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18G Upgrade, Suggestions?

59295 Views 495 Replies 32 Participants Last post by  Rescuer
Hey everyone, so I am planning to upgrade my turbo to a TD05-18G 8cm from Kinugawa. Currently I have a Cobb DP and Invidia Q300 CBE and was hoping for some suggestions or feedback on my plans for my power modifications.

I plan on going with:
DW65 fuel pump
ID1000 injectors
Cobb SF intake with heatbox (maybe, depends on my ability to grab one from a buddy of mine)
And of course a good pro-tune

Any suggestions, feedback, what would you do differently? Thanks!
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I see you decided to keep your Q300 :) That looks like a pretty solid setup. Have you given any thought about who is going to be performing your tune?
Yeah, decided to keep it. I'm probably going to get it tuned in SoCal by Cobb since I'm in SoCal a lot now. Do you have any tuner suggestions?
Sounds like a good plan to me. what brand turbo are you planning on running?
I got in on the groupbuy at Nasioc for Kinugawa
Sweet. Mine's working great. I thought I had an issue originally but it was my inlet holding things back. I would suggest getting a better inlet while youre doing this if you can. I was having trouble pushing past 22psi on my 18g and now realize that it was the inlet keeping back my airflow. The 20g didn't want keep pressure past 20psi and would fall rapidly until i put the inlet on and now it'll hold 25psi+. I never would've thought it was that big an issue till it happened to me.
thanks for the heads up on the inlet! any particular one you went with or recommend or am I ok with the one from perrin? Thanks!
I don't think we have too many options like the sti intake guys have. Perrin worked great. I suggest doing it while the turbo and intercooler are out so you can get the back hoses attached more easily. You should be able to pull it through without the turbo on.
you gonna run e85?
Seems like a nice solid set up!
I'd look at that cheaper alternative to the PW TMIC though, the CNT Racing one
They're half the price of a new PW ... that's the cost of a decent tune, right there! :icon_cool:
I'm looking at the same turbo down under in Australia, but with stock
Fuel Pump
Air Intake
I do have a HyperFlow TMIC and TurboSmart Kompact BOV
I'm looking at the same turbo down under in Australia, but with stock
Fuel Pump
Air Intake
I do have a HyperFlow TMIC and TurboSmart Kompact BOV
If you plan on upgrading injectors and pump later on it sounds like a good plan. If you don't forsee yourself doing that in the future the vf52 would be a better option/or whatever the japanese Legacy GT equivalent has in your hemisphere.(I'm guessing your 08 has the LGT style intercooler).

Reason being, the 18g tends to spool about 700-900 rpm later than a vf series so you lose a bit of quick off the line turbo time. Couple with that that running out of injector/fuel on the top end and cant run the turbo as far as possible and youve limited yourself to having a bit of midrange power and not as much elsewhere. Whereas the vf series will give you a broader range of power. you'll get a full low end power and nearly as much as possible on the turbo with minimal fueling issues on the top end.

The 18g will still be better than the TD04 turbo but not as strong as a vf series without the supporting fuel mods.

Due to fueling the 18g and vf52 will have relatively the exact same upper rpm possibility.

Just food for thought.


Here's a completely non actual graph(not real in any way, i just used paint to make it) to show you the approximate difference between having the same fueling capabilities and where you'll gain with a vf model. In the top end I only seperated the lines to show see them differently but in reality they'll be pretty much on top of each other.

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^^^ Thanks Superacerc, my tuner is pretty conservative, so I'll have a chat to him and see what he thinks.
I agree the VF52 would be the best option, just the price of the TD05 18g is almost too good to refuse. But if I have to do supporting mods then it'll probably work out the same as paying for a VF52.
Might be able to find a used one. The price is tough to beat though and would allow you room to upgrade.
great discussion here guys, very good points

you gonna run e85?
i'm leaving the option open to e85 in the future, but I probably won't do that for a long time, i'll probably stick to crap California 91 here.

I spent a long time debating between the VF52 and the 18G, and ultimately decided it wasn't that big of a difference, but went with the 18G just to get a little bit more potential out of it since i'll be upgrading a bunch of things, and I didn't need the turbo to hit so hard soon and it still gets plenty good spool early. Definitely a lot of pros and cons in that debate but it's not that big of a difference in my opinion. I may also end up going to a 20G in the future, but we'll see how I like the 18G first. My goal is a street friendly turbo and the 18G and VF52 are great candidates for what I have in mind.

Not gonna lie, I still debate between whether I should have gone with the VF52 or not but I think i'll be plenty happy with the 18G, plus it was a pretty good deal with the group buy.
With full fuel support though you'll get more top end out of the 18g. It'll definitely be quicker than the 52 with no pressure loss at redline. You'll like it.

A td05 20g will spool essentially the same as your 18g(mine actuall spools quicker with the inlet changed~3500rpm). The hot side is the same. You'll just have more air flowing through. There's no downside to a 20g vs an 18g as long as theyre both td05s. Theres no reason to move to a laggier td06 with our automatics since the spool is higher in rpm and we cant use that area anyway. A td05 and td06 20g both make the same power just at different rpm levels.

If you haven't bought a turbo yet and are going 91oct you might as well get the td05-20g. On 91oct you still won't be over the engine's power limits and itll spool the same as the 18.
yeah, I already got the 18G. It was about 2 weeks after I received it that it dawned on me that I probably should have gone with a 20G, but not much I can do about it now and we'll see what happens. I'll probably find that the 18G is plenty sufficient for a while and i'll enjoy it as long as I can I guess.
Definitely no problem with the 18g. I loved mine. Just more future potential with the 20.
A td05 and td06 20g both make the same power just at different rpm levels.
I would like to disagree with this.

Yes, you will move the entire powerband up with the TD06 but you will also be able to get considerably more power from it.

And when we look at the TD06SL2 or H the potential is even higher than the "base" TD06.

It seemed that manufacturers typically rated a normal td05 20g and td06 20g with the same hp rating. I'm sure there are some differences in the more specialized wheel setups, but would an auto Forrester forced to shift at 6100rpm see any real performance gain by switching from, lets say my td05 20g to a td06h sl2 version? And would it offset the fact that I would lose a fair amount more spooltime?

I figure if you put my turbo against nates, same car same psi target and timing mine should make the car a faster car having earlier spool and being able to maintain the same pressure till redline. Our cars are forced to shift so early I dont think its beneficial to go td06. There are some special turbine versions that should make some difference though I agree there. But same standard compressor turbines and housings with just different hot sides dont seem beneficial to move up.

If course im bench racing here so its purely speculation. Id be very interested to see it tested though.

Keep in mind our low redline patrick. We don't have the luxury of a manual shift SH model xt here in the states so higher shifting isnt an option at all. Were stuck at lower rpm levels where the td05 doesnt have a chance to run out of top end.
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