Before you think, one of these again I have done my research and used search on multiple forums. I am tossing up whether to go the GT28R or RS turbos once the motor is rebuilt with forged internals etc (ie boost CAN be increased over 21psi - GT28R efficency point). Why I can't make up my mind is because there are so many variances in both the turbos (.64 or .8something) and with different mods. This is the dyno graph of the GT28RS turbo from Z1 motorsports - which from their spiel identifies that they have modified the turbo to be less laggy by changing compressor covers Z1 Motorsports Spiel "We've taken the Disco Potato and given it a twist. Besides some modifications to make it a bolt on, the Garrett GT28RS is being used in its off the shelf form by JWT for their sport 700BB upgrade. Z1 also used this turbo in its "stock" form for a few months, but quickly realized that this turbo (the Disco Potato) wasn't well suited for the output of 1.5L (one side of the VG30DETT). It's laggy and doesn't produce substantially higher output numbers to excuse it. Through modifications in compressor cover clearances and changing the turbine housing to a smaller A/R, we have increased the response of the turbo without significantly affecting the peak output. The A/R ratio of the compressor and turbine covers are the same as the HKS 2530, with the same Garrett ball bearing center cartridge. This winning combination results in the best all around turbo for the Z32's over 500 whp, at a great price! Will flow 28psi and can produce 600+RWHP on race fuel with proper tuning and moderate modifications" vs dyno of aus300 high HP members This shows that the two people I know that have the 28RS's Shifter and UAS are obviously quite different in power. It would seem that shifter's motor is more like the one we are planning on building but has no relationship to the dynograph shown by Z1 - does this mean that to compare apples with apples that we compare UAS car to Z1 although dyno of Z1 is on race fuel???? Onto GT28R - this is very hard to get dyno graphs on but..... and on race fuel Is it just me or does the GT28R on race vs GT28RS on race fuel look EXTREMELY similar power at rpm's until it gets over around 4500rpm?? If this is true and I am reading it right then the Z1 GT28RS kit spools and makes the same power as the GT28R until 4500rpm and then keeps increasing until 6000rpm where it reaches its peak of around 600rwhp. The reason being that from posts that I have read on tt.net and others is that GT28R really is just an awesome turbo for those who don't want to have to rebuild their motor and that those figures can be achieved on around 18psi standard internals but for those who rebuild motors to be able to handle over 20psi and have the extra moola might as well go GT28RS because they are more power and spool just as well because they are newer design and technology. Thoughts? Am I way off track?
The 28RS is only going to be good with the 0.6x housing and with a lot of head work and manifold work/new manifolds. UAS still couldn't explain such the large difference between shifters and their track car. I thought all the mods were the same/similar besides some head work. I went for the GT28RS but got race heads from SGP racing to match them. The smaller housing is an option when you order them, not *only a Z1 thing*. I don't believe bigger valves make much of, if not any difference at all in our heads, but I don't know why UAS is so much quicker on the spool than most other GT28RS setups.
from what i hear gt28rs is laggy unless modded exhaust housing etc. gt28r starts to spool close to stock? depends what you want out of your car... Personally i'd get a turbo upgrade which spools as low as possible, giving a fat power band. (rather than nothing up to 4500RPM, then hold on!!!) lower spooling cars are so much more drivable, with less worries about when changing up to the next gear and not being on b00st. (gotta love the stock turbos... if only we could get 300 rwkw out of them )
Keep in mind also UAS car has a higher compression ratio to mine and a much lighter drivetrain. Also where I have a stock diff, driveshaft and UD pulley, his are all MUCH lighter. His timing was also much more advanced where mine was actually retarded a tad from memory. Also normal 98 octane fuel for me. And mine went to ~20psi and his up to 25psi or so. If I had gone the GT28R route, sure I might spool a tad earlier, but my turbos would be working much harder to get me less power that I am enjoying now. And I certainly wouldn't have that nice sharp curve. And while that comparison graph doesn't look so hot, in the real world, I dont have any problems or frustrations with power delivery. Its a power curve that I just will never get 'used to'. The 2 turbos are really quite different to each other. I would go for the RS only if you want to see more that 400kw. If your more than happy with ~350kw, then go for the R (imo)
The main difference between the two is the housings isnt it. Doesnt the GT28R use a .62 housing while the GT28RS uses the .86 which would explain why its laggier and capable of more power or do they modify the clip and/or wheels sizes aswell.
Few things. For the comparison the UAS car is on racefuel for its runs. Its always on racefuel for any largish dyno numbers as far as I know. John has commented a few times that he normally runs a lot lower power otherwise. You would have to check with him but its just what Ive assumed from previous posts so apples to apples comparison. Best graph Ive seen so far is Mikes dyno which you dont have on there that currently tops the dyno list. Fast spool and great top end but a lot of work to the engine. He's using the 28RS turbo with the .64ar. Id only go the 28R personally if I only wanted 350ish rwkw. Which for street/track is plenty. If your spending money on the engine then just get the 28RS then at least you have the option of more power if you want it and the spool up is just as good IMO.
So are chart right? Do the 28RS turbos spool just as quick as the 28R as per the dyno charts? In practice from what I've read this is not true as some of you have stated, the 28R spool quicker, but this isn't reflected on the charts. Does anybody have a chart of mike's run with his relative mods? I can't find anyone's mods now since the server was upgraded. Nate
My impression is the 28R will spool faster than the 28RS on a stockish engine. On an engine with some work, i.e. flowing better it seems the 28RS spools just as quick. If I was doing work on the engine, i.e. rods, pistons, cams, manifolds etc I would only bother getting the RS personally.
Would the 28R turbo spool quicker Than on the dyno chart with those kind of mods? You would think with the race gas dyno has already done those mods (due to the outright HP) and that therefore that is really what the 28R's potential is - I'm not going for highest power but it seems silly not to go with the RS if we are doing all the porting and manifolds etc which we intend to do.
The 28R will always spool slightly quicker. To look at it in a different way, the RS is really just like a high flow R.
UAS ZEd with S15 turbo's or GT28 hose inlet not flange. 98 octane pump gas with octane booster. And below is with GT28RS hose inlets not flange. Also these were extrude honed. C16Fuel used here. Bigger turbo but spool very similar on my car at least and less heat and stress and holds boost better at higher rpm and boost levels. Also more power. Can now get bigger again with same fitment at 440hp each or a bit less with smaller rear housing option.
That's shorely not psi boost on the right? 40psi and 35psi?????? Or is this another type of measurement like kw is to hp?
The top curve your refering to is the power reading on the left side in kw's, the lower curve is the PSI reading on the right. Damn 40 psi would be like riding a giant grenade lol Ben
Interesting dyno charts John, thanks for the info I wonder what sort of power you would have pulled with GT28R turbos on race fuel?
More but? As you can see the boost drops off and this is with NO boost controller as in wastegate hoses OFF to get it to boost as much as it could, and it couldn't hold the boost as turbo's were over. With the GTRS custom with extrude honing they flow much better at higher boost.
Re : woops....... I thought the tip off might have been when it only produced 300kw @35psi.....but when 5psi & race fuel were added for a gain of only 3kws even the blondes in the audience were scratching their heads
