[ZmanM3]

Originally Posted by Mike@PowerHouse

Just so you guys know I am on here to help spread tech to you guys and maybe get some of you to look at things from a different perspective, this perspective will allow you to have a better understanding of how and why things work like they do.

Here is a link to a post I made in regards to RWHP numbers, hopefully you can understand that they are simply a gauge,
http://s197forum.com/forum/showpost....0&postcount=30

Boost in PSI is often times wrongly viewed. It is really Intake manifold pressure vs. atmospheric pressure, or manifold pressure delta-p. Because we seldomly know the actual atmospheric pressure we simply refer to manifold pressure as boost.
Superchargers are driven by the crankshaft, which means that the supercharger will always drive at a specific ratio when compared to the crank. This ratio is what determines supercharger speed, this speed is what dictates how much air (CFM) is drawn into and processed by the supercharger. This CFM or volume of air being pumped out of the supercharger creates "boost" or manifold pressure delta-p.
This "boost" is actually the engines reluctancy to accept a given volume of air. This can be realized in a case where someone may add ported heads, cam and stroker kit to a supercharged angine, if the pullies remained unchanged you will actually see the "boost" drop. Is it because the supercharger is delivering less air?, no. It is simply because the engine is more accepting to the volume of air being delivered by the supercharger, remember the blower speed and volume are unchanged because our drive ratio is the same as it were before our stroker/head/cam/ swap.
Some people refer to pullies as "14psi pulley", not the case, the pulley is a given diameter, not a given pressure.


Now if we have a day when the bar. press is low we will still see the same "Boost" (because our pressure delta-p is the same) but the actually the air delivered to the motor is less than it would be on a nice, clear, high pressure day. That is why cars run better in nice weather. This is also why there are weather stations and correction factors built into dyno's. These correction factors are what HELP stabalize the dyno results from day to day.

There are tons of reasons why boost will vary from car to car, here are just a couple,

1st, sensor or gauge calibration.
2nd, Atmospheric pressure.
i altitude
ii barometric pressure (weather)
3rd, Engine airflow

I say this because I have seen threads where members will literally butt heads over 1-2psi and 5-7 rwhp.

With all the above in mind lets say The manufacturer advertises 7 psi, and customer "A" nets only 6.25psi, was he wronged? Would it find its way to a forum and state that he was robbed of .75 psi, possibly. If it is under estimated, then the results are only a bonus. Kinda like finding a $10 bill in the dryer that you had no idea you lost.

With all the above variables in mind, you have to understand that this stuff needs to be averaged and underestimated.

Originally Posted by Mike@PowerHouse

This was brought to my attention from another board member and I just wanted to throw it up here.



There is one statement I think needs to be clarified slightly:

"Now if we have a day when the bar. press is low we will still see the same "Boost" (because our pressure delta-p is the same) but the actually the air delivered to the motor is less than it would be on a nice, clear, high pressure day."

This is actually incorrect. The blower (or turbo) doesn't product a Delta-P, it produces a pressure RATIO due to compression (either by actual compression inside the compressor or due to the act of positively displacing air into a confined and limited space).

If your blower is producing 14psi of boost on a day when the air pressure is also 14psi, then your pressure ratio is 2:1 and you actually have 28psi absolute pressure in the intake manifold and 14psi absolute pressure on the outside.

Now, if you take that exact same blower and run it WAY high up where the outside air pressure is only 7psi, then your blower would still make that same 2:1 pressure ratio and you would see 14psi absolute on the outlet of the blower, assuming you could keep everything else exactly the same.

A little mind exercise also shows how these things can't be Delta-p devices: If you ran an engine with that produced 14psi of boost, you should be able to run at normally aspirated power levels in space... But as a pressure ratio device, you know that two times zero is still zero and that engine quit running long before it got up to space.


Again thanks for pointing that out

Originally Posted by JimIII@JDM

Mickey,

Yes it is a BOLD statement but i stand behind it. What your seeing for HP numbers on the internet is a base kit from Edelbrock. Besides my car which has a built 298 motor and our custom tuning. Now your car has a stock motor but it too has an aftermarket tune. Not the Base Saleen tune like in a 475 kit that only makes 395-400 RWHP on Twin Screw with 7 psi boost. If your only seeing 6 psi boost its from your port work. Boost is a measure of restriciton. If you ported the blower and created better air flow you get less restriction!!!! Hence your higher HP numbers on less boost! So your old technology Saleen blower is going to make more power than the New technology Edelbrock blower. Rob Simons designed the E Force and is the same guy who designed the Saleen Series VI. He took all the knowledge he learned building the Saleen and one up'd himself with the E-Force kit! The TVS technology gives you more midrange and low end power than a huge Twinscrew blower spinning at a slower RPM. The smaller TVS blower car is going to have more feeling for a STREET car.


The Average boost is what we are seeing for the most part of the run, on the Edelbrock we are seeing the boost climb towards the end of the run.

The Edelbrock is not the exception to this, ive seen this on every Roush TVS blower we have done here too.

Also boost can be influenced by variable cams. If you retard the cams the boost will ramp up.

It is the characteristics of the TVS design that i feel is what builds the peak RPM boost. The harder you spin it RPM wise the more boost it makes.


JimIII@JDM

Thanks for the great info guys!