mx5-kiwi

A bit of preliminary investigation and advice on turbo's please. Current project is to dry sump but after that we want to push for more power.

not sure if race car or turbo section is best here...race car thread tends to have more experienced answers, please move if better suited elsewhere

It is possible we are discussing two issues here.....bare with me.

We are running the Garret Gt2860rs and looking at the Garret page the boost map seems to be quite low (lower than I had previously thought)...Do you think it is right or do they have the wrong map showing?

https://www.garrettmotion.com/racing...urbo/gt2860rs/


As I say, I was under the impression that the 2860rs was suitable to 400-450? not the 350 they suggest and certainly not by the boost map they reference..?

Reason for asking is that after the recent tune to 20 psi and new water meth kit (peak of 344 HP atw and 330 ft lbs) we are seeing torque peaks at 5400 and HP at 5700.

Once again, I would have thought the turbo would carry through higher than that m(could easily be mistaking with 0 experience at this level). I appreciate that the head and other factors affect this (our head is flowed to 600+hp) but standard valves and cams. forged pistons (8.8:1 from memory).

The tuner says he thinks it is likely the cams causing the drop off...

Once we get the dry sump sorted we want to push the boost up towards 24-26 psi and judging by the current published Garret map we are already at the end of the 2860's limits.

So, suggestions sought for,

- hanging on to the power longer in the rev range.

- Is it likely the cams are a limitation at this point?

- do we need a new turbo as per Garrets current listed specs and if so is the EFR 6758 the answer for our goals?

Edit: It appears my knowledge of the 2860rs is well out of date and wrong. Other questions re cams, turbo upgrade etc still valid (I think...).

i.e Is the additional cost of the EFR valid if the boost below 4000rpm is barely significant...?

(Presumably the next step up in garrett is cheaper than the EFR (if you see where im coming from?)

codrus

Perhaps you're thinking of the GTX2860 instead of the GT2860? The GTX turbos used the same turbine but got a new compressor section that significantly bumped up the flow at higher boost numbers.

--Ian

sixshooter

iTrader: (12)

The EFR will be better everywhere. I run a gtx2867r but know it's limited.

You left out a lot of details on your setup. Which head? Which intake manifold? Which exhaust manifold? What diameter exhaust? What lifters? What AR is the exhaust housing? Intercooler size? Intercooler piping diameter?

344whp is a lot for any Miata trans. It won't survive on the track at that level. K Miata BMW transmission swap would serve you well.

nitrodann

So long as torque is kept below 320 or so ft lb and the clutch is sensible with a driver who isnt extremely hard on the gear, we have proven time and time again that this is not true.

2c

Dann

mx5-kiwi

Thanks for replies, I appreciate this is all a bit vague.....just hoping for a bit of direction and to flesh things out a bit.

I especially updated my Signature with this prior to posting, is it showing up?

99 head, ported and flowed to 600+hp. Solid lifters, Kraken manifold, 2.5" DP and exhaust with no cat or muffler only a 20" resonator, flat top intake, standard Gt2860rs turbo..not sure of AR etc other than that. something i hadn't thought of though....2" in to intercooler and 2.5" out. Intercooler is double the common size (approx 12" high).

Nitrodann - I am pretty gentle on gear but blew a standard 6 speed and a strengthened one in subsequent meetings at approx 280 WHP. Hampton Downs has a rise that you exit corner up rise changing from 3rd to 4th and bam both times same place about 40 meters after gear change (peak torque). First one was in damp conditions (possibly related to in and out of traction/wet patches)

6 speeds here are now $1200 each...the K-miata swap was hellishly expensive with exchange rate, freight etc but we just couldn't afford to keep going through 6 speeds any more.

Very pleased with kit but would MUCH prefer it came with a lighter flywheel (FYI).

sixshooter

iTrader: (12)

My 6 speed failed at just over 300whp on the track. Mode of failure was separated 4th gears (pressed together gears became un-pressed). It was about 60 degrees F ambient.

Now I have BMW 6 speed.

Goingnowherefast

iTrader: (1)

With all due respect, one of the biggest gains (regardless of turbo choice) should be a full 3" downpipe ASAP. That alone will remove a large bottleneck.

As for the original question, I would recommend an EFR 6758 or 7163 (running low boost) for your application. The transient response and boost control alone will yield massive gains. Compressor maps only tell part of the story. Again, with either of these setups I cannot stress enough the importance of a v-banded 3" catless downpipe and exhaust. Backpressure is the enemy.

Savington

iTrader: (31)

lol

mx5-kiwi

Thank you, yes that is our next move. I have a 3" DP on Back Order with Kraken already. Hoping to see that early February.

What advantages do you see with the EFR at similar boost levels to the 2860?

- Presumably 20lbs boost on each turbo will provide the same power...? but at reduced temps maybe?


- Do you race guys run a muffler or resonator setup? Seems like a silly question BUT our engine is VERY quiet and could easily run with straight through (no muffler/resonator) at the moment.

Also, our exhaust points down at the ground, is there any thought on this causing any issue...I often wonder if it could cause back pressure issues as we (miata's) are so low. Or even slight lift...340 hp at 7000 rpm HAS to be a lot of air....again probably a bit silly

Just one of things that never got changed from the 1600 days when noise was more an issue..

Goingnowherefast

iTrader: (1)

Nice. That alone will provide a large benefit in spool time, response and power.

A good amount to unpack here so let's go through the theory...

PSI (bar) is simply the pressure per unit area that the air molecules exert. The kinetic energy of air is proportional to the temperature. Sizing your turbocharger correctly to stay inside it's efficiency range is integral to sizing a turbocharger. Thus in the simplest terms, it is comparatively "easier" to produce 20 PSI of less dense air on a smaller turbocharger than it is on a larger unit that's moving denser air. (Note density = mass/volume of air in this case).

Nerd talk over, let's breakdown what this means:

1. In general, a larger turbocharger will move the same amount of airflow with less heat. (See compressor maps)
2. The same "larger" turbocharger will produce less backpressure on the turbine side of the turbocharger.
3. The less backpressure you have on the exhaust side (also why I recommend a 3" exhaust), the more air can be moved through the engine (which is simply an air pump) at a given boost pressure.

Results?

What this means is that you have cooler air entering the engine and less backpressure. Thus, in this example an EFR 7163 will produce more power at say 20 psi than a GT2860 and I'm willing to bet a case of beer and my engineering degree on that.

sixshooter

iTrader: (12)

Additionally, the more efficient compressor of the same diameter will have less loss of energy to heat, yielding a denser charge and making better use of the energy (horsepower) provided by the turbine's efforts. You want the energy captured from the exhaust to be as efficiently turned to lbs of airflow as possible. Some turbos have better designed housings, turbine wheel shapes, turbine wheel materials, bearings, compressor wheels, compressor wheel materials, and so on. The nuances become big differences when the boost goes up. But what I'm saying is very general. I'll let others speak to the details.

mx5-kiwi

I never factored boost pressure and effort to drive etc. Thank you. EFR much higher on the "next parts" list now.

So, upgrade path from here.

Dry Sump.
Upgrade to 3" DP and exhaust.
EFR 6758

On a slightly differerent tack...at what point do the OEM cams or valve sizes become a limiting factor?

at 340 whp are getting close?

emilio700

iTrader: (3)

Your data point seems to be the sole inhabitant of the post 300lb survivor category. No one else has gotten close to that. An hour or two total d/c street driving at that level perhaps, but certainly not a full year of competition (30+ hours).
That your torque rating comes with the caveat that is must be driven with significant mechanical empathy either means you aren't racing it or you imply that no one else knows how to drive their Miatas like you do. In either case, that caveat renders the data point moot. don't you think?
What I read is exactly what you wrote, if you are exceedingly careful, you can get it to stay together at absolutely no more than 310lbs. I suspect you are right but ain't nobody got time for that "careful" shenanigans

We all want a close ratio 5 or 6spd that will survive maybe 2 years of race level pounding at 400 lbs. That same hypothetical box would last forever at 300 lbs no matter how hard yo tried to break it. The AZ6 with it oh so tender aluminum shift forks is not that transmission.

emilio700

iTrader: (3)

You didn't mention what your specific power goal was. EFR6258 will make 440whp on a build engine on E85. Ours with a BP6D head, stock cams had a powerband that extended to about 7800rpm then fell off gradually, 32psi. Cams would extend that but the peak whp wouldn't change much. That's dictated by peak CFM from the compressor. I don't recommend cams frankly. Just build a good head. BP6D has huge oiling issues, The tiny bit of blowby is handled by the catch can/separator just fine. The oil dumped into the head by the VVT system overwhelms any PCV we could dream up so the dry sump is the right call there. If you had not planned on it, I recommend the BP6D head. The gains in spool and low end are huge. Enough so that even in w2w and qualifying laps you can reduce the number of shifts, still needing to modulate thruttle off slow turns even in 4th gear. A BP05 or BP4W simply won;t spool the same way.

Full whammy BP6D build on 110 octane race gas fed by an EFR6758 should make something like 525~550whp. You need a lot of tire and aero to use that much oomph. That leads me to steer you towaqrds the "smaller" EFR 6258 for the little bit of response gain.

nitrodann

The gearbox doesnt care what your horsepower is, it only cares about the peak torque load it is expected to see.
I dont tune my customers cars such that they have a peak torque, I tune them to have a flat torque curve from the lowest rpm possible to redline, therefor there is no peak.

The hardest driven ones we have have had the PPF replaced with a gearbox crossmember and diff mount in an effort to keep the torque loading on the gearbox case as low as possible. We also have a hell of a lot of 300ftlb cars used as street/weekend warriors doing track days reliably with these numbers. They all use a nice sensible clutch and have held together. I know they don't all last forever but I believe that for the price of a used 6 speed the longevity of these cars gearboxes is acceptable considering the use. And it's certainly not a twice a year gearbox replacement in the cases of these cars, racecars included.

I do believe that having a flat torque curve rather than an aggressive one helps, and I do believe that solid engine mounts and gearbox crossmember are significant factors in reducing the torque load on the gearbox case and therefor keeping the gears together. I also believe that you cannot quantify mechanical sympathy, and that statements like 'I dont want to be nice to it, its a racecar' are fine, im just saying that these people are not tearing the gear selector out of the box and they are releasing the clutch in a timely manner without holding the throttle pinned and dumping the clutch. I know people that can break anything in 5 minutes because they are extremely hard on the gear, and in that case I believe that a 6 speed isnt the right gearbox for even 200ftlb.

Im not interested in arguing about it, Im only interested in giving my experience.

Dann

k24madness

iTrader: (6)

Savington

iTrader: (31)

+1

mx5-kiwi

"I would consider selling the current setup and replace it with Trackspeed EFR. You’ll be MUCH better off in the long run."

Yep working on this. Thanks for the clarification everyone.

mx5-kiwi

EFR 6758 on its way from a local supplier. Sadly, despite trying to always support the Miata community (and I do buy almost all large items from either Trackspeed or 949/Supermiata) the landed cost with the poor exchange rate, freight and customs tax meant it was going to be over $1k nz more if I bought from overseas. (sorry Andrew :( )

Now just waiting for the new Kraken 3" v band downpipe.

I dont know how I missed it but found the dyno sheet thread last night. That answered / explained a few of my questions above as well. So once again, thanks for all the advice (and the 1 minus cat *******!).

I'll hopefully show a before and after dyno sheet comparison in that thread in the next few months. Now to sort out the dry sump.....(and try and find more funds!!)

Goingnowherefast

iTrader: (1)

I will literally send you a case of some great US beer if you don't pick up 20+ whp on the same boost.