fan size help quick

Ok how big should my fan be I want a mechanical one my fan shroud seems to be able to take 19 inches. Or should i stick to the size that is in there now .I have a 4 blade and from end to end it is about 17".I will go to 6 blades of course .but can I go bigger on the diameter:huh:

The answer to your question (as brought forward) is pretty simple as the '71 429CJ and SCJ took a 19" clutch fan with seven (7) blades.

In contrast, the '71 - '72 250 six and 302/351s took a 17 1/2" fan with four (4) blades.

Please keep in mind that based on your previous posts, you have made significant changes (engine wise) and that old 4-bladed fan may no longer be adequate for your cooling needs. Since you have said you want to/plan on using a mechanical fan, I would strongly suggest the use of a clutch type fan, considering the modifications you have made.

Please bear in mind that a 7-blade fan (or 6-bladed) offers greater cooling capacity than the 4-bladed one but reduced efficiency as it consumes more power. The clutch-fan only consumes power when needed. You mentioned the shroud; that is good as a lot of the 4-bladed fans did not have shrouds. Any fan with more than four blades needs a shroud.

Hope this helps!

BT

Just a ? why not go with an electric fan. One they come on only when needed with the proper temp switch and two there is no loss of power that other wise would be another resistance on the crank.

I know there is a bit more fab work involved but the benifits to me out way the cons of it. Griffen and BeCool have kits for a direct replacement for set ups with up to 22 in fans or dual off set 10 in fans. If you want i can see about getting the part numbers for everyone. I have a friend that works at BeCool and he can usually get me the part numbers for things that arent on there web page.

Dont mean to jack your post

Cory

Thanks for the quick reply's guys the reason I needed it is my engine will be here this weekend so I need something quick.I will get the 6 or 7 blades for now cause I want to shred some tires asap.And I can get one the day after I order it ,and they are pretty cheap .So I don't mind getting one even if I get rid of it soon.once the car is on the road I will check my options either a clutch fan or electric.


and does the size of the fan have to match the fan shroud or just fit inside

EX. could I use an 18 inch even if the shroud is for a 19"

I measured the shroud and it is a little over 19 " in diameter sumit seems to direct me to a 19.312 fan.

No, the fan does not have to "fill out" the shroud, if that is what you are asking.

However, fan placement is important for proper cooling. Spacing from the radiator is critical, as is the shroud depth and width.

Engine driven fans work best 3/4 to 1" from the radiator surface. Additionally, fans need to be placed halfway into and out of the shroud. For proper positioning, you should use the correct fan spacer for your application.

Hope this helps.

BT

thanks guys I ordered an 18 inch {Flex a lite}mechanica. It is rated at 7000 rpm and as for the spacer I have one on the fan that I have right now if it is wrong I can get one in a day.