Hi all, sorry for my first post in here being one of a problem/technical nature, and I'll be sure to put up a proper intro and build pics of my bike when it's done, but time is tight and ive been let down by other groups and forums with them not responding (at all).




I have built a 2006 Triumph Daytona 675 with a GT15 turbo. The manifold is home made, there is no intercooler, the charge pipe and airbox is home made. It's running PC3 management with an uprated fuel pump, begi fuel regulator and a oil pump on the turbo oil feed as I mounted it too low.




It's at the point where its on the rollers. it's putting out 8psi from 4k right up to as far as the bile wants to go, but it's putting out 10-15bhp less than the stock NA bike.


Current thinking is that the turbo is too small and its causing a backpressure issue, but I'm not 100% sure I understand, especially as it isn't boost-creeping at higher revs.


Do you think I might be able to to get around such a fault with an external wastegate (currently using the GT15's internal), or will changing out the turbo for a larger one be the only way?


Unless we are mis-diagnosing and theres another reasopn why it's doing more boost and less power and we're not seeing it... suggestions welcome!!!


Thanks in advance, all.

 

I'd probably throw a backpressure sensor on there and see how much of a restriction the turbo is in the exhaust.

 

What AFR were you targeting on the bike? Did you lower the compression of the engine with a thicker head gasket by chance? If so, you may want to look there, bikes don't like low compression unless you are running a big turbo with lots of boost....I learned the hard way with my turbo gixxer 1000. I know it's been a while, so if you found a solution, I'm interested in learning about it. A GT15 @ 8psi may be operating outside its efficiency range? You may want to try a t25 turbo rated at a max HP of around 250 if you want to run it at 6-10psi....those gt15's are rated right at 100-150hp max (probably around 12-15 psi since I didn't look at the compressor maps)...