Author Topic: A/R - and the gt1752  (Read 6907 times)

Offline dub-disaster

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A/R - and the gt1752
« on: April 25, 2010, 04:05:38 pm »
hi all,
    after much research into this i have decided to sell up my k03 stuff and opt for a gt1752 becase i think it is overall a more efficient urbo at the boost pressure i want to run on my 1341 engine. i hve nly just learned to read compressor maps and the compressor maps i have got fr the gt1752 are only speculations as there isnt one officay publised but i obtained this info from a mini fourm and comparing his turbo to a k03 i have found that:
@ 20 psi/ pressure ratio of 2.36 the gt1752 run on a 1341 is,
5% more efficient @ 4k rpm
7% more efficent  @ 5k rpm
17% more efficent @ 6k rpm
18% mre efficient  @ 6.5k rpm

the compressor maps that i used are  the ones ive posted below ignore th red line on the k03 one as its not m calculation it was somthing somone did to do wth a 1.8 20v.
  im also looking at a gt2056 the slightly bigger brother think is found in the mg zt ? to the gt1752 but i think the 2056 is prbably a little to big a maybe more suited to competition/track cars but it is a very good turbo non the less,

The main question i have is i know that the A/R effects spool up time a top end flow th bigger the mor flow ad the mallerthe faster th spool up but from whati can see the A/R on the saab variant  is  .53 and correct me if im wrong but i think the k03 is around.44 i think that maybe.53 isa little to large just wondering if any on knows if they do a smaller housing that could be fitted  or if .53 will be ok?
 
  Also wonering if any one knows the spec of the psd schrick turbo cam as i have a newman copy of the shrick turbo psd cam an i want to know if its going to be ok to run with this turbo or wether i should be gong for a tamer gt cam to help spool up due to the larger A/R.


  i am planning on using a 9:1 cr and am hoping  by using a more efficient turbo i could get away with running higher boost like 20psi with out the addition of aquamist  would this be ok or would i need to drop the compression ratio to 8.5:1 to avoid using water/methnol injection or maybe jut run on 97 ron fuel as im after nice off boost car.

ko3 compressor map

gt1752

got al the calculatiopns ive done here aswell i can post tem up if people are really intrested!

Offline Andy

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Re: A/R - and the gt1752
« Reply #1 on: April 25, 2010, 09:24:25 pm »
Have a look on the Saab forums for the GT17 maps - sure I've seen them on there somewhere!

Bear in mind that the GT17s don't last brilliantly on the Saabs either, whether that's because of the turbo, or because of the oil sludging/starvation issues that plague Saab 9-5s I'm not sure. So be aware when buying second hand...

The GT20 series is used on some Saabs too - some 9-3 models if memory serves.

Offline dub-disaster

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Re: A/R - and the gt1752
« Reply #2 on: April 25, 2010, 10:25:02 pm »
Yea I have heard a few stories of the gt17 not lasting brilliantly but looking at the efficency of it compared to a k03 it looks a bit better so I'd like to give it a go. What's your opinion about the cam and the A/R of .53 on it?
Also when running 20psi on a 9:1 cr is that where water injection comes in as a det prevention aid aswell as charge cooling or can you run 20psi on a more efficient turbo without it ?

    Thanks
« Last Edit: April 25, 2010, 10:39:02 pm by dub-disaster »

Offline Tommo

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Re: A/R - and the gt1752
« Reply #3 on: April 26, 2010, 06:22:11 pm »
We fitted a GT17 off a saab 9-3 non-aero to my mates 1275cc mini, with a standard head, accralite pistons, metro turbo cam and on 18psi it made 147bhp and 176 lbs ft of torque. The turbo is a fantastic bit of kit for a small engine and its just right for the mini. Apparently those turbo's are all the rage on the turbomini forum now after we fitted one, noticed the price of them shoot up on ebay.

If I was you i wouldnt worry about low compression ratio affecting how it drives off boost, it will still drive fine even at 8:1. Mine is around 8.7:1 and it is great off boost, and will take plenty of pressure.

Whatever turbo you choose just make sure you arent going to run it into surge, its easy to size a compressor too large when you want to make big figures on a small engine.

The turbine housing on my car is a .49, full boost by around 3500 revs, just right for the street.

Ive said this to a few people who have asked me questions, but just look at what the R5 turbo guys fit as upgrades, its a pretty similar capacity and them guys know what does and doesnt work. IIRC they often go for the T25 from the rover 420/620 turbo's, Which is pretty much what I have.

Offline Tommo

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Re: A/R - and the gt1752
« Reply #4 on: April 26, 2010, 06:28:06 pm »
As for GT17's not lasting long, im sure on a SAAB they still last over 60,000 miles. If you get 20,000 miles out of one on a 200bhp polo I dont think thats bad.

Offline dub-disaster

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Re: A/R - and the gt1752
« Reply #5 on: April 26, 2010, 07:58:45 pm »
So what would you suggest is the ideal cr from the avalible 8:1 , 8.5:1 , or 9:1 ??
and should I be running this shrick turbo cam or should I go with the tamer gt cam ?
I've looked at the r5gt boys and they mainly use hybrid turbos costing in the region of £500 I'm sure there great but mode than. I wanted to spend !!
« Last Edit: April 26, 2010, 08:59:21 pm by dub-disaster »

Offline Andy

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Re: A/R - and the gt1752
« Reply #6 on: April 27, 2010, 12:25:08 am »
I'd go for 9:1 myself, makes for a nice drive off boost compared to 8:1 - unless you're planning lots of boost for dyno bragging rights.

As for GT17 longevity, just be aware of the issues they have in their native environment, not so
much because you'll blow one up on a Polo, more because a lot of second hand ones will be pricey, or fucked!

Cam choice will be interesting. Suck it and see with the turbo cam, and switch
to a GT cam if you think the turbo spools too late.

Offline Tommo

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Re: A/R - and the gt1752
« Reply #7 on: April 29, 2010, 05:22:57 pm »
Dyno bragging rights FTW! haha.

Yeah I would say 9:1 would be fine too, but isnt a standard G40 8.5:1? And they drive ok off boost? Although I suppose the supercharger cuts in quite early. Dont forget you have more displacement than stock with 1341 too. Personally I would always err on the side of caution when it comes to C:R, especially with aftermarket pistons.

Offline dub-disaster

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Re: A/R - and the gt1752
« Reply #8 on: April 29, 2010, 06:26:12 pm »
I found my g40 when it was supercharged around 150bhp felt a bit weedy of boost ! Normal compression ratio is 8:1 I thought on a g40, my 1341 that I've got ain't selling so I'm going to stick with 9:1 accralite bottom end and probably end up getting some sort of water injection to help prevent det under heavy load aswell as cool charge.
    Just out of intrest any one ever melted a forged piston on a turbo g40 lump??
« Last Edit: April 29, 2010, 11:06:14 pm by dub-disaster »

Offline hayesey

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Re: A/R - and the gt1752
« Reply #9 on: April 29, 2010, 09:53:51 pm »
standard CR is 8:1 yeah.

Offline jez1272gt

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Re: A/R - and the gt1752
« Reply #10 on: April 30, 2010, 06:45:08 pm »
i have a brand new decompression plate for use with 1341cc Accralites and a metal head gasket (mk4 polo) if anyone is intersted. It will reduce the compression ratio to approximately 8.2:1.. i cant remember the exact figures but if anyone is intersted i will dig them out and let it go for £100 posted with the correct sealing paste.. Went and sold the accralites didnt i  ::) !!

Offline Tommo

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Re: A/R - and the gt1752
« Reply #11 on: May 05, 2010, 05:08:51 pm »
TBF I dont think you will have many issues with det on 9:1 if you size your compressor right. I ran mine at about 1.2 bar on the standard 1.3 spi bottom end which is 9.5:1 IIRC and it was fine, not even one det mark when I took the head off after about 5k miles.