Looking at upgrading from a gt42 to gt47 turbo in my Cosmo and now have to choose what size hotside A/R i what any suggestions? Options are 0.96 1.08 1.23 or 1.39 at the moment the engines only slightly ported but looking at going bridge port next year. The gt42 i'm running at the mo spools up at 3000 revs with a 1.08 hotside has anyone out there used a gt47 on a 20b so they can give me some sort of a clue as to where to expect the power to come in with the different hotsides.

Kevin

I run my 20B with TURBONETICS T70 "P" trim turbine 1.00a/r.

My engine is street ported, i had try 1.15a/r and no more power but more lag (not on the dyno).

My suggestion is go with turbine that help to kick hard on the road https://www.nopistons.com/forums/pub...1047683473.gif , don't go with turbine that is just good for dyno #.

Think i'm going to stay with a 1.08 hotside if it raises the spool point to 4000rpm with the bigger turbo then it still leaves me with 3500revs or so on boost. Not sure how laggy the gt47's going to be, its a fair bit bigger than the gt42. I know its a big lump to spool up but the roller bearings should help. If its too laggy then i'll just go for the bridgeport a bit earlier than planned.

Kevin

question: if you're sure that you're going to bridge it at a later point in time, then why not go up to the 1.23 now? won't the bridgey need the larger turbine housing?

I'm running a 1.32 on a T-76 and have no lag at all with a big street port. Hitting boost by 2K when WOT.

I've been dealing with garrett technical on this one and it looks like i'm going for a gt45. The gt47 isn't built to the spec of the gt45 the metals used will not take the same temps that the gt45 will plus the 47 is a plain bearing as opposed to the roller bearings in the 45. For purely drag racing then the 47 is fine but not upto long term street driving

Kevin

Hey brother run a 1.15 or if your real keen and can handle a bid of lag and have a bit of extend porting 1.22 keep with ya T6 flange ya cant go wrong

:-) put my last dollar on it

Ended up with a t4 flange and 1.22A/R divided housing should be running in a few weeks so i'll wait and see.

Kevin