Red Rider

Thanks Smitty. I'll start at 93-94 and increase if necessary. I sure don't want any pinging, so if it were to happen even with the higher octane then i'll do the disconnect. Then there's always Scalberts IC

Red Rider

Keep us posted on the IC Scalbert, when will you have a photo of the finished product ?

Seattle Cl-S

Should I be disconnecting my actuator then??? We have 92 octane up here.

I really need to get back to the track. My 14.1@102 is shameful!

Seattle Cl-S

So I hooked up the boost gauge tonight finally. I know nothing about vacuum/boost so maybe someone can chime in.

When I'm in PARK, the gauge reads about -20psi in the vacuum side. During normal driving (static throttle input) I also show vacuum (about -10psi). At WOT, the gauge jumps to around 5-6psi on the boost side (I'm running the HBP). Does this sound normal? I would think that I should always get positive boost bouncing between 0 and 5-6psi.

Allout

Sounds like a good reason to get some lightweight forged wheels

Allout

Tom,

I'm not an expert in this but it sounds normal. You expect the intake manifold to have vacuum when the butterfly on the throttlebody is closed. Pistons on the down stroke are sucking in air and fuel. As you open the butterfly, it transitions from vacuum in the intake manifold to boost as the blower starts working. If you were to take the reading on the other side of the butterfly(on the side of the blower), you would see 0-6psi boost

Seattle Cl-S

Maybe I should meet Mattg at the track and swap wheels with him for a run or two...

Seattle Cl-S

That makes sense after reading your post. You're such a smart one.

scalbert

Probably next week. That is if it is ready before I head to Miami for a Conference. Otherwise it will be the following week just prior to shipping the system to Chemmech.

scalbert

Yes and no. You are correct about the vacuum and boost but not the locations. The blower is after the throttle body. However, there is an intergral bypass valve in it which opens under vacuum to allow both the inlet and outlet to be at the same level. But this still doesn't mean there would be boost. Since the blower is after the TB it can turn all it wants and it won't make any boost since the supply is restricted. The bypass just smooths operation and increases fuel economy by reducing the load during idle or cruise conditions.

scalbert

You are right where you should be.

The idea is not to always be in boost, your fuel economy and engine life would go down the toilet. You want vacuum, it is your friend.

Having 20 - 21 inHg vacuum is perfect when at idle. You will vary vacuum levels based on conditions; go down a hill without your foot on the gas with the engine braking and you will see upwards of 25 - 28 inHg (almost an absolute vacuum). This is the way it should be to keep fuel economy and those accessories, which depend on vacuum, happy.

Now when you dip into the throttle the vacuum decreases and gets close to zero. Dip into the throttle a bit more and you cross zero and start getting into boost. If you put the same gauge on an NA car you would see a similar decrease of vacuum but instead of going into boost it would stop just shy of or at zero. Back to the SC car, apply even more throttle and boost goes up even more all the way to WOT and maximum boost for that given blower size to engine size and engine speed to blower speed ratios.

What limits the boost at part throttle is the throttle it’s self. It restricts the amount of air the blower can pull in and push into the engine. A larger throttle would most likely give more boost per the same throttle position and potentially more at WOT. That means that a dirty filter can also impact boost levels as it is another restriction in the path, but probably not measurable though (just an illustration).

So to sum up, 20 inHg vacuum at idle and 5 - 6 PSI boost at WOT is perfect for your set up. Also, play with the throttle some and watch the boost. You will see you can control the level perfectly with throttle. That is one of the finer things about this style blower, the very linear ingress into boost and power based on throttle position.

Seattle Cl-S

Sorry Allout, but Scalbert is even smarter.

Allout

I would have to agree. I'm no expert and would defer to Scalbert any day of the week. I just learned a ton through this exchange myself.