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Performance Tuning for the Tahoe

The Hx-52 is a big turbo. If you have a pro 52 then it has an even bigger turbine wheel! Regular 52 won't really light with less than 400 hp worth of fuel .Pro 52 will take even more airflo an fuel to get it to light.
 
I have both ,they look the same. I was able to light a HX 55 on my 6.2,and over 60 psi boost. The HX 55 has a bigger turbine,and a smaller compressor inducer.
 
I finally got to test my Snap On timing meter . I have +2 at idle and -15 at 3000 rpms. This is ignition timing,not injection. If any one has factory specs let me know. It bothers me that there is advance built in the cam lobes. The best I can come up with is 6.2 degrees more advance at full fuel,if you are using all the cam lobe. So I guess I should have -9 degrees at 3000 rpms,and the advance arm in the retard position. This should give me -2 at full fuel. I never did fully comprehend the variable advance . I can only imagine were the cam ring is positioned at any time. Is the cam ring moving that much,or does the ignition change on its own at higher rpms ? I guess the injection timing has to advance pretty much to keep the ignition timing were it needs to be.
 
Why would the advance arm be in the retard position at 3000 rpms? Did you set it up that way? At least from what I can tell, the advance arm starts moving almost immediately after idle.
 
The arm takes away about 5 degrees of advance . Turning the bottom allen screw,will change timing the whole way across. Adjusting the cam on the throttle shaft will change the amount of retard. Increasing the charge pressure will advance timing,possibly more so at idle and part throttle.
 
I thought the arm advanced the timing as throttle went up? to compensate for injection lag. Unless I am misunderstanding what you are saying and that you mean it takes away 5 degrees at idle in comparison to full throttle. And when you adjust the screw on the bottom, will the advance piston follow it? Meaning if it is unscrewed out most of the way, does the advance piston still contact it at idle?
 
It takes away advance when the arm moves. What it does is regulate pressure that is advancing the piston. With the screw most the way out,the small button/plunger should still contact the arm. I have the timing set at-2 at idle and -8 at 3000 rpms,but sounds like to much. Idle sounds ok though. It runs exactly the same,just louder. I would almost bet money that one plunger is stuck. The only other option is that a turned up stock pump puts out less fuel than I can remember.
 
Ha 6.2 your last thought may be the right one :)

Hmm ok I thought thats what advanced it. So does fuel pressure within the housing advance the piston then? Although I haven't touched the screw, I have the cam piece on the throttle shaft adjusted so that it takes more throttle to move the arm, thats what I had to do to get it to stop missing so bad at low idle, but now the truck is like dead past 2200 rpm.

So you have found -8 is too much, how can you tell? Just by sound or performance? I am interested in all this as these types of small adjustments make just as much a difference as anything else it seems. is there any other way to get timing specs on our trucks? Where did you get the meter?
 
I got the meter on ebay. I pulled the pump tonight. The plungers were fine. The limiter spring was an L-2, apparently not a sweet one. I removed that,and the adjuster screw. I also did a quick cam ring grind job. The lobes got a little steeper than they should be,but this makes it run better. It might brake a cam pin,by and by. I did this,and cranked the advance screw in 1/2 turn. The rest of the pump,except the governor, is bone stock, I didn't even adjust the charge pressure. She runs now. :thumbsup: Turbo lights a hair past 2000 rpms ,and I seen a little over 30 psi boost. Now my tranny slips even more when shifting . It feels pretty good when the converter is locked in,and lug it in 2nd or 3rd,and light the turbo. My gearing no longer feels to high. :thumbsup: I was not expecting the power to increase this much. :) I will have to do some more tranny work,and a better torque converter.
 
Awesome, now time for vids, I wanna see it in action!!

The L-2 spring is whats in my pump as well, so you just remove them and the spring screw and it works fine??

I got a couple more questions here, first, you said you turned the advance screw in 1/2 turn, is that from all the way out? Also, what did you use to grind out the cam ring? Also, what have you done to the governor?

One last question, you have mentioned the charge pressure a few times, how do you monitor that and how do you adjust it? Does the cap in the back adjust it? Sorry for all the questions but I am very curious, my truck IMO is running pretty crappy right now.

I will have to keep an eye out for a meter, glad to hear she is running good! I wanna see a video!
 
hey 6.2 thats awesome ya got it figured out! what about the lift pump? did you just dead head it or run the return into the feed? i got my truck all together today except the lift pump, regulator, and filter setup. plan to try and figure that out tonight yet and fire it up. i should be able to bring my old ip down some night this week if you still wanna look at it.
 
I have the fuel regulator turned tight,which makes it dead head,I didn't really see any difference either way. I did notice it seems to start harder,since the pump was apart. Although I think its the 24 volt glows, and colder weather. We took the Tahoe on a 180 mile trip,it worked fine and got 19.6 miles per gallon. The allen screw was adjusted from where it was. It seems every pump has it adjusted at a different spot. The charge pressure adjustment is an allen screw straight inside the fuel inlet. There is only two places to check charge psi,the little locking screw on the charge pump cover,and the big allen bolt on the bottom,that fastens the head to the housing. I drilled and tapped the bottom bolt on my 6.2. I would like to go off the top bolt,but not sure how. Will probably have to braze something. There is a Stanadyne adapter for this.
 
The start of the cam lobe should be smoothed out,when eliminating the leaf spring. I used a die grinder with about a 3/4 inch stone. I got a bit carried away,and the lobes also got fairly short and steep. So far the cam pin is holding. I might get some cam rings machined properly sometime .
 
Sounds good to me! I wanna see it accelerate now!

As for charge pressure, is that the scew that is at the top of the filter screen?

I didn't get a chance to work on the pump this weekend, but last week I bought a blue Holley on ebay with a regulator to put in sometime. This old pump still doesn't run right, it cut fuel on me once and the timing seems messed up on it. I have the pump set right on the line, and I have found that messing with the cam piece on the throttle shaft makes a huge difference in sound and starting ability. With the thing adjusted to retard timing later, it starts like a champ with no smoke, but it is very chatty, less power, and smoky at low rpms. Adjust it to retard sooner, and it carries on and blows white smoke on startup, but runs and revs smooth and quiet, with more low end power but less smoke.

I may not mess with it much until I get this new pump in.

Anyways I would be interested in the modified cam ring whenever you get something figured out or I would be more than happy to test various rings too if need be.
 
Seems pretty quick. I wonder how many of the tricks you do to the mechanical pumps can be done to a electronic one to get more fuel?
 
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