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Old 03-28-2004, 02:08 AM
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Question Supercharger fact or myth???

I have heard that you have to re-tune, so to say, your engine about every weekend or all the time if you run a supercharger, is this true? And if im being too blunt then i'll explain more: i hear from half the people that you have to adjust the timing, rockers, and lifters just about all the time if i were to run a 6-71 or 8-71 Weiand street supercharger on a 427 (which that shouldnt matter all that much i think), and the other half says that you should only have to do it around every due tune-up. Superchargers are kinda complicated for me, along with gearing and drivetrain, but i kinda figured that the later was true and that you could do it with the tune-up. I guess i should get a "Supercharger Bible" but that cost money, this is free, God i love this forum, you cant beat free. But if anyone could help me out, id appreciate it.

thanks,
classic

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Old 03-28-2004, 04:34 AM
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even so I haven`t delt with superchargers, I would think tuning it often would be called for, since with that much cash and power invested under the hood, if it goes lean disaster can result and fast. as far as adjusting the rockers go, if the valve train uses hydraulic flat tappets or hydraulic roller tappets, there would be no need to adjust them often, once you have them adjusted there set unless a rocker arm nut backs off. if running solid tappets, flat or roller, then the need to adjust them often would arise, but it wouldn`t matter what was on the engine be it a turbo, supercharger or natraully asperated, the valve train don`t know whats doing the breathing of the engine. while it is true you can do some adjustments with hydraulic cams and make up some difference in how the engine performs, it`s not as much as it would be with a solid cam. If I were running a supercharger, I would tune it quite often, since I`d want to keep my engine intact, but since it wouldn`t be a daily driven vehicle, I would only do routine checks before I ran it, timing, fuel pressure, float settings, plug readings etc. I wouldn`t run a supercharger on the street with a carb, I`d rather spend my time doing other things than constatly tuning it, if it were a fuel injected vehicle, like a camaro or mustang with computerized spark and fuel management I wouldn`t worry about it since the computer does the work for you.
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Old 03-28-2004, 08:34 AM
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You don't have to re-tune Superchargers that often. If they get setup right the first time it should be just like any other carburetor setup. If you have access to a wide band 02 sensor and a dyno then you might want to tune about twice a year, once for the cold months and once for the warm months. Unless it just gets to running bad and needs a tune. The only time you should re-tune is during drastic weather changes Summer / Winter and if you add more boost to the mix.

If you've got to re-tune your carburetors on superchargers that often you might want to look at the carb manufacturer and not the supercharger.
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Old 03-28-2004, 09:51 AM
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Basically what "some people" have told you is NOT true. There is no need to tune them any more than any other car. I have only had mine together about a month, it was easy to tune (maybe I just got lucky).

I have yet to put in on the dyno, but that's where you can get all the fine tuning if you want to drain every bit of power out of it.

Once you get it tuned it should stay tuned just as with any type of car. The key is monitoring all aspects of the engine (water temp, oil temp, oil pressure, boost, fuel pressure) These things will usually tell you when something is going wrong.

I agree with Jamnut about the tuning for time of year/outside temperature but, this applies to all carbureted performance cars.

As far as solid cams, you don't have to adjust them that often. Just make sure you run good nuts and locks. You should check the lash every oil change (or every other). If you run good oil and good nuts and rockers., you will see that when you check them they rarely are out of adjustment.

Royce
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Old 03-28-2004, 10:44 AM
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is it also true that the efficiency of the supercharger goes down after a few months due to the temp of the engine/supercharger mix? Cause i heard that the supercharger raises the temperature drastically, and that the only way to guarantee that the supercharger will run efficiently is to get an intercooler. And what would be the average temp of an engine, a 427, with a 6-71/8-71 supercharger, would anybody know???

thanks,
classic
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Old 03-28-2004, 12:40 PM
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The efficiency of a blown motor is degraded by heating the intake air during the compression process of the blower. The efficiency loss is dependent upon how hard the blower has to work to achieve the desired boost. You mentioned 6-71 and 8-71 blowers for a 427 cubic inch motor. An 8-71 blower running at 1:1 with the crank will make an estimated 12 lbs. boost on that size motor. A large bore 6-71 will have to run 7.5% overdrive to make the same boost and a small bore 6-71 will have to run at 27.5% overdrive to make the 12 lbs. of boost. So...from an efficiency perspective, you'd be better off running the 8-71 to make the desired boost on that size of motor. The slower you spin the blower to make the boost, the less heat you are putting in the engine. It is not true that the efficiency goes down over a few months due to the temp, it is that way out of the box. The efficiency of a blower will degrade with time due to wear, but wouldn't be noticeable over a couple of months unless something was drastically wrong.

It is not true that you need an inter-cooler to run a blower. The need for an inter-cooler is dependent upon your set up and vehicle use. Obviously, if you were trying to squeeze the most hp out of a motor for drag racing, an inter-cooler should be considered as any other enhancement modification.

A properly set-up blower motor won't run any hotter than a normally aspired motor with a properly functioning cooling system.

Go to different blower companies on the web, they have a wealth of free information. Try http://www.blowerdriveservice.com/ and just browse their different links. I'm sure other blower companies have good info as well.

As far as injected versus a carburetor, it's not any different than the same decision on a normally aspired motor. What do you prefer and better yet, what can you afford? Blower motors need to be run a little richer to avoid detonation. The ideal A/F ratio of 14.6 is too lean for a blower. As discussed earlier, no additional tuning unless it is set-up improperly and you are "chasing" the set-up. The only difference I see, is to make sure the blower belt is in good shape cause it won't run without it (and carry a spare).
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Old 03-28-2004, 02:25 PM
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What? Tune them every weekend? No. Standard tune up, nothing different. Now on a 671-871- and the like, you could always be playing with the carbs to see whats the best settings you can get from them, but constant tune-ups is not true.
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Old 03-28-2004, 04:08 PM
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besides who the he*& would tune there motor every weekend?
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Old 03-28-2004, 05:40 PM
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In the book it says that a blower(unless super hi horse race motor) that you will have no troubles with supercharged motors. You get better gas mileage at cruise rpm's and it starts easier to. You cant beat em for looks and performance. HG
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Old 03-29-2004, 08:12 PM
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How can a supercharger ever increase gas mileage?
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Old 03-30-2004, 08:31 AM
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A supercharger increases gas mileage when HOT making boost. The reason is because the rotors spin and mix the air/fuel better. This promotes a more efficient burn. Now if you are on the pedal you can forget that, you will make more power and have WAY less gas mileage. I get 10mpg with my 8-71 blown small block with two 750 double pumpers. I got about the same with my previous naturally aspirated engine, single carb 3 less cubic inches, same car.

Royce

Edit: I meant to say NOT where I typed in HOT above. (NOT making boost).

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Old 03-30-2004, 10:00 AM
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The cooler the incoming charge and/or the higher the compression ratio, the more thermally efficient an engine will be. An automotive engine is simply a heat engine and energy extraction efficiency is a function of temperature difference in the cycle. The bigger the difference between the lowest inlet temperature and peak combustion temperatures, the higher the efficiency. Blowers do heat the incoming charge but that is after the cold air has been ingested to the system so that heat is useable. The higher overall efficiency comes from the higher compression-higher peak temperature in the cycle.
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Old 04-01-2004, 12:22 PM
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Oh mommy, this conversation is getting over my head. I thought superchargers were essentially always producing boost, as opposed to turbos.

Are we talking about engine efficiency or fuel efficiency? I'd buy that a SC improves engine efficiency, but that doesn't necessarily translate to better fuel efficiency, does it? I mean, I've heard V8s are more efficient engines then 4 cylinders, but obviously they still burn more fuel.

My very simplistic way of looking at this boils down to A/F ratios. If the SC stuffs more air into the cylinders each cycle, more fuel needs to be added also. Where has my logic gone wrong? (seriously)
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Old 04-01-2004, 12:47 PM
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LOL

No blown engines are not always making boost. I am talking roots type blowers here. I can drive my car all day and not make boost (actually make vacuum).

In order to make boost you have to have the throttle blades open. Boost is the measurement of backpressure in the manifold (really not an accurate way to judge performance but, that's a whole other discussion). There will be no boost/backpressure as long as the blades are closed or only open wide enough to satisfy the engine, once you open them all the way up then the blower has more air/fuel to work with and will force more into the same space, this creates boost/backpressure. This is a way over simplified version. Blower speed also has to be take into effect, at slower speeds the blower turn slower and therefore doesn't move as much air.

Now if you have very restrictive heads/intake you will see more boost and more often as the backpressure/boost will build easier, this does not mean you will make more power. For example an engine making 12 lbs of boost with very small restrictive heads will not neccessarily out perform an engine of the same size making 8 lbs of boost with very good flowing heads. Flow is still king when trying to make power naturally aspirated or forced induction.

Royce
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Old 04-01-2004, 01:04 PM
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There are two efficiencies associated with IC engines. Volumetric Efficiency (VE) refers to the amount of fuel/air charge actually introduced into a cylinder vs. the actual capacity of the cylinder. A naturally aspirated engine will always have a VE lower than 100% since it depends on creation of a vacuum to fill the cylinder and there will always be a small amount of exhaust gasses left after the exhaust stroke. A super charged engine can have a VE of over 100% since the exhaust gasses can be totally blown out of the cylinder with positive pressure during valve overlap and since the cylinder is being fed fuel and air under pressure.

A high VE doesn't necessarily translate into high Thermal Efficiency (TE) which relates to how well the fuel energy is converted to mechanical energy. An IC engine, being a heat engine, generates higher TE as the compression ration goes up. VE is helpful there too IF it is controlled and raw fuel is not blown out the exhaust. A super charger can increase TE (fuel efficiency) buy increasing compression and peak temperature and by increased VE if it isn't working with a radical cam that allows fuel to be blown through the engine.
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