67mustangat16":2va8bff8 said:
I'm using a 200 six and wouldn't a big downpipe into a dual 2" exhaust make much less back pressure than one with a single 2"?
It is just extra work. Why you making me to the maths..?
using the internets..
http://www.mathgoodies.com/lessons/vol2 ... _area.html
Area of a circle= (Pi)(r)(r)
So..
a 3" pipe = 7.065 square inches
a 2.5" pipe = (3.14)(1.25)(1.25) = 4.90square inches
a 2.25 pipe = (3.14)(1.125)(1.125) = 3.975 square inches
a 2.0" pipe = (3.14)(1)(1) = 3.14 square inches.
Personally, I'd just go with a single 2.5" all the way from the turbo to the exhaust tip, and if you want the look of a dual tip system, have it welded on at the very end. Otherwise you have a lot of tubing to bend and get looking nice for not a whole lot (or any) performance gain.
And after that, I got curious to see what size tubing should go from the pressure side of the turbo to the carb/Throttle Body..
A T3/T4 with a .60 AR (estimated)
I use more power of the internets...
http://www.falcon6handbook.com/compcalculator.asp
VE = 80% (from their default settings)
Randomly chose a turbo calculator, using their defaults where specified and the VE from the falcon performance handbook.
http://www.rbracing-rsr.com/calcboost.html
I took a screenshot, slapped it into mspaint, saved as a JPG, resized it to fit the forum rules and viola!
It says we need 13lbs of boost on a 200 to make 300hp, and that will require 408CFM of air movement.
Then back to the googles for more potentially faulty internet research and I turn up this page (completely unverified, but sure sounds good)
Okay this is a quote from a book called maximum boost. There is a certain air velocity that shouldn't be reach. It shouldn't reach 450 feet per second b/c that will cause a restriction.
To calculate cfm you multiply desired bhp by 1.5. Then you use the formula velocity=airflow/area of tube
For example a 400bhp car will have 600 cfm and we are going to use a 2.5 inch diameter piping. So we use the formula velocity = [600cfm/pie{2.5/2}^2
So velocity equals 293 ft/sec. This means we are under 450 feet and we are safe from restrictions. Any tubes bigger then 2.5 will cause lag.
More maths.. grr
oki, lets use his digits to see where we need to be...
300*1.5 = 450 CFM (pretty close to the 408 calculated earlier)
Now using that velocity formula, I'll try random (common) pipe sizes
2.0": 450/3.14 =143.312ft/sec
2.25" : 450cfm/3.975 = 113.35ft/sec (3.97 calculated earlier from pipe diameter square inches)
2.5" : 450/4.90 = 98.4ft/sec
3.0" : 450/7/065 = 63.7ft/sec
And more potentially 'research'
http://honda-tech.com/showthread.php?t=1202591
turncoat":2va8bff8 said:
Okay then, let's see how much the charge pipe size (and thus volume) affects lag time:
Every foot of 2" x 0.065" tube will hold 0.095 CF.
If you can flow 400 CFM from 0 to 15 psig (please excuse the simplification of the transient, it's just a quick estimate), you can pressurize the charge pipe from 0 to 15 psig in 0.014 seconds. (Note this is not spool time, just the time it takes to fill a pipe given a certain flow which is what we are trying to isolate)
Change to 3" charge piping, your volume increases to 0.22 CF and for the same scenario, the time to fill increases to 0.033 sec..
So the question is can you feel the extra 0.019 sec it takes to get to 15 psig when you increase your charge pipe size from 2" to 3"? Not likely.
Please don't pick at that the calculations were massively simplified, it was just to verify the hunch that charge pipe volume is not a very sensitive factor in the common sizes.
The problem with the first post is velocities are calculated for a given pipe size and flow, which is relatively insignificant. What you want is pressure drop as the main component in sizing the charge pipe. Use the link in my previous post to calculate pressure drop
So basically he says it doesn't matter, use whatever comes along the cheapest or looks the best under your hood.
There are some good books on this subject, quite a long time ago I bought/read Corky Bell's Maximum Boost book, but I have yet to install anything... so if anybody will less potentially bogus info wants to slap me upside the head, I'm good with that..