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 Post subject: Miata engine turbo help.
PostPosted: February 11, 2013, 7:01 pm 
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Hi all,

I'm looking to do a somewhat mild turbo setup with my 1992 1.6L Miata engine. I would like to run a reliable 7 or 8 pounds, with the potential to boost up to 10 or 12 if I took it drag racing. I'm going to a junkyard in a couple days and (hopefully) picking up a turbo and wastegate from a 1994 Laser RS, or a T3 from a 1997 Volvo 850 T5. I'm sort of leaning towards the DSM because they have a built in wastegate and a good BOV. What do you think? Keeping in mind I am on a junkyard budget.

My other question is what sort of ancillary equipment I would need, such as boost controller, sensors, etc. I also have no idea what to do for an ECU. I've been told I can work with the stock Miata ECU but I don't know how effective that would be. Is Megasquirt turbo capable? What other cheap ish options do I have?

Thanks a ton!

--Eric

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PostPosted: February 11, 2013, 8:23 pm 
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How much power are you looking to make and where in your power band do you want it? Are you looking for big peak power or a much wider powerband (with a lower peak) that can be used in daily driving?

What are you doing for engine management? To be able to take advantage of a turbo, you need to be be able to modify your fuel delivery and, more importantly, you ignition timing. You'll need to be be able to adjust those to meet the characteristics of your engine once its running with boost.

An additional concern may be your fuel delivery system. Can your set-up keep up with the needed fuel flow for your engine? Are the fuel injectors, fuel pump, pressure regulator and other components sized correctly for your needs?

Are you planning on running gasoline (pump or race gas?) or possibly E85? While E85 gives very economical power in turbo applications, it will require roughly 20% more fuel for the same power as gasoline. So again, larger injectors, fuel pump, possibly other fuel system components, etc.

Can you find any data on the engine's volumetric efficiency (VE)? VE determines the volume of air pumped by the engine at a given RPM, and that help determine the correct sizing of the turbo.

Those are some of the questions I usually ask myself before I ever start thinking about which turbo to use. Once you know where you're going in terms of power and other needs, then you can start to think about compressor maps and boost levels to achieve the result you're looking for.

You can just pick a turbo and slap it on, but given the amount of work required and potential costs required to make a non-turbo engine work properly with a turbocharger, it makes sense to do at least a bit of preliminary engineering to make sure your solution at least fits roughly the performance goals you have.

For many engines, there are already home-brew recipes for for various turbos. It might make sense to see what others have done and gain the benefits of their work.

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PostPosted: February 11, 2013, 8:57 pm 
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Location: Boulder, CO
erioshi,

I'm looking to make around 180-190 horsepower reliably, which, by the calculations in "Maximum Boost" by Corky Bell, would be doable with around 8 pounds of boost.

It is going to be a street car, but I will also be using it for all types of racing. I would like to keep the powerband as long as possible for autocross use, but since it is a light car I wouldn't complain much about a little bit peakier of a powerband. I am leaning towards the DSM turbo because supposedly it flows better for longer than the Volvo, and can make more than the boost I want stock.

From research on the topic on Miata forums, it looks like there are a whole lot of plug and play injector options available to me. As for engine management, I really don't know where to start with that. I would like to run normal pump gas as well. I don't want to run E85 but I would be fine running Premium.

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PostPosted: February 11, 2013, 9:09 pm 
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Joined: July 6, 2009, 11:50 pm
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I have a 90 Miata with a 1.6L and am using a Mitsubishi 14b turbo from a Talon. It's definitely not the best turbo. It's old technology, spools rather slowly, but they are cheap, widely available, and make decent power. I got mine as a package with a bunch of other pieced together parts to make a kit so that is why I'm using it (starion front mount intercooler, 550cc injectors, AEM EMS, ect). The cheapest route for supporting mods would be larger injectors (around 550cc/min), megasquirt, and some form of intercooler. The Miata fuel pump, and fuel rail are more than capable for those boost levels so don't worry about that. A wideband O2 sensor is a worthwhile investment as you will have to tune for the turbo and new injectors. At 11psi I made 201whp and at 14psi it put out 229whp.

Image
Image

As you can see the 14b doesn't fully spool until ~4000rpm. One of the fastest spooling junkyard turbos I've seen was a VNT turbo from an early 90's turbo dodge. It spooled by ~2500rpm and made a peak power of ~200whp. http://www.miataturbo.net/dynos-timeshe ... yno-52553/


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PostPosted: February 11, 2013, 9:13 pm 
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Zac,

Wow! That's not nearly as extensive as I thought I would need for that kind of power. What do you use for a Fuel Pressure Regulator? And what injectors are you using? Are they the Supra 550cc injectors or did you go a different route?

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PostPosted: February 11, 2013, 9:20 pm 
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It looks like you have some good information to start with. I'd probably next look to see what most turbo Miata builds use for engine management, and also look into the type of components they are using to hit your goal. It's also worth seeing if that power level requires cams or any other additional components.

The book is a great place to start, but be sure to cross reference your expectations with data from real world builds. Seeing a number of completed and running builds using the recipe you are considering adds some validation to your choices.

It sounds like you're not likely to make this kind of mistake, but I'd caution others against seeing one "exceptional results" type build, and then using that to set their own expectations. Unfortunately many of these "internet super-builds" prove impossible to reproduce when done via home-brew, either because the stated results were "optimistic" or some additional, undisclosed "secret sauce" needed to achieve those results.

It looks like you should have no trouble finding the information you need.

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PostPosted: February 11, 2013, 9:41 pm 
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ThunderHeide wrote:
Zac,

Wow! That's not nearly as extensive as I thought I would need for that kind of power. What do you use for a Fuel Pressure Regulator? And what injectors are you using? Are they the Supra 550cc injectors or did you go a different route?


The fuel pressure regulator is the stock Miata unit. The 550cc injectors i'm using are the redtops from an RX7, but be careful when ordering these because they can come in low impedance or high impedance. You'll want the high impedance ones (10-12 ohms i think) that use the stock Miata injector plugs. There are also some RX7 units that use a different square shaped connector, stay away from those because the injector tips are larger and wont fit in the Miata manifold. There are lots of other factory applications for injectors that will work as well (supra, ect.).

I'm using an AEM EMS for engine management but I wouldn't recommend it. It seems to be temperamental and does strange things every now and then. There also isn't a whole lot of support as not many people are running them. The most common by far, and cheapest, in the turbo Miata community is the megasquirt. You can get plug and play megasquirt units for the Miata and there is a ton of support for it.

The only other real mods I have for the engine are a mandrel bent 2.5" exhaust from the turbo back, into a magnaflow muffler. The engine itself is bone stock and has 250,000km's on it and still going strong.


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