maximum fan speeds

[davemenche]

I have a type I motor, with stock cooling system. I'd like to try speeding up the fan with a smaller top (generator side) pulley, and a shorter v-belt. This will change the ratio, and speed up the fan.

What are known safe limits for the fan speed (using a stock fan, no speciall welding or balance work)? (expressed in either fan rpm, or engine rpm (with stock pulley))

What can be gained by a welded, balanced, or other modification to the fan to increase its safe rpm limit?

What is an upper rpm limit for the generator, any concerns with that?

I'd like to get some input on rpms that fans have turned (stock or modified) on other engines, maybe high revers? I do not want to needlessly risk destroying my fan, and other conponents by stupidly over speeding my fan.

reason I want to try this is my car has non-stock tire size, so it tends to run the fan and motor slower, and a much bigger motor will soon be installed, and it will have extra cooling needs. The motor in the car now is stock, but is instrumented for testing, to see what might work or not on the bigger motor. So far the motor testing has shown a big improvement with sealing the bottom of the engine bay, and opening up the top. (this is for a Kelmark GT kit car )

thanks in advance for any advice on safe fan speeds, or any other suggestions.

dave

[Guest]

Dave, you need a larger bottom pulley, not a smaller top pulley.

The circumference of the top is as small as it can be for the type of belt
(v-belt). You will eat belts by going in that direction.

Go larger bottom!

Did you open the side vents in front of the rear *fenders*?
That helps a LOT!


Don

[MASSIVE TYPE IV]

I have blown fans just at the edge of 11,500 RPM fan speed without being welded... I consider 10,000 safe, no more than (thats 6K with the stock drive ratio)

I once blew a welded fan at 12,600 or so fan speed and it was nasty, ripped the whole shroud off the engine and scattered parts everywhere.

[A_67vdub]

I once blew a welded fan at 12,600 or so fan speed and it was nasty, ripped the whole shroud off the engine and scattered parts everywhere.

Ya know, I bet you could make a good amount of cash selling videos of that stuff.



Steve

[davemenche]

What I was thinking of was a 356 porsche top pulley. It is a direct bolt on, and is roughly 3.5 inch inner belt dia, verses about 4 inch on the stock VW pulley, so about 16% increase in speed would be expected. You are right, probably do not want to go to much smaller, but it has worked on a 356.

Questions: Where can I get a larger bottom pulley, and what interference issues might there be with the tin near the pulley, there doesn't look like that much room, how is this done? Anyone done this?

By the way, I did notice on a stock pulley,a slight increase in oil pressure (hence temp of oil) when I went from the largest possible belt size (no shims in pulley, belt riding high, even with pulley edge) to a smallest belt that would fit (maximum number of shims, belt riding low in pulley.) This changes the ratio somewhat. I'd guesstimate maybe around 5% faster fan speed if the effective belt diameter is decreased say 1/4 inch or so (ie belt would sit 1/8 inch lower in pulley with the shorter belt, and most shims). Only noticed the diffence on high speed long freeway runs. Just a few psi better, but near resolution of my gage, diodn't see it on head temp, but head temp gage is graduated in 50 F marks, so I would be able to detect changes much less than 15 F or so) I am hoping for further improvement with the 16% smaller 356 pulley.
At any rate, on my stock fan, if I keep it below 4500 engine rpm as I usally do on this 1500cc stock motor, them my fan speed will still be below 10000 rpm, so I should be ok.

Thanks dave

[Glenn]

I've exploded a stock fan on a 1776 and the engine was well under 7000rpm.

I only use welded fans now.

[MASSIVE TYPE IV]

I have blown a stock fan at 5200 crank speed with a 356 top pulley..

BTW, adding extra ratio only cooled the heads 5 degrees better in my testing... The oil did see a bigger change.

[davemenche]

Looks like i will still be under the speed even with my smaller pulley as long as I do not rev this old engine, my self imposed redline is usally 4200 rpm or so.

When the big motor goes in (2180cc) I will definatly get a balanced, welded fan, as that motor will be a rever.

For the cooling question about ducts, no, the fenders are stock on the kelmark. To get more air in the now sealed engine bay (save for the two stock long vents on the deck lid), I propped open the deck lid by about an inch. This lowered the fan inlet aair temp (measured with probe), and also resulted in improved oil pressure, and cooler heads. It was a pretty conclusive test, drive down the highway, prop it open, it cools down, stop and close it, and drive away, and it heats up back to original temp.
Final fix will be for me to add two more long vents so I would then have a total of four on the deck lid. Then I should be able to close the lid, and still have enough intake air.

dave

[aircooledtechguy]

When those larger than stock pulleys came out a few years ago I was living in central CA's San Joaquine Valley (IMHO AKA - Hell) I was offered one for a great price and installed it. Read here about the installation and how well I found it worked:

http://www.aircooledtech.com/over-sized_pulley/

[MASSIVE TYPE IV]

More air is not the key.... CORRECTLY POSITIONING OF THE AIR IS VITAL!

The reason the temps dropped in town is between gears you were sending burst of air hard at the cooler and heads and that cools quickly. That is how I cool engines between runs on the dyno- by blipping the throttle like mad.

I tested the same pulley and it did really nothing but make alot of noise... I ended up using mine on my cam lifter fixture, I didn't want to waste a good one. I also wanted more fan sped because sometimes the fixture will only be running 3-500 RPM to test the results of a poor break in of a cam and lifter set

[dstar]

-----Final fix will be for me to add two more long vents so I would then
have a total of four on the deck lid. Then I should be able to close the lid,
and still have enough intake air.

dave

Here is a pic of one with a 428 Cobra Jet intake on the back.
I am sure that will push enough air in there at speed without
having to resort to using a whole bunch of additional intakes.

Keep it clean looking and cut the fewest holes as possible in
your *hood*!



Also, the first Kelmarks had vents on the sides, that kinda tied the top\front of
the rear fenders to the rear\back valances, because they were rear engined V8s
and needed the extra cooling.


Here is a pic of that setup. Sorry, but I dint say it was a GOOD pic
of that setup.....you can barely see it.



Don

[James2]

Imho you barking up the wrong tree. The solution is to get more air into the motor. The cure for the larger tires is a shorter fourth gear.

You need to speed the motor up, not just the fan. The increased load on the engine will offset the increased cooloing. plus the fan will not move 20% MORE AIR JUST BECAUSE it moves 20% faster. And if it did, it would NOT relate into a 20% cooler engine.

[davemenche]

Ok, We got the 356 pulley on the kelmark, and we found an old belt in the parts bin. it is a Pheonix / VW brand, size 9.5 x 900. p.n. 11903137B. I think this was from my fathers old 61 Bug, it has the VW logo on it. Here's the question. Why does a assumed OEM (has VW logo on it) V-belt fit nice on the 356 pulley? This belt is much too short for the stock VW pulley I had on the kelmark (which is using a 1967 stock 1500cc motor).

The belt that was on the kelmark, with the stock VW pulley was USA made with markings: 35515 4698:8 It was much larger dia. than the 9.5 x 900 belt that is on the car now with the 356 pulley.


Did VW use different pulley sizes over the years? and if so what years?

What else could explain a stock looking belt with VW logo on it that is too small to fit on the stock pulley equiped 1500cc motor?????

My Bentely manual does not list the stock belt length, nor do my other manuals.

for the kelmark scoops, mine is a late Kelmark, no fender scoops. I think double the existing inlets (West Marine sells them) will work, ram air might be better, but with my current engine, I think I will get all the air I need for now with four inlets, and deck lid closed. I did try a 5 inch dia aluminum dryer duct thru the fire wall, aimed right at the fan intake, the other end snaked down to near the tranny nose, and aimed directly in the air stream under the car. It gave no indicated imporvment in inlet air temp, It also picked up dust and leaves, which will clog up the cooling fins

This is one reason I periodically clean my cooling system. On a cold engine I spray non flammable engine cleaner in the fan inlet (at idle speed) and in any hole I can get to on the shroud, and also under the car on fin bottoms) after letting it soak, I blast it all away with water from a hose, under tha car, and thru the fan (at idle speed). This gets rid of the oily coating on the fins, that retain dirt and dust sucked in by the fan. This should help the cooling, as it improves the heat exchange when the fins are clean. A film of oil with dirt, even 1/32 inch think is sure to reduce the heat transfer. but I have not proved it, just seems like a good thing to do.

[MASSIVE TYPE IV]

A stock belt is 9.5x905 for a 15/1600

The 4o Horse used a shorter belt as it had a smaller diameter crank pulley.

sound slike you havea 40 horse belt.

[davemenche]

Thanks for that input on belt sizes. I could probably go whith even a smaller belt, as I still have room to add more shims in the 356 pulley, maybe a 895 or 890 size if such a beast exists.

Interesting that the 40 HP engine had a "power pulley" on the crank. Guess VWs way of improving cooling when they upped the engine performance was to increase the crank pulley, rather than decrease the fan pulley.


dave