This is a dumb question, but I have to ask.
I have been reading and building a spreadsheet using the equations in the complete turbocharging guide.
If I start at my peak rpm and target boost PSI, If I reduce my rpm to find my next PR & inlet PPM numbers to plot on a chart.
Do I reduce the boost psi?

 

or do I assume I am going to make peak boost at a low rpm lets say 2600 rpm and the stay at peak boost at 5600 rpm?

 

I guess I need to read more on boost control, maybe that will help me understand how boost PSI relates to rpm.
I think my Holley HP EFI can control boost. that is probably the best route for me to go.
I can read up on their stuff. Unless there is a better way to do it.

 

I'm kinda stuck in a catch 22, I have a lot to learn. Need to ask questions. But the answers might not be strait forward depending on the build.
I was thinking of starting a build thread so we can talk specifics in relation to my setup, but I don't want it to seem like I am expecting yall to do all the work for me.

 

You are right as it will depend on the combo and what you want.

If you are running a smaller exhaust housing to get boost up sooner in rpm, and if your wastegate is sized correctly or at least big enough, then yes, you could see you target max boost psi at a low rpm such as 2,600 and keep it right there through the rpm range.

If the turbo is on the large side for your combo, you won't get target max boost a low rpm and it will more gradually come on as rpm pick up.

If the turbo (exhaust side) is small, but the wastegate is also too small, target max boost will come on quick and low rpm but as rpm increase, the boost will creep higher. This is known as boost creep and happens for other reasons as well.

 

Thanks for the reply, That makes total sense.

When I'm plotting points based on the rpm range I want. (2600-5600@10psi boost)
I can get that range to fall to the right of the surge line on most the turbo maps I am messing with.
But I was thinking ok what if I decide to push the boost to 20psi one day. I plot those points and the lower rpm fall to the left of the surge line.

Its not necessarily a bad thing right?

Its basically just reducing your peak boost rpm rang/window?

Then you just try to set it up so boost builds to the peak boost @ the target rpm that falls on the right side of the surge line?

 

Yes, you dont want to have a situation where you are on the left side of the surge line and I don't even like to flirt over close to it. If you are going from a 10 psi setup to possibly 20 psi, there is a chance you will need a different charger or a bigger exhaust housing to lower drive pressure at lower rpm.

Also, a ported housing turbo tends to have a surge line that is more favorable of lower airflow and higher pressure ratios.

 

The HP system will allow you to build a boost map.
Suggest you spend the time reading the tutorials at Holley.

 

The HP system will allow you to build a boost map.
Suggest you spend the time reading the tutorials at Holley.

 

Will do, I figured that My HP ecm will be the best way to control the boost.
I know I'm just scratching the surface. I just read the boost vs time and I didn't catch on.
I found where someone said they have map control, Going to look for a write up on it. Hopefully that will make more sense to me.

 

Holley's 2 solenoid pressure source set up seems like it may be a bit much for my street cruiser.
Its obviously better, but I guess that is something I just have to decide on.
Crap, this was so much easier as a concept. Oh well time to tighten up the belt a notch.