Post by jetdriver on Apr 25, 2014 23:32:02 GMT -5
I am trying to diagnose my latest GT build. It is my second one and is giving a little starting trouble.
Important stuff:
Comp inducer 2.129"
Turbine exducer 2.67"
Garrett T04B
Flame tube is 2.5" step to 3.5" tapered to 2x3" for turbine inlet, 12" long.
(20) .25" primary holes (10 axial 10 radial)
(8) .3125" secondary
(5) .625" tertiary
CC is 5" diameter.
I am running on propane, and it is hard to get "over the hump" on start. What is a reasonable Egt limit for these builds? I have the egt probe 2" behind the turbine wheel in a 3" pipe without any cone, and I try not to exceed 1000 degrees F. Maintaining 800-1000 degrees takes a few minutes of oil warming before ramping up to idle. If I open the fuel valve more, it changes the combustion noise dramatically with fast rising egt, but no faster rpm rise. The engine runs well after getting up to idle speed. Unfortunately I have not been able to get my laser tach to read the comp nut yet, so I am going off P2. Idle is about 800-850 F and 5 psi. It has good throttle response. So far I have run up to 15 psi.
I am a little short on primary and secondary holes according to jet specs, but I thought drilling more holes was easier than welding them closed. I really did not expect to have this trouble after getting pretty close to the jet specs calcs, and having a turbo with the favorable turbine to compressor ratio. My last build was alot of "that looks about right" with a small 2" diameter chamber on a tiny t25 turbo with a smaller turbine than compressor and a dreaded annular bypass at the end of the flame tube. But it ran perfect!
I appreciate any advice!
Important stuff:
Comp inducer 2.129"
Turbine exducer 2.67"
Garrett T04B
Flame tube is 2.5" step to 3.5" tapered to 2x3" for turbine inlet, 12" long.
(20) .25" primary holes (10 axial 10 radial)
(8) .3125" secondary
(5) .625" tertiary
CC is 5" diameter.
I am running on propane, and it is hard to get "over the hump" on start. What is a reasonable Egt limit for these builds? I have the egt probe 2" behind the turbine wheel in a 3" pipe without any cone, and I try not to exceed 1000 degrees F. Maintaining 800-1000 degrees takes a few minutes of oil warming before ramping up to idle. If I open the fuel valve more, it changes the combustion noise dramatically with fast rising egt, but no faster rpm rise. The engine runs well after getting up to idle speed. Unfortunately I have not been able to get my laser tach to read the comp nut yet, so I am going off P2. Idle is about 800-850 F and 5 psi. It has good throttle response. So far I have run up to 15 psi.
I am a little short on primary and secondary holes according to jet specs, but I thought drilling more holes was easier than welding them closed. I really did not expect to have this trouble after getting pretty close to the jet specs calcs, and having a turbo with the favorable turbine to compressor ratio. My last build was alot of "that looks about right" with a small 2" diameter chamber on a tiny t25 turbo with a smaller turbine than compressor and a dreaded annular bypass at the end of the flame tube. But it ran perfect!
I appreciate any advice!
