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Old 10-18-2008, 01:24 PM   #1 (permalink)
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Default GT25 a good choice?

i've been looking at the GT series a lot lately, as i'd like to boost my project but don't want to deal with lag. so i'm wondering if the gt25r is a good choice, because it seems to be the same thing as a gt28r (when comparing gt2554r and gt2854r.) i know the gt28 has a t25 turbine housing but if the compressor sizes are the same does this mean they're the same turbo for all intents and purposes?

i used the compressor map reading for dummies thread to map the smallest gt25r for my 1.5L engine and this is what resulted:



so i intend to harvest 16psi and it seems the max flow for my engine would lead to about 240hp, but it's still in a pretty good efficiency range. so my question about that is: will an intercooler be necessary?

the CR would be 7.8:1, so quite low, and i'm hoping for 220whp. according to the cfm per rpm calculator, the turbo could be spooled at 2500rpm which is great, but i don't want to risk extending spool time with a shitload of piping just to cool the air if it's not necessary to reach that goal.

Help?
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Old 10-18-2008, 01:55 PM   #2 (permalink)
 
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at that psi, i think youll have to, in fact i think that if you pass mora than 5psi youl need an intercooler, besides with an intercooler youl be just extending spoll by 500rpm as much.
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Old 10-18-2008, 01:56 PM   #3 (permalink)
 
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also what engine do you have?
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Old 10-18-2008, 11:00 PM   #4 (permalink)
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d15 block, d16 head
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Old 10-19-2008, 01:52 AM   #5 (permalink)
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I would put a small fmic on there. You can make a backdoor entry to minimize piping length. Colder intake temps are always good.
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Old 10-19-2008, 02:02 AM   #6 (permalink)
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I think you will get compressor surge unless you messed up on the formula.. what you put your VE , max rpm at?
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Old 10-19-2008, 09:45 AM   #7 (permalink)
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Originally Posted by steinar View Post
I would put a small fmic on there. You can make a backdoor entry to minimize piping length. Colder intake temps are always good.
yeah i've seen those on the side-mounts but nobody seems to sell them... i guess a small side-mount next to the rad might work, but if the turbo is in peak efficiency for most of the powerband will it even heat the air up enough for an i/c to be practical?

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Originally Posted by es01civy
I think you will get compressor surge unless you messed up on the formula.. what you put your VE , max rpm at?
the calculated VE came out as 90 and i set max rpm at 7000
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Old 10-19-2008, 12:38 PM   #8 (permalink)
 
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Read this book from HPBooks HONDA/ACURA engine performance buy Mike Kojima you might re think running the T25 if your planning on running that high of boost I would run a T3 or T3/T4 hybrid if I was planning on any thing over 200 HP.
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Old 10-19-2008, 12:52 PM   #9 (permalink)
 
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^Never mined that last post just looked at the gt series I was thinking old factory t25 from like an eclipse or something
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Old 10-19-2008, 01:09 PM   #10 (permalink)
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should be a great turbo for fast spool and decent power, the low end torque will be nice.
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Old 10-19-2008, 01:13 PM   #11 (permalink)
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Make sure you have a reliable BOV at those pressures. make sure your connections on the charge piping is tight as hell too, (hairspray blowdryer method).
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Old 10-22-2008, 05:54 AM   #12 (permalink)
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Quote:
Originally Posted by dan15b View Post
yeah i've seen those on the side-mounts but nobody seems to sell them... i guess a small side-mount next to the rad might work, but if the turbo is in peak efficiency for most of the powerband will it even heat the air up enough for an i/c to be practical?

You can just use a normal fmic and take it to a place that can weld aluminium. It takes 10-15 minutes and wont cost you much Just make sure to fill your engine mounts ore get some reinforced ones, sot the engine doesnt move too much...



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Last edited by steinar; 10-22-2008 at 05:57 AM.
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Old 10-22-2008, 06:01 AM   #13 (permalink)
 
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Radiator shops will do intercoolers for you. What is the old driver's side inlet used for now steinar?
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Old 10-22-2008, 07:18 AM   #14 (permalink)
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Its welded shut with a 4mm plate. If you spot my intercooler from the front it looks like I'm running a fake one
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Last edited by steinar; 10-22-2008 at 07:20 AM.
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Old 10-22-2008, 07:20 AM   #15 (permalink)
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Quote:
Originally Posted by danz View Post
I just typed this up, and dont want it to get lost. Sorry if u mentioned this already rrussell but its good for noobs to read twice anyways!!

Calculating Air Flow;

CFM = L x rpm x VE x PR / 5660

where;
L is engine capacity in L (1.6)
rpm is desired engine speed (lets say redline at 7400)
VE is engine volumetric efficiency; our d series being very efficient stock, use 95% here.
PR is pressure ratio (Pr = Bp + Ap / Ap)
Bp = boost pressure, Ap = absolute pressure.

remember, the atmosphere puts 14.7psi of pressure on us at sea level. so boost pressure (lets say you run 7psi) plus absolute pressure divided by absolute pressure gives us the pressure ratio. example:
Pr = 7 + 14.7 / 14.7
Pr = 1.48

CFM = 1.6 x 7400 x 95 x 1.48 / 5660
CFM = 294.12 at 7400 RPM

to convert CFM to Lb/Min (which most compressor maps are in) multiply your CFM by 0.07.

And now you know!

to give a bit more background on volumetric efficiency

when you have a 1.6L engine, and it breathes exactly 1.6L of air in its intake, you are at 100% volumetric efficiency. Our cross flow motors do a good job of this from the factory. some might even say they flow closer to 100% VE.

and one more thing... when you are looking at the compressor maps you will see a "surge line"

you must stay to the right of the surge line!!

to find out if your turbo will stay out of surge...

divide your Lb/Min by 50%, and by 25%. plot the 50% value at the same PR you plan to run the turbo at, and plot the 25% value at 0 PR (the bottom of the graph). connect the two dots with a line. if that line crosses the surge limit, or comes close, choose a turbo slightly smaller.

Source;
Forced Induction Performance Tuning - A.Graham Bell, amazon.com
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Old 10-22-2008, 07:57 AM   #16 (permalink)
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Quote:
Originally Posted by steinar View Post
You can just use a normal fmic and take it to a place that can weld aluminium. It takes 10-15 minutes and wont cost you much Just make sure to fill your engine mounts ore get some reinforced ones, sot the engine doesnt move too much...



WOW plastic zip ties on exhaust heat wrap.... that is the best fail post i seen all week.
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Old 10-22-2008, 11:13 AM   #17 (permalink)
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WOW plastic zip ties on exhaust heat wrap.... that is the best fail post i seen all week.

LOL! Yeah, well... Its not actually exhaust wrap, its something I found at work for shielding wires I think. Anyway I dont remember why I even put it there, cause its really not needed... And the zip ties still lives!

Nice find, though
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Old 10-23-2008, 01:54 AM   #18 (permalink)
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^^

Wow, another fail post... I thought you were talking about the oil feed line...

The zip ties on the exhaust manifold were temporary of course. I ran of steel clamps and wanted to wrap the manifold before I mounted it, so I did it that way. They were replaced before startup
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Old 10-24-2008, 06:50 AM   #19 (permalink)
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thanks guys, some great info. lovin the header wrap steinar, was it a pain in the ass to wrap the log?
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Old 10-24-2008, 07:48 AM   #20 (permalink)
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No, not at all. Taking it off and putting it back on after the manifold cracked was worse, the stuff is itching... lol
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