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Discussion Starter · #1 ·
I was wondering how much of a difference it would make to have a 9 psi AED kit comparing to a 6 psi AED kit. I am very close to ordering the standard 6 psi kit, BUT COULD have the extra cash for the 9 psi kit within a month if it is at all worth it...I mean it IS an extra $700.l

Any numbers?
 

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Discussion Starter · #2 ·
SORRY...didn't read post below:rolleyes:
 

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I'm not going into all the reasons....

Majik said:
I was wondering how much of a difference it would make to have a 9 psi AED kit comparing to a 6 psi AED kit. I am very close to ordering the standard 6 psi kit, BUT COULD have the extra cash for the 9 psi kit within a month if it is at all worth it...I mean it IS an extra $700.l

Any numbers?
why you might or might not go to the 8# pulley at
some point. If you stick with your current mods,
you MIGHT be better off staying with the 6# pulley
that comes with the 'Bird kit. Later on, you can
always switch to the smaller pulley and it won't
cost you an additional $700.00 for the pulley either.
 

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Yeah...but the AED is already cooled and that's what we're talking about.

Boost does not equal power......increase VE and boost goes down.
 

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AED Specialist
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Seabass is correct...

You don't want boost, since when you compress air, you heat it. You want lots of cfm, little to no boost and or course no heat.

Getting that can be tricky. Also you guys talk about boost pressure as being relevant to pulley size. It's not. EECDOC ran the same smaller pulley as I did. He saw 8 psi of boost and I saw 9.5 psi.

The AED kit is intercooled and it does drop the blower discharge temps by a good number, but that doesn't mean it can't hurt the engine even with the stock pulley.

A-Train
 

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Just to beat this thread to death....

A-Train said:
You don't want boost, since when you compress air, you heat it. You want lots of cfm, little to no boost and or course no heat.

A-Train
of course Seabass and A-Train are correct and they always
make this point when this discussion surfaces. To back them
up, my son has a GTP and belongs to http://www.clubgp.com/
and, as you might imagine, many of their members are vey
serious about making intelligent modifications.

As our two senior members have often emphasized - air flow
is the key - not "boost" or pressure. The GTP boys understand
efficiency and are very pleased when read (what you read on
your boost gauge) boost drops down towards zero. As A-Train
just pointed out - when you read boost, you're really reading
a "waste" factor - as the pressure you're reading is going
unused and also causing additional unwanted heat.

A well balanced SC/Engine combo will have a "read" boost
approaching zero. So all those "old fashioned" approaches
used on NA and carbureted engines (back when) to increase
VE still are valid under an SC application (ie head work,
cams, runner size and length...just to name a few).

Also remember that as power and pressure rise (even with
"perfect" efficiency) so does heat and pressure so, as A-Train
has often pointed out, hyperpathetic or forged...well tuned
or not...do the chances of engine failure....though obviously
less so the better built and tuned your engine is (most of the
time).
 

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Mushroom Stamp Layer
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Tony...I just want to clarify where you said <i>"Also you guys talk about boost pressure as being relevant to pulley size"</i> . It is relavent to pully size when you talk about smaller pully=more boost (until the point of things breaking). Now yes the whole "I'm running the 12# pully" means nothing to me as you maybe running 17# or 8# of boost with that pully.

Increasing volumetric effciency (VE) helps bring your boost number down. Say your running 10psi....you port and polish your heads and intake...now you may only be running 7-8psi of boost....are you making less power since your running less boost...ofcourse not...your making more power more effciently.

Heat is bad
 

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AED Specialist
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Only two things apply...

Cylinder pressure and blower speed are effected by pulley diameter changes. Boost will in theory go up when you go with a smaller pulley, but it doesn't translate to more power. More boost does not equal more power, not on every application.

Open the inlet and boost goes up. Why? Did the pulley diameter change? No. Did the blower speed increase? No.

A swap to a smaller pulley on "your" application with no other changes should yield a higher boost number on the guage. However, if you changed exhaust (to something less restrictive), used a smaller diameter inlet tube and a smaller throttle body, boost would stay the same as before. Again, boost is just a measurement of how much restriction you have (or flowing I should say) in your inlet.

On my car, I made 285 RWHP with the stock inlet tube. When I swapped to a 3" OD tube with less bends, boost pressure shot up, but the RWHP figure went to 325.

My point is, these posts refer to the AED kit as a 6 pound and a 9 pound kit. Well if you have PI or SVO heads, a free flowing exhaust system, and the AED kit with the stock pulley, you wouldn't even see 6-psi. Maybe 5 psi if you were lucky. Did you make more power than a guy seeing 6-psi with stock heads and a stock exhaust, most likely YES.

Seabass is correct, you want the system to be more efficient. VE or volumetric efficiency is nothing more than load or theoretic airflow divided by actual airflow. As VE goes up, power does too.

A-Train



The left side is a hypereutectic piston from my old 4.6L engine. The right side is a forged 5.0L piston. Notice the hole in the piston where the ring land is supposed to be. Boost is bad.
 

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Just to add another case in point:

Factory heads, cam...12psi boost on the guage.

New AL heads (2.02) and nitrous/blower cam...9psi, same pulley, same everything. Dropping boost is not a bad thing!

What would make me happy would be to see 9psi with a smaller pulley (after opening up the exhaust further)...that = more flow = more power to be made.

After all these real world examples and technical explainations...maybe people will start to believe it. More is not better :(
 
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