Dougs951S

So guys, I know this has probably been discussed ad infinium, but I cant seem to find a concrete answer on this. I am currently running a k27-7006/8 and gearing up for a new DBB turbo, either a 50 trim or a 60 trim. I just moved to a new city where I have access to E85 across the street from me, so that being said, which would you guys rather take? I know the 60 trim will spool a few hundred rpm later than the 50, but how much more power can I expect if running E85? I know its worth ~40ish hp over the 50 trim while running 93. How does the 50 trim compare to the k27? With the right supporting mods, could I make 400 whp with a 60 trim on E85? it seems doable with 21-22 psi if I looked at the map correctly. I cam currently still running the AFM and will likely get the turbo before converting to MAF and running E85 full time; how would the two turbos compare in that situation running 93? Boost would be around 17 psi.

Paulyy

Tinker with this program i made up. It has both compressor maps you've mentioned.

There's no difference when you use the fuel. It's all the VE (volumetric efficiency) of the engine. the more you have the more power you make on the same boost level.

The more boost you run, yes the more power you make. but it's not always the case. some turbos cannot produce more boost and flow more air.

You'll probably find that you will have little gain with the 60 trim. the idea is to stay in the efficiency islands, the closer to the first island, the cooler the intake air temps will be, resulting in a better combustion.

I typed in a few numbers on the program
400hp
11 afr
.5 BSFC
90 degrees intake temp
.8 VE %
6200 RPM (is usually peak hp)

https://rennlist.com/forums/944-turb...am-inside.html

Dougs951S

So as I understand it, any given turbo will only flow X amount of air at X pressure ratio. No way to "force it" to flow more air at a given ratio by forcing it into a less effecient island, IE farther to the right along a horizontal line. So then why does the 60 trim make more power? it seems to me that at any hp target, they require the same boost level to achieve it, and since the 50 trim wheel has less rotational inertia it should spool faster and should therefore be the overall better turbo? I thought that a larger turbo could flow more lb/m of air with less pressure, so I dont completely understand how that program can derive a pressure ratio simply based on the information i typed in, and a desired power level. wouldnt the pressure needed to make X power be different for two different sized turbos that were presumably flowing different amounts of air? Saved that program by the way pauly, great stuff!

333pg333

Paulyy, once you put those factors in, how does the comp map vary? I'm a bit confused? Perhaps I'm doing it wrong.

Dougs951S

^right, this program seems to show any two given compressors as essentially equal for any given power goal so long as you are not surging or over speeding it. Dont understand it myself.

Paulyy

First off, basically everything is off the garrett website. All the program does is compair compressor maps with a desired horsepower target. All the numbers you punch in determine how much boost you need to run to achieve your target power goal. It's not spot on, just a guid in choosing turbo compressors.

It doesn't tell you how much power you'll make with different compressors. That a program cannot figure out. That needs a lot of factors.

most of the time you gain power when you change turbos is the exhaust housing flows more air, creating less back pressure. which changes the characteristics with the turbo.

If you have the 50trim with a #8 housing then swap it to a 60trim with a #8 housing. you'll loose spool time but might gain in top end if the 50trim is loosing breath.

But if you look at the maps and want to run higher boost, the 50trim would be a better option as it can still breath at higher boost levels, as the 60trim cannot.
If you punch in 450 hp target you'll see that the 50 trim is more in the middle (ideal) spot then the 60 trim is more on the edge (more heat)

does that make sense now?

333pg333

Ah, ok. I couldn't see any red dots with what I was putting in. They must have been way too far off the right hand side. Something that I'm inputting is wrong. The BSFC is a bit of an unknown. I'll play around. Thanks.

refresh951

Patrick,

I use this tool quite a bit (thanks Paulyy). I used some previous dyno sheets to back out some estimates for VE and BSFC.

Paulyy

Patrick, you've probably put a whole number instead of a decimal.

Thanks Shawn! What did you VE did you end up with for maximum hp? ~6200 rpm

refresh951

IIRC VE 0.9 BSFC .51

The dyno was my old 2.5L, stock 8V head, 340 rwhp

I am assuming slightly better VE with my HF Head and other mods for 3.15L

White_951

Doug,

My question to you is what kind of driving will you predominately be doing? Stop light to stop light or track days......

My target was top end for my track car and I went with the 60...if I was staying on the street I'd go with the 50 (or 54), regardless of fuel availability....

333pg333

How do you calculate the VE and BSFC for a race 8v head on a 3.1L motor? Is the VE only based on the head or is it the whole system? ie I/C, pipes, t-b, plenum, intake, head/cam, headers, exhaust etc....

refresh951

These are VERY ballpark numbers. The only purpose is to try and pick a reasonable compressor for the application. VE would certainly depend on many factors; head, intake, exhaust, cam, etc.

onspeed

Where in Austin are you? IIRC, there's only like 3 stations with e85 in a 50mi radius of downtown

Dougs951S

San Marcos, actually. The station with E85 is off highway 80 and 35.