Your approach seems valid one. Based on that 5lbs would be dancing on the edge (blower wise), 4lbs would be safe, and 6lbs and over would be gambling with increasing risk. That is assuming that we are getting blowers that can pass same quality checks as ones on L can and not some "rejects" that can not quite sastisfy L specs, but are fine for detuned engines. Can someone find out what these blowers can really handle RPM wise?

Only question after that would be what engine and transmission & co can handle (rods etc wise) and what computer can handle. IF and only IF we have identical engine components (quality wise) as Ls (see above) we could say that engine should be able to handle it. Considering that none of trucks that had 8lbs lower and that had thrown rods or something had issues with tranny & co we could assume that tranny & co can handle 4-6lbs on lower. Therefore, only remaining question mark is over computer.

Until we can answer a) is quality of components on HDs exactly same as one on Ls, b) what are RPMs that these blowers can handle, and c) what computer can handle, my gut feeling would tell me go with 4lbs lower and you will have high chance of being safe.

ZoranC

 

Hey, RichB....

Thanks for the info. Would you mind giving me a little behind the scenes on the forumla here? What is teh 1.84, 2.7, and the 14.7. Are they related to atmospheric pressure, air density or what?

Thanks!

Ken

 

Back to the top, as I'd like this discussion to continue. This is one thread to bookmark for sure.

 

Something has been bothering me about this thread and I finally figured out what it is:

Everyone seems to agree that an L is fine with a 2lb lower pully and no chip. Logically, then the HD could probably safely run an additional 2 lbs. Earlier in this thread however, there are indications that a HD would be fine with the L 5 lb pully and no chip. I am not sure that is safe to assume. There are significant differences here. An L with a 2 lb pully is only running 2 lbs of additional boost. A HD with an L 5 lb pully is generating 4 lbs of additional boost. They are both turning the blower at approximately the same RPM and both generating the same approximate 10 lbs of boost so the likelihood is that mechanically there wont be damage but whether our computer's basic tuning can handle 4 additional lbs is unproven and probably risky. An increase from 6 to 10 is pretty huge. I don't know that there is that much margin in our programming.

If anyone does this, get a dyno with a air/fuel and let us know.

 

Let's go back to the numbers.

Everyone assumes that an L with a 2lb lower is safe with no chip. (nevermind those with 4's and 6's swearing its ok)

L upper is 2.93" and the L lower is 7.4" (so is ours). 7.4/2.93=2.5256 ratio in stock form. When you add a 2lb lower as measured my a 2lb metco (8"), 8/2.93=2.7304 drive ratio.

The HD upper is 3.25" **note** this was given to me and I measured mine crudely and looks correct. as stated before, I will try to get a pricision guage on it to know *exactly*. The HD lower is the same size -- 7.4" so, 7.4/3.25=2.2769 ratio. Adding a JL 5lb lower (8.75") gives us the following: 8.75/3.25=2.6923 final ratio. That is slightly *LESS* than the L ratio meaning you would be running just slightly less than the L with a Metco 2lb lower... Again, step in and tell me where my math is wrong if it is.

If you use the JDM 2lb lower as the measurement (7.8"), your final boost will be slightly higer than the 2lb lower on an L. I would like to get the measurements of the JL, Metco, and ASP, PSP, etc. lower pulley diams for reference.

Ken

p.s. I'm working on some more numbers... lol

 

As another response to your post,

I think what you are saying is:

Regardless of what it means on an L, you are still putting a 5lb pulley on a stock computer system.

I assume you are concerned that the stock HD computer system does not have the ability to compensate beyond a 2lb increase as the L does.

Unfortunately, this is not something I can get first hand. While I have been told by someone who knows ford engineers that the HD comptuer system is tuned out *at least* as far as the L, I have no way to confirm this.

Just for the record, if someone wants to come to my house and take my 6lb lower off and put a 5lb lower on, I would be happy to remove my chip and take it for a dyno first and a 1/4 mile run 2nd...

Ken

 

Ken,

Right now the HD community is putting a lot of stock in what the L community has found because we don't have direct evidence of our own. I'm just not sure we should be.

You are right and I agree 100% that the L can handle 2 lbs without any chip and that an L in such a situation will be producing 10 lbs of boost (8 stock + 2 mod) - 125% over stock. The 5 lb L lower on the HD also produces 10 lbs of boost which should be safe for the motor but can our computer handle 167% increase in boost without a chip? I have to speculate that if I was Ford I would not build that much margin into my tuning.

We know that we have a different computer than the L (the computer codes are different at least) and that the L computer has a margin of at least 25% in the computer. In theory we have some people that say the L can handle 150% of stock by using a 4 lb pully with no chip. Almost no one is saying the L can handle a 5 (163%) or 6 (175%) lb pully without a chip. The computer just doesnt have that much margin.

I am not going to say that the HD won't be able to handle the L 5lb lower without a chip. You may be right that L and HD have the same or very similar tuning - but why then 2 different computers; is SVT that arrogant? But knowing that we have 2 different computers, an increase of nearly 170% over stock would seem to be too much to run unchipped. I'd be very happy if it were otherwise. I'd like to run a 5 lber unchipped.

Someone bring Ken a 5 lber so we can settle this. lol

 

yes, but that's another topic.... lol

The stock computer is basing a whole lot of it's calculations on one thing: Air flow through the MAF... Since we are using damn near everything identical in terms of intake, maf, blower, etc. I would be willing to bet that calibration tables that exist in the Harley are quite similar to that of the L simply because of the common inputs. So many things are the same -- RPM limiter, boost bypass triggers, etc. etc. etc., that the programming MUST be nearly identical...

But then again, that is pure speculation on my part...

I don't know if it was thunderkiss or shadow9 over on world that said they had worked with a tech at ford that worked on HD calibrations and was told that the calibrations on the harley go out farther than the L version. I can't find the post. Maybe someone else remembers it...

Again, hearsay, and at this point, you guys know that I like to do the research and have hard facts...

Ken

 

Exactly! This is all based on assumption that all mechanical parts are identical and can withstand same amount of stress. Before proceeding with any figures we should first find out is this basic assumption true or not.

ZoranC

 

Hey Rich, I just built a web calculator (that I will post a link to when it's done) to make this calculation, and when I put in stock pully #s, it shows the L to make 10.6 psi with a 2.93/7.4 and the HD to make 8.1 with 3.25/7.4 any Ideas where I'm going wrong... do you not get these #'s when you plug them in? Once I get it figured out, I'll post the online calculator to make our brains hurt less...

 

Need to hunt him down over on NLOC, but I belive this would be in a perfect world where the blower is 100% efficient and there are no losses due to parasitic drag and so forth. I could be wrong, though.

Ken

 

cool, will do... my FTP doesn't seem to want to connect right now anyway, so I'll do it from home... here's the code if anyone wants to upload it... nothing fancy...

<html>
<head>
<title>Untitled</title>
<script>
function calculateBoost(){
a = boostform.lower.value
b = boostform.upper.value
num = 1.84 * (a/b)
denom = 2.7
boost = (num/denom) * 14.7 - 14.7
boostform.boost.value = boost
}
</script>
</head>

<body>
<form name="boostform">
upper pulley diameter: <input type="text" name="upper" size="6"><br>
lower pulley diameter: <input type="text" name="lower" size="6"><br>

<input type="Button" onclick="calculateBoost()" value="calculate boost"><br>
estimated boost output:
<input type="text" name="boost" size="6">

</form>


</body>
</html>

 

Another brain fart for the enquiring mind:

Pullies have been sold for the L for a long time and are rated at a certain blower boost in a perfect world. Actual net boost is not accurate. I don't have the numbers or engineering skills to begin to present how much *actual boost* one gets on an L from a 4lb lower, but consider this:

An L running a 4lb lower is said to make 12lbs of boost. The PSIG comes from blower RPMS, right? A HD with a 6lb lower is also said to make 12lbs of boost. Ok, Einsteins... here's the question:

If the are both turning 12lbs, why are the ratios so different? If the ratios are different, the blower rpms are different and if the blower rpms are different then there is no way the boost level is the same.

So, in other words, a 6lb lower on a harley is not making 6 additional pounds of boost, regardless of how you compare it to what is happening on the L with the same sized pulley....

If you do the math.... lol... then a 6lb lower produces a similar ratio to the L running a 2.8lb (approx) lower. So that's just under 11. Just for the sake of argument, let's call it 11.

Therefore, our 6lb pulley is actually making "5 lbs" of boost...

Ken

 

I think ZoranC may be on to something here too. If his concerns over different internals leads us to realize the HD's have a higher compression ratio than the L's, we have another worm to add to the can...

 

Hrmmm, higher compression ratio could be a good thing, up to a certain point. Boost raises the Dynamic Compression ratio, so until you get to the point where too high a DCR starts to cause detonation from too high combustion temps, a little more compression could mean more power from the HD motor at same boost levels. (Assuming there is a difference, and that at the same boost levels, both motors can handle it equally well) I'm on numerous turbo lists having owned turbo cars in the past, and compression ratio arguements have been raging for years. Is it better to run more compression, less boost, or less compression, more boost (in terms of reliable power output)? I don't know. The higher compression motor would appear to have more throttle response and "low-end" I would think... shoot I don't profess to actually know though