Physics and Math heads help please

[Lazy Racer]

I understand a blower will normally increase power between 1.5 and 1.75hp per ci at 5psi boost. So by example, if a blower @ 5psi adds 1.5hp per ci to a 281, you can expect 421hp (281 x 1.5). The eforce blower claims to improve performance of a 281 @ 5psi to 466 which using this equates to 1.65hp per ci (466/281).

So, if you install a stroker crank/rods to take ci to 322, it seems logical to say that you could expect the first blower to give you 483hp (322*1.5) and, then, 322*1.65 equalling 531hp for the Edelbrock?

Then, how can I calculate the above scenarios to account for an increase in boost to say 8 then 12, 15 PSI?

Or is it simply a case of trawling manufacturrers published dyno charts...this is laborious, it'd be nice if I could have in my mind 1.5 - 1.75 at 5, x @ 8 and Y @ 12 etc, any ideas?

 

[Dex]

i love lamp

 

[Stangtuner]

Well your first equation does not account for variables, such as cfm of the blower ( different sizes of housings) ,volumetric efficiency, atmospheric pressure, or temp.

So everything after that would not necessarily be very accurate.

For instance a Honda 1.6 B16 will make 300whp with 15psi

I guarentee you the same turbo kit on a Hyundai 1.6 will not produce the same results due to Vtec, Heads, Compression, tuning.

 

[Lazy Racer]

Well your first equation does not account for variables, such as cfm of the blower ( different sizes of housings) ,volumetric efficiency, atmospheric pressure, or temp.

So everything after that would not necessarily be very accurate.

For instance a Honda 1.6 B16 will make 300whp with 15psi

I guarentee you the same turbo kit on a Hyundai 1.6 will not produce the same results due to Vtec, Heads, Compression, tuning.

OK, but im not on about different cars, Im on about a stock S197 with a 281, then the same car stroked. I appreciate its not possible to be 100% scientifically correct but its not a bad rule of thumb.

 

[Lazy Racer]

i love lamp

Whats lamp?

 

[Stangtuner]

OK, but im not on about different cars, Im on about a stock S197 with a 281, then the same car stroked. I appreciate its not possible to be 100% scientifically correct but its not a bad rule of thumb.

If all you wanna do it multiply, 1.5 x CID Then yeah it's a good rule of thumb for THAT instance.

Because if you're telling me @ 5psi it's adding 1.5 hp per each cc of 281cc = 421rwhp
then by that SAME equation @ 15psi (5psi x3) it's adding 4.5hp per each cc of 281cc then= 1,263.5hp ??

As you can see, that would not be very accurate.

If it is, THEN SIGN ME UP!

 

[Lazy Racer]

If all you wanna do it multiply, 1.5 x CID Then yeah it's a good rule of thumb for THAT instance.

Because if you're telling me @ 5psi it's adding 1.5 hp per each cc of 281cc = 421rwhp
then by that SAME equation @ 15psi (5psi x3) it's adding 4.5hp per each cc of 281cc then= 1,263.5hp ??

As you can see, that would not be very accurate.

If it is, THEN SIGN ME UP!

Yup, that clearly aint so. I guess you dont know either

 

[94tbird]

If all you wanna do it multiply, 1.5 x CID Then yeah it's a good rule of thumb for THAT instance.

Because if you're telling me @ 5psi it's adding 1.5 hp per each cc of 281cc = 421rwhp
then by that SAME equation @ 15psi (5psi x3) it's adding 4.5hp per each cc of 281cc then= 1,263.5hp ??

As you can see, that would not be very accurate.

If it is, THEN SIGN ME UP!

because the formula is completely wrong/Doesnt completely apply. Logically it may be correct but its not real world conditions. You will never see perfect conditions. As stated above it doesnt factor in cfm of the blower ( different sizes of housings) ,volumetric efficiency, atmospheric pressure, temp, drivetrain losses, accessory drag, how much HP it takes to turn the blower including many more.

One of the largest drawbacks on PD blowers is the Intake side of the blower (Intake manifold feedinbg the blower, TB, Intake tube, Filter) Generally you will not see restrictions till about 10-14psi depending on the blower and its efficiency

for what its work i picked up 28.8rwhp upping my boost from 8 to 10 psi on my 2.4L KB. Lets round it to 30 to make things easier. By that math, it is 15rwhp per psi of boost. Now i dynoed at 470rwhp on 10psi on a the KB tune. 15rwhpx10psi=150rwhp subtract the 150 from 470 and you get 320rwhp. That would mean my car made 320rwhp without the blower Now i did have some other supporting mods like an eH20 pump, aluminum driveshaft, aluminum flywheel ect but those dont equal the difference of aproximately 50rwhp. This is becasue the efficiency range of the blower is in the 5-8psi range. That doesnt mean you wont make more power with a higher boost, but the increases fall off for every lbs of boost you add.

That was on a dynojet. Now had it been on a mustang dyno the numbers would have been lower, but the ratios would have remained true

That is a prime example of why that equation should not be used

It is also a well known fact that most manufacturers post Flywheel HP numbers because they are higher and look more impressive than the RWHP numbers but RWHP is all that matters, second to track times lol

 

[94tbird]

270RWHP Stock

470RWHP @ 10psi

200RWHP Increase

281ci

avg 20RWHP per psi

200RWHP/281ci=0.7117 hp increase per cubic inch

saying 1.5hp per ci is like saying a 150% increase in power. will never happen

 

[Androdz]

and then 1 psi is not the same as 1 psi on another turbine or another s/c set-up.

 

[Lazy Racer]

Interesting stuff, I got the 1.5 psi theory from a Popular HotRodding article a while back, Im trying to see if it holds across other motors out of interest but also as another way of gaining a better understanding of forced induction. As a loose rule, its not a million miles out. The tricky bit as you point out is when you increase boost coz again as you say, you have increased air temps, inlet restrictions etc.

Off thread (maybe a good thing!) At what boost on S197s does the air temp begin to negatively affect power? Ive found mine suffers from heat sink at the track - Could a stroked (302) 3V efficiently handle 15lbs using a Saleen blower? (Assuming all necessary upgrades to fuel etc are done). I suppose the stock cams/heads are fine for this?

 

[94tbird]

Interesting stuff, I got the 1.5 psi theory from a Popular HotRodding article a while back, Im trying to see if it holds across other motors out of interest but also as another way of gaining a better understanding of forced induction. As a loose rule, its not a million miles out. The tricky bit as you point out is when you increase boost coz again as you say, you have increased air temps, inlet restrictions etc.

Off thread (maybe a good thing!) At what boost on S197s does the air temp begin to negatively affect power? Ive found mine suffers from heat sink at the track - Could a stroked (302) 3V efficiently handle 15lbs using a Saleen blower? (Assuming all necessary upgrades to fuel etc are done). I suppose the stock cams/heads are fine for this?

stock heads and cams have been proven to go 9's in the quarter mile. I did change my cams but im guilty as charged when i admit i did it for sound and i dont care if i lost or gained power from it. I will say this for the cams, the car pulls so hard past the 1/8 mile mark, much harder than before.

The problem with heat isnt the size of the motor, its the intercooler, the heat exchanger, the pump, amount of liquid, ect. The saleen's die around 14-15psi mostly because of this, but also due to design. Ther efficiency range is lower because they werent designed to handle high boost. Look at what Techo, all of the saleen guys work there now, is doing with their blower. Much larger displacement, higher efficiency range, better, larger, DUAL core intercooler, ect.

There is a reason why KB went with the H kits, why roush changed to the TVS. Look at the exit port's on each blower . by changing the design of the port, either making it longer or shorter, wider or thinner, you change the power efficiency of the blower.

One of the only major differences between the KB 2.6 and the 2.6H is the exit port. that change makes the 2.6H's efficiency rage 15-20psi vs the 2.6's 5-8

I used to have a pic of the 2.6 and the 2.6H side by side showing the differences. Im going to have to try and locate this.