What does A/R mean turbowise...?



What does A/R mean when referring to the compressor and turbine sides if a turbo. I cant figure it out.

How are the measurments calculated?...like a .60 on the compressor side and a .48 on the turbine side? What do the numbers represent?

What would be a good combo for a 300 twin turbo. A garret t3? Like the numbers?
A .60 /.60? for both? Or a .60/.48 for both?

What would be an ideal turbo if it were just a single?...Garret t4? with smaller trims?

thank you for any info..

A/R is a reference normally applied to the turbine side. The compressor side is udualy described in terms of "trim." A/R is the ratio of the cross-sectional area of the turbine nozzle divided by the radius to the centroid of that area. The higher the A/R number the slower the turbine will run.

Get MacInnes's or Bell's book if you want it explained correctly. ;)

Turbo size depends on the intended RPM range of the engine. For a low to mid range boost a pair of T025s might work. If you want to use more RPMs then a pair of small trimmed T03s. For a single turbo a T03 in Super 60 trim would work well on low to mid RPM and a T04 with S3 trim would extend the RPM range quite a bit. The sizing functions at: http://www.turbofast.com.au/javacalc.html aren't a bad place to start
So can the super 60 trim just be added to a standard T03 turbo?..or does the compressor housing need to be changed as well....that is if i built my own turbo?...Parts are availiable to biuld a super 60 T03, but im not sure what exactly would need to be done.


There is no "standard" T03 or T04 turbo. There is a series of turbines and compressors which fit a common bearing housing. Any T03 or T04 can be fitted with any appropriate turbine or compressor. There are also hybrid models which combine the two sizes, typically for big HP boosts on mid-sized engines.

You really need to get Bell's and MacInnes's books if you're going to get serious about this turbo thing. They cover both theory and hardware in detail. Bell is much more oriented to EFI and MacInnes to carbs, but they both have a lot of indespensable info.
Hey SR,

Do you really think the Garret Hybrid turbos will work on the 300?

The Exhaust to Intake pressure difference would make cam choice critical. You couldn't have any overlap at all because the gasses would want to flow back ward into the intake.

I've called around to several turbo outlets like TurboCity and I get conflicting information on the hybrids.

What's Your opinion?

The hybrid, as I understand it, would probably be the wrong choice for a 300. They are normally used on upgrading mid-sized turbo engines like the 2.3 Ford. The small turbine has lower inertia and smaller volume than the T04 turbine so the assembly spins up faster than a T04 and reaches a higher RPM level than a T04 turbine would. The larger T04 compressor generates more airflow and pressure than a T03. All of this is good on a 2.3 but doesn't make much sense on a 300, you have enough exhaust flow to spin either turbine to a usable level pretty quickly and you're not likely to try to reach the same boost levels as someone who's upgrading an already turbocharged 2.3.
Thanks StrangeRanger, i will go and get that book..illlok at abaook store or get it online off amazon. It looks very helpful...plus ill learn alot bout turbos which will be that much better considering im taking Diesel classes here at UAA for college for a Diesel Tech Degree. Ill ave jumpstart on turbos more than most people my age...

My Dad is also planningon helping me with my turbo project. Between the two of us..we can figure it out..but that book will be very helpful

I'm pretty sure I saw a copy on E-bay when I searched under "turbocharger". I just got my copy but haven't had time to do more than skim through it. Looks like good stuff in there.