Hope this is ok to put here as I don't know if I will be left stranded or not. Sorry this is so long. I am not real mechanical but try to gather info to help my mechanic who does work on TD's. I have a modified Spirit RT, as some of you may have seen my earlier thread. I have a person with a 1986 Corvette convertible that wants to race me. They said the engine has been modifed to be like what they used in the pace cars I assume at that time. I would love to win this race and should be able to with my beast. However, the beast is a little shaky at this time and I would really like to solve some of my issues before I race them if any of you can help. I tried to make this pretty detailed.
My setup is currently Spearco fmic, mbc, Garrett gt 30, + 40s, afpr, wideband, stage 4 fwdp cal, 6 puck clutch and now a walbro 190 fuel pump. I used to hold 20 pounds of boost without any problems and afr was mostly good all around. I bought a walbro 255 but it was bad. Anyway, my mechanic installed a walbro 190 pump he had and re did the vacuum lines to look cleaner. Mbc comes from on line right from wastegate I think. Now, the idle is rough. Car starts ok most of the time but then within minute or so settles to low idle around 500-650 rpm with rich a/f ratio around 9-10.
First problem, I can't seem to get the fuel right no matter what I do to the fuel regulator. The car want to be very rich in high vacuum, (more than minus 10 pressure or so), and is around 8.8 to 10 or so. Then when I am cruising with the boost around neutral it is around 10-12 or so. However when I try to partially boost at say 5 to 12lbs and feather the gas to keep it in that range, the a/f gets lean somewhere in there for a second or two and sometimes I can feel the Cal pull back timing for a second or so as well. The a/f will be around 12-13 but has a few jumps up to 17-19 for the split seconds as mentioned. Especially if I am in fairly low rmps, start to give it a lot of gas, but not floored, for a second or to where turbo just starts to ramp up and I then left completely off the gas fast; then I can many times feel that timing hesitation for a second or so. If I give it say more than 3/4ths to full throttle I am back to the rich condition even as the rpms go up to redline around 8.5 to 10 again. When I adjust the fuel leaner, the idle improves slightly but the partial boost is even leaner. Also, if I richen it a lot the partial boost seems better but the car is even richer and more sluggish on the bottom and at full throttle.
Problem two is the boost creep that has reared its head even before I took my car back to my mechanic for the fuel pump and a new gas tank.
The boost will go to where I set it on the gvalve initially but after 4000 rpms or so it will continue to creep till redline or cal pulls back timing at wot. I have gvalve set around 20 or so and it creeps till I have to let off around 24 or so for fear of detonation. Seems this way in each gear. I tried adjusting the wastegate arm looser but doesn't help. I also wondered when I loosened the arm on the wastegate I took it off the place where its connected to screw the arm out. The little thing, I forget what its called, where it hooks back on towards the turbo housing turns freely when I turned it with my hand with the wastegate arm disconnected. I thought when I messed with it months ago it was tight and wouldn't move but I could be mistaken. My turbo is internal wastegated GT3076r and was wondering if something was keeping the flapper from opening correctly. Or what else could be wrong? What about the fuel pump. I seemed much better off fuel wise with the stock pump. I know there could be another issue causing the problems like timing off or something else. Gas mileage has suffered as well lately. Was always getting over 20mpg with some extreme driving thrown in before these problems. Now I seem to be around 17 or so.
Despite all of this, the car is still fast and fun to drive as long as I feather the gas around 3/4 throttle and careful not to floor it to keep the boost around 20 and a/f ratios are good at that point as well around 10.5-11.5 or so. Can drive normal with no problems other than rough idle and occasional slight leaning out.
Trying to get an idea where to start. I believe my car was around 400whp at 20lbs before these problems but probably not now. Any suggestions and help me beat that Vette!
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Originally Posted by tazaroo
12.57@104 :O) 
