can any one help guide me in putting a turbo system on a 4.2 sel, and would it give me better fuel mileage? I am thinking of doing this on our 90 sel and on our 91 2.6 190. any info would be greatly appreciated.

It's not an easy task especially on the V8.
Main concern is fuel enrichment.
It will not increase fuel economy and potentially decrease if you have a heavy foot.
Even a DIY done correctly will cost $3-$5K.

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1971 280SL ROADSTER
1988 300CE TWIN TURBO WIDEBODY
1994 E320 CABRIOLET
1999 C43 AMG
2005 G55K AMG
2008 CLK63 AMG BLACK SERIES

it would be easier to go with NOS.Add water injection to save a little fuel if you turn up timing.turning up timing does help fuel mileage,you can splice a 1k resistor inline with red wire going to coolant sesnor near thermostat.be sure the run all premiuim gasoline.NOS you can run safely a 125 wet shot,kits on ebay used from $250

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt

Would running premium knock out any increased economy? I'd like to trick my car into thinking its a tad warmer, so it will run a hair leaner. But if it has to have premium then its a lot of waisted effort, I could be wrong.

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

I thank every for your comments on turbo charging, I was not looking for an increase in power but a better mileage, I see all the newer autos are set up with a turbo and thought there might be some use for the old timers. thanks again but its a subject left alone.

The way you get better mileage from turbo-ing your car is to install a considerably smaller engine and boosting it to the same power level as the previous engine.

Turbo-ing your current engine may make it more efficient, but it wont directly translate into more MPG. Trust me on that one. I get about 2 MPG (city) less with my turbo and I have to burn premium. To be fair though, I beat the hell out of it on a regular basis.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Engines are more efficient when run at higher loads. When a engine is throttled, not much volume of air is flowing through the engine and effective compression is very low reducing efficiency. If you have a smaller displacement engine and throttle it less, efficiency goes up ( until you need to run full rich to keep combustion chamber temps under control ) .

BMW did some testing for fuel economy and found that when accelerating from a stop, less fuel is used when accelerating at 70% throttle than slowly accelerating at something like 20%. If you go over 70%, fuel enrichment kicks in and will reduce ecomomy.

As post 6 says, small engine for efficiency and boost to get max power back. It does not take much to push a car down the road at 55 MPH ( 20 / 30 HP ? ) , it does take more power to go up hills / go faster / accelerate.

So , unless your cars are under powered to the point then are into fuel enrichment constantly, a turbo won't help much.

SAAB did use a low pressure turbo on ONE exhaust bank to help a V6 motor gain some efficiency, not sure if it did much. SAAB was also experimenting with a variable compression piston engine, the block was hinged on one side parallel to the crank.

NOS is a dead end for what you want to do.

actually... the way turbo's increase efficiency is by increasing their load with gear changes.

increasing the engines HP in same chassis with same gearing lowers efficiency (MPG)
you have to get taller gears to make the HP push the vehicle same speed, but lower RPM to realize the economy improvement.

if you want the 420 to use less fuel, you'd need to change the diff to a taller set of gears, if it's already a 2.24, that's fairly difficult. if it's a 3.07, or 2.47 there is room... you could also increase the tire diameter.

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My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

The only reason I'd install Megasquirt or turbos on my 420 would be for more power. Leave efficiency to the diesels.

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'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

once again I thank all for your input, but it sounds as if this maybe an expense that will give no fruit.

It would give a lot more power output, but not any efficiency gains. The power increase would also then likely require transmission/driveline upgrades to cope with the power increase properly.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)