This is exactly the reason I chose to lower the restrictions in the entire system.. the easier it is to get air in, the less work it does to make the same power and will make quite a bit more power at the same boost levels..

Theres nothing saying going with a bigger turbo isn't a good idea.. I just think that its more prudent to optimize what is there until you get to a point where your no longer making appreciable gains, then upgrading to a larger turbo would be an option to me.

 

I've been trying to get some hard info on the "Evo400" conversion. I'll send off an email tomorrow, but does anyone have any hard info or experience with that kit on EvoM? From what I gather, it's a re-work of our existing turbo, or was for the earlier Evos.

 

You can define spool-up delay as the time it takes to reach a given boost pressure.

If you do this, you can break the delay into multiple factors:

-Moment of inertia: this is where the size and mass of the rotor come into play

-Mechanical power transmission friction and power losses: BB sections are used to reduce these effects

-Delay due to compression side (in)efficiency and exhaust stream power needed to drive the compressor to discharge air at a specified boost pressure

-Delay due to (in)efficiency of turbine

So, if you increase one of these factors, say the moment of inertia of the rotor, you can theoretically make up for it by decreasing other factors.

However, the definition of spool-up first given is a naive one. A better measure would relate to the slope of torque increase due to the turbo. As it has been mentioned in this thread by others, and me in previous threads, it's not the raw boost pressure that makes the power, it's the increase in torque due to a more efficient locus of operation with the "bigger" turbo.

So suppose I'm making 7 psi of boost at some midrange RPM point on the small turbo and 5 psi on the bigger turbo at the same RPM point. If the 5 psi air is sufficiently cooler, and the bigger turbo's turbine is causing less backpressure than the smaller one's, I will be making more power at 5 psi boost than on the small turbo at 7.

At that point, it would be foolish to complain about "spool up" just because the bigger turbo hadn't hit the same boost pressure at the same RPM point, right?

 

A stock turbo with 10.5 exhaust housing, ti wheel and ball bearing cartridge should give better spool than stock and more power up top. UK people certainly seem to be excited about this set-up. Mitsubishi for the MR RS model has essentially this set-up w/o the ball bearing.

A relatively small turbo is nice for road use - Audi/VW goes that way and it's very satisfying to drive in day to day use with the exception of a lack of top end power. But with cams that definitely does not seem to be an Evo problem.

I would still want to put my money on the above combo for daily drivability, as it is essentially a slightly improved factory RS set-up.

 

And don't forget that even if you do run a bigger turbo where you would only have say 15PSI when @ the exact same RPM you owuld have 21PSI on the stocker, you will more then likely have more POWER on that 15PSI, and then from 15PSI to 21 on teh bigger is a flash where all 4 wheels break out in 2nd gear......

 

Its nice to see some of us understand that boost pressure is a reflection of a restriction (forcing airflow) Regardless of the solution, removing the restrictions will lower the boost pressure required to make the same power given the exact same turbo, in turn raising the boost on that same turbo (within reason since efficiency comes into effect) would result in even more power..

Now.. with all of that said, compressing air makes heat.. so the more you compress it, the more heat it has.. so the less work you have to do to to get the same volume of air into the engine, the more power you can potentially make.. you can also get more air volume into the engine with less work. .etc.. etc..

So what does all this mean, that the solution isn't always giant turbos or staggeringly high boost pressures, but AIR VOLUME.. you can do it with a bigger compressor, less restrictions, more boost, better flowing head.. or all of the above.. But which will work best for you depends on your goals.. My opinion is that a basically stock turbo will realistically do the job for 90% of us.. Make the turbo work less hard, and you can make it move more air at lower pressures (or the same levels) I think that should be more than enough to keep most of us happy..

The big problem is the "Turbo mentality" which always takes the stance that moving more air with a bigger turbo will overcome the inherant restrictions in the system.. And to some extent thats true.. But I come from the Normally Aspirated school of thought were you can also produce significant power by allowing the air to pass through the entire system easier, which also applies to any forced induction application (within reason there are a few caveats such as cam timing and overlap, and exhaust scavanging) since less waste means more power.. and the waste is expressed as heat generated by restrictions, compressing the air, boost pressure without increasing volume by much, and of course other efficiencies..

Anyone with cams may have noticed that before you installed your cams you had a particular boost level with a manual boost controller, but afterwards, it was a little lower and you had to adjust it accordingly since the valves open a little longer and higher, your allowing more air into the engine, so you reduced a restriction slightly..

and so on and soforth..

Now that I'm done with my theories and all the academic discussion... a BB conversion has desirable traits, if not we wouldn't talk about the big turbos with BB's to allow it to "spool earlier" (also note I'm not against big turbos, but prefer to use servicable components)

Spool and drivability are really perceptions though.. If you have a turbo capable of producing the same level of power at low RPM as the stock turbo, but peaking higher later, its of course gonna feel the same in daily driving, but of course make more power.. so if you want a bigger turbo kit.. just look at that aspect..

What I always was looking for was to produce torque at lower RPM, and horsepower at higher RPM.. and for me that was using the most efficient stock sized turbo I can find.

 

yes.....

 

Actually, the solution (if by that you mean the way to make "more power" at a given engine speed) is air mass, not air volume. To be more direct, it is the quantity of air molecules you are interested in increasing.

 

Actually I had meant mass.. but point taken..

 

I do have this conversion on my JDM Evo 8.

In conjunction with the BB converted turbo, I have also got Tomei 260/11.5 in/ex Procams, ARP head studs and Tomei headgasket along with a series 2 Tomei ECU.
needless to say, all piping is bigger from the Turbo to tailpipe and air filter to engine together with a 42.5mm ID tubular SS manifold.

I opted and Dave (evo400) sourced for me a TD05-HR-10.5T turbo and did the necessary conversion mods at Turbodynamics.

In conjuction with an AVCR, I am running a peak of 1.7par and a held 1.45 bar in all gears. Incidentally I can and have hit 2 bars on first and second gear but I ran out of both boost controller and boost gauge to figure out how much.

In terms of drivability, this is a monster on the road. I have yet to get my car properly custom tuned but the release of my intended EUC has been delayed . Nonetheless, I have no problems outrunning just about anything in the first to third gear. until I have my ECU in I willeave of the flooring it hard for the higher gears.

it may not have as high a peak hp fig as a bigger turbo but it gives a greater area under the power curve which makes for very enjoyable driving. And out of the lights, if driven in anger, not many cars can catch you for the first coupla gears.

Dave's own car runs piper cams, headstuds ad the B conversion along with a GEMS ecu and the usual intake exos mods I suspect.But dun take my word for it.
go here

www.evo400.co.uk

Personally find that if you live as I do in a city where you spend alot of time NOT cruising on the highway.This is a fantastic conversion. But is you want huge HP for long distance go, maybe something bigger may give you more bang.

 

nice one asidbryne, hope you get the ECU soon! which one you going for?

Chris.

 

Thanks chris

I am awaiting on the Hydra 2.0 ecu.

go here
http://www.carmodifications.com

I have obtained the interface software and manual and am well pleased with its GUI and functionality.

Hopefully when my ecu is ready i will get ome dyno figures posted.

 

I wonder what is involved in hooking that ECU up.. It would be interesting to see actual photos of the unit..

In any case.. Its nice to hear from someone actually WITH a BB conversion.. I have the TD05-HRA-9.8T Which is pretty much identical to the USDM turbocharger except with the Ti internals... An earlier post mentioned that the shaft was NOT Ti, and I believe that is actually correct.. But the exhaust wheel (which is normally the component with the most mass) is Ti.

Of course, we're still waiting to hear about someone doing a BB conversion here in the USA where its more practical for me to ship my turbo..

It only goes to show that there really is no "Wrong" way to go about this. Expecially for a daily driver.. If your going for the magic 9 or 10 second quarter, of course you need a monster turbo.. But you also need just about everything else to be certain it will hold up.

Many people, Buschur racing is a good example have gotten nicely into the 11's on a stock turbo, and this was without head work, optimizing the exhaust manifold and O2 housing, stock intake manifold, etc.. So its obvious that there's more to be had in optimizing what is there. But we'll find out soon enough.

 

As far as I am aware, the ecu comes with a vehicle specific loom very much like a power fc.

I believe the scoobies are alreasy using it under the element tuning label of Nemesis.

Like you say, what you want the car to do should dictate what you do to the car interms of turbo choice etc.

Great drag cars are rarely as drivable (relative) as a car set up for track and even then it depends on the track, smaller tighter tracks may not favourt big turbos since they never get into their power band and are too violent when they do.
Similarly while a track car can run a remarkably quick 1/4 mile time, it will not be able to compare to a car set up for drag.

The thing that attracted me to this turbo was large amounts of torque at relatively low rpm. While others may provide more power or torque at higher rpms, the idea is that I will be out of the corner quicker and while a bigger turbo may start to reel me in, they would have to first pass me and then get out of the next corner quicker.

diff horsed for diff courses....

 

asidbyrne - thanks for the Info. I've seen alot about this conversion posted elsewhere, but very little in the way of hard facts. Most of my hard driving is on road courses, and a number of those are smaller tracks. There is one with a monster 5200' (almost 1 mile) front straight that I get to play on though; lots of speed.

I have been to the website, but it doesn't seem to be anything more than a collection of spalsh pages. I was hoping to see at what RPMs full boost would be available and some information on what WHP that people have made with that turbo. Any info is appreciated!