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Performance Tuning for the Tahoe

I now have the advance piston travel limited with a spacer. Finally got the tranny in and drove it. I made one trip around the block, came back and immediately retarded the timing 1/8 inch. Still have some timing issues,it seems to vary a lot with throttle . I might up the injector pop pressure for this reason only. Right now they are at 1600 psi,and power didn't seem to drop any.
 
You still having good power ? As we understand it, the internal housing pressure adjusts the timing to compensate for the increasing rpm's of the motor.....we had a problem with one of our pumps, pulling air in the seal for the advance plunger.....could watch the bubbles when moving the lever externally. When you are adjusting your timing, are you using your timing meter ? Where are you set at at idle, as compared to a higher rpm ?

Could you post up a video, so we can see how the Tahoe is running now ?

This timing issue, among others is the reason, that if we are able to just enlarge plunger size and the corresponding charge and delivery passages, we prefer to attempt that route, and try to keep the pump as stock in it's operation as possible. Keep at it, when you finally have the formula figured out, many will be trying your mods to the pump and injectors.
 
I didn't check the timing with the meter. It varies a lot with engine load,no load is white smoke,and full load is nice and black. The timing issue started when I lowered the compression. But the major variation is an additional problem. Not sure if its in the pump or the low pop injectors.
 
Well I bumped the pop pressure to 3200 psi. It helped some,more cackle. It sure runs good, except light load. Just putting it in gear will clear up the smoke, the tiniest load will turn the smoke clear.
 
One variable it would be nice to remove from these pop pressure tests is timing. One of the old SnapOn meters (and others) would allow setting each pop setting to the same base timing.
 
I have one. It works,but there is no way to get full load timing . There must be no smoke or it will not read. The higher pop pressure gave it more timing,and it idles with a very slight lope. Power seems about the same.
 
Well I removed my advance piston spacer . I swapped the advance regulator spring for a DS4 spring,stiffer and longer. It now has a fully working advance. The massive timing variation with throttle/load did not change. I suspected a fuel return issue,pulled the line while running,major return volume. This is possibly coming from the advance regulator,that is dumping 110 psi instead of 50 psi. One reason that I had blocked the piston in the first place. I had it running without the fan to get it to about 190 degrees. It would still smoke white pretty bad at part throttle and haze at idle,but blip the throttle and it would cackle,like lots of timing. Guess I'll try some stock injectors next. I wouldn't mind trying some test stand nozzles ,they have a 360 degree spray pattern.
 
Installed some stock injectors,set at 2600 psi. Timing advanced a little. Still retarded at about half throttle,no load. I reinstalled my advance spacer,now it's about the same as when I started. I checked fuel return,and it's a lot. If this wasn't supposed to be a daily driver,I'd lock the timing. Not sure what's up with the massive fuel return,it could be the accumulators. I might end up putting a stock charge pressure regulator back on.
 
Took the spacer back out. I tested and tuned for quit a while,played with the allen screw,and adjusted the advance cam. I kept advancing the allen screw untill it lost power,then retarded it one turn. It has 12 degrees injection timing at idle. For some reason it didn't want to read correctly at higher rpms. I used an injector line adapter and a gas timing light. I believe the best way to set the advance curve would be on a test stand. I think the timing is still on the high side,lots of top end power,and 0 power below 2000 rpms. White smoke is all gone,but the engine was nice and warm,from lots of thrashing,seen close to 45 psi boost,and 1400 egt's.
 
No it a 6.5,stock bolts in the heads and mains,no girdle. It peaks at 42 psi now with more timing. I want to make a video sometime.
 
Checked max rpms at the top of first gear. Seems to hit a wall at 4200,this is with no governor. It will free rev 4500 or more. Part the problem might be top end timing,or turbo drive pressure. Main problem is the way the ip is designed,higher rpms equals less fill time,same thing for internal advance. I watched the black smoke compared to boost,and it was still there at 25 psi,and clear at 42 psi.
 
We need to get you on a dyno.....start checking in your area for possible places and pricing. Will go and bump the dyno fund threads, and see if you can be nominated.
 
6.2 turbo said:
I checked fuel return,and it's a lot. If this wasn't supposed to be a daily driver,I'd lock the timing. Not sure what's up with the massive fuel return,it could be the accumulators. I might end up putting a stock charge pressure regulator back on.
Click to expand...

There is 2 allen "screws" inside your pump. Make them 1/4 turn tighter.
 
Do you mean the accumulators ? On my 6.2 I tightened them against,some heads don't have them anyhow. I noticed an increase in charge psi at full throttle afterwards. I had it cranked to 150 psi,but it would still drop to 80-100 full throttle. Sometime I want to check plunger fill psi.
 
Not sure what they're called. But the screws are hollow, with springs and plungers underneath.
If you have them in against, then your whole issue is charge pump flow, and the reason your timing is all over the place is due to that.
Feed the pump about 60-80 psi, then see what happens :)
 
That was not the Tahoe pump,this one stays over 100 psi all the time.
 
Got this thing running again. This time a stock compression 6.2. Turned the fuel back a lot. Having trouble getting any power past 3500 rpm. Boost peaks at 25,and drive psi is never more than 25 psi. At low boost, drive psi is lower than boost psi. More timing helps only slightly . Midrange power is fine. Low end power is totally gone. At least it starts easily. I said it before, I think it matters if it's too lean.
 
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