EO2K

iTrader: (37)

All torque all the time. Modulate it with your foot. Problem solved.

18psi

iTrader: (76)

He's too painfully ignorant to realize that 99% of the cars on the road are driven below 4k 99% of the time and not everyone drives 10/10ths on their way to the grocery store.
Or that part throttle boost in the upper gears at low rpm/high load is delicious in a street car, its what just about everyone wants, as evidenced by every automaker under the sun building more and more tiny turbo cars.
Why not run a 7163? Or a 9180? I mean we all want 800whp from 6-7k right?

I love a 6258, but let's not be silly and say that a smaller snail isn't even desirable for some people.

acedeuce802

iTrader: (1)

Agreed with this. There is a huge different in the way the power band feels between OEM systems and systems that are sized for #allofit. Spooling at 3000 rpm is fine for performance because you're always above that if you're in the correct gear, but getting the torque curve to be low, instant, and smooth is a totally different feeling. Some desire that feeling, and don't want the rush of torque increase between 2500 and 3500 rpm.

Savington

iTrader: (31)

So wrong it hurts, dude. Nobody here is suggesting full torque at 2500rpm is a good thing (mostly because we disposed of techsalvager a long time ago). What you fail to realize is that most people on this forum don't have 300+whp turbo cars. Most people have a stock engine and want to make 220 or 230whp.

If you take a big turbo that isn't being used to its potential and go smaller, there are a huge number of benefits. You get a little more torque down low, you lose nothing up top, and your throttle response/linearity improves dramatically.

Vincentmiata

We want 1000rpm full torque all the way to the redline

EDIT: and about 600whp

18psi

iTrader: (76)

I would even settle for this

Vincentmiata

But without the supercharger whine

18psi

iTrader: (76)

There's no supercharger on the car with that plot

Leafy

iTrader: (1)

Its just got 4 extra cylinders.

18psi

iTrader: (76)

6. But who's counting

Vincentmiata

Looking at the torque and HP i would say a Viper with a little tune

18psi

iTrader: (76)

Correct you are.

I'd also settle for this




In a miata

Vincentmiata

only 819whp?

nbfather

I keep telling my son about the awesome sauce of just being able to grunt away in 5th or 6th gear or drop a gear or two and be able to have big power everywhere at every rpm...

Unfortunately the allure of the big HP is strong! He comes by that honestly!

I had him look at your torque/hp and comparing it to the few dyno graphs I could find on the 6758....It doesn't look like the 6758 has more horsepower until 6000rpm or so.
From there the torque is in the expensive part snapping range....
I may have seen a light go on.

So how do you perfect your build?
If someone gave you $5000.00 and said go spend this on your current motor (can't spend it elsewhere)...What would you change?

Jamie

nbfather

Savington,
Not sure where your post went, but I appreciate you taking the time to explain how turbos work....I am already there....How everything else works with the Miata engine...I am just starting to learn
I have looked at every dyno curve I could find on both turbos....Not just one.
I haven't bothered reading the compressor maps, because of the built in air flow issues of the Miata power plant...I figured I was better off reading dyno graphs and replicate a proven build then venture off into the unknown.

18psi mentioned there was at least 350hp on tap with his EFR 6258 built (I heard enough air to support 350hp)...Which was why I asked the question...That and if he could, how would he move the power around.
Once a turbo reaches the end of its flow map there is no more power to be made...I understand that.

Not trying to frustrate you, rather trying to sort out which way to point my horsepower hungry son....Who is too inexperienced to realize there is more to a build than a big horsepower number.
FWIW my son has a reading comprehension disability....Which is why I am here figuring out the Miata rats nest on his behalf.
I do appreciate you taking the time to point out the error of my thoughts! I am learning as fast as I can!
Thanks again!

Jamie

Savington

iTrader: (31)

OK, I re-re-read and the points I made here were valid. I thought for a moment that you (Jamie) were comparing the 6758 to a Viper engine, which made my argument pointless and silly, but it seems the point is worth making after all.

This belies a fundamental misconception of how a turbocharger alters the powerband of an engine. Turbochargers move air based on turbine speed and pressure ratio. Engine RPM has very, very little to do with it (for our purposes, we can say it has nothing to do with it). If you are operating the turbocharger in an area of its compressor map that it's happy with, it will continue to chuck out that mass of air irregardless of engine speed.

Let's take a hypothetical example to show how this works. We have an EFR6258 on a built longblock with a stock '99 head. That turbo will happily produce enough airflow to make a flat 300whp from 6000rpm to 7000rpm, but no more than that. (hypothetically.)

Now let's fully port the cylinder head so that it moves more air given the same cam profile. Torque increases across the board, as does power. The same 300whp that used to be from 6000 to 7000rpm now occurs from 5500 to 6500rpm. Same power = same airflow requirement. Past 6500, the turbo runs out of breath, and suddenly you see a power drop at high RPM, even though nothing else has changed.

Add a set of camshafts which improve breathing again, and the problem gets worse.

You cannot look at a single dyno chart and infer what a turbocharger is capable of doing. You need to have a broader understanding of the engine and its capabilities. In this specific case, your assumption that the 6758 "doesn't make more power until 6000rpm" won't hold up if you look at enough charts comparing the two. All else equal (RPM, boost, etc), the 6758 will make more power at every RPM. The 7163 will make more power at every RPM than the 6758 will.

With turbo selection, there is some give and take, but it's not as extreme as you think it is in this case. In general, when going bigger, you give up a small amount of low-end power and response in exchange for power gains everywhere else. The biggest difference between a 6258 and a 6758 is in the response, IMO (I've driven both extensively in the same setup). There are probably some small torque differences under 3000rpm, but north of that, the 6758 is king.

Replicating a proven build is one of two ways to build a great car. I highly encourage going that route. The other route involves an awful lot of time and money figuring it out yourself

shuiend

iTrader: (24)

90% of the time I'm driving my turbo car is on the street to and from work. I want torque from 2000 to 4500rpms because that is where I spend most of my time on the street. It's hard to hit 7000rpms in stop and go traffic.

18psi

iTrader: (76)

On that car, to me the powerband is perfect, and it felt fantastic. I likely wouldn't move anything around at all. It's great for street, track, you name it.

However, if I didn't have a built engine, and wasn't planning to make over 300, I'd probably get me the even smaller EFR and enjoy even more lowend thrust and snappier response (if that's even possible, lol, the 6258 already shines at both those things.....we shall see of course).

Chilicharger665

iTrader: (2)

AFAIK, 99mx5 is making 375 whp and 319 tq on his 6258. Did he switch to a 6758 when I wasn't looking?

nbfather

Now that I am off the pain pills and wine (not a great combo) because of a double root canal and a nasty sinus infection....My brain should work a little better!
I see I said some interesting things!
Feeling like an idiot!

I read 99MX5's build front to back. What a great build!
He nuked a stock block with 10PSI boost on a 6258....I didn't know that was a thing until then!!
Did some digging around and it sure is!
He is also at 4000 feet...I wonder about the correction factors?
A quick read of the compressor map says the 6258 is good for 43ish pounds of air which kind of surprised me!

If you look at 18PSI's build and its boost table, you can see that he is all the way down to 16 or 17 psi at the HP peak.
IIRC that is 8 pounds down from 99MX5s. There is a fair bit more left on tap and the bottom end/mid range would be a different level.

More boost 18PSI!!
Let her rip! You know you want to!