GT25 and GT28 spool
 

Hello guys!

After reading many threads in this forum about spool data on the several turbos that exist, I became even more confused than I was before. Especially after reading the 'Show us your spool data' thread, I was amazed by the way different configurations on the manifold/dp/exhaust system affect the turbo spooling up.

There doesn't seem to be much info around for the 1.6 engines either!

So I'm thinking I might just go and ask you guys this directly: What kind of spool speed can I expect from a GT25 or GT28 turbo?

I'm going to lay out my expected specs... I expect my turbo to reach around 0.4 BAR (that should be more or less 6 PSI) for now. I will be achieving this with an OBX manifold (got one for crazy cheap, brand new), and home-made downpipe. Probably going for 2.5" for the downpipe section. The exhaust system is a Cybox 2" stainless, and that's gonna have to do for now. Using RX8 450cc injectors and MS1 for fueling.

Lastly, the turbo. I will most likely either be using a GT25 unit off of a CA18DET. If that doesn't work out, I will instead buy a GT28 chinacharger most likely, and upgrade it to a proper unit once if finally kicks the bucket. I've seen these cheap turbos last very long when not pushed to their limits, so that's what I'm going to do.

China-specs on the turbo:
Turbo model Compressor details Turbine details
GT28 GT2860 GT2860-2 a/r 0.42 a/r .64

So, your thoughts on how the turbo will spool? At what RPM can I expect the full boost (6PSI) to be available? And any other thoughts regarding the setup I have thought out?

Cheers, and thank you!

OBX manifold will crack before it spools the first time, this thread is irrelevant.

If you buy a Chinacharger without reading about Braineack's setup first, you are doing it wrong.

Yes yes, I know you guys hate the cheap stuff, and that I should have gone to a cast manifold or one made by someone who understands their business, yada yada...

But that doesn't really answer my questions, does it?

Neither will we.


They have been answered many times before. Stop asking questions and start reading, there is a wealth of knowledge about Chinese turbos on this site. If you would have searched first you would know that.

I mean it's not like Brain even hides his. He loves showing how his $120 Churbo outperforms the real garrets.

It does answer your question. It won't spool at all with a cracked manifold. We do not mind cheap if it is going to work. We mind cheap when we know it will break and you will just have to buy something quality anyway. It is literally just like burning money when you buy an obx manifold.

Maybe you didn't read that part where I did say I have searched... I haven't found the said post about brain's turbo though :hustler:

Still have no idea about how these turbos would perform. I reckon I have a more restrictive exhaust than most people here and that should account for something. And so would the OBX manifold with the primaries being the same size on one side and the other.

About the OBX manifold, it's not like I've spent much on it, so don't fret over it. I don't expect it to last forever. When it does break, I won't be losing my sleep over it either, it was nearly for free! I've read all sorts of different things about it too, there was even a thread around here that mentioned a bunch of people never having any problems with theirs. I bought it second hand for half the price, from someone who just had it laying around. With a target of 6 PSI and almost no expense, I'll take my chances.

https://www.miataturbo.net/diy-turbo...37/#post957509

That took less than 2 minutes.

https://www.miataturbo.net/attachmen...ine=1370009167

Thanks, I did see that thread but there's not really much to learn from it, apart than a GT28 spooling faster than a T3 (which I at least thought was pretty obvious... May be wrong!).

But how fast would the GT28 actually spool? 6 PSI isn't that much, I can see people in the spool data thread hitting 6PSI anywhere from 2500 to 3500RPM. That's a huge band. The sooner the better, so what exactly comes into play there?

No one is going to be able to give you an exact rpm for spool. I can tell you that the larger the diameter of your exhaust the faster it will spool. The better your intake breaths the faster it will spool. If you have an EBC hooked up and tuned properly it will also spool faster. The best way to get faster spool is to swap out your 1.6 for a 1.8 because the 1.6 spools like shit and has no low end. There are too many factors to tell you that your specific setup will make 6psi by xxxx rpms.

Fair enough. That helps a bit! I know you can't really estimate on the expected spool based on just a setup description. What I wanted to really know is which factors play in which way with how the turbo spools.

So thank you! :)

I was actually also hoping that someone had or went through a very similar setup, and share their results. That would be nice!

I have played around with a few homebuilt turbo projects before. This is the first time I'm doing it in a miata. I don't really want to change my engine to a 1.8, I'd rather simply get a smaller turbo... Actually, I don't want one any bigger than I might need!

Still from my last project which used a GT12 on a 1.2 liter engine, a GT28 seems like such a huge leap!

We have several guys running GT3071Rs on 1.8 liters, along with some giant Holsets and there is even talk of 7000 series Borg Warner EFRs. Time to rescale your thought process :party:

This thread makes me sad:facepalm:

OP what you're trying to do is like make shoe polish out of a pile of shit because it's already brown.

Stop being an idiot.

I promise I will, when you start being constructive ;)

There are dozens of dyno plots posted for what you're asking about.

They all vary, because there are hundreds of variables for each car, setup, location, and conditions. If you're asking for anything more specific than a compilation of all posted charts and taking the "average" of each and hypothesizing what you should be seeing from yours, you're an idiot.

The sad part is that in threads like this, everyone is ACTUALLY being constructive by telling n00bs like you that are too stupid and cheap to embrace the truth, that the mistakes they're about to make can be avoided and would save them time and money, and yet you're in complete denial.

We would be COUNTER-CONSTRUCTIVE if we told you to run this terrible setup you're planning to run.

Do you even comprehend what's being relayed to you?

I do. If I choose to go forward with it, it is my responsibility. I find it reasonable to at least try, given the (almost null) cost involved. It's not like I've just started messing around with miatas or other cars yesterday.

You guys really don't have to be dicks about it. This forum would be an awesome forum if 50% of all posts were actually informative and constructive instead of simply treating other people like they're ignorants and not adding up anything new.

It's not like I haven't done my research or know the risks of using the OBX manifold. I've never even asked about it in the first place. My only concern was regarding turbo spool, and which turbo size would suit this engine better.

In fact, if the OBX does break (which I plainly believe will happen, sooner or later), I'll be fabbing up my own manifold. I'm not in the least worried about it.

Few points to make.

1) you talk to much and are a whiney know it all bitch. We aren't your servants.
2) everything I've read from you I've read the Answers to several times over before.
3) if we answered the same questions all the time (as if we don't) then more stupid lazy people would stick around and our forum would look more like cr.net

Go search and stop typing 10 page responses.

I hardly know it all, or I wouldn't be asking... Sorry if that's the idea I got across. I'll just search some more on the subject for now.

CR is awesome by the way :)

looking forward to the, "why did the obx manifold fail thread" but i doubt he will even make it to the installation stage.