By removing the runners you would be converting the MP112 lower intake to a TVS style lower(wide open).

 

Well I guess I was wrong when I said all Magnacharger MP112 bases are the same. While doing some research this morning I found a couple of photos of a Magnacharger kit off for a rebuild from a 2004 GTO. As you can see the inside of the lower base is far different from our trucks. The runners are so short that they just shoot right into the intake ports on the head. The intercooler setup is also vastly different. I would presume the reason for this is the low cowl height on the GTO. After seeing this, I doubt low speed torque/throttle response would be sacrificed all that much. Lets face it, these GTOs are no light weights, although they are lighter than my truck. I think my next step is to contact Magnuson and see how they respond.

 

I agree with MikeGyver, altering the runner length of the lower manifold is only going to alter the torque production out of boost. Once the manifold is pressurized the runner length is not going to contribute to the intake velocity as that will be dictated by the pressure at the intake valve. The longer runner length can contribute to a cfm restriction under pressure but I don't feel you would reach this limit with a 112 head unit. One thing I think opening the lower manifold up will help with is IAT due to the decreased turbulence and air flow direction changes from the intercooler to the runner entrance; very similar to what the TVS guys are doing with the spacers to raise the intercooler up off the floor of the manifold.

 

Cakes, I studied mechanical engineering and did a bunch of research on a single cylinder fuel injected yfz450 engine. While I'm not sure as to how the entire magnacharger kit is layed out, designed, etc, I think I might have some good info for ya.

As I'm sure you know, tons of NA vehicles run intake runners of different lengths to dictate where peak torque occurs. I designed the intake runner length on that single cylinder based on Heimholtz's Reflective Wave theory (I think that's what it was called). We knew we wanted peak torque at X rpm, used a series of equations, and came out with a intake runner length to use in order to achieve greater torque gains at X rpm...and it worked! I'll see if I cant find my report, the reflective wave equation, and the dyno graph.

If I recall correctly, the shorter the runner length, the greater the torque curve will be shifted toward the right, or to higher RPM values. So based on the opening and closing of the intake valves and the waves the action creates will be reflected within the length of the intake runner, and by shortening runner length the ram air effect would occur higher in the rpm range then it would with the longer runners. As to how much power will shift to the right, I'm not sure. Also, you'll want to try and make the runner lengths as close to exactly the same length as possible, so that all intake runners/cylinders are tuned to the same rpm.

I hope you get a chance to do it and show that it works, it would back up all the hard work I put into my degree HA

 

Yes you are right, a short runner will produce torque higher in the rpm range and a longer runner will move it down. (I say torque because HP is mearly a calculation of torque output at an RPM level)

I don't think the issue is so much with the length of the runners although I do believe they inhibit flow at higher rpms. Couple this with the fact that the intercooler exit is so close to the runners themselves, we have a huge CFM restriction. This is the reason most people are having great results with the phenolic spacers. It moves the intercooler away allowing for more flow and also increases the plenum volume those large runners can use.

My thought was to essentially do the milling of the runners to add plenum volume, aid in cfm flow through the intercooler and reduce some low speed torque to better aid traction and hopefully breathe better up top. Again: TPI vs LT1...

 

All very good info. You have to throw it out the door as soon as you start pressurizing the inlet air, though. Wave theory, air velocity, runner length, etc, are as you stated, important for N/A operation. It is all based on the elasticity, and momentum, of air in the intake runner. At the rpm that the length and diameter of the runner are tuned for, the column of air will still be moving from the last intake cycle when the intake valve opens again. Therefore, at the target rpm range, there will be a natural supercharging effect. It is because the piston does not have to draw on the air in the inlet port to get it moving, the air is already moving. Under boost, the air is always pressurized, at all engine rpm.

 

I'll buy that. I figured it couldn't hurt to add something I thought might help. Wouldn't you think that there would still, at least partially, be some wave reflection effect even though the plenum is under pressure?

As you said, plenum size can definitely have an effect on the torque and throttle response. I read a paper where they tested plenum size and how it affected power on one of those 450cc single cylinders, and power and throttle response increased up to the point where the plenum volume was 10x that of the engine displacement...kind of interesting. Again this was naturally aspirated, so idk how boost would complicate all these phenomenons...

 

Definitely out of my league here. I did not know that wave reflection was used to tune anything on the intake side other than sound, as in a Hemholtz resonator. I know that exhaust tuning is all about wave reflection, but I thought that intake tuning is all about air velocity, not the speed of sound. I do know that air (exhaust) velocity and volume has little effect on wave speed in the exhaust system, so yes, wave reflection in a pressurized intake should be the same as in a N/A intake.

 

I received an e-mail back from Simon Gale at Magnuson. I sent him the same post that was put on here and here is his response:

"In theory, your thoughts sound correct. I don’t have any numbers I can give you, as I have not done any back to back testing of a manifold with runners versus one without on a truck. You are right that if you were to mill out the runners from the manifold, you would accomplish two things. One would be a drop in torque since runner length will be reduced. The other would be an increase in HP, as the plenum size will now be larger (you are also right that we milled the runners out on the GTO system to drop the overall height of the system).

We do have a separate manifold tub for the GTO models, but simply switching to this part, you would have to modify other parts of the system. You could use your current part and modify it yourself, then you wouldn’t have to change anything else on the system."

I was thinking that if I did go through with this, it would be a great opportunity to also build and install a much larger intercooler that could run the entire length of the supercharger base. Because of the height increase, it would also enlarge the plenum area.

 

I'm glad you got some confirmation from him.

As I thought about it more, it wouldn't matter if the engine was NA or boosted to still have the reflective wave theory applied. Im having trouble explaining it well, but in each situation (NA or boosted) there will still be vacuum with respect to whatever the plenum pressure is, atmospheric or boosted. So Im pretty sure a ram effect would occur in a boosted engine in the same manner it would in a NA engine, however a boosted engine certainly complicates the matter a heck of a lot lol.

MikeGyver, volume doesn't have much to do with wave speed, but the pressure sure does. As pressure increases, wave speed increases as well. I'd have to look at some equations to determine if the relationship is exponential, linear, etc but with a pressurized volume or air the wave speed would always be changing with respect to the amount of boost at a given instant. Crazy STUFF HA

CAKES, keep us informed, I want to see how this turns out. I love this stuff, just have to figure a way out so that I can do it for a living Not much need for this knowledge in the Marine Corps lol