i am setting up a single turbo on an 85' irocZ w/ 305ci, and in looking for a turbo i have become confused on how big of a turbo to have. i only plan on boosting 10psi (AT THE VERY MOST) @ 3500-5500rpm. i have been looking around a compressor maps and using pressure equations, and both are leading me to a small turbo which is okay. my problem is, to me that doesn't make since, because a engine with more cubes will have MORE exhaust gas energy than an engine with less cubes. Basically and four cylinder will have to rev higher then an eight cylinder to accomplish the same quantity of boost on the same size turbo(?). right now i have a Garrett T3 w/ A/R of i(0.48) e(0.49), if i could get a larger exhaust housing an drive up exhaust A/R the turbo might be fine(?). How does the A/R on the intake side affect the spool up time and boost pressure? here are the equations i have been using and the maps i have been looking at.

Pr = 1.88 Boost 10psi

Pco = B + Atm + Ipd [10(psi) + 14.7(psi) + 3(psi)]= 27.7psi
Pr = Pco / Atm [27.7(psi) / 14.7(psi)] = 1.88psi

Compressor Maps-http://www.turboneticsinc.com/comp_maps/fig1.html

Equation- Pr = Pco / Atm
Pco = B + Atm + Ipd

Pr = Pressure Ratio
Pco = Absolute Turbo Outlet Pressure <psi>
Atm = Atmospheric Pressure (14.7psi) <psi>
B = Boost (MAX) <psi>
Ipd = Intercooler pressure drop <psi>

 

give me a horsepower requirement and what type of exhaust system meaning

1)header
2)some type of log

i'lll reccomend something for you. Also give me the weight of the car

 

Wow, where did you get those equations? I can’t make heads or tails how you got those trim/A/R #’s computing boost and pressure ratio. I’ll tell you right now, 2 T3’s that size would barely give you what you’re looking for and with that small an exhaust A/R (I haven’t heard of a .49…) would probably cause a restriction.

You really need to do a bunch of reading if you want to understand the sizing and compressor maps, but to get you started you need to find your pressure ratio (which you have) convert it to a density ratio (easiest to just look up on a chart, the math involves estimating your compressor efficiency, converting it all to *R and then calculating the temp raise due to the pressure rise + compressor efficiency (actually inefficiency) and using boyle’s law to convert to find the density, which in your case works out to roughly 1.45 without an intercooler, the better the intercooler the closer you’ll get to your 1.88 pressure ratio), and CFM or Lb/Hr (at 5500, assuming that you’re at about 80% VE):
CFM= (305/12^3) * (5500/2) *.8 = 388cfm, which is roughly 26.8Lb/Hr

Now you take your density ratio (again, 1.45-1.88 depending on intercooling), multiply it by your air flow (CFM or Lb/Hr) and find a compressor map that that amount of air is on the map at a pressure ratio of 1.88.

A quick look at the standard Garrett Compressor maps, it looks like a T04b H3, V1/V2, T04e 46, 50, 54, 60, as well as 60-1, T61, 62-1, T64, T66, T70, T72, T76 will all work OK, with the 60-1, T61, 62-1 being the best fit (you’ll be right in the middle of the efficiency island).

Exhaust A/R sizing is more an educated guess, I don’t know of any accurate way of computing it. You’ll have to take into account the size of the engine, the exhaust routing before and after the turbo, camshaft, what RPM you want it spooled by… for most of these I’d venture a guess that you’d want something in the .8x range…

 

B] 89ProchargedROC [/B] -[list=A][*] the car is mostly stock, 3" catback, gutted cat, 3.42 gears, and a 100hp shot [*] power increase- MORE
on desk top dyno, i can get up to 235HP @ 5000rpm. missing key info
-lift v. cfm @ pressure drop
-head chamber volume
-head gasket bore
-head gasket thickness
-piston down from TDC
-volume above piston
with this info the DTD should be dead on.[*] 3" pipe from the turbo all the way to the muffler (dynomax) and no cat.[/list=A]

83 Crossfire TA - [list=A][*] where the formulas wrong?[*] both A/R were cast in to the intake/exhaust housing[*] the turbo came from a late model Saab 9-5 Garrett T3-?H4?[*] where can i go to buy different intake/exhaust housings?[*] i understand the surge limit, THE ISLAND, and efficiency range. you have suggested the T-62, looking at the compressor map http://www.turboneticsinc.com/comp_maps/fig9.html, to me it looks like the plot (1.88,10) put the turbo in surge area.[/list=A]

here are the other formulas that i have been using.[list=1][*] Pco = B + Atm + Ipd[*] Pr = Pco / Atm[*] Di = (B + Atm) / (R * 12 *(460 + It))[*] Mf = Di * Ci * (RPM / 2) * VE [*]CMf = Mf * (sqrt(CIT / 545)) / (Atm / CCIP))
Pco = Turbo Outlet Pressure [Absolute] (psi)
B = Boost (psi)
Atm = Atmospheric Pressure (psi)
Ipd = Intercooler pressure drop (psi)
Pr = Pressure Ratio
Di = Air Density [intake]
R = 53.3 (constant)
It = Intake Tmp (^f)
Ci = Displacement (ci)
VE = Volumetric Efficiency (%)
CMf = Corrected Mass Air Flow
CIT = Compressor Intake Tmp
CCIP = Corrected Compressor Inlet Pressure[/list=1]

 

To be honest with you RallyeNate, I’m a bit lost on what you’re doing. Going over the equations they look like they should be reasonably correct, but I’m not sure where you’re going with them or even where you got it from.
# 1 -> yea, it will give you the correct # but I’m not really sure what that number really gets you since it doesn’t account for intercooler efficiency, pressure drop due to temp drop…
2 -> Pressure ratio… yea, boost is pretty much meaningless, but pressure ratio really gives you an idea of how hard the compressor is working… this one is useful
3 -> Di appears to be the same as what I was calling Density Ratio. I see the conversion to Degrees R, but I’m not sure why you’re using a constant and multiplying by 12… I wouldn’t use a constant that is the same as the units for something else in the equation, could get confusing… It's probably approximatly correct but I didn't try running some #'s to make sure. I hate equations with 'constants' without any indications of where they were derived from.
4 -> That’s what I did in my example assuming that Mf is CFM
5 - > I’m not sure what this is giving you (honestly I didn’t stare at it for more then 10seconds) what are you correcting for?

The math I showed you pretty much covers it, and if you put that point on the map you get a point where the red dot is on the attached map.

The saab is probably a 42 or 45 trim T3 with a .48A/R turbine, which is a little tiny turbo, 2 will be on the small side on your small block

 

To be honest with you RallyeNate, I’m a bit lost on what you’re doing. Going over the equations they look like they should be reasonably correct, but I’m not sure where you’re going with them or even where you got it from.
# 1 -> yea, it will give you the correct # but I’m not really sure what that number really gets you since it doesn’t account for intercooler efficiency, pressure drop due to temp drop…
2 -> Pressure ratio… yea, boost is pretty much meaningless, but pressure ratio really gives you an idea of how hard the compressor is working… this one is useful
3 -> Di appears to be the same as what I was calling Density Ratio. I see the conversion to Degrees R, but I’m not sure why you’re using a constant and multiplying by 12… I wouldn’t use a constant that is the same as the units for something else in the equation, could get confusing… It's probably approximatly correct but I didn't try running some #'s to make sure. I hate equations with 'constants' without any indications of where they were derived from.
4 -> That’s what I did in my example assuming that Mf is CFM
5 - > I’m not sure what this is giving you (honestly I didn’t stare at it for more then 10seconds) what are you correcting for?

The math I showed you pretty much covers it, and if you put that point on the map you get a point where the red dot is on the attached map.

The saab is probably a 42 or 45 trim T3 with a .48A/R turbine, which is a little tiny turbo, 2 will be on the small side on your small block

 

235hp more that what you have now?

just give me a number and i can select a turbo for you. You already stipulated the rpm band and the inches....just give me the hp you want

 

83 Crossfire TA -
I found the reason i kept coming up short on the air flow, other then my programming error i have never had a problem with the fourmulas. As i said before the Saab turbo would be to small even for a twin turbo setup. i plan on running a single turbo set up with the T62 turbo.

89ProchargedROC-
235HP i know is a bit high of a stock camaro, but with out the listed information that's is as close i a can get. i am just looking for a good increase in power, i still have a stock bottom end.




Where can i go to get different turbo housings and turbos?

 

OK....one more time.

HOW MUCH HORSEPOWER WOULD YOU LIKE TO HAVE?

This is a question you must answer so that i can help you reach your goal of XXXhp @ a low 5500rpm

thanks

 

89ProchargedROC-
i understand that you're looking HP number, i am not trying to meet a certant hp number. if have a number, i am looking for a 60-50% increase in power from stock so about 130-110HP.

THANK YOU

 

89ProchargedROC, I’m somewhat curious about what you would suggest and how you got to that answer (are you looking it up on a chart somewhere, reading maps, using software?) because I really believe that choosing turbo compressors by HP desired can be a big mistake, so I’ve got two loaded example/questions for you:
both trying to make 450hp and both using a very efficient, water to air intercooler
- the first is a 383 (very mild, L98 cleaned up ‘vette heads (about 185cfm intake ports), log manifold, tame cam, TPI) trying to do it at 5000rpm
- the second is a 3.8 (heads that flow about 160cfm intake, running TTA manifolds and open downpipe) trying to get it done at 4500rpm.

What would you recommend and how did you choose it? (please don’t take it as a trick or anything, I’m just trying to understand what others use as a decision process for this, personally, I'm happy being a raw #'s and then go out and try it person, then double check the #'s so I know that they work right both ways, but don't like charts, rules of thumb...).

 

Thats the wrong map, thats for a 60-1 T3, this is the one for the turbo you have.

 

I’m hoping that he realizes that, and assumed calling it a T62 was a typo. When I cropped it and put the point on it I made sure to leave the 60-1 lable on it.

 

83 Crossfire TA-
i did see the lable on the compressor map and T62 was a typo.

Jester-
i thought it was a given that the map 83 Crossfire TA used, was for the 60-1 not the t3.

 

I am not too keen on what works for the v-6ers.....but i have been around quite a few turbo/twin turbo setups on v-8s on chevys and on fords and kinda know what to expect.

for the 383.....it would depend on on what kinda pressure you are willing to run. Answer than and i can finish the question

 

Hey RallyeNate, your mention of a programming error has me wondering, have you written some code to help with this? I often put together spreadsheets to do stuff like this but haven't bothered with one for turbo sizing (yet).

 

Yes, i wrote them in my fortran90 class a couple of years ago.
those formulas i posted before are the programs i wrote.

 

Wow, Fortran… slightly scary. Why were you learning Fortran (I know that current CS majors take “this is where we came from’ classes which basically have them programming in a string of outdated languages to show them some concept of how they evolved)? To date myself some, when I was in college I did a lot of ‘structured programming’ in Pascal.

To repeat some questions from before, where did those formulas originally come from and what is the Mass Flow and Corrected Mass Flow describing?

 

Well, that’s sorta the point. What I’m willing to run and what I’d need to run could be 2 completely different things, and most people would have a hard time guessing how much boost they’d need to make the HP they want. I might be willing to run 20psi if I have to to get the power, but in this case I wouldn’t need that.

Lets say that I’m willing to run up to 25psi on both. Why would it being a v6 make a difference? Are you basically making a suggestion on what you’ve seen works? That side of the example could just as easily be a late ‘90’s ford 4.6 SOHC, a 289 Ford or a 283 chevy, all pretty much stock, or even a 305 that you expected that HP peak at a slightly lower rpm. Sorry for being slightly cryptic, but I’m more curious about how you’re going to answer the question, without biasing the answer with my own thoughts on the subject.

 

83 Crossfire TA-
Sorry i dont remember where the formulas came, i would like to know myself. I would like to reread that arctical because i haven't use those programs in so long, i forgot how to use the variables. well i am sort of an Mech. Eng/ Auto Tech/ Info Sys/ EMT Major in other i dont know want i want to do, 3yrs 90cr hrs later! if you want, i could probley email you a copy of the programs, all four or five of the fit on a 3.5 floppy.
I think the Mass Air Flow display how much air it will that to feed the engine and the Corrected Mass Air Flow will give the answer you need for the compressor graph not sure, i was lucky to find the programs, sorry it has just been so long since i've used them.

 

i am basing on my choice on what has worked in the past for quite a few turbo V8 combos i've been around. The turbo 6 is a different animal and im not going to be ignorant and say that i could suggest something for a motor i dont know much about and/or any experience with.

If you were willing to run 25psi through a TPI intake to only achieve 450hp at the crank, that sure would be one hell of a tiny turbo; ie small trim T3. If you want to run say 10-15psi and achieve 450hp out of the setup you mentioned....i would reccomend a Garrett T4 with a V1-trim in a T04E .60 housing (4" inlet 2.5" outlet) with a .69a/r exhaust housing. It should have great spoolup and make the hp goal and even possibly more

 

Well I feel a little stupid for bringing up a topic that hasn't been posted on for a few months. I've been searching these forms for hours durning the past 3-4 days on turbos and for the past few months on s/c setups (plus I will be ordering some turbo books, so I'm learning, not just throwing unresearched ?'s around) and so I thought I'd just reply to this one since it seems to be where I want to go.

A single turbo (T5x/T60/60-series?) on a recently rebuilt 305 TPI (nothing fancy, rebuilt about 3-5K ago by previous owner) with 8-10lbs of boost should get me around 350 RWHP, right? Stock our motors are supposed to have put out around 220hp/270tq. I would think that a T4 would be too small, but since I haven't gotten my turbocharging books yet, the best I can do is make an educated decision from reading the hundreds of posts and engine builds on this forum. Since horsepower gets you there faster as a measure of time, but torque gets you off the line faster, I would be happy to see around 350rwhp/400rwtq on an intercooled (don't know where to put the ic yet) T4/T5x/T60 turbo running 8-10lbs of boost. But maybe I'm just daydreaming of getting that much power out of a 305. The TTA guys can do low 12s/high 11s with 375/450, so I guess I'm thinking why not the V8? I won't be doing drag racing at the strip (maybe once to get some ETs) so I want this to be built for street kills (and I know I can't beat everything.) If it were a strip car, I would be shooting for 12s. Keep in mind I'll also be doing some body mods like SFCs and a 6 pt rollcage to stiffen up the chassis, so that should help with traction and handling. Maybe box the LCAs and build a wonderbar and front strut brace too.

I'd like to see the boost kick in around 3K rpms and go until 4500 or so... more of a torquey motor, since when stepping on the gas hard from a stand still, the tranny normally shifts around 30-3300, so I don't want to wait until 3500-4000 when the turbo kicks in. But I don't know what's best, so help finding a boost/shift combo would be great. With the 700R4, I cruise around 2K rpms at 65mph, around 23-2400 at 75. With the new turbo technology out, there shouldn't be much (if any) turbo lag... at least that's what I've been reading. Does that mean that when you hit the gas the turbo kicks in sooner, say 2500 instead of 3000, or does the engine rev up faster? What defines "kick in"? A turbo should be making some amount (not the full amount) of boost the whole time the engine is running... Maybe a bigger turbo is better, but I've always heard "err on the small side when building an engine." I haven't driven a turbo car, so I donno if it's ok until you hit the turbo and then there's no stopping, kinda like a 2-stroke?

I'm sorry that this is another one of those "umm... help me I need a turbo" posts... But I've read and read and read and have these questions... at least it's on a thread of a similar topic, and not a new thread.

 

Well, that's 220 at the crank. I have no idea what they dyno. Assuming that is actually an accurate number you'd need to give it about 10-12psig to make about 350hp at the crank.

That depends on what your goals are, but to put 350 to the crank a T4 would nont be too small.

I hate that stupid analogy… torque is how much twisting force you have available at the crank, that can be multiplied by gearing, torque converters, there are assorted losses…

Assuming that your car is set up correctly and properly geared to take advantage of the power band wherever it falls, all you have to do is talk about HP and you'll get a proper indication of the cars performance (assuming you know the weight).

Absolutely no reason.

 

oooooook... Well then, here are some more questions.

Why not? The V6 can't weigh that much less (200lbs?) So taking that into account, why couldn't a turbo V8 with the same specs be almost the same as a V6? I did a search for this and wasn't able to come up with any answers.

The WRX STi has 300/300 and a curb weight of 3200lbs and runs in the 12s. The Lancer EVO also runs in that range too. So, why couldn't T/As which are around 3800lbs be able to run 12s with a 375/400 setup? Don't flame me here, I'm just curious why. I know the new engines are high tech, but in most cases, hp is hp and tq is tq.

Can you give me the calculations to figure this out, so I can build the car that I'm looking for?

 

I think that you misunderstood me… to clarify, there is no reason why 1.2L more displacement with 2 extra cylinders and other wise very similar proportions to a 3.8L buick (well, larger valves), wouldn't make significantly more power then a comparable setup on the smaller 6.

First, advertised HP is not necessarily what it really makes.

Second, I already said, torque has nothing to do with how fast you will run assuming that your drivetrain is geared… to match the power band, you will run roughly the same times with 500hp at 3200rpm as you will with 5000hp at 7000rpm, you'll just need different gearing, converter, driving techniques… to do it.

Third, I doubt that this will come out here, and if it doesn’t do a search online, there are loads of calculators and web pages devoted to this, but here:

 

Nope, looks like the formulas didn't come through (I'm betting the cube roots killed it...) look around online, there out there.

 

Ok. Hey thanks for all the help.

I've searched the internet and haven't found the gear ratio formulas yet, but I found the ET formula, so I post it here in case anybody else wants to use them.

Calculate 1/4 mile ET and MPH from HP and Weight

ET = ((Weight / HP)^.333) * 5.825

MPH = ((HP / Weight)^.333) * 234

Go here for an online calulator.

So, using the online calc (don't have time right now to run the numbers manually) it would take 350 RWHP to get a 12.5 out of a 3500lb car. That translates to around 385 at the crank (assuming 10% loss) and I think I would be hard pressed to get a turbo 305 to 385hp on stock insides. Maybe I'll do it anyways for the experience of building a turbo.

 

The HP in both of those assumes HP at the crank.

Also, typically drivetrain losses are around 15% for a manual tranny and closer to 20% for an auto (FWIW, typically a manual tranny car will run a slower ET with a faster MPH and an auto a faster et with a slower MPH…)