View Full Version : Modifications

09-19-2002, 02:18 PM
Hello, how is everybody doing? I was just wandering if anyone has modified their 190 SL engine and if it's practical. I'm really interested in getting the supercharger down the road if I know that it won't cause damage on a rebuilt engine. And since our mechanic is still waiting for some parts, I would like to tell him that I want some work done so it can handle the supercharger when we decide to install it. What is the max power that the block can handle? What work would you have done? Port and polish heads, etc.???

Thank you,


robby ackerman
09-19-2002, 11:41 PM
Theoretically a superchager should be easier on an engine than a non-blown engine. A wet mixture is never placed on the cylinder walls because the fuel is mixed better with air. The vacuum used by an unblown engine to fill the cylinder with fuel/air also exerts a suction that draws oil past the piston into the combustion chamber. In a blown engine this doesn't happen. Supercharging eliminates loss of power at altitude and high temperature. Peak bearing loads on the blown engine are decreased because the higher combustion pressure opposes the inertia forces which tend to literally throw the pistons up in the cylinder head. Running a boost pressure of 5 psi does not cause the engine to exceed the tolerances established by the manufacturer.

That said Dave Coleman, an engineer and someone that has super/turbocharged 100s of engines told me to use the stock engine. I suggested using a 5-main bearing block and he said to stay with my 3-main block.

I've been told by people that never had a supercharger on their 190SLs to expect 50,000 miles instead of 100,000 miles before a rebuild. So I don't know if that is fact or urban legend. How many years will it take you to put 50,000 miles on a 190SL? Quite a few.

What could you do to make your engine last longer. You could bore it and sleeve it with modern hardened liners.

I intend to put the supercharger on my stock block and when/if it blows up I'll try to determine what caused the damage and go from there.

09-21-2002, 10:15 AM
Thank you for the info. Where could I pick up a Judson Super Charger? The member your buying it from, was it his, or does he sell them?

Thank you,


robby ackerman
09-22-2002, 09:00 PM
In the past 18 years I've seen three for sale. I don't know where you can find one. Do some web searches and post an inquiry on this and some of the MB websites saying you are looking for one.


Gary Cox
09-22-2002, 11:16 PM
Robby...Tim Grainey in San Francisco just installed one on his car. You may want to exchange info when you get to yours. Kosta, I have all the components for a kit except the blower itself. The intake is unique to the 190sl but the blower was used on alot of applications and are avail periodically. This kit will be avail when complete or before if you want to hunt for the blower. You can email me @ gkc@adelphia.net.

Bill Lamb
10-03-2002, 11:54 PM
Im curious about what kind of controller an auto engine turbocharger has. If it has a fixed waste gate, then I'd think the turbo would "bootstrap", meaning the more throttle, the more exhaust gas, implying more turbo rpm and therefore more boost. That's a sort of positive feed back loop that makes it hard to control engine speed. Aircraft turbo setups have a complicated control system that regulates the boost to just the right amount, depending on altitude, manifold pressure, temperature, etc.

Robby, your comments on the advantages of a turbo are interesting. But I'd think that for normal "street" driving, the manifold pressure would be below atmosphere (i.e: vacuum) most of the time, so you'd still have potential for oil pumping if the rings or valve seals are bad.

I would think the potential for detonation would be greater on a stock engine with an aftermarket turbo, especially without an intercooler. Engines specifically designed for turbos tend to have lower compression, and to have fuel injection so that one cylinder doesnt' go lean before the others.

Detonation margins are reduced with high cylinder pressures, high temp, and high comression, and lean mixtures. Best run on aviation fuel, 100 octane!

Bill Lamb

robby ackerman
10-04-2002, 12:25 AM

Okay ... I'm using a supercharger not a turbocharger. The turbos I'm using have wastegates set to release at .9 A. The supercharger has no dumping mechanicism and builds to a max of around 5 to 6 psi.

I must retard the timing significantly and your comment about one cylinder running lean is the case since I'm not using fuel injection. The number 4 cylinder will not get as much fuel and I thought I'd run a cooler plug in that cylinder.

Your comment about manifold pressure being below atmospheric pressure most of the time ... the Judson replaces the vacuum in the manifold instantly in proportion to the load placed on the engine. We agree there. The engine is supercharged only when additional power is needed. The additional HP is not required at idle nor at normal highway cruising though it is fair to say that volumetric efficiency is improved even at idle.

Re upper cylinder lubricant, the Judson has an oil resevoir that hooks into the carburator after the fuel and air mix. It is set to use a qt of oil every 500/1000 miles so it acts as an upper cylinder lubricant. This is yet another reason to retard timing.

10-04-2002, 07:34 AM
Everyone talks about the Judson supercharger because it was the only one that made an adapter kit that fit the 190SL. Rather than use the Judson, that had rotating Bakelite vanes that were prone to ware and failure, I would adapt a modern Eaton supercharger that has been installed stock on many modern cars. I have installed an Eaton unit from an early SLK in my 1987 2.3-16 with great success. The unit is about the same size as the Judson but will run thousands of miles. The Judson utilized a funky single barrel carburetor where if you fabricated your own, a nice Weber or digital fuel injection could easily be installed.

10-10-2002, 08:24 PM
Your discussions of supercharging in several threads makes interesting reading. Can you answer a few questions for me.

1) Why does one cylinder go lean before others and why number four?

2) How does the Judson replace vacuum in proportion to load? It would seem that manifold pressure would be directly proportional to rpm.

3) Is the oil injection for lubricating the Judson or the engine?

Thanks - Walt

robby ackerman
10-10-2002, 09:51 PM

I'll answer the two easy questions now and get back to you on number two.

#4 runs lean compared to the other three because the Judson uses its own intake manifold and ... the compressed fuel air mixture gets pushed into the manifold opposite cylinders 1 & 2 then travels down the manifold to 3 and finally 4. Theory says that each cylinder receives a uniform charge. I have been told that in actuality #4 runs leaner than the other cylinders.

The oil injection is to lubricate the vanes in the supercharger which rotate and seal against a steel housing and to serve as an upper cylinder lubricant. The oil is sucked into the carb body below where the gasoline and air mix and is ahead of the supercharger. There is a 2 qt tank that sits in front of the battery and it uses SAE 10 weight detergent motor oil, not an upper cylinder lubricant many of which are primarily cleaners. It is adjusted so that at an idle of 1000 rpms there is one drop of oil every 3 to 4 sec.

On long descents it is necessary to open the throttle occasionally to insure adequate lubircation because of the high vacuum.

robby ackerman
10-10-2002, 11:00 PM
2) How does the Judson replace vacuum in proportion to load? It would seem that manifold pressure would be directly proportional to rpm.

Supercharging increases horsepower by increasing the torque, (due to improving the volumetric efficiency which increases the compression ratio) not by increasing the rpm of the engine. You get more power without increasing engine speed. The Judson is a positive displacement rotary vane unit and it compresses the fuel/air mixture. The fuel/air mixture is introduced into the superchargerís intake port, compressed by four phenol-impregnated vanes and blown out the exhaust port. The temperature of the mixture in the intake manifold has not increased because of the volume change as it enters the intake manifold. Some engineers recognize this as the most efficient supercharger for automotive applications. A rotary vane supercharger is not dependent on engine speed, like a centrifugal unit that blows and compresses air within its own housing. Also the Judson is different from the two or three-lobe Roots units. The Judson is based on the rotary vane pump principle used in a lot of fuel and none automotive water pumps. A rotary vane supercharger replaces the vacuum in the manifold in proportion to the load placed on the engine. There is always vacuum in the manifold at idle and when the engine is not under load. Vacuum is replaced with pressure as the throttle is opened and the engine is placed under load, and the highest boost pressure is obtained under full throttle. Under load more air is available to be compressed. Forget rpms. At idle we are measuring about 18" of vacuum and floored abut 5 psi of boost pressure

As an aside - stress on engine components such as the crankshaft increase with the square of the speed. So at redline of 6000 rpm the engine is under 4 times the stress compared to 3000. With a supercharger you increase the firing pressure and donít need to build rpms to get power.

10-11-2002, 09:34 AM
I understand the gains in power due to improved volumetric efficiency, although I always look at it from the viewpoint of how a process will generate more heat. Iím hung on the rpm angle, but perhaps from a misconception. Isnít the supercharger a belt driven device and would it not therefore have a boost relationship directly proportional to engine speed.

To ask the question another way, say you are cruising down the interstate at 4,000 rpm at half throttle. How would that differ from coming off a high turn at Indianapolis at full throttle, accelerating for all your worth, and at the instant your engine goes through 4,000 rpm. The only difference I see is the increased volume of fuel/air mixture and a higher pressure on the inlet side of the super charger * * * Eureka * * *, I see the light ! At a given rpm, assist is proportional to throttle opening (higher inlet presussre, thus higher outlet pressure) which is another way of saying proportional to load. And as I reread your reply, that is exactly what you already said. Hope I got it right.

Thanks, and I agree, it is a good thing Pea Soup experienced the virus -before- being fitted with a Judson.


Bill Lamb
10-11-2002, 01:48 PM
Thanks for a clear explanation of how the Judson supercharger works...

I would still be concerned with detonation, which is more likely at the higher manifold pressures you'd see with the Judson. If you're going to call for a given power setting (MP times RPM), by
using higher MP and lower rpm, then I'd think the possibility of destructive detonation would be increased.

Also, Im not sure I understand why the compressed mixture isn't much hotter than ambient. If it expands into a higher volume, as you say, then the temp will drop, but then, what have you gained with the supercharger?

I might consider using the Judson on my 5-main bearing engine. :D

Bill Lamb

robby ackerman
10-11-2002, 02:43 PM
Bill & Walt

You engineers! I was sure someone would question the volume and temp decrease from the perspective of a pressurized manifold. Vacuum is present in the manifold except under load. Walt, you explain it. I'm a number cruncher and it is hard for me to explain this stuff :)

Knocking is a BIG issue and I'll retard the advance some 30 or 40 degrees. I don't know yet how much but it will be significant. Right now I'm running 45 degrees ignition advance at 3000 rpms.

Bill Lamb
10-11-2002, 03:46 PM
Retarding the ign timing would help, but with late timing, you will compromise all the torque and power you're paying for! With late timing, not all the fuel charge will have time to burn be4 the exh. valve opens.

What does Judson say about timing and detonation issues?

10-11-2002, 04:03 PM
I'm glad you are not asking a lot from a guy who flunked thermo! The following is offered for the truly masochistic:

As everyone probably realizes, if a gas expands it will cool. In the example we are talking about, an expansion out of the supercharger into the intake manifold, cooling would occur but there would also be a change in pressure. The relationship between pressure, temperature, and volume is defined by the "equation of state of an ideal gas".

pV=nRT or p1 v1 /t1 = p2 v2 / t2

p is pressure in atmospheres
v is volume in liters
t is temperature in degrees Kelvin
nR can be considered a constant

Most gases will approach this relationship which is based on Boyle's Law (for a given mass of gas at constant temperature, the pressure is inversely proportional to volume) and Charles Law (for a given mass of gas at constant pressure, the volume is directly proportional to the temperature).

In the original example, if we look at one pound of air from initial conditions, the supercharger would raise the pressure, reduce the volume, and raise the temperature. As it expands into the intake manifold, the volume would increase resulting in a drop in pressure and a drop in temperature. However, the temperature and pressure would be above initial conditions and volume less. The exact relationship could be determined by taking measurements on Robby's screamer when he finishes.

So, do all superchargers/turbos have the throttle plate -before- the compression?


Pat Ballogg
10-11-2002, 09:51 PM
My wife looked over my shoulder while reading Walts reply and said " So those guys have gas problems too" - "Different kind of problem dear". Anyway, I've never messed with carburated superchargers but there is a slight increase in temperature from the compression of the air mass in any supercharger. Proper fuel flow is the key to detonation aversion. In the case of fuel injected units you raise the injector pressure to overcome the increased air pressure. The fuel cools the air mass and chambers as in all cases. I raised my injector pressure from 45lbs.sq.in under max load to 78lbs. I also added an advance control unit that reduced the timing 2 degrees for every pound of boost up to 8 degrees max. This was a conservative set up. If I were being more aggressive with boost etc. an intercooler would be called for to reduce the thermal issue. All modern units have a bypass valve that disengages the unit at idle, coast and low load. On a mechanical unit I doubt that this happens so every driving issue has to be addressed. In a carburated unit the fuel is introduced further 'up stream' so as not to fight the air pressure. Carburated intake geometry ( polishing/porting) - the longer intake the better for atomization and even flow seems to be the key. I remember pre war techniques on MG's where the carburator was mounted outside the cowl where the fender would normally be mounted. No matter how it is set up on a mechanical unit the devil will be in the minute 'fettling' to get it right.

robby ackerman
10-11-2002, 10:14 PM
So, do all superchargers/turbos have the throttle plate -before- the compression?


No, many superchargers have the throttle plate after compression. Jim Villers has experience with binding throttle plates on his after.

I appreciate you mentioning Boyle's Law. I went to school at the College of William & Mary. On the old campus is the Wren Building, designed by Sir Christopher Wren and next to it is a building that was donated to the College by Sir Robert Boyle.

robby ackerman
10-11-2002, 10:35 PM

You inquired about what Judson says about retarding the ignition advance. They say that Bosch distributor VJ4BR11 must be used and that the ignition timing should be set so that firing occurs at top dead center.

Their service bulletin provides this data:

RPM Advance in degrees
700 0
1000 5
1250 8
1500 10
1750 11
2000 12
2300 15 max

allowable tolerance is minus two degrees. This is 30 degrees less than what my current max advance is.

robby ackerman
10-11-2002, 10:47 PM
stress on engine components such as the crankshaft increase with the square of the speed. So at redline of 6000 rpm the engine is under 4 times the stress compared to 3000. With a supercharger you increase the firing pressure and donít need to build rpms to get power

What does this mean in practical terms? When I drive route 33 through the Blue Ridge Mountains or take I-64 through West Virginia there are several third gear hills that I take at 5500 rpms and I'm running along at 55/60 mph. With the supercharger I can leave it in fourth gear and at 4000 rpms I'd be moving along at 70 mph - faster with less stress on the engine.

Now where is that 5-speed transmission?

The carb that comes with the Judson is a single barrel Holley. I have a two barrel Weber 32/36 DGV that will flow more air and has a progressive linkage that can keep performance and economy in balance. A problem I have heard about the Holley is that it runs out of fuel at top end. I'll have to see if I have enough room under the hood for the weber. If not I may have to install a BIG hood scoop. :)

10-12-2002, 01:34 AM
How about the one that was on the prototype? do they make that hood and how much is it? If not, do you think a body shop could modify a regular hood?


robby ackerman
10-12-2002, 05:10 AM

Seriously, I'll not modify the hood. I'd modifiy the intake manifold or use a different carburator like a sidedraft SOLEX. :rolleyes:

10-12-2002, 10:37 AM
I knew you'd have to use a Solex to do it right!:D

10-14-2002, 10:10 AM
Wonderful discussion ... Too bad that I was out of town during the flurry of postings.

I will add a few items that may simplify the discussion. Engine power is a function of the Mean Effective Pressure on the piston and the engine RPM. Pressure is generated by the burning of the fuel. Superchargers increase the amount of fuel and air in the cylinders and when this additional fuel is burned, it raises the pressure on the piston. The higher pressure generates increased torque which increases the power output at all RPM's. The higher pressure (and increase heat) will cause additional stress on all engine components.

The throttle plate regulates the volume of air and fuel passed into the cylinders, regardless of whether it is before or after the supercharger.

The Judson is a "correct" historic supercharger but is very inefficient compared to the modern Eaton units.

Bill Lamb
10-14-2002, 08:58 PM
The change in entropy of a system is given by the expression


Where q is the ammount of heat, and t is abosulte temperature. In all systems, the entropy will increase. A broader interpretation leads to the conclusion that the entropy of a system is a function of its disorder. Therefore, all systems will become more disorderly, like my garage :D

I almost flunked thermo too, and that was a long time ago...

10-15-2002, 10:13 AM
It's gettin deep, pull up your pant legs!:eek:

10-15-2002, 04:42 PM
Robby et all - I have been reading about supercharging, gaining just enough knowledge to be dangerous. In the literature, there was some limited discourse on the desirability of changes to cam timing, specifically, to reduce intake/exhaust overlap. With the Judson's low boost, this may not be an issue, but wanted to know if it would be a consideration.


10-16-2002, 01:24 PM
Most sources tend to recommend keeping the stock cam verses installing a "high performance" cam. The cam grind is less important on supercharged engines because you can fully control the volume of the air fuel charge with the boost pressure.