how much power is lost at 5200ft above sea level

[Bottoz]

I'm ordering the 230... that has the stock 3.35 inch pulley. I'll be changing to a 2.8 soon as I get it.

[RyanD]

[quote="krispy"]
Bottoz,

You are right, I looked at the email Brammo sent, and he gave me the outside and inside size, and
I read it wrong.  The Pulley is a 3.00 (inside).  So I should get a 2.7/2.6, now what do I have to do?

[/quote]

Keep in mind that a smaller pulley with the 8000RPM redline on the 300HP engine may put you close to the RPM limit for the supercharger.  Someone should be able to do that calculation.

Also, an absolute pressure pop-off valve would protect your engine when you go from elevation to sea level.  I'm not sure if such a thing exists though.  I know they make gage pressure pop-off valves for turbo engines.  They also make absolute pressure boost controllers for turbo engines.

[Bottoz]

I thought the Brammo 300 was a 7k redline. Either way, the M62 Recomended Max Continuous Blower Speed = 16,000 rpms. With a 2.8, blower speed is 14,000 rpms at 6,250 rpms.

The Stock ECOTEC does have an ECU controlled bypass valve. Here's some info on that:
The boost bypass system on our superchargers has three parts: the solinoid, the actuator, and the butterfly valve (normally closed). The actuator is a diaphram/piston that has two chambers and a small metal shaft that connects to the buterfly valve. When the ECU triggers boost bypass, it opens a soliniod allowing charged air (in the range on 12+ psi stock to about 18+ with a very small pulley) to fill one of the chambers of the actuator. When this happens the piston in the actuator pulls on the shaft which opens the butterfly valve allowing charged air back into the inlet side of the supercharger instead of forcing that air into the engine.

The ECU uses boost bypass to bleed off some of the boost just before you hit the rev limiter to prevent damage from the engine getting fuel (or spark) cut off at maximum boost. The problem with this is that if you change the pulley, the computer detects that you are hitting the "maximum boost" (near 13 psi) and opens the bypass while you still have a lot of RPM's left to climb.

The idea of boost bypass is that if you allow the computer to open the solinoid, but do not allow the charged air to reach the piston chamber on the actuator, the butterfly (bypass) valve will never open. Many people on this board have this mod done, and it is considered a 'safe' mod, but remember that you are disabling an engine protection feature.

The following statement is true for a stock or near stock setup, but with signifantly smaller pulleys the boost bypass opens earlier:

The boost bypass valve opens up at 6,000rpm and bleeds boost off untill redline. The bypass mod disables it keeping it closed all the way up untill redline. You will see no difference in power under 6,000 rpms if you disable it. They only increase in power comes after 6000 rpms where you will see an additional 10hp gain in peak hp.

[krispy]

Hi Bottoz,

I ordered a 2.8in pulley.  It should be here in a week.  what mods do you plan on running on your atom with the 2.8 in pullet?

[Bottoz]

[quote="krispy"]
Hi Bottoz,

I ordered a 2.8in pulley.  It should be here in a week.  what mods do you plan on running on your atom with the 2.8 in pullet?


[/quote]

I've ordered the 230 aka GM Stage 1. Since I'll be losing 3psi due to altitude, I want to get the performance I paid for. Therefor, I'll be switching to an 2.8 at first... to see where that puts me after some Dyno Runs (Yes Bruce, I said the D word) and 1/4 pulls (OMG, someone driving an Atom in a straight line.. GASP!) If I'm satisfied with the 2.8 I'll leave it there, then swap back to the stock pulley when I do track days at lower altitude (including Atom Fest 07). I'll monitor A/F ratio and injector duty to see if I can go to a 2.6.

I may fab some side panels myself... and may do some fluid changes after engine brake in (Blue Marble Oil, ATE Super Blue brake fluid, GM Synchro Mesh tranny fluid, Redline Water Wetter for the Intercooler.) And possibly a custom removable Roll Bar when required for Time Trial or Wheel to Wheel racing groups.

I'm on a budget. Grass Roots racing. Can't get all carbon fiber this and that, and can't afford the factory 300. So... gotta make due with what I've learned in past vehicles.

Krisy (or any other US Atom 300 owners) - could you hook up a boost guage and let us know how much pressure the blower on the 300 is making?

[Quark]

Botoz, FYI i was just at the Brammo factory and noticed a new prototype design for the bold on roll bar. More of a curve on the top bar. Looks very nice.  Dont know if it is available yet. 

I cant stand the look of the original but would consider the new one. It is still using the same diameter tubing.