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Discussion Starter · #1 ·
Hi!
Has anyone experimented with these turbos? For a personal project I am building a Golf Rallye and want to push around 450 crank HP (about the limit that the Syncro system can take). I will be modifying the gearbox and rear diff in the future so maybe budget a maximum HP of 550, but consider 450 for now...
I will be overboring to 1.9l, using aftermarket ECU, large FMIC with water spray - all on an AGU large port engine.
I know the GT's are ball bearing items, what kind of response are you seeing with these turbos? Considering I want to see a maximum of around 550HP at some point, would the 28 be a better option? I only see the 25 rated at 450HP on most websites (AR depending). Also, what AR's are you guys going for with an engine of this displacement? At what point is max torque achieved? Does it hold for the rest of the rev range as well?
The car will mainly be used for sprinting (drag strip) but will see occasional track use.
Anyone share any thoughts on their own setups?
Thanx...
 

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Re: GT25R or GT28R? (VoodooMotorsportUK)

Well, I have been doing a bit of research, looking at compressor maps-BUT- have no actually experience will the two. It seems that the GT28RS would be a better fit for what you are trying to do.
Good places to go are: http://www.smokemup.com/auto_math/turbo_size2.php
for airflow numbers.
and http://www.turbofast.com.au/tfcalc.html for calculating HP numbers.
Looking at the compressor maps at http://www.atpturbo.com it looks like the GT30 might be pretty good.
I do think it is a very bad idea to bore the engine over. The incremental increase in displacement, it seems to me, to be more than offset by the unreliabilty factor at high boost. Even in 1.8 form, there is not much space between the cylinders for a head gasket to do a good job of sealing.
 

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Re: GT25R or GT28R? (Stroked1.8t)

Quote, originally posted by Stroked1.8t »
you will not see that kind of power with either of those turbos, neither flow enough air to support that amount of power

yep
i would definately go with a gt30 or check with innovative,turbonetics or precision turbo's


Modified by spoolin turbo s at 7:19 PM 1-13-2004
 

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Discussion Starter · #6 ·
Re: GT25R or GT28R? (bobqzzi)

Quote, originally posted by bobqzzi »
Well, I have been doing a bit of research, looking at compressor maps-BUT- have no actually experience will the two. It seems that the GT28RS would be a better fit for what you are trying to do.
Good places to go are: http://www.smokemup.com/auto_math/turbo_size2.php
for airflow numbers.
and http://www.turbofast.com.au/tfcalc.html for calculating HP numbers.
Looking at the compressor maps at http://www.atpturbo.com it looks like the GT30 might be pretty good.
I do think it is a very bad idea to bore the engine over. The incremental increase in displacement, it seems to me, to be more than offset by the unreliabilty factor at high boost. Even in 1.8 form, there is not much space between the cylinders for a head gasket to do a good job of sealing.

Great, thanks for the links! I have been on the Ray Hall site before, very useful.
I tried the atpturbo site the other week but it kept dropping to some other weird site - seems back to normal now??? The GT30 does look promising, but I guess the power will not come in until after 4500rpm (looking at dyno plots on their site) but I guess this is to be expected.
I feel what you are saying about the stock head gasket - the bore size is 82.5mm which only leaves a few mm between bores. I am taking it out to 83mm (leaving crank and rods stock) so I will gamble with a (copper) gasket bore dia. of 83 or 83.5mm and see how it goes. I guess I wont know unless I try and if I blow the gasket or block I will just deal with it!
Looks like I will have to sit down and do the maths anyway, to see where to go from here...
 

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Discussion Starter · #7 ·
Re: GT25R or GT28R? (Sleeper GM)

Quote, originally posted by Sleeper GM »
The turbos you are considering (GT25 and GT28R) will not flow enough air to produce 450 hp .... try the GT30 or 35 ..... I think the GT28RS is only rated at 350 max hp.

Yeah, I saw those figures on the APT site but I am confused...
Their Dyno plots quote HP figures at the wheel, does that mean that their turbo specific HP figures are also at the wheel??? Also, assuming their figures are somewhat conservative (for the average street user, whereas a drag racer will be happier to run higher boost and accept reduced turbo lifespan), a GT28RS producing 350HP might be capable of over 400HP at the wheels? What do you reckon?
Looking at this Australian website http://www.japparts.com.au/products/Turbo.htm they seem to do similar turbos with different AR combo's producing real good HP, I think these are crank HP figures.
 

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Re: GT25R or GT28R? (VoodooMotorsportUK)

Quote, originally posted by VoodooMotorsportUK »

Yeah, I saw those figures on the APT site but I am confused...
Their Dyno plots quote HP figures at the wheel, does that mean that their turbo specific HP figures are also at the wheel??? Also, assuming their figures are somewhat conservative (for the average street user, whereas a drag racer will be happier to run higher boost and accept reduced turbo lifespan), a GT28RS producing 350HP might be capable of over 400HP at the wheels? What do you reckon?
Looking at this Australian website http://www.japparts.com.au/products/Turbo.htm they seem to do similar turbos with different AR combo's producing real good HP, I think these are crank HP figures.

I'd forget Wheel HP numbers, as those are subject to major variations in the dynos and engine . I'd just go with the airflow calculations. You need about 32 lbs/min to make 350 HP (about 15psi at 7500rpm), and about 42lbs/min (about 25 psi at 7500rpm). On the GT28 RS compressor map the latter is way off the edge.
 

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Discussion Starter · #9 ·
Re: GT25R or GT28R? (bobqzzi)

Quote, originally posted by bobqzzi »

I'd forget Wheel HP numbers, as those are subject to major variations in the dynos and engine . I'd just go with the airflow calculations. You need about 32 lbs/min to make 350 HP (about 15psi at 7500rpm), and about 42lbs/min (about 25 psi at 7500rpm). On the GT28 RS compressor map the latter is way off the edge.

Know what you're saying. It would be easier if everyone stuck to crank HP when quoting figures, but then again in the real world (of drivetrain losses) wheel HP is what your car is actually putting to the ground.
I think GT30 sounds like the way to go for me.
Also, does anyone have any experience of the maximum power the Haldex 4WD system can handle?
 

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Re: GT25R or GT28R? (VoodooMotorsportUK)

The number I was quoted was inputshaft max tq at rear drive shaft is 1800 tq (that takes into account the gearing increasing the relative tq), but the actually transmission (MQ350 if you're lucky) is rated to whatever the conversion from nm to ft/lbs, something like 275 ft/lbs i think.
 
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