ok - before anyone flames me...I've spent the last hour reading the search results for max rpm....

so it appears we have an AMG "handbuilt" 3.2L V6 engine.
Why on earth does it only do 6200rpm?.....
Apart from the obvious...air/fuel....SC speed limit.....
What internal mechanicals are stopping it from doing a more reasonable 7,000 or even 7,500 rpm like other cars can.
When I was a kid - things weren't limited - it was up to the driver to change gears before he saw a piston fire through his bonnet. Guys would balance and blueprint their motors in their Ford Escorts and the Capris and get 7,000 rpm no sweat....
Mind you they were only 2L or so....

but hey - as I awlays say...Can't be 2 hard......can it?

PS _ I did read an interesting thread about the Taiwanesse guys pumping this baby to 3.7L and 500hp.....whooohoo....

 

you will get a lot of answers on this one. I would suspect, the engineers were going for peak HP while maintaining an engine that would also have parameters for good fuel mileage as well. You can build engines for HP, and more rpms, but the fuel mileage will suffer. I think it is a balance of the 2 myself.

 

Stress increases as the square of the rpm, going to 7000 is just a hand grenade with no gain in power, losses increase and power falls off with the torque peak. OBTW there is a warranty issue which is why they have added the bas/esp. Woody

 

I would venture to say...blower. look up how many factory blown cars have rather low red lines. My cobalt SS SC is a blown 2.0L, factory red line is 6600rpm. I've since changed that to 7200rpm however.

Most, if not all, blown cars will simply generate to much heat at that high of an rpm for no benefit.

 

yes - to remove the SC from the equation - an after thought was to rephrase the question and ask - why a stock 320 couldnt do 7000rpm....

but then I got thinking.....how about 32Krazy's (Steve) new 996 GT2.....???
"......
In 2000, Porsche launched the Turbo version of the Type 996 for MY 2001. Like the GT3, the new Turbo engine derived from the 911 GT1 engine and, like its predecessor, featured twin-turbos and now developed 420 PS (309 kW). Also like its predecessor the new Turbo was only available with all-wheel drive. A US$17,000 factory option, the X50 package, was available that boosted the engine output to 450 PS (331 kW) with 620 N.m(457 ft·lb of torque across a wide section of the power band. With the X50 package in place the car could make 0–100 km/h (0–62 mph) in 3.8 seconds. This package is named as Turbo S in Europe. Later on toward the end of the 996 life cycle, a 996 Turbo S coupe also returned to the US along with a new debut of the Turbo S Cabriolet boasting even more power— 450 PS (331 kW) and 620 N·m (457 ft·lbff)— than the regular Turbo. The Turbo can reach a top speed of 189 mph (304 km/h).
........"
Plenty of boost and I'm thinking you get these numbers from a 3.6L - I figure its redline capability is what gets it up there (although I havent found figures yet)

 

factory redline on a 996 turbo is 6200 rpm. mine is modded so redline is 7000 but the ecu records every cycle over 6200 as a type 2 over rev.
also its apples to oranges. twin turbo vs small s/c 3.2 v6 vs 3.6 flat 6. 2 completely different animals.
on my slk32 i had as high as 6900 rpm rev limiter and it didnt do any good. outside the peak limits of the engine. power is at peak boost from about 2200 rpm to about 5900 rpm. after that your just beating on the engine with little gains for the effort

dont forget the s/c boost is almost 90% at 2200 rpm and turbo boost climbs from 3000 and builds as the car revs higher until peak turbo efficiency at about 6000 rpm. (maybe a bit higher with proper fueling and tuning)

 

can these engines be bored out to a 3.7l?! im sure its a new engine when its done , but if it can be , its an interesting concept!

 

Startech 3.8L

 

By chance is this also true with the XF? I would hate to have an engine failure and have it not covered because of a few over-revs. If true is there any way to clear this 'LOG'?

 

does startech still do this stuff?

 

I think I almost hit the limit while trying to time a 1/4 mile run on the highway and got a check engine light... code had a bunch of cylinder misfires but i cleared them and no further issue... not something i want to make a habit of though

 

would be nice if the same SCharger and IC setup could bolt straight on.....
possible if its a simple bore and stroked M112

 

I believe the redline RPM is determined by the valves. They just can't keep opening and closing faster and faster. Also, the cylinders won't fill completely at an RPM that's too high.

 

Just to piggy back on 6000rpm....

The valve springs is more likely what you had in mind. They get more or less mushy at the higher rpm levels. Meaning that they wont fully open and close with each cam revolution as intended, commonly called valve float. Filling the cyliders is not an issue cause we are cramming it in there with the blower. Another issuse that may or may not be on this motor is rod bolt stretch. With high rpm comes huge forces to be dealt with. Not sure if the factory stuff would be able to keep it all in check.

 

What kind of hardware is in the shortblock? Cast, forged?

 

interesting - I would have thought AMG would have used top quality materials for the valves/springs - stranger things have happened with these cars though.
But I do believe the SLK32 has forged pistons and CRods etc as opposed to the X320 series which I believe are of lesser grade....not sure on springs and valves.

It's strange the SLK32 redline rpm hasnt been re-rated when compared to the X320 series, but some reports (32Krazy et. al.) have indicated the SC runs out of efficiency above 6000rpm and going to 6500rpm as he did, held little if any gains.

Always the optimist, Id' like to continue to challenge some of this previous work.
Heading for 19+ psi boost (on the 61/155mm pulley config) and consistent 50C (122) Max AIT's and <13AFR in my SLK32 - but a lot of work (maybe a year) to get to that ellusive >320kW to match the car's namesake. Will all be worth it in the end.

 

Hi,

I have managed to complete the project. We have been able to det the peak rpm delimiter to 6800rpm where we dont see any drop in hp or torque before reaching the Max rpm.

 

Did you happen to log IATs or EGTs?

 

Great work guys!
Hmmm.....big drop in torque, not much hp gain, maybe 10hp if you are lucky.
so as 32_Krazy indicated in his SLK32 - little gains.

SilverA....In your min, is it still worth chasing? Improving VEff./valve timing??

 

The valves aren't the problem. It's the springs and the fact that there was a trade off that had to be made in the form of better fuel economy vs stiffer springs so the valvetrain doesn't start floating.

BTW, what mods have you done to your car Billy22Bob? I'd start with the the basics before worrying about bumping the rev limiter.

Merry Christmas everyone!