FMIC -- Is this big enough?
 

Hey guys!,
I was wondering how large an intercooler 'must' be to effectively cool about 12-15psi of boost (from a T04 60-1). Will the 3.5x18.5x6 core from spearco work well for this setup? How much more effective is a bigger core? (Say 4.5x25x6.5?)

Thanks!,
Manolis

I have the same question. I"m going to go with the biggest unit I can fit in there with out too much modification to the front. Have you measured the space in the bumper yet, I haven't had the time to.

C

I haven't measured the space yet -- I'll have a chance to check up on that tomorrow probably (big AP Bio. test tomorrow :-( )

Taller and wider is better than thicker. IMO the 4.5" Spearco bar & plate IC's are too thick for street use.

The Spearco catalog lists performance data so that you can compare the IC cores. Basically, bigger is better.

I have a Spearco 2-182 core in my FC (3.5x15.6x20" + about 3" more on each side for end tanks). The definition of installation "without too much modification" will vary with individuals. I think that it is best to make a cardboard mockup first to see how you like the fit. Be sure to plan out your piping, too.

3.5" x 6" = 21"^2 of internal flow area
4.5" x 6.5" = 29.25"^2 of internal flow area

Stock FD = (roughly) 2.5" x 11.5" = 28.75"^2 of internal flow area

Evil Aviator's core = 3.5" x 15.6" = 54.6"^2 VERY NICE!

To keep pressure drop low, you want to have a large internal flow area. I would not recommend the two sizes originally quoted for that reason alone.

-Max

Hey Evil...
 

Do you have any pics of the IC installed in your car? (It sounds HUGE!)

How much difference in cooling effectivity would a 3" difference in length make? (17" vs 20")

How about the 3.5 x 13 x 17? (The car is street driven, so i'd prefer to leave the front end more-or-less intact)

Anything over 3 to 3.5" in thickness is not worth it's weight and basically is ineffiecent.;)

Evil aviators core is nice.

Re: Hey Evil...
 

Click on the gray "www" button below, and then click on "RX-7 Picture Gallery". You will see the "Intercooler" link at the bottom of the web page. Sorry, only the 20B car pictures work, and there is no link to the tech info yet. :(

The piping isn't done yet because I'm still waiting for the TB intake elbow. However, you can see that the Spearco 2-248 FMIC definitely fits. The hood latch was removed and will be replaced by hood pins. The radiator and oil cooler were moved, but are still fairly close to their stock positions. The battery, wiring harness, solenoids, etc. were relocated. None of the bumper or supporting structure needed to be cut, but some holes will need to be cut to run the 3" IC piping through the body behind the headlights. I suppose that you could run the pipes below the radiator, but they would be pretty close to the road.

Hey guys, all that internal flow area stuff is great for speculation, but the Spearco catalog lists all of the statistics, which you will find do not exactly conform to the internal flow theory. You can look up for yourselves what different core dimensions will do for you, rather than having to listen to some dork like me who will probably tell you the wrong info, anyway. The catalog is only $3, and if you whine enough you may even get it free. :)
http://www.spearcointercoolers.com/

Re: Re: Hey Evil...
 

That is true in a sense. The flow area is directly related to pressure drop for a given "family" of cores, but there is a wide varaition among different core families. There is enough variation that directly comparing the dimensions isn't useful. Unfortunately, it is difficult to tell which family a given core comes from, so it is probably best to go by Spearco's flow ratings for each core rather than trying to compare the dimensions.

That said, the core families that offer more pressure drop per unit area are probably more efficient at cooling, so it still makes sense to get the largest internal flow area that you can.

Also, I misinterpreted the dimensions listed in the original post. Spearco lists the first two dimentions as the internal flow area, so the 3.5x18.5x6 size actually has an internal flow area of 3.5x18.5 that will flow through 6" of core from top to bottom (or vise-versa). That is not the orientation that is commonly used for FMICs on RX-7s but might be reasonable if it cooled well (check the specs before you buy).

My intent was to raise the issue of pressure drop. Most people seem to be unaware that it matters, and unaware of the what characteristics yield good or bad pressure drop. A really long IC with little internal flow area will not be as good, for example, as a core from the same family that is a little taller and less long. I think this is one of things that makes the difference between a car that makes good power for its "mod list" and one that leaves the owner scratching their head why it isn't performing up to their expectations.

Does anyone have links to flow charts for the Spearco cores? I couldn't find them on the Spearco site. I believe that they are available in the Spearco literature, but it would be nice to see them online somewhere.

-Max

Re: Re: Hey Evil...
 

Such a useful dork you are. So when are you gonna finish up that car of yours!

Re: Re: Re: Hey Evil...
 

You're back on the forum. I guess your mommy changed your diaper this afternoon.http://www.plauder-smilies.com/peepwall.gif

Re: Re: Re: Hey Evil...
 

What? I thought that the only important thing about intercoolers was how shiny they were! Hehehe. Seriously, though, I went through all of the Spearco data to try and apply the internal volume theories, and it didn't work. Maybe I missed something, so if you can show me how the number-crunching applies, then I would appreciate it. Otherwise, I think it is just easier to use the Spearco charts and be done with it. Yes, the pressure drop is important, but so is efficiency. I have seen a lot of big name brands talking smack about their low pressure drop, but conveniently ignoring their product's poor efficiency. Much like most other engine performance products, density is the bottom line.

Hopefully before you get one of your own. :D

The guy who is going to install the larger fuel cell won't be back from Spain until mid-January, so it will still be a while. Also, I'm still waiting on the Wolf EMS. In the meantime, Scott is making me a composite dash for my SPA gauges, and I'm working on cleaning up the engine bay a bit by reworking some of the wiring, routing the remaining AN hoses, and designing a composite fan shroud.

Re: Re: Re: Re: Hey Evil...
 

I tried to do the analysis and find the families from the dimensions and flow ratings alone but it wasn't enough information for me to find the groups. I attached a zip file to this message that includes a Java program with a IntelliJ project file, a data file of the IC data, and an Excel worksheet to help identify what techniques might be helpful in finding the groups. You can drastically change how it groups the cores by changing the error tolerance of finding a match, which is why I believe that this method is insufficient for finding the groups. It is an interesting problem, but I don't think it can be solved conclusively from the data provided. Check it out if you are a bored computer geek. ;)

I still believe that the basic formula applies and is valid within a given family of intercoolers. Indeed, the problem with the analysis is that there are too many solutions to make a determination. Here is why I believe it is possible to find the coefficients in the equation for a given family:

- an IC core is like a rectangular pipe that is totally blocked for some percentage of its area, which is simply the areas in which air from the outside flows through the core
- the part that isn't totally blocked is partially obstructed by the turbulators inside the internal flow channels
- the blockage of the internal flow area increases with the length of the internal flow channels, as the air has to travel through a longer path of the partial blockage

Here is the formula:

Flow = (BaseCoefficient - (Length * LengthCoefficient)) * InternalFlowArea

This just makes basic sense considering the known construction of an intercooler core. Nothing magic here.

How useful is to know these coefficents? It is of no practical use if you already have the flow rating. It would be useful to calculate the flow if you were going to change the size of the intercooler core. It has some value if you are simply interested in what characteristics of the core affect the flow properties.

This formula misses some things. It ignores various things about fluid flow for the sake of simplicity. It also tells you absolutely nothing about efficiency in terms of temperature drop.

So, I don't think it is impossible to come up with an equation that will accurately predict the flow rating of a core based on its construction and dimensions. That is to say that I DO believe that there is a basic relationship between internal flow area, length and flow capability (think about it for a moment: there has to be). However there are some coefficients in the equation that are particular to a given family of ICs, and there is enough difference between different families that you cannot directly compare ICs for flow capability by dimensions alone. And finally that the flow rating and dimensions alone are not enough information to determine the value of the coefficients.

If you are reading this and think it is a big waste of time, please don't waste any more of your time by flaming me. I know many people aren't interested in this kind of thing. Sorry to waste your time if you don't care. But some people are interested, so I posted it.

-Max

Oops, forgot to post the file. Here it is...

Yeah, I compared the Spearco bar & plate IC's because I figured that they had the least manufacturing differences between the different cores, but I still didn't find an accurate equation to estimate performance. I think that the scale effect may be a large factor in this.

Thanks, I'll check out your program. BTW, I'm not a bored computer geek; I just quit my flying job, so now I'm on "vacation". :)