Ok, here's one for the smart people! I plan on running 2 x 235 cfm inline fans ducted via naca ducts to some modified cylinder head tin on my new drag motor. The fans I want to use are 100mm diameter, naca ducts are 75mm diameter, it would be much neater to run 75mm into the cylinder tin also... If I run a reducer on each side of the fans will it cause a huge restriction or will it cause a higher velocity due to the smaller ducting diameter?? I hope this makes sence!

Cheers
Mick.

Best off with squirrel cages sitting straight on top of the barrels. like the ones on mine. Very easy,cheep and work well. was able to drive to the stageing lanes do a run and drive dack to the pits with no problems.

It's about 200 bucks for the cage fans, about 50 bucks each for the inline fans... The cage fans don't blow 235 cfm, they are quite bulky and they will only draw in the hot air that's already hovering around the motor... I'm trying to draw in cooler air because I have the added heat of boost.... That's my theory anyway.

Not if you duct air to them. plus using the original tinware the blow the air were its needed!!!! Have you priced naca ducts????? You may be suprised

http://www.biasboating.com.au/High_Capacity_Bilge_Blower_100mm_p/4647.htm 

Bout 15 bucks each on eBay... Really it doesn't even have to be naca ducts either. I could mount a intake in the guards and plumb it to there.... As I said in the first post there will be cylinder head tin modified to take the ducting...

Here is an idea... Ben suggested naca ducts, ducted to an air box in the parcel shelf with the fans mounted in it... Meaning no restriction on the intake side, only reducing it to 75mm on the outlet side.

Like this

That was supposed to be top secret!!!

Really? I can get rid of it if you want.... I didn't think it would upload straight off my phone!

nah its cool. your ice idea is good too.

Yeah as I said to Ben, to gain lower temps you could even add ice into the box so the fans are essentially drawing cold air instead of ambient temp air....

You might be better off putting th ice effort into an intercooler.... Cooler intake temps = cooler head temps. If you are running a draw thu setup this is not an option though....

I like the air box idea, you could put bell-mouths on the fan inlets to keep the air low clean / reduce turbulence.

I'm a bit rusty on fan theory but I do remember axial flow fans are most sensitive to inlet losses, and do not build much pressure (which means any pressure drop will have a big impact).

The closer you can get the fans to the heads te better, to reduce ducting losses, but I think they will be close enough as you draw them. I would try to run 100mm out of the fans, and equivalent area of inlet into the box (ie if using 75mm, run 3or 4) to avoid pulling a vacuum (not that the fan will pull much of a vacuum, but it will hurt its efficiency) in the air box. Venting the air box into the cabin would stop this too.

Yeah doug, draw through setup... No intercooler.

I've read that Naca ducts don't work all that efficiently due to the way they're mounted (usually in back windows) to make full use of this type of ducting you need to stick them into the air flow.

Really, it's not about the naca ducts being effective at catching the air, just a place to draw cooler air from.... You could really just do away with the naca ducts and draw the air from a vented ice box or even just draw the air from the cabin of the car....?? Just as long as its not recycling the hot air from the engine guess???

I wonder what the current draw on those bilge blowers is like... are you planning on running an alternator Mick ???

Then I wonder what the hp loss of a normal cooling fan is compared to the alt ???

You don't get anything for free...
Most electric fans won't generate the same pressure as the mechanical fan. Check out spal fans and their CFM rates pending static pressure.
I wasted plenty of time researching this, albeit for a different use...

Yes to the alternator, from what I have read they draw less current than a squirrel cage fan... As far as hp loss, I have read approx 15 hp through the stock setup and that is a big heavy alternator running a fan.... Plus the up side is more room to play with by getting rid of the stock setup.