# Is my turbo math correct?



## nissan300zxmike (Nov 1, 2005)

I want to select a decent sized turbocharger for the vg30e. I've been looking at Garrett's new turbochargers ... the GT's. I found that the GT35R (Ball Bearing) supports displacements of 3.0 to 4.5 litre. So thats where I started, I know that the engine isnt exactly 3.0, 2,9XXcc's right? like alot of engines that are just rounded up displacement (correct me if im wrong, i wanna learn)

well anyway...here it goes

cid x rpm x .5 x Ev
Airflow Rate = ------------------
1728 

183.07 cid ... lets say 5000rpm .... .5 (engine fills its cylinders only half the revolutions) and 80% volumetric efficiency / 1728 to convert it to cubic feet.

183.07 x 5000 x .5 x 80 / 1728 = 211.8 cfm ... so its "flowing" 211.8 cfm ( i used to work at a vw high performance shop that does heads, builds turbokits(i headed that dept after 8 months) carbs machining, kits, jetting etc (i headed it too) and custom built engines...i have never figured out flow PERFECTLY like my boss who ported heads did...he is "one with flow" if i may put it ... well i guess the 25+ years of experience he has porting / building heads allows him that )

anyway...lets do 13lbs of boost... 

14.7 (absolute) + 13 / 14.7 = 1.88 ... wow only at 13/lbs it'll be forcing 88% more air in the engine 

211.8 x 1.88 = 398cfm convert to lbs/min 398/14.472 = 27.51 ... magic numbers 27 lbs/min and 1.88 PR

the goal is to get the highest efficiency right? it lands RIGHT on the center island










thanks in advance ...i gotta hit the hay its 4:27am :asleep: im going to be dreaming about me being royally FU$#$% because i have a vg30e with 9:1 c/r that would be VERY fun with that size of a turbo *sarcasm* ... ill start looking for a turbo engine


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## nissan300zxmike (Nov 1, 2005)

ah f$%* ... that was the gt30r map not the gt35r. heres the gt35r map










turns out the gt35r has a lower efficiency for this engine


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## Matt93SE (Sep 17, 2003)

what are you wanting to do with it?

I know a guy in australia that's putting a GT35/40R in his VG30E Maxima... IT will be used only for drag racing though, so the lack of low end power is fine for him. it'll be right in the sweet spot at the high end with the monster cams and MOTEC... not a ton of boost off the line so that it doesn't rip the tires off the pavement, then builds and is a rocketship once its rolling.

Sooooo... what's your goal with this engine? all around good power? go with the GT30. want more power on the top end, and willing to compromise the bottom end a bit? then go with the GT35.


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## nissan300zxmike (Nov 1, 2005)

no power whatsoever until the boost comes on, and when it does...hello heaven! lol 

cruisin' on the freeway at 3000 rpm lets say...engine is just kicking back havin fun, if someone pulls up ill wake up the turbo 

i like how "88hybrid" from zcar.com did their turbo system setup, im going for something very similar to that, and i love the home made intake manifold


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## THE BIG ONE (Oct 30, 2005)

Yes, that's correct as far as I noticed from quickly rechecking your math. Becareful on the conversion from CFM to lbs/min. I've seen formulas with numbers from 1 cfm = 0.069 to 0.076. You used 0.069, which is the same that I use. Personally I'll be using a GT35R myself. It'll spool 20 psi around 3100 or so, and have enough flow for over 700hp. It's a very nice turbo. Here's a conservative map I did (I'll do another one later, with decent valves (Ferrena), decent valve springs (Shneider), and a nice set of cams, a VG30ET will breath nicely up 7000ish rpm, and likewise flow quite a bit more.


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## nissan300zxmike (Nov 1, 2005)

Thanks The Big One  ... gt35r *le drool*


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## Spongerider (Nov 18, 2002)

nissan300zxmike said:


> no power whatsoever until the boost comes on, and when it does...hello heaven! lol
> 
> cruisin' on the freeway at 3000 rpm lets say...engine is just kicking back havin fun, if someone pulls up ill wake up the turbo
> 
> i like how "88hybrid" from zcar.com did their turbo system setup, im going for something very similar to that, and i love the home made intake manifold


Nice looking motor!!


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## asleepz (Feb 24, 2004)

Very nice indeed. Is the intake manifold just a hallow collector?


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## JAMESZ (Mar 12, 2004)

Matt93SE said:


> GT35/40R in his VG30E Maxima... IT will be used only for drag racing though, so the lack of low end power is fine for him. it'll be right in the sweet spot at the high end with the monster cams and MOTEC... not a ton of boost off the line so that it doesn't rip the tires off the pavement, then builds and is a rocketship once its rolling.


I'm using a GT35/40R, and I shouldn't have a lack of low end power. It all depends on the set-up.


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## Matt93SE (Sep 17, 2003)

Excuse me.. "lack of low end power" should be replaced with "turbo won't spool as quickly"..

I'm not sure where the tiny stock T28 and T3 spools up, but I'm sure it's a lot lower than a GT35R.
nonetheless, the VG30E has plenty of low end torque, so there's no worries in it getting off the line.


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