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Demo Derby Engine Cooling

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Demo Derby Engine Cooling

Postby Kalvin » Sun Jun 05, 2011 3:25 pm

Customer wants a SBC for his derby car. Claims some will run for an hour without water. Plain 350 engine, small comp cam, RPM Air Gap with Edelbrock 600 carb. I coated the pistons, Plumbed intake back to front and put water to center of heads, but wonder if there is more tricks I should consider. With no water, what I have done will not matter. Your thoughts, please?
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Re: Demo Derby Engine Cooling

Postby crazyman » Sun Jun 05, 2011 4:50 pm

Weld on cooling fins?
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Re: Demo Derby Engine Cooling

Postby af2 » Sun Jun 05, 2011 5:30 pm

Radiator in the trunk with the lines inside the frame and an inline water pump.
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Re: Demo Derby Engine Cooling

Postby jdavis » Sun Jun 05, 2011 6:14 pm

Low compression, run it a bit fat on fuel, moderate timing, big oil cooler with active fan maybe more than one, biggest pan you can find and fit, use a bbc oil pump.

Oil will generally start to break down quickly and even boil above 120C, that will be the death blow a lot of times. Put good heavy synthetic oil in it. When the water is gone the oil is your coolant. You want to try for any heat rejection you can get. Might even be worth putting some of the monster Lincoln junkyard fans on under the hood to draw air across the engine.

Buy pistons with a ton of ovality or add to taste, and build loose to the bore. Which should take care of a lot of the piston seizure. When the engine fails tear it down and look at the load bearing surface to determine changes for the next iteration.

Make the water loop as tough as possible within reason, and oversize the hell out of it, make it hard for the engine to get warmed up with the cooling loop intact so you at least start at a low temp when it does fail.
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Re: Demo Derby Engine Cooling

Postby nova john » Sun Jun 05, 2011 9:27 pm

Thinking outside the box here- are engine swaps legal? A hopped up corvair engine or air cooled diesel could probably run for days without overheating.
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Re: Demo Derby Engine Cooling

Postby ricks57 » Sun Jun 05, 2011 11:12 pm

Hi,
Your customer is right, they do run a long time without water. We ran them in the derbies and then tried to blow up the engine afterwards with no water and they just wouldn't die. I always used synthetic oil. Lots of guys use Slick 50 or other additives. Pure water with Water Wetter or equivalent will keep it coolest. Keep the heater hoses connected and run the heater on full blast. As was mentioned once you loose your radiator the oil is your coolant. Maybe a high volume pump, larger oil pan, oil cooler. Run the exhaust out the top by turning the exhaust manifolds upside down or buy headers built that way by DEC, keeps a lot of heat out of the engine compartment. An electric fan mounted to the radiator will move with the radiator instead of having an engine mounted fan which will cut the radiator up when they get together. When the engines get really hot they seize up, but once they cool off they usually start right up again, so build the engine loose, loose ring gap, loose piston gap, etc.
Good luck,
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Re: Demo Derby Engine Cooling

Postby WESTOF7 » Mon Jun 06, 2011 12:23 am

They last a lot longer than you would think.
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Demo Derby Engine Cooling

Postby Mike Laws » Mon Jun 06, 2011 4:13 pm

Apologizing in advance for the shameless plug; however we've sold many piston oiling/cooling kits for demo derby engines. Water loss is taken for granted by those expecting to be around at the end of the derbies and as mentioned; oil becomes the coolant.
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Re: Demo Derby Engine Cooling

Postby DaveMcLain » Mon Jun 06, 2011 4:49 pm

I've done piston cooling jets and then used a big Chevy oil pump in the engine. I feel that excessively low compression would be much more of a detriment to cooling than higher(but not too high for the fuel) compression. Lower compression running cooler is a myth. I would probably just run the car on 110 gasoline, hone the guides, give it lots of piston to wall and reasonable bearing clearances.
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Re: Demo Derby Engine Cooling

Postby jdavis » Mon Jun 06, 2011 6:09 pm

I beg to differ Dave. The heat rejection calcs and wiebe equations say otherwise. You end up with a different temp profile in the cylinder over the comp stroke/start of combustion.

For what its worth I wasn't suggesting excessively low compression either. Just that its wise to avoid the urge to bump it up depending on chamber and piston design.

If you're able I would run something besides gasoline to keep the piston temps down if you cant do oil squirters.
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Re: Demo Derby Engine Cooling

Postby nitro2 » Mon Jun 06, 2011 9:35 pm

jdavis wrote:If you're able I would run something besides gasoline to keep the piston temps


Yes. Methanol, E85, etc. Even blend your own E20 or E30 (ethanol and race gas) if it absolutely has to be "gas", then run it rich. Any type of alcohol or alcohol blend is a very good coolant, particularly when run rich. Just don't accidentally run it lean.
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Re: Demo Derby Engine Cooling

Postby ZIGGY » Mon Jun 06, 2011 9:51 pm

In my observation, there is a point beyond which richening a methanol mix will cease to cool and will begin to overheat.
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Re: Demo Derby Engine Cooling

Postby Kalvin » Mon Jun 06, 2011 11:21 pm

All of this talk is great and appreciated! Thanks and if you have more it is welcome. Thinking outside the box, I need an oil cool Duetz diesel! My brother -in - laws skid loader is about to become immobile.Lol
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Re: Demo Derby Engine Cooling

Postby Q-ship » Tue Jun 07, 2011 1:42 pm

I could give you a several first hand stories of big block Mopars surviving long periods of time (as much as 38 minutes), with no cooling system whatsoever, and winning, or at least placing, in demo derbies.

Not that big block Mopars have anything over anything else, it's just that the big Chrysler cars work very well for demo, and I have used dozens of them over the years.

In every instance, the formula is the same. Heavy high quality synthetic oil (about a quart, to a quart and a quarter over filled, to help increase windage), stock rod/bearing combinations (as they have the oil squirter holes in them to help cool the pistons/cylinders), plenty of ignition advance (not more than stock, but do not block off the vacuum advance, or lock the timing), sufficient octane to eliminate possible pinging (straight race gas does not work well), ever so slightly rich (but not too rich) on the fuel mixture, and a step or two colder on the plugs (may be harder to start when cold, but they work great when hot).

As someone else pointed out, you MUST plan for total cooling failure as it is very rare to keep the cooling system intact and still be running at the end.

Most people make several fundamental mistakes in as much as their game plan wouldn't work on a street car, much less the extremes of demo derby (such as reduced timing, too rich, etc;).

Compression is not a real concern (within reason) as long as you have appropriate octane, as all the engines I have ever run had factory ratings of 10.1:1, which translated out to a true 9.5 to 9.7:1. As with any performance engine, compression ratio is totally meaningless, as cylinder pressure is the only valid measure, and I have found that mid 140's to 150 is ideal for derby.

Though there are many, many other factors that can/will take you out of a derby, just make sure you don't rely too heavily on cooling. In fact you should use an old fan belt and cut it about 2/3 the way through in a couple of places so that if the radiator jams the fan, the belt will break. a nice new belt will probably put you out ... this, and all my other points, were learned the hard way.

Hope some of this helps, and good luck.
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