May the Miata gods and Keith help me!

Hello folks,

I'm probably committing a MiataTurbo sin here but I'm at a bit of a cross roads. At the moment I have a lovely 02 Miata with roughly 58k on the clock. As of right now I have a good bit of modification for autocross and its dual-hatting as a daily. This will change before boost happens, but make no mistake, this will still have some daily love from time to time. At the moment I am piecing together my turbo kit and have acquired the following items:

Rebuilt SR20 T25G (T25 with a 80 compressor housing. For those giving psi/torque this is JB turbo a little bit larger than a GT2554R according to my reading. I am aware this could be a rod killer in the low end)

Kraken Full Kit with 3" turbo back exhaust (The name does not represent the quality, its a beauty. Besides the exhaust, I will for sure be intercooled and am considering e85 for added safety, though I wouldn't mind 91 friendly numbers). 

My goals for now are 210-250whp with a reliable non-block killing level of torque. What I need clarification on is  what size injectors I need and what level of torque will help me enjoy my setup for years to come as I build an engine for something greater (or at least giving this turbo all it can take!). I want to say RX8's blue tops (540cc) but I feel like it might be worth me looking at something EV14 higher than 700cc as I do hope to run e85 as a measure of cooling (Vegas heat scares me). I'm already set on a MS3 Basic from Rev given the VVT as well as a tune by one of the local recommended tuners. My second problem is I don't know what torque and horsepower rating to request with respects to reliably running this engine in the local heat. To clarify, I wont be autocrossing during our 120 degree days, but I will be driving it to work from time to time to enjoy the car. When things cool down, I'll for sure be autocrossing the car, with thoughts of tracking not distant in my mind. 

Please forgive the wordy post. I love to research, but I've become stuck search for answers to these questions and see that you folks are a bit more informative.

I'm no expert on boost, but I've been doing some research as our NA may head down that path in the future.

AIUI, torque is what kills the rods; and 230-250 wheel torque is the limit, depending on use, and your level of mechanical empathy.  At around the same level the 5 speed trans becomes a consumable.  I would expect that 200-220 at the wheels will be plenty entertaining, at least for a while.  220whp is the cap for the S1 Supermiata class, and this is achieved with a spec turbo setup that is capable of well over 300hp, so tuning for your goals is certainly realistic.

ID1000s seem to be the injector of choice these days if you're even considering E85.  And no need to upgrade down the road with a boost ready short block.

I would be tempted to stick with one of DiY's PnP MS3 or Pro offerings for the stateside support.

Heat management is more an issue of properly setting up your cooling system than the actual HP level, though you are, obviously, developing more heat at higher levels.  The formula is pretty well figured out at this point:  good radiator, re-route, good ducting and sealing.  The more serious track cars are also using an oil cooler.  Some searching on MT.net will turn up all the details.

If that turbo is the size of a 2554, you're going to be limited to roughly 230 rwhp. It'll choke off the top end, not kill your rods down low. It's also going to run hotter than a bigger turbo at the same power level - that's one reason the S1 Supermiatas run such a big turbo, also the sizing of the BBR ND turbo setup. That will determine the size of injector you need. IIRC you can feed that with 440cc injectors, then add about 50% of you'll be running E85. The EV14s will help you maintain good idle with 700s.

Don't forget good fans for your cooling. It's not the trendy answer on some of the track-biased forums, but street cars aren't trendy and street cars need fans. That's going to do a lot more for you than ducting and sealing will. You've stayed away from FM parts so far, but nobody else on the market has a fan setup that comes close. You need a good shroud and high-torque motors (aka, non slimline). I don't usually call out specific competitor products, but Mishimoto fans are a considerable downgrade from stock.

Cooling doesn't matter for autox as the runs aren't long enough to tax the system.

Keith Tanner said:

If that turbo is the size of a 2554, you're going to be limited to roughly 230 rwhp. It'll choke off the top end, not kill your rods down low. It's also going to run hotter than a bigger turbo at the same power level - that's one reason the S1 Supermiatas run such a big turbo, also the sizing of the BBR ND turbo setup. That will determine the size of injector you need. IIRC you can feed that with 440cc injectors, then add about 50% of you'll be running E85. The EV14s will help you maintain good idle with 700s.

....

Keith, first off thank you for replying. As for the power capability of the turbo I suspected I would be lower in the range and that wont be an issue. This set up is to get my toes wet and learn the in's & out's of a non-factory turbocharged car. Injector wise I would love some head room and it sounds like 700+ EV14's will fit the bill. I had a suspicion earlier I would be running too much if I looked at 700-1000cc injectors, but from what I hear its not like the olden days where higher injectors meant pig rich high idles.

Cooling has become a topic of research of mine lately. I'm aware that stock radiator is prone to cracking and rather small in design and have since looked at other methods. I know the be all answer is FM for the radiator and fans, I'm curious what the answer is for a mostly fun street car with some autocross on a budget. I was almost set on an FM radiator with the stock fans set in parallel before your reply, and now I'm intrigued.

Also though the turbo kit is mostly DIY, quite a few other parts on my car are FM and I'm thankful for the quality ;) On the subject of the turbo, I'm aware it will run hotter and thats the part I've been researching cooling options on (primarily contemplating e85-flex or methanol injection). I'm confused as I thought the smaller turbine would push a good bit of torque in the low end, making rod strength a concern. The turbo choice was for availability, easy of rebuild, and a good all around fun turbo before I get serious, hopefully I choose the right turbo.

In reply to Rodan :

Thank you for pointing me towards the 1000's on injectors. I've scoured MT to find some of these answer but I seems to get loss in the discussions sometimes. I'll look more into cooling to get some info as well as see what Keith says to get an idea of my needed and possible cooling options.

My street car is a mostly fun street car with some autocross, and I don't even remember what radiator it has. I think it's an old-school aluminum race rad, not a crossflow. It does have the Airflow kit, that solved overheating problems on the highway.

I know it does have the 2554, though. Feels snappy, but definitely suffers at the top end compared to the 2560 and we have to pull a bunch of timing out of it.  The small turbos feel like they have more torque because of the shape of the curve, but in reality they're actually making a bit less torque than the 2560s. It's just that the 2560 keeps going so the bottom end feels weak by comparison.

I know we've got a 2554 vs 2560 dyno chart somewhere but I can't find it.

Injector choice is going to depend a lot on your budget.  RX8 540s should get the job done on gasoline, but will be close to maxed out using the stock non-referenced fuel pressure regulator.  If you're willing to spend a bit more and get some room for growth, then the ID1000s are a great choice (personally I don't see any reason to buy 750s).

You might want to consider fuel pumps & regulators.  The stock pump is OK at 200 rwhp, 250 it's a bit more marginal.  Upgrading the pump, however, leads to it likely overwhelming the stock regulator at idle, so the scope expands rapidly.  Pretty soon you've got FM's big fuel kit with -6 AN lines everywhere.  BTDT. :)

As far as driving it to work in the heat, I wouldn't worry too much about that.  The MS3 will compensate for high intake air temps by retarding the timing, and you can always just not drive it as hard. :)  One of the nice things about turbos is that with electronic boost control you can have different boost levels with the same hardware.  There's a table of boost targets that's set up with throttle position on one axis, so you can have it not deliver full boost until you go WOT, this really helps with drivability.

Keith Tanner said:

My street car is a mostly fun street car with some autocross, and I don't even remember what radiator it has. I think it's an old-school aluminum race rad, not a crossflow. It does have the Airflow kit, that solved overheating problems on the highway.

.....

 

I can see the short comings for sure, and was originally headed towards a 2560, but settled on the T25G given its ease of availability, ease of rebuild, and with the journal bearings I was hoping the spool would move a little bit upwards to great a solid midrange.  I also felt like it was a good safe turbo given the dyno sheets I've seen torque wise, being I didn't know what would be considered safe torque at the time.

Let me know what you think, here are the specs I typically find for the T25G (SR20 Red Top):

Compressor Trim 60
Compressor Inducer (mm) 43.3
Compressor Major (mm) 56
Housing A/R 0.80

Turbine Trim 62
Turbine Major (mm) 53.8
Turbine Exducer (mm) 41.7
Housing A/R 0.64

For comparison: GT2554R and GT2560R .

Let me know what your thoughts are as it seems to find itself almost exactly on the middle of the two. I dont mind less torque then similar turbos, I just want enough to have fun and enjoy it at the AutoX now. Once I build a spare VVT engine and have learned enough I'll look at larger turbos to consider.

codrus said:

Injector choice is going to depend a lot on your budget.  RX8 540s should get the job done on gasoline, but will be close to maxed out using the stock non-referenced fuel pressure regulator.  If you're willing to spend a bit more and get some room for growth, then the ID1000s are a great choice (personally I don't see any reason to buy 750s)

.....

Thank you, given what Keith has said about the EV14's and what I'm finding for pricing, I'm think a 1000cc injector is a better choice. The local tuner is capable of getting the FIC1000+ injectors for $400 with adapters and harness adapters.  I might have to look further into those and see.  Luckily as well I'll for sure be adding electronic boost control as a measure of tuning. when you say not deliver full boost do you mean like a boost by RPM/Throttle setup that varies based on input? I've seen this done when I had my previous VW's and it was always intriguing to see a proper means to vary the power. 

The 2554 is fun for sure. There's a reason it's still on my street car. But mostly it's the feel of fun, the dyno sheets tell a different story.

All turbos have boost by throttle :) Don't want full boost? Don't press on the pedal all the way.

In reply to Keith Tanner :

May I ask what your dyno sheet says for horsepower and torque? Also is this on a stock engine?

With a 2.5" exhaust and 91 octane fuel, my PEAK numbers are 210 hp and 212 ft-lbs. That's one point on each of two curves, not a description of the entire curve.

Stock MSM (aka 1999) engine. Hydra ECU.

In reply to Keith Tanner :

Sounds very respectable. I'd be ecstatic to be at that numbers starting off. Hopefully, my 3" exhaust and VVT help me with achieving that or more.

The VVT doesn't really do anything for peak power in our experience. The 3" might help, but I suspect the turbo is the larger restriction. If peak power is your goal, start with a different turbo. If you want a fun street car that's not a dyno queen, you're going in the right direction. Your higher compression will hurt peak power but will make it spool nice and quickly.

In reply to Keith Tanner :

Peak power is definitely not my goal. Right now its to learn and modify without feeling like a criminal (something I ran into with my VW's). Fun street car I can drive, autox then drive home. Correct if I'm wrong but hopefully my tuner can work some magic with the timing and fuel to offset the lower boost I'll be running given my compression ratio. This isn't a bother as I'll likely be building another engine on the side in the following year for a larger turbo, once I'm better versed on the aspects of turboing the miata.

Keep in mind that your horsepower figures may be higher than Keith's due to his altitude of 4600 feet in Grand Junction, CO.

In reply to kb58 :

That is a good point. I myself am from the Springs and despite being stationed in random other places (Vegas at the moment) I always think I'm fighting altitude for power. 

... while noting that turbos are somewhat self-compensating for altitude. That is, higher altitude means less resistance is seen by the compressor due to the thinner air, so it spins faster. Similarly, higher altitude means there's less back pressure on the exhaust, again allowing it to spin faster. It's not 100% self-compensating, but does work in your favor to some extent. Much more so than a supercharged car, for sure.

The results of altitude are generally slower spool and a bit more backpressure - more than the change in ambient pressure. The latter only becomes noticeable if you're running a smaller turbo and you start to fall off the island. So between a slightly larger turbo and your 2000' altitude (if memory serves) you may not see the power taper off up top quite as much.

The higher compression ratio means you'll make more power at a given boost/timing level, but ultimately it will hurt you as you won't be able to run as much timing or boost before you get into detonation. So it's great for response, not as good for peak numbers. These are physical limits, "good tuners" still have to work within them. But for a fun street car, it's the way to go. Don't obsess over power numbers, which is so easy to do. Obsess over response and engine safety, then drive and enjoy. Tell everyone it makes 400 hp because it doesn't matter.

High compression plus E85, now THAT is a fun combo.

In reply to Keith Tanner :

Numbers aren't important to me anymore. I'm honestly frustrated with the numbers game thanks to my VW's. Right now I just want a light quick/fast/fun car I can toss around and enjoy. I've had a miata before and I fell back in love with the power to weight ratio. This time I'm looking forward to boost as it will be a new experience in a sub 3000 pound car. I feel like 200-250 will be enough to keep me grinning while I build a spare engine and learn that neck of the woods. Also good memory on that altitude. Now how about our difference in heat?

In the past few hours I've looked up a few radiators and I'm curious if your stage 1 and 2 fan kit will fit a stock or a replacement like the CSF radiator? I love the cross flow setup you have, but I'm falling for the two rows and fitment of the CSF given a local autocross wonderkindt showed me his. It looks like the mounting points are the same as stock.

Keith Tanner said:

All turbos have boost by throttle :) Don't want full boost? Don't press on the pedal all the way.

Maybe up in CO, but down here where we've actually got air, my Miata would happily make full boost at 50% throttle.  It wouldn't quite make full power due to pumping losses, but it would hit the target map.

By TPS-based boost control I mean that your target MAP depends on throttle position.  7 psi at 40% throttle, 10 psi at 60%, 13 psi at 80%, 16 psi at 100%, stuff like that.  It's a huge help for linearizing the throttle response on a turbo car, IME.

In reply to codrus :

I might have to look at this and consider it for my autocross map. I was originally looking at boost by rpm or boost by gear, but this sounds like a more well rounded approach.

In reply to s0n1cm0nk3y :

The one thing I didn’t notice is any effort spent on your piston rings.  The stock end gaps will probably butt together under the added heat of boost. 

Metal expands when hot. Throw more heat into the cylinder to make more horsepower and the rings will expand  to the point where the stock ring gaps will close up and then force the piston tops off.  

With High miles you might get away without opening up the ring gaps but I doubt 58,000 miles is enough. Others with a lot of Miata experience should chime in here

Nothing to worry about, the internals will handle this easily. 

I tend to think of the throttle as a torque request. I've never needed to play games with the boost control to get the torque I want when I want it. What it actually says on the boost gauge doesn't matter, what matters is what's going to the tires.

Keith Tanner said:

Nothing to worry about, the internals will handle this easily. 

I tend to think of the throttle as a torque request. I've never needed to play games with the boost control to get the torque I want when I want it. What it actually says on the boost gauge doesn't matter, what matters is what's going to the tires.

I agree with the desirability of the torque request model, that's the goal.  Non-TPS boost control can't achieve this on a turbo car because the throttle plate only influences the engine's VE, while airflow (and thus, to a rough approximation, torque) depends on both VE and on MAP.  By allowing throttle position to drive MAP as well as VE you get closer to an ideal linear torque response.  This more boost you run, the more this matters.

A few years ago I switched control systems from one that didn't support this to one that did, and was very surprised at the difference.   My brain had adapted to the response of the non-TPS system so I had some re-learning to do, but once that was done the car was easier to control.