Educate me on why 340 fan is not symmetrical

[jawbone]

Why is it on some radiator fans the blades are symmetrically spaced and some are not. In the process of purchasing fan for my 340 but am reluctant due to the blade orientation. It's a 340 fan with 2 1/4 pitch part number 2863 215. My research indicates this is for a 340, Mine is a 70 model engine going into a 68 Barracuda. Any help would be appreciated.

 

[TrailBeast]

Why is it on some radiator fans the blades are symmetrically spaced and some are not. In the process of purchasing fan for my 340 but am reluctant due to the blade orientation. It's a 340 fan with 2 1/4 pitch part number 2863 215. My research indicates this is for a 340, Mine is a 70 model engine going into a 68 Barracuda. Any help would be appreciated.

The fan blades are spaced such that the center of mass is placed exactly on the fan axis to minimize fan vibration. The resulting fan noise is 11 dBA quieter in discrete noise level than the even bladed fan system.

 

[KosmicKuda]

IIRC, generally it is better to have an odd number of blades, fins, etc.

Chrysler Engineers were very thorough in designing all the elements of a car. You can bet your fan was thoroughly tested and refined to the Nth degree before it was released for production.

 

[YY1]

Also, so you can get your hand and a wrench in to undo the bolts.

 

[Ottmundr]

My dusty memory is telling me that it is to reduce noise.

 

[jawbone]

The fan blades are spaced such that the center of mass is placed exactly on the fan axis to minimize fan vibration. The resulting fan noise is 11 dBA quieter in discrete noise level than the even bladed fan system.

So the fan is still balanced through horizontal and vertical axis as well?

 

[pishta]

noise reduction comes to mind. The even spaced "chopper" blades create a frequency (google chrysler air-raid siren) and if you can break that frequency up (different blade spacing) you can reduce the drone. To think Chrysler developed this minute feature and ignored UTG's slant six "oil sloshing problem on rear rod bearings"? C'mon man!

 

[jawbone]

Thank you everyone for your quick and informative responses. Jeff

 

[ch1ll]

Blades non symeteric to prevent harmonic vibration at resonate frequency. Do you have the fan clutch for that fan? This fan was used with a fan clutch. The 213 fan did not, used on 1968 340. The issue you will have to address is the distance from fan to radiator which may require a spacer or the correct length fan clutch.

 

[ir3333]

Nope...i know a bunch of guys that worked at GM.The unevenly spaced units were made by guys who came back from lunch drunk.

 

[Lord Sparky]

It’s shape makes me uneasy. Yet some famous super-models have unbalanced facial features.

 

[ch1ll]

Are you using the 70 and up aluminum water pump? Are you installing air conditioning?

 

[jawbone]

Blades non symeteric to prevent harmonic vibration at resonate frequency. Do you have the fan clutch for that fan? This fan was used with a fan clutch. The 213 fan did not, used on 1968 340. The issue you will have to address is the distance from fan to radiator which may require a spacer or the correct length fan clutch.

I intend to use a clutch with this application. Noticed the 213 is a 1.5 inch pitch for the 340 and 383 specifically for Barracuda and Dart. Though I want the correct fan for the Barracuda, thanks for your comment regarding fan clutch. Really would like to use one.

 

[jawbone]

Are you using the 70 and up aluminum water pump? Are you installing air conditioning?

The water pump has become a major issue. No AC. Have all the makings for the aluminum pump but the fan shroud I have is for a 68. Looking into swap using pre 70 pump but pulley acquisition has become a problem. Just went through that with aluminum pump. Then there's the issue of the radiator.

 

[ch1ll]

The 69 and down water pump is cast iron and shorter length, I’d go with the 70 and up. Your not going to know where you are until you start assembling and getting mocked up. See alot of spacers of various lengths for sale on fabo. Search function is your friend. Rock auto has new clutches but you have to inquire about lengths.

 

[ch1ll]

What size alternator are you going to run and what type of radiator? In my opinion, a fan shroud is mandatory, even if it is home made.

 

[jawbone]

The 69 and down water pump is cast iron and shorter length, I’d go with the 70 and up. Your not going to know where you are until you start assembling and getting mocked up. See alot of spacers of various lengths for sale on fabo. Search function is your friend. Rock auto has new clutches but you have to inquire about lengths.

Did a mockup just for the aluminum pump. Now I am possibly going to change to pre-70 pump. This is for radiator issues (inlet and outlet). Was told the Hayden 2947 was the answer. Low profile clutch. Will not know for some time.

 

[jawbone]

What size alternator are you going to run and what type of radiator? In my opinion, a fan shroud is mandatory, even if it is home made.

Currently have the single field alternator. Not sure what amperage it is but will work for my initial needs. Have a lead on a 68 340 only radiator #2898026 and same year shroud. This is why I may switch to pre-70 water pump but pulleys are a crap shoot and very expensive. They are advertised for 69 and earlier but will not know until I made another mockup.

 

[jawbone]

The big question to me is if you have a 68 radiator #2898026 that fits your 68 fan shroud would you swap to pre-70 water pump. It's almost like you have to.

 

[413]

@jawbone look at the center star of the fan, unequal size holes drilled in The triangles the fan blades are riveted to. It is balanced, and the uneven spacing stops noise.

most 340’s came with that 215 fan, was there a big fan problem or a recall? Nope

 

[Mike69cuda]

The 2947 clutch is misery to install. The access to bolt it to the water pump is so tight that you can’t use bolts. I had to use studs and nuts. Don’t use it unless you absolutely have to.

 

[jawbone]

The 2947 clutch is misery to install. The access to bolt it to the water pump is so tight that you can’t use bolts. I had to use studs and nuts. Don’t use it unless you absolutely have to.

Thanks for the response. This may be more reason to go with pre-70 water pump to get more room.

 

[4spdragtop]

I would say go era correct, so stick with 69 and earlier, it may initially be a pain, but once you have all correct pieces it will work perfectly. I may be be wrong but chk the 68 340 rad, I recall there were 2 different specific #'s. Auto vs std(cooler lines vs no lines).
Repop new wp are available for 69 and down. Problem with them is the bosses arent machined 100% to oem spec(mine wasnt anyway)

The big question to me is if you have a 68 radiator #2898026 that fits your 68 fan shroud would you swap to pre-70 water pump. It's almost like you have to.

 

[Inertia]

Timing marks, timing cover, pulley depths, lower rad hose, power steering pump brackets, location are all diff between cast iron/alum water pump.
Just so you know.

 

[RustyRatRod]

Three reasons. It moves more air, it's quieter doing it and there's less drag than a symmetrical fan because of how it breaks the air up. The MP engine book has covered all this in good detail for close to fifty years. The problem there is also three fold. First, people refuse to believe what they read. Secondly, people won't read what you tell them. Lastly, now, unfortunately, the MP engine book is getting difficult to find copies of. I think the last printing was the ninth edition for both the engine and suspension manuals. I used to preach those manuals hot and heavy around here, but I just gave up for the three reasons mentioned above. Especially the first reason. People just will not believe the information in those manuals. They'll argue every step of the way the information is "wrong" as if they somehow know more than all of the racers and engineers whose vast knowledge spans well over 100 years collectively.