diesel11679

OK. Author Corky Bell in "Maximum Boost: Designing, Testing and Installing Turbocharging Systems" says to keep the air velocity below mach 0.4.

3" diameter pipe has a cross sectional area of 7.07 square inches. Let’s say the speed of sound is about 1100 feet per second. Mach 0.4 = 440 ft/sec = 5280 inches/second.

At this flow rate (5280 inches per second), you are flowing a volume of about 5280*7.07 = 37322.21 cubic inches / second = 21.60 cubic feet/second = 1295.91 CFM. 3” diameter pipe should flow 1295.91 CFM maximum under “maximum” boost.

The density of air is about 0.073 lb/cubic foot, so 1295.91 CFM = about 94.60 lb/minute.

If you are running at about 14.7:1 AFR, then you would require about 6.44 lb of fuel per minute, or 386.40 lb/hour.

If you assume 0.6 lb/hr/BHP fuel requirement for a turbocharged engine, that means you have enough air to make about 644 BHP?

I know air density is subject to change with temperature and elevation, but is this calculation any bit realistic? I’m not sure but I thought 3” plumbing would flow enough air for more horsepower than that? 644 BHP isn't much on a 20B? Does that mean I need bigger than 3" plumbing? With this calculation 2.5" piping would only flow enough for 447 BHP, which still seems low to me.

Sojin

Well the piping dose not make to much of a diff the speed in the pipe will change for the amount need just helps flow 3 would be good but what u want is a turbo that can back it up

diesel11679

Good point, a good turbo like a GT42 should back that up. Turbo would just cause increase in velocity of air since crosssectional area of tubing remains constant. Breaking the velocity suggested by Corky, but allowing enough airflow to allow higher hp. Thanks.

killalot13601

iTrader: (5)

It does make a difference, in terms of velocity. If course you can make more power out of 2.5 but then ur exceeding mach .4 which is what Corky Bell says is not optimum. If you can get 3 or bigger then that is you're best bet. 2.5 is small, Im basing most of my reply off what U posted, I actualy learned a bit from it and really need to pick that book up.

How I would figure the size see what percent of an increase 2.75 is over 2.75 and increase ur BHP by that much and u should get what u are looking for? I really am not to sure just trying to help.

Evil Aviator

Turbocharged? At what point in your calculations did you increase the air pressure?

Let me know if you have any specific questions. You are all over the ballpark, and it's difficult for me to follow.

No

diesel11679

Figure out the % difference in area using the piping diameters 2 1/2" and 2 3/4" THEORETICALLY, you should be able to see that much increase in bhp AS LONG AS your fuel system can supply that much more and your turbo can maintain the same velocity through the bigger pipes (which will in turn flow more CFM just due to the larger crosssectional area of the larger pipe)

toplessFC3Sman

iTrader: (1)

You dont seem to be accounting for the amount of boost you're planning on running. The calculations you're using have the density of air at atmospheric pressure (14.7 psi). If you are planning on running 15 lbs of boost, then the density will approximately double.

0.074 [lbs/ft^3] * (14.7 [lbs/in^2] + amount of boost [lbs/in^2])/14.7 [lbs/in^2] = the density that you should be using. The power will be quite a bit more if you account for the increase in density due to pressure.

arghx

iTrader: (3)

Any time you are doing custom turbo setup stuff, it's good to both use a calculator AND just see what other people are running. I have the Greddy 3 row kit. It is 2 1/4" piping coming from the turbo to the hot side of the intecooler, then 2 3/4" from the cold side of the intercooler to the TB elbow. The intercooler measures ~ 26" x 12" x 3" with 2 3/4" end tanks. I am running 18psi of boost on this setup (60-1 T04S turbo). No dyno numbers yet but I expect 400whp.

diesel11679

I've talked to a couple people with the GT42R since this thread started. Everyone who is putting 750hp down or expects to put 750hp down at the wheels is running 4" piping. Which makes since with my calculations (4" would flow more than enough to support 1000hp), however GT42R is only rated up to1000bhp (from Garrett's website) Figure 25% to 20% drivetrain loss and your looking at 750-800hp at the wheels. Thanks for everyones input on this though.

arghx

iTrader: (3)

you need to look in the single turbo subforum. turbos tend to make less power on rotary's than on piston applications.

diesel11679

Where did you come up with that anyway? There might be an fuel efficiency issue but rotary engines move more air than their piston counterparts...? Rotaries spool up turbo's faster...

arghx

iTrader: (3)

Let me clarify. A given turbo generally makes less horsepower on a rotary than a piston engine. Since you are into calculators, the rough guideline is that on a piston engine you will get about 10whp per lb/min of air give or take a little bit. On a rotary it's closer to 7.5 lb/min (multiply by 14.27 if you want to think about it in CFM). Rotary's also need big hotsides compared to their piston counterparts I think because of the port overlap.

Just look at the turbo kits out there. The smallest one HKS used to sell for the 7 was a T04E. That's good for probably 400whp on a 4 cylinder. You're not gonna get that on a rotary. A 60-1 T04S turbo is also really common and will make 450-500whp on a piston engine, but is going to peak around 400whp on a rotary (generally speaking, depends on manifold, porting, tuning, etc). Put a GT35R on an Evo and get ~500+ whp. Put it on a 13B and you're closer to 400. Think about how big the stock turbo is on an FC and how little power it really can do. 250whp max and that's only holding 6-7psi to redline... if it were possible to put that on a 4 cylinder it would go over 300whp easy I think. Compare it to an Evo III 16G turbo which is of similar size (actually the hotside is smaller) and can do over 300 to the wheels on a DSM.

More people can chime in on this and I probably didn't do the best job of explaining it fully (because I don't understand all the little reasons), but there is a reason why people put the same turbos on 13B's than they do on Supras and often make less power.