Super efficient FI setup for bottom end?

[stonebreaker]

I'm learning about forced induction. I've done a lot of reading, but my practical experience has been limited to a 150 shot on my impala.

Anyway, I'm gathering, based on what I've read on the forum, that the stock bottom end is good for around 500 to 550 wheel horsepower. Is this torque limited or is it actually horsepower limited? Peter from APS's GTO made 520 rear wheel tq at 4500. From a theoretical standpoint, if the top end were capable of it, could the stock bottom end support this level of torque at say, 6000 rpm? Nevermind the realities of fuel octane and such, this is a theoretical question.

What I'm trying to figure out is whether, on a stock bottom end, what would be the most efficient setup.

Building boost costs horsepower. engineeringtoolbox.com/specific-work-turbo-machines-d_629.html shows how to calculate the specific work of an air compressor. Assuming a flow into the engine of around 55 lbs of air per minute and 75% compressor efficiency, each psi of boost costs approximately 20 horsepower to generate at WOT. More air mass means more horsepower needed per pound of boost.

In a stock shortblock situation, it seems to me that if there's a hard shortblock limit on total torque/horsepower, then every pound of boost is 20 hp that isn't going to the rear wheels. So, if one engine is getting X grams of air into the cylinder at 6 lbs of boost, and another engine, identical except for better heads, is getting the same X grams into the cylinder at 5 psi, then you end up with a net gain of 20 hp.

I understand that most intercoolers cost somewhere between 1 and 2 psi of boost. That's another 20-40 hp lost. It seems, therefore, that methanol injection should be worth 20-40 hp over an intercooler.

I guess what I'm getting around to is that if a stock shortblock can generate, oh, 500 hp with 7 lbs of boost at the turbo, then by using efficient heads and methanol injection instead of an intercooler, could be worth perhaps 50 to 60 hp.

Does this line of reasoning make sense? Or am I just pissing up a rope?

[Exotic Performance Plus]

No, I don't think you are pissing up a rope on your thinking. An intercooler though, is a very efficient means of reducing the heat generated by compressing the air. Like the supercharger, the intercooler is always there for you, with no hiccups that can potentially destroy your engine.
On my Mustang Chassis Dyno, 500 rwhp seems to be a good number to call it quits on pushing the stock bottom end. We've had success with one LS1 ProCharger equipped engine that has been at 575rwhp for several years in a Mazda RX7, perhaps the weight of the car and it's lack of traction play a part in it. The tune is the key ingredient in keeping the pistons in one piece. The air/fuel ratio needs to be fat at wide open throttle, somewhere around 11.2/1. One tank of bad gas can spell disaster, which is one reason why I don't like to send customer's out with more than 500 rwhp in their cars with a stock bottom end. The stock maf is another reason, as it can be tapped out in that range. When that happens the tune past that point is basically going into speed density mode. Weather changes and many other factors then become critical when pushing the stock bottom end. Bob

[stonebreaker]

Well, I guess what I'm trying to do is figure out the best way to eliminate parasitic horsepower loss. For example, according to the formula on this site, at 55 lbs of air per minute, a compressor (doesn't matter what kind) at 75% efficiency, is using about 20 hp per pound of boost. This means that, assuming for the moment that the parisitic loss of the compressor is actually 20 hp per psi, that a car making 540 wheel horsepower on 8 lbs of boost is actually making 700 available horsepower - 540 at the wheels and 160 hp going to the compressor. If I can get the same amount of air into the cylinders on say, 6 lbs of boost, then I should make 580 whp instead of 540, since the power that was going to the turbo is now available for the wheels.

First and formost, are the heads, it seems to me. in order to drop the boost by 2 psi and still fill the cylinders with the same amount of air, you'd need (2 psi/24.7 psi absolute) heads with roughly 8 or 9 percent more flow. I'm sure there's a more complex mathmatical formula somewhere that takes viscosity into account, or maybe not since the head flow numbers already take viscosity into account, but does this seem like a reasonable assumption?

Secondly, the intercooler. Several sites I have read say that an efficient intercooler costs between 1 and 2 psi. That's 20 to 40 horsepower wasted pushing the air through the intercooler, and seems reasonable to me since an efficient intercooler must induce turbulent flow in order to avoid boundary layers. Thus, from a theoretical standpoint, alcohol injection is going to make 20-30 more hp than an intercooler on the same airflow.

You mentioned the reliability of the intercooler and that certainly would be a strong factor in its favor; but, considering that E85 is not only 105 octane, but has a higher heat of vaporization than methanol, wouldn't this make a strong case for converting over to dual-fuel? Particularly for a maggie or lysholm supercharger?

And yes, I realize this is all theoretical and real-world things like MAF limits and heat soak get in the way; but it's still useful, it seems to me, in order to map out my mods. And anyway, it doesn't really matter what the limiting factor IS - whether bottom end strength or MAF limits or whatever - as long as you plan out your mods to get the maximum return for that limit, yes?

[ericwilloughby]

(doesn't matter what kind)

Yes it does. It may take 100 HP to drive a SC or a turbo. The differance being that the SC's 100 comes from the crank. The turbo's comes from the mostly free exhaust gas still expanding.

[ericwilloughby]

You are not being specific enough whether your boost is coming from a SC or TURBO. We all know that the SC is half pising up the rope because like you said, It's costing you 20 HP per PSI of boost to genarate. Not so with the turbo.

[ericwilloughby]

I just realized something. A 500 WHP SC car is much more likely to break an engine than a 500 WHP turbo car. Because the engine is actually making about 100 HP more. It's just not making it to the flywheel.

[ericwilloughby]

It seems that you are mistakingly assuming that your turbo is a parasit. The only loss you have there is the extra back pressure in the exhaust system. Check out this thread. http://www.ls1.com/forums/showthread.php?t=13352&page=5
We have determined the HP loss of both the SC and turbo.

[ericwilloughby]

So although good heads are and always have been a way to get more A\F in the cyl. They are a waste of money when all you have to do is turn up the boost and burn E85. Most of us don't have the boost option and heads a lot cheaper.

[stonebreaker]

Eric,

Thanks for your responses. I read the link you provided, and while it's an interesting discussion, there wasn't really anything resolved. Granatelli has some practical experience, but he contradicted himself several times and I got the impression he's a lot more familiar with the sales side of things than he is with the engineering side. Also, the fact that his vette's exhaust made over 7 psi of backpressure even with no boost, means his exhaust was restrictive and therefore invalidates any results he got. (He's selling turbos and not twin screws, so I wouldn't expect him to endorse anything else anyway.)

The magazine test on how much boost it takes to reach a horsepower goal for different types of FI was enlightening, but flawed. The 144 supercharger isn't a twin screw type, for one thing, nor is it sold by Kenne Bell. It's actually an old school roots supercharger sold by Holley/Weiand. So the question of which type of forced induction setup is more efficient, is still up in the air. Also, since the turbo system replaced the stock exhaust but the supercharger kits didn't, I'm not that suprised the supercharger kits required so much boost. If nothing else, the fact that the vortech kit required as much boost as a roots blower to make the same peak horsepower should have tipped you off that there was something goofy about that test.

However, I'm not trying to decide which type of forced induction is best. Well, I am, but before I even get that far, I'm trying to figure out if reducing the amount of boost needed to make a given amount of horsepower, will allow me to make more horsepower at the rear wheels without overstressing the shortblock. Whether or not this is possible will affect my mod path.

[Zakar]

you could call a turbo a good recycler of wasted exaust energy

[stonebreaker]

you could call a turbo a good recycler of wasted exaust energy

The turbo isn't using "wasted" energy. The exhaust pressure to turn the turbo comes from the pistons, and it's a pumping loss. If the exhaust back pressure didn't affect engine power output, then why does opening up the exhaust make so much horsepower on an LS1?

If the exhaust pressure doesn't affect power output, why then don't car manufacturers put exhaust turbines on hybrids to generate even more electricity instead of turning the generator with the engine's crank?

[ericwilloughby]

Yes it is using wasted exhaust energy. The vast majority of the power turning that turbine is from the still expanding gasses. But having said that, it does put a little more pressure in the ex pipes. As we have been talking about in the other thread it seems that 6 lbs of boost on a sc costs 80 or so hp and on a turbo 20 due to extra back pressure. Or 100 vs 30.

Of course extra ex pressure affects power but you lose 20-30- to gain 100-150.

[ericwilloughby]

Why don't car manufacturers put exhaust turbines on hybrids to generate even more electricity instead of turning the generator with the engine's crank?

I called my cousin who has a 2006 Honda Civic Hybrid. We don't think it has an alternator. Because it does not have the typical bat that is used to start the car there is no need for it. So the crank is not turning a generator. We think. He is checking.

The AC generator\turbine in the exhaust is a GREAT idea. The first problem I see is cost. The next is being a very fuel efficient engine. Say almost twice that of a normal car. There is less waste in the exhaust to utilize. I wouldn't know if there would be half or not. Instead of putting a generator in there why don't they just turbo charge the car and make the engine even smaller??

[stonebreaker]

I called my cousin who has a 2006 Honda Civic Hybrid. We don't think it has an alternator. Because it does not have the typical bat that is used to start the car there is no need for it. So the crank is not turning a generator. We think. He is checking.

The AC generator\turbine in the exhaust is a GREAT idea. The first problem I see is cost. The next is being a very fuel efficient engine. Say almost twice that of a normal car. There is less waste in the exhaust to utilize. I wouldn't know if there would be half or not. Instead of putting a generator in there why don't they just turbo charge the car and make the engine even smaller??

The main generator that the engine attaches to instead of the tranny, also functions as an alternator. Since the battery pack on hybrids is so high voltage (140 volts on the Honda), a traditional alternator wouldn't work anyway.

I think, if you examine the hybrid concept, you'll see why they didn't include a turbo on a smaller engine. BTW, I don't know where you get the idea that a hybrid's motor is more efficient than a normal car's. Don't you think that if they could make a hybrid car's motor more efficient, they would apply the technology to ALL their cars? Anyway, my list of reasons why hybrids don't have turbos:

1. Hybrids are already about $7500 more than a comparable non-hybrid, and a turbo system is going to add to that.
2. Hybrids use battery power to accelerate, so they don't need a high horsepower engine. All they need is an engine that will meet the AVERAGE power demands of driving - the batteries supplement when extra power is needed.
3. You can't really mod a hybrid for more power. Well, you can, but it involves modifying the electrical system components, not the gasoline ones.
4. Turbos really aren't all that efficient. The highest island efficiency I've ever seen for a compressor wheel is 76%. Even if we assume the turbine is also 76% efficient, it can't hold a candle to an electric generator, which is 95% efficient or better.

I also don't know where you guys get this idea that turbos run off of "wasted" energy in the exhaust gas. Turbos create back pressure. If you go back to the Granatelli thread, I seem to recall that his system produces about 1.5 psi of backpressure for every pound of boost, which is right in the middle of the range, according to Vizard and Bell. Backpressure doesn't just push against the turbo - it's also pushing back against the pistons, which means the engine has to expend extra energy to pump the exhaust gasses out of the cylinder. You can find good info here: http://www.gnttype.org/techarea/turbo/turboflow.html

Scroll to the very bottom of the page, there is a link to a spreadsheet you can download that will calculate everything.

[ericwilloughby]

It seems you really dont have a clue and are missing the point most of the time. I was goin to rebute your points but I've decided I just dont care enough. Well shit, I guess I do.

1. Maybe true.
2. The electric motor is 10 HP. Not really much help in accelerating.
3. Why would anyone want a hybrid for power.
4. Who cares if a turbo is'nt efficient. It's uses spent exhaust energy, so what are you afraid of, the exhaust being wasted on its way out the pipe. There is no need for a comparison of turbo to elecrtic motor. Why try? It's not one or the other. Use both.

AGIAN. Of course extra ex pressure affects power but you lose 20-30- to gain 100-150.

[Reggie West]

Backpressure can be controlled by the exhaust housing size of the turbine.

I cant remember if it is 50% or 150% of the boost levels on the compressor side but there is an ideal match for backpressure.

In either a SC or turbo set up you have to have bigger headers and exhaust pipes to scavenge the increased gases being pushed out of the motor.

I am not so sure about the 75% efficiency levels of the turbos stated here. There are turbos that run at the 90% efficiency levels and then some but that is due to matching backpressures correctly so the compressor can do its job.

[stonebreaker]

It seems you really dont have a clue and are missing the point most of the time. I was goin to rebute your points but I've decided I just dont care enough. Well shit, I guess I do.

1. Maybe true.
2. The electric motor is 10 HP. Not really much help in accelerating.
3. Why would anyone want a hybrid for power.
4. Who cares if a turbo is'nt efficient. It's uses spent exhaust energy, so what are you afraid of, the exhaust being wasted on its way out the pipe. There is no need for a comparison of turbo to elecrtic motor. Why try? It's not one or the other. Use both.

I didn't realize the honda hybrid was such a scam. 20 hp? They're only producing it to stay in the market against toyota. Sheesh.

Your mistake is assuming the turbo runs off of waste energy. It doesn't. The backpressure it creates costs horsepower to push through the system. LGM advertises a 30 hp and 40 tq increase on a stock LS1, just by going to a free-flow exhaust system on an NA motor. That's on a drop in backpressure from 7 psi to 2. To get back to the hybrid argument, this horsepower required to run the turbo requires that much added fuel, exactly opposite of what you want in a hybrid. If you're using a turbo to gain 150 hp, you're burning 200 hp worth of fuel to do it. Instead, by taking the horsepower from the gas engine that's not currently being used to run the car, and storing it for later use in the batteries, you conserve fuel - in theory, anyway. That's why they're not using a turbo. What you may not know is that the torque from an electric motor is not dependent on rpm - it makes the same amount of torque from 0 rpm all the way to its limit - in the case of the prius, the electric motor makes 295 ft-lbs of torque from 0-1200 rpm. The prius uses all that torque to get the car moving, and only then does it start up the gasoline motor. I thought the honda worked the same way, I didn't realize the electric motor on the honda was so weak.

Personally, I think hybrids are a clumsy solution to the problem, and I don't like'em. Their heart's in the right place, but the whole hybrid idea is lazy thinking. Even at three bucks a gallon, I'd have to SAVE 50 gallons a month over 5 years to even break even on the price of the hybrid system. I don't even use 50 gallons a month, and I drive an SUV to work. I think GM's and Chrysler's variable displacement technology is far superior.

[stonebreaker]

I am not so sure about the 75% efficiency levels of the turbos stated here. There are turbos that run at the 90% efficiency levels and then some but that is due to matching backpressures correctly so the compressor can do its job.

These are the only turbo maps I've been able to find on the web, and the highest efficiency is only about 76%; and that's only at a pressure ratio way higher than I'd run on an otherwise stock LS1.

[ericwilloughby]

I didn't realize the honda hybrid was such a scam. 20 hp? They're only producing it to stay in the market against toyota. Sheesh.

Your mistake is assuming the turbo runs off of waste energy. It doesn't. The backpressure it creates costs horsepower to push through the system. LGM advertises a 30 hp and 40 tq increase on a stock LS1, just by going to a free-flow exhaust system on an NA motor. That's on a drop in backpressure from 7 psi to 2. To get back to the hybrid argument, this horsepower required to run the turbo requires that much added fuel, exactly opposite of what you want in a hybrid. If you're using a turbo to gain 150 hp, you're burning 200 hp worth of fuel to do it. Instead, by taking the horsepower from the gas engine that's not currently being used to run the car, and storing it for later use in the batteries, you conserve fuel - in theory, anyway. That's why they're not using a turbo. What you may not know is that the torque from an electric motor is not dependent on rpm - it makes the same amount of torque from 0 rpm all the way to its limit - in the case of the prius, the electric motor makes 295 ft-lbs of torque from 0-1200 rpm. The prius uses all that torque to get the car moving, and only then does it start up the gasoline motor. I thought the honda worked the same way, I didn't realize the electric motor on the honda was so weak.

Personally, I think hybrids are a clumsy solution to the problem, and I don't like'em. Their heart's in the right place, but the whole hybrid idea is lazy thinking. Even at three bucks a gallon, I'd have to SAVE 50 gallons a month over 5 years to even break even on the price of the hybrid system. I don't even use 50 gallons a month, and I drive an SUV to work. I think GM's and Chrysler's variable displacement technology is far superior.

You are crazy. You don't know what you are talking about. Especially about turbos. All the hybrid's use a 10-15 HP motor. The electric motors torque max is at 0 rpm and decresses linearly at rpm increases and reaches 0 ft\lbs about 3600 rpm.

[stonebreaker]

You are crazy. You don't know what you are talking about. Especially about turbos. All the hybrid's use a 10-15 HP motor. The electric motors torque max is at 0 rpm and decresses linearly at rpm increases and reaches 0 ft\lbs about 3600 rpm.

The prius' electric motor makes 295 ft-lbs of torque from 0 to 1200 rpm, and has a peak of 67 hp at 1540 rpm.
http://www.toyota.com/prius/specs.html
WHO doesn't know what they're talking about?