Again as I stated before I am new here and by no means a mechanic but am mechnically inclined. I am getting heavier into fixing my truck though, playing around with it and loving it to death.

Now my question is I was toying with ideas on how to play around with my truck. A cold air intake idea stopped quickly after finding it has no use on my truck. And I do not want to buy a bigger carb, yet, at least with gas prices.

After doing lots of reading so far to my understanding a lot of these carbs are also rated for cfm's, Im guesing into the carb for air/fuel mixture. Also from my understanding my stock carb has a very low cfm rating. Correct me on any of this if I am wrong and feel free to explain it more in depth to me(that would be very nice too.)

Anyway to my understaning it would make a lot of sense to me if when standing still or going very slow if I could force a LOT of air into that carb very quickly I could essentially get more power out of it until the engine gained more power/speed. I don't want to use a turbo, no experience, time or money. So what I was thinking was using a computer fan.

Now Im not a mechanic but I am one hell of a computer and computer cooling wiz. I am going back to school for IT administration and regularly practice computer modding and custom cooling schemes. Some of these computer fans can push up to a few hundred cfm's. I was looking at one fan in particular that would push something close to 91 cfm's under extreme pressure. Would it be feasible to hook this to a seperate intake near the air filter For when I am not moving or going very slow to be able to switch on manually and get a little more boost from the engine and lower end power more instantly?

Now there are many other fans and ways to push the air in the carb with this kind of scheme I can think of. There are a lot of fans to do this with too. I thought of using a computer modding fan because it draws very very little power while being able to push a LOT of air under a heavy pressure. But I dont know if forcing air into the carb will work or is a good idea and if so how much do I need to push with a stock carb.

 

Your motor is 300 cubic inches. At three power strokes per rev that's 150 cubic inches per revolution. 1500 cubic inches per hundred rpm. At idle, 700 rpm, that is 10500 cubic inches per minute. Or 73 cubic feet per minute. At 3,500 rpm that would be 365 cfm. So you can see that the engine demand would quickly exceed the fan output and the fan would ultimately become an obstruction.

 

What you're talking about is an "electric turbocharger"... something which had been tried many times but never made to work practically. Seems like a no-brainer on the surface, but when you start doing the math you see it's a catch-22. For a given engine RPM you need your turbocharger/ supercharger fan to flow roughly 2.5 times the CFM of the engine to generate each 1psi of boost. Most 'chargers deliver between 4-7 psi of boost. Scale that up and you see the 'charger needs to move LOTS and LOTS of air to be effective.

The "box fans" used for cooling computers are designed to generate a large volume of flow at low pressure, not high volume at high pressure like the centrifugal fan of a turbocharger. The CFM flow vs. backpressure curve for box fans is inverse; the higher the backpressure gets the more the flow rate drops. You'd simply need too many of them to see even the slightest pressure boost. Mount one to a small sealed box, attach a pressure gauge, and you'll see the fan can only generate a couple of PSI [if that] in a static air volume. Open up the smallest hole in the box to simulate air flow into an engine and you'll see the pressure drop to zero instantly. They're air movers... not compressors.

Even with very efficient modern electric motors driving a proper centrifugal fan you run into the problem of system efficiency. The alternator saps power to make the electricity to turn the fan. The average automotive alternator isn't very efficient so you have a mechanical power-in to electric power-out loss. On top of that you stack the power-in to airflow-out loss of the electric motor and fan assembly. Add it all up and you're actually losing power over most of your engine's RPM range.

There are a few commercially available electric "turbochargers", but the ones that actually "work" do so just barely on small displacement engines, and then for only short bursts like you'd see for drag racing. The bearings in electric motors aren't cooled and lubed by a flowing oil source like a turbocharger impeller, so if they run for long they'll simply melt. The electric 'charger I'm quite familiar with uses a 5" diameter 20,000 RPM electric fan drawing 60 amps and generates only 1psi of boost in a 3 liter engine. It can only be run for ~30 seconds at a time without burning itself up. That +1psi of boost = about a 5% horsepower gain... not much.

 

then you take an AC compressor running off of the engine and convert it into compressed air and nozzle it back into the turbo. But I haven't figured out the details yet.

 

Close. CFM=((CID x RPM)/3456) x VE Assuming VE .66(Everything I've come across shows this engine to have a poor VE) the unboosted CFM at 3500rpm is just over 200. (VE of 1 has CFM at just under 304).

Assuming that you can get an 8psi boost the the CFM jumps to 254 at 3500 with a VE of .66.


If I understand the original posters desire, over pressuring a draw through carberator has additional problems. I haven't looked at them since I'm working with an EFI system as my base "what if".

 

I dont want a constant boost like I tubo would give. I just want to be able to give it more air for more power off the draw manually.

Like say I was going to need to pull a freightliner from a ditch or such, nothing big, just a 20 foot box. Going from a dead stop I would like to be able to manually switch on a fan or such to give it more power right from the start then to platue at it's normal draw. Maybe just be able to turn on a fan for a second until I get the truck moving.

But after being explained from bdox's post this still wont work. After I rev the truck to something modest and nominal, say 2500 rpm's, the truck would be sucking more air then I could give to it with a seperate ducted fan making what I want to do pointless.

I have seen those little electric "turbos" and though they MIGHT work for what I want to do the price and power gain from it wont be worth it. If I could do it for very cheap I might consider it.

I originally thought of something like a computer fan, say something like an overvolted 120mm double or triple stacked 3 blade delta, or the same for a couple of Vantec tornados as they would easily be able to supply 120 cfm's a piece for the 80mm's (I cant remember the push for a 120mm off hand) and with a double or triple stacked fan they would greatly increase the pressure of the fan. But again I would need something like 3 of these setups of double stacked fans with a direct 80-60 mm feed straight to the carb which I dont want to do because I cant filter the air. Oh well.

Bdox, I did take your suggestion from my other post and started looking around the I6 forums to see what I can do. My first priority is to get my back axel fixed. It starts to vibrate at 45 miles per hour and gets rather strong and noticeable at 55-60 mph. After I get that fixed I am going to look into replacing the rocker arms with the chevy ones and going from there.

 

You face the same issues if you want any type of "boost", even if for a brief shot of power. First is that you need a blower/ fan/ whatever capable of providing over double the CFM flow of the engine at a given RPM. Simply equaling the flow of the engine does nothing but keep the fans from creating drag. You need 2.5 times the engine flow to get just 1psi of boost, and computer cooling fans aren't going to do this unless you use bunches of them. Remember their CFM ratings are only valid for "unrestricted" flow. Same for radiator cooling fans and the like.

Other issue with carbed setups is that the whole carb needs to be enclosed in a pressurized box. If you try to cram pressure down the venturi you won't get any usable fuel flow, in fact you'll get gas spewing out of the bowl vents. The "cheater" way around this is to run hoses off your pressurized air feed to all the fuel bowl vents, equalizing pressure so gas will flow normally. This does work... but soon you'll have all sorts of gas leaks from the excess pressure inside the carb.

The only workable "on demand" boost system is good ole' nitrous. A bone stock 300 should be able to take a 50-75 HP shot with no problem, 100 hp if you're careful. A ready made kit will run you about $400 and provide 5-10X the power boost of any sort of electric turbo setup. Of course that kind of $$ will buy you some real full-time performance like a new cam...

 

My first priority is to get my back axel fixed. It starts to vibrate at 45 miles per hour and gets rather strong and noticeable at 55-60 mph. .[/QUOTE]

Are you hearing any metallic sounds? It is more likely to be something to do with your tires or wheels. Check to see if they are out of round. If they are true, balancing might fix it.

 

[QUOTE=SR_Crewchief]Close. CFM=((CID x RPM)/3456) x VE Assuming VE .66(Everything I've come across shows this engine to have a poor VE) the unboosted CFM at 3500rpm is just over 200. (VE of 1 has CFM at just under 304).

You are right of course.

I was just running the most basic numbers because they are easy to follow, and I wanted to illustrate the point and not get overly technical.

 

Are you hearing any metallic sounds? It is more likely to be something to do with your tires or wheels. Check to see if they are out of round. If they are true, balancing might fix it.[/QUOTE]

My father and I had it up on a lift and looked at it.

Right before I noticed the vibration we changed the u-joints. We checked and all pins and everything is in place with them.

I dont hear any metallic noises or any of the such. Just a vibration. Up on the lift though with the truck accelerated t0 25-30 mph we did see a big consistant hop in the rear driver side tire. We also found close to 1/2" of play in the drive shaft? My dad came to the conclusion after loking at it that the rear differentials were going bad and the cheapest way to fix it would just be to get a new axle.

If you have anymore suggestions though that might lead to a cheaper/easier way to fix it I would be more then happy to invistgate them.

 

Sound like the pinion bearing is gone. If you have no experience with differentials, it's probably best to swap it out. If it moves a half inch, the ring and pinion may be gone too.

 

do you mean it rotates 1/2" around the circumfrence of the driveshaft, or that it moves that much laterally? if it is only a rotational play, its really no big thing. either way, your dad is probably right. a good ring and pinion will probably run you more than a used axle, and you still have to do all the rear end work. swapping out the axle is no biggie and shoud only take an hour or two. i know i got mine from the junkyard for 100 bucks, changed over the brakes and i was good to go.

 

Im going to go with the option of buying a rear axle at this point. One slavage yard wanted 300 for it. I havnt been able to call any others yet.

Anybody by chance know the ratio and size of the backend for an 83 f-150 i6 carbed?

 

the rear end ratio can vary quite a bit, but most of them have a small stamped metal tag on the back that states the ratio. any good junkyard would probably be willing to make sure that they match it up. check around some more, there is a good chance you can find a good rear end for less than that.

 

My father and I had it up on a lift and looked at it.

Right before I noticed the vibration we changed the u-joints. We checked and all pins and everything is in place with them.

I dont hear any metallic noises or any of the such. Just a vibration. Up on the lift though with the truck accelerated t0 25-30 mph we did see a big consistant hop in the rear driver side tire. We also found close to 1/2" of play in the drive shaft? My dad came to the conclusion after loking at it that the rear differentials were going bad and the cheapest way to fix it would just be to get a new axle.

If you have anymore suggestions though that might lead to a cheaper/easier way to fix it I would be more then happy to invistgate them.[/QUOTE]

If the vibration started right after you changed the u-joints, I'd say to start there.