Picture this: have a turbo that delivers 40+ lbs of boost that goes through an intercooler, then to a 20 gallon reserve tank (in the trunk?). The reserve tank has a 7 psi regulator that feeds back to the intake manifold. I presume there's a BOV before the reserve tank and MAF after it.

Would such a set-up eliminate turbo lag and provide a near-constant 7 lbs boost regardless of RPMs? Would the turbo provide enough pressure at higher RPMs to compensate for the lower RPM driving? I'm not talking daily-driver type of stuff but autocross or track events. Is there some basic flaw in the idea that I'm missing?

It's a wacky thought I know, but then I also did the math to figure out how long a standard scuba tank could provide boost as a poor-man's FI. :p
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EXPATRIATE INSURANCE FORUM

 

First off there would be so much heat at 40 psi that it wouldn't even be funny. To get a turbo to provide that much boost, you'd need to have a pretty large turbo that will probably have a pretty good amount of lag to it. Second of all, how will you regulate this pressure in the tank? If you have enough airflow to provide 40 psi to it but only need 7 after it, where does the excess go? The simple answer is that it is either blown off and totally wasted or it goes back through the turbo. Either scenario is not a good idea. There were some RX-7 people who sat down one day to figure out how large an air tank would have to be to provide an engine with boost for even a short trip down a drag strip. I think it was determined that the physical amount of air that the engine would need in cfm would drain a car sized tank of highly compressed air completely of in a couple of seconds. Remember that it's not the amount of pressure that is important. It's the amount of airflow. My air compressor in my garage sits at 120 psi right now but has no airflow. That means no power can be made from it. You couldn't get a large enough volume of air to make it work. There is no free power.

Technically if you want no lag you must completely remove the turbo. There is always lag as there is always a certain amount of time that it takes the air to get to the engine after you step on the throttle. Even naturally aspirated cars suffer from this. It is more appropriately called fuel lag as there is a delay in the time it takes to get the fuel supply (air and gasoline) to the combustion chamber where it can do work. No lag would be no running engine. Forced induction lag is boost lag. It's the time it takes for pressurized air to enter the engine. An easier way to do it is to keep the turbo spinning fast to minimize this problem. Turbos can be made to make boost when not under load. People already do this on drag cars to give them the power off the line. With a little ecu tuning this is easy to do. You retard the timing and run really rich when not under load. This lets fuel get through the combustion cycle and burn in the turbo itself. When it burns here it also expands and spins the turbo up. You can get boost this way. It is very effective but extremely hard on your turbo. Your way of doing it does not address how to get the turbo spinning initially. You just want to get it up to speed (a much higher speed that takes longer to get to) in order to make a certain amount of boost and then bleed off what you need. This is hardly productive. If you could get a turbo with an exhaust side small enough to spin up to 40 psi of boost when not under load, it would be such an incredibly large exhaust restriction that it would be absolutely choking your engine. That would be robbing the engine of far more power than you are trying to add back in. Not a good idea.

 

now why does that air compressor analogy seem familiar... :p

 

Good post RG.

My initial reaction was being able to sustain the pressure while giving up such a large volume. You explained it even better

Cheers,
Hymee.

 

What might work is to pipe a line of compressed air into the exhaust just ahead of the turbo and use that to spin up the compressor during no-load. Might be good for a few seconds of full-boost. Of course, so is rev'ing the engine with the clutch in.

The anti-lag system that RG mentions was initally used in WRC cars to keep their huge turbo's spun up. Of course, on a stock car, it would probably blow the exhaust apart in a thousand miles. I think on some of those cars, they actually put a spark plug in the exhaust manifold.

The only way to really minimize lag without a system like this is to vary the size of the turbine and compressor so they are more optimal at all rpms. I suppose something like an Aerodyne is the right direction, although that still has lag. Variable vanes; allows it to spin up faster. Of course, the basic size and shapes stay the same, so there's a limit as to how much you can do with this.

 

Actually the most promising system to date is a dual-powered turbo that uses an electric motor at low RPMs which gradually tapers off as the more traditional exhaust driven part kicks in. BMW has done some research on this and their prototype gets to full boost/torque/hp at 1500 RPM and pretty much stays flat all the way up to redline. Impressive technology.

Until then I'm just thinking of creative ways to address the problem.
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Csi Advice

 

If people would just size their turbos properly for street use such as the tiny turbo with the Greddy kit, lag wouldn't be an issue. There's always supercharging.

 

have the clutch put on your roots blower like mad max and have it click off as soon as the t78 spools

 

During the turbo years in F1 they used a butterfly on one side of the turbo and an iris on the other. Thus closing off from ambiant pressure during shifts or light throttle. Thin air keeps the wheel speed up longer. No density to resist rotation.

 

f1= teh sophisticated

 

Funny :D ....... to bad they don't have a blower that works like that.

 

mad max!!! mad max!!

gimme an a/c clutch, a tool shed, no sunlight for a week, and a half-oz of crack and i'll show you an electric-clutch blower :D

 

Why would you need an electric clutch? why not have a a belt driven gear connected to a centripetal clutch so when it reaches high enough rpm it will automatically disengage. Effectively making it work like a supercharger at lower rpm speeds and a turbo at higher. Just a passing thought.

 

I actually just read a small article on rotarynews.com.
Link: http://rotarynews.com/node/view/381

 

Or there is VW's new solution for their small displacement engines.

Supercharge AND turbocharge. Allegedly the engine returns better gas mileage than a comparable turbocharged engine, as the supercharger negates the need for massive throttle openings to get the car moving. I cannot imagine the complexity or nightmare that the engine bay is, however...
I'm just no fan of FI in general tho.. I *hate* what turbos do to throttle response.

 

Twin-charging isn't really new, but I don't think any manufacturer has done it on a normal production car. There are quite a few different ways to configure it, with varying degrees of complexity. There used to be some Group B rally cars that did this (Lancia Delta Integrale S4?), to great effect. There's also twin-charging kits for the MR2, Mini, and soon the Miata.

 

Actually, I was wondering something similar as the original idea (top of thread) of a tank of air with a regulator... What if you didn't have a turbo, but this could be a poor man's boost. You have an air tank in the trunk that can supply 30 seconds or so of air at 7 psi higher than ambient, and one of those cheesy electric compressors that constantly keeps the tank pumped up with a shutoff when it's maxed.

Okay so the basic equipment might run $100. Then you need to add a high pressure line from the trunk to where ever the gate is, and you'll need to reprogram the computer. What would the whole install cost? $1,000?

It ain't turbo, but for someone who wants a kick on a straight away or autoxing, it might just do the job.

There's also a benefit if you let the tank sit: The compressed air heats up, once the heat dissapates, the expansion of 20 or so PSI to 7 PSI cools the air down significantly.

I didn't think of this concept in terms as PUR NRG suggested a turbo assist. A friend and I were kicking around the idea of how to get around air flow restrictor plates used in racing: If you take the above idea, intake the air from behind the restrictor plate so no one can argue your using outside air, then add the mods so the compressor only kicks in to pump the tank during lower than max revs, and only release the pressure on straights when at full throttle. So you still have the restrictor plate, but are sucking up air when the restrictor isn't really restricting, then using the air when the restrictor is an issue.

 

Never going to work. The engine draws something like 200+ cfm of air. Your average scuba tank at 3000 psi holds 80 cf of air. That means you could supply air at ambient pressure for 24 seconds, or air pressurized at above ambient (say 7 psi) for even less than that. To provide this, you incurr at 40+ lbs weight penalty for the filled tank.

Engines use more air than we realize.

 

Oh yeah, I remember the old Lancia raly car that ran a dual charging setup.. But no one has ever done it on a production car. I'm kinda surprised... it seems like a lot of complexity and risk for a manufacturer to take on a street car.

Didn't know people made such kits for other cars, I'll have to check those out!

 

The whole setup sounds complicated, more than likely due to this basic equation:

pV=mRT

But at least you're thinking PUR NRG. I haven't put down a thought here in over a year.

Psylence, HKS, a few years ago, developed a twin-charger kit for the DC2 Acura Integra. It put out crazy horsepower for its time, however they knew there were better ways to use forced induction. Also, I believed they had a twin-charger kit for the AW11 MR2 (Gen I). It's been discontinued for a long time.

Someone here mentioned a VANT turbocharger, or in laymens terms, an Aerodyne unit, though other companies have them. I remember MazdaManiac saying something last year that these units were underdeveloped when they first came out (I made a thread last year about VANTs). Personally, I like the idea of changing the geometry of the turbine blades. I believe Garrett has had a VANT (I'm sure you can find the article on the webpage). BW has an interesting staged turbocharger setup, however it appears to use up too much space.

 

VNT turbos? I'm pretty sure that the 1.9TDI volkswagen engine uses/used one of those. Could be wrong tho...

 

You might be right. It seems to me VANTs, VNTs or whatever the hell they call them now work better on diesel than on gasoline engines. I can't remember the reason. Maybe Jeff or Fred might want to jump in and explain it better? Also, I think Cummins might use them on their turbodiesels.

 

I was reading through and didn't see anybody mention NOS. Can't NOS be setup to negate turbo lag?

 

Sure, but it runs out. Way more effective than trying to use compressed air though, but not as cheap.

 

Once I had the crazy idea of using a small jet turbine from an RC aircraft. The idea would be to divert air from the compressor section to the intake to provide boost, and once the rpms come up, route the exhaust gases into the turbine section, allowing you to reduce the amount of fuel needed to keep the turbine spinning. No idea if it would actually work.