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Discussion Starter · #1 ·
Mark, I would LOVE if you could brake down the amount of boost you are getting at specific RPM's with your kit. I personally don't care which kit you refer to (S1, R1, S2, R2), I would just like to see what max boost your running, and how it is incrementing on the focus. SVT or ZX3 (of course my interest is for the SVT).

The reason I'm asking for this, is because in a previous thread you stated that one kit was making 9 PSI at 2750 RPM's. Which would be INCREDIBLE! I just hope that's on what of the Focus kits. Can you brake down the boost by RPM's on any of your kits? I don't care about the HP numbers, just the amount of boost.

Thanks!!
 

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I'm curious to. Please no "coulda woulda shoulda", what do the Focus kits actually *do*. Not a challenge, just pure curiousity.
 

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im interested too
 

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Discussion Starter · #9 ·
:bumpage:
 

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bela, the S2-R (as it's tentatively called) will make about 9psi just under 2800 at WOT in 1st with a pulley set for 16-18psi and bypassing at 12. A 16-18psi pulley yields the highest hp/psi on average of about 10.8hp/psi, so I would reccomend basing any bypass systems off of one.

I don't care about the HP numbers, just the amount of boost.
The output would be most important. If you are putting out 12psi and only making 270hp, then who cares what the boost is at when someone else is making equal power with less boost and more power with equal boost with a more efficient system. A lot of people lose the concept and feel that "boost is boost" when in fact, it is not. The amount of boost is not nearly as important as power output.

Mark
 

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Discussion Starter · #11 ·
wolff... the reason I didn't care about you providing horsepower numbers is:

1. I didn't want to lock you into having to give horsepower numbers.
2. I understand that most in lower RPM's where the engine efficiency is greater, will result in nice torque gains.

I will say that if you were getting 9PSI on a 16-18 PSI pulley, that's pretty awesome, considering most centrifguals are said to have boost increases exponentially as RPM's double. So Typically a 9PSI pulley at 3K RPM's would normally equate to 81PSI at 6K RPM's. But obviously that's not how things are with you guys, and your SC transmittion is pretty nice!!

You listed that this was taken in 1st gear. Any reason the boost would differ at 2800 RPM's in say 3rd gear at WOT?
 

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belacryf,

I take it you mean 18psi at 6krpm. But this would not be true in the real world. Factors such as exhaust backpressure and head/cam restrictions would show a higher manifold pressure. Remember that "boost" is just a measure of positive pressure in the intake manifold. On a car with a fixed boost level, like a supercharged car, the more the system can flow in and out with the same pulley, the less manifold pressure it will show (a lower boost reading) because a higher percentage of the air originally sent to the manifold is now being ingested. Things like alternate cams and/or a ported head will show less peak boost, and lower compression will show less boost under peak (with a low boost pulley [sub 15]), but both would give a greater capacity for more power. The gauge that used to say 11psi at redline, would now show, say 8psi because the system is more efficient at ingesting the boost and has greater capacity. Inversely, putting on a 20psi pulley and attempting to ingest all 20 of that PSI will result in a peak-boost less than 20psi because it will be too much pressure for a restrictive system. The gauge will show as much boost as the system will handle before it starts to leak, or attempt to exit out of the path of least resistance. Having a system that can accept this level of CFM would show a higher boost reading with the 20psi pulley as a result of less system resistance. The task at these levels of boost, is to find the threshold that your set-up will take before it starts to blow past seals, rings and couplings, or to get a higher flowing system that will take this level of boost.

The gear won't have a drastic alteration in boost/rpm. This is just used as a specific refference as to where it was read.

Mark
 

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Discussion Starter · #13 ·
No I didn't mean 18PSI, I mean 81. From what I've read, boost increases with the square of RPM. Here's an snippet from another website that illustrates how I undestand it...

The amount of airflow a centrifugal delivers (literally blows) increases roughly at a square of its driven speed. It is NOT linear. So say at 3k rpm it delivers 'X' airflow. At 6k it now delivers roughly X^2 airflow
So (assuming an equal efficiency across all RPM's which we know isn't true, but it helps for this purpose) if at 3K your delivering 9 PSI, then at 6K you'll be delivering 9^2 (or 81 PSI).

This is why I asked for a breakdown by RPM. Because it would be very telling of what kind of feel you can get, if you see how boost is incrementing with RPM.

Maybe the fault in my thought process has to do with equating boost to airflow. I'm not sure how PSI truly relates to flow ,if we say 2500 CFM creates 9 PSI on the SVT zetec, then 2500^2 at 6K = 6250000CFM... would that be the equivalent of 81 PSI??? or at least close enough for theories sake??
 

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From what I've read, boost increases with the square of RPM...if at 3K your delivering 9 PSI, then at 6K you'll be delivering 9^2 (or 81 PSI).
This calculation certianly is not accurate. Let's say for hypothetical purposes at 3000rpm a centrifugal were making 1psi, now double that RPM to 6000, then square the psi according to the formula, it's now making 1² or 1psi x 1 = 1psi. @ 6000rpm. This would illustrate that the boost is not a square product of double a given RPM.

The formula did mention 'flow' rather than pressure (which is the opposite of flow), so that would incite CFM or FPS, but even still, this is not true. Just to use a maximum, in the event that CFM was the intended unit of measure, the blower will max out in the area of 1100cfm. To use the same graph lets say the blower is now at 6000rpm and it's producing 1100cfm. If this formula were true, that would mean that at 3000rpm, it would have been making 33 cfm. The average person can unleash more than 33cfm from one visit to Taco Bell, so the formula is definitely innaccurate.

The only applicable formula for centrifugal blowers is: CRPM x crank pulley(aka drive pulley):blower pulley(aka driven pulley) ratio x blower transmission step-up (in the C1's case, 5:1). At a given amount of blower RPM, the blower will be making a fixed amount of boost virtually every time.

Ex: 1000rpm x 1.0:1 x 5 = blower RPM. The listed formula will only apply to this blower, or any other blower with a step-up of 5:1. You can use this formula on any centrifugal blower, just replacing the last figure (5:1) for that respective blower's transmission.
 

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Discussion Starter · #15 ·
Ok cool... thanks Mark. Can't wait till you hear from CARB and release some final numbers on that kit
 

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Here is where the square rule comes in. I got this from Corky Bell's Supercharged book, btw.

It is in fact boost, because the centrifugal is a compressor. Boost is dependent on RPM, in the way that Bela indicated, but is the pressure ratio. So 9psi is actually 1.6122 (9+14.7/14.7). Now double that RPM, and you square the PR, 2.599. Boost = 23.5 psi, THEORETICAL. Take into account heat and drive loss, and Wolff's numbers make a lot more sense.

If I weren't holding my newborn daughter, I'd try to figure out what RPM the bypass opens. Somone else can do that.
 

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Discussion Starter · #17 ·
Cool.. thanks for the explanation Rich.. I need to finish reading that book! That makes alot more sense
 

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Here is where the square rule comes in. I got this from Corky Bell's Supercharged book, btw.

It is in fact boost, because the centrifugal is a compressor. Boost is dependent on RPM, in the way that Bela indicated, but is the pressure ratio. So 9psi is actually 1.6122 (9+14.7/14.7). Now double that RPM, and you square the PR, 2.599. Boost = 23.5 psi, THEORETICAL. Take into account heat and drive loss, and Wolff's numbers make a lot more sense.

If I weren't holding my newborn daughter, I'd try to figure out what RPM the bypass opens. Somone else can do that.
You weren't taking into account that the "compressor" spins in a fixed amount - in relation to the crankshaft. If you "double" a given RPM (for crankshaft or the compressor), then realize that the engine is also spinning (proportionate to the compressor) faster and "accepting" (into the engine/intake) roughly the same amount of boost as it was at lesser RPMs.

The RPM does not change the boost ratio. Mabe in the future there will be forced induction units that can change speed or the pitch of the fins independant of the source - which, in this case, is the crankshaft.
 

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Don't forget, it's not that easy. The compressor speed is dictated by engine rpm. And the compressor is capable of making almost any pressure ratio OR cfm based on the engine's needs. If you look at a compressor graph, you'll see speed lines that cross multiple pressure and cfm lines.

Basically you have to pick the speed line you're on, then determine how much airflow the engine can accept. The result is a pressure that backs up in the intake manifold, and that would be your boost.

So, the whole thing is very hard to do.

Also, don't forget, that the engine Volumetric Efficiency changes with rpm as well. Etc. etc. etc...

I think it's way to complicated to predict. Suffice it to say, the common phrase "boost is proportional to the square of the speed" is way oversimplified.
 

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Can someone please tell me when the street kits will be available with the SVT? I thought it was going to be august, and I still havent heard anything. I am a little anxious to get this for my SVT as I need more power.
 
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