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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Monster CIS, is it a Miller Cycle?

Hi everyone, it has been a while.

...627HP@5300 Torque: 658Lb/Ft(892Nm)@4600 on mainly stock 930 Euro components and on pump gas - well, 98 octane over there...

I have long wondered about the "Monster CIS" motor and how such achievement was even possible. (I know how to get the fuel!)

This builder achieves more efficiency out of a two valve air cooled motor than most builder's seem to get from even a water cooled four valve motor. He does it at a very low rpm and can run up to 1.3 bar boost with a single plug without issue.

Well, I am wondering if he might be a student of the "Miller Cycle" (MS) motor.

Standard 4 stroke motors have an expansion stroke that is very close to the compression stroke in length.

With a Miller the compression stroke is shortened. Shortening the compression stroke reduces the power lost building compression (pumping losses). It also can makes for less heat from compression. As we know heat is one of our biggest issues.

If the combustion chamber is not reduced in size like is typically done on a MS motor, that would allow much more head room for boost.

Of course, the power stroke could also be lengthened to capture more of the combustion cycle's power. This would move the TQ peak to a lower rpm as seems to be the case with the build.

The Monster Builder has noted that he uses a custom cam of his own design.

He also used stock displacement, stock euro headers, a custom turbo for the application, an intercooler of his own build, and a boost management strategy (to 1.3bar tapering to .9 bar) to stay within fueling limits.

So here is what I am thinking he may have done besides building a great motor with an efficient intercooler.

He may have shortened the compression cycle and lengthened the power stroke / expansion cycle. Not sure if he reduced the compustion chamber size.

With this he would need a special turbo matched to the build. Said turbo would have to have a smaller hot side than usual to allow for early boost he achives and work with the lower exhaust gas production at lower temps.

This might fit how he can make so much HP with the stock headers.

It also would have to have a larger compressor to support the higher HP levels.

In my mind I wonder if this is the last piece of the puzzle?

The best.

Monster Build:
Cis monster

Miller Cycle"
Miller cycle - Wikipedia, the free encyclopedia

Originally Posted by zcoker View Post
I don't know if this site has been posted here before and it probably has yet I've never come across it: 627HP@5300 Torque: 658Lb/Ft(892Nm)@4600 on mainly stock 930 Euro components and on pump gas - well, 98 octane over there.

SpezialMotorer-Engine Development Click under project section.

I know that many here place solid limits on the CIS system and I'm just learning about it myself but this says otherwise.

If I know the Swedes like I do with bmw's, this is true information. We doubted a long time their claims on some of their bmw motors but they have some s38's over there pushing 1500hp and running 7's in the 1/4 mile - varied. I guess those long, cold winters over there afford them plenty of time to tinker and build these monsters. Very interesting to see some things taking way beyond the norm (like they always seem to do) in spite of the speculation and doubts. I sure would like to see more info on this build but the Swedes are quite tight lipped with their projects.

Last edited by 911st; 08-29-2011 at 04:58 PM..
Old 08-29-2011, 04:51 PM
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