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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 02-29-2012, 02:06 PM   #1
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Default Somebody School Me In Turbos Please

ok so i've decided to try my hand at building a diy turbo kit. i know i could just order a begi or fm kit and have done with it... but where's the fun in that?

i've read the great big diy sticky more times than i care to count, and i'm part way though maxmium boost. but i still have some questions.

my biggest question is how do i figure out what turbo i want to use?!

which i can break down in to three subquestions.
  • First: What's the difference between the types of bearings? (Journal, Wet Float, Ball, ect)
  • Second: Internal or External Waste Gate? which is better and why?
  • Third: What do all these numbers mean in the real world?
    • Compressor trim: .60 ar
    • Compressor Wheel diameter: 47.20 /60.00mm
    • Turbine wheel diameter : 46.32 / 52.95mm
    • Exhaust trim: .86ar

for the record i'm building a
  • 1990 1.6L
  • intercooled
  • water/meth injection
  • diymspnp 2.0 (speed density & wideband o2)
  • enthusa dual racer turbo exhaust
  • shooting for 200whp

and yes yes i know the stock diff will probably cut loose at some point. i'll burn that bridge when i get there.
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Old 02-29-2012, 02:25 PM   #2
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1. journal = wet float; these are just your typical brass sleeve with tiny holes that oil can pass through and lubricate the walls on which the trubine shaft will ride.

ball bearings; prett ymuch the same things as a pilot beraing or what you'd put in your rollerblades.

2. ewg is better; flow/control.

3. compressor a/r in teh real world means dick. dont even worry about it.

looks like you're looking at a t28 turbo?

Last edited by Braineack; 02-29-2012 at 03:34 PM.
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Old 02-29-2012, 02:37 PM   #3
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Like Braineack said. Ball bearings provide less frictional losses of power than journal bearing turbos. Less contact surface. Journal bearing turbos are less expensive, ball bearing turbos have a faster response time than journal bearing turbos, generally anyway.

Also check out Garrett's website. They have a turbo size calculator based on your engine/hp specs. I thought it was pretty useful considering when you put in the miata specifications it gives you the same turbo that FM provides in their kits, if that means anything at all. Might be able to get you in the ballpark for your desired turbo size.

Last edited by cwall424; 02-29-2012 at 02:48 PM.
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Old 02-29-2012, 02:41 PM   #4
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Originally Posted by offsprg01 View Post
Second: Internal or External Waste Gate? which is better and why?
It depends on your application. For ~200whp, an internal wastegate is going to be plenty efficient and more cost effective. However, an external wastegate is better overall because it flows better than an internal wastegate reducing the risk of overboosting, and its more reliable overall, but it is more expensive.

From my personal experience, if you do decide to get an internally gated turbo, make sure you get a downpipe that actually allows the internal wastegate flapper to open all the way. I would highly recommend ARTech for all your manifold/exhaust related needs. I would not recommend a BEGI-s downpipe. That is what I originally had and it was a pain. I wish I got my downpipe from ARTech first.
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Old 02-29-2012, 04:28 PM   #5
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alright so looks like i'll end up with a journal bearing t25 or t28 turbo then. as it seems to be fairly cheep and fits the bill for my engine size and power output according to garrett's website.

however i can't seem to find one that is NOT internally waste gated. is there a way to block off the internal gate so you can use and adjustable external gate to make for easier tuning? the only external wastegated t25's i found were oil cool only. i really want oil and water for reliability concerns.

also when looking at spooling times which numbers from question three help reduce lag? i'd assume the trim numbers are what i'd be looking at, particularly on the exhaust side. but then again i could be wrong.

bah never mind on the numbers thing i guess. just reread braineack's post, apparently they really don't matter so much.

@palmtree do you have any contact info for artech? a quick google search showed up a window tint company in our area. is that them?
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Old 02-29-2012, 04:36 PM   #6
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For your goals, my SR20 turbo would be perfect for your application. PM me for details.
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Old 02-29-2012, 04:39 PM   #7
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Quote:
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For your goals, my SR20 turbo would be perfect for your application. PM me for details.
Why is it that every time I check a post in here, I see you posting this most of the time in threads Thirdgen?
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Old 02-29-2012, 04:50 PM   #8
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Quote:
Originally Posted by offsprg01 View Post
however i can't seem to find one that is NOT internally waste gated. is there a way to block off the internal gate so you can use and adjustable external gate to make for easier tuning? the only external wastegated t25's i found were oil cool only. i really want oil and water for reliability concerns.
You do not need an external wastegate for a T25. While external gates can provide a more precise control, they really don't start making sense in a Miata until you get into the GT2860+ and approaching 300whp. The additional cost of a manifold and the external wastegate itself makes it not cost effective in the 200whp range. You will be completely fine with an internally gated T25.

For your goal, I highly suggest a used Garrett T25 from a Nissan SR20det motor. They are plentiful and cheap, and are good for up to about 15psi, which even with a conservative spark map, will get you to 200whp no problem on a 1.6.

For your budget, I'd also recommend a set of used RX7 injectors and an FM Stage1 Clutch. Water injection is a bit of overkill for you build... can't hurt, but your money is better spent elsewhere at this point.

You also need to fill in your signature with sumthin, and add your location to your profile.
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Old 02-29-2012, 04:52 PM   #9
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Lol. It seems like every Newb lately has the same goals and wants the same turbo. I just throw mine out there as an option. Perhaps a for sale add would be better.
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Old 02-29-2012, 05:16 PM   #10
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i can't ever seem to remember to put the info in my sig on any forum i'm on. i put a link to the site we are posting all the build logs to on the car.

so far we have
stage III clutch and 8lbs fly wheel
all new suspension (fm-vmaxx and poly bushings, hard on the kidneys but handles great)
stock brakes with ss lines hawk hp+ pads

various other non performance related crap.

the goal here is a budget built hotrod as this drive train will not stay in the car permanently. we'll be finding a new home for it after we swap in the v8. (more than likely in a locost build) for now i really want to learn how to tune FI cars as i have never done so. everything i've built has been NA. so that's the reason for wanting the water injection, and adjustable waste gate. i know they are both overkill for 200hp. i just want to tinker with them to learn how it all works.

first step is to convert the engine to megasquirt. once i learn how that works then we're going to start throwing turbo parts at the car.

so if we stay with an internal waste gate can something like

http://www.grimmspeed.com/catalog/index.php?cPath=151

be used to control the waste gate?
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Old 02-29-2012, 05:27 PM   #11
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bah never mind on the numbers thing i guess. just reread braineack's post, apparently they really don't matter so much.

the compressor a/r doesnt matter. everything else ABSOLUTELY 100% matters and are very important. I can tell by your numbers you are listing of a t28 sized turbo is all; a GT2860 if you will.
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Old 02-29-2012, 05:41 PM   #12
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@palmtree do you have any contact info for artech? a quick google search showed up a window tint company in our area. is that them?
Just PM him on the forum.

https://www.miataturbo.net/artech-fabrication-miata-accessories-79/

His lead times are pretty lengthy. But his product is more than worth the wait.
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Old 02-29-2012, 05:45 PM   #13
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ah i stand corrected. and i just cut and pasted those numbers from some where on the internet. i've already forgotten where. i just kept seeing similar number pop up and had no clue what the ar number meant.

so i guess my original question is still valid then.
  • Compressor trim: .60 ar <-- this mean dick
  • Compressor Wheel diameter: 47.20 /60.00mm <-- what does changing these numbers do?
  • Turbine wheel diameter : 46.32 / 52.95mm<-- what does changing these numbers do?
  • Exhaust trim: .86ar<-- what does changing this number do?

so we we say up the diameter of the compressor wheel what happens?
if we do the opposite what is the result?

same thing for the turbine and exhaust trim.

sorry if these are stupid questions. i'm sure corky explains them in maximum boost, but i guess i haven't gotten there yet.


oh and one other thing. is there a specific ratio to look at that provides faster spooling over max boost? again sorry if these are dumb questions but i've not built a turbo car before.
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Old 02-29-2012, 06:58 PM   #14
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Old 02-29-2012, 07:06 PM   #15
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exactly what i was looking for!!!!!!
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Old 02-29-2012, 08:40 PM   #16
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once you read through we can discuss how it pertains to a miata engine.
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Old 03-01-2012, 12:53 AM   #17
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so after reading braineack's link and a another chapter in corky's book. i think i may have over boosted my brain...

so correct me if i'm wrong but i think for my application (200whp 1.6l) i'm looking for a turbo with a smaller turbine ar (area/radius of housing) to help make boost in the lower rpm band since a small turbine ar will spool faster.

Compressor A/R: doesn't matter according to garret and braineack
Compressor Wheel diameters: face size / base size (larger diff between numbers flows more air)
Turbine wheel diameters: face size / base size (larger diff between numbers flows more air)
Exhaust A/R: between .60 - .70 should be the range for a 1.6l from what i gather

so am i getting close? or am i way off base?
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Old 03-01-2012, 01:59 AM   #18
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Don't over think it, turbo knowledge will come with time. It's one of those things you learn by doing, at least for me it was.

Find out what turbos will give you your 200hp on your 1.6, and get one, don't worry about what the specs are. An SR20 T25, Greddy TD-04, etc. Find one of those and buy it. Thirdgen and I both have one available and there's SR20 T25s all over the place for $100ish dollars that just need a $80 rebuild.

Never helps to read the tech articles mind you, but don't freak out too much.
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Old 03-01-2012, 09:47 AM   #19
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Quote:
Originally Posted by offsprg01 View Post
Compressor A/R: doesn't matter according to garret and braineack
Compressor Wheel diameters: face size / base size (larger diff between numbers flows more air)
Turbine wheel diameters: face size / base size (larger diff between numbers flows more air)
Exhaust A/R: between .60 - .70 should be the range for a 1.6l from what i gather

so am i getting close? or am i way off base?
I think you have the general idea.


as for A/R, it depends on the footprint as it's a relationship to area and radius, where the t3 footprint has a much larger area than hte t25. Therefore, a .48 A/R (which I use) would be the same as a .63 A/R on a T25.

A .63 A/R T3 housing, on my car, would spool like ---- but increase my topend potential significantly.
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Old 03-03-2012, 01:52 AM   #20
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@curly i'm not really overthinking it, i'm just doing my home work and trying to understand exactly what's going on. i have specific goals for this power train and a very limited budget to do it in. i also only have one chance to get it right since the 1.6l will be getting pulled out for the v8 swap within a year.

ok so now for the parts list. just trying to make sure i haven't forgotten any thing.

still need to figure out where i get the studs to mount the turbo...

i apologize in advance for all the ebay links. some of these products will come from other sources. i just used ebay to get an estimate of the total.

total looks like right at $2000 with everything i've listed plus a little padding for extras that are bound to pop up. so call it an even $2200.

so that leaves me with 2 questions:
  • did i miss anything?
  • and will some one please talk me out of jumping on the ms3 bandwagon and saving a couple of c notes?
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