding.
Any Vertex that hasn't had a "rare-earth" or Neodymium upgrade will slowly go dead. Sprintmag I and II, Super-Mag I, II, III all use ferrite based magnets. Sprintmag III and +, Super-Mag IV, V and + all use Neodymium magnets that don't lose their charge with use.
We have a couple of big magnet chargers here in the shop that dump energy into big windings. The charging fixture is setup a certain way with these coils and the magnet/poleshoe/shaft assembly is mounted in it. When the coils of the charger are energized, the magnet is charged back to full strength again.
It takes quite a lot of use for the magnets to discharge enough to have an issue with performance.
Spud
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Now I know! Many thanks Spud.
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A III is about as big as you can go with a SBC and a blower, and one has to machine the "DOG-BONE" bearing covers for clearence.
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A III is about as big as you can go with a SBC and a blower, and one has to machine the "DOG-BONE" bearing covers for clearence.
A III can run the small cap and it's the same diameter as the mag housing. A IV or bigger is the same housing, but they require the big cap (4 7/8" diameter) and that can cause clearance problems. With no setback, the big cap will fit on most any 6-71. There are a few 8-71's that will allow the big cap in the stock location without whittling on the blower bearing plate, but most require an offset drive or moving the mag to the front of the motor. Anything bigger than an 8-71 and there's no way anything is going to fit without moving the mag.
Spud
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Or.....put the mag up front. Much easier maintenance now.
(http://www.meansracing.com/anrasummer2014/10574367_879589975386064_1559184674385234778_n.jpg)
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I do run the small cap, the clearence was for the generator body
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I don't know Greg, she looks high maintenance to me...oh, you mean the mag! ;)
Spud
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so mag is that anew slang name for I am looking at?
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C'mon guys, nobody is noting what a bitching FED that car is??
I'll, however, refrain from commenting about the model, 'persuaded' by Greg's avatar.
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LMAO
I love the front mount mag though. Out of the way, works GREAT.
The model is Elizabeth Mayree. Total sweetheart.
Thanks for the compliment on the FED. I love my little tank.
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I've seen such a wide variance with intake manifolds. I run a TBS intake, and my SMIII cleared mulitple 6/71's by more than a 1/4" (generator or cap)
I went to the front drive for maintenance, and had Spud do the MSD cap converation
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Guys. Whats the big deal with maintenance when the mag is mounted in the stock location?
.......I hate bending down to those front mounted mags :-\
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One does not have to re-install and time the mag if you need to pull the heads. For Chevys and 392/417 type engine, if you bang the blower off the manifold it does not bend the magneto
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No plug wires hanging down
can pull the intake without drama
easier to prime motor if needed.
Great spot to dump in 8 quarts of 'cold' 50w oil
Looks cool
all the chicks dig it
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...
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all the chicks dig it
I'm sold!
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I might try some Fuel next season. Just to make sure the 7 sec run will be there.
I have stock main caps, alu rods, forged steel crank and forged pistons. Around 14:1 in CR. Stack injected sbc.
I have read in Spuds nitro notes that above 25% the stock main caps might crack.
So around 20% seams to be "safe".
BUT, will my SprintMag handle this? Lets say the SprintMag will be recharged and in perfect condition.
Or do I have to move up to a SuperMag?
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A good, tip-top Sprintmag will do fine for you at 20%.
Because of the compression ratio I'd put a quart of toluene in your 5 gallon jug of mixed 20% to help prevent detonation and cracked main caps. Especially if your cam is a fairly short duration grind with not a lot of overlap.
Have fun!
Spud
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The cam is an Isky rr-735.
Dur in 278°, dur out 286° @ .050".
Overlap is 111°
Do you think the cam is long enough to be able to skip the toluene?