Reducing the gap, stock cooling fan

[steve57]

In a recent discussion on the other forum about cooling fans, Kevin Nash made some suggestions on how to improve the stock cooling fan performance by reducing the gap to about 1/16 of an inch between fan and top cover. Basically the fan either needs to be shimmed upwards or fan bearing needs to be adjusted upwards. Pulley also has to be reduced in height to match this change to keep it in alignment with idler pulley. Anyway, thought I would give it a try. Existing gap.

shim, made from old cooling fan flange, cut down pulley next to stock pulley.

reduction in gap.

. Looks like it will work fine.

[66vairguy]

I suppose if you are in Bakersfield you need the extra cooling. especially today (105F there as I type this) !!!!!

I've run my 66 140HP with the A/C on at 88F without issue with stock fan gap.

I'm glad you realize the fan pulley has to be at the correct height (not sure how you will do that). Years ago a fellow did a CORSA article were he found the fan belt tended to come off if the pulley (via bearing height) was not within 1/8" of specification.

Let us know how it works out.

[NMVair]

Yeah, what is the stock gap?
Did you take a before temp. at specific conditions?

[steve57]

Yeah, what is the stock gap?
Did you take a before temp. at specific conditions?

Stock gap as explained by Kevin Nash. He’s done the testing, I believe him. I do not have a head temperature gauge, so no before readings
Re: cooling fan
Posted by: 63turbo ()
Date: June 20, 2023 01:45PM

So, how many of you have actually done any experiments along those lines to tell if it makes a difference or not??? it actually make a large difference if the gap is closed enough. The pulley must be lowered by the same amount that the fan is raised to not screw up the alignment. One way to actually do that is cut the bottom of the pulley off, machine a new bottom that will press in, and weld it in place and reface the surface. Another way is to buy an airflow pulley, this takes care of it in a really slick manner. Another way that has been done is to put a large weight on the opening of the shroud and bend it lower. A 4rth way is to cut the ring portion of the shroud out, and do this to another scrapped out shroud and flip the ring upside down and soft mount it to the other shroud. Goal is to get around a 1/16" gap, as this gets the gap about as tight as it needs to be, which is approximately 6% of the fan blade height. The stock mag fan gap is 15% of the blade height... you may as well subract 15% from the height of the blades!!

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]

[Nashfan]

Right on Steve for doing this and posting on it!! The stock mag fan gap is supposed to be around 3/16, and this is a HUGE fan gap! A VW fan gap is only 1/32, and amounts to 3% of the blade height! They get MUCH more out of their fan relative to its size than a mag fan equipped Corvair does!! When making a change like this, what you are likely to see for cooling benefits is to drop the max temperature, not the average 'light load " temperature. 110's will typically run between 300 and 350 head temperatures, depending on the load, although if the load is hard enough will sometimes go higher than 350. All that assumes a good head temperature gauge and thermistor.

[66vairguy]

Right on Steve for doing this and posting on it!! The stock mag fan gap is supposed to be around 3/16, and this is a HUGE fan gap! A VW fan gap is only 1/32, and amounts to 3% of the blade height! They get MUCH more out of their fan relative to its size than a mag fan equipped Corvair does!! When making a change like this, what you are likely to see for cooling benefits is to drop the max temperature, not the average 'light load " temperature. 110's will typically run between 300 and 350 head temperatures, depending on the load, although if the load is hard enough will sometimes go higher than 350. All that assumes a good head temperature gauge and thermistor.

A question! Would it be just as effective to install a plastic lip around the fan inlet that would reduce the gap vs. raising the fan (and cutting the belt pulley down)??? Yes making one part would be work, but if the part was mass produced it could be cost effective and easy to install.

Just asking --- no flames needed.

[Nashfan]

Yes, as far as the fan gap goes. However, every corvair out there has a different fan gap based on the installed bearing height and variability of the shrouds, so one ring that fits all wont do that very well unless it has some way to adjust. The other genuine concern is simply having a plastic anything that close to the fan blades, because of chunks of plastic could find their way into the engine. Some other things are, its not only the fan gap that is the problem... its the fact that the rim of the pulley is a huge blockage to flow. This is what the airflow pulley is all about, and really does work!

[Nashfan]

Now for a shameless plug for the airflow pulley kit: currently these are only available in the stock 1.58:1 pulley ratio, but in the future, theres going to be a couple of alternate pulley ratios available, a 1.25:1 and 1.42:1. Theres so much airflow potential from adding the airflow pulley + a guidevane bellmouth that its entirely possible to slow the fan speed down and NOT lose cooling if you play your cards right! since these mount exactly the same as the stock 1.58:1, if your fan and pulley had the proper alignment and good fan to shroud clearance with the 1.58:1, it will have the same vertical alignment with the alternate pulley ratios so to change the pulley ratio is a simple matter of swapping the pulleys and adding a set of shims to re-angle the alternator and idler, and use a longer belt.
Heres a size comparison of these pulleys

[steve57]

Thanks for comments, Kevin Nash! The fan modification seems to work quite well. Unintended consequence, until the lower shroud doors open, pushing enough air past the closed heater box flap like the fan was on low speed. Using an infrared thermometer shows over 100 degrees at the heater outlet under dash when driving vehicle. Looks like I need to block off heater tubes at lower shrouds. I believe it’s going to help AC condenser run cooler. I might also purchase an Airflow pulley for this project if cost is reasonable .

[66vairguy]

Thanks for comments, Kevin Nash! The fan modification seems to work quite well. Unintended consequence, until the lower shroud doors open, pushing enough air past the closed heater box flap like the fan was on low speed. Using an infrared thermometer shows over 100 degrees at the heater outlet under dash when driving vehicle. Looks like I need to block off heater tubes at lower shrouds. I believe it’s going to help AC condenser run cooler. I might also purchase an Airflow pulley for this project if cost is reasonable .image.jpg

Is your A/C R12 or is it the newer R134a?? With R12 the A/C cooling drops off at idle, but the system pressure stays reasonable. With R134a the expansion rate at higher refrigerant temperatures is considerably greater to the point of damaging the compressor!! The fix is to install electric fans on the condenser for R134a. The fans will also result R12 outlet vent temperatures being lower while the engine is idling at a stop light, or slow stop and go traffic. While I've never done a test, folks that install condenser fans report lower engine operating temperatures around town with the A/C on.

R134a absorbs heat as well as, if not better than, R12 so no change is needed at the evaporator core. The condenser is the problem since R134a gives up heat less effectively than R12. Clark's sells a serial/parallel condenser for R134a (to keep the refrigerant in the condenser core longer to cool it). You can use the old R12 condenser for R134a, but it won't be as effective as the new unit (same size as old unit).

[belaraphon]

I didn't see any mention of whether there was a measured cooling issue or just wanting to improve the cooling. I recently got my car on the road and tested it at 99 F driving around town for a couple of hours. It ran cool (About 320 at the cylinder head). I have the factory stock fan height. I was careful to deflash all of the cooling fins when rebuilding it, using a 12 row oil cooler and a larger aluminum oil pan with aluminum valve covers. I added that stuff because I was living in Florida at the time and the car has AC.

I haven't completed hooking up my AC yet, but in anticipation of that, I installed a custom trunk mounted condenser. I don't know if I will get that finished this summer in time to test it this year. But that is touted as one way to help cool an AC Corvair. Clark's sells a kit, but I made my own to preserve trunk space and make it so you cannot see the opening on the front of the car. The big benefit of course is not have the air heated by the condenser being pulled into the engine.
Matt

[66vairguy]

I didn't see any mention of whether there was a measured cooling issue or just wanting to improve the cooling. I recently got my car on the road and tested it at 99 F driving around town for a couple of hours. It ran cool (About 320 at the cylinder head). I have the factory stock fan height. I was careful to deflash all of the cooling fins when rebuilding it, using a 12 row oil cooler and a larger aluminum oil pan with aluminum valve covers. I added that stuff because I was living in Florida at the time and the car has AC.

I haven't completed hooking up my AC yet, but in anticipation of that, I installed a custom trunk mounted condenser. I don't know if I will get that finished this summer in time to test it this year. But that is touted as one way to help cool an AC Corvair. Clark's sells a kit, but I made my own to preserve trunk space and make it so you cannot see the opening on the front of the car. The big benefit of course is not have the air heated by the condenser being pulled into the engine.
Matt

Good question about cooling. GM tested Corvairs at their desert proving grounds and they did not have a cooling issue UNTIL emissions controls WITH A/C were on the cars. This was in 1967 and GM quietly discouraged dealers from selling A/C on 67 Corvairs. A/C was discontinued for model years 68 and 69. NOTE: Calif. cars had emmisions controls on 66 models, EXCEPT A/C Corvairs that were exempt from the Calif. rules!!

Chevrolet engineer Benzinger gave a great presentation at one of the CORSA conventions that was transcribed and published. Benzinger was questioned about the lack of cooling for the Corvair turbo engined cars. Benzinger said that after about a minute of full throttle at boost the engine would overheat, but of course in less than half a minute the Corvair would be at maximum, and illegal, speed. For brief full throttle use, as in passing, there was never an issue with overheating. It should be noted the 62 Olds turbo Jetfire had the same issue, but it was controlled with a timer and/or speed sensor to reduce boost via opening the wastegate. This made the car operator error proof, but the Olds system was so complex the technicians could not troubleshoot or repair it. It went away, meanwhile the simple turbo Corvair survived and if the operator ruined the engine it voided the warranty due to improper operation (standard practice for Chevrolet on 60's performance cars).

[Nashfan]

Thanks for comments, Kevin Nash! The fan modification seems to work quite well. Unintended consequence, until the lower shroud doors open, pushing enough air past the closed heater box flap like the fan was on low speed. Using an infrared thermometer shows over 100 degrees at the heater outlet under dash when driving vehicle. Looks like I need to block off heater tubes at lower shrouds. I believe it’s going to help AC condenser run cooler. I might also purchase an Airflow pulley for this project if cost is reasonable .image.jpg

Right on Steve!! That unintended consequence is the "evidence" that you made a good improvement to your cooling!
The airflow pulley kit is 190.00 and is available through American-pi. Im not sure how much inventory Ray has on these at this time. The sure way to get one is to participate in the group purchase for the fan run... you dont have to buy the fan to get the pulley. Just order the pulley!

[belaraphon]

All of this talk about the large gap between the fan blade and the housing degrading the efficiency got me to thinking. Some of the solutions looked kind of complicated to me so I decided to do something a little different. I have a spare 140 top shroud so I took a 1/8" x 3/4" steel strap and bent it into a circle to fit into the groove on the edge of the air intake. It fit perfectly into the groove and projects down vertically from the opening. At 3/4" it was too tall and I had to grind it down to get the gap I wanted (as planned). I brazed it into place and once painted it looks like a factory set up. My gap it tight (.050") and I found that you must bolt the shroud down to check the gap as it compresses a little when bolted down.

Final notes: It's getting cold here now so a good summer time test will have to wait until next year. While the 1/8" thickness fits in the groove nicely it does make grinding the steel strap down more difficult so if I were to do it again I would use a thinner steel strap there. Top photo shows the shroud installed with the ring. Bottom picture shows the bottom side of the shroud with ring installed.

[toms73novass]

I'd be curious how that might work.

I conceptualize things visually, and how I interpret it like a set of windshield wiper blades. If you get the blade closer to the windshield it can move more water (air is also a fluid). So by moving the fan closer to the shroud less air can escape over the blades and more is forced down into the engine.

[Nashfan]

All of this talk about the large gap between the fan blade and the housing degrading the efficiency got me to thinking. Some of the solutions looked kind of complicated to me so I decided to do something a little different. I have a spare 140 top shroud so I took a 1/8" x 3/4" steel strap and bent it into a circle to fit into the groove on the edge of the air intake. It fit perfectly into the groove and projects down vertically from the opening. At 3/4" it was too tall and I had to grind it down to get the gap I wanted (as planned). I brazed it into place and once painted it looks like a factory set up. My gap it tight (.050") and I found that you must bolt the shroud down to check the gap as it compresses a little when bolted down.

Final notes: It's getting cold here now so a good summer time test will have to wait until next year. While the 1/8" thickness fits in the groove nicely it does make grinding the steel strap down more difficult so if I were to do it again I would use a thinner steel strap there. Top photo shows the shroud installed with the ring. Bottom picture shows the bottom side of the shroud with ring installed.

Heck of a job and a very clever alternate way of doing that! SLICK!