Howard Coleman

iTrader: (6)

surgeline and spool

--------------------------------------------------------------------------------

i am upsizing my twin garrett to4 setup compressors and am deciding between 2 wheels that have the same 41 lb/min flow, the same excellent efficiencies but differ as one of the wheels has a better surgeline.

here are the numbers locating each turbo surgeline:

bar------------to4 s3---to4 46----to4 46 Super
------------------surgeline location
------------------pounds per minute
1.4------------7.5------- 8.9------7.5
1.6------------10---------11-------9
1.8------------13.5-------13.2----10.75
2--------------16.5-------16.5-----13.25
2.2------------19.1-------19-------16.2
2.4------------22---------22.8------18

my current turbos (to4 s3) were purposely selected for early boost ( 1.9 X 2.75 comp wheels) and are not efficient above 30 lbs/min. the to4 46 is really good from 30-41 pounds and if you note the comparative surgeline above it looks like both of the larger wheels have as good or better surgeline location, especially the Super.

does the Super to4's surgeline location being further to the left indicate earlier spool than the standard to4?

the to4 46 wheel is 2.003 X 2.95 and the to4 46 Super is 2.003 X 3.2 (making it a 39 trim so i am wondering why the Majestic Turbo site refers to it as a Super 46)

kevin draper at Majestic advised me to go w the standard 46, that the surgeline location is not a big deal. there is a significant advantage based on the above numbers for the Super. based on my dealings w vendors ( both turbo and engine vendors) over the last few years i have gained a great deal of skepticism. there's alot of brainpower here and i would be delighted for any help.

based on my 2200 logged miles on the current to4 s3 wheels i expect to have no problem swinging the larger compressors.

howard coleman

z8cw

Howard,
Your observation about the super trim is absolutely right. My opinion is that the super fits our engines better. We do need a compressor that can build boost fast and doesn't flow so much. A larger exducer with a smaller inducer will exactly do that, build boost faster. I guess they call it super 46, to not confuse it with their regular 40 trim. What ports are you running?

CW

Howard Coleman

iTrader: (6)

CW,

thanks for the reply. i appreciate your comments

Brian Caine (BDC) did my ports. they are nicely curved race/streetports.

here are 20 pics: http://bdc.genxracing.com/HowardColeman/index.html

howard coleman

z8cw

These are nice ports. Would you have a dyno sheet with an accurate boost level. I could interprolate your flows with this. Given a street port your current turbos most likely outflow your engine already; i.e. larger turbos will not have any effect on HP. If you want to run more boost then you have to upgrade. Your table indicated "bar" as the first colum, I am pretty sure you meant pressure ratio. To read a flow map correctly you need to figure out what pressure ratio matches up with your boost levels.

For example:
sea level intake pressure 14.7PSI
air filter pressure drop .5PSI
INtercooler pressure drop 2PSI

The pressure ratio will calculate as follows (boost +14.7-.5 )/ (14.7-2). So at 15 pounds of boost you will have a PR of 2.3. I like to measure the PR that way since I never take my boost right of the turbine outlet but rather of the intake manifold. If you drive your car at higher altitudes the PR will rise for the same amount of boost and you might need a different turbo.

I attached a flow map with a stock port at 4k 5k and 7k rpms for the super 40. This turbo seems to large for stock engine as a twin set-up.