How To: Read Compressor Maps

[Brent 930]

The A/R sizing is linear to boost so what boost level you run won't matter. Also to what trim you use. You might want to buy a book on turbo charger design. In any case you will want to be prepared to change up the turbine housings for a different A/R since getting it right the first time is unlikely.

[Def]

Don't necessarily size the A/R for the boost you want to run, size it for the power you want to make. That determines the mass flow through the turbine housing, and in general is a much easier number to deal with.

Just look for similar examples of cars with similar displacement and boost(or power) and see what turbine housings they are running and maybe wheels if that's an option.

[Def]

Oh yea, as for speed of the turbine wheel - that's almost a non-issue. With big power and pressure comes BIG compressor wheels. They take much less RPM to push more air than smaller compressor wheels. Their tangential velocity at the tip is greater just due to the fact that they are much larger.

Turbine wheels are usually smaller than the compressor wheel, so no worries there.

[Brent 930]

Also running too high boost for the compressor wheel can cause it to overspin. You can clearly see the rpms of the compressor on the map and more boost the faster the wheel is going to be spinning. Again if the turbo is matched even close then it shouldn't be an issue.

[Def]

Also running too high boost for the compressor wheel can cause it to overspin. You can clearly see the rpms of the compressor on the map and more boost the faster the wheel is going to be spinning. Again if the turbo is matched even close then it shouldn't be an issue.

This is a common problem with some factory turbos that use ceramic compressor wheels. Their tensile strength isn't as high as other materials they're usually made of, so they have a tendancy to just let the blades go at higher boost than stock.

I know Skyline GTS-T turbos do this with only 3-4 psi more than stock and some breathing mods. I haven't ever heard of a non-stock turbo doing this though.

[highboostingm3]

Def:
What is your input on using a T4 turbine housing rather than a T3 turbine housing? The subject came up in another thread that you could get similiar spool characteristics with a T4 turbine housing if the A/R is low enough. Is there a formula to figuring out the spool characteristic of the turbine wheel? Say to figure out what is equal to a T3 turbine housing that has a .82 A/R(pretty standard size I guess)?

I was thinking by comparing the s50 to the 2jz-gte engine. The displacement is the same(3.0L). The head on the s50 flkows a little more than the 2jz-gte head. The intake manifold on the s50 flows less than the 2jz-gte. However they are somewhat similiar, so I was thinking if you did a turbo setup similiar to the type we are doing right now with s50, could you have nice power with full boost by 3200 rpm? Could you do this with a T4 turbine housing you think? If you did...would a .58 A/R choke your engine too much with backpressure?

[Def]

Unfortunately, turbine housing and wheel choice has to be pretty much based on "best guess" and seeing what works for other people.

A smaller A/R on a larger turbine housing can give you slightly better spool, but it is pretty close either way with the same turbine wheel. For instance, a 0.63 A/R T3 housing will spool up a GT2871R w/ a T3 housing about 200 RPM sooner the same as turbo using a 0.86 A/R T25 housing(on a 2.0L 8.5:1 CR 4 banger - SR20DET). The smaller A/R value means that the radius is tighter, but the area is larger on the bigger turbine housing(T3 inlet is larger). So this gives the exhaust gasses more centripetal acceleration to spin the turbine wheel up. The mass flowrate is about the same for these two turbine combinations, so the power capacity should be about the same.

Now you can't just go putting a huge turbine housing with a small A/R, as there is a limit here. If you put a larger housing than is really needed with a small A/R, the exhaust gasses will lose kinetic energy, and the spool will suffer as the turbine wheel isn't getting a little "shove" from each exhaust pulse since it slows down too much with the larger area.

It's all a careful balance act.

As for the 2JZ vs. the S50 - I'd say whatever works well on the 2JZ will work almost the same on the S50 and vice versa.

The only thing is, any turbo that can spool up by 3.2k RPM is going to run out of flow much above 450rwhp probably. Can't the stock twins do about that on a 2JZ with bolt-ons? That's probably why you don't see stuff like that on Supras, when they change out the turbo, they want a big step UP in power.

Try to find other people using the same housing you are and a similar wheel(since that also influences how much the whole exhaust side can flow), and see how much power they can make before the exhaust looks like it's choked. That'll be roughly the same for your engine too. Now, a 0.58 A/R T4 is still pretty big, so I'd say it could support 500+rwhp without too much trouble depending on the turbine wheel. I mean, heck, a 0.63 A/R T3 housing with a stg5 T3 wheel has pushed over 600rwhp, which is an extreme case, but it still shocks me how much exhaust flow must be going through that thing! So you can push turbines pretty far, but you run into some nasty effects with rising exhaust manifold pressure.

[BoostedE21]

I must say this thread has help out a bit. But i have one question. Let say you are looking at a comp map and you plot everything and your line starts before teh surge line (to the left it), what does this mean. And whats going to when there is a "surge"? What turbo would you guys thinks is good for a 2.0L 4cyl 8V motor (My motor), what sizes should I look for?

[Def]

Sorry, didn't see this before.

Surge can damage the turbo bearings by making it basically "choke" due to the low flowrate. The blades basically stall, and the bearings take some abuse. It kinda sounds like a "bird sound" repeating really quickly when it happens.

I think a T28 or small T3 would be a good turbo for your engine. They'll probably support about 250rwhp or so.

[MrBlonde]

..
What turbo would you guys thinks is good for a 2.0L 4cyl 8V motor (My motor), what sizes should I look for?
..

Garrett GT28R - you've got three choices for housing size.

[EEEEeeee36]

I must say this thread has help out a bit. But i have one question. Let say you are looking at a comp map and you plot everything and your line starts before teh surge line (to the left it), what does this mean. And whats going to when there is a "surge"?

Just to clarify what surge actually does....Surge is basically when there is more pressure in the intake manifold then the compressor is actually putting out. The reason it chokes is because the engine can't take in as much air as the turbo compressor outputs. So since the engine isn't taking the air in it builds-up in the intake manifold and it builds up more and more as engine speeds increase, until the points at which the engine hits an rpm high enough to start pulling the air in - after the surge line on the compressor map. When surge happens, you have high intake manifold pressures pushing back against the compressor wheel. The compressor wheel can be forced to slow down, almost to the point of wanting to go the opposite direction. Obviously you don't want the turbine spinning with all of the exhuast pressure on one side of the shaft and the opposite force applied on the compressor side of the shaft, that is what causes the damage. The bearings can then also make contact with the carriers because the oil flow rate slows and because of the excessive vibration from the opposite forces on each side of the shaft... then you get bearings with grazes or flat spots, and that prohibits them from freely spinning. Hope this helps, just wanted to give you a visual since it's hard to comprehend it without pictures usually.

[Def]

Just to clarify what surge actually does....Surge is basically when there is more pressure in the intake manifold then the compressor is actually putting out. The reason it chokes is because the engine can't take in as much air as the turbo compressor outputs.

It's helpful to think of it as a turbo thing, not so much an engine problem. While different sized engines can take it different mass airflow at different pressure ratios and RPMs, it's the turbo that will determine whether the combination will hit surge or not.

A turbo is a compressor(not a positive displacement pump like a twin screw SC), so it doesn't move mass air so much as it accelerates air outwards to compress it in the housing. So in ambient air, a turbo would spit out air at some certain pressure, and the mass flowrate would be high because of the low restriction(it's just dumping out). Put a low RPM engine in the way, and it sees lots of restriction when it first spools. If the turbo will surge, it will actually get to a point to where it is trying to output a certain pressure, but the compressor is too large to generate that pressure with the massflow it can put out with that restriction.

In essence, the turbo "starves" of air, and the blades stall out. The pressurized air then can "surge" back out of the turbo until it can stop stalling the compressor blades. Usually this happens so quickly that it makes the characteristic "bird chirping" sound of the pressure waves hitting the compressor wheel.

So EEEEeeee36, you were almost correct. The distinction is that it's not the engine that's choking, but your turbo choking from the lack of air it can push through the engine at that pressure ratio and RPM point.

Everything you said about the bearings and whatnot is spot-on though.

[EEEEeeee36]

Thanks. I wasn't trying to be as technical as yourself however, because the audience seemed pretty 'noob' to the turbo stuff. It's hard to visualize a lot of the what goes on with the compressor and how it relates to the compressor map, so I was just trying to put it into terms he would understand. Trying to say the compressor 'starved' for air when the basic concept is that the compressor just spins to push air based on the turbine wheel speed might confuse the beginner turbo enthusiast.

[Def]

I admit it, I'm a huge dork!!!

[EEEEeeee36]

I admit it, I'm a huge dork!!!

Well, Geek is probably more appropriate, or maybe nerd. Don't worry though, I am in the same boat

[///M P0WER]

I dont have access to most of the maps there but would anyone of you recommend a turbo that is comparable to a GT35R. Everyone seems to be running this and I just wanted to go a different route. I like the efficiency of theGT but just thought if you guys were to goa different route to get same or almost same results, what set up/combination turbo would you get.


Thanks for all the info

[EEEEeeee36]

I dont have access to most of the maps there but would anyone of you recommend a turbo that is comparable to a GT35R. Everyone seems to be running this and I just wanted to go a different route. I like the efficiency of theGT but just thought if you guys were to goa different route to get same or almost same results, what set up/combination turbo would you get.


Thanks for all the info

^ :

If it ain't broke...???? Just curious, because a lot of people have had success with the GT35R and Garrett is one of the highest performing/quality turbo companies out there, why would you want a different company to do your turbo? Not that other companies couldn't, but the reason you find a lot of people using the Garrett's is because they basically wrote the book on super high performance ball-bearing turbos.... If I were to look for another company though, I would look at www.innovativeturbo.com. I've worked with them before and they are awesome too. They can pretty much build anything you want, and they actually helped 3K Borg-Warner (supplier of OE turbos to EVERY major vehicle manufacturer, and exclusive supplier for Porsche and Audi at least) develop their "Airwerks" turbo line, so they know their stuff. They also have an option on any of their turbos to do a ceramic dual ball bearing which supposedly even reduces lag off of the Garrett dual ball bearing system. If you have questions, email or call Rick - his info is on the contact page.

[EEEEeeee36]

BTW, here's an example of one from that company that is fairly close (actually handles a little more air) to the GT35R:





The price on that one is $849.99, but if you want the Dual Ceramic Ball Bearing built in it's an additional $900.00! Not that it's not worth it, but that's about $400 more than you can find a GT35R for, although this one can handle more boost. Hope this helps!

[///M P0WER]

BTW, here's an example of one from that company that is fairly close (actually handles a little more air) to the GT35R:





The price on that one is $849.99, but if you want the Dual Ceramic Ball Bearing built in it's an additional $900.00! Not that it's not worth it, but that's about $400 more than you can find a GT35R for, although this one can handle more boost. Hope this helps!

I share your belief of why I like Garret but at the same time I like to test different ways to see what else is out there. If everyone sticks with a GT35R then how else would we learn "new" things. I'm not knocking the GT35R, just wanted to have an alternative.

Thanks for the map. What do you think of a BB T64? pricewise might not be worth it though

[EEEEeeee36]

I share your belief of why I like Garret but at the same time I like to test different ways to see what else is out there. If everyone sticks with a GT35R then how else would we learn "new" things. I'm not knocking the GT35R, just wanted to have an alternative.

Thanks for the map. What do you think of a BB T64? pricewise might not be worth it though

I don't think a T6 of any sort would be a good idea on a 3.0 liter engine... there isn't enough air to push it. You'll surge almost the entire time! You need to hit at LEAST 50lbs air/min to begin to use the GT60 series - look at the previous post to yours... the M3 doesn't hit 50lbs/min until almost redline. The biggest turbos that have been used successfully on an M3 are GT42s...

[///M P0WER]

i was referring to the turbonetics T64 with a ball bearing option , not the GT series.

Anybody else got any suggestions?

thanks

[Wheeeels]

Sorry for going so far back in time in these postings, but I'm a little confused about the compressor map plotting. When plotting engine airflow on the map, say for 3000 rpm (at the knee of the curve), isn't that putting a point at a fixed compressor rpm? My confusion comes from wondering how I know that my turbine will spin at that rpm (since compressor and turbine must spin as a unit). If it spins faster or slower is that effectively moving that point vertically up and down? And is that a problem?

I myself am trying to come up to speed on turbos. Any good common sense, practical reading material suggestions would be welcome.

[Def]

Try to find some compressor maps with speed lines. They pretty much slope from top left to top right, and each line is a constant speed. So you can build higher boost at lower massflow with one compressor speed, or run the same speed at a higher massflow but lower boost. When you watch the engine consume more mass flow at the same boost level(i.e. powering through a gear), the compressor speed must naturally speed up to provide more massflow at the same boost.

I don't really follow you on the "spinning faster or slower" question - I think you're missing that the wastegate adjusts the exhaust flow through the turbine so that you get a certain boost pressure. Given the exact massflow and pressure ratio at that instant you could get very close to the real rotational speed of the compressor wheel(and turbine wheel as well since they spin together). The varying turbo speed is just a result of controlling the boost via a wastegate, and more boost = higher speed all things equal.

Corky Bell's book "Maximum Boost" (I think that's what it's called, I've never read it) seems to be a good intro to turbochargers on automotive engines.

[EEEEeeee36]

i was referring to the turbonetics T64 with a ball bearing option , not the GT series.

Anybody else got any suggestions?

thanks

By "T6" I meant any of those series - T64, T66...point is if you use a turbo that flows as much air as 50lbs/min you will surge constantly. I only pointed out the GT42R because it has had good success at making huge horsepower, although extreme planning and caution would be advised with such a project as those who have used it go through engines pretty quick (as mentioned previously Mert has gone through six...engines that is). I referenced InovativeTurbo as a good source of turbos, and a good place to call if you want something custom. Also, if you wanted to look at a Turbonetics, then you may want to consider something along the size lines of a T-58 or possibly a T-61, although I'd just be speculating because I haven't seen compressor maps for those turbos, just the T-64 or T-66.

[EEEEeeee36]

By "T6" I meant any of those series - T64, T66...point is if you use a turbo that flows as much air as 50lbs/min you will surge constantly. I only pointed out the GT42R because it has had good success at making huge horsepower, although extreme planning and caution would be advised with such a project as those who have used it go through engines pretty quick (as mentioned previously Mert has gone through six...engines that is). I referenced InovativeTurbo as a good source of turbos, and a good place to call if you want something custom. Also, if you wanted to look at a Turbonetics, then you may want to consider something along the size lines of a T-58 or possibly a T-61, although I'd just be speculating because I haven't seen compressor maps for those turbos, just the T-64 or T-66.

Then again, you also have the price consideration... they are not very cost effective either.