GTII 7460R vs BBK Full photo shoot
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GTII 7460R vs BBK Full photo shoot
Let me start by saying that this isn't a 1:1 comparison. The BBK has been extensively ported by MAP (and it shows). With that said, there are still some interesting things to compare, and my assessment without taking off the compressor covers to get a better look at the compressor wheels is that the GTII could almost be considered a ball bearing BBK, and the two turbos ought to perform very similarly. Dyno testing will take place in early November.
coldside inlet compared - Visible wheel diameter is 54 mm for both turbos. GTII is six blade while BBK is five blade. Balancing cutouts visible on spindle nut of both turbos. BBK compressor cover and passages are slightly larger than the GTII.
hotside outlet compared - Wheel diameter is again 54 mm for both turbos. As mentioned by others, larger wastegate hole is evident on the GTII. More balancing cutouts on the GTII.
GTII turbine wheel - 12 blade wheel. Trailing edge of blades is reinforced. Casting was touchup machined to accommodate wheel. It can't be seen too well, but there is a sharp transition from the turbine opening to the flare that extends to the gasket surface.
BBK turbine wheel - 11 blade wheel. Excellent porting job by MAP can be seen.
coldside inlet compared - Visible wheel diameter is 54 mm for both turbos. GTII is six blade while BBK is five blade. Balancing cutouts visible on spindle nut of both turbos. BBK compressor cover and passages are slightly larger than the GTII.
hotside outlet compared - Wheel diameter is again 54 mm for both turbos. As mentioned by others, larger wastegate hole is evident on the GTII. More balancing cutouts on the GTII.
GTII turbine wheel - 12 blade wheel. Trailing edge of blades is reinforced. Casting was touchup machined to accommodate wheel. It can't be seen too well, but there is a sharp transition from the turbine opening to the flare that extends to the gasket surface.
BBK turbine wheel - 11 blade wheel. Excellent porting job by MAP can be seen.
Last edited by mrfred; Oct 15, 2010 at 02:16 PM.
Thread Starter
EvoM Guru
iTrader: (50)
Joined: Mar 2006
Posts: 9,675
Likes: 132
From: Tri-Cities, WA // Portland, OR
hotside inlet compared - Not much to say. BBK has been ported.
GTII hotside inlet "A" - Rather large "shelf" can be seen near top of passage. Shelf is part of the flow path to the WG hole. Needs to be cut down a bit with some porting.
BBK hotside inlet "A" (ported) - OEM passage is larger, in part, due to the porting, but also the passage extends deeper to the axis of the turbo. It can't be seen in the photos but the passage on the BBK extends all the way down to the wheel.
GTII hotside inlet "B" - Clean design.
BBK hotside inlet "B" (ported) - Even after porting, OEM passage has a bump that is not present in the GTII passage.
GTII hotside inlet "A" - Rather large "shelf" can be seen near top of passage. Shelf is part of the flow path to the WG hole. Needs to be cut down a bit with some porting.
BBK hotside inlet "A" (ported) - OEM passage is larger, in part, due to the porting, but also the passage extends deeper to the axis of the turbo. It can't be seen in the photos but the passage on the BBK extends all the way down to the wheel.
GTII hotside inlet "B" - Clean design.
BBK hotside inlet "B" (ported) - Even after porting, OEM passage has a bump that is not present in the GTII passage.
Last edited by mrfred; Oct 15, 2010 at 02:18 PM.
