PDA

View Full Version : Intake and exhaust effect on PSI



lee1rbc
08-13-2009, 07:54 PM
I was wondering what effect freeing restrictions on intake and exhaust have on PSI boost.

I am assuming if I remove the stock filter, MAF and TB and install a Cone filter, 73mm MAF and 70mm tb, that my psi would drop.

Also I am assuming the same can be said with exhaust. Just wondering what experiance You all have with this.

sinhumane
08-13-2009, 08:02 PM
here we go again.......

psi is completely irrelevant to how much power your engine is making....

wour blower is positive displacement, meaning it doesnt compress air, it just moves it at a faster rate than the engine can consume, resulting in a positively read pressure, not vaccuum.... your psi reading (as inaccurate as it is) is just a number, telling you what your manifold pressure is...

the drop you see in your psi level (again, in the manifold) is related to your engine being able to consume and expel more air because of an opened up exhaust and intake.

stacking boost in your manifold will give you gains, no doubt, as the boost changes your flow characteristics, resulting in more air being essentially forced into the cylinders.... but the gains are substaintial when your engine can actually use this air with much less effort, enabled by a freer exhaust, ported heads and intake, higher lift/longer duration cam, etc...

this should be a sticky. :)

lee1rbc
08-13-2009, 08:17 PM
soooo... I guess my assumption is correct? In other words by freeing up resistance I allow the supercharger to run more free, resulting in more horsepower and lower psi? thanks

Young-SC-Owner
08-13-2009, 08:22 PM
soooo... I guess my assumption is correct? In other words by freeing up resistance I allow the supercharger to run more free, resulting in more horsepower and lower psi? thanks

As an answer to your question, your correct.


He just sidetracked from the real question:rolleyes:

sinhumane
08-13-2009, 08:24 PM
i explained the principle... so he understands, sidetracking or not. no need for commentary. :rolleyes:

thanks for putting it in gorilla terms for him. :o

lee1rbc
08-13-2009, 08:30 PM
LOL. :D Who You calling a gorilla :D

lee1rbc
08-13-2009, 08:36 PM
my goal is to install a full exhaust and intake along with upgrading my IC and then bring boost back up to maybe 10 to 11psi. I live in Florida so last thing I want to do is push this supercharger.

sinhumane
08-13-2009, 08:49 PM
the supercharger is not really what you are pushing... cool that charge air down with a double or front mount intercooler, port the blower. that will reduce air charge temps, allowing you to run more overdrive safely without the computer pulling timing on you in the topend.

Silenced
08-14-2009, 12:35 AM
I was wondering what effect freeing restrictions on intake and exhaust have on PSI boost.

I am assuming if I remove the stock filter, MAF and TB and install a Cone filter, 73mm MAF and 70mm tb, that my psi would drop.

Wrong.

-2TC

David Neibert
08-14-2009, 11:52 AM
Improving flow prior to the supercharger inlet will generally increase boost, because more air will enter the blower. Improvements to the intercooler can go either way...better flow would result in less pressure drop (increase boost), but better cooling of the air would result in lower boost (hot air expands).

Improvements to cylinder head flow from changing the cam, reworking the heads or improving the exhaust flow will usually result in lower boost.

David

lee1rbc
08-14-2009, 08:59 PM
Improving flow prior to the supercharger inlet will generally increase boost, because more air will enter the blower. Improvements to the intercooler can go either way...better flow would result in less pressure drop (increase boost), but better cooling of the air would result in lower boost (hot air expands).

Improvements to cylinder head flow from changing the cam, reworking the heads or improving the exhaust flow will usually result in lower boost.

David

Interesting, so let me get this straight:rolleyes:

Basically the way I am thinking about this is if I took the blower OFF the car and used it like a leaf blower, there would be No psi because the blower would be allowed to just blow the air out into the open. If I restricted the intake side there would just be less air going thru the blower creating vacuum. But if I restrict the outlet it would start to create pressure.

David Neibert
08-16-2009, 08:46 PM
Interesting, so let me get this straight:rolleyes:

Basically the way I am thinking about this is if I took the blower OFF the car and used it like a leaf blower, there would be No psi because the blower would be allowed to just blow the air out into the open. If I restricted the intake side there would just be less air going thru the blower creating vacuum. But if I restrict the outlet it would start to create pressure.


The examples your using don't make any sense :confused:

lee1rbc
08-16-2009, 09:16 PM
The examples your using don't make any sense :confused:

I have that gift.:D

From what I hear You guys saying is that if there were no restrictions on the blower there in theory would be no PSI. PSI reading is basically because the motor can't keep up with the amount of air being pushed out of the blower.

That is why improving exhaust, cam, head work can lower PSI - because the motor is able to handle more air.

At the same time if I remove restrictions before the blower (MAF, filter,tb) psi #s can rise because the blower can know intake more air forcing more air to be pushed thru the motor.

David Neibert
08-16-2009, 09:27 PM
I have that gift.:D

From what I hear You guys saying is that if there were no restrictions on the blower there in theory would be no PSI. PSI reading is basically because the motor can't keep up with the amount of air being pushed out of the blower.

That is why improving exhaust, cam, head work can lower PSI - because the motor is able to handle more air.

At the same time if I remove restrictions before the blower (MAF, filter,tb) psi #s can rise because the blower can know intake more air forcing more air to be pushed thru the motor.


Yes...and it makes sense this time.

lee1rbc
08-16-2009, 09:35 PM
Yes...and it makes sense this time.

Thanks, just want to try and get an understanding of this car before I go spending money on it.

Silenced
08-17-2009, 01:46 PM
I have that gift.:D

From what I hear You guys saying is that if there were no restrictions on the blower there in theory would be no PSI. PSI reading is basically because the motor can't keep up with the amount of air being pushed out of the blower.

That is why improving exhaust, cam, head work can lower PSI - because the motor is able to handle more air.

At the same time if I remove restrictions before the blower (MAF, filter,tb) psi #s can rise because the blower can know intake more air forcing more air to be pushed thru the motor.

yay :D

Now teach the others :P

lee1rbc
09-14-2009, 12:15 PM
:rolleyes: OK, this is what I have done and the results. I tuned the car (plugs,wires).My max psi was 12psi.

2. I install a K&N cone filter with 73mm MAF. I then did the leak test and fixed 3 leaks. My result was a peak of 13psi.

3. I have just finished removing all exhaust from the manifold back and replaced it with a true dual 2 1/4 mendrel bent exhaust. No cats, two resonators into two flowmaster. Now my result is a max of 11psi.

I also have installed an IC fan and have the radiator fan on all the time.

Next step is a 5% pulley and then a dyno run.

thunderkid84
09-14-2009, 01:03 PM
:rolleyes: OK, this is what I have done and the results. I tuned the car (plugs,wires).My max psi was 12psi.

2. I install a K&N cone filter with 73mm MAF. I then did the leak test and fixed 3 leaks. My result was a peak of 13psi.

3. I have just finished removing all exhaust from the manifold back and replaced it with a true dual 2 1/4 mendrel bent exhaust. No cats, two resonators into two flowmaster. Now my result is a max of 11psi.

I also have installed an IC fan and have the radiator fan on all the time.

Next step is a 5% pulley and then a dyno run.

sounds good. after that dyno run you should look at putting a 180 t-stat in and then getting a tune for it as well as lowering the temp at which the radiator fan comes on.

personally, im not a big fan of re-wiring the rad fan to be on all the time.