turbo sizing question...because i have NFI

[wingman]

I've decided I'm probably going 1J, but not because I think the 7M sucks....I am going for some pretty high goals though and need some help because turbo jargon is spanish to me.

My goals:

500+ on pump
600 on C16
spool by 4000rpm
flow to 9000rpm (yeah I know that's high, and I know the work involved)

I'd like to keep it a twin setup, and I'm willing to sacrafice a tad bit of performance to do so.

I've looked at the GT3076R with a 1.06 turbine A/R...but that may be a bit too big for what I'm going for. I'm looking for the most useable powerband up until 9000rpm and no more. Just a wild guess tells me that the GT2876R with a .86 A/R might be better, but like I said I have NFI what I'm doing looking at compressor and turbine maps. I've thrown quite a bit of time into researching but without knowing how to properly match turbo size to engine goals I'm getting a bit lost.

thanks in advance!

 

[rakkasan]

I've decided I'm probably going 1J, but not because I think the 7M sucks....I am going for some pretty high goals though and need some help because turbo jargon is spanish to me.

My goals:

500+ on pump
600 on C16
spool by 4000rpm
flow to 9000rpm (yeah I know that's high, and I know the work involved)

I'd like to keep it a twin setup, and I'm willing to sacrafice a tad bit of performance to do so.

I've looked at the GT3076R with a 1.06 turbine A/R...but that may be a bit too big for what I'm going for. I'm looking for the most useable powerband up until 9000rpm and no more. Just a wild guess tells me that the GT2876R with a .86 A/R might be better, but like I said I have NFI what I'm doing looking at compressor and turbine maps. I've thrown quite a bit of time into researching but without knowing how to properly match turbo size to engine goals I'm getting a bit lost.

thanks in advance!

Really simple, buy Randy's set up. $4100 will get you exactly what you're after, turbos & all...

 

[T34418L3ONE]

yup, if thats what your going for you really cant pass his deal up.

 

[wingman]

is Randy becauseican?

I looked at that, but I'm not fully confident that the turbo's will flow up to 9000rpm, plus his setup on race gas is equivalent to what I want on pump. I may be able to go without the turbo's though, does the hot side have the same footprint between all the GT30 and GT28 models?

 

[RacerXJ220]

I'd recommend buying the kit anyway, and selling the turbos to make up for that cost a bit.

 

[tissimo]

gt2540s

if your going to 9k you can sacrafice a little spool..

 

[Raptor Racing]

, but like I said I have NFI what I'm doing looking at compressor and turbine maps. I've thrown quite a bit of time into researching but without knowing how to properly match turbo size to engine goals I'm getting a bit lost.

thanks in advance!

Having the ability to read turbo maps and picking the right turbo are always 2 different things. I learned this lesson long ago when trying to pick turbo's for my 5m/7m twin turbo project on my mk2. I found that the best thing to do is go and talk to the people using the turbo's you're thinking about using. My research brought me to 300zx and 3000gt owners who were delighted with the GT2535's due to their quick spool and high 500rwhp limit.

Now having said that it doesn't really answer your question. If you want to know the basics on how to go about reading turbo maps I've edited a little write up I did for Yannis when he was picking his turbo's for his twin turbo 7mgte. I'll go through an example and hope it'll make sense...I am by no means an expert so if anyone see's any errors in my theory by all means let me know:

The 1J is approximately 152ci...before we start to map out any turbo's we need to determine how much air the motor can 'flow'. The formula to determine cfm(cubic feet per minute) at 80% volumetric efficiency is: rpm x ci x 0.80/3456. Since most compressor maps today are in lb/min not cfm we need to convert this. The conversion at 80 degree F is cfm x 0.075 = lb/min. Since we are talking about a twin turbo set up we will be dividing the result by 2, since 1/2 the engines output will be powering one turbo and 1/2 will power the other. Seeing that we are calculating the flow of a turbocharged engine we must also consider the added force the turbo will add, according to MacInnes and Corky Bell we must multiply the flow rate of the engine by at least 1.62 which indicates that under the given condition an engine will flow 1.62 times more air with a turbo. So, with the above information we will have the following flow rates:


1500rpm = 3.20 lb/min
2000rpm = 4.2751 lb/min
2500rpm = 5.34 lb/min
3000rpm = 6.4125 lb/min
3500rpm = 7.48125 lb/min
4000rpm = 8.55 lb/min
4500rpm = 9.61875 lb/min
5000rpm = 10.6875 lb/min
5500rpm = 11.75625 lb/min
6000rpm = 12.825 lb/min
6250rpm = 13.359375 lb/min
6500rpm = 13.89375 lb/min
7000rpm = 14.9625 lb/min
8000rpm = 17.1 lb/min
9000rpm = 19.2375 lb/min

Now...we can map the horizontal portion on compressor maps....we still need to understand the vertical scale called there pressure ratio. Pressure ratio = ambient pressure + Boost Pressure/Ambient Pressure...so the formula determine pressure ration for 10psi will be: 14.7 + 10psi/14.7 = 1.68....so here are the pressure ratio's of various boost pressures using the above formulas:

5psi = 1.349 pr
10psi = 1.699 pr
15psi = 2.0489 pr
20psi = 2.398 pr
22psi = 2.538 pr
25psi = 2.748 pr
30psi = 3.048 pr

Now that we have both we can map out turbo's. If you go to www.atpturbo.com you can get some maps. For example if you look at the compressor map for the GT25R you will see that at 5lb/min which is roughly 2500rpm on a 2.5L motor 5psi is not completely out of the question. By 4000rpm the motor will push roughly 15psi and between 7000 and 9000rpm you have approximately 22psi available to you...keep in mind that this is all theoretical and 101 other factors will have a say in this.

Now if you look at the maps you will see little islands...the closer you are to the island in the middle the more efficient you are running that turbo. On the GT25R map the inner island is 73% efficient and the other two are 72% and 65% respectively. The figures I have given above are not close to the major efficiency islands, but I figure with ball bearing turbo's boost will come a little earlier and change the graph a little. I know there are things that can't be exactly calculated, such as intake, exhaust restriction, head flow, temperature, humidity, elevation etc...these calculations are just giving me a rough idea of what I'm looking at.

The problem with relying strictly on maps is this: there are far too many variables to calculate and this method IMHO should only be used to give you a rough idea of what turbo’s to consider. People like Randy have taken all the guess work out of this equation and have selected and dyno’d a set of turbo’s with absolutely amazing results. If you actually look at the turbo’s he’s using (I believe it was GT28RS) and map them out you would probably have never picked them…but real world use and theoretical calculation will always be 2 different things.

Anyway, I hope this helped out!!

 

[89turboguy]

^^^wow......sticky?

 

[CFSapper]

shit gotta get in this so i can use this for later

 

[bigaaron]

500 on pump gas might be pushing it, you are going to need over 20psi and that is where it gets a little iffy on pump gas, at least on 91 octane...

 

[IJ.]

George has really simplified this subject as there's a LOT more math involved ! (thanks George)

You can spend hours and hours matching on paper and many times the result is less than ideal in the real world.

 

[wingman]

Yeah it definately helped, never thought I'd be able to read those damn things...and judging by what I've written down it looks like I'd have to go with a hybrid.

Going by the compressor map, the GT28 with a 44.5mm inducer, 60.0mm exducer, 55 trim, and 0.42 A/R would provide the best flow across the chart in a twin setup. For the turbine I'd probably have to step it up a bit from the standard configs with a 53.8mm wheel, 76 trim, and a 0.86 A/R. I could very well be wrong though.

Since as you say results are often less than ideal, and going by the fact I'm looking at a hybrid turbo with no charts of the two halves together, I'm guessing it would be better to go a little bit larger and give a room for error.

 

[IJ.]

You need to be really careful with hybrids as you can end up with either a Surge or a Choke Monster!

Unless you have a big R&D budget it's better to canvas for real world experience with a particular combination!

 

[wingman]

ouch...don't want that.

overshooting a bit, would this turbo be a good choice in the .86A/R, or maybe something smaller? It's about as close as I can get to what the numbers say, but just a bit larger.

 

[Raptor Racing]

Wingman;

what are your reasons for shying away from the GT28RS; according to my basic calculations that turbo can get you 22-24psi well into 9,000. It's a proven turbo that you can't really go wroing with IMHO. Twin GT28's have been proven to produce more power than most people's wallets can support time and time again. I'm not sure I see the sense in going to an unknown hybrid that might or might not net you the results you're looking for...just my 2 cents.

 

[IJ.]

Wingy: This caught my eye>> "Ideal for smaller displacement engines making up to 400 hp"

You're going to have to look closely at flow through the Turbine section as well as the 1Jz @ 9000 is going to be passing some serious volume of gases!

 

[wingman]

Wingy: This caught my eye>> "Ideal for smaller displacement engines making up to 400 hp"

You're going to have to look closely at flow through the Turbine section as well as the 1Jz @ 9000 is going to be passing some serious volume of gases!

that was another question of mine, i was figuring the exhaust gas flow based on the intake gas flow. 9000rpm = 19.2375 lb/min on both the intake and exhaust side. Is this correct, or will heat expansion dramatically effect this number?

as far as the 28RS, the compressor map does seem to stretch out quite a bit farther...which seems like a good thing, but I'm still a bit weary as to which one would be better suited to my application.



edit: I took the liberty of putting both maps side by side to make comparison a bit eaisier for all of us:

 

[IJ.]

Wingy: There's a LOT of expansion!

This is why I chose the 1.06ar for the 3540 so it can still breathe at 8000.

 

[wingman]

so basically on something like this .86 A/R would be seriously choking it off at upper RPM levels:



or am I simply reading this wrong again? Like you said a hybrid is probably a bad idea, since I don't have gobs of money to toss at mapping it...but I don't know how else I'd find something capable of breating to 9K....or would that extra 2.2lb/min leave enough room for gas expansion?

 

[IJ.]

The smaller Turbo's you're looking at while they'll make the power you're shooting for it's going to be at much higher boost so you can either run low static compression or high octane fuel.......

My pick would be a 3540r with a .8xar turbine.

GT's have changed the goalposts for sizing turbo's.