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FMIC pressure drop; Solutions???

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Old 11-28-04 | 05:27 PM
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Angry FMIC pressure drop; Solutions???

I just installed a fmic in my 7 and it looks great, water temps stay down as soon as I drive over 35mph (70 degrees outside), its an bar and fin type (dont know the manufacturer)but it has an pressure drop of 4psi at7k RPMs. IT is very efficient as keeping the conpressed air cool but its a bottle neck in the system. Im thinking of putting the smic back on if i can make the car at least as fast as it was. Should I turn the boost up? Am I stock runing 11psi @ 4500rpms - 7psi @ 7000rpms? What can I do?


To those of you who are about to tell me to do a seach, well I did for an hour and I got everithing from oil changes to threads about guys needing advise about girls, and if this new thread sounds like another one... What is the use of having a 'Post a New Thread' button on this web site?....

any POSITIVE ,hater-LESS input appreciated.Thank you
Old 11-28-04 | 05:30 PM
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well all FMIC will cause pressure drops..how are the piping setup? you said you dont know the manufacturer but can you describe the piping?

i seen piping that had bends galore which lead to a 5-6psi drop..
Old 11-28-04 | 05:38 PM
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sounds more like a wastegate problem than something to do with the intercooler
Old 11-28-04 | 05:55 PM
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I agree, as far as i understand pressure drop, it is something that is constant and not going to change through out the RPM band. I've heard issues like this cause by the stock twin setup.
Old 11-28-04 | 05:56 PM
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Originally Posted by ulost2my7
well all FMIC will cause pressure drops..how are the piping setup? you said you dont know the manufacturer but can you describe the piping?

i seen piping that had bends galore which lead to a 5-6psi drop..
Im using the stck (90 & 45)2 3/4 elbows to 2 1/2 ss pipe straight each side to either side of the ic 2 3/16 tank nipples , core is about 12 x 24 x 2 . I strong ly believe the bar&fin core is the cause but what can i do 2 work around it?
Old 11-28-04 | 06:00 PM
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Waste gate work perfect holding 11.5psi before; did NOT touch that at all.....
Old 11-28-04 | 06:06 PM
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for a second I though the bottle neck was the ic 2 3/16 in/out pipes; but the stock smic bottle necks inside also at 2 1/4 in/out pipes. 1/16 of an inch should not cause that much of a pressure drop. I probably need a twice as much bar&fin core. Should I turn up the boost? or thats not an option.
Old 11-28-04 | 07:52 PM
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Tube and fin (Japanese tuner style)? Or bar and plate (Spearco style)? Tube and fin usually flows better and cools less for a given size. An internal flow area (on the IC core) of 12x2" is pretty small for a bar and plate core, but might be enough for a tube and fin. However, the flow capacities vary widely within each type so I can't really say for sure if that is the problem.

Pressure drop is the difference in pressure before and after the IC, and is greatest when the engine is at maximum flow (high RPM, high boost). Any kind of restriction (and everything is some kind of restriction -- throttle body, manifold, pipe bend, just a plain pipe) will have some amount of pressure drop. The magnitude of the pressure drop at your engine's maximum flow rate indicates just how much of a restriction that component is in your system. If you are experiencing a drop in boost as seen on a boost gauge, the amount of the drop is not a direct measurement on pressure drop in the IC. Pressure drop is not a drop in boost pressure as seen on a boost gauge. However, it is likely that the new setup has more pressure drop than the old one if you did see a drop in pressure on your boost gauge. It is important to differentiate the two, however, since I am sure we could fiddle with your boost contol system and get you back to your previous boost pressure (no more pressure drop?), except your car would still be down on power (ahh... pressure drop is still there).

One relatively easy way to get an idea of the pressure drop in your IC (and whatever else is between the gauge connection points) is to grab a second boost gauge and connect it to the piping between your turbo and IC. If that gauge reads 16 psi while your normal gauge reads 10 psi, you have 6 psi of pressure drop between where the gauges are connected. That's a lot.

The 2 3/16" inlet and outlet sound too small. There is some threshold of air speed over which things get ugly (450 feet per second, by Corky Bell's estimation). Also, if the stock IC has 2" long in/out pipes with the 2.25" ID, it might be much less restrictive than longer pipes with a 2 3/16" ID. You also have several changes in pipe size that are not present in the stock system. Changes in size add restriction. Post a pic of your setup.

-Max
Old 11-28-04 | 07:52 PM
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heres some pics
Attached Thumbnails FMIC  pressure drop; Solutions???-pict0022.jpg   FMIC  pressure drop; Solutions???-pict0021.jpg  
Old 11-28-04 | 08:01 PM
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Tube and fin.

I would replace those stock rubber elbows with some smooth silicone. Though I might wait until I was more sure that the core you have will flow enough.

You can get the core flow tested somewhere. Get the stock core flow tested, too. If the new core isn't better than the stock core, ditch it. Or you could save money and have a little fun by flow testing them with a leaf blower and a sensitive vacuum gauge. That turbo minivan guy did that with some mufflers and I think also with some intercoolers. A quick search yielded a different page with leaf blower flow testing info: http://home.earthlink.net/~tmahon281/tech.html. Basically, you hook up a leaf blower to the IC and measure the restriction with a vacuum guage (or a pressure gauge depending on how you set it up). IC--gauge--sucker end of leaf blower. The more vacuum you get, the more restrictive the core is. Again, you could compare the results to the stock core for a frame of reference.

-Max

Last edited by maxcooper; 11-28-04 at 08:12 PM.
Old 11-28-04 | 08:25 PM
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thz max
I strongly agree the core is the corporate here and it will definetly underflow the stock unit. I guess ill have an ic for sale suited more for a honda. It really sucks all this time and money wasted in this install amounted to decreasing power of a good running car. Increasing boost would be like a liability instead of a solution. I cant have the power of 7psi @7000 rpm even with the avantage of a cooler charge.
Old 11-28-04 | 10:39 PM
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The intercooler probably doesn't flow that well anyway, but all those bends, the ribbed hoses, and long thin pipes look mighty restrictive to me. The bends in the ribbed hoses alone would cause way more restriction than a nice mandrel bent ic pipe. Think about the air not only having to deal with a 90 degree bend but also having to do it while running into ribs sticking out along the way. Those are the stock IC ribbed pipes?
Old 11-29-04 | 07:01 PM
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Someone said that all intercoolers cause some amount of pressure drop, whether its .25 psi or 5psi. Lets say that I took my car to some installing/tuning shop and had an IC intalled by 'proffecionals'; my car,your car even the car down the street would show some kind of pressure drop therefore decreasing performance somehow. If I pay $$$ and my car was actually slower, I would be pretty obbset myself. What would they (installers) recommend to do? Its it the nature of the beast or can something be done to (other than sell you an monster core IC) make the costumer happy?

P.S.The factory hoses and all those few beens(compared to other installs) are most likely causing about an 5% pressure drop; maybe .25psi wich is nothing compared to the 4psi Im really trying to bring to light on this thread. But thanks for noticing.
Old 11-29-04 | 07:34 PM
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it is not realy accurate to measure the pressure drop when the intercooler is cooling. if the air charge is 100c and 10 psi before the intercooler and 50 c after the pressure will be lower just from the temp drop.
Old 11-29-04 | 08:10 PM
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Hmmm thats an all different can of worms.Thats how a/c's work. Still; should I get a boost controller and raise the boost the 4psi im loosing?....

I want my car to be a least as fast as it was with the stock smic.
Old 11-29-04 | 11:53 PM
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Question

Originally Posted by mad_7tist
it is not realy accurate to measure the pressure drop when the intercooler is cooling. if the air charge is 100c and 10 psi before the intercooler and 50 c after the pressure will be lower just from the temp drop.
what makes you think air being pumped at 500 cfm will behave like a static, closed, constant volume of air?

Last edited by KevinK2; 11-30-04 at 12:14 AM.
Old 11-30-04 | 12:12 AM
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Originally Posted by Rotarius
..... should I get a boost controller and raise the boost the 4psi im loosing?....I want my car to be a least as fast as it was with the stock smic.
Make sure you first do what max said ... move boost gage hose to port on back of y-pipe.

If it holds 12 psi there toward redline, but drops to 7-8 psi when measured at the manifold, then put stock IC on and run at stock boost. The stock IC already has an excessive 2.5 psi drop at high revs when at 12 psi at the manifold.

For higher boost, make sure you don't have a boost leak or another restriction, then go water inj'n or get a real intercooler system designed for high flow.

If you are currently at 4 psi more drop than with stock ic, just cranking 4 more psi boost will get you 6 across the IC system .... not real smart tunning.
Old 11-30-04 | 10:06 AM
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kev the question is what effect temp has on the pressure. moving or not if the air is chilled it will reduce in pressure and in speed. it is just a inaccurate way of deciding the pressure drop. the volume of the intake tract is always the same, the mass of air traveling through it changes with temp and press
Old 11-30-04 | 11:36 AM
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Originally Posted by mad_7tist
kev the question is what effect temp has on the pressure. moving or not if the air is chilled it will reduce in pressure and in speed. it is just a inaccurate way of deciding the pressure drop. the volume of the intake tract is always the same, the mass of air traveling through it changes with temp and press
not that simple. look at a fixed volume (like 1 cup) of air, flowing through IC. Let 1 = before IC, and 2 = after. Per ideal gas law, where ni is basically the mass of air in the fixed volume:

P1/(n1*T1) = P2/(n2*T2)

The temperature drop after the IC is usually balanced by the increase in mass (density), with no related change in presssure, so that T2/T1 = n1/n2 = density ratio. T is in deg K or R, so % change is not as big as one might guess.

Check writings by Corky Bell or George Spears (spearco) ... IC pressure drop is dominated by flow resistance, not temperature drop. I could build a big A/L IC with liquid nitrogen that was 200% efficient (based on ambient air reference) with less than 1/2 psi pressure drop.
Old 11-30-04 | 07:39 PM
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Originally Posted by KevinK2
......................
If you are currently at 4 psi more drop than with stock ic, just cranking 4 more psi boost will get you 6 across the IC system .... not real smart tunning.
The IC its causing a 4 psi drop so if the stock IC its 2.5psi then I must have a 6.5 pressure drop.

The 1 Million dollar question is:
Can I turn up the boost to conpensate for the pressure drop?

Would that make the turbos go beyond their efficiency thresholds? Would that cause the turbos to generate so much more heat ;that even with the new FMIC the charge temperature would be the same as the stock SMIC?[ Going back to square one?] What do people with aftermarket intercoolers do usually?

Help please!
Old 11-30-04 | 07:59 PM
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Originally Posted by Rotarius
The 1 Million dollar question is:
Can I turn up the boost to conpensate for the pressure drop?
No, you can't. You could turn it up to get back the boost, but you will still suffer a severe power defecit if your IC is really that restrictive. The turbos will be making something like 17.5 psi of boost just to get 11 psi in the manifold. That means more heat simply because the air is compressed more, and perhaps also because it is likely to put you in a less efficient spot on the compressor map. It also means more backpressure since the turbos will have to do a lot more work to create the higher pressure. More backpressure means less flow for a given boost level. For example, you will flow more air through the engine running 11 psi with 15 psi of backpressure than you will running 11 psi with 36 psi of backpressure (don't focus on the numbers; I made them up -- focus on the concept). The amount of power you make is directly proportional to the amount of air flowed, so lots of backpressure means less power.

Imagine pinching down one of the intake pipes. It is clear that this would rob you of a bunch of power. A restrictive IC system has the same effect. It might have some positive side effects in the area of charge cooling, but there are IC systems that cool just as well without choking the engine.

Everything has some pressure drop (even a straight pipe); the idea is to eliminate severe restrictions. Any IC that has more pressure drop than the stock IC is not suitable for use on the FD, IMO.

I made a web page some time back that discusses this a bit. It has a little model you can play with. The numbers in the model are intended to be roughly "true" for the FD's engine system, but they are just guesses and should not be taken seriously or used in other calculations. Don't focus on the numbers; I made them up -- focus on the concepts. I never wrote the rest of the pages I meant to write for this section, but this one is fairly complete:
http://maxcooper.com/rx7/how-to/fuel_system/why.html

So that's the conceptual stuff. I still don't know quite what is wrong with your system. It could turn out that you just have a boost control issue (bad solenoid, check valve, etc.) and that there is absolutely nothing wrong with your IC. Or maybe there is a mouse in a pipe. Who knows? However, if your IC really is choking your engine excessively, the only good solution is to get rid of the restriction by reworking or replacing the IC system.

-Max
Old 11-30-04 | 08:10 PM
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You can run 19 at the turbos to get 12, and quickly cook your turbos, and severe local heat could cook o-rings seals too.

Good IC kits don't have that huge pressure drop ...

Re-read post 17 for what to do.
Old 11-30-04 | 08:23 PM
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thx Max.
IC for Sale anyone?... ... wrong forum.
Old 11-30-04 | 11:23 PM
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not that simple. look at a fixed volume (like 1 cup) of air, flowing through IC. Let 1 = before IC, and 2 = after. Per ideal gas law, where ni is basically the mass of air in the fixed volume:

P1/(n1*T1) = P2/(n2*T2)

The temperature drop after the IC is usually balanced by the increase in mass (density), with no related change in presssure, so that T2/T1 = n1/n2 = density ratio. T is in deg K or R, so % change is not as big as one might guess.


where is the extra mass coming from? the turbos flowing more air? that would be at a high boost level pre intercooler right?
Old 12-01-04 | 03:38 AM
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Since we're on the topic of pressure drops and temperatures. etc. -- I posted a spreadsheet in another thread that you can use to "play" with various parameters (boost, pressure drop in the intake system & IC, etc.) and see what happens to some other stuff (pressure ratio, compressor outlet temp, etc.) -- and the numbers are correct (you can trust them and they can be used in other calcs) in this one:
https://www.rx7club.com/single-turbo-rx-7s-23/temperature-intake-air-285228/

-Max


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