Turbo choice for TT4 - ~220whp??
 

So, 10 years into this Miata thing the chassis is ready, cage is built, and we've got lots of track time N/A under our belts. Time for some power, and I'm looking for some advice on turbo choice. Car is a VVT swapped NA running on MS3, primarly just for HPDE fun, but I'm also interested in running NASA TT4 or similar TT classes. I expect 220-225 whp to do the trick.

No big HP goals down the road, been there, done that with fast cars and $$$$ costs. Already have a Kraken T25 manifold/downpipe and intercooler core in hand. Also have a spare VVT engine, and have been collecting parts for an engine build, but hoping to run the current motor for at least a year .

Now I know the best answer is probably K swap, and I've seriously considered it but the additional cost and install time would push this back at least another year.

I'm looking primarily at GT2560R and GT2554R, both are tried/true Miata turbos. Is there any reason to go with a GT2554R over the GT2560R on a track car that is unlikely to ever be under 3500rpm on track? Some old threads praise the GT2554R for anything under 230whp, but that was 10-15 years ago, and a lot has changed since then. I know the current trend is "EFR all the things", but with my power goals an EFR seems like overkill, costs almost double what the GT turbos cost, and would require buying another manifold/downpipe.

Are there other (T25 pattern) turbos I should be considering?

I would look at both the gtx2860 and 2863. They are certainly more capable than your target, but will also require less wastegate and lower manifold pressure to hold 220hp. If you truly are always over 3500, the 2554 and 2560 lose their advantages.

Edit: VVT will provide very little advantage there as well, and is quite a bit more complicated. BP4W would be my advice.

Thanks, I'll take a look at those.

VVT engine has been in the car for a few years, and I've got another one under the bench. I'm kind of committed... ;)

A GBC22-350 might be worth trying out when they come out in a few weeks.

I was discussing turbo sizes for a turbo race car yesterday. His thought is that a larger turbo makes the car easier to drive. A slightly slower spool up might be the difference smoothly laying down power and laying rubber coming out of a corner. I've already got a EFR6258 (GTLC at ~200whp), but we discussed GT28XX turbos as an alternative.

TT4 alright alright alright. :party:

If you're going with the more budget friendly Garrett (still awesome turbos as well), you'll be sitting right in the fat part of the compressor efficiency island with a GT2560r for that power level. I tried to find dyno plots for the GT2860r but the only one I found made like 280whp at 12.5 PSI on a BP4W on the larger .86a/r turbine housing. Maybe a .64a/r housing on the GT2860r would be good but when you're down around the 8 to 10 PSI mark I'm guessing to keep it around 225whp, and you start to fall into the bottom of the compressor map and that size turbo would really like to be running a bit harder in order to be more efficient. The larger turbo is going to stress the engine a bit less though, and should have lower compressor outlet temps so you'd be dumping less heat into your radiator via the intercooler, I just wish someone had some lower boost plots of it to see how it does. Your perfect turbo size is unfortunately in between the 2560 and the 2860...

Of the ones mentioned, for 220 rwhp a 2560 would be my choice. The 2860 hurts spool and while you may never be below the boost threshold that still means it's a bit lazier on the transient throttle response even at higher revs. My Miata has a GTX2863R in it and the difference in response between it and the 2560 that it replaced is noticeable.

My TT4 car doesn't have a turbo of any kind in it, though. :)

--Ian

:D I looked hard at the K swap, but it would take me at least a year longer to get there... and have you seen prices on K24Z3 engines lately?


That's kind of where I'm at... most of the info available are builds looking to get max power, not trying to be efficient at 220whp.

Seems like the answer keeps coming up 2560...

Quick look at Car-Part says they're up to $600 to $800 range now. Geez. They used to be available for $400 all day, but honestly they are still cheap. Good Miata engines are going for the same price or more, and if you end up doing a basic refresh and rods/bearings you're already WAY over the price of the K. The big appeal to me was dirt cheap repair cost in the event of catastrophic failure, just drop in another junkyard motor and be on my way instead of potentially trashing a built Miata engine that cost 4k+ to put together.

I don't blame you for going the turbo route either though, it's still a good way to do it especially since you're already kind of set up for it.

Let me ask a few more people tomorrow about the turbo size and I'll reply again.

if these are affordable that gets my vote, but if it's within ~$300 of an efr 6258 I don't see a reason not to upgrade to ceramic ball bearings over the journal (or go back to the 2560r tried and true). The GBC22-300 might actually be more efficient for your application looking at the compressor map.

On Co-Part they were $900-1200...

Should be about the same price as a GT turbo, and the compressor map looks great, but I wonder what it gives up with journal bearings?

I would go with a 2554, Plenty of headroom at that power level and throttle response is unbeatable compared to what is mentioned here.
And you would benefit from a functioning vvt.

VVT is working, and has been since the car was swapped 4 years ago.

Thanks all, for the info and input.

Okay, GT2560r, final answer lol.

Yup. :D

https://live.staticflickr.com/65535/...c3568fb0_c.jpg

Excellent. There's going to be some good competition forming for TT4 and ST4 for next season for sure. Yourself and @yuba with the turbo Miatas and we can see how it stacks up against a K swap. I also know of like 4 or 5 other people that are currently building for that class as well. BMW's both E36 and E46, Honda Civic, maybe an S2k or two.

The only other thing the car still needs is suspension bushings, and I'm on SadFab's waiting list for a set. I'm also collecting parts to beef up the shortblock on my spare VVT engine, but I'm hoping the current engine will survive the low boost for the first year.

That's a pretty turbo, glad it got to you quickly.

Curious to see your dyno once you're done. :) Happy to see another TT4 car out there.

When I was tuned at UMS they showed me what the Evo10/VVT motor that Austin ran in nationals years ago made and said it was on the verge of spitting its guts out down low. I made something like 248 wheel torque at like 3500 or 3700 being conservative on their dyno and the VVT/Evo build came on like 500rpm earlier.

220whp says you're also going to be on 100tw, which makes me happy since I'm unwilling to pay for purple tires. I've been considering adding power to run TT3 for contingency since 4 is dead this year.

Who knows, mabe ill show up to an AZ region ST4 race to play with you guys. I need more turbo miata competition ;).

I'm going to pretty conservative to try to preserve the stock internals on the current engine... 248tq at 3500 would probably put me in a panic... :p

I need to get everything installed so I can weigh the car and figure out my target ave. HP. My engineering "WAG" is ~218-220, but I haven't weighed the car since I built the cage, so there's a LOT of estimating at this point. I've been running Toyo RRs, and am planning to stick with them. Not the fastest, but have been a good balance of grip and longevity. Hoosiers are not in the plan. LOL.

Current goal is to have the car ready for the October NASA event at AMP.

Make it happen captain. We usually have an event at Chuckwalla in February each year that has good turnout because it's a SoCal crossover. That would be a good one to maybe put on your calendar.

I think a lot of ST4/TT4 guys are going to be running Toyo RR as well. They have the best contingency now and they are cheaper and last longer than Hoosiers. I'll most likely be on RR's and I think there's a good chance a kind of "gentleman's agreement" for the class might emerge where we all just run RR's. They have sizes to fit everyone.

We could consistently have 7+ people running in ST4 if it gains enough steam... and the other thing that happens when a class gets going is that it gets easier to draw more people out of the woodwork in or convince them to build up to it.


List of cars I know in AZ that are either eligible caged racecars or currently being built:

Turbo Miata
Turbo Miata (Building)
K24 Miata (Building)
E36 M3
E36 M3
E46 Sedan (Building)
E46 M3 (Building)
350z
Subaru BRZ
Mini Cooper S
EK Civic (Building)
CRX Civic
S2000
Infiniti G20


If just half of those show up that's a class of 7 in race group and maybe some super sizing into TT as well.

The Maxxis contingency is better than Toyo since it pays out 1, 2, and 3 if there are 5 in class. Toyo only pays out to first if there are 5, so if you're slumming it on non-hoosiers and aren't able to win you can still pick one up.

I've run the Toyos a few times this year, but I am going back to the Maxxises rather than juggle tires depending on the landscape.

Just to be clear, so I don't raise any false expectations, my plans are for TT only. The additional risk/reward of W2W just doesn't pencil out for what I want out of track work at this point in my life.

I wouldn't worry about it, I'm also not really interested in W2W right now either. We only have one ST4 car running events locally right now - a first-year in a BRZ. The Mini-S mentioned prior only runs ST the first few events of the year to meet the minimum event count to run nationals.

I'm not sure which S2000 Arca is talking about, but if it is the yellow one it is going to be running TT1-3, depending on contingency. It is a turbo car with three settings between 275whp and 475whp and the owner already races SM.

The mini would run more races if there were people to race. There's also a 350z that has run locally a bit that I talked to. The S2000 is blue from socal but they run with NASA AZ for some reason, not talking about the yellow one.

Same here. I'm hoping I'll be able to go down later this year.