Need help choosing which GT2871 to take (maps included)

[guillermoe]

Hi! I heard this forum was full of KA-T experts so I come to ask them to help me with a difficult choice.

I am about to start a turbo setup for my KA24DE with 200 HP in mind but then I read about the group buy for GT2871's and decided this was too good to be missed so I changed my mind to a 250 HP setup.

Fact is I am a real noob about turbos theory and, even when I have been trying to read and learn, I am not really sure I have learnt enough

Ok, I made some number and placed them over the maps of the turbos which seemed as the best options for me. Can you help me to check them and tell me which one of them would be the best choice... and why.... please?

***Edit*** Whoops... forgot to tell you... red line is for 300 HP, blue for 250 HP and green for 200 HP.

[guillermoe]

Please, I need some help.

[Brandon93240]

I'd go with the last graph myself. The 52 trim and 60 a/r will be more balanced. I wouldn't even consider the 48 trim 70 a/r. The 48/60 wouldn't breath as good on the topend as the 52/60. I am drunk so I may have to reread this later today after I sober up some more.

[Chezedik]

The '76 functions better at lower boost, which is important for a budget build. Boost will be slower, but overall power will be significantly better. But as for most of us, you need to decide which is most important:

Engine life v. response v. total output. For my money it is all about the bigger exhaust wheel. You will get better engine life (from lower boost levels) and better power. If response is more important to you go smaller, but then you need to run higher boost levels to meet your goal (=shorter service life).

[guillermoe]

Engine life v. response v. total output. For my money it is all about the bigger exhaust wheel. You will get better engine life (from lower boost levels) and better power. If response is more important to you go smaller, but then you need to run higher boost levels to meet your goal (=shorter service life).

Thanks for the info Now I have one more question for you.

From what I am learning about turbos I can remember that total power is created by the quantity of air reaching the engine, the A/F ratio and some weird thing called bsfc (sp?). The air flow is created by the quantity of pressurised air existing in the system... the more the pressure more air flows when released right? If this is true, how is it I need to change the boost settings when using different trim turbos to achieve the same power goal? I thought the boost needed for... lets say 300 HP in a KADE... would be always the same... no matter the turbo being used. Hope you could clarifying this to me n00b

[Brandon93240]

So are you completely set on going the t2 route? A straight t3 would yeild better results on the ka and would cost alot less out of pocket. I know you have a goal of around 250 hp, but like everyone else after turboing your ka you will want more power I promise you.

[Chezedik]

Efficiency has a lot to do with that, and the bigger the turbo the more efficient it is, and therefore the air will be cooler upon induction. The pressure has to do with the the ability to increase Volumetric efficiency. If air pressure is doubled, all other things being equal, the engine's capacity doubles. The problem is that all other things are not equal. In the compressor, when you have a lower efficiency the air leaving the nozzle will be hotter, and since the efficiency of your intercooler is expressed as a percentage, it will be hotter, and therefore less dense. This explains why it takes more boost to achieve the same goal on smaller turbos. Also, they tend to have smaller turbines, which will hurt VE by causing the engine trouble in clearing it's charge. So big turbines are important for bigger power too. This is why so many people do not run a T2 turbo, it is just too small for decent power levels in the KA.

[guillermoe]

Aahhh!Thanks Chezedik, now I understand what you mean. It seems you really have good experience with turbos... such things cant be learned with books (at least the ones I am using, which just use perfect state formulas and stable heat processes). Thanks a lot for the info

So are you completely set on going the t2 route? A straight t3 would yeild better results on the ka and would cost alot less out of pocket. I know you have a goal of around 250 hp, but like everyone else after turboing your ka you will want more power I promise you.

Haha.. yes, I suppose you are right. This is my first turbo project and after some research, and based on my power goal (want a drivable, fun car), gt28 seemed the perfect one for me. I still had some doubts so I made this thread to ask for suggestions. Was trying to decide correctly and take part on the GT2871 group buy made by Dieselman.

[Chezedik]

A T3 Super60 would be much more affordable and just as much fun if only for a slightly slower spool. Unless you go with the stg1 .48 turbine, then they are likely similar as a GT28, but will choke up badly.

I would suggest something that is completely off the wall. Spool is good. You need to consider a few things, 1) Spool can help prevent wheel spin. 2) Spool means higher exhaust flow, and eventually higher top end power, which is the end goal in a 4cyl. 3) Spool feels good, even if you don't want to admit it. Spool is like loosing your virginity, it gives you the opportunity to pine over something and have it be amazing (assuming you don't cry afterwards, and end up with a bloody d!ck, HA!). Generally speaking, the longer the spool the better the drool when boost hits.

[AceInhole]

Waiting for spool sucks. The Top Gear video with the Evo getting pulled on by a minivan is priceless (simply because the Evo is too low in the rpm range).

I'm running the 2871R .64 right now. I wanted the .86 housing but was in a rush to get a replacement turbo to make an event (SCCA National Tour).



This was done on my spare head with stock S14 cams. Hopefully it'll breathe a bit better up top with some BC cams and light headwork. I'm debating getting a new housing (the .86A/R) for it as well. In the end, it depends on what you do I guess. I need a responsive setup that gives me power when I want it, which is why I've continued using the smaller turbos.

[guillermoe]

A T3 Super60 would be much more affordable and just as much fun if only for a slightly slower spool. Unless you go with the stg1 .48 turbine, then they are likely similar as a GT28, but will choke up badly.

Dude, tried to forward some question about this to your email but it seems no longer active. Can you give me your actual email plz?

[Chezedik]

Sure, it is Chezedik240 at yahoo dot com.

[Chezedik]

Those are nice numbers from a T2 body at only 14psi. What is the tune?

[sunnys14]

massive tq numbers aceinhole, do you mind telling me what your setup is? stock motor or built?

[AceInhole]

massive tq numbers aceinhole, do you mind telling me what your setup is? stock motor or built?

Stock head (screwed my dual 248 cam setup with an oil starve), rebuilt bottom end with 8.5:1 comp JE pistons, total seal rings. Stock rods and crank.

I ran the copy of my original manifold (that SSAC and others sell all over ebay) after my "original" cracked (as "original" as a modified SR manifold gets) . GT2871R .64 turbo as stated before, ebay O2 housing and downpipe, Greddy EVO TT exhaust (nice and quiet) round out the bolt-ons.

Fuel and timing are controlled by an Emanage Ultimate, with SARD 850cc injectors. Boost is regulated by a Greddy Profec-B.

[sunnys14]

seems like you have a lil bit of power drop off due to the stock s14 cams.

[AceInhole]

seems like you have a lil bit of power drop off due to the stock s14 cams.

It's cams, intake plenum, and I probably could have a more efficient/ better flowing intercooler. I tried getting more aggressive on the timing but it started pinging, so I couldn't get much from there. Fuel, as you can see, is perfect. Steady at 11.4 ± 0.3

I'll be hitting the dyno again with BC V2 cams and either a custom or the Xcessive intake plenum, along with a better IC setup. It won't happen till after October though, when I've finished sorting the chassis (custom lower control arms with more adjustment than necessary ).

[Blue Ka-t]

What is your timing at 4000rpm at 14psi. I plan on running about 16* on 93 octane at 4k then back up to 18* by redline.

Are you datalogging knock through the emu? What frequency do you have the sensor set at, or is it nonresinant?I am running the emu on my ka-t too, Its a good tuning tool with the map sensor.

[Blue Ka-t]

What is your timing at 4000rpm at 14psi. I plan on running about 16* on 93 octane at 4k then back up to 18* by redline.

Are you datalogging knock through the emu? What frequency do you have the sensor set at, or is it nonresinant?I am running the emu on my ka-t too, Its a good tuning tool with the map sensor.

Guillermoe, i would consider a 50trim t3/t04e with a stage 3 wheel and .48a/r exhaust housing. I get full spool (10lbs) by 3200rpm with a .63a/r housing. You would probably get 10lbs at 3000rpm with the smaller housing.

[AceInhole]

I believe I'm running knock as non-resonant. It seems to pick up on noise pretty well. It's really too bad there's no function for pulling timing on knock, though.

My timing was left at something like 12-14(deg) at 4k to 5k(RPM). From there it goes up to about 16deg.

[C-Kwik]

Thanks for the info Now I have one more question for you.

From what I am learning about turbos I can remember that total power is created by the quantity of air reaching the engine, the A/F ratio and some weird thing called bsfc (sp?). The air flow is created by the quantity of pressurised air existing in the system... the more the pressure more air flows when released right? If this is true, how is it I need to change the boost settings when using different trim turbos to achieve the same power goal? I thought the boost needed for... lets say 300 HP in a KADE... would be always the same... no matter the turbo being used. Hope you could clarifying this to me n00b

More pressure only works if the density of the air remains the same. As air gets hotter, it is less dense for a given amount of pressure. In other words, hotter air at the same pressure has less air mass (molecules). There are two major components to making power with a turbo aside from the obvious, which is boost pressure. Efficiency is key.

Based on the operating range where you want the most power, you choose a turbo that best fits along with the necessary boost level you would need to reach your power goal. The efficiency shown in a compressor map has a direct relationship with how aerodynamic the innards of the compressor is under the given parameters (boost and airflow). Better aerodynamics means the turbo heats the air less as it pressurizes it and the less turbine shaft torque is needed to spin the turbo to obtain the desired pressure and flow. For best results in the desired operating range, choose a compressor to match that operating range and then choose a turbine that is most efficient at around the same range. T3/T4's do not fit this description. They are a compromised design where some of the top end turbine efficiency is traded off for the ability to spool up a larger compressor wheel at a lower RPM. It's not a terrible trade off by any means, but depending on your goals, if you want better upper range HP, then a T3/T4 may not be the best choice.

The other side of this is also turbine efficiency. While this is a bit more difficult to plan for, it is important to consider how efficiently a turbine can convert the heat and pressure into mechanical energy. Less efficient turbines will require more pressure and/or heat to spin a given compressor. This generally means you will have more backpressure in order to achieve the pressure differential across the turbine that you need.

Most people will tell yoou that bigger turbos are more efficient. DO NOT follow this rule of thumb. Bigger turbos do generally allow for more power, but even that notion can lead one to a poorly chosen turbo. Most motors can work quite well with a large variety of turbos, but the operating range of the turbo and motor need to be matched for best results.

Large compressors do not handle low airflow conditions as efficiently as smaller turbos. For example, if you had a motor that flowed about 15 lbs/min maximum at 9 psi, and you tried to apply even the touted T04E 50 trim compressor, you'ld barely reach the 74% efficiency island at redline and be below that number at any other RPm below redline. Since you won't reach the 78% efficiency island that turbo offers with such a motor, the peak efficiency won't make any difference. Not to mention that the turbine will probably be way out of efficiency for the amount of airflow going through it. Add to that the larger sized wheels and it will be a slow spooling inefficient turbo.

But, if you look at a T3 46 Trim, you'll find that the peak efficiency island occurs before 15 lbs/min at 9 psi while getting close to the 70% mark at redline. Much of the engine's operation will have crossed through the 74% efficncy island. With smaller wheels, there will be less mass to move and the turbine will likely be operating efficiently where the engine will be seeing boost. The bigger is more efficient theory doesn't work here.

As for which turbo is the best match, the last one shows you are maximizing the use of the peak efficiency island. This would likely give you the most overall power (average power across the powerband). Understand that peak power is not as important as overall power.

[Brandon93240]

I said the same thing just in fewer words, I don't always feel like typing a novel, plus there's a crapload of info across the web that I recommend everyone to read when ur not in the loop about decisions ur trying to make about what equipment to choose.

[C-Kwik]

I said the same thing just in fewer words, I don't always feel like typing a novel, plus there's a crapload of info across the web that I recommend everyone to read when ur not in the loop about decisions ur trying to make about what equipment to choose.

Uhh? Are we competing or something?

[Brandon93240]

Heck yeah, lol.

[Brandon93240]

Just basically stating that I'd already said that in my first post without all the tech. I guess being a mod u have more time to spend on here than some and explain the how's and why's. I do sometimes but not usually.

[guillermoe]

Well, right now I am in that stage where all tech info is welcome. I am sure you all have your own experience and a different story to tell about your turbos and I am willing to read all you have to say. My local crew has been criticing me for not just buying a kit but I really think this is the best way to learn how everything works.

[C-Kwik]

I guess there is nothing wrong with some friendly competition. I think I won though.

Actually, I posted with this kind of detail for years before becoming a mod. Unfortunately, it's a bad thing for me sometimes as I end up spending too much time here. Not that I complain...

[Brandon93240]

Yeah, thats why I never really go to deep, some ******* always trys to out do you(wink wink) or proove you wrong with some bullsh!t they read in StuperStreet. I remember u being on here a while, didn't u have a ninja for ur sig or something? Anywho even though this is ot, what kind of ride are u in again?

[WDRacing]

For the record, NO ONE beats C-Kwik when it comes to turbo tech.

You guys may have "hinted" at what he said...but that is a far leap from actually providing the info.

When Chano posts something, he gives you the theory, then explains it to you. Rather then just saying...do this...cause it's better.

I go to Chano for turbo tech myself and I'm a genius.

IMO the T3/TO4E turbo in 50 trim is simply THE only option that should be used if price and range are being considered. The only real decision is whether to get a .48 AR or .63 AR exhaust housing. Since you're not looking for a lot of power from the get go, the .48 would be a better choice and it still allows for growth. The .63 will lag more, but it will give you a better chance to increase the boost once you catch the boost bug.

You guys must remember that boost is like Heroin...a little is great at the beginning, but you'll be cranking it up within 6 months So plan ahead and you'll save yourself a lot of money and hassle.

WD

[Brandon93240]

We're just having some friendly fun, well atleast I am, I'm sure he is also. I don't get online forums alot, when I started in cars the internet didn't even exist yet, same as u Wd ur 32ish right? I'm a few years older than you. But for the record I do have alot of turbo experience. I worked for Conley's for a few years and I was also on the project team With Mr. Kent who turbo'd the first TNT Viper hear in Houston so I have been around the block a time or two. But for the most part I'm a man of few words. But thats why Ckwik is an asset of a mod. I don't have the desire to explain things indepth and its good that he does and or enjoys it.