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Old 09-06-2010, 10:39 PM   #1
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Default Getting confused by Garrett's turbo listings

On Garrett's website there are two 2860RS's? What's the difference?

http://www.turbobygarrett.com/turbob...#BB%20T-Series

And by the looks of it, the compressor map for a GT2860R-5 (same turbos I ran on my GTR) should flow better than an RS? I'm really starting to get confused. There are like 4 turbos that are all 60mm 62 Trim .60 AR and they all have different compressor maps.


Basically I am looking for a turbo that will flow 300whp on a 1.6L but not have crazy on throttle lag between shifts. I have a ton of head work done including oversize valves and a built bottom end going in. If I go this direction I will be v-banding the turbine and running external gate. 94 Octane all the time with water injection while at the track. Not tuning for it, just running as a safety. Won't run more than 16PSI or so on the track. Longevity is key. I was going to go Rotrex for a while (and still may) but I want to see what I can put together with the same $2800 I would spend on a rotrex... but turbo. So far it would be quite the hot setup.

That starts a whole new question. .64 or .84 housing.
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Old 09-06-2010, 10:54 PM   #2
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Originally Posted by falcon View Post
On Garrett's website there are two 2860RS's? What's the difference?
Different turbine AR. 739548-1 is a .86, 739548-5 is a .64,
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Old 09-06-2010, 10:54 PM   #3
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http://www.turbobygarrett.com/turbob...R_707160_5.htm

This turbo looks like it should be able to flow 300whp on a 1.6L at 18PSI and 280whp at 16PSI...

According to this formula from RX7club.com using 7500RPM and 1.6L in the equation instead of what's there.



Quote:
So to figure out how to do it you need to figure out these few things.

1) Pressure ratio, This is simple 1bar+boost/1bar = X or 14.7+boost/14.7 = X

EXAMPLE: 15lbs 14.7+15lbs = 29.7/14.7 = 2.02
So 15lbs equals 2.0 roughly on your comp map.

2)VE(volumetric efficiency) This can vary on opinion(some say more some say less) but I run 90% for a few reasons.

3)Displacement (again opinions very) but plug in the number 2.6 and it all works good. Plus you will be using a rotary equivalency factor later in your math.

Once you know those things you can plot a point on the compressor map and see where you land simply by adding RPM into the equation.

Displacement x RPM x VE x PR / 5660 = CFM

So 2.6L x 8500RPM x 90%VE x 2.0PR /5660 = 702.82 CFM or 49.25 lb/min

Plot that on a 35R comp. map and you see that your in a mid 70% efficiency at 8500 rpm. Not too bad.

If you wanna get a guess as to WHP, way back in the day I was told 1lb/min = 10hp It seems somewhat true, but basically you are slightly more than that at torque peak and slightly lower than that at HP peak. So we take the middle ground. So all you need to do is move the decimal over one place 492.5whp (that would be piston motor) We don't have any of those.

To figure it out for a Rotary you would need to do it a little different. 1lb/min equals a little over 7.5hp.
I use 1lb/min= 7.69hp and it seems about right. (If you want to be a little conservative just use 7.5)

This is a ESTIMATED number that I have seen to be pretty constant over the years of comparing cars I have worked on and owned. Others who have put their math up on here only confirmed this for me to some degree.

So 2.6 x 8500 x 90 x 2.0/5660 =702.82 or 49.25 lb/min x 7.69hp = [email protected]
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Old 09-06-2010, 10:55 PM   #4
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Different turbine AR. 739548-1 is a .86, 739548-5 is a .64,
Ahh.. gotcha. Thanks.
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Old 09-06-2010, 10:58 PM   #5
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http://www.turbobygarrett.com/turbob...R_739548_9.htm

And here is another... they state it as "a disco potato with a GT2560R compressor housing"...

Seems like this turbo with a .86 tial v-band would be farily 'spooly' and creat big power. It dosen't seem to choke until 24-25PSI which I will never run.

18PSI or 2.22 Pressure Ratio needs 29.22 lbs/min and if you plot it out on this map it is still in the 74% efficiency zone which is very good.

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Old 09-06-2010, 11:12 PM   #6
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Old 09-06-2010, 11:16 PM   #7
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its a decent turbo, but in real world apps they seem to peak around 18-19psi.

if you end up with a 2860, get the 0.86 housing for sure.
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Old 09-06-2010, 11:20 PM   #8
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Ya I figure if I go 2860, the .86 housing and if I go RS the .64.

Thanks Joe, missed that one.
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Old 09-06-2010, 11:29 PM   #9
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Honestly, from both what I've calculated on my own as well as the experiences of others, a .64 AR 2871 seems like it'd be a great turbo in the high 200s. Not real sure about the goal of good spoolup and 300 HP on a 1.6 engine, though. Granted, mine only has a few ounces of headwork vs. yours with a whole ton.
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Old 09-06-2010, 11:40 PM   #10
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Well your ounces might be the same as my whole ton. Now going to compressor on the 2871... there are a few different ones listed. Which one would be the one to go for? I'm not really worried about spool up since I will be over 4000RPM most of the time... more concerend about "lag". As in.... hit the throttle and how long it takes to hit full boost when the engine is already in it's sweet spot.
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Old 09-07-2010, 12:19 AM   #11
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2PSI-20PSI Goes 2, 5, 10, 12, 15, 18, 20 on the map.

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Old 09-07-2010, 12:26 AM   #12
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if im sitting in a cell where my car will be boosting full boost, it takes a very minimal amount of time for full boost to hit.

however i am using AEM boost control paired with an external wastegate.
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Old 09-07-2010, 12:34 AM   #13
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I would be running an external gate, most likely a 38mm Tial and my Apex'i electronic boost control I already have
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Old 09-09-2010, 08:02 AM   #14
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aye this thread is indeed similar to mines!!!!!!
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Old 09-09-2010, 09:30 AM   #15
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Quote:
Originally Posted by falcon View Post
2PSI-20PSI Goes 2, 5, 10, 12, 15, 18, 20 on the map.

so you don't plan on hitting 20psi until 7000RPM? Why not buy a rotrex?
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