Yellow Bullet Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
I searched and found a thread in the turbo section that talked about this a little, but not quite enough.

I'm looking at putting a P1SC kit on my '98 Ram V10 (8.0L). I'm just going with the 8psi kit to help with towing. Exhaust is a no-brainer but on the intake side it turns out the V10 uses the same TB as a 5.2.

What confuses me is the TBs are flowed using vaccuum, not boost. If the procharger puts out 1200 cfm max, which of these TB's would you guys suggest? A little smaller to retain velocity or bigger to allow max air through there? :smt102 These are my options:

980cfm
1050cfm
1100cfm

I've never messed with forced induction before, so your help is appreciated. Thanks!
 

·
Registered
Joined
·
48,027 Posts
On our site, accufabracing.com, in the Tech Section, I have listed our TB's and the CFM numbers. We flow our TB's on our flow bench just like they flow carburetors, at 28-inches of water. The numbers shown are "naturally aspirated" numbers. With forced induction (blower or turbo) the numbers can be two to sometimes three times as much as shown for N/A. One other thing. CFM numbers for TB's are not all the same for a given TB size. For instance, our 75MM TB will outflow other companies 75MM TB, etc. Air entry in front of the throttle plate area and air seperation over and under the throttle plate makes a huge difference in CFM between one brand or the other.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #3 ·
Thanks for the info George - much appreciated. I read through the tech pages and what I read makes sense, but I don't think I'm any closer to an answer. The truck V10 uses a 2V throttle body. I've found a couple vendors that make direct replacements with the flow numbers that I've listed.

If the stock motor makes 305/450 hp/tq and my +8psi result is about 450/620 hp/tq, and the P1SC says it flows 1200 cfm, how many cfm would you recommend the TB flow?

Thanks again!
 

·
Registered
Joined
·
48,027 Posts
Thanks for the info George - much appreciated. I read through the tech pages and what I read makes sense, but I don't think I'm any closer to an answer. The truck V10 uses a 2V throttle body. I've found a couple vendors that make direct replacements with the flow numbers that I've listed.

If the stock motor makes 305/450 hp/tq and my +8psi result is about 450/620 hp/tq, and the P1SC says it flows 1200 cfm, how many cfm would you recommend the TB flow?

Thanks again!
Regardless of the maximum CFM listed for the supercharger, the engine will only be able to use what it can use. The question is, how much CFM can your engine pump out? In a naturally aspirated mode (technically about 15 PSI at sea level), there is a common "ball park" formula for this. Displacement (in cubic inches) X RPM divided by a constant, 3456. For instance, a 400" engine at 5000 RPM can only "pump" 578 CFM, naturally aspirated. I'm sure that this formula is not right for a supercharged or turbocharged engine but it does give you the idea. Let's say that your engine is only capable of moving 578 CFM through it, the 1200 CFM blower will just raise the back pressure onto itself. You will see this on your boost gage as an "increase in boost" but in reality, all it is is an increase in back pressure. Remember, boost is a function of PSI (air that is NOT getting past the closed intake valve) and CFM is a function of volume. Pressure and volume are not the same thing. An illustration of this is a supercharged or turbocharged engine with stock heads that is showing 10# of boost on the gauge. Now the owner installs some good heads with bigger ports and valves, and the boost goes down to maybe 7# but the volume (CFM) goes up. In this situation, the engine makes more HP with less boost (which is really less back pressure). Engine HP is more of a function of volume than boost.

To get back to your specific application, you will probably get enough increase in volume through your OEM throttle body with the forced induction and not need to change it. I think that it will flow double what it would flow naturally aspirated, whatever that is.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #5 ·
Awesome - thanks George. I'm a meteorologist and I deal with airflow concepts all day, so the pressure -vs- volume concept you're talking about makes perfect sense. The drop in back pressure that you described is exactly what concerned me when I started looking into this TB thing.

Thanks for your time!

Carter
 
1 - 5 of 5 Posts
Top