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Old 11-17-2007, 07:17 PM   #1
Liam
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Default 18G on STi, 20G worth it?

Hey guys, sorry for another 18G and 20G thread. But I really have to ask because I have something really don't understand (after all the searching of cause )

I've seen a lot of 18G and 20G on 2.5L with all supporting mod
And the 18G can usually archive 300-310whp after a protune.
And a 20G can usually archive 320-330whp after a protune.
I am of cause talking about on pump gas.

While 18G will spool almost like a VF39 on low-end and net more power on top. The 20G will spool slightly slower and gain more top-end compare to the others. (vf39 and 18G)

But, I've noticed something.

On third and fourth gear (talking about 6 speed). the 18G will produce almost same amount of power and more torque than a 20G, and it usually spool faster and more responsive.

With those extra lag and less responsive, and only 10-20 extra up top (pass 5000rpm) on 5th and 6th gear on pump gas, is that really worth to jump to 20G without giving 18G a try?

I know people say 20G is a better suit for 2.5L and especially STi has a stronger tranny. 20G should be a more impressive setup. But my question is, which one will work better on a Daily Drive car and on 91 pump gas with minimal supporting mod?

Since from my understanding (please don't me if I am wrong ><...)
A 18G should be a better TQ monster on low-end and a City daily driver because it has better response and more TQ on 3rd and 4th gear. 20G will only be more powerful on Freeway or Track because it will net about 10-20 extra HP than a 18G on 5th to 6th gear.

Since I only use car my to daily drive and not much freeway to run. And I am only interested in Canyon run. I don't drag my car and track.

Will a 18G a better suit turbo for me?

Thank you very much guys ><!
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Old 11-17-2007, 07:37 PM   #2
STimo
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IMO an 18G isnt even an option for the 2.5L, it's not a big enough step and you should just keep the VF39, unless you're a hard core autox guy and want to hold a bit more power to redline, other than that i dont think an 18G is worth all the money.. The 20G though for a DD is a great choice IMO, you'll notice a good difference in power and you'll hold boost to redline unlike the VF39, with a slight hit in spool which IMO isnt that big a deal at all, lag is way overatted.. Plus later down the road if you wanna do a race gas map that'll bump power to the upper 300's whp depending on what dyno.. I'd definately go with at the very least a 20G for the 2.5L..
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Old 11-18-2007, 01:39 AM   #3
Traxamillion
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18g-wrx
20g-sti
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Old 11-18-2007, 05:05 PM   #4
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Actually the 18G will spool as fast or faster than the 39. Several have done it, all of them reported this. Its an awesome match on the 2.5 motor. That said, its still a bit small. With lower octane you will be able to run less boost for the same power on a 20g
as the air charge will be cooler and less det prone, which helps with the octane problem.

The 18G is most definately a good sized step about a vf39, anyone saying otherwise hasnt done the upgrade or had one that was set up poorly. A 39 is comperable to a 16G, and going from a 16G to an 18G on the 2.5 is a BIG step up. The 18G holds a lot more power to redline than the 39 and the huge 3000rpm hit that makes subbies so tough to drive smoothly is flattened out. Turning it into a very VERY smooth strong pulling, wide powerband.

The 20G is also an incredible daily driver turbo on the 2.5 as long as its tuned right. I am running a TD05-20G 8cm with a 44mm Tial EWG and at no point in the entire power band do I not make more power than stock. There is no "lag" issue and it feels great with plenty of low end power. Its not just a top end power turbo, my midrange is VERY strong, and my low end is definately good as well.

IMO the TD05-18G 8cm is argueably the ultimate street turbo on the 2.5. That said, the 20G is also a VERY good street turbo. I would definately take the 18G for autocross though.
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Old 11-18-2007, 08:39 PM   #5
06_black_wrx
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Traxamillion, Im curious as to how you came upon your findings?
There are wrx guys running 20g's with no problem, why are they limited to the 18g and the sti gets to go bigger?
I have an 06 wrx and might want a 20g and am still researching, which is why I want to know.
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Old 11-18-2007, 08:57 PM   #6
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I am betting he said that due to transmission reliability issues.
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Old 11-19-2007, 01:15 PM   #7
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yessir.
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Old 11-19-2007, 02:35 PM   #8
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I ran an 18g on my 05 STi for about a year and it was great. It has a nice powerband and it made decent power. I've only seen a few maxxed out vf39s get what my 18g did on minor mods.
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Old 11-19-2007, 05:54 PM   #9
ALaDDiN
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Old 11-19-2007, 06:17 PM   #10
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i am also running a td05-20g 8cm turbo on my 2005 legacy gt. I used to walk out of every auto x with a cup/trophy, when i tried with my 20g it was not so much the same. Its a great DD turbo however, the low end snappiness is a little less responsive but that could also be from a fmic. After 3500 i am over 300wtq with this turbo until about 6k when it starts falling on its face because of stock cams.
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Old 11-19-2007, 08:26 PM   #11
Iflysti06
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20g ftw
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Old 11-19-2007, 08:26 PM   #12
Iflysti06
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make us all happy! :P

Last edited by Iflysti06; 11-20-2007 at 01:28 AM.
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Old 11-20-2007, 12:41 PM   #13
teiva-boy
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It would be interesting, if the OP would replace the words 20g with FP Green, and the word 18g with 20g... What would NASIOC posters then select as the "preferred," power adder.

My vote goes to what you are willing to pay in regards to what performance goals you have with your vehicle.
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