Power per psi, non linear, why? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 25 Old 07-09-2012, 01:28 PM Thread Starter
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Power per psi, non linear, why?

Ive noticed that a lot of the power numbers I see for these cars show very non linear figures as far as the power that they produce per psi.

For example:

6 psi 370 rwhp
9 psi 420 rwhp
11 psi 488 rwhp

So from 6 to 9 psi we saw about a 17 rwhp gain per PSI....but when the boost goes from just 8 to 11 psi, we saw a gain of 34 rwhp per psi, DOUBLE what it did before?

Another example:
9 psi: 505 rwhp 463 rwtq
12 psi: 545 / 518 + 40 3 psi 13.5 hp per psi
15 psi: 610 / 577 + 65 3 psi 21.5 hp per psi
18 psi: 691 / 656 + 81 3 psi 27 hp per psi
23 psi: 759 / 716 + 68 5 psi 13.6 hp per psi

So obviously we can see that at 18 psi the turbo seems to make the most hp per psi. That figure quickly drops back when the boost is cranked up to 23 psi.

So my question: Is this all based on the turbos efficiency range or what?

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post #2 of 25 Old 07-09-2012, 01:31 PM
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lots of factors involved

heads...cam specs...motor build...

turbo specs...efficiency of the turbo will fall off in the higher psi depending on the turbo...just as any blown vehicle...the power has it's "sweet" spot for making power where it is most efficient...


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post #3 of 25 Old 07-09-2012, 01:44 PM Thread Starter
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Hmm, interesting, do it could be possible that my ported heads, big cam, edelbrock 4.6 2v needs more boost to get into its "sweet spot" and make good power?


cause it made weak power on 9 psi lol....like the type of #### I would expect if I had stock hci

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post #4 of 25 Old 07-09-2012, 06:27 PM
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Like mentioned, so so many factors for this, every setup is different.

The turbo's compressor map and specs play a big role into power relative to boost depending on its map.

A smaller turbo in a better efficiencey range and pressure ratio (compressor map wise) can easily make more power than a larger turbo thats spinning slower and close to flow surge. But turn them up and the smaller turbo will start to fall back to the bigger turbo.

In my opinion you what the smallest turbo with the best flow and lowest inertia (billet wheel/bb) for your setup while still making the boost and power level you want. This is key, you dont want too small or too big. To do that effectively you need to look at your setups displacement, compression, volumetric efficiencey(heads, cams valve intake, exhuast size, intended rpm, etc) Map that out and then compare it to where you are on your turbo's compressor map.

You also have to keep in mind turbine size and housing a/r too based on overall flow for that power level. Also goals for the car fall into here to, you want a fast spooler on the street or big top end pull for the track. etc.

07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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post #5 of 25 Old 07-09-2012, 06:34 PM
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Here is a basic calculator to help you determine your pressure ratio per boost level on your engine. This will let you plot pr related to flow on the compressor map for your turbo.

Compressor Flow Map Calculator

So just an example, enter 4.6L, 85% volumetric efficiencey which should be close to your setup. 9psi and 6k rpms. On the chart you will see at 9psi you have a pressure ratio of 1.61 and a flow of 46.8 lbs per min at 6k rpms (i will just go to redline and do that but you can plot your pr to flow throughout the rpm range to get the full curve.)

Now i will plot this on a common T70 turbo compressor map to see how your setup does on that turbo.
Yellow is the area of max/idea efficiencey and the red dot is where your max flow and max pressure ratio would be for that turbo.




Now you can play around with different turbo compreesor maps and different boost levels and actually plot your entire curve to see how well that turbo does on your car for your boost level. Where you plot on the map will determine hp since, peak gains will be in the middle of the map. So this turbo on your car would only be around 55-60% efficient which means little less flow little higher iat etc. Get back in the 75% range and you will make more power at the same boost level on your car. BTW the new billet bb turbo's out there have max efficiencey ranges in the 85-90% range vice a cast journla bearing turbo with a max range around 70-75%. Also a billet compressor will flow more air at a lower pressure ratio which means more power.

Anway there some info to have fun with lol

07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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Last edited by lightblade; 07-09-2012 at 07:00 PM.
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post #6 of 25 Old 07-09-2012, 06:43 PM
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On a side note if you have a big cam not setup for a turbo you are likely hurting spool, mid range power and torque, tighter lsa and bigger overlap will bleed off boost and effect performance. You very well could pick up power with stock heads and cams since you may get better volumetric efficiencey, in general turbo's do no like agressive cams or need ported heads. I have seen guys with the wrong cam on a turbo setup on the 3v go back to the stock cam and pick up power throughout the curve.

Here is a pic of one such 3v with a helion turbo setup testing different aftermarket cams, the stock cams made more power everywhere over the higher lift, tighter lsa cams. Not only through out the curve but look at the midrange difference, its huge!

stock cams vs hot rods vs detroit rockers.
Blue is hot rod cams. Red is stock cams. Green is detroit rockers. All at 16 psi.


07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
[email protected],[email protected]

Last edited by lightblade; 07-09-2012 at 06:45 PM.
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post #7 of 25 Old 07-09-2012, 06:47 PM Thread Starter
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Quote:
Originally Posted by lightblade View Post
On a side note if you have a big cam not setup for a turbo you are likely hurting spool, mid range power and torque, tighter lsa and bigger overlap will bleed off boost and effect performance. You very well could pick up power with stock heads and cams since you may get better volumetric efficiencey, in general turbo's do no like agressive cams or need ported heads. I have seen guys with the wrong cam on a turbo setup on the 3v go back to the stock cam and pick up power throughout the curve.

Here is a pic of one such 3v with a helion turbo setup testing different aftermarket cams, the stock cams made more power everywhere over the higher lift, tighter lsa cams. Not only through out the curve but look at the midrange difference, its huge!

stock cams vs hot rods vs detroit rockers.
Blue is hot rod cams. Red is stock cams. Green is detroit rockers. All at 16 psi.


Wow, thats insane.....the stock cams make way more hp and tq than those other cams, everywhere....

maybe my cams are killing power.....jeez
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post #8 of 25 Old 07-09-2012, 07:03 PM Thread Starter
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jeez do.Turbo Cams even out perform stock Cams?
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post #9 of 25 Old 07-09-2012, 07:03 PM
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What are the specs. Compare them to stock or a turbo specific mild stage 1 cam And see where they fall.

Also look above I posted some compressor map info and a calculator for ya to play with.

07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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post #10 of 25 Old 07-09-2012, 07:20 PM Thread Starter
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Quote:
Originally Posted by lightblade View Post
What are the specs. Compare them to stock or a turbo specific mild stage 1 cam And see where they fall.

Also look above I posted some compressor map info and a calculator for ya to play with.
I looked at it but thats gibberish to me + comp doesnt public compressor maps for their turbos

Heres my cam specs:
Cam specs are as follows:
531/531 in/ex 292duration in/ex 114lsa
228/[email protected] 531/531lift 114lsa.


I mean I dont think they look that bad?

but im not sure what to look for here

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post #11 of 25 Old 07-09-2012, 11:59 PM
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No they arent that bad on the cams. What are the specs of the turbo you have.

07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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post #12 of 25 Old 07-10-2012, 09:58 AM Thread Starter
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67mm billet wheel comp turbo .96 a/r Journal bearing

I pmd you
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post #13 of 25 Old 07-10-2012, 12:23 PM
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Surprised there is some actually good info in here. Its been a while since i have seen this


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post #14 of 25 Old 07-10-2012, 01:22 PM Thread Starter
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Lol xomprssor map what's that!
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post #15 of 25 Old 07-10-2012, 02:19 PM Thread Starter
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Quote:
Originally Posted by lightblade View Post
Here is a basic calculator to help you determine your pressure ratio per boost level on your engine. This will let you plot pr related to flow on the compressor map for your turbo.

Compressor Flow Map Calculator

So just an example, enter 4.6L, 85% volumetric efficiencey which should be close to your setup. 9psi and 6k rpms. On the chart you will see at 9psi you have a pressure ratio of 1.61 and a flow of 46.8 lbs per min at 6k rpms (i will just go to redline and do that but you can plot your pr to flow throughout the rpm range to get the full curve.)

Now i will plot this on a common T70 turbo compressor map to see how your setup does on that turbo.
Yellow is the area of max/idea efficiencey and the red dot is where your max flow and max pressure ratio would be for that turbo.




Now you can play around with different turbo compreesor maps and different boost levels and actually plot your entire curve to see how well that turbo does on your car for your boost level. Where you plot on the map will determine hp since, peak gains will be in the middle of the map. So this turbo on your car would only be around 55-60% efficient which means little less flow little higher iat etc. Get back in the 75% range and you will make more power at the same boost level on your car. BTW the new billet bb turbo's out there have max efficiencey ranges in the 85-90% range vice a cast journla bearing turbo with a max range around 70-75%. Also a billet compressor will flow more air at a lower pressure ratio which means more power.

Anway there some info to have fun with lol


Awesome info there man, only problem is how accurate is that without a compressor map?

Would that be comparable to a 67mm billet wheel turbo?

At least on 15 psi it should put me up in the yellow

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post #16 of 25 Old 07-11-2012, 04:23 PM
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The compressor map is different for every turbo, thats just one I grabbed off the internet real quick. So you plot you setups calculated pressure ratio and flow rate on the x/y axis on the compressor map to see where you are throughout the rpm range and boost level your at. It helps to have a dyno of your boost curve to so you know how much boost your making at that rpm to see what your pressure ratio and flow is. I will take the time one day and plot a full line from 0-20psi with rpm to see what it looks like.

Some maps aren't published and are proprietary, especialy on the newer billet wheel designs since that stuff is still hush hush mostly.

The big difference for a billet wheel designed turbo is ir raises the cdm flow range of the turbo through out the rpm range and greatly lowers boost threshold, it also shifts the surge line to left since it flows alot more air per shaft rpm. Also as I mentioned that cast wheel t70only has a max efficiencey of 75% for its size where as a billet wheel of the same size will have a max efficiencey range approaching 90%.

07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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post #17 of 25 Old 07-13-2012, 03:55 AM
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Quote:
Originally Posted by justinschmidt1 View Post
jeez do.Turbo Cams even out perform stock Cams?
Keep in mind the comparison he posted are n/a specific cams vs stockers, not turbo cams vs stockers. Generally an n/a camshaft is just WRONG for a turbo setup, and CAN easily perform worse than a stocker cam setup. Stock cams in most engines are fairly turbo friendly it seems, at least compared to their n/a grind counterparts.
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post #18 of 25 Old 07-13-2012, 11:46 AM Thread Starter
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Ya....kinda pissed I don't have stock Cams in her now.

Wonder if I could slide them in without ripping the motor apart.
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post #19 of 25 Old 07-18-2012, 01:50 PM Thread Starter
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Originally Posted by lightblade View Post
On a side note if you have a big cam not setup for a turbo you are likely hurting spool, mid range power and torque, tighter lsa and bigger overlap will bleed off boost and effect performance. You very well could pick up power with stock heads and cams since you may get better volumetric efficiencey, in general turbo's do no like agressive cams or need ported heads. I have seen guys with the wrong cam on a turbo setup on the 3v go back to the stock cam and pick up power throughout the curve.

Here is a pic of one such 3v with a helion turbo setup testing different aftermarket cams, the stock cams made more power everywhere over the higher lift, tighter lsa cams. Not only through out the curve but look at the midrange difference, its huge!

stock cams vs hot rods vs detroit rockers.
Blue is hot rod cams. Red is stock cams. Green is detroit rockers. All at 16 psi.



Stock cams: 193, 216 @ .050 Duration
.432, .432 lift
The LSA is not listed.

hot rod cams
Intake 221
Exhaust 240
Lobe seperation 110 degrees
Lift .470

Found these specs for the new Brenspeed Detroit rocker blower grind cams.

thumpers
Intake
Lobe lift.450
Duration at 50: 234.00 at 200: 179.00 offset at 50: .4
Advertised duration:273.00
Exhaust
Lobe lift:.450
Duration at 50:239.00 at 200:180.00 Offset at 50:.4
Advertised duration: 282.00
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post #20 of 25 Old 07-18-2012, 01:52 PM Thread Starter
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Seems lik the turbos like the low lift/ low duration stock cams
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post #21 of 25 Old 07-18-2012, 07:28 PM
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Yeap thats the trend it seems for sure. The stock 3v cams have a 117.25 lsa btw.

The higher lift and longer duration in the more agressive na cams shifts peak rpm to the right in an effort to hit higher peak power just before redline, ie centri blower or na setup.

Turbo's like to hit peak boost and torque down low to mid which will pull power through mid range and up top due to its efficiencey over a blower. For this you acutaly want less duration (notabley less on the exhuast size for a turbo specific cam) and a wider lsa, a little mroe lift doesnt hurt up top depending on where your reving to but again you dont need alot of lift with a turbo setup.

From my experience you want to setup a turbo car for low mid rpm range and then let it works its magic from mid to high rpm. Thats how you get that long pulling sensation through the gears and that wide torque/power band , this goes in hand with the lower 3.27-3.31s gear you want for a turbo setup as well. Hence why more agressive cams say you need 4.10s and a stall etc. they are deisgend to shift tq and power higher in the rpm range which you just dont need or want with a turbo, it does it all on its own lol

Btw my cam specs are: 222/235 .490/.480 115.5

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S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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post #22 of 25 Old 07-18-2012, 09:18 PM Thread Starter
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Hmm my cams don't see much crazier than yours? What's your overall duration?

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post #23 of 25 Old 07-19-2012, 10:34 AM
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Those are just the cams I had since it was setup for na before. While yes they arent bad and dont look that different than yours, a change of a degree or 2 of lsa or .01-.02 in lift is a big difference. Thats why my tq suffers, if i had to do it over again I would have left the stock cams in. And still if I ever need to go into the heads again, stock cams will be going back in for sure. I am able to overcome the cam more due to vct, without that my numbers would be suffering even more.

07 Grabber Orange GT Prem/Vert/6060/3.55
S&H Twin turbo kit, 6262 oil-less Comp turbos
9:1 compression 281, turbo cams, e85
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Last edited by lightblade; 07-19-2012 at 10:37 AM.
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post #24 of 25 Old 07-19-2012, 01:00 PM Thread Starter
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Quote:
Originally Posted by lightblade View Post
Those are just the cams I had since it was setup for na before. While yes they arent bad and dont look that different than yours, a change of a degree or 2 of lsa or .01-.02 in lift is a big difference. Thats why my tq suffers, if i had to do it over again I would have left the stock cams in. And still if I ever need to go into the heads again, stock cams will be going back in for sure. I am able to overcome the cam more due to vct, without that my numbers would be suffering even more.

Yea, so you think the stock cams are the way to go?

My only other idea was those recession buster cams....they look like this.
2VRB1 are recommended for NA PI and turbo PI head 2V engines.
220/219 duration at 050
500/500 lift at the valve
114LSA

For comparison here is stock PI cam
STOCK PI CAMS

200/209 duration [email protected] .05
505/531 lift

I thought the LSA was 115?

Basically the recession bustes have a little more duration, less lift, and I guess the lsa is 114 instead of 115?

IDK, im kinda thinking the stock cams will give me what I want.

Realistically I could probably just rev my setup out to 6500 rpms and have a well performing car but I would really like the shift the power curve to the left, especially with the auto, these 4r70w dont like being shifted above 6500 from what ive read.
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post #25 of 25 Old 07-19-2012, 09:51 PM
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I almost bought an 02 GT last year that had HP Twin 57', 302 stroker, the lowest/least ported MMR heads, STOCK PI CAMS, Bullitt Intake, and it made 600 rwhp on 14 psi. Looked like the stock cams did well, and that was a selling point for me at the time, although Im sure a nice pair of specific ground turbo cams would do wonders as well. Just not blower cams, they seem to suck with the turbo 2v's.
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