I'm replacing the factory dual fan setup with a single fan. I would prefer to use the factory relays and keep the wiring clean. I've already figured out all the wiring, but I cannot find anywhere what the amp rating is on the relays. Also, no where can I find what the factory dual fan cfm rating is. If anyone has any of this info it would be greatly appreciated.
thanks,
-V

 

I went to the C5 fan upgrade from DeWitts. They claim to have double the the flow rate (3260cfm combined, 1630 cfm each, per DeWitt's catalog).

If they are correct, that puts factory in the area of 800cfm each and 1600cfm combined.

http://www.totalperformanceengineeri...roducts_id=392


http://www.dewitts.com/download/catalog.pdf

FWIW..........

Good luck......

 

Thanks for the tip. Never thought of checking that out. I do know they use spal fans, which is what I plan on using, but in a single large diameter.

 

The relays are not that big. I'd be surprized if they were more than about 30A or 40A rated. I think you'd be pushing it to run a very large single fan motors off one of those relays.

Not sure why you don't want to stick with 2 fans with the factory wiring. The low speed fan will help with fan motor wear and even current draw which equates to either less alternator load or a lower battery drain.

Peter

 

So far I've been told the factory relays are either 30 or 40 amp. The fan I'm planning on running is 18-20 so I should be good.
The factory fans work pretty well, but they are restrictive at speed. No problem with cooling on the street. I simply want to clean things up and remove some weight. Just a cleaner install. On the race track however, the less stuff behind the radiator the better the air flow and the better it cools. I'm keeping the factory fans in case the one I install does not work. Part of the reason I want to make the factory wiring work. I really only need a fan when the car is stopped. At speed fans are not needed.
As far as the battery and current draw, etc, there is actually less with my setup. The factory uses three relays. One powers both in series, but goes through a second toggle relay before hitting the second fan, at low speed. It's really not low speed. Just more resistance using one relay for two fans so the fans get less power. The high temp switch energizes the toggle relay, which switches to direct ground, and at the same time energizes the third relay to directly power fan #2. In that case both fans get full power through individual relays. It's a bit complicated, but makes the computer do less work.

 

The factory fans aren't that restrictive at high speed as long as they are free wheeling and not powered on. The PCM should shut them off when the car's speed hits 35 mph. That is the point where the fan is actually running slower than the air trying to go through it. When it is powered on it will resist running faster. I ran many Wide Open Throttle hours at triple digit speeds with both of my C5s and did not have a high speed cooling air flow problem. I had seen oil temps as high as 319 on my 03Z but solved the problem with a larger radiator with built in EOC. The radiator dropped the oil temps from 319 to the 230-240 range and the coolant temp from 230 to 200. The issue isn't air flow but the cooling surface available. By going to a single 18 in. diameter fan you will not increase air flow enough to get the same cooling effect as increasing the cooling surface. How much more air flow will you get from one big hole in the shroud Vs two smaller holes? My quick estimate shows you may gain about 30 sq inches. Or about a 12% gain in high speed air flow.

The fans do really run at a low speed. DC motors vary speed based on voltage. Cut the voltage in half (that is what the relays do by running the fans in series) and the motors run at half speed.

Bill

 

The factory fans are not the restriction. The shroud is. I actually have an aftermarket radiator with EOC, and some openings in my shroud at the bottom. It all works well, but I'm doing some work on my car and this time I plan on installing a different radiator with my own custom mounting. Anyhow, the single fan is lighter and will not have a shroud so a portion of the core will be open in the back. I do understand how a shroud works and at very low/no speed it makes the fans more effective at pulling air from the entire core. Although this is not a dedicated race car, I have set up all the race cars with either fans as mentined above or no fans at all (best, but need an external fan placed in front of the radiator every time the car comes back into the pits). Cooling at speed is not a problem with the c5, but IMO could be better with what I plan on doing. It will be an experiment no doubt.
Running wide open throttle while at high speed will always keep the car cool long as there is decent entry/exit. Actually, in qualifying (race car)I sometimes tape up the air entry as much as possible to improve handling. On my C5 with better air exit the restriction would be reduced to aid in moderate and above speed airflow through the core. Depending on the rest of the venting (hood, undercar, etc.) lift can be reduced as well.
I agree with you on the fans. I tried to explain it above.

 

FYI, I put an open Spal 16" fan on my 65 Impala rad and it will not keep my weak 350 cool at idle/low speed. At 18/20A it sounds like you're looking at about the same fan.

Another FYI, the power drawn and air flow will be fairly proportional. So, if your fan will draw less power than stock then it will also most likely move less air.

Peter

 

See if you can find a shroud from a 97. They had more openings in the shroud to allow air to pass through the radiator at speed. The openings had rubber flaps over them so when the fans were on the flaps closed so air was pulled through the radiator. I don't know when GM went away from this style shroud, my 97 had one but my 03 did not.

Bill

 

On my current shroud what I did was use an air saw and cut out openings on the bottom anywhere that there was not any support ribs. Can't say how much it helped, but it certainly did not make the car run any hotter.
Thanks for the tip on the spal. Seems like the factory fans always flow more. I wonder what brand they use. Spal is pretty much the go to fan company. Although black magic does make a large single that pulls some serious air, but does not fit a corvette very well.
I'll just have to try and see how it goes.

 

If you want a single fan that moves air I think it was the Lincoln Mark 8 fan that is crazy powerful and was being used by the Chevelle guys. You need a 70A or larger relay to run the thing. I'm quite sure it moves over 3000cfm, maybe 3400cfm or 3600cfm.

The general consensus I got from the hot rod type forums was dual aftermarket fans with a shroud was needed to get the required airflow to cool the higher HP big block cars. A single OEM one like the Lincoln or duals like the Vette or 4th gen F-body would also usually do it.

Not sure on your track vs not a track car. If you're track only the Spal might cut it for the short periods it runs at idle. On the streets you might overheat if you get stuck in stop and go traffic.

Peter