At least one piece missing from the boost calculator which may be effecting the real world results is the lack of a temperature variable. Pressure is a function of temperature and volume. Maybe this is designed for boost where the temperature is absolute zero (-459 deg F) - how an egine might run at that temperature is something else entirely. I wish I understood the formula better - at least the calculator came with the disclaimer that it would "determine the resulting maximum boost this combination will produce on your engine" rather than produce the actual boost experienced. If someone can explain the formula, maybe we can tweak it to produce real world results.

 

Some thoughts on the question for the enquiring mind posed by Ken - and btw thanx for beginning such a fun thread:

The question raised here is exactly why I went the additional step and calculated blower rpms as an indication of boost generated. I assumed that the L community has correctly rated their pullies based on the boost increase observed. My results, confirm the point Ken is making but are not as optimistic. I am willing to admit that my numbers are wrong.

What I did was develop the ratio (lower/upper) and multiple the resulting ratio by engine speed to determine blower rpm. I have made no measurements of the pully sizes but have instead used the data presented by Ken above.

In stock form the with 7.4 lowers and 2.93 and 3.25, the L and HD turn the blower at 13133 and 11840 respectively (using 5200 as the engine rpm). Adding a 2lb L lower at 8 inches (from Ken's measurements above) the blower speed increases to 14198 and 12800. A 4 lb L lower at 8.5 inches provides 15085 and 13600. A 5 lb L lower at 8.75 gives 15529 and 14000. A 6 lb L lower at 9 turns the blower at 15973 and 14400.

Matching up the blower rpms as an indication of boost generated, the 6 lb L lower on a HD falls somewhere between the L 2 and 4 lbers although closer to a 2 (HD with an L 6 is 14400 and an L with a 2 is 14200 and 15100 with a 4). This indicates that the HD with a 6 lber should be putting out slightly more boost than the L with a 2 - about 10 lbs of boost or +4 lbs (this is where my numbers and Ken's disagree as he sees the closer to +5 lbs). For comparison to get the HD to generate the blower rpms and boost of the L with a 6 lb lower, the HD will need a 10 inch lower pully.

Something interesting is that the HD with a 5 or 6 lb L lower produces very similar boost as indicated by blower rpms - only 400 rpm different and both are very close to the 2 lb L. One ( the 5 lber) however maxes the SC at the reported maximum safe rpm while the other exceeds it (the 6). On the other hand, the L with a 2 lber already exceeds that point so the reported safe blower rpm could be conservative.

 

Compression ratio for supercharged HDs is 9.0 (per User Guide), which is exactly same as for standard F150 (per same User Guide). Compression ratio for Gen 2 L is 8.4 (per people that have User Guid for it). I don't know what is true reason that resulted in this difference (was boost lowered for truck to be able to take it due to weight difference, or because internals are not same, or because of some combination of factors, whatever they might be) but until we find answer on question are internals exactly identical any discussion about safe levels of boost increase is, in my opinion, not taking biggest "make or break" assumption into account.

ZoranC

 

http://en.carpoint.msn.ca/Vip/Engine...F-150/2003.asp

that shows the 2003 5.4 supercharged HD and L motors having the same bore,stroke, and compression.

http://ca.autos.yahoo.com/newcarguid...320021107.html

same, but is for 2002 harley

http://www.bonforums.com/trucks/harley_supercharged.htm

states what roush has always said: same exact motor, detuned by 20 horses. Yes, I realize it is 40 less...

Ford tech on phone told me it was "his understanding" that they were the same motor...

Still in search of the ford tech that can TELL me for sure they are the same...

Ken

 

None of these are official Ford sources or statements. So far Ford has been quiet in answer to our questions on this and other site, even though their "corporate spies" are quick to react when it comes to posts that help them with voiding the warranty or handling anything else that would hurt them. Why?

Until I hear official Ford statement anything else can have possibility of inaccuracy.

ZoranC

 

Here are the actual numbers... both rpms and ratios... see what you think...

 

Ken,

I agree 100% with your spreadsheet. Only difference from my numbers (posted earlier in the thread) is that I used 5200 as the redline rather than your 5250. Where does our truck shift at WOT?

I also read through some old posts on World that indicated that the HD computer is filled in at least as far as the L. I think it was a Shadow9 post - thanx for pointing me in that direction. As a result, I am tempering but not totally removing my concern about our computer being able to handle the L 5lb lower with no chip. Lets says I'm now more sure that its ok than I am skeptical it is not.

 

I shot an e-mail with a link to this thread to a relative who might know a little about these blowers, or know someone who does. He know a little about cars, particularly Fords.

I still like the Truckin' article on the L blower, though I wish it had been in a more "rear-world" environment. Dynoing with the hood up and 100 octane is cheating. With the same setup and pump gas the numbers would've still been close but detonation would have been more apparant.

 

I have been told it shifts at 5250 and 5300, but I am almost certain it is 5250...

that truck in truckin would have exploded at that boost level without the 100octane....

And people keep asking me why not just buy an L upper and a 4lb lower? True, that gets me what I am after, but, if I am a new modder (have spent no money yet):

A one piece pulley in 9.43" would be $200bucks or so. Remove stock lower, bolt in the replacement with three bolts and you're done.

OR, install a 4lb lower (same price/process) plus buy an upper pulley at $80 bucks or more and then $25-50 for a puller unless you can borrow one. In this scenario, I have spent more time and money to accomplish the same goal. AND, I have ASSURED myself of a voided warranty, even if I go back to stock since changing the snout pulley is damn sure going to upset your ford dealer when they service it...

Less money, less hassle. Why isn't anyone but me interested in a 9.43" lower?



Ken

 

I _might_ be once I fix my truck (I am finally making some good progress there) and depending on what we find out about rods and safety levels.

ZoranC

 

I spoke with Rich and the 1.84 is litres of displacement from the blower and 2.7 is the engine displacement divided by 2. In case you hadn't figured it out, 14.7 is psi at 0 altitude...

Ok, so let me take a moment to illustrate why this formula is cool to me:

1.84x(8.5/2.93) plus the rest of the formula is for an L with a *4lb lower*... 14.36 is the result.... Same formula applied on the HD is *13.xx*. So... working backward (pluggin in 14.36 as my desired result), solving for X in the formula, gives me 9.4277, but was off by a few thousanths since I initially rounded...

1.84(X/3.25)
---------------- x14.7-14.7=14.36
2.7


1.84(x/3.25)
-------------- = 1.97687
2.7

x/3.25 = 2.90084

x=9.43 (9.4277)

Isn't this fun?

Ken

 

So, in "for dummies" edition you are saying that proves that 7lbs lower would put supercharger at RPMs that are its maximum safe and would still be safe without a chip? Am I correct?

ZoranC

 

No, what I was illustrating is that by mathematical calculation, a 9.43" pulley will produce exactly the same amount of boost on an HD that an L will produce with a 4lb lower. (we already knew this from the tables in this thread)

It is essentially mathematical proof of what mmyek and I were tossing back and forth in terms of ratio, rpms, and actual boost...

We did it much simpler by looking at the chart. The formula is a more complex way of showing the same thing. The formula itself does not take into account any losses due to heat, drag, or other inefficiencies of the blower/intake system of the engine. Notice that plugging in a 6lb (9") lower in the formula nets something like 13lbs...

Really, it's just fun with math, nothing more. It's a way to REALLY know what the potential boost you are adding is.

Now what I need are forumlas to calculate the lost boost due to heat. Obviously, as boost increases, heat increases. As you heat air, it expands. Therefore, the blower is becoming less and less efficient as you increase the boost level. I need this little formula and I should be able to put together my own version of the famous blowerrpm.xls that is floating around. I'd like to be able to say boost in a perfect world, acutal boost because of heat inefficiencies, blower rpms, etc.

Why? I guess just cause I want to.

Ken

 

What would be even more interesting is equipping them and measuring real boost in manifold.

Is there behind this some idea brewing in your head for a practical benefit?

ZoranC

 

more accurate data when one tunes a motor means less likelihood of error and therefore less change of the dreaded kaboom...

Unfortunately, I am obsessed with research and I want to know what I am getting into before I do it. I have already "done it" in terms of mods, so I am trying to figure out exactly "what i've done" after the fact.

Several stopped to consider the 2lbs less on an HD, but noone really ever put a calculator to it. I did and a couple of people chimed in and concurred so now we have more data than we did before...

I still have a LOT of research to do.

Among other things, I am still trying to figure out how to measure absolute manifold pressure so that I know what boost we are running *exactly*...

And... tuners may just discover that an informed customer is a better customer since they are more able to draw their own conclusions about exactly what they are doing...

Ken