well my hx 35 has given up the ghost, started rubbing on the impeller side. so i installed a new hx 55 i had at the shop with a 19cm ex housing. now i have this terrible stumble, it won't hardly rev over 3k, it would do 4800 or so before. so i took it home and checked the timing, right where i set it at 16 btdc. now it will rev over 3k going down the road and i still can't figure where i am getting all the boost. i am pegging out at 50 plus psi. i am not sure how high it is going. but i really didn't think i would get that much boost with a 19 cm ex housing, so looks like i will be hooking up the waste gate. but this stumble has me stumped a bit, it ran fine with the 35 but now it stumbles and smokes like the timing is retarded. i will check the fuel pressure tonight and see whats up. the overflow seems to be working fine, i just hand pumped it last night to see if it was bypassing.

 

no one has any ideas? the more i think about it i belive i am getting too much fuel when the rack starts to move. i will try some different plate styles to limit the bottom end a bit. i was getting 8#s of boost at 3k free rev with the 35, now i have 1 or 2#s at the most at 3k. if i ease into the throttle, real easy it will rev up smooth but i have to be real easy. so at lunch i will tear into it and make some adjustments. mike

 

I remember reading alot that the 55 was a pretty big turbo to spin. The low end lag/stumble seems to me that there is too much fuel for the fire. The over fueling can cause misfires and "put out the fire" with too much fuel. The large exhaust housing and huge compressor wheel is gonna give next to no boost at low loads, which may make cruising a little toasty.

I think you are on the right track to trim the fuel delivery back. The low end fuel has to be trimmed out IMHO...

J-eh

 

I would think you need some more timing, hell we set street trucks with stock chargers to at least 18.

 

running empty the egts wen't up 150 or so degrees at 65 mph. i can still hit 1400 and 110mph. that is as fast as i have been since i put it on. i am going to bump the timing up to 20 or so. i don't think it will kill the head gasket since i have no boost to speak off below 2300 or so. and i have a 17cm exhaust housing i need to get and put on there. i will figure out how to make this thing hit and run as i think it should. it is more of a challenge than anything else.
it hits so hard at 2700 that it is violent, i mean i can hardly watch the gauges because i am too busy driving it. i will figure it out before i bolt the twins on.