Ive currently got a ebay gt45 on my car making abit over 600 flywheel hp. The specs on the turbo are compressor: 69-98mm turbine : 77.5-98mm 1.05 split t4 It was making 600 on 32-33psi, I recently wound it up to 35-36 and it definantly feels stronger. But Im just unsure why its taking some bigish boost to make the resulted power and Im thinking it could be turbo efficiency. Its got a long runner intake on it similar to the rajab design and the plugs are even. Im looking at the ebay gt42 which is compressor 74.8-102mm turbine 75-82mm 1.05 t4 split. Im just wondering if yeah the compressor will flow more but will it choke in the rear with the smaller turbine? Cheers

Give the proboost gt42 a go that will get it going 76mm front wheel and not so bad for lag either i have never had an issue with mine good bit of gear

Do a bit of reading on compressor maps, a lot of the big turbos don't even wake up until 40+.

yeah I've had a look and its hard to tell what map to use but using the 68-1 map its off the top of it already lol. The gt4202 is still nicely on it but still unsure on how the more restrictive turbine will affect power? The 42 has a curved turbine with a higher trim than the 45 with straight blades and lower trim. It would be nice with a turbine flow map aswell lol. Cheers

the turbo your using is a turbine/compressor mismatch(ebay gt45, Y2000K etc, all same..) they work decent(not fantastic) on rotarys and v8s' due to the larger than gt42 turbine the comp wheel is nothing special lb flow wise so its always going to be the killer and its always going to be lazier than it should be due to the oversize turbine. its probally taking biggish boost as its a non gt old school comp wheel... on u.s forums they say the comp wheel is closest to the masterpower T70 from memory(just what i have read) back in the old day Ta45s used 40psi to run 9s @ 140mph in vls and C16 a GT 4294 will do the same on 10 psi less... the 76mm ones are a much better comp/turbine match, but thats also a big stepup in turbo sizing.... the S trim 75mm gt4202 turbine woudn't affect power at all, the turbine you have is to big already cheers darren

Is there such thing as a too big turbine wheel compared to compressor yet the whole idea is to have minimal backpressure as possible? Looking at the ebay gt42's which have the same specs as the gt4202r Im thinking they must be a fair copy and probably a better match for my setup.

of course there is, you just run out of compressor flow, or over turbine and make no more power than a smaller setup and a lot of lag depends on engine size and ve, changes with every motor same with exhaust housings, you can over exhaust housing a turbine wheel, does same thing.. the turbo you have is well known to be over turbined, for a 6 cyl is would be better teamed with a 68mm Q trim turbine i would think cheers darren

I was thinking the compressor would have to be struggling with the massive turbine on a smallish engine lol. Thanks for clearing it up mate . Cheers Some original photos have not been recovered yet.

i look forward to seeing what you do next! cheers darren

Hmm prob see how far i can go before it runs out of compressor which i think im virtually at lol. Gona change the gears n let it rev abit. Cheers