DrTurbo

I'm currently running an 8psi WG spring with no boost control. Haven't had time to tune for higher boost. My setup makes full boost (8psi) by 3000 rpm. Keep in mind that this is a custom 1-off I designed while I was at Garrett. Unfortunately, this combination of parts in not generally available. Its a ball bearing turbo and has a divided turbine housing which really helps with boost response, especially on a rotary when combined with my HKS divided exhaust manifold. This turbo will also support more than 18psi at high efficiency. I designed my system for road course duty so spool up from low rpm wasn't a big concern for me. Still, full boost at 3000 rpm is very streetable and only ~500 rpm later than the stock twins. Plus, I'm making 50 more rwhp than stock at 4psi less boost. My backpressures and EGTs are way down which makes for a much more reliable system. That was my main goal for a track setup that regularly sees 20-40 minute sessions at full load.

patsmx5

iTrader: (16)

So is my GT3271 a good size turbo for my 1.8? From what I can tell, it's efficient to 23 PSI. I bought it because I wanted to go to 300whp from the begining and after building a motor sit around 350whp. I'm around 270 right now. It's not the fastest spooling turbo, but the power is nice.

That turbo setup you posted is badass. What paint is that on the charge pipes? Makes them look cast.

EDIT: And why is my turbo called a GT3271 instead of a GT3278? It's a .78 hotside divided turbine.

DrTurbo

What makes a "good size" turbo is somewhat dependent on your goals. My 1.3L rotary breathes like a 2.6L piston engine so it is much bigger than your 1.8. Turbo selection is often a compromise between top end power (max flow capacity) and boost response. You should choose your turbo size based on what is the most important to you. There is also the important issue of properly matching the compressor to the turbine. This is very important in achieving the maximum possible efficiency from both wheels. From there, it gets pretty technical so I won't get into it. My guess is that you could have made your power targets with a 3071 and potentially achieved better spool up but it is impossible to say for sure without doing the design calcs. Anyway, it sounds like you are doing pretty well with what you have.

With regards to your GT turbo nomenclature question, the reason your turbo is called a GT3271 is because it has a 71mm compressor wheel. The GT32 identifies the turbine size and the 71 identifies the compressor size. The wheel trims and housing ARs are not indicated in the designation.

There is no paint on any of my aluminum hardware. It is all bead-blasted. That is what give it the dull mat finish look. You have to be really careful when handling it though. If you get oil or dirt on the mat surface, its really hard to clean.

DrTurbo

Thanks to everyone for the warm welcome. I've been scouring the forum for the past 2 days straight gathering info and trying to learn as much as I can from what people have been doing. I think I'm ready to start making decisions and gathering parts from my own turbo build. I have lots of questions and want to get as much advice/input as I can as I go. My last question for this de-noobing thread is - where is the best place to put my pre-planning/build thread. Here is a little background:

I'm starting with a 99 NB with a completely stock drive train. The car has already seen extensive track time (~10k miles). It's a fantastic track car just as Mazda built it but, as everyone who has a Miata knows, its HP challenged. The goal is ~200rwhp with a focus on durability and thermal management for road course track duty. The car will regularly see 40 minute sessions at full load on the high desert tracks of SoCal. I already have a brand new Garrett GT2560R that has been sitting in a box in my garage for 7 years waiting for this moment.

Rafa

iTrader: (22)

My suggestion would be in the "Builds" Sub-section of the "Media" Section but you could also do it in the "DIY Turbo" Section.

The_Pipefather

iTrader: (5)

Dear Dr. Turbo,

Can you please point me to SAE papers or other technical publications on CAC sizing and the relative merits of bar-plate vs. tube-fin CACs? I personally think the latter is better for a street-driven or auto-x vehicle where low lag is important. I have searched the SAE database and found none. Does garrett not publish at least some of their findings?

Thanks.

DrTurbo

Unfortunately, I don't have much for you. I used a bar-plate Garrett cooler in my Rx7 because it was readily available. I think the Garrett cores are all bare-plate but I am not sure. I used the internal CAC design code to select the fin sets and do the heat transfer calcs. As far as pro-cons go, the tube-fin is definitely lighter which has its obvious advantages. A heavy front mount gives a big polar moment penalty. A bar-plate core has higher thermal mass and would take longer to heat soak giving some advantage for short duration performance like autocross or drag runs.

DrTurbo

For anyone who is interested, I started a thread on my build plan here:

https://www.miataturbo.net/forum/t31289/