A big issue is the idle..........by my laymans logic the pistons will still be sucking in air on the downstroke and since so little goes in for idle the turbo could simply add a little if needed but i doubt it will need to do much for idle, mostly for getting it going........
A turbocharger does not have the capability of doing anything at idle. It requires increased engine load, which increases exhaust flow to spool it up, hence the reason for turbo lag. You would not be able to rely on a turbo for what you want to accomplish. Like I said earlier, a mechanically driven supercharger would be the answer, but they have efficiency problems, which would most likely negate your entire efforts.
Why wouldn't a turbo, if properly set up, increase efficiency? Follow the air/exhaust flow: energy is used to suck air into the engine. In the cylinder it's compressed, ignited, and comes out the exhaust port hot and under some pressure. The turbo takes some of the otherwise wasted energy in the hot exhaust, and uses it to push the intake air into the engine, which means no pumping loss. That'd seem to equate to a more efficient engine, wouldn't it?
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Why wouldn't a turbo, if properly set up, increase efficiency? Follow the air/exhaust flow: energy is used to suck air into the engine. In the cylinder it's compressed, ignited, and comes out the exhaust port hot and under some pressure. The turbo takes some of the otherwise wasted energy in the hot exhaust, and uses it to push the intake air into the engine, which means no pumping loss. That'd seem to equate to a more efficient engine, wouldn't it?
I have to agree with this. Especialy reading the article about the Turbo cars being more efficient than their NA counterparts, A turbo is run soley off of the exhaust So all it does is make FREE power , By free i mean it doesn't drain anything from the motor, Like a supercharger does.
It's a highly plausibe way to add Fuel economy to your car
I say go for it
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A turbo is run soley off of the exhaust So all it does is make FREE power , By free i mean it doesn't drain anything from the motor, Like a supercharger does.
It's not 100% free, as a turbo adds backpressure to the exhaust side. Of course, the gain from increasing intake pressure is greater than the losses from backpressure, so there is a net gain.
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Exactly. You can use a turbo to either gain power with the same size engine (keep the same mpg in normal driving, with more power when you want it), or to use a smaller engine for the same power, and typically better mpg.
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you must be referring to a four cylinder, I hope. The other engines are simply crazy or exotic with turbo.
a four cyl does benefit.. subaru has been doing this forever. the 1980s versions are the act of math you are looking for, some even had carburators and turbos, all tuned by thier own extremely tight emission standards.
the timing of injection does play a factor in your quest..a downdraft carb cammed engine can make use of a smaller turbo, the injection will stay a slob with the same boost. in fact, that drove alot of hillbilles with thier subarus crazy...the carb cars with no turbo got twice the fuel mileage and passed them on the highway...
also, if you are over 9 to 1 compression, there willbe trouble, even for gentle turbo.
you may opt for a small charge another way to conquer the zero.
I still seek 3psi, coincidentally, for the similar reasons you are pursuing.
you must be referring to a four cylinder, I hope. The other engines are simply crazy or exotic with turbo.
a four cyl does benefit.. subaru has been doing this forever. the 1980s versions are the act of math you are looking for, some even had carburators and turbos, all tuned by thier own extremely tight emission standards.
the timing of injection does play a factor in your quest..a downdraft carb cammed engine can make use of a smaller turbo, the injection will stay a slob with the same boost. in fact, that drove alot of hillbilles with thier subarus crazy...the carb cars with no turbo got twice the fuel mileage and passed them on the highway...
also, if you are over 9 to 1 compression, there willbe trouble, even for gentle turbo.
you may opt for a small charge another way to conquer the zero.
I still seek 3psi, coincidentally, for the similar reasons you are pursuing.
awesome!
the subaru stuff sounds good I will try and do some more research.
I am aware of the psi limits and computer stuff on stock engines..........I will try and cross this bridge when I come to it but a low application turbo would be my aim anyway.
What I need to know is the lowdown on the cam profies I was thinking about - can it run smoothly without any scavenging?
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This has merit as it is done on Diesels and Direct Injection Gasoline engnes and is not done for power necessarily. It's a little bit beyond my scope of understanding but it seems like the idea isn't to increase manifold pressure past 30HG but to get almost barometric air pressure and essentially is just to decrease pumping losses. It should mean you can run higher loads than you normally would but the octane requirements would probably go up. This would work under cruise if you changed your gearing to be taller and should still be good for MPG until you start getting positive manifold pressure. But really this is a very advanced topic and I'm not so sure it can be done DIY without a lot of turbo knowledge and also the tuning of the engine for such conditions that it doesn't run pig rich into boost land.
A small enough turbo can start generating some pressure below 1500RPM but even Factory built turbo cars don't usually generate "positive" air pressure until at least 1500-2000rpm and they're usually designed to be pretty small and quick. The Ford Taurus SHO is advertised as having full torque from 1500RPM and the Cobalt SS when it switched to turbo from the supercharger was getting full torque at 2000rpm. The Ford Taurus uses a pair of GT1548(I think the last two numbers are correct). It's essentially the Turbo of choice for a low output single turbo Geo Metro sized engine like a 1.0l or 1.3l, but runs out of efficiency past 12lbs of "Boost" and bigger engines. If you use one in a bigger 4 cylinder like a 1.6L it'll work for what you're proposing but no one in the "Tuning" community will take you seriously . A small enough turbo could do the scavenging job that you're talking about. But it's a serious undertaking.
This has merit as it is done on Diesels and Direct Injection Gasoline engnes and is not done for power necessarily. It's a little bit beyond my scope of understanding but it seems like the idea isn't to increase manifold pressure past 30HG but to get almost barometric air pressure and essentially is just to decrease pumping losses. It should mean you can run higher loads than you normally would but the octane requirements would probably go up. This would work under cruise if you changed your gearing to be taller and should still be good for MPG until you start getting positive manifold pressure. But really this is a very advanced topic and I'm not so sure it can be done DIY without a lot of turbo knowledge and also the tuning of the engine for such conditions that it doesn't run pig rich into boost land.
A small enough turbo can start generating some pressure below 1500RPM but even Factory built turbo cars don't usually generate "positive" air pressure until at least 1500-2000rpm and they're usually designed to be pretty small and quick. The Ford Taurus SHO is advertised as having full torque from 1500RPM and the Cobalt SS when it switched to turbo from the supercharger was getting full torque at 2000rpm. The Ford Taurus uses a pair of GT1548(I think the last two numbers are correct). It's essentially the Turbo of choice for a low output single turbo Geo Metro sized engine like a 1.0l or 1.3l, but runs out of efficiency past 12lbs of "Boost" and bigger engines. If you use one in a bigger 4 cylinder like a 1.6L it'll work for what you're proposing but no one in the "Tuning" community will take you seriously . A small enough turbo could do the scavenging job that you're talking about. But it's a serious undertaking.
hi - thanks for the input there is a lot of good advice there.
i appreciate it would be quite a tuning undertaking.........would be a good exercise to learn from which I might try........need to secure a budget first though and of course time!
I see what you are saying about the technique to reduce pumping losses at cruise. It would be tricky and time consuming to tune.
In terms of the cam profile idea the aim is simply to prevent fuel going down the exhaust unless it is a result of incomplete combustion. As long as I could get it to idle and rev ok I would be happly. If the cam profile is used then I was thinking of having the turbo there to help control the airflow as required to compensate.
Cordelia - '15 Mazda Mazda3 i Sport 90 day: 37.83 mpg (US)
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The overlap on most cars is not an issue as they operate at very lower RPM. What you are talking about is something that happens to Racing cams at low RPM, they will literally pull fuel out of the cylinders and therefore have no power. The only minor details is dealing with a small econo engine that has one cam that is for a more mid RPM peak. They don't have a turbocharger of any sort beyond the cam and so might have a teany bit of overlap and duration(things that affect scavenging of the cylinders).
Most of the old Ford engines had low profile cams and usually would generate peak torque between 2k RPM and 3k RPM and reach peak HP between 4k RPM and 5kRPM but they're usually much bigger displacement Ironblocks than their competitors especially Foreign cars.
I've been looking more and more into taking a "small" displacement Honda or even Toyota engine because they use multi cam systems. If the low cam has a low enough Torque peak it could be used with a turbocharged system and still maintain cruise at low RPM in a much bigger heavier vehicle or just a taller geared car. Honda and Toyota use smaller displacement 4 cylinders than Domestic cars but I'm talking like taking a Honda Civic Hybrid's 1.3L (only because it came with a manual transmission) and putting it into a midsize/sports car. An engine swap is usually beyond the scope of most people but it's one of the best ways to acheive an ends and when you're into ethanol and turbocharging you really have to think small to find something that replaces a bigger engine yet has a smaller displacement. If you go from a 2.0l to 1.6L sure you'll save gas and can usually, gear or cam your way to enough power. But with turbocharging you can get a bigger engine's power from a smaller displacement and pow suddenly a 1.3l or 1.0l starts to look like enough or even too much. If I wanted to drive a Focus or a Civic it'd be much easier because they already have small engines but I want to drive an RX-8 kind of vehicle, it's more aerodynamic than a Focus but it's 3k lbs and light on it's feet. If I put a 1.3L Civic hybrid engine in it I'm crazy but if I turbo charge it I'll be fast enough for my taste and the MPG with Ethanol will at least be better than the Gasoline MPG was with the Rotary.
With the right engine the cam profile doesn't necessarily need to change just the intake/exhaust system and gearing. Anything to do with a FWD gearing usually requires dropping the whole front subframe and pulling the transmission, unless you get lucky enough to have OD accessable like the Geo Metro.
Another way to harness a turbocharger in the exhaust is to use more EGR flow into the intake. EGR is just burn carbon and such and doesn't add heat to the combustion process but just takes up space in the chamber and cools the heat of combustion down. A study I've read suggests the upper limit is 40% EGR recirculation before the engine starts to have problems. If you mix lean Air:Fuel Mixtures with EGR you can still maintain exhaust temperatures but I just haven't delved enough into it to figure out the tuning aspect. How do you even control EGR? Theoretically though this means you can have maximum Volumetric Efficiency at 75% throttle if you're using 33% EGR and the mixture can be leaner than Stoich for a better BSFC. And a better part throttle fuel efficiency since throttling has a major effect on Fuel Economy.
While you're considering this you should know that a turbo charger adds load and works off of a load. A turbo usually doesn't add much air pressure to the intake side at low RPM because it doesn't have enough exhaust pressure to do so. A small turbocharger will build pressure faster but will max out at lower levels than a bigger turbo charger. And individual turboes are designed for different maximum levels of pressure. A factory turbo engine usually has a lower torque peak because the cam can be lower profile because the air pressure is high enough. If you build this, you're going to want a wastegate or boost controller to keep the resistance low enough that the turbo charger doesn't put too much load on the engine or increase the engines power beyond what you need, I'm not incredibly knowledgeable of the specifics at this point but the EGR works into this too in small displacement turbocharged engines by cooling down the combustion during part throttle allowing the turbo charged engine to run leaner mixtures at part throttle or even 3/4 throttle with less overall power as a result therefore more throttle less fuel consumption.
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. A small enough turbo could do the scavenging job that you're talking about. But it's a serious undertaking.
