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T518z - 8cm vs 10cm - Tech Questions

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Hey guys,


I've dug through some old threads but still trying to find a few questions left unanswered:


- Does the 8cm version have any backpressure issues above 250rwkw? E.g. what backpressure/boost ratio is commonly found at 20psi+, is it less than 1.5:1?

- Is the ramp rate of the 8cm version a lot more savage than the 10cm version? Which one would be faster off the mark?

- In track conditions, does the 8cm version hold its own or does it get choked up top/end up with heat issues from being at high rpm....

- In terms of throttle response (e.g. driveability), which version is easier to drive?


I drive my car mainly through the mountains and im starting to get regularly involved in track days, so I'm wondering which would be a better match for the car. Everyone seems to be telling me the 8cm coupled with HKS 256 cams is a match made in heaven for the S15, and the 10cm version will be a bit too laggy for a spirited street/track car...


If i ended up porting the motor etc, would the 8cm still be a good match?


Thanks in advance.

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for starters, this is a great turbo but 90's technology, terribly outdated. there are so many better options on the marketplace today, with much better response, power and reliability.


By far the worst thing about a t518z is the lack of boost control. if you have cams and aim for 20psi you will have trouble holding boost to redline (mine dropped off to 16psi at 7200rpm, with a consistent drop from 5500rpm onwards). the other big issue is a massive boost spike as you come onto boost during the peak torque area of 4000-ish rpm, which will make it hard to keep steady boost throughout the higher rev range. this is with arguably one the best boost controller on the market, dual solenoid blitz sbc type r.


i only ended up making '216kws' at 16psi by redline, but everything up to 5000 rpm is better than expected (dyno numbers arent conclusive but merely an interpretation of math equations and educated guesses, it certainly feels way better and more powerful than a 230kw 180sx i used to have). i'd expect about 240+kws if i could hold 20-21psi to redline. I'd be surprised if you made 250kws right off the bat with a VTC sr20.


i have a t518z, 8cm housing, poncams (256/256) and all the usual supporting mods. had it retuned on the weekend and a good tune / tuner makes a huge difference to daily driving. with the 8cm housing you will get a very livable compliant daily driver, good power and torque low down (ie sub 3-4k rpm).


Ramp up between 3k to 4k is great fun, you'll lose traction in second but not third (should be on 20psi by about 3700 rpm with those cams)


You will probably want to look into a bigger throttle body, as we found that 50mm sr20det TB is choking it in the higher rev range. the 3.69 diff ratio certainly doesnt help either (but again, its good if you daily it).

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The 8cm will ramp up quicker than the 10cm making it more lively.


With a t518z being a reasonably small frame turbo I wouldn't look at anything except the 8cm rear housing, I wouldn't have though that back pressure would be an issue, esspecially if you have a reasonable manifold.


If you are half serious at circuit work you should easily be able to dial in enough grip to handle a t518z and the ramp of the 8cm.


I would have though porting would be a waste of time for a turbo sr20 making around 250kw. If anything you'll just shift your power curve upwards, working against the smallish responsive turbo.


From back in the day Purtells t518z setup was very good,


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