Vario-Ram vs. X-51 Intake

Does anyone know if an X-51 intake manifold is better than Vario-Ram? 2002 C4 soon to be 4.0 Liters.

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Can't help other than to point you to this: http://www.pistonheads.com/gassing/topic.asp?t=1225218 which may answer your questions.

Thanks, Macster. The link was for a 997 but was interesting. I think I will wait until I can ask Dwaine Dement @ Vision Motorsports, where the engine is going for rebuilding. Dwaine offers an X-51 intake manifold upgrade but I am not sure there will be much advantage to adding one. It might be required when going from 3.6-4.0 liters.

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By all means ask Dwaine Dement. Since he is the builder he would be in the best position to know the answer. FWIW, and probably not much, my preference would be to fit the stock intake manifold with its VarioRam feature. Doing this means you have less to debug or sort out and can focus on ensuring the engine's ok and then break it in as per the builder's guidelines. This also gives you the time to establish a base line of the engine's performance and behavior and over time get a feel for if the engine is being held back, so to speak, by the stock intake system.

I would do what Dwain recommends. He has way more experience than any of us and he will be supporting your engine. My race car has never run better since I handed my car to Vision. I do what they recommend, period.

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It will increase high rpm horsepower with some loss of low rpm torque, with 4 liters you probably won't miss the torque. To maximize the benefit of the X-51 intake you will need bigger cams, etc. X-51 manifold looks better too, so you will have a reason to "pop the hood" to show people your new engine.

Without the X51 heads you'll see little gain, and some losses when using the X51. The X51 heads have the bifurcation point of the ports moved up in the intake tract of the heads a full 1 inch. This matches the characteristics of the X51 intake well. This does not match the standard Carrera head well at all. I found that even with my R51 heads, that outperform the X51 by 12% across the board and 14% at peak, that the standard Carrera intake performs best. When using the X51 intake with them, we have to add material in the ports and move the bifurcation point higher to keep the same RPM range. I am not a fan of the X51 heads, or the intake. Even at 4.2 liters the standard Carrera heads impress me more, especially in the ability to build a fat, flat torque curve and provide excellent throttle response. I found a good combination when using the standard Carrera intake and camshafts with X51 heads, only changing the lobe separation between the intake an exhaust cams, and retarding overall timing 3*.

Dwaine charges $3,300 for the X-51 intake manifold so I would imagine that includes any work involved. I am going to wait until I take the engine down to him to bug him for any answers. He and I are going to sit down at lunch and go over the build and this is one of the questions I plan to ply him with. Dwaine is so busy I just hate to bug him and take up his time. Dwaine did tell me he normally leaves the heads alone and that a brain reprogram is really not needed. I think I will have an Evoms reprogram since there will be such a substantial amount of enhancements, it just makes sense to optimize the process. The reason for this thread was to quench my curiosity as to why the X-51 intake manifold might be a substantial improvement over the V-Ram. I had an early '89 Carrera that we put a '97 V-Ram engine into and the V-Ram was really nice. Porsche also kept the V-Ram for a few years so it must have worked fine!

Hi Jake, You were on my 'short list' to have this work done. The mechanic [Clint @ Euro Trends that came to your rebuild course] informed me you require the whole car when doing work like this. I will post the progress and results of this project as it progresses. The engine will probably go down to Vision next month [03/2015]. Thanks for all of the good input!

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Clint is a good guy. Yes, I do require the whole car, I never trust my reputation to an "installer" who won't install, start up, and break in, and dyno my engine like I will. This is how I have been able to only have two warranty claims in the last decade- I find and correct any issues before the car leaves my care and control. Dwain will take care of you. Engine builders are all different and we have our own ways. That's what characterizes what we build. When I developed the 4 liter combination I first tried it with "as cast" (stock) 3.6 heads and then pulled the heads and added 10,15 and 17% volume increases to them and reinstalled/ dynoed them at each step. The 15% heads were the key, as I was able to maximize swirl and increase port velocity the most on the flowbench with this combination. The engine picked up almost 30HP and 4 MPG over the stock ported heads. It had the broadest power band and the best throttle response. I did that with a stock ECU tune also. It's all in the combo. Finding the combo can take a decade.