Necessity for alternator on race engine?

Competition engines and ancillaries - general discussion
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1969race125
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Necessity for alternator on race engine?

Post by 1969race125 »

I run a normally-aspirated 2L 8V TC race-spec motor in my Fiat 125 race car.

At my last meeting the bolts holding the lower alternator mount to the block sheared, and the fan belt fell off. For the final race we simply removed the alternator and fitted a shorter belt direct to the water pump pulley.

With the big heavy alternator now sitting in my tool box, and having already suffered various other problems with it (snapped upper mounts, oil leaks from lower mounting holes, etc.) I'm thinking that perhaps the car is better off (and lighter!) without an alternator altogether.

Does anyone else have experience running their race engine without the alternator? It will obviously stress the battery more, but the only auxiliaries I run are a data logger and various gauges and warning lights. I guess longer races in the rain could be a problem (with headlights), but mostly our races are only twenty minutes or so and it ran fine for this time at the last meeting. A quick charge between races would allow a fully-charged battery each time. Are there any issues I have overlooked which might cause a problem?

I run a lightweight Odyssey aircraft battery, so I could always change that to a bigger battery with more capacity, although that would offset the weight gains somewhat.

Andrew
Julian
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Post by Julian »

An alternator doesn't *waste* energy, it provides the electrical energy you need to run the car to the best of its ability. In theory the only thing you need the battery for is cranking the engine over and priming the ancillary systems. Without the alternator you are reliant on the charge of the battery which is at a lower potential than the alternator output and of limited capacity.

Yes you can opt for a larger battery but this completely offsets any weight saving and still doesn't give you the full voltage. There is also the matter of what you are going to do if the battery runs flat for any reason.

The best option if you want to save weight is to convert to a race-spec alternator. These are much lighter than the old alternator you would have been running and less prone to failure. You can perform a similar trick with the starter motor too.

I'm not saying either of the parts are going to be cheap or that you won't need a degree of fabrication to fit them but these are the least compromise option.
Guy Croft
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Post by Guy Croft »

Those 124 alternator brackets are a nuisance; the later generation where the lower bracket was a cast section of the block were better but both types as I experienced on my 124 CSA tend to see fracture of the upper tensioning bracket.
Certainly I favour Micro Vee (Poly Vee) or toothed belt drives on alternators and water pumps for motorsport use. They won't invert and fly off which is going to be your next problem after you've got the bracket to survive, and you need a lot less pre-tension in those belts and get almost no belt resonance too so I guess the strain on the bracket is lot lower. In fact so much better are they you can actually use a plastic top brace with a toothed belt, I've done it. Plastic, like nylon, being a 'living hinge' flexes and absorbs the shocks travelling through the belt from the crank harmonics. Steel doesn't.

Frankly though in my view - in 20 minutes racing - a well charged battery should cope with no alternator at all, we ran the NHRA 2 liter in 40 minute races with Bosch electronic ignition and full instrumentation, Facet Red Top pump, brake light and never saw the sealed race battery give up. If you're using things like heater, wipers that's another matter.

Julian's point about race alternators is a very good one. They are way lighter than the monstrous OE thing.

GC
Last edited by Guy Croft on January 12th, 2007, 10:49 am, edited 1 time in total.
1969race125
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Post by 1969race125 »

Thanks Julian and Guy for the excellent advice.

I am also running an electric fuel pump of course, and electronic ignition.

In the final race (less alternator) I actually ran a full 0.8 seconds per lap quicker, although that was more probably due to track familiarity and the fast 124 in my rear view mirror!

I spoke tonight to a friend who has run his Viva GT race car for ten years without an alternator and has experienced no difficulties, although he is adding one shortly in order to compete in tarmac rallies.

Julian - any advice on brands / suppliers for lightweight race alternators?

Thanks again
Andrew
pastaroni34
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Post by pastaroni34 »

I have seen many people use an alternator from the SOHC engines, I think it is a 30amp bosch. Its quite a bit lighter and they are cheap.

Where is it that the upper bracket normally fractures? I am reproducing the original brackets here but I have never seen this problem, if I could know more on how to remedy this then I could hopefully improove on the design.
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA
1969race125
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Post by 1969race125 »

Thanks Jason.

My top brackets have cracked twice, both in the same position: at the 90 degree bend, at the block end of the radius.

Once I noticed the crack before it broke completely - the other time it broke right through while racing.

Andrew
petert
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Post by petert »

You may been able to get away without an alternator on a carb. engine, but it could be a serious problem on a fuel injected engine, leading to lean mixtures. More so if you tuned the engine with a working alternator, delivering around 14V. Even with a fully charged battery, you'll only have around 12.5V under load with no alternator. Imagine what's happening to the injector pulse width?

Here's a correction map from a Haltech ECU which illustrates the problem.
Attachments
battery correction.jpg
battery correction.jpg (23.37 KiB) Viewed 8887 times
1969race125
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Post by 1969race125 »

Thanks Peter - yes my car runs DHLA carbs, so no injector issues for me.

Update on my first full race weekend without the alternator: I encountered no problems, car ran as quick as ever (subject to driver concentration levels!). I put the battery on the charger between races, and was careful to limit the amount of electric fan time, but the battery reached full charge again in plenty of time for each subsequent race.

I am still looking at fitting a lightweight alternator replacement when possible, as I think a wet one-day race meeting with lights, wipers, and less time between races will stretch the lightweight battery.
Any suggestions/experience on suitable alternator replacements are welcomed.

Andrew
Fiat Racer Don
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No alternator

Post by Fiat Racer Don »

When my 124 was alive, I went back and forth between alternator no alternator. I ran a 60 minute enduro with no alternator - no problems. You will have to charge it up in between. In my new car being built, I will go without.

I use an OPTIMA battery - lots of CCA for a small battery/weight. Gel type.

I dyno a motor with and without and found I gained a few HP without.

Don Tuscany
CSA FIA GrpIV Reproduction underway
Don Tuscany
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