Company Logo
Internet Explorer

Sorry! Your browser is not supported.

To view this site you can download a newer version of Internet Explorer.

Forum » Off Topic Discussion » Choosing a Turbo

Choosing a Turbo

Off Topic Discussion

If it's not really about tuning or wiring. Then it belongs in here.


Page: 1
Author
762 Views

Hey guys, Ok so I understand how to read compressor maps... and working out the corrected air flow and pressure ratio... But what do you do when multiple turbos seem to suit when you plot points for Max Torque and Max Power on the compressor maps.

For example, We are going to be chucking a Turbo on a 5.0L VS 5Speed Work ute... We have a choice between a GT3076R and a GT3582R

As you can see in the attached image when you plot the points on both maps they both run right through the center efficiency islands, The 3076 has a little more Surge protection while the 3582 has abit more headroom...

Obviously you want as little lag as possible and good transient response, So is it a matter of choosing the smallest possible compressor for the power figure you are chasing? Or is your choice based on compromise and experience? Say in this example we are chasing 500flywheel hp, My guess would be the GT3076 would be the best choice but If we decided to raise boost and chase more power the turbo would be near its limit. But would it be the best choice for that power level?

At the same boost level would you expect the same peak power with the GT3076 and the GT3582? Or would the 35 make more power even tho the boost level is the same, does it just move more volume of air easier? but would be laggier?

Also stuck the GT4294 in there, as you can see the plot points land nicely on that map also... but I would imagine it would be very laggy???

When it comes to choosing Turbine A.R's there is even less info out there... Everywhere will tell you a smaller A.R will give quicker response but limit max power and vice versa with a larger A.R, But how do you know at what point a smaller A.R will limit max power? if you are only running across the lower levels of the compessor map do you then choose the smaller A.R. or maybe if your only to the left of the map as is the case with the GT4294? Or is it just a experience/trial and error deal...

Thanks

Basically just looking for some tips or abit of a guide...

Attached Files

I'm more a NA guy, so definitely NOT an expert on turbo, but here is how I see it from my understanding.

First, I would say that the compressor map show you only half of the data.
You also have to consider the turbine map, and in that regard Garrett doesn't seem to provide great data.

GT3076R: smaller turbine so you can expect to get boost at lower RPM (less lag), but as the same boost level you will also get less peak power -> as you can see on the compressor map, as the RPM increase (airflow), you get out of the maximum efficiency of the turbo.
(with a smaller compressor wheel you move less air, so that should be expected)
As you also mentioned, you have only a very little room for more boost since you would almost reach the choke line of the compressor map.

GT3582R: a little bit more lag but better peak power (same rules apply for the turbine and compressor wheels)

GT4294: might have been good for a high reving 5L engine (with higher boost also), but considering your data, the UTE engine doesn't seem to rev very high. If you dont like lag, I would avoid that choice.

After having spent the last 2 years using a GTX3076R in competition and running it at 500ish bhp I can tell you that it begins to blow very hot air up at those boost levels and power range. We're moving onto the GT3582R as it stays in it's efficient boost range for longer giving us a wider power band further up the rev range, Staying above 70% efficiency where as the 3076 was dropping down into the 60%'s and as a result torque dropping off

I'll admit that when it comes to turbocharger, I always tend to be a 'bigger is better' kind of guy :) It probably stems from my background in drag racing where bigger usually is better. I really struggled with the selection of a Borg Warner EFR 6758 for our 86 - It's about the smallest turbo I've ever fitted to an engine!

So on to your question. While both turbos on paper will meet your power aims, the turbine side of the 3076 is going to be very tight for a 5.0 litre engine. In fact even the 3582 is quite a 'small' turbo for that engine capacity. Garrett list the 3076 as suitable for a 1.8- 3.0 L engine for reference. the GT3582 on the other hand is recommended for up to 4.5 litre.

I personally would be looking at something with a larger frame such as a GT4088 or similar. These are recommended for engine capacity of 2.0-6.0 litres so you would be right in the middle of the recommended range. I have a customer with a built 5.0 litre in a 69' Monaro that runs a GT4202. This car made 440 kW at the wheels on 15 psi and despite what is on paper a large turbo, it makes full boost by about 2500 rpm.

Not sure if this information will be helpful or just confuse you further :)

It all comes down to airflow, at the end of the day the engine is an air pump and a turbo is another air pump. If you have a small engine (pump) driving a big turbo (pump) the engine needs to work hard to drive the turbo, increase the engine size and you'll have a bigger pump which doesn't need to work as hard giving less lag.

I wasn't paying attention to your application properly, I was working off my experience with a 2.5litre inline 6.

Your compressor maps from the manufacturer show their efficiency ranges in corrected airflow, this is a key element when spec'ing your turbo. I've seen lots of people worrying about what boost they'll run to hit the sweet spot of high efficiency and ignoring the air flow side.

Sounds like a fun project! I would love a turbo V8 someday.

Anyway ... man, I can go on for ages on this topic - but I will just get into the main points that stick out, and try and keep it as simple as I can while hopefully giving something useful for you to think about and explore on.

1) What VE numbers & rpm are you using for that engine, and what mods does it have? The flow points you have plotted seem ULTRA conservative even for a stock dirty old Holden 5litre V8, so much so that I think if you rely on what you are showing here you are going to run into strife trying to run ~13psi.

2) Not much is mentioned here on turbine flow. Very loosely, the ability to make the max power with minimal boost comes down to a combination of engine volumetric efficiency (most traditional way of adjusting this is the ratio between exhaust manifold pressure and intake manifold pressure), the density of the air going into it, and the ability of the engine to make x power from a given amount of fuel flow (BSFC) - and realistically in aftermarket tuning the best way of making a meaningful change to BSFC is changing fuels, so when picking a turbo you consider the influence you can have on VE (turbine flow & efficiency) and air density (compressor flow & efficiency).

With those fundamentals taken into account, I've used Borg Warner's MatchBot to throw together a real quick example of what I would have expected from a mild Holden 304 turbo setup running the boost you mentioned - this represents the smallest turbo from the Borg Warner umbrella I'd consider using on your motor, it's roughly the equivalent of the GT3582R.

The numbers I've put in won't be perfect, but should be close enough to give an idea... aside from what I'm sure you'd look at here (Vol Efficiency, compressor outlet temp, boost pressure, the compressor map etc) a couple of other key things to look at in this will be exhaust manifold pressure and engine delta pressure. See this is building up ~6psi "excess" over the pressure at the intake side of the engine? Gases want to equalize in pressure, that will mean there will be a tidal influence than makes the exhaust pressure want to use any chance it has to flow back out the intake - which is one of the reasons you can over cam a turbo engine, or under turbo a high-flowing engine as the case may be ;) 6psi excess is getting up a little bit, it's workable but it's starting to choke the engine a little... so again, this is the smallest hotside turbo I'd think about using on your motor tbh. It would work well enough up to around 17psi, but not ideal.

I wouldn't put anything smaller than a GT3582R (or the .91a/r T4 twin scroll S300SX 83-75 I used for this example) on your motor, a GT3076R will choke the crap out of the turbine side and you'll need more boost to make a given power level which strains everything (especially the turbo and exh. manifold) and will make it potentially knock limited at higher rpm. As Andre mentioned, something in the GT40 range would probably not be a bad call... GT42 may be excessive unless you have a built motor. I'd consider looking outside of Garrett's collection, too.

Click this link and have a look and a play:
http://www.turbos.bwauto.com/aftermarket/matchbot/index.html#version=1.3&displacement=5&CID=305.1&altitude=500&baro=14.502&aat=75&turboconfig=1&compressor=83s74&pt1_rpm=2000&pt1_ve=75&pt1_boost=5&pt1_ie=99&pt1_filres=0.08&pt1_ipd=0.2&pt1_mbp=0.5&pt1_ce=66&pt1_te=75&pt1_egt=1550&pt1_ter=1.22&pt1_pw=17.46&pt1_bsfc=0.43&pt1_afr=12.5&pt1_wts=300&pt1_wd=83&pt1_wd2=74&pt1_wrsin=69033&pt2_rpm=2500&pt2_ve=85&pt2_boost=10&pt2_ie=95&pt2_filres=0.1&pt2_ipd=0.2&pt2_mbp=1&pt2_ce=70&pt2_te=73&pt2_egt=1600&pt2_ter=1.44&pt2_pw=22.46&pt2_bsfc=0.45&pt2_afr=12.3&pt2_wts=320&pt2_wd=83&pt2_wd2=74&pt2_wrsin=73635&pt3_rpm=3000&pt3_ve=90&pt3_boost=13&pt3_ie=95&pt3_filres=0.12&pt3_ipd=0.3&pt3_mbp=1.3&pt3_ce=74&pt3_te=72&pt3_egt=1650&pt3_ter=1.62&pt3_pw=30.9&pt3_bsfc=0.48&pt3_afr=12&pt3_wts=340&pt3_wd=83&pt3_wd2=74&pt3_wrsin=78238&pt4_rpm=4000&pt4_ve=95&pt4_boost=13&pt4_ie=92&pt4_filres=0.15&pt4_ipd=0.4&pt4_mbp=1.5&pt4_ce=76&pt4_te=71&pt4_egt=1650&pt4_ter=1.77&pt4_pw=41.17&pt4_bsfc=0.5&pt4_afr=12&pt4_wts=368&pt4_wd=83&pt4_wd2=74&pt4_wrsin=84681&pt5_rpm=5000&pt5_ve=90&pt5_boost=13&pt5_ie=90&pt5_filres=0.18&pt5_ipd=0.5&pt5_mbp=1.8&pt5_ce=72&pt5_te=70&pt5_egt=1650&pt5_ter=1.91&pt5_pw=43.79&pt5_bsfc=0.52&pt5_afr=12&pt5_wts=400&pt5_wd=83&pt5_wd2=74&pt5_wrsin=92044&pt6_rpm=5500&pt6_ve=85&pt6_boost=13&pt6_ie=90&pt6_filres=0.2&pt6_ipd=0.6&pt6_mbp=2&pt6_ce=66&pt6_te=70&pt6_egt=1650&pt6_ter=2&pt6_pw=41.53&pt6_bsfc=0.55&pt6_afr=12&pt6_wts=400&pt6_wd=83&pt6_wd2=74&pt6_wrsin=92044&;

Just my 2c - anyway, hope I've been more useful than confusing :)

Thanks Guys!

Lith, How did you work out how much pressure there would be in the exhaust manifold? Doesn't this depend alot on manifold design, wastegate size, A/R ratio etc?

Everything makes sense and sounds like you are all speaking from experience but it keeps leading my back to my initial question... For a newbie to turbo selection, The only info provided is the Compressor map, and as my first picture shows the points I plotted on the maps fell nicely within multiple turbo compressor maps from the 3076 right through to a 4294 so how do you systematically choose which one is the best? Are you all purely drawing on past experience and/or what you have seen/heard other people have used on other combinations? Or is there a step by step process and certain information you need and then you can choose the ideal turbo?

With regards to this engine, it is a 100% stock 304, I know the stock Banana intake manifold is a massive restriction. In stock form (retuned aftermarket ecu) Peak power was at like 4200rpm And even without a AirCleaner the engine was drawing a vacuum in the manifold under WOT from about 3000rpm so I know she doesnt breathe well... We were actually given the GT3582R by a Customer... we looked at the ute, looked at the turbo, looked at the ute.... nuff said. But that lead me to the exercise of checking out turbo maps etc to see if this turbo actually suited, the 3076 and 4294 example given was just to show my point from above. Id really like to learn how to better select turbos to give better advice to customers.

So Lith, please do go on for as long as you would like about this topic :D appreciate every letter :)

> How did you work out how much pressure there would be in the exhaust manifold?

I wouldn't call it "work out" so much as make some assumptions and throw some numbers into something that does some math to forecast a general outcome - again in my initial post I see it was more as an example, at least to show the variables but also get a bit of a general low-fi picture of the kind of thing your engine may want. It's really effectively educated guesses to get in the ball park.

>Doesn't this depend alot on manifold design, wastegate size, A/R ratio etc?

Yes it does - check the muffler system backpressure and turbine efficiency bits, between those (which tbh I left as those values seem to give results "middle of the road" if not a bit conservative in most cases I've played with it) and the turbine expansion ratio values you need to change after you've filled *everything* else in so as to make the dots on the turbine map line up with the Phi curve of the turbine housing and wheel you are exploring the idea of using. The exhaust back pressure numbers are calculated by matchbot and seem to be relative indicators at the least, for what it's worth using this and using Garrett compressor and turbine maps I was able to help select an upgrade for a mate from a .84a/r Garrett T04Z to a 1.05a/r EFR8374 and give some assurance that the end result would be more hp/psi from the anticipated relative back pressure as well as spool better - that bit more on an assumption/educated guess that the smaller wheels with lighter materials would be more responsive ;)

> Everything makes sense and sounds like you are all speaking from experience but it keeps leading my back to my initial question... For a newbie to
> turbo selection, The only info provided is the Compressor map, and as my first picture shows the points I plotted on the maps fell nicely within
> multiple turbo compressor maps from the 3076 right through to a 4294 so how do you systematically choose which one is the best? Are you all purely
> drawing on past experience and/or what you have seen/heard other people have used on other combinations? Or is there a step by step process and
> certain information you need and then you can choose the ideal turbo?

OK, I should make it clear here I am not a professional with this and learning as much as everyone here should be - so yeah there is some experience, but I definitely don't have all the answers and don't take all of what I say as gospel so much as stuff to get some direction to explore and investigate :) You don't only have a compressor map, Garrett provide turbine maps as well. If you want to try and make the pressure calcs line up to suit a Garrett turbo with a provided turbine map then adjust the turbine expansion ratio so that each of the corrected turbine flow parameters can land on the turbine efficiency curve for the turbine you are investigating then the rest of the math should roughly line up... that should also help build a little bit more info over what you already have.

So more on the point of your questions, I use a mix of everything really - a mix of experience, stuff I've read in books and forums and talking to other people to learn how to work it out. I don't necessarily use a set pattern as you often have varying amount of information and requirements to work with and some are VERY on the beaten path so it's easy to say, others are way out of my direct experience etc so I have to rely more on reading and theory though where possible I'll rationalise things I've come up with against more known combos to make sure it seems plausible. The whole process I go through with any setup is probably a bit hard to nail down. For what it's worth both with my own tuning, reading other people's builds and what they've got out of turbo combos etc I've seen patterns showing where turbines/compressors/other bits all start maxing out or working better or worse when done in combination with other things and start connecting patterns of why people (OEM or otherwise) have done certain things which previously just seemed like "The thing you do". Tuning is a huge thing, and I think of turbo selection as part of it as there are so many overlaps and so much interdependancy for something to perform. Unfortunately because compressor etc maps are even thin on the ground for new turbos etc, it makes it pretty hard to give a clear path to follow to just work it out - and even if you do have a good amount of info you have to be sure you are using the right things to work out what suits.... for example, cases where gauge pressure and pressure ratio on compressor map are a bit more deviated than what most "how-to guides" will suggest, such as with your car which draws vacuum at wideopen throttle or cars running restrictors in the turbo inlet.

> With regards to this engine, it is a 100% stock 304, I know the stock Banana intake manifold is a massive restriction. In stock form (retuned
> aftermarket ecu) Peak power was at like 4200rpm And even without a AirCleaner the engine was drawing a vacuum in the manifold under WOT from about
> 3000rpm so I know she doesnt breathe well... We were actually given the GT3582R by a Customer... we looked at the ute, looked at the turbo, looked at
> the ute.... nuff said. But that lead me to the exercise of checking out turbo maps etc to see if this turbo actually suited, the 3076 and 4294 example
> given was just to show my point from above. Id really like to learn how to better select turbos to give better advice to customers.

Ahh whoops, I actually trolled Holden specs and used the HSV 185i peak torque and power numbers (& rpm) to try and anticipate what the VE curve may be like - guessing it's just the normal ~165kw one then? I just redid the math and its a bit closer to yours, but still not the same - looking at maybe 48lb/min? Better safe than sorry, I reckon.

Fwiw even if your thing manages to pull a vacuum (WOW! and you're not at altitude?) if you are aiming at 13psi boost gauge pressure then this will probably need to be factored in when thinking in terms of plotting the compressor map. If the throttle body or something about the manifold design provides that kind of restriction then you will get a pressure drop between the compressor outlet and your manifold pressure reference source, so if you want ~13psi/.9bar of boost then you will potentially end up needing a PR of 2 (or more? depending) to get that at the gauge. Convoluted way of saying that if I'm right that you are aiming for around 13psi your turbo will make up for that restriction and then throw 13psi of boost on top of that, big gains to be had - especially if you don't choke the hotside. It also means you can't necessarily fully count on the "NA" flow of the engine to establish what it's going to flow like at gauge pressure, if you were really wanting to get technical you could work out the pressure drop versus baro through the rev range to work out how much you need to make up.

> So Lith, please do go on for as long as you would like about this topic :D appreciate every letter :)

Will try, but I don't want to write too much - doesn't feel right typing it all out, instead of sitting there with a rum spouting so people can't call my on my bullshit ;) Feel free to keep asking stuff or questioning my reasoning, again I'm here to learn and definitely don't profess to be an expert on this kind of thing... just interested, and have had some pretty decent results with this kind of thing which have kindof encouraged me a bit :D

Thanks Lith, Interesting reading...

I wasn't so much Targeting 13psi, more so was targeting 350rwhp. So was using the boost adviser on Garrets website... Used 500hp as the flywheel figure (allowing 30% loss) This was before I tuned the stock setup so I put mid range as 3000 and Peak at 5000rpm and 13psi is what it Said was required and that corrected air flow. (46.7)

Cool - I should have posted an updated Matchbot post after that rant above, but 46.7lb/min and 48lb/min are within a reasonable range of error I reckon (it's going to be hard to pic an exact level) so it all is pretty comparable. 30% is a hell of a transmission loss! What power did it make on the dyno NA?

Let us know how you go - hope some of the ramble I gave was useful!

Cheers,
Dan

It's probably worth mentioning that in the future we intend to develop an advanced turbocharger course that will be the perfect way of answering many of the questions you've posed. I've found that the topic of turbo selection and sizing is still largely misunderstood and hopefully this course will help.

Looking forward to that one!

The best I could make was just over 200rwhp with the MS ECU

Cool, that's roughly what I would have expected - sounds good :) One of the first things I do to get a thumbsuck of where I might expect things (before going into the real serious math) to be needed assuming a not heavily knock limited setup and the turbo is well matched you could get a rough idea of the pressure ratio you should expect to need by dividing your target power by your current power... ie, 350whp / 200whp = 1.75, which is in the territory of what you are shooting for. So far I've found it to work out surprisingly well but it obviously doesn't give you your airflow requirements

Another thing to think about is what kind of constant load will you be placing on the turbo that you decide to go with.

I've never had a turbo go bad on me (except a K04 factory turbo, and it was covered under warranty because so many of the seals were going bad). I'd like to think it's because of the amount of constant load that I place on the turbo, along with how much of the compressor map I actually utilize.

I usually try and figure out how much HP I actually want to run, and then add 80 hp to that because I know that I will want to make more power even after reaching that original HP number. Then I figure out with my 3.0L engine, how much air will I need in order to pressurize the engine to make that HP. So I look at compressor maps and see which turbochargers can move that much air around the 78-80% efficiency range of the turbo @ that amount of air that I need.

For daily driving purposes, I want my boost pressure targets to be around where the 78-80% efficiency range is of this turbo. That way, I will be running this turbo up around where the air stays cool and isn't heating up too much (and also the RPM load of the compressor wheel is well within range as well, which should help with longer bearing life). And if I want to make that additional 50-80 hp, I can maybe push it up into the 85-88% efficiency range.