Build Thread Enola- Finishing touches

a91what said:

I am using a mini cooper bypass opened when under vacuum. 1"hg will open the bypass fully. It is a 1 3/4" pipe.

I believe that the purpose of the bypass is to prevent SC surge. Not feed the engine air at idle/part throttle. The SC is still spinning, forcing air through the system. The bypass creates an equal pressure on both sides of the SC, quieting it's operation and reducing heat. I believe that all the piping is creating dry flow drag reducing the air velocity thus requiring the engine to Rev higher to stay running. But as of yet this is all theory.

My previous setup utilized 2 TB worked well but was ugly as sin. I may revert back too the dual TB setup to elevate this issue.

For the record the TB I am using is a 75mm piece. The intake was ported to match.

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skyline247 said:

Well, after thinking about it a little more and seeing the recent responses, I agree that the extra length between the supercharger and intake manifold is the problem at lower rpm. In a simplistic sense, the flow rate into the engine is a function of delta pressure between the plenum and the cylinder (let's say delta p = positive intake pressure - vacuum). At higher rpm, your vacuum is higher, as well as the pressure of the incoming air from the supercharger spinning faster. I'm going to go with my initial theory. With the throttle body right at the intake manifold, the supercharger is drawing in air at atmospheric pressure with the flow rate dictated by the pipe area. At 800 rpm in this setup, the supercharger is pressurizing the flow enough to produce the required delta p at the intake manifold to sustain the engine. With the throttle body in front of the supercharger in the closed position, you are creating a big enough drop in flow and pressure that the pressure rise across the supercharger at 800 rpm is not enough to cover the extra loss from the piping and the required delta pressure at the manifold. In other words, both the lower vacuum and the lower pressure out of the supercharger are effectively reducing the delta p. You can't do anything about the vacuum but you can impact the intake pressure. The three options I see are:

1. Figure out a way to make the throttle body more open at 800 rpm than it normally would be (increase flow, reduce pressure drop across throttle body).

2. Figure out a way to draw some outside air into the intake behind the throttle body (if you already have a method for this, I apologize for missing it).

3. Two throttle body setup.

All of these let the supercharger add work to more flow at a higher pressure which would result in more pressure going into your intake manifold.

In the conventional setups you reference, the shorter distance between the supercharger and intake manifold make this pressure loss minimal compared to what you have. Its not so much the volume as the length. The extra surface and turns hurt your total pressure and dynamic head (velocity). In the usual setups, I believe they actually favor the throttle body upstream of the supercharger so that it isn't pounding the TB with pressurized air.

I may have repeated some of my initial post, but hopefully this clarifies what I think is happening. I may be wrong or I may be right. I may be oversimplifying it but it's the only way I can rationalize the results in my head right now.

Either way, I have to commend you for the work you've done so far. It really does look good. I understand the frustration but you are going to have a pretty cool and unique setup working soon.

...I will stop writing such long posts now...

Sent from my Nexus 6 using Tapatalk

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a91what said:

Oh and I am drawing in a it behind the throttle body... iac feeds plenum directly.

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