91diesel

My boost gauge is hooked up past the throttle body so it is showing the boost at the cylinder, and it still never shows a vacuum although it is capable of it. OK I shouldn't say never because occasionally when I let off the throttle on the highway it dips to maybe 2-3psi vacuum for a second or so, but never at idle.

Herblenny

Anything after TB I consider to be intake manifold pressure. I'm not too familiar with diesel but I know most gas turbo engines will create vacuum when TB is closed (like the NA engines). If you don't pull much vac, you might have some issues with your engine. But again, i'm not much of a diesel guy so I'm not 100%.

Crawdad

I can't count the number of people on various different forums that have had the 'inspiration' to put a 12v fan in the intake to "produce a small amount of boost/positive manifold pressure". It doesn't work, it will cause a huge intake restriction, and you are wasting your time. You can believe me or not, or you can try it yourself, but the results will be the same.

abecedarian

turbos, lag and BOV:
Turbo lag is caused by the fact that an engine's exhaust gas velocity is too low at low rpms and throttle position to spin the turbo fast enough to make boost. turbo lag can be minimized by choosing different turbine and compressor housings that raise the impeller speed and move the air quicker and sooner, but then you run into the problem of "running out of boost"- where the turbo cannot supply enough air for the engine to maintain an elevated power level. twin turbo setups can overcome this to a point, where a small turbo provides lower rpm boost and the intake switches over to a larger turbo when engine rpm's are high enough to create boost with that one. If I'm not mistaken, some Supras and some Mazda's had a staged twin turbo set up for this purpose.

Turbos are 'slightly' restrictive when they are not making boost, but the compressor wheels are designed in such a way that their impact is minimal. If you're feeling bored, put a vacuum gauge in front of the turbo and another after it and see what the differential pressure gradient is. you'll find it's rather miniscule.

Blow off valves are usually used on turbo & supercharged engines to 'blow off' the boost in the intake when the throttle is suddenly closed, i.e. at a wide-open-throttle shift, in order to prevent the pressure wave created when the throttle closes from travelling back through the intake and damaging the charger, or as a fail-safe boost limiter in case of a wastegate malfunction. blowing off the pressure also prevents compressor surge in a turbo and actually allows it to spool up faster when the throttle re-opens.

Diesels and Vacuum:
most diesel engines do not have throttles in the traditional sense. engine speed is controlled by how much fuel enters the engine, not how much air, so the intake tract is open from the valves through to the filter. therefore, there is no way for a diesel engine to create vacuum... unless the air filter becomes clogged for instance. a vacuum/boost gauge will not show vacuum under normal conditions.

electric fans (redux):
I too am amused and frustrated by people falling prey to the notion of 'put an electric fan in you intake for more power and economy'. If it worked, every vehicle would have one.

If you decide to install a fan, the best option is the 'squirrel cage' or 'scroll' type. They generally flow more air at any given shaft rpm than a comparably sized axial flow fan. If you're really bored why not try an impeller from a vacuum cleaner?

As a side note, what's going to happen when the engine needs more air than the fan can provide and overspeeds the fan causing it to explode? ... all those little pieces will fly up the intake and into your engine. Heck, it sometimes even happens to turbos and superchargers when that unfortunate backfire occurs.

Herblenny

THanks for that info... I had no idea. Learn something new each day

Blackulua

go with a regular 22re with a comp cam 260s.Im having 23.1 mpg with 1300 miles so far on my rebuilt believe or not.I have 4:56 gears with 31's and the trucks moves pretty well on the highway.

abecedarian

here's another little tidbit- when you see black smoke from a diesel tailpipe, it's because there is too much fuel and not enough air, dirty air-filters are a prime cause. not being in the proper gear, or accelerating under load are other possible causes.
Continuous black smoke usually means an improperly adjusted injection pump, a badly clogged air-filter, clogged exhaust or needing valve adjustments among the many other causes.

Blackulua

I do have the LCE headers and 2 1/4 exhaust pipe and the truck is a 4wd daily driver.My 2wd truck with 220,000 miles and still going has about 26 mpg engine kept stock and just kept timing stock and oil changed.

91diesel

"Diesels and Vacuum:
most diesel engines do not have throttles in the traditional sense. engine speed is controlled by how much fuel enters the engine, not how much air, so the intake tract is open from the valves through to the filter. therefore, there is no way for a diesel engine to create vacuum... unless the air filter becomes clogged for instance. a vacuum/boost gauge will not show vacuum under normal conditions."

While this is true the toyota 1KZ diesel, among other diesels toyota makes, does have a throttle plate. I believe they put it in to smooth out the shutdown and for emissions. Regardless, it does have a throttle plate and I can get it to show vacuum for a second if I rev and let off, but only 1-2psi. Any ideas why gas engines would show vacuum in this situation and not a diesel?

abecedarian

gasoline powered engines, as presently designed, utilize a throttle plate in the intake stream to meter the amount of air entering the engine, and consequently the engine speed. this is due primarily as a result of gasoline engines being 'spark initiated combustion', where fuel and air are introduced into the cylinder and an external event, the spark event, initiates the combustion process within the cylinder
diesel engines rely on compression ignition- where the temperature of the air in the combustion chamber is raised sufficiently high due to the compression of the intake air charge to result in the spontaneous combustion of the diesel fuel when the fuel is injected into the cylinder. consequently, injecting fuel at the proper time and volume based on throttle position will affect the idle speed.
Diesel engines 'run' on detonation, gasoline engines avoid detonation.
we could hold a whole separate discussion about detonation and conflagration, but then again we're not discussing rocket engines.

generally speaking, a throttle plate inline with the intake tract is meant to provide some modicum of vacuum to devices that require it. as well, it could also be to limit the amount of air entering the system in order to acheive a more balanced air-fuel ratio, a lean ratio actually to limit particulate/soot emissions.
I assure you though, that the throttle plate on those engines is not there to, and does not, adversely affect engine power or performance.

Herblenny

Very interesting.. Never really looked into Diesel engines and I'm learning quite a bit. Thanks guys!

STEvil

Got some examples? Very little info out there.

They are actually best for pressure but if you over spin them they are more liable to break apart than a normal style axial fan. A vacuum cleaner fan might work ok, they are designed to work in higher restriction than the average electronics cooling fan.

The fan would not be able to do any damage to the engine if placed before the air filter. If it is capable of pushing more air than the engine can use then you can not over spin it. As previously calculated a 22R can use approximately 220CFM of air flow at 5500rpm (stock red line for the longblock version found in the 1986 SR5 Pickups). If the turbo is making maximum boost at that RPM (6-8psi in stock trim according to a forum post somewhere on here) then there may be a possibility that a crappy fan could be over spun to the point of being broken. Given that most 12v fans can be run at 24v with no worries to structural integrity (just the motor might cook a bit sooner) its not really something to worry about. The restrictiveness of a fan should be less than that of a turbo.

Something else that should be considered is the MTBF of the fan used. A "vacuum fan" I dont think would last very long. Squirrel cage fans are a bit unreliable (at least the ones that seem to be used in vehicle cab air conditioning/heating systems), and electronics cooling fans (standard ones) are usually good for quite a while if you buy the right ones. Buy crap and you get crap.

Thanks to those who are being constructive btw.


Also sorry for any typo's, my motherboard fried last night and i'm using an older PS2 keyboard at the moment thats got really weird feeling keys on it..

Matt16

I just got 25mpg with a loaded 4Runner. Stick to the lowest speed you can manage in 5th gear, build up speed slowly before a hill, then use the momentum to make it up.

abecedarian

another thing to think about is that when the turbo spins up enough to become useful, it is pumping more air than the engine displacement requires, which then becomes boost. at ~7.s PSI, you have increased the amount of air 50%- from ~220 to ~330 cfm. at ~14.4 PSI, air volume has increased ~440 CFM.

a way to possibly overcome overspinning the fan would be to have a secondary air flow path that is held closed (possibly by a combination of a lightweight spring and the slight positive pressure from the fan) until the engine begins drawing more air than the fan can supply.

either way, for an electric fan to be useful for the purpose you're suggesting, it would have to be capable pushing air in faster than the air would leak back through it at the lower air-flow rates.

STEvil

I dont think air compresses at a 1:1 ratio with CFM, does it?

Either way fans for 500cfm is not an issue, a pair of Delta TFB1212GHE's at 14.x volts should do very close to that. To overspin a pair of those you'd have to be running 20+psi given a 1:1 cfm:psi increase and at those pressures you're probably not worried about the low end of the scale where the fans are concerned.

Here's info on the Delta GHE's btw. http://www.xtremesystems.org/forums/...ad.php?t=92731

I have a bunch of the 60mm ones hanging around, they are rated at 80cfm each.

EDIT

Thermo-electric generators to replace the alternator. eehh.. dont think so.
http://www.xtremesystems.org/forums/...d.php?t=190398

abecedarian

you must've missed my point- that for a fan (or arrays of fans) to create boost it must be able to flow more air forward than what leaks backwards. when more leaks backwards then forwards with a turbo, you get compressor surge and maybe even stall.
It doesn't matter if a fan can flow 500 CFM. what matters is that the fan can flow 500 CFM and not allow any of the extra air to flow backwards through the fan.

STEvil

If there is air flowing backwards though the intake system there is an issue somewhere that the fans are not going to be related to.

The fans do not have nor provide high static pressure but only overcome some of the intake restriction similar to what would happen using a larger diameter (less restrictive) intake.

abecedarian

if you want the fan(s) to overcome restrictions in the intake they must create a higher pressure gradient around the restrictions than the vacuum of the engine requires.
The only way to overcome a restriction is to force air around it.

STEvil

Which is what a fan does. It does not produce a high static pressure like a turbo or supercharger. It is volume oriented, not pressure.

Herblenny

I hate to tell you this, but thats not going to work!

STEvil, I still think you don't quite understand how turbo system works... If you put this fan in order to be efficient, it would need to be in enclosed surround or part of the intake.


Just by looking at this fan, All I see is restriction. There is NO WAY, it would push enough air. If your idea were to be true, people would use radiator fans in conjunction with intake.. But NO ONE DOES THAT!! Have you seen some of these electric radiator fans?? They are at least 2x the size of what youve shown. If your idea were to work, It would be easier for you to just divert the air from rad fans to intake.. But it doesn't work!