electric high volume fan? work same as a turbo July 17, 2013 01:35PM
you can buy high density fans 300-500 cfm. we can not run turbos so thinking of plumbing one of these on the intake side of a diesel motor. any thoughts on how it might work. forcing more air in has got to make more hp. fans are 5 inches in diameter 2 inches thick very easy to fit in the intake pipe.
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Re: electric high volume fan? work same as a turbo July 18, 2013 04:39AM
I have looked into doing this in the past. It is borderline cheating- you are basically adding a super charger. That being said, I learned a great deal about it. Here are a couple of the most informative replies I got at that time.

It depends a lot on your valve stuff. Many (especially older) 4 stroke engines do not achieve good flow at speed, having a flow deficit primarily due to intake related problems. A little pressure can make a very nice difference by helping overcome those problems. Intake problems are usually unsynchronized pressure waves in the intake and exhaust push back because of low pressure in the intake at valve opening while residual exhaust pressure remains on top of the piston. One of the reasons higher compression engines make better power is that they pump out the cylinder better, which leads to less intake blow back. That is one of the reasons why there is no set formula for power produced vs compression ratio.

To throw some light on the situation, With proper exhaust tuning on a two stroke, the exhaust pulse actually pulls a vacuum at the end of the exhaust stroke, sucking some intake charge all the way into the exhaust pipe. The exhaust pressure wave bounces off the end of the pipe and returns to put pressure back towards the piston, pushing the charge back in. Gains for typical dirt bike numbers are around 2:1 in pumped volume. More is done for the 125s, less for the 500s as they could afford to sacrifice peak to get better (wider) torque curves.

I can tell you squirrel cages don't provide very much pressure, but can enhance flow a significant bit. Problem is they usually can't provide enough flow at higher RPMs. With old V8 big blocks you could get a nice boost off the line, but it flattened out quick and became a restriction somewhere around midrange. (Heater motor experiment :lol: ) And since blowers are a single speed device, they don't follow your engine. (That can be changed with some extra volts and a control circuit of course) And if on gas, you need to find all your carb vents and make sure they are routed to the breather pipe at some point after the blower. Many automotive carbs vent into the air cleaner anyways so this usually isn't a problem. Tractor carbs however...


and

Info like this is generally hard won and few will pass it around. Most I have talked to have never come close to understanding why their machine do what they do.

Forewarning, I'm tired so this is gonna be rambling :lol:

At 300 cubes, you have about .175 cubic foot of base theoretical displacement. Ifn it makes 2500 rpm then ya get ~435 cu ft then divide by 2 because of the 4 stroke dead cycle. Result is ~218 CFM at 2500 at 100% efficiency. Not a lot in many ways. Ifn you are turning faster, scale accordingly.

If you want clues to your engine and whether it will pay off to tweak it, put a good flow meter on the intake and put the engine to full load at any measured rpm and do the math. From there you have a good starting point as to what techniques will help. Ya never know. Some engines are poor, some will simply surprise the crap out of you.

Now for the harder stuff. You may want to skip the drier parts.

Boost is always a double edged sword. Small gains can often be very easy and cheap, but not always. Getting an absolute gauge pressure sensor hooked to an o-scope is your best friend for that. Nowadays those sensors are cheap and on every car, but I don't know about their frequency response which is critical to preventing errors in the data. Good ones used to be horrendously expensive. And you have to be willing to some drilling, up to possibly sacrificing a head in the process. This part can be very difficult. And improper probe positioning can destroy the measurements. <_<

On another note, trying to put gain into non tuned systems requires brute force efforts like turbos and such. They absorb power and all of them are wave time dependent to some degree, meaning they have a input/output transfer function that isn't linear. And yes that still includes superchargers (mostly due to cam.)

Btw, do you mean 100 or just 10? Yeah there are conversion losses, but that is a lot of input for a 300 turning slow.

I'd say that 100HP is pretty far on up the scale. I had a air compressor based on an IH UD18, and those run not too much over 100 HP. Couldn't find specs but we think it put out something like 365 CFM at 100 psi. Two stage compression, a very large inter-cooling radiator, 6 pistons total. The kind that drives jackhammers and large pneumatic drills on tracks. A 301 gas isn't making a whole lot more pressure than that during compression stroke. Well, 350ish divided by 218 gives about 1.6 so that raises that 100psi to roughly 160 (gauge, ~175 absolute) in the intake manifold. Woo doggy, she be going fast with that kinda pumpage. Problem is, that is fairly high efficiency pumping. Very heavy machinery in use.

Now for other numbers. A squirrel cage centrifugal blower, of which there are literally 1000 variations, makes up to maybe 0.25 psi on a good day. Typically much less, and nothing stellar. They also have a distinct upper limit at which they flat line and you gain no more. Deeper centrifugal blowers like Paxton can make up to 100 inches pressure water. 100 / 12 = 8.3 feet of water, and with water at .446 per vertical foot yields 3.7 psi gain, ifn I got every thing right. Paxton rates their 1200 CFM unit in the 10 HP range. Go here for an interesting curve showing pressure vs flow. For roughly 10HP their 1200 unit will get you ~3.7 PSI at 400 CFM. Of course now your engine is breathing at 14.7+3.7 = 18.4 psi. It will walk the dog pretty darned fast, not to mention impress all your neighbors.

Working with a 301, you need 218 CFM at 14.7psi (0 altitude at 100% pump at absolute gauge) to break even. Anything less, and the engine is outrunning the compressor. To get say 1/2 lb boost, you need to hit 15.2 psi, which gives 15.2/14.7 = 1.035%, times 218 CFM = 225 CFM. (There is only 3.5% difference.)

Now, are all these number accurate? Mostly. There are so many supporting factors that you can get lost in them. And many factors cancel out others etc. I've left out thermals effects entirely, mostly because we don't need them at these pressure changes. And all of this is very specific to a given situation. We didn't go into altitude compensation because wherever you live isn't going to change that much. Probe positioning is very important, but is a category all unto itself and not necessary for rudimentary work. What is presented here are rudimentary items to provide some background.

Now for the meaningful part, for who ever actually read this far :lol:

If you engine is only pumping at around 75% at rpm (we won't talk about Chevy heads here), a 3 percent bump can gain you more than 3 percent. It may easily put you into the high 90s (efficiency) because of overcoming the problems mentioned earlier. (We didn't even get to talking about intake impedance mismatches) Thats why a small boost on a Chevy truck has rather dramatic effects. It overcomes serious deficiencies in the intake system. You can as much as double a Chevy on only 6 lbs boost due to more air at the same rpm and the ability to make better torque at higher rpm.

Now, will that 301 see big improvements? Hard to say. These are IH tractor engines, and they run at low rpm. At a given loaded rpm, figure a 5 to 7% bump for a 3% boost. If you are trying to go up in the rpm band and are running into flow loss, you could expect more like 20%, but I have to say I'm not accustomed to thinking in the under 4500 rpm arena. It is easier to hit a 10% change with toluene and corresponding timing adjustments.

Now as to learning more, the automotive engineering books sold by MIT can provide a lot of insight, but at times they aren't all that easy to read. :rolleyes: On the web, I don't take too many people seriously. Basing knowledge on changing a part and hoping it did something at the track kinda falls into the hobby category. Fun, but you wouldn't bet your job on it.
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Re: electric high volume fan? work same as a turbo July 18, 2013 07:55AM
That was alot of info. Looks like i have some calculations to do. thanks
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Re: electric high volume fan? work same as a turbo July 18, 2013 02:38PM
Assuming 100% volumetric efficiency, a 4-stroke engine air flow in CFM is: displacement X RPM / 3456. As simple as that.

So if you have a 400 cube engine at 4000 RPM, that engine is moving 463 CFM of air. Now if you put a 500cfm fan on it, the engine will still only flow 463cfm at the cylinder head, so this 500cfm fan will compress the air (kind of like a roots blower). Without going into all the math, assuming you can raise the air pressure by 0.5PSI (boost), with an 80% efficient fan, the air density increases by 2%, but the air temp goes up as well. Compressing air causes the temp to go up (can't defy physics). So just based on the air density increase alone, this would be a net HP increase of 2%, however this is reduced again since the air temp is higher.

You are better off bolting that fan to the fender to cool you off on days like today.
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Re: electric high volume fan? work same as a turbo July 19, 2013 03:47AM
i would agree it is HOT!!! thanks i can switch from turbo to no turbo in 10 minutes might just go back and forth thanks
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