MrTodd

I've been reading up a LOT about turbocharging within the past few days. I started from knowing pretty much nothing, but now I feel I understand most of the general and some technical aspects of turbocharging.

So, obviously I'm debating on the two turbo's listed in the title. The GT25R vs the GT28R (not the gt28rs, mind you).

My planned build will be a D16Z6, with a moderate compression ratio of about 9.8:1 (forged pistons with welded combustion chambers). I will be porting the head. I will be adding an aftermarket camshaft, along with plenty of other engine mods to aide in performance and reliability. Please note that I am NOT asking how to build my engine, I'm only concerned with choosing a turbo in this post!

My main concern at this point is spool, and overall compressor and turbine efficiency. I need a turbo that will spool FAST, <U>but I need it to keep breathing up until the 7200 rpm redline!</U>

I was considering the T3 Super 60 at first, but now I feel that the GT28R and the GT25R would be a closer match to my preferred setup, mainly due to the ball-bearing design. My target WHP is 220-260. I'd like to achieve this goal with as little boost as possible, and again, using the quickest spooling turbo I can get my hands on. My car (civic cx) is a daily driver, but my car is going to be tuned mainly for autocross - that's the only reason why I'm modding my car. Now, I'm not new to solo2, so please don't try and tell what I need to do in order to fit the profile.

I'm liking the specs of the GT25R, but I'm afriad the powerband might fall off just before the 7.2k redline (which I WILL be reaching consistantly, yes, especially in auto-x). I've heard nothing but good things about the GT28R, and I know it would be an excellent turbo to go with my plans - but if I can still achieve the peak performance with an even faster spooling turbo than the GT28R, I'll go for that instead.

Any advice/experience would be greatly appreciated.


:::Edited for spelling/grammar:::


Modified by MrTodd at 9:27 PM 11/12/2005

MrTodd

Please help me out on this one you guys...

Hasn't anyone used the GT25R turbo?

MrTodd

No one?

dpetro1

well i really think you should try the autocross section and see if you get anymore help. i think most people here are going to say gt28r because it will make more power and still spool quickly. there are a few variations on both turbos but i think the most the gt25r can make is like 280 (60 trim .60 AR compressor). that might be good for your power goals but like you said you dont want something that is going to run out of efficiency.

http://www.turbobygarrett.com/....html

check out this site for more info on both turbos. maybe someone can help you read the compressor and trubine maps to help you make you decision for your specific application.

remember though HT is a place that loves big turbos ie sc61 and gt35r.

MrTodd

Hey thanks for the reply - I'm keeping this out of the Autox/RR section because I'm hoping for more techincal insight about the specific turbos, I'm not worried about the detailing of autox terms at this point.

I dug up some more info, (I have been reading up on Garrett's website for a while now, but I found something else) I've noticed that whenever I think aloud (or type what I think) I tend to make progress, so here it goes.

I'm aware that Garrett offers the GT25R and the GT28R in varying trims, but apparently the "GT28R" that most people refer to is actually in the GT25 family. Apparently, there was a recent change in model numbers and such... Take a look.

Here is a website that shows the common GT usage nowdays - showing the most common stock, or generic details.

http://www.atpturbo.com/root/t...p.htm


----


SO - according to the above website (and to further clarify my reasoning) it looks like the "GT25R" is SPECIFICALLY referring to the smallest GT25 frame turbo, which is this:
http://www.turbobygarrett.com/...3.htm
Supporting up to 250hp according to ATP Turbo. (don't know if it's crank or wheel)

The common usage "GT28R" is referring to this one:
http://www.turbobygarrett.com/...4.htm
Supporting up to a claimed 310hp, again according to ATP Turbo.

According to the above references, the ONLY difference between the two (other than the GT28R's available stronger housing & compressor/turbine material) is the COMPRESSOR. The so called "GT28R" has a larger compressor which has more flow 'capacity' than the GT25R. The exhaust/turbine's are IDENTICLE between the two. According to Garret's website, they say the turbine housing A/R & size has the greatest effect on spool time. So in the case of the "GT25R" vs the "GT28R", the 250hp restriction of the GT25R is due to the compressor.. This is an interesting find for me, because I was under the impression that most 'high-rpm' power restrictions of turbos is due to the restriction of the exhaust turbine, by causing too much backpressure.


....However, you must consider one more thing. Take a look at what Garrett has to say about compressor A/R....

Note that although a larger compressor will outflow a smaller one, the smaller one is more efficient in low boost applications. But is it that big of a deal? Will the increased 'efficiency' of the GT25R compressor make a notable difference in the powerband under the curve? According to my above theory, if the GT25R turbo falls off in higher rpms it will be due to insufficient compressor flow. If this is a potential problem, then my modifications would only increase the chance of insufficient compressor activity, (ie oversized valves, turbo camshaft, larger & shorter I/M and larger T/B) giving it a higher chance of 'falling off' at higher rpms.

Hmm... So it looks like I need to learn how to read compressor maps then, as my choice falls only on the compressor performance.

a1320addict

iTrader: (1)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MrTodd &raquo;</TD></TR><TR><TD CLASS="quote">(don't know if it's crank or wheel)</TD></TR></TABLE>

most of the ratings are done by what the turbo can actually flow, so essentially its crank hp, one thing to really consider is the effect your other modifications will have on the turbo's performance. for instance, you mentioned a larger intake manifold; some of the larger intake manifolds take away a little from the midrange and make gains in the top end, and/or vice versa.

i ran a gt28r on my previous setup, .63 a/r on the turbine, b18c1, and the turbo had no problem of falling off at ~ 8100, at around .5 bar. the nice thing about the gt series turbos is that you can screw around with the a/r's on the turbine without effecting spool that much. personally...i think you're right on the ball with a gt28r...youll have very quick spool and maintain efficiency in the powerband you are after.

i'm a big fan of the "smaller" garrett gt-series turbo's. especially in a daily driver situation, they make tons of torque, usable power, and the added reilability of a ball-bearing turbo is great

good luck with the build

dpetro1

well it seems the new terminology is saying that any gt with a 53mm turbine inducer is a gt25 while the gt28 has the 53.85mm inducer. so the gt25r and gt28 do not have identical turbine properties.

http://www.turbobygarrett.com/...t.htm

this shows all the gt turbos side by side. so when you are reading the number gt is goes like this

gt - turbo series
25 - refers to turbine inducer diameter
60 - refers to compressor exducer in diameter
r, rs, etc - refers to special properties ie ball-bearing

so there are only a few variations on the gt25 but the gt28 has many. you can pretty much get any combination of trim, AR or wheel sizes.

i did notice though that the onlt difference between the gt2554r and the gt2560r is the compressor exdeucer is larger. im assuming allowing for more flow and more hp (notice it also has a lower comp AR).

the turbine does dictacte spool-time mostly so i wouldnt wory about compressor AR too much. garrett even says the effect is minimal.

i say your best best is to take your time with the maps and see what would work best with your setup. it seems that either would work i dont think a .64 turbine AR is gonna fall off up top on a d-series whether it be on a 25 or 28.

MrTodd

Hey thanks for the insight bro! After taking more time to read up on Garrett's 'Turbo Tech' articles, I'm finally beginning to understand reading the compressor maps.

According to the GT25R compressor map the smaller compressor *should* provide very efficient compression of up to 210-225 HP (crank, again thanks yehiknowrite), but it will QUICKLY lose efficiency when more air flow is required. So, this means that after I reach the crank HP of ~220 the powerband will quickly taper off and die as the engine wants more air, which would most likely occur in the higher RPMs.

Looking at the GT28R compressor map it seems like there is MUCH more room for the compressor to flow in an optimal range of efficiency... This compressor would allow me to hit my ~230WHP mark that I'm aiming for, with room to grow if I ever wanted to.


So I looked at a couple D-series dyno charts with 10psi boost numbers as a reference.

(D16Y8, stock)
https://honda-tech.com/zerothread?id=1289362
(D16Z6, forged pistons/rods, 9:1 C/R)
http://forums.evans-tuning.com...=1391
(Stock D16Z6, ~9.2:1 C/R)
http://forums.evans-tuning.com...=2017

The answer to my initial question is becoming more loud and clear. After looking at the above dynos, it's becoming apparent that the GT25R turbo won't cut it. All of the above SOHC setups are showing 200WHP numbers before the redline, one of which is hitting that at 5krpm! Of course, I know these numbers are somewhat affected by the choice of turbo (and tuning), but the fact remains that a 1.6L D-series WILL run out of breath before it hits the redline if using the GT25R; however, I'm assuming this could be corrected with a lower amount of boost (ie definitely under 10psi).

When looking at the compressor maps, it begins to make even more sense where the problem lies - again backing my theory of the GT25R compressor being too small. But since both of the turbos share the same turbine & turbine housing, I should expect to see VERY similar spool times - but the GT25R should have a *slight* edge in power under the curve, even though I *should* see the same amount of boost with each given rpm.

In the end, it looks like I'll be picking the GT28R... However, if I would have set my HP goals to something lower, the GT25R (in theory) *should* provide a slightly more aggressive powerband, IF it were ran in a boost level of under 10psi (i'm guessing somewhere between 5-8psi).

But hey, if anyone see's a flaw in my thinking, please inform me! Hopefully I've been reading things correctly.


Modified by MrTodd at 11:41 PM 11/13/2005


Modified by MrTodd at 12:23 AM 11/14/2005

MrTodd

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dpetro1 &raquo;</TD></TR><TR><TD CLASS="quote">well it seems the new terminology is saying that any gt with a 53mm turbine inducer is a gt25 while the gt28 has the 53.85mm inducer. so the gt25r and gt28 do not have identical turbine properties. </TD></TR></TABLE>

You're right, according to Garrett's terminology. The problem I was addressing is the fact that many performance shops that sell turbos (in this case, ATP Turbo) aren't up to date on the terminology! In my above post, I'm addressing the issue of the GT28R as seen here, as you can see by clicking the wording, the so-called "GT28R" turbo is using the 53mm turbine, which is considered by Garrett to be a GT25 ball-bearing turbo.

This just goes to show that there is an increased need to take a closer look at exactly which turbo you have, or are going to buy. Your "GT28R" may not be a true GT28. Obviously, in this case both are actually GT25 turbo's, even though the advertising would lead you to believe otherwise.

And again, just to clarify, I'm comparing the GT28R and GT25R as defined by the ATP Turbo website - which also happens to accurately represent the 'common' usage of each model name.


Modified by MrTodd at 11:58 PM 11/13/2005