if it cost 8 grand to drop in a turbo i would do that. i mean as long as the gain is worth it i mean im not going to spend that much if im only getting 50hp you know. and i dont want a srt because i want a 6 speed and i like the flip up wing.

 

Assuming good tuning:

~444hp equals about 290.8psi BMEP
~491hp equals about 321.5psi BMEP
~571hp equals about 374.2psi BMEP

An estimated 350psi BMEP is about the "safe" limit for engines sleeved the way ours are. If you're looking for a "glory run" car then you could probably hit 400psi BMEP and around 600hp, but then you would eventually experience failure modes which would be associated with cylinder wall stretching/walking.

Also, aluminum's lack of fatigue limit would mean that failure would be an inevitability - the question would be "when" and this would be associated almost directly with ignition timing so that peak cylinder pressure is minimized.

BMEP being one power-related metric. The other is RPM. If the redline is raised 1000 rpm, and the head is modified to support the additional flow required, then 16% more power is available without additional strain on the cylinder walls. Might as well use those fancy high-strength pistons and rods for something...the question is whether the balance shafts can take the additional speed without spinning bearings.

Keep in mind that a Porsche 911 GT2 makes 520hp, and that's not necessarily at the wheel, and it has a closed deck, AND it has 0.4L more displacement.

 

The trans is the same more or less as that in the C32 and E55 AMG's and is very close to the same as the one used in the Dodge SRT8's, so it should be good for at least 5-600 hp before any issues.

Loungin, you guys are my hero's. I looked at the vids and the layout of the turbo and plumbing is just plain genius. Well done lads! This looks like a package that could be transplanted onto other SRT6's or C32's. By taking the 50-60 hp that is lost in parasitic losses to spin the supercharger, you automatically gain that all back at the rear wheels with the turbo set up. The only real down side is the little bit of lag, but in a well matched turbo, that is very small. So if a pullied C32 or SRT6 running 17-18 psi (a safe amount) makes 335-365 at the wheels (depends on the state of tune), then getting 395 to 425 with a turbo is piece of cake. Again Kudos on an excellent job.

Irish

 

In all truth I think the Charger/Magnum/300 were all based off of the E-Class platform... So to see similarities between the too would be expected...

 

I need to get smarter and look up stuff. Thought that the rest may not understand the BMEP discussion, so here is more definition. Woody
- Brake Mean Effective Pressure -

BMEP: An important performance yardstick


We have covered the topics of Thermal Efficiency and Volumetric Efficiency as methods for estimating the potential output of a given engine configuration.
Brake Mean Effective Pressure (BMEP) is another very effective yardstick for comparing the performance of one engine to another, and for evaluating the reasonableness of performance claims or requirements.
The definition of BMEP is: the average (mean) pressure which, if imposed on the pistons uniformly from the top to the bottom of each power stroke, would produce the measured (brake) power output.
Note that BMEP is purely theoretical and has nothing to do with actual cylinder pressures. It is simply an effective comparison tool.
If you work through the arithmetic, you find that BMEP is simply a multiple of the torque per cubic inch of displacement. A torque output of 1.0 lb-ft per cubic inch of displacement equals a BMEP of 150.8 psi. in a four-stroke engine and 75.4 psi. in a two-stroke engine.
(The discussion on the remainder of this page is with respect to four-stroke engines, but it applies equally to two strike engines if you simply substitute 75.4 everywhere you see 150.8)
If you know the torque and displacement of an engine, a very practical way to calculate BMEP is:
BMEP = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

(Equation 8)
This tool is extremely handy to evaluate the performance which is claimed for any particular engine. For example, the 200 HP IO-360 (360 CID) and 300 HP IO-540 (540 CID) Lycomings make their rated power at 2700 RPM. At that RPM, the rated power requires 389 lb-ft and 584 lb-ft of torque respectively. (If you don't understand that calculation, CLICK HERE)
From those torque values, it is easy to see (from Equation 8 above) that both engines operate at a BMEP of about 163 PSI. (1.08 lb-ft of torque per cubic inch) at peak power. The BMEP at peak torque is slightly greater.
For a long-life, naturally-aspirated, gasoline-fueled, two-valve-per-cylinder, pushrod engine, a BMEP over 200 PSI is difficult to achieve and requires a serious development program and very specialized components.
For comparison purposes, let's look at what is commonly believed to be the very pinnacle of engine performance: Formula-1 (Grand Prix).
An F1 engine is purpose-built and essentially unrestricted. For 2006, the rules required a 90° V8 engine of 2.4 liters displacement (146.4 CID) with a maximum bore of 98mm (3.858) and a required bore spacing of 106.5 mm (4.193). The resulting stroke to achieve 2.4 liters is 39.75 mm (1.565) and is implemented with a 180° crankshaft. The typical rod length is approximately 4.016 (102 mm), for a Rod/Stroke ratio of about 2.57. These engines are typically a 4-valve-per cylinder layout with two overhead cams per bank, and pneumatic valvesprings. In addition to the few restrictions stated above, there are the following additional restrictions: (a) no beryllium compounds, (b) no MMC pistons, (c) no variable-length intake pipes, (d) one injector per cylinder, and (e) the requirement that one engine last for two race weekends.
At the end of the 2006 season, most of these F1 engines ran up to 20,000 RPM in a race, and made in the vicinity of 750 HP. One engine for which I have the figures made 755 BHP at an astonishing 19,250 RPM. At a peak power of 755 HP, the torque is 206 lb-ft and peak-power BMEP would be 212 psi. (14.63 bar). Peak torque of 214 lb-ft occurred at 17,000 RPM for a BMEP of 220 psi (15.18 bar). There can be no argument that 212 psi at 19,250 RPM is truly amazing.
However, let's look at some astounding domestic technology. The 2006 Nextel Cup engine is a severely-restricted powerplant, being derived from production components. It uses a production-based cast-iron 90° V8 block and 90° steel crankshaft, with a maximum displacement of 358 CID (5.87 liters). A typical configuration has a 4.185" bore with a 3.25" stroke and a 6.20" conrod (R/S = 1.91). Cylinder heads are similarly production-based, limited to two valves per cylinder, but highly developed. The valves are operated by a single, engineblock-mounted, flat-tappet camshaft (that's right, still no rollers as of 2007) and a pushrod / rocker-arm / coil-spring valvetrain. It is further hobbled by the requirement for a single four-barrel carburetor. Electronically-controlled ignition is not allowed, and there are minimum weight requirements for the conrods and pistons.
How does it perform? At the end of the 2006 season, the engines were producing in the neighborhood of 825 HP at 9000 RPM (and could produce more at 10,000 RPM, but engine RPM has been restricted by means of a rule limiting the final drive ratio at each venue). 825 HP at 9000 RPM requires 481 lb-ft of torque, for a peak-power BMEP of nearly 203 PSI (14.0 bar). Peak torque was typically about 520 lb-ft at 7500 RPM, for a peak BMEP of over 219 psi (15.1 bar).
THAT is truly astonishing. Compare the F1 engine figures to the Cup engine figures for a better grip on just how clever these Cup engine guys are.
To appreciate the value of this tool, suppose someone offers to sell you a 2.8 liter (171 cubic inch) Ford V6 which allegedly makes 230 HP at 5000 RPM, and is equipped with the standard iron heads and an aftermarket intake manifold and camshaft. You could evaluate the reasonableness of this claim by calculating that 230 HP at 5000 RPM requires 242 lb-ft of torque (230 x 5252 ÷ 5000), and that 242 lb-ft. of torque from 171 cubic inches requires a BMEP of 213 PSI (150.8 x 242 ÷ 171).
You would then dismiss the claim as preposterous because you know that if a guy could do the magic required to make that kind of performance with the stock heads and intake design, he would be renowned as one of the pre-eminent engine gurus in the world. (You would later discover that the engine rating of "230" is actually "Blantonpower", not Horsepower.)
As a matter of fact, in order to get a BMEP value of 214 from our aircraft V8, we had to use extremely well developed, high-flowing, high velocity heads, a specially-developed tuned intake and fuel injection system, very well developed roller-cam profiles and valve train components, and a host of very specialized components which we designed and manufactured.

 

woody,

i'm intrigued by the article... do you have a link so i can read more?

 

If you click on the click here part you get back to the article. Woody

 

Thanks...I started reading that whole thing... really interesting article...seriously. Nice find.

 

I am not surprised to hear this. The Chrysler 300 and Dodge Charger are the two domestic sedans that I have driven with the "Best" road feel. They have a planted feel that reminded me of my first AMG the C36. Not as good but very similar in feel. They have good steering and the best brakes in their class, all courtesy of Diamler-Benz. Now with Fiat in charge, I wonder what they will have? Best engine note and worst electrics?

As for Woody's informative disertation on engine dynamics and mean effective pressures. He is right on the mark. This sheds some light on things but also causes one to wonder what majic AMG is using? For example:

A stock 3.2 liter C32 or a SRT-6 (195 cid) dynos 287.7 rwhp @ 5850 rpm (from drag times). This works out to 258.3 ft-lbs torque @ peak hp rpm. And using the same equations it calulates the pressure to be 199.8 psi. Sounds pretty close to maxxed out. Now another C32 dynos 328.1 hp at 5900 rpm using a evosport pulley and chip set. Most of this gain is coming from increasing the boost in the intake tract. This C32 is putting out 292.1 ft-lbs at peak hp rpm. Which works out to a calculated pressure of 226 psi which exceeds the F1 engine in the earlier example. Hmmm are we driving grenades? Experience would indicate that we are not.

Still to further confuse the issue, a brilliant fellow removes the supercharger and replaces it with a turbocharger. In so doing, he runs the same boost pressure and thus the same cylinder pressures. Since his turbo is driven off the exhaust gases instead of the crankshaft like the SC'er, the turbo cars output at the rear wheels is greater to the tune of about 60 hp (according the lysholm screw supercharger map). So, his car is making something like 388 rwhp at the same pressure as the supercharged engine that made only 328 hp. So which engine is stressed the most? Neither. They are stressed the same but the turbo engine has more of its power available to do work at the wheels, thus its peak available output is greater.

Now the examples of the F1 and NASCAR engines are both describing normally aspirated engines. They run in the extreme spectrum of performance and are above the 200 psi theoretical limit and they run with little if any safety factor. The normal limits for N/A spark ignition engines is closer to 125-150 psi.

In the examples that I am using, the C32/SRT-6 is a forced induction engine. The theoretical maximum of 200 psi applies to the N/A engines, but how does it apply to the forced induction engines? It is a valid question. In fact the theoritical maximum for forced induction engines is different. A range of 180-250 psi is not out of the ordinary. But, I suspect that the calculation of pressure should be made using the crankshaft numbers before any losses are subtracted for such parasitic functions like driving the supercharger on a SC'ed engine. Because we already know that the pressures in the cylinder of a turbo or SC'ed engine will be the same at the same boost pressure (all things being equal) despite the specific output dyno numbers being quite different.

Soooo, with that in mind a turbo engine making 388 hp from a 3.2 liter (195 cid) displacement at 5900 rpm has a BMEP of: 267 psi. The same engine running the same boost with a supercharger but with 60 hp of parasitic loss to drive the SC'er off the crank will dyno 328 hp at the same rpm, more or less and will also experience the same mean effective pressure of 267 psi. This can be achieved with relative reliability because of the fact that a good bit of the pressurization is taking place outside the engine by the turbo or supercharger and that all is fairly gradual compared to the events during the compression stroke. So, is a 3.2 liter turbocharged engine that makes 428 hp at 6000 rpm on the verge of self destruction? Probably not. But there may not be that much more left on the table either.

For reference, at the end of WWII forced induction pistion engine technology was reaching its practical limits. Rolls Royce built a version of the Merlin V12 that was running 36 psi of boost on 150 octane fuel. That engine had a BMEP of 404 psi. Modern modified racing versions of those engines are stressed even further. My long winded point is that the maximum BMEP for FI engines is not the same as for N/A engines.

One last extreme example was the BMW 4 cylinder 1500cc turbo used in F1 in the 1980's. They only needed to survive for one race and were stressed to the limit. They could make 1000 hp in race trim or as much as 1400 hp for qualifying or for last lap passes by turning up the boost. They were limited to 11,200 max rpm. In race trim, they were running a BMEP of about 773psi and over 1000 psi for qualifying!

The 3.2 liter SC'ed V6 used in the C32 AMG and the Chrysler Crossfire SRT-6 was rated 349 hp at the crank and using the SC'er map this was subtracting ~45 hp to drive the supercharger, so the total output was closer to about 394 hp @ 5850 rpm. That is crank hp not wheel hp but the engine sees the same pressure eitherway. These numbers work out to a BMEP of about 273.5 psi (HP x 792,000)/(CID x RPM)=BMEP. Those numbers are above the so called normal range of 180-250 psi for forced induction engines but is well below the theoritical maximum assuming the Formula 1 turbo was at that or a bit above it. Calculating the theoretical max in this case is more complex becuse it depends on how much of the compression is taking place outside the cylinder before the compression stroke as well as intake air temperatures and density, etc, etc. It is complex. Bottom line however, it this. Forced induction is magical. It enables the engine to perform more work with less displacement. If you boost the intake pressure to one atmosphere (14.5 psi) you essentially double the torque output. If an engine makes 349 hp at 14.5 psi boost using a supercharger the same engine will make more hp with a turbocharger at the exact same boost. The difference is the amount of hp required to drive the supercharger. Spinning the supercharger faster to make more boost increases the parasitic loading and that is not a linear function. In general with our engines, the added load to increase boost from 14.5 psi to 18 psi (24% increase) is 33%. I am generalizing here cause I am too lazy to look up the supercharger maps. Point is that you cannot get unlimited boost with the SC'er because there is a point where the loads go off the chart.

Back to the cylinder pressure discussion... Regardless of what the BMEP is, it will be the same for both the Supercharged and Turbocharged engine if the boost is the same. That is why most FI engines use turbos. The supercharger is fun cause it makes boost instantly and at low RPM's and that makes it very practical for everyday use but if peak output to the wheels is the goal, then the turbo is the way to go. It is laggy and harder to modulate by the driver but once on the boil and making boost, it will accellerate faster than its supercharged counterpart. A logical question is then why to top fuel dragsters only use supercharged engines. Simple, the time it would take to spool up the turbos is too long and they would be too hard to modulate and drive at the outputs involved. Most top fuelers are not horsepower limited, they are traction limited. They can make more power if/when track conditions allow them to put it to the ground. I was once told that it would take a street hemi engine (426 hp) to drive only the supercharger of a typical topfuel drag engine.

This only scratches the surface of this subject but points out nicely that if the AMG engine is reliable at 18 psi boost using the supercharger it will also be reliable at 18 psi boost using the turbocharger. Most of the gains are coming from the reduction is parasitic losses at the crank and some possibly from improved intake charge cooling since that is a very weak link in the AMG C32/SRT-6 design. I am impressed by the elegant design and the results!

Irish

 

I actually dyno'd mine today at Eurocharged. 262.4 rwhp @5300 and ~270tq @3500 peak on a dyno dynamics.

So 287 is probably on a mustang dyno.

As a point of reference it is probably a better idea to take stock hp/tq ratings of the manufacturers spec sheet...

my $.02

 

After reading this sentence it got me to thinking. How would a turbo's turbine housing like/deal with nitro? Probably not too well I'd guess. $hit those turbines would probably end up being grenades by the 60' mark!

 

First of all, I'm not sure where this limit of 200psi BMEP for an engine came from. That's not a correct number.

One thing you have to understand is that BMEP is not related at all to cylinder pressure.

When one talks about BMEP limits, you're talking about the force being placed upon the pistons, piston bearings, rod, rod bearings, crankshaft, crank bearing, the main caps, and eventually the whole block. The cylinder wall takes some of this force as the piston moves downward as the force being exerted is not totally parallel to the cylinder. Tolerances, piston skirt, cylinder wall shape, piston material, and squareness of the engine contribute.

The comparison between engines in different racing series is largely moot, most of that discussion comes from a history of F1 being perceived as "technically superior" and US Championship Cup racing as being sort of a "redneck sport". Naturally, there's going to be some type of comparison saying, "look, cup engines are right up there engineering wise". The reason this sort of comparison isn't fair to make is because the types of engines used in each racing series are not dictated by technical limits, but instead by the rules set forth by the owners of the racing series. Therefore, the BMEP of an F1 car is irrelevant, mostly because they are forced to use small displacement V8's revving to 18k or more rpm. This means that the rods, bearings, pistons, cylinders etc are at least 4 times stronger and the valves actuated much faster than the lower RPM cup cars.

(Granted, cup cars have great engines, I wouldn't argue if I had an 850hp 5.7L NA engine in my car.)

Consider, also, that there is a significant difference between a car that has to deal with a BMEP of 220psi for 3 hours straight, and a car that makes 220psi for 13 seconds at time, perhaps 300 times a year for a total usage of 1 hour at peak BMEP. That means that you'd have to do a quarter mile run every day for 3 years to run the equivalent of, on average, one NASCAR race.

This is why the average street engine can be tuned to 350psi or more BMEP - because the average driver is not sitting there running at WOT for an extended period of time. This is also the reason why highly tuned drag engines, especially "SpoCom" (Sport Compact) drag racers pumping 4 bar boost into 2.0L engines making 900hp have to rebuild their engines perhaps ever 12 runs or so. This is because they are making BMEPs up into the 650psi+ range. We're talking about total engine lifetimes measured in minutes.

I'm not sure I understand that statement.

My understanding is that turbochargers can deliver significantly larger volumes of air at higher efficiencies with less parasitic drag. Superchargers are used mostly because they are simple to engineer into an existing engine and are space-efficient.

 

The BMEP limit of 200 psi is a "so called" theoretical limit for N/A engines. It is one of the design parameters. Another reference places the practical range at 125-150 psi but it really depends on what you plan to do with the engine and how reliable must it be. It is not the only measure of stress, but is a good general measure. High BMEP means more torque and more power at a given rpm. And more stress.

"One thing you have to understand is that BMEP is not related at all to cylinder pressure." Huh?? It is one of the measures of pressure (BMEP). It is a mathematical calculation of Mean Effective Pressure. You are right in that it is a way of expressing the mechanical stress on the pistions, rods, bearings, etc, etc. But it is only one measure. There are others such as rpm and piston speed that all come into play as well on the stress an engine experiences.

"Regardless of what the BMEP is, it will be the same for both the Supercharged and Turbocharged engine if the boost is the same. That is why most FI engines use turbos. "

My statement above may be too general. What I was attempting to explain is that the engine (pistons, rods, crank, etc), cannot tell from where the boost is being generated when you go to calculate the BMEP or the peak pressures or the IMEP, etc. All it knows is that the inlet tract is operating a some known boost pressure above atmospheric. The fact that this is from a turbocharger, or a supercharger is largely irrelevant when discussing the BMEP. Now it is true that the turbo, being driven from the hot exhaust gases has lower parasitic loads than the supercharger. Both can be made to pump more air, but at differing costs to the engine.

I'm not sure where you conclude that superchargers are used because that are easier to design and space efficient that turbos??? Turbos and superchargers are just two different ways to achieve a goal of more output. Turbos are more efficient but have other design issues to deal with. Heat, lag, flow rates, etc. It is not that one is better or worse, but just different. For a given boost pressure however and thus for a given BMEP limit, the turbo with produce the higher ouput torque and HP, simpley because it does not use any of the power to drive the compressor.

Go back and re-read the articles referenced by others for a more thorough explaination. I hope, this helps.

Irish

 

I am not trying to sound like I have all the answers on this subject cause that is not true. I am facinated by engines and tuning challenges. I have been onvolved with forced induction engines (mostly turbos) for over 25 years. So, please do not take my earlier posts wrong. I learn as much from you guys as anybody. But the net is a source of truth, half truth and totally wrong statements, lol. Sometimes it is tough to sort the real information from all of the chaff.

My original post was only to point out that when determining the maximum allowable BMEP for any engine, it is not the same for N/A vs forced induction and even then it also depends on what the engine application is to be. Formula 1 or NASCAR or top fuel engines limits are not really applicable to street cars which we hope to drive for several years even if not a full throttle all the time. We should strive to keep more safety factor in our limits unless we want to be buying lots of expensive engine parts.

Irish

 

I don't want to imply that I was accusing you of being a know it all, I just like the subject of forced induction.

 

Heres and idea. Keep the stock s/c to make up for the lack of spool with the turbo. Run a rear mount turbo in the back like the Squires setup. This should take care of any lag related problems and increase cfm.

 

yeah see i was thinking the same thing i was thinking getting a junked srt engine and droping it then rear mount..

 

Was going to do that.... but this project was a lot more fun . STS is to easy.

 

Yes, and thank you Brian, get everything worked out so you can offer the NA guys a turbo setup in the future

 

You'd still be spinning the blower though. The only way to do this is how Mohammed Ben Sulayem did his C32. He has 2 separate throttle bodies, one for the blower and one for the turbos. He also set it up so that the blower would turn off after the turbos reached boost.