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Discussion Starter #1
OK, I have a question. We all know that the deisel responds VERY well to a turbo. The DMAX is the first turbo that I have ever owned. There is only on problem (if you could call it that) and that is the spool-up time for the turbo. I now know what turbo lag is.



With that I now have to ask why not a supercharger? If the airflow being forced makes that much of a difference with a turbo then how much better would it be with a supercharger? You would get boost from idle on up. I would imagine that the power would come on instantly instead of the turbo lag. So Why not a supercharger instead of a turbo?





Mike
 

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Some Detroits use a supercharger. If I'm not mistaken weren't superchargers first taken from diesels to use on hot rods?
 

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The turbocharger is more efficient as it uses normally wasted energy in the form of heat for it's drive power. A Supercharger uses crankshaft power for it's drive.
 

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some larger engines are sc'd and tc'd... the SC for some pre-lag power and the tc for the big power later on..
 

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Discussion Starter #5
So if I understand you correct. A SC makes better power down low while a TC makes bigger HP on top?


Would a SC help to spool up the TC? What would the differences be in head pressure between a SC and a TC?


Got my wheels turning now..
 

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the boost from either is dependent entirely on the setup, you can put crazy pulleys on a SC to spin it faster and get more PSI but you start going out of the effiencency range of the SC, just like a turbo, wrong size turbo for the application and you get cruddy efficiency, which equals tons of extra inlet heat at little more gain in HP. Problem with a SC is it robs off the crankshaft HP, you get power off the bottom, but it flattens out up top, with a turbo you get very good power to redline and its basically driven for free of exhuast gas and heat, what else can you ask for! Properly designed turbo setups really don't have tons of turbo lag. SC vehicles give good torque off the bottom great for light to light racing, but if your gonna race the whole 1/4 mile you can get off the line with a little less HP (IE not spin too bad) then the power comes on full for the rest of the run!!! My next project is fitting a pair of turbos to my '92 5.0 Mustang, just need to finish my research and come up with some more money to make it the way i want it!
 

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The Detroits with blowers are two-strokes. They have a closed crankcase so they need a blower to get air in. They can put a turbo on top of that. There are intake ports around the bottom of the cylinder. When the piston drops, they are uncovered and the blower shoots the good air in and at the same time the four exhaust valves open on top, which push's out the bad air. The piston starts coming up, covers the intake ports, the exhaust valves close, compressing to the top, a shot of fuel, bang, piston goes down, and round and round it goes. A pulse of power every time the piston comes up instead of every other time like on a four-stroke. I was never a big fan of them. I remember the guys that had the 12V71. We used to call them "The buzzin dozen." A vee 12, 71 series engine. (71 ci per cylinder) Later they came out with the 92 series. Some people used to put the smaller ones like 3-53's and 4-53's into pickups.


Anyway, a two-stroke with a closed crankcase would not run without a blower or some way to change out the air charge in the cylinder.


Steve
 

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Discussion Starter #8
This is cool!I have never really had a conversation reguarding the differences of a turbo vs a Supercharger before.


To be honest I have always just assumed that a SC was a little superior to a turbo because of the bottom end grunt.


From what I am reading a properly tuned engine could really benefit from both a SC and a turbo. Maybe have a SC with a clutch on the pulley...(like the ac pump) that way at a certain RPM the SC would cut out and allow the turbo to kick in.


THAT would be a cool project for some deep pockets.



Maybe when I finally build a pro street truck it would be something to look at.


I still ponder the advantage that this set up would have for our racers out there. The SC to get off the line...( better 60' times) Then the turbo for top speed. I wonder if the Alli could take it?



I bet that would put Suncoast to the test..


Trivia! Anyone ever heard of a setup like that?
 

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most of the SC's i see don't have great intercooler setups... hence they run good the first run then go down hill.. i for one am still glad i have a turbo on my diesel.. after all, it sounds cooler!
 

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I thought that was what SC in a bottle was for. (NOS > turbo lag)





If a SC quits turning NO air is going into the motor w/o some kind of dual inlet intake and some way to stop the air for coming out the turbo at low rpms.
 

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Most of the time you will see twin turbo setups to cover the lag issue. A small turbo for quick spool up and a good hole shot and then a big honkin hair dryer to make the monster boost on the top end.


You mainly see the twins on the Cummins but it can be done on the Dmax like Clint at ATS has shown. If you were building a truck from the ground up you could make all sorts of room for the twins and not have to worry about the SC issues.
 

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You also need to look at the differences between superchargers and blowers. A centrifugal supercharger is essentially a turbo (nonpositive displacement) that is pulley driven. A blower is a positive displacement pump...the ones used on Detroit 2 strokers. Military Hemitts have 500 hp, 8V-92's with a blower and twin turbos. Most blowers are still sized by Detroit engine sizing. A 6-71 blower will be used on a 6cyl 71 cu in per cylinder motor. Top Fuel dragsters use 14-71 blowers. DDC never made a 14-71 engine but they still refer it to that way.


Blowers are usually mounted in a way that if it isn't turning the motor won't get air. Turbos are setup so the motor can get air without turbo boost. Centrifugal SC's can be setup on gassers for push or pull. Push air through the carb/fi or pull from under the carb/fi. Since we are talking diesel I'll skip a detailed explination. Turbo is king in 4 stroke dieselville. If there was a good reason to use a SC vs. a turbo on a diesel I'm sure super stock tractor pullers would be all over it.
 

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Lonewolf:


It all comes down to efficiency as to which one is used. A sc/turbo set up really isn't used because it would be more efficient and cost effective to use 2 turbos. Why pay for a sc when you will only use it for to have the turbo spool up quicker. Use another turbo and that will take care of the lag problems like BMDMAX said. As for racing, they will leave the line at higher rpms to take care of the lag issue if using only 1 turbo.


Efficiency of power adders:


turbo - 92%


Centrifugal supercharger - 85%


Roots supercharger - 40-50% The main reason these are still around is because of the "look" you get with them on your car. They are still used in racing because of the swept volume they produce over a centrifugal. And most pro classes don't allow a centrifugal.


Just my 2 cents


GSXR: are you interested in buying a twin turbo set up with motor. Still needs assembly. PM me if you are
 

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One thing that creates a turbo lag like problem is the MAF sensor on our trucks. To get the turbo to spin up,you need more heat. To get more heat, you need to add fuel. On a mechanically injected engine, you mash the pedal, the pump gives more fuel, you get a puff of smoke, the turbo spins up and away you go with a minimum of lag. On our engines, because of restrictions on visible smoke, when you mash the pedal, the ECM consults with the Mass Airflow Sensor to see if there is an increase in air flow. When there is enough of an increase, the EMC commands more fuel, the turbo spins up, and away you go. That is why often times when the cruise asks for a speed increase, nothing happens, then you get the downshift and are off like a rocket. I find this more of a problem at my altitude of 6000' than at Sea level.


If I am in error, please feel free to correct this.
 

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Horse Trainer,


I agree that if the MAF was used as it is in most engines you explaination is accurate. I haven't figured out exactly what the Dmax uses it for. Example, unplug the darn thing and you'll have no drivability issues and it may be quite a while before it trips a MIL. Maybe it is used to set long term fuel trims or something?
It's there so it must be used for something, but it shure dosen't seem to have as big an effect as it seems to in spark ignition injected engines.
 
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