Supercharging

[EdKiefer]

Originally Posted by Old Tele man

...as well as the static compression ratio, from typical 10-11:1 down to around 9:1 or so.

...and let the blower "relief" value dynamically 'control' the actual working compression ratio.

Whats interesting is OEM seem to be running pretty high CR . I notice the eco-boost ford V6 is 10.0:1 . Also the new Audi S4 and BMW 335i also run 10.0:1 CP (one SC and other twin turbo ).

Not sure on how much boost there running, my guess under 10lb boost.
Found nice test results between the two .

Comparison Test: 2010 Audi S4 vs. 2009 BMW 335i

[gone-ot]

...agreed, but those higher CR numbers are typically the benefit of using direct injection (into the cylinder) instead of normal manifold injection.

...the direct injection both cools the cylinder and allows it to ingest 100% air--rather than the typical less dense A/F-mixture--during the intake stroke. This permits the use of higher CR because the fuel is NOT present during the compression portion of the intake stroke, and is only present at the instant combustion is appropriate to occur (assuming properly 'timed' injection/ignition calculations).

[user removed]

Also direct injection can be in several separate injections which allow for much more precise control of peak combustion pressure. Mazda is bringing out an engine with 14 to 1 on gasoline.

While turbocharging does utilize exhaust pressure and heat, it is not free. The same heat could be used to generate electricity without increased back pressure, or a turbine that is rotating even when there is manifold vacuum.

Boost pressure creates back pressure in the manifold and allows more heat to escape into the cylinder head and manifold. That's why you see them red hot when in a lot of boost. Higher exhaust temperatures create additional losses.

Now, if you do a Gale Banks setup on a 2.5 liter 4 cylinder engine in a full sized truck then you get the best of both worlds. High BSFC when under light loads and power when you need it. Think of the power to weight of the big rigs and there relative mileage compared to passenger vehicles.

In sequential direct injection (diesel and gasoline) you can eliminate pre ignition and create a stratified charge with a portion of the fuel, then add other injections during the down stroke of the piston to produce pressure when the leverage is better, rather than trying to ignite all the fuel at the same time.

regards
Mech

[EdKiefer]

right, direct injection has big advantages there, also variable cam timing to optimize cam timing (can optimize dynamic compression) .
My comment on it being free was compared to belt driven SC's .

I think for trucks a turbo diesel would be best for heavy truck but yes small 4 cylinder would definitely work in heavier vehicles than the norm .

[NHRABill]

I have a relevant point so bear with me here:

I have a Superharged vette I built many years ago and in doing so you plan for the purpose of how much boost you want to create. For my case originally I wanted A tough street car so i chose to go with Dished pistons and 76cc heads which put my compression ration around 7.75 : 1 I was planning on 6-8lbs of boost and aprox 550hp 540lbs. tq to the rear wheels under full boost my compression ration would increase to apx. 11.5 : 1 This eliminated the need for racing fuel to avoid detonation and pinging.

It wasn't long before I had to make some changes to the setup many times the big gains came from better flowing heads keeping the same bottom the increased runners and valve sizes swapping out the old cast iron 194 / 150 to a set of 2.10/ 1.60 with 220 runners was a wake up call of an extra 70HP and loss of 50lbs of steel for aluminum and titanium. Only prolem was I now had 65cc which pushed my compression ratio non boosted to almost 8.75 to 1 which means under boost I was pinging detonating everywhere fouling plugs unless I ran at least 98 to 112 octane fuel.. The larger valves and runners helped and the higher compression was more responsive under normal load but as boost increased I was in for a world of hurt. So what to do swap the plleys and overdrive the supercharger to about 18lbs of boost and switch off from Gas convert to Methanol. instant 800hp LOl like it is that easy many other things needed to be done also but you are getting the short version


Ok so you get the point that a inefficient conventional old school 6-71 supercharger needs to be matched to the ride and despite all of the new technology and injection systems out there I have never agreed with what I see the auto manufacturers doing over the past decade making cars with smaller displacement and higher compression. yes sticking a turbo on or a supercharger gets them the cheap HP they need and makes them more manageable. but 13:1 compression ? i would hate to own that car... 87 octane will not cut it that boy will need 92 octane and even that is almost not enough for it.

I had other cars where I went the opposite route High compression placing dome psitons into that famous V8 SBC 350 couple that with 64cc heads and oon you have 12.5 to 1 compression and congrats you just upgraded to premium fuel unless you want to change your plugs once a month. or rebuild the motor cause your valves are coing to shoot through the hood of the car.
yes the camshaft profile has alot to do with it but it is simple math too much compression = more fuel being burned faster it also shortens the life of that motor because of the heat that it produces under load.

Under-work a Big motor it will last forever overwork a small motor you will be replacing it soon. instead of making tiny 12:1 motors that you need to gear to hell to get them to move because no power is made till you hit 3,000rpm. Heck these small commuter cars rev 3500rpm @65mph...
Take a look at the non turbo standard mid sized dieseld from the 80's they don't break 4,500 rpm the compression is dirt low and they have more toque to get you moving with much less effort. You can leave a 3.08 rear gear in with a 4 speed overdrive and cruise 65mph turning a calm 1900rpms with an average gm trans 700r4 4l60 etc...

i don't understand why everyone wants a 270hp minivan. with a freaking turbo it makes no sense.

Please excuse my rant but I have few people that can follow me or have the intrest to. I don't mean to give the history lesson prior but that is the teacher in me. I really should sleep instead of making posts at 4 am I am not making sense anymore

[EdKiefer]

one drawback of roots blower is there no easy way to cool charge with a intercooler and you have no way to alter cam timing like new engines .
Modern 4 valve head chambers with center spark plug are also more efficient than older 2 valve wedge heads, can run more compression in general . Above features and direct injection the newer tech engines it starts to really add up on improvements compared to older engines .

The good thing on the newer breed of eco-turbo . I class eco -turbo as ones were there more for drive-ability then peak HP .they produce good gains in TQ at low rpms and are not peaky like older performance turbos . This gives a fat low rpm TQ curve (look at BMW TQ rpm range I posted link above its like 300ft/lb at 1400 rpm

On gearing my 08 Honda 2.4 5speed auto cruises at under 2k rpm doing 60 . Maybe older 3 and 4 speed needed to be gearing higher cause not so many gears . In Honda both 4th and 5th are overdrive ratio's .

[SentraSE-R]

The problem with superchargers is they always rob power, whether boosting or not. Turbos don't have that problem, thus making more sense for economy-minded drivers.

[comptiger5000]

I agree, turbos are more efficient than superchargers. Also, with lower parasitic loads, the same amount of boost will produce a bit more power with a turbo.

[NHRABill]

Don't think that there would be many that would argue that a turbo is the most eficient of the 3 types of forced induction. But a good ? is what turbo setup is most efficient?

I have always found the tailpipe turbo STS style is the best route for effiencey and installation No need for a intercooler when it is where the muffler is located. It keeps engine temps down and cools the charge in the longer travel distance back to the intake. I know someone with this setup but he is tuned for power not mpg

[Daox]

I'd say a traditional turbo location is most efficient. It is positioned up front to get the most boost as quickly as possible. If you move it back, you reduce the amount of power it captures.