Jay Johnson

iTrader: (16)

I'm looking for information on the effects of varying the AR on a Turbo.
Example of a high-rev'ing 6.0L LSx.

T76 with .86AR
vs.
T76 with 1.15AR

Post up or point me to some internet info on this.


Jay Johnson

otherwhitemeat

iTrader: (3)

the bigger one makes alittle more power but in a higher rpm range, and comes on slower.

BigJls1

you know I have noticed that a majority folks in this forum know how to get a high horespower car, but dont have the really really technical info like your ?. I asked a similiar ? about A/R and didn't get alot of respose (aside from superman and jake@epp). anyway I personal think that
A/r has alot more to do with power than the mm of the turbine and compressor wheel. but to try to help with your ? the first turbo with a 6.0 will probaly boost early like 2000 to 2500 rpm but will choke the high rpm, this turbo will make great torque number down low, this turbo will feel awsome " by the seat of your pants" however probaly will not be the fastest in the 1/4 mile. the second turbo will boost later maybe 3500 ( this all depends on front or rear mount) but when it does boost it will not have the area resriction that the smaller a/r has and will in the 1/4 probaly be faster. you stated that the motor was a high rever if you go with the bigger turbo I think in th 1/4 youll be happer but on the street the smaller will seem more fun as boost will be alot more and earlier.

just my .02

JD_Z28

iTrader: (19)

My thoughts exactly and that why I went with the .96A/R.

engineermike

I think everything you posted is true except for this part. I believe the exhaust wheel size and compressor wheel size are far more important than the A/R ratio. Some guys have gained over 100 rwhp by swapping compressor sizes, but only 15 rwhp with a higher A/R.

Mike

BigJls1

dude the compressor size is the A/R

area of the compressor housing diveded by the distance to the center of the compressor wheel.

Ryan K

iTrader: (11)

Uh, wrong end. While Compressor AR is important, it is rarely advertised. .96 & 1.15 ARs are a reference to the Turbine housing.

Ryan K.

BigJls1

It is true you can gain alot from a more aggesive wheel trim on the compessor side. 100 hp sound a bit much, but the a/r of the turbine ultimatly controls the boost threshold or (form when boost starts till when you basicly cant flow enuff through the housing any more) the housing the guy ?ed are obviously exhaust housing based on the sizes indicated so my respone was based on the tubine housing. also true is a more ageesive wheel in a larger housing will make big hp numbers but will take more flow to get moving ie a drag car that wants alot of boost at high rpm. Anybody that gains 100 hp from a wheel is going to give up some down low boost where as a properly flowed housing A/R will still boost early and not choke the high rpm. yes the wheel changes alot. I presonal think the housing has more to offer but will agee this could start a whole new thread, so Ill 1/2 agree with the post above me.

BigJls1

ryan k, I am wrong typeo, i ment turbine housing has more to do read my last post sorry

6techniques

iTrader: (7)

x2

Im running a 1.10 A/R here and with 370 cubes, I feel it will be right where I want it. Anything smaller and it will become a bottle neck.

BigJls1

6

are you a rear mount

6techniques

iTrader: (7)

nope, Im running a Pham single kit with an s400 based turbo.

sampson

iTrader: (1)

BigJls1 is right

more info about it: http://www.turbobygarrett.com/turbob...o_tech102.html

BigJls1

Great link

If you notice they dont spend alot of time explaining the wheel they say some times a differnt wheel can flow more and some time not
however they spend alot of info on the effects of the a/r hhmm........
one may conclude the a/r has alot to do with turbo selection I will now shutup on this topic. Im not trying to

ExTurbo

i agree with bigj it all comes down to how fast you want the turbo to spool...there will also be a small difference in power (lower AR = less Hp) but i dont think were talkin a huge difference...on an 346ci or bigger id go with the bigger AR unless you want instaboost with a wider power curve...i wouldnt say that the bigger AR is gonna get better ET's every time its based off of power under the curve as well...if your doin alot of highway racing sometimes a faster spooling turbo will make the difference in a race

sampson

iTrader: (1)

Yeah, older wheels maybe the same size and AR as the newer GT wheels, but the fin make up of the newer wheels will spool the turbo faster.

engineermike

Okay, let's compare two turbo's. The PT67GTQ and the PT76GTQ, both in a .96 A/R. The 67 is good for 790 hp, while the 76 is good for 975 hp. 185 hp is a huge difference, all with the same .96 A/R GTQ exhaust side. Playing with the A/R will NOT make this much difference.

SS4Matt

iTrader: (4)

very little talk is made about A/R's around here.....keep it coming!

engineermike

There's a reason for that. All of the small frame turbo's that we can fit in the engine bay of our cars are too small for 350+ cid anyway, so everyone (including myself) jumps straight to the largest A/R available to help with the backpressure problems associated with these too-small turbo's.

Mike

BigJls1

But mike your changing the compessor wheel or the turbine wheel in the two turbos you mentioned ?