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Turbo Technology

Tommyk

By Tommyk,
in Engines & Forced Induction

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Tommyk

Posted
Posted

I spent about 6-7 hours last night reading up on turbochargers, and other technologies, trying to make the right choice on the next car.

Having experienced the garrett gt2860R turbochargers, I can happily say that doing some proper research is a valuable thing. I thought I might like to share/ask for your opinions on what ive learnt to maybe shed some of the myth behind turbochargers. Theres a lot of stuff I didnt know, that I now know :(

First of all, the reason for me spending the entire night :happy: reading up on this stuff, is that I wanted to find a turbine which had fast spool and decent output. My current setup is (was) a garrett gt2860R-5 bolt on turbine. Funnily enough, garrett has uprated these turbos to 360hp (which is probably the reason why they were a bit laggy and power hungry).

http://www.turbobygarrett.com/turbobygarre...0R_707160_5.htm

I have compared many dyno sheets to my own particularly in terms of spoolup time and can happily say that there is negligible difference between these and the HKS branded 2530s. Full boost hits at around the 4800 rpm mark, which is precisely on target with the hks units (based on my mods :P )

For after market turbine statistics (the other than genuine) this chart is excellent in comparing turbine stats

http://www.geocities.jp/bnr32labo/sub10.htm

The second thing I tried to find, is another turbine set with very similar specifications. And i found this:

http://image.www.rakuten.co.jp/wildhippo/img10301215989.jpeg

Now the hks ARMS 7660 has a slightly smaller compressor wheel, and has a smaller A/R on the compressor. Its spoolup is very similar to mine (I had 0.5 bar at 3300rpm just like in the pic). Full boost hits at about 4800rpm. Note - these are all on a stock bottom ended rb26. If anything, these should spool up quicker than a 2530 due to the smaller compressor housing.

Based on all these facts (or whatever you want to call them) I started comparing turbine technologies for my next possible turbo setup. I was quite keen on the gt-ss turbines, but i seriously doubt they can make the power that I would like them to (500-550 REAL ps). Now all the turbos here are made by garrett, and I dont believe there is any whoop-dee-doo in the hks compressor covers of all the hks gt series turbos (could be wrong) that actually make a difference.

A quick comparison between the hks gt-ss and the tomei arms 7655 which are a very similarly sized turbo and are rated at very different power outputs. For example, as a twin setup, the tomei 7655 are rated at 500ps, and the gt-ss are rated at 320hp each. Now, noting that more flow through a turbine can only be achieved by having a larger trim on the compressor OR exhaust wheels - trim is the squared ratio of inducer/exducer in the compressor/exhaust wheels. Now noting this, the 7655 turbine wheel exit diameter is an extra 5mm in size. This clearly suggests that the turbine will not run out of puff in the top end side of things (am i right or wrong?) and the tomei should flow more, albeit with a slightly slower spoolup?

I've been wondering about this all night, as to why the power differences are so significant. Im tempted to fork out the extra 100,000 yen for the tomei turbos, but nobody has used them, and nobody either here the uk or nz has an opinion on them. Google searching japan reveals nothing. So im not sure what to do?

P127_01_arms.gif

This graph shows the relative spoolup of the tomei range of turbos - its interesting to note, that there is a significant difference in output between the 7660 and the 7655 turbos even though there is only a few mm difference in comp wheels.

Suggestions & opinions? Im probably going to get blasted for the anti-hks stuff ive said :( But are they really as good as they say they are, or are they just fairly well matched turbine units to the rb26

Another thing I've been wondering, what would it be like to runu a slightly larger turbo but change the headgasket to something a bit thinner. Eg, there are 0.9mm metal headgaskets out there that raise comp to 8.7:1 . Would this be a safe manner of reducing spoolup times, while running no more than 1.3 bar, or is this unsafe ?

Cheers

Tommy

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