smokeum99ta

Right now i'm not really looking for anything more than what I have but would like to learn more about turbo's for future mods. I understand the basics on what a turbo does and operates but theres always more. I try to keep up reading through threads but I get lost and it all starts sounding like a foreign language to me. Maybe someone could break it down to me (and others that are scared to ask) as if I were a two year old. I feel dumb asking but there no such thing as a dumb question in my eye's. I'm just trying to understand what i've got involved with.

pmtg

im thinking you just want to learn more about turbo's in general, not what specific turbo will work for your truck...if so, this should help some...
http://www.turbobygarrett.com/turbob...ch_center.html

smokeum99ta

That will work. Thanks Next i'll ask about which one for me once I figure out what i'm gonna get for my truck.

GFB

Too bad trims, A/Rs, and compressor maps seem to be all hush hush for those that sell turbos for our trucks.

Then you just end up buying what somebody else has because they have a similar setup and say, "yeah, I really like my turbo," or you have to listen to a sales guy recommend you buy this or that for your setup--because that's what he has in stock at the time.

HOHN

That's one of the reasons I'm STRONGLY considering going with a Garrett or T-netics turbo.

The reason the "diesel turbo" vendors can get away with no sharing specs and hiding behind some claims of magic turbo voodoo is that we STILL buy their turbos!

Lately, I've become of the mind that if a vendor won't show me his compressor map, then I won't show him my credit card.

Sounds like a fair deal to me.....

jh

Ph4tty

You are correct that there are a lot of different termanology used when discussing turbos.

When discussing exhaust housings everybody uses the a/r which is like .87 or 1.01 as opposed to the 12 or 14 that holset uses. Since we have stock holsets, several marketers refer to their housings using holset values. However they measure them, the larger housings will flow more heat out while the smaller ones will spool faster.

I'm still turbine challenged, but from what I understand a high pressure turbine will offer better spool, while a low pressure wheel keeps drive pressure down for performance applications. The "super" 62/66's you'll hear people talking about are using a low pressure wheel. I need Hohn or Brdanon to school me on the garrett wheels, unsure how they compare

Compressors are easy to understand: the bigger compressor generally flow more air, but the heavier wheels will take a bit more to get going. The 62/64,.. people refer to is the compressor inducer, or how many mm across on the small end

XLR8R

With a few measurements and some simple math, the trim & A/R for any charger can be discovered.

HOHN

I don't know anything about anything, but here's what I think I know:

I think of the compressor wheels in terms of inducer and exducer diameter. The closer they are to each other, the higher the "trim" and the more potential flow for a given EXducer diameter. The farther apart they are, the less flow potential, BUT-- the lower trim will enable higher pressure ratios.

What happens if you have a given inducer diameter, but you make the exducer larger? In this case, the air is "flung" out at higher velocity because the the angular momentum is higher with the larger exducer. So while you won't gain any flow (assuming your at max inducer flow capacity), that flow will be available at higher pressure ratios, and the compressor map will have a narrow breadth of operating range, but give you more PR capability.

Now, if you have the exducer diameter constant (say 88mm), and you raise the inducer from a 62mm to a 64mm, you've increased the "trim" and also increased the flow potential, but you've lost PR capability. You've basically made the compressor map broader and more useful at lower PRs but given up to some degree the ability to be efficient at high boost pressures.

Lower trim compressors that work well at high pressure ratios also tend to go into surge more easily. These truck are about as bad as it gets, trying to make big power from low rpm AND low displacement. Huge PRs is the only way to get the air we need.

From the HTT site on their compressors:
62mm IN=87mm EX trim= 50.7
64mm IN= 92mm EX trim= 48 trim
66mm IN- 96mm EX trim= 47 trim

Thus, we can see that the HTT compressors are relatively low-trim compressors designed for the high pressure ratios our trucks need.

Compared to popular Garrett compressors:
61.4mm IN= 82mm EX (GT37) trim=52
64.5mm IN= 88mm EX (GT40) trim= 52
67.8mm IN= 94mm EX (gt40) trim= 52
70.3mm IN= 94mm EX (GT42) trim=56

Most of the Garrett compressors are a 52 or 56 trim. That's better for a larger displacement engine with better breathing or more RPM, like a dmax or p-stroke, but the Cummins needs to be force fed a little more brutally, and the lower trim compressors work well for this.

In a twins application the Garretts will be awesome, because the higher PRs (and higher trims) aren't needed, and you gain efficiency and breadth of operating range.

But as a single turbo, the HTT turbos will a better fit. Just get the bigger housing if you go with a 64 or 66 and that will help keep you out of surge.

Keep in mind also that his doesn't scale linearly. A bigger compressor wheel will generally have more PR capability, even at a higher trim. For example, a smaller GT35 56 trim wheel tops out around 3.5PR, but a 56 trim wheel on a GT42 can go well over 4:1. The 47 Trim wheel on the GT55 will go almost 5.5:1 PR on the map!

Justin

RowJ

A/R = Area over Radius!
Simple for you maybe.... but measuring the area of a cone shaped 'air horn' takes calculus...No?

RJ

RowJ

It gets even more difficult. I went looking for books on turbo chargers about two yrs ago. Only found four... of which only one suits our purposes, IMO. And it's 10+ yrs old!

But for anyone that wants to really understand, and get an advanced education on turbos (and is willing to trudge through the technical learning process), I would recommend "Maximum Boost" by Corky Bell. Nothing on diesels...but a good read.
It started sinking in, for me, about my fourth time through it.

There is another turbo book that is much older, but has a full chapter on diesels! I loan it out and can't recall the name... sorry!

RJ

HOHN

Nope. You're just taking a "slice" of the turbine scroll at that particular radius.

No calculus needed. But a bandsaw and a spare housing might be useful

RowJ

Yup! Thanks Justin... forgot all cross sectional A/R's in any given turbo scroll are equal!
Sorry Mike. Hate it when I can't remember what I thought I knew!
I better read Corkey's book a 5th time!

RJ

GFB

+2. I've read it once and yeah, it wouldn't hurt to re-read it as there is TONS of great info about forced induction in general, specifically turbo applications.

XLR8R

I'd measure the cross-sectional area of the compressor's outlet (or the turbine's inlet) and divide it by the length of the radius from the shaft axis to the housing's circular perimeter. (This is when a picture is worth at least a hundred words! )

Usually, the turbine housing's A/R is the spec in consideration, since compressor A/R differences don't have nearly as much effect on performance.

HOHN

Honestly, the "turbo tech" series at the Garrett website (duplicated almost entirely in their catalog) as about as good a turbo 101 primer as a person could ask for-- FOR FREE!!

jh