Alright y'all i've got some major questions i need cleared up about Flow and VE in choosing compressors and turbines.

Here are some facts
S13 SR20DET motor
Greddy Intake Manifold
JWT S4 cams 264 duration 11.5 mm lift
stock ports
stock 8.5:1 compression
GT3037s turbo
this setup made 357rwhp @15psi with a 2.5" exhaust

121 x 7600rpm / 1728 x 2 = 266cfm airflow. add boost multiplier of 2.02 for 15psi it comes to 537cfm. Convert to lb/min 537 x .069 = 37lb/min. Now if we assume the lb/min to HP comparison of 10hp per lb/min thats 370flywheel hp let us assume that this setup is surely not at 100% VE because of the exhaust


the same motor but with 9:1 pistons and rods
made 392rwhp@15psi with no exhaust
and 457rwhp @20psi no exhaust

the lack of exhaust and higher compression helped. but the HP level indicates 110% VE and higher. at 20psi the motor is supposed to flow 44lb/min. If we assume the motor makes 10hp for every l lb/min of air, thats supposed to be only 440flywheel hp.....i'm making 457Rear wheel hp.

The volumetric efficiency variable is really messing up my compressor choice. People say theres no way a SR can be that high a VE. these dynos numbers are on 2 different dynos. can we then assume that this setup makes more HP per lb/min of air?

Is there any possibility this turbo i've chosen a T04e 50 trim with O trim T4 turbine side will make the 400hp @15psi i want? with the 10hp per 1lb/min assumption i'll be choking the compressor at that boost level. using a 100% VE calculation @7600rpm its on the right side of the best efficiency island.

This math is really pissing me off cuz there are too many variables and they are ******* with my head. I plan to put a MAFS sensor on a flow bench and have airflow to voltage output chart, then datalog the output of the mafs when its put on my car. the power is there though, the car went 11.39 @ 119 with 2550lbs race weight.(the motor used is the first example given....the built one let go last season)

where am i wrong at? my next compressor choices are 62-1 or T58 or T61. max power will be 400rwhp at lowest boost possible, no higher than 15. I just dont wanna see this turbo choke on the dyno with a new manifold i'm building for it.


[Modified by Greaser, 7:40 PM 2/19/2003]

 

Greaser-

What are you doing here?

 

whats up man. i'm trying to prove me wrong and right and the same time. there are too many trains of thought for sizing. and i'm combining them all and coming up with some wrong stuff.

one train of thought is to use a hp goal, then plot that point on a map using 10hp per 1 lb/min

another is to use a calculator which implies a variable for VE.

VE is what is screwing me, or the two dynos i go to are both reading 50-70rwhp HIGH

 

Great post!!!

Unfortunately, there may not be much help for you here. Seems like there are several competent builders on this board, but "engineering types" are scarce as hen's teeth.

In the past, I've had good luck with my "uber-techie" questions on the JYturbo list at Yahoogroups.com. The membership is primarily F-body owners (weird for a turbo list...), but they love number crunching. There are some extremely knowledgeable people on the list. The bad part is the amount of volume that list generates. Usually about 200 messages per day, and many of them are pure crap. I would definitely suggest "digest mode" if you subscribe. Good luck. Give us the results if you find out what's going on!

 

well i think i'll just test this compressor out on this motor. i fear that VE of this SR20 is higher than what people say isnt possible. We'll find out on the dyno when the mani is done. cuz the setups without exhausts bolted on go into 105, 110 and even 120% VE.......

there was a post on another board where we calculated VE with A/F at a certain RPM and a certain fuel pressure, certain fuel injector flow rate, boost pressure, and air density. it came out to 107%

whats funny is this is on a LOG manifold i built. now i'm building a long tube header for the turbo to be mounted in the front of the block with a 4" downpipe and exhaust. i wanted 400 hp at the lowest boost possible.

 

are people not understanding this? my post?

i hear about this 10hp per 1 lb/min airflow alot for hondas and nissans..... its a given my motor has made 392rwhp @15psi it CAN make 400 with some cam gears. which is where my 400 number comes from


so 400rwhp = 45lb/min (400rwhp =450 flywheel hp)

an SR20 at 7600rpm @15 psi makes 31lb/min @ 85% VE
an SR20 at 7600rpm @15 psi makes 37lb/min @ 100% VE
an SR20 at 7600rpm @15 psi makes 45lb/min @ 122% VE

Am i to assume that my motor has to flow 45lb/min of air to make 400rear wheel hp? This equates to 122% VE!!!! 37 / 45


Something is wrong here. its either my SR20 makes more hp per lb/min
392rwhp@ 15psi.....450.8flwywheel hp / 37lb/min= 12.1hp:1lb/min

or the VE is actually up that high. I'm going to look at a map of a GT3037s compressor now to see if it is choking at 45lb/min @ 2.02 PR.


Please theorize with me.


[Modified by Greaser, 12:12 AM 2/20/2003]


[Modified by Greaser, 12:21 AM 2/20/2003]

 

I really think its good that you are thinking about it with formulas, but is it law? Yes you have the laws of physics that can not be broken, what who is to say that the figures in your equation are correct?

Yes, we have compressor maps and some formulas that we can follow but you have to understand that the variable change everything. Just today I was talking to a former garrett employee and we were discussing some of their new compressor maps. His quote was, "we dont really like to put out maps because 1) No one doesnt really knows how to read them 2) they are not accurate and 3) People mistaken them as God's Law and follow them." Yes, they are good reference, but not law and you shouldnt let it be your deciding factor into buying a turbo.

Thinking is great for the mind, but dont over do it.

art

 

you are over-analyzing this. like art said not all the factors in ur equations are set facts. if u put in estimations for factors u r only gonna get an estimation as a solution. trial and error is the best way to find ur perfect turbo.

what is ur goal? just to make big #'s at low boost? a 62-1 or T61 is a HUGE jump from a 50 trim t04e.


[Modified by DIRep, 4:40 PM 2/19/2003]

 

Well I doubt I can keep up with you, after reviewing this post, however I'm willing to think about the project.

I was always to understand that CYLINDER PRESSURE and port velocity are the key players in determining power output. The camshaft is the controlling factor for both of these parameters. By optimizing the timing events within the crank cycle for the required rpm band, the cylinder pressure can be tailored to compliment the engine geometry and components. A minimum flow rate exists for a particular cross-sectional area. And average cross-sectional area may need to be calculated with all manifolds included, the manifolds may help exhibit higher velocities than normally conceived with normal port area calculations. Of course forced induction and high volumetric efficiency motors have breathing capabilities beyond their cubic inch limitations and will follow these trends a little DIFFERENTLY. In these special cases, the engine components must reflect this increased breathing capability. In short, if an engine has substantial intake flow capability, then the exhaust side must be equally sized, regardless of the engine's cubic inch displacement or horsepower rating. What kind of cylinder pressures are you calculating? To end with, there may be something esle to consider, that is way beyond me, is Inertial Wave Tuning effects. With that said I'll try to conjure up some theories if I get the time.

 

I thought VE's well over 100 percent are very possible with a turbo car because of the definition of VE. It is defined as the ((actual cfm)/(theoretical cfm) x 100) When you calculate theoretical cfm you are not taking into account the fact that the motor is forced inducted. In a forced inducted vehicle it seems very possible to me for the actual cfm to equal or surpass the theoretical cfm and therefor create a ratio greater than 1 which in percentage is over 100. *shrugs* thats my take on VE anyway

 

I agree!

EDIT: remember that an S2000 makes around 130% VE and that is a NA engine


[Modified by GZERO, 12:29 AM 2/20/2003]

 

UH Greasy your thinking too hard and relying on too many factors and forumlas and REAL WORLD answers. I had this conversation with Seth about the whole hp per pound thing and what's wrong with that is say at 1-10 psi you may be making say 10 hp per pound but then 11psi and higher you start making 12 hp per pound it gets into its efficiency range for the turbo, Like when you have a really small turbo say a TD04 stock DSM turbo it makes great power at low rpms and boost but turn in up and it starts falling off up top and no matter what you do it doesnt make anymore power the more you turn the boost up. Its like my old T3/TO4B S trim compressor wheel(SMALL) after 19-20 psi it wasn't doing anything more, let's make the 400whp turn up the boost, so little or nothing gained, OUT Of efficiency. OK Greasy talk at ya later. I thought 60-1s sucked but 62-1s are the bomb?

 

have you tried this yet?
http://www.turbofast.com.au/javacalc.html

http://home.earthlink.net/~tailwags/...urbo_math.html (my web page, a little weak, but it explains it well, no Hp though)

One thing you are missing is the mutiplier for the density ratio (it won't be 1:1 as you calculate due to increases in temperature), and I wouldn't get hung up on VE.. it's a fudge factor for bad heads on NA engines....

You can only make enough power based on the FUEL you use, not the air... but since fuel is hard to measure, people use air instead. The problem is, that's hard to measure too.

If you know your IAT, you should get real close, but use BSFC as a basis for power/ efficiency.

 

i broke out some of my combustion books with javier tonite and i was gonna help you do some calculations until i realized that youre the flaming ******* from freshalloy.

go away.

 

HAHAHAHAHA! LOL! Hey Derek I guess the feelings are mutual between you and Geoff. LOL! 60-1s RULE Greaser!!!

 

i knew that was coming ffgeoff. i posted anyway. call me a flaming *** hole all you want, you are the ******* if you have information with no offer of help. Somehow i became a flaming *** hole by trying to help you at first. but you are too stuborn to see that there MAY be better solutions out there then a 60-1 @25psi.

I'm here saying that i may be wrong and you still wont help?

 

60-1 is hard to beat for $

as for help, here u go
VE=actual mass flow/theoretical mass flow
theoretical mass flow=working volume*average density

if u can pull the data/voltages from ur car, then this becomes relatively easy. the b14's(sentra/200sx) have both IAT and MAP sensors. i dont know if the S13's do. with values of temp and pressure u can calculate average density. if u can save the logged data to a text file, then u can import it into a spreadsheet or math program and calculate/plot VE.

there are other eq's that model VE. i found one that considers both mass flow rates of fuel and air and intake and exhaust pressures. the above method seems like it's easier.


[Modified by javierb14, 2:38 PM 2/20/2003]


[Modified by javierb14, 2:46 PM 2/20/2003]

 

There was another thread on Freshalloy we gathered all that information and found VE to be 95% on the setup with exhaust and 105% on the no exhaust setup. It was rather intense but theres still alot of variables.

we used fuel injector flow rates, duty cycle, air temp, boost, rpm, a/f ratio. I'm using a Tec II ecu and i have both the 15psi and 20psi dynos on datalog along with dyno charts and a/f posted. The only way i think i can find true VE without variables is to
a: buy a big bore MAFS sensor
b: put that MAFS on a flow bench
c: chart the airflow vs. voltage output of the mafs under certain airflows.
d: run the MAFS on my car the next time its running, datalog the voltage output and then refer to the chart i had made. BOOM. theres my answer. it can only be +/- 10% for weather conditions. Do you aggree with this idea?


I agree that i may be overthinking this, but i'm overthinking this to learn.


also i agree the big flow T04B is hard to beat for price(and even flow rates of comparison compressors). If the 50trim doesnt work i'm going 62-1 with Otrim T4 turbine. nearly identical in price. Only the T58 and the T61 start going in the 1,200 and higher ranges. Heck my GT3037s i paid 2,000$ straight up for.



[Modified by Greaser, 11:21 PM 2/20/2003]

 

have u considered the SC61 turbo from precision? looks very good on paper....im putting one on my car

so basically u r going to test the big bore MAF and plot voltage vs mass flow? from this data u should be able to come up with the "translation" tables. i pulled these from the sr20forum.

SR20DE 0 to 5.12Volts 5.12 Volts indicates a flow good for approximately 280-300hp on an SR20DE


Z32-VG30DETT 0 to 5.12Volts 5.12 Volts indicates a flow good for approximately 500hp on an VG30


with this data u should be able to use the VE=actual/theoretical model with good results. can u save the data from the TECII as text? if u can, then u can plot the VE vs RPM or whatever.....to analyze/optimize whatever u want. what kind of MAF, cobra?



[Modified by javierb14, 3:58 PM 2/20/2003]

 

You're going to need something else to tell you the actual air density beside's the MAF. From what I've seen flowbenches don't generally tell you what the actual air density or temperature is. With out a basis how do you adjust or recalibrate the readings you pick up? MAF's also work with current along with voltages. MAF is more accurate than the older speed density system you're trying to calibrate for. If you account for all of those variable's plus a few more that may have been missed here it should work fine.

I would get a non-mounted MAF from Digi-Key or Honeywell instead of a mounted restricted one. Cheaper, and easier to work with.

As far as over-thinking don't worry about it. That's what real engineers like to call progress. Better than settling for what's available and being lazy right? Also means you can make it cheaper. Which is always a benefit.

 

Yes, and i can then have a more narrow range of airflow assumptions. Using the two airflow assumptions listed in this thread the range is very wide. This will narrow it down considerably and i'll accept certain err in air density or temperatures.

i dont think it can go text, but i can build a chart if need be. i currently use speed density load sensing. so i wont be able to use the map as indication of VE. I was gonna use a Q45 MAFS....but after talking to a TEC II engineer thats retired, he said the MAFS on the TEC II systems werent as good as i thought they would be. Becuase a MAFS corrects fuel trim for VE changes, put cams in; you get more air. More air, the MAFS sees this. the MAP doesnt. which is where my idea with a flow bench came in.

I havent seen a SC61 on paper. can you link me? if i could get a GT35 compressor on a O or P trim turbine i'd buy. (i have this theory of trying to reach higher intake manifold pressure than exhaust manifold pressure)

 

i was gonna use a temp sensor, gm style.

i've never even been in the same room as a flowbench. i just have ideas in my head of industry tools to use to find out what i need. whether or not they will find it out is where you guys tell me or where i find out on my own .....thus learning more.

what does mounted vs. non mounted mean? i've never heard or seen any other than automotive design MAFS.

 

the sc61 has a GT40 comp wheel and there are a few options as far as housings,turbines, turbine housings and AR's.

HT thread about SC61
https://honda-tech.com/zerothread?id=419064

Precision Turbo addy, sport compact section
http://www.precisionte.com/

 

holy ****, 56 trim GT wheel with a T04 turbine for that price....****.

my 76mm 52 trim was the **** in the GT3037s.....i just sold it cuz i wanted bigger turbine area. yeah if this 50trim falls on its face i'll be making a purchase. thanks for the link.

 

contact Arturbo, he's a dealer
https://honda-tech.com/zerouser?cmd=viewprofile&id=346