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Tahoe HX 35

spdgofast

Well-Known Member
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Location
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Ok guys, I thought I would start a thread about my 2 door Tahoe that I recently purchased so I could get used to posting so when I get started on my P400 going into my Burb that I will be well acclimated.
So here we go, so I purchased a 1999 Tahoe Z71 with 200K miles on it and on the drive back to Florida from Indiana it ran good and got 16.5 MPG @ 2000 RPM & 70 MPH. After going through and changing all of the fluids I have installed a HX 35 with a Holset 14 CM exhaust housing along with one of racedaymechanics down pipes and spring controlled w/g actuators. I also installed a 4" intake and AEM dry filter in the K47 airbox like others have done. Well I guess I was a little disappointed with the performance, granted it still has a stock tune and exhaust but a 3" D pipe. It's real laggy and black smokes out of the hole (no way I could tow anything). I have set the W/G actuator in its softest position without the W/G being able to flop open & closed and I can get 15.5 lbs of boost under high RPM acceleration which is where I want to limit it due to the fact that it has stock head gaskets and bolts. I am really not happy with the boost being @ 7.5 lbs cruising on the highway @ 75 MPH seeing how I am hopeing to get this thing to get like 20 MPG cruising on the highway and I know that you don't want that much boost when cruising @2000 RPMs in my opinion. My only hope was that I could put a softer spring in the W/G actuator when I get the computer reprogrammed so that the W/G would stay opened more while cruising and the additional fuel= exhaust will still hold the 12 to 15 lbs under acceleration even though the W/G will be opening with less resistance but I really don't think that will work but that is my plan as of now. My next move will be the exhaust system and we'll see how she likes that. As always I value the input and opinions of other members.
 
IMO HX35 is too small. The HX40II will still be a little high boost at cruise 6PSI on mine - it is the side affect of a spring waste gate. Only the ATT or the vac system could drop boost to zero at cruise. The ATT on my 1995 is 0 PSI at 70 MPH cruise and the HX40II was 6 PSI.

Other members have loosened their WG spring and found some MPG increases.

You need a tune. Too much fuel down low and no turbo to burn it like the GMx would. All turbo's can smoke before the turbo catches up. Again tuning can make a difference. As the factory tune defuels in the upper RPM you will be disappointed without a tune.

Weak wastegate settings will pop the wastegate off early and smoke bad when you are putting the throttle to it.

For 20+ MPG remove the turbo and go NA. Otherwise live with the economy loss this manifold design and turbo gives you.

3" downpipe is fine. The rest of the exhaust needs to be 4".
 
With the electronic motors you are going to need a tune for the ecm.... and I think you will have better luck with the Holset pressure actuator for the W/G than a spring type....
 
14 turbine housing isn't a good match for stock fueling. The 12 works great on a DS4 pumped truck, even with a performance ECM.
 
14 turbine housing isn't a good match for stock fueling. The 12 works great on a DS4 pumped truck, even with a performance ECM.
Yea, for what I am doing with this truck I wouldn't be surprised if I go with the 12 after I'm done with the exhaust and the tune.
 
Holset dealers ----- I have only found 2 different part## for the 14cm gated hsg. 3580651, 3529874..... These are big $$ items new or used just for the bare hsg, Holset gets 550-600$ new, if you look long enough you can find a used one, but they are still lots of money.... I got lucky and found a Holset rebuilt unit for under 400$...

I found that the 12cm works great with the electronic pumps and the 14cm works great with a db2 that has been turned up a good bit....
 
Ask the turbonator bros. They have a link for just about any holset part you could need and the prices are pretty fair.
 
The one I have came from banks and I bought it off another forum. Here is a link to one I found before I bought mine. I was torn between buying a CKO 40 II or spending the same money for the 14 cm hsg and put it on a HX 35 that I had from the 12 valve Cummins that I was going to put in my Suburban but I sold that motor and opted to go with the P400 due to the ease of installation over the Cummins.
http://www.gillettdiesel.com/14cm2wastegatedturbinehousing.aspx
 
Well guys, I got the F intake manifold installed today and now I'm happy, it really woke the truck up and got rid of the lag and black smoke off the bottom end. Now that I am getting correct boost level readings and no exhaust in the intake the boost readings are as follows, cruising @ 2100 rpm 70 mph=5.5 lbs , 2250 rpm @ 75 mph 6 lbs of boost. I did a couple of WOT runs from a dead stand still and the first one hit 10 lbs of boost and the second one hit 11 lbs and instantly either went into defuel mode or limp mode and I had to disconnect the batteries to reset the computer to wake her back up. I would deffinatly have to recommend anyone doing a turbo upgrade on a EGR S manifold equipped truck to plan on the addition of the F manifold ASAP. Now I really can't wait to get the exhaust freed up and get the new tune. My thanks go out to mikek3500 for getting me the F manifold so quickly.
 
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