Turbo Maps

[CTX-SLPR]

Howdy,

Well as my signature says, I'm a physicist and that means I like math and modeling stuff. Because I have a 256 engine, custom downpipe, and quite possibly custom headers in my '64 Riviera, I'm looking across the full spectrum of turbos as to what to use. I created an excel spreadsheet based off of the equations from Garrett's Turbo103 and tried to model the curve from 3000-6000rpm in 200rpm steps using boost. This has not gone well and trying to match the curve I found on what was supposed to be a stock turbo. While I got it to match roughly with a volumetric efficiency that goes from around 20% at 3000 to 75% at 5000. See the attached plot.



Does anyone have any insight into using turbo maps to select a turbo?

Thanks,

 

[JT'sV6]

Squirrel Performance

Just punch in your data.

Only wish precision had compressor maps.

 

[Hot Air]

TX SLPR,
I'm a mechanical engineer...I hated physics until I figured out that engineering is based on physics so I have been a fan for 40 years. Send me your e-mail address and I will send you a copy of an Excel spreadsheet that I worked up on turbos. It is based on Corky Bell's book on turbocharging. You will need to input your data in the yellow cells.
Conrad

 

[bison]

Howdy,

Well as my signature says, I'm a physicist and that means I like math and modeling stuff. Because I have a 256 engine, custom downpipe, and quite possibly custom headers in my '64 Riviera, I'm looking across the full spectrum of turbos as to what to use. I created an excel spreadsheet based off of the equations from Garrett's Turbo103 and tried to model the curve from 3000-6000rpm in 200rpm steps using boost. This has not gone well and trying to match the curve I found on what was supposed to be a stock turbo. While I got it to match roughly with a volumetric efficiency that goes from around 20% at 3000 to 75% at 5000. See the attached plot.

View attachment 141851

Does anyone have any insight into using turbo maps to select a turbo?

Thanks,

I have a lot of insight on the maps. They only tell a little though since the ex side is usually the limitation on the turbos most guys use on here. They can be run beyond the map also. Precision doesnt list compressor maps but you can make a general one with some data logs if you have a temp sensor at the compressor outlet. The overspeed limit is at least 15% higher on the billet compressors. Ive ran the 60-1 at 30 psig manifold on a 231ci with the minimum pressure drop at the inlet and an old Precision fmic. It took me to nearly 128mph@3500+ weight. The same compressor in the 6031 will fall way short because of backpressure on the ex side. You will notice the stock compressor will out run the ex wheel on the TBO348. Back pressure will be super high over 4300 rpm with your engine. The compressor will have a littel more in it although it will be way off the good part of the map. As you can see by the chart the TBO348 woudl be a really good turbo for a 2 liter that revved to 6000 that was running 25psi but would likely still hit back pressure before the compressor was out of steam. The engineers did this because the response is way more important than peak power.

 

[bison]

Howdy,

While I got it to match roughly with a volumetric efficiency that goes from around 20% at 3000 to 75% at 5000.

The volumetric efficiency (actually properly called mass efficiency since were talking about air) is actually closer to 75% between 2800 and 3200 and tapers off after that on the stock LC2 calibration. Another reason the stock turbo worked so well and many turned their car into a turd by changing it without changing other components back in the early 90's.

 

[Jonasterg]

CTX-SLPR, Hot Air, et al.,

Any willingness to share your spreadsheets / equations with me? I'm an Aerospace Engineer (CFD, hydrocodes) and have always been interested in this information but never really dug into it.

If not, and you can recommend some good books, I'd certainly appreciate it. Thanks.

 

[jlat]

hello; Glad to see there are some brains around. I'm a HS grad. that has a couple of toys to play with. How's the V6 working out in that Riv.?
IBBY

 

[CTX-SLPR]

jlat,

I'm still getting it working without a turbo right now since there are a lot of custom parts that would be at risk with the turbo if my newbie tuning skills go wrong. This weekend I'm going to try to get it driveable but that's mostly dependent on me fixing the brakes. Turbo will come later after I'm sure the mechanicals are functioning and I have a chance to improve my tuning skills with an NA tune.

bison,

While I have a stock turbo sitting in a box for initial implimentation I don't plan on using it long term. Does the exhaust side become a limitation on all turbos or just the 3-bolt flange that's stock on the Buick headers? While I would like to make this a general discussion on how to properly use a turbo map, I do have some specific goals that we could use as an example for how to use a map to select a turbo.

Application: Roadracer/Autocross with some drag strip useage (12.0s limited by no cage)
HP Target: 650hp
Engine combo: 256cid (3.995in x 3.400in bore x stroke), Champion CNC irons, Comp 212/212 roller, 1.65 rockers, ported stock intake, 7.9:1 static compression
Trans: 4L80E with a ProTorque 3000-3200 stall lockup converter
Rear Axle: 8.5in 10-bolt with 3.42 gears, Detroit Tru-Trac
Downpipe: Custom 3in to a rear mounted transferse muffler into 2x 2.5in tail pipes, external gate
Headers: Currently modified Postons, custom headers are likely in the future.

Thanks,

 

[87GN_70GS]

HP Target: 650hp

You will need roughly 65 lb/min of air.

In the example above, the max air the compressor will flow is apprx 36 lb/min or roughly 360 hp, and that is at a lower efficiency.

Try to find a map with 65 lb/min at a decent efficiency (usually to the right of max eff island) at a reasonable pressure ratio.

HTH

 

[Jerryl]

......... HP Target: 650hp
Engine combo: 256cid (3.995in x 3.400in bore x stroke) . . .

Crank or WHP, and what fuel?

 

[John Wilde]

TX SLPR,
I'm a mechanical engineer...I hated physics until I figured out that engineering is based on physics so I have been a fan for 40 years. Send me your e-mail address and I will send you a copy of an Excel spreadsheet that I worked up on turbos. It is based on Corky Bell's book on turbocharging. You will need to input your data in the yellow cells.
Conrad

Conrad, I would love a copy!!!

 

[Jerryl]

. . . . Well as my signature says, I'm a physicist and that means I like math and modeling stuff.
Does anyone have any insight into using turbo maps to select a turbo? . . . .

PS:
You are going to LOVE this link.
Turbocharger Compressor Calculations

 

[JT'sV6]

Since the subject of backpressure was brought up, I have a question about it and wondering if anyone has any experience.

With methanol injection cooling the combustion process and also effecting egt's, how does this effect backpressure? Is this why so many have had good results with the stock turbo and methanol injection? Have also read somewhere a while ago about someone injecting straight water precompressor to relieve backpressure.

This only makes sence to me, the hotter the air, the more energy and expansion of the gases that has to make it's way through the turbo. Cool the gases and there is less energy and backpressure.

 

[John Wilde]

Since the subject of backpressure was brought up, I have a question about it and wondering if anyone has any experience.

With methanol injection cooling the combustion process and also effecting egt's, how does this effect backpressure? Is this why so many have had good results with the stock turbo and methanol injection? Have also read somewhere a while ago about someone injecting straight water precompressor to relieve backpressure.

This only makes sence to me, the hotter the air, the more energy and expansion of the gases that has to make it's way through the turbo. Cool the gases and there is less energy and backpressure.

To make a long story short no.
I will let someone smarter than me respond in detail.