miatex

Hello to all...

I have this turbo setup, my exhaust is a 2.5"dp and then a 3" Dp back (No cat), I believe for this size turbo and size engine the spool is OK, but my question to you guys is...

Would a 0.48AR hotside make a world of difference down low?

I am planning to go up to 18-20psi on my built engine. I got the 0.63AR to avoid that being the bottle neck for higher RPM power on higher boost.

Now I believe 18-20psi is not that high to make the hotside choke the flow with this size turbo.

Now going to a 0.48 AR will give me a much better low end response and spool, or it will be a few RPM not worth doing?

Thanks!

miatex

fmowry

iTrader: (8)

.48 hot sides aren't that expensive. Get one and try it out. It should reduce spool. It also shouldn't be that much of a bottleneck at 18 psi.

Frank

Braineack

iTrader: (62)

I'm with stupid. however, the .63 will have greater potential to make more power per psi.

miatex

This was exactly my thinking when I bought it...

Has anybody had experience with both so they can provide insight about both.. I know they are not very expensive, but if I can avoid it why not right?

miatex

m2cupcar

iTrader: (5)

What stage wheel is the turbine? That makes a big difference in the spool too. If it's a stage1 ford style five bolt, I'll trade a .48AR of the same.

Braineack

iTrader: (62)

from what I've seen, in my own experience a well as others, the .48 isn't much of a bottleneck. but it's the overall size, speed, ans stage of the wheel that really dictates the power.

for example...the .63 might only provide a touch more power up top, if a stage I wheel, while spooling 500rpm slower. Only because inducer is only so large and can only spin so fast.

Throw a stage III wheel in the mix, and while the spool will suffer even further, the power will dramatically increase. This is due to the larger diameter inducer and style of the blades; allowing for better flow through the wheel, more air being pushed through it, and spinning it faster.

IMHO, even if you have a stage III wheel, stick with the .63. Since you'll be running large amounts of boost, might as well let it breathe the best it can. You should still be making full boost under 5K, so you still have a usable powerband. Although a .48 with a III might be an interesting compromise.

miatex

I have the stage III wheel, I am seeing full boost at around 4300rpm which isn't bad for the 1.6, but if with a .48, I see full boost by 3800 that would make a world of difference on the street...

Braineack, I didn't really get when you said Throw a stage III wheel in the mix, and while the spool will suffer even further, did you mean the spool with the .63 will be much worse than with the .48 with the Stg3 wheel?

miatex

Braineack

iTrader: (62)

a

fmowry

iTrader: (8)

We have different definitions for "large amounts of boost". I'll bet the .48 isn't a bottleneck at 18 psi even on a stage III. Probably not until 22+.

Frank

Braineack

iTrader: (62)

larger for a miata.

I agree, from what I've seen, the .48 is not a bottleneck. Remember I run the same, and I know the peak efficiency is right above our maximum CFM in the exhaust so it's a good match

But the .63 doesn't perform half bad down low either, and it could be the difference of +50rwhp at the same boost, if that's what we are shooting for here...(although I'd personally want full boost below 4.5K)


I suggest the stock IM would be a good thing to get rid of at this point....

y8s

iTrader: (8)

remember that .48 on a T3 is not .48 on a T25. it's a ratio. so if the radius of the housing is bigger, so is the flow area.

your car wouldn't spool a .2 a/r on a T88

Braineack

iTrader: (62)

i know....im pretty sure we are all talking about a T3 A/R here

y8s

iTrader: (8)

i know, but i want to make sure he isn't thinking in tiny turbo terms.

miatex

To be perfectly honest, I know we are talking about a T3 frame, but my understanding of the AR is less than satisfactory.

In my head is working the rule of thumb... for a given size frame, a lower hotside AR should mean better spool.

I do not know however how to calculate at what flow level would the 0.48AR on the T3 should start to begin to be an obstruction. I read it is about 22+psi, that means the 0.48AR should be ok for my intentions.

If someone can help me understand how the ARs work, it would be great...

I know it has to do to the relatino about inducer/exducer... but that tells me nothing really

miatex

Braineack

iTrader: (62)

its a simple equation....in the dumbest explanation: it's how big the passage to the turbine is. If small, it's easy to spool the turbo fast as the velocity will be high, so the airflow will move faster over the wheel. But as the engine turns faster the volume air flow of the exhaust increases as well. So what happens with a smaller A/R housing, is that you simply choke up top, instead of the exhaust freely flowing over the turbine, the engine wastes energy forcing the increased volume through....less energy pushing down pistons, means less torque/hp

likewise, when the housing is larger the spool suffers. Mainly because at low rpms you simply aren't pushing enough air volume over the turbine to spin it fast enough. But as the rpms increase the exhaust will be able to pass more freely over the turbine wheel as the housing itself is not a restriction and causing extra backpressure.

there are select few turbine maps available from garrett, all in t25 size. however, the next step up in size, is close in relationship to a t3 housing.

t25 t3
.48 .36
.63 .48
.86 .63

what a turbine map shows is the peak efficiency of the turbine wheel. basically the point of air flow volume that it will start to choke out at. The max efficiency for a T3 .48 housing is somewhere around 17-18 lb/min. Assuming Garrett's standard conversion for ambient conditions and absolute temperature (13.7psi and 86*F), that equates to about 260CFM.

a 1.6L at 20psi (1.38DR) will displace something around 272 CFM. a touch over the peak efficiency. so it really shouldn't prove to be much of a restriction. mind you this is math and not the real world, but it should prove fairly close to real world experiences.



you also have a greater power potential right now because you have a stage III wheel. the turbine size dictates the shaft power. really, the faster you can spin the wheel, the more power to be made. my stage I turbine wheel may only have enough power to flow 300cfm through the compressor wheel, while yours is large enough to turn you compressor to push 400cfm.

on top of the overall diameter, the style of the blades is different to ultimately allow air to flow pass it easier, thus again, more power potential. but with increased stages and turbine sizes, you see slower spool, which is why you see 9psi at only 4300RPM. But if you can deal with the slower spool, you turbo is going to perform like whoa up top. otherwise, the .48 might be a worthwhile investment. just realize it may be hard to source a stage III one that matches.

m2cupcar

iTrader: (5)

Find a .48 housing from an OE app that fits your dp and have a shop overbore it. It'll help some, but I think what's really killing spool on your 1.6 (besides it being a hybrid) is the stage3 turbine.

miatex

m2cupcar, your last comment really surprises me, I thought the Stage3 wheels was actually better for spool!! For what I read, you have a similar turbo setup (Except you have a 2.0 )

Also I don't think my spool is that bad for the little engine, i was just wondering if it can be better....

miatex

hustler

iTrader: (6)

I have a .84ar and a stage 3 turbine...lol.

Hopefully the 1mm overbore and 99 head with electronic boost control will make 12psi by 4k rpm.

m2cupcar

iTrader: (5)

w/o complicating things, just remember smaller turbos generally spool quicker- stage1 is smaller, but it's not going to flow what a stage3 does at higher rpm and boost. A smaller AR is definitely the simple way to start spooling the turbo sooner. I'm only running a .48AR because that's what I had...

hustles you're running a t2x, so it's like running a .63 t3 turbine... and the compressor size has everything to do with equation