Engine/Transmission (1994 - 1998) Not sure what's goin' on......

[JGheen]

My set-up is in my sig and I have a few questions about my performance. Kinda long so bare with me.

I was doing some extra driving yesterday, so I thought I would do a couple of hard accelrations and see how she is performing. Well, I have been wondering about this since my most recent bombs of the #10 plate and the 3GSK. During acceleration I notice that my boost peaks at 36# in 3rd gear and 38 to sometimes 40# in fourth gear. Does this have to do with the engine having more time to spool the turbo in 4th rather than 3rd? Also, could this be the result of changes in atmospheric pressure? I ask this cuz I have noticed as the season has changed over from winter to spring and summer, the air dries up and the pressure seems to drop some out here in southern Cali. So in other words, I can get 36-38# on average in 4th on a hot day(90+*F) and on cooler days or in the morning before the sun bakes the air up, I can get 40# in 4th gear. Does anyone have an explaination as to what is happening?

Some other issues I wonder about are whether I am making too much boost. My wastegate is apparently set at 43psi according to the sticker on the "Banks Big Head". I have not adjusted the wastegate at all and am NOT running a boost elbow. But the strange thing is the turbo almost acts like the wastegate is pinched or just barely getting enough pressure to open up. The line is not leaking and I am running a 1/8" NPT barbed fitting from the AFC with a short piece of tygon clear tubing connecting it to the hard line across the engine to the wastegate actuator. As I stated above I am making on average 36# on every shift except for 2nd of course. Some people have told me that I am making too much boost and just heating the intake air with that high boost. I have only noticed my EGTs to really soar in 4th gear, 38-40# @ 2800-3000 rpm. Once the EGTs hit 1200 and the revs pick up to about 2800+ they go to 1300+ almost instantly. I guess what I am asking is, does it sound like I am making too much boost for the fuel alotted? The amount of smoke is not that much and clears up quick after the turbo fires and revs pick up past 1700. My AFC housing is full forward and #10 plate is about 3/4 full forward. Any suggestions as to what you guys think would be greatly appreciated. Sorry if this doesn't make much sense, but I couldn't wait to ask this until next weekend's Fetival in the Foothills where I would be able to possibly explain it a little easier and not so long.

 

[CumminsPower98]

I can comment on some of this. First off it is normal to have higher boost readings when the temps are down because the air is more compact. As far as I know 35 PSI is about the end of the map for efficiency on the stock HX 35. I'm no expert on this so I will let others comment further.

 

[JGheen]

Originally posted by CumminsPower98

First off it is normal to have higher boost readings when the temps are down because the air is more compact. As far as I know 35 PSI is about the end of the map for efficiency on the stock HX 35.

That's what I figured about the outside air temps and their relation to boost pressure. Colder air is more dense than hotter air. But what about the difference in boost peaks from gear to gear? Is this due to the engine's ability to have more time to spool the turbo in 4th gear rather than 3rd gear?

On the HX-35 efficiency map, I have heard that also, but I am wondering how much that differs when one installs say a 16cm turbine from a 12cm turbine? I would think that larger housing would increase the efficency map closer to 40psi. But I am running a 14cm turbine and from what the EGT and boost tells me I may be making too much boost for the amount t fuel I am pushing and this is causing the compressed intake air to be too hot. I am very close to installing a thermocouple post-intercooler on the intake to see just how hot my intake air is.



I read this quote from Geno's Garage site. Where is everyone getting the 35psi number from for the max rated boost of an HX-35. This here says 44psi is the max. Now I don't believe everything I read, but this is coming from a reputable source.



Geno's quote: The HX-35 and HY-35 turbochargers are rated for a maximum boost of 44 PSI. To safely reach 44 PSI, the turbine housing MUST be sized to keep the choke point above 40 PSI. The 12 cm2 housing chokes at about 32 PSI and the 9 cm2 single port housing chokes at somewhere below 30 PSI, so be careful about pushing the stock turbocharger beyond 30 PSI!

 

[JGheen]

Come on guys, I know my posts are long but am I not making any sense? Does no one have an answer to what I am trying to figure out?:{

 

[Deezul1]

In 4th gear you are there longer and the engine works harder than in 3rd. When we Dyno we do it in 5th gear as the HP will be higher than in 4th as it works the turbo more and it wont peak out as quickly.

 

[JGheen]

Thanks for that dyno info. , Deezul. I figured that is why I can get more boost in 4th than in 3rd. That is quite interesting about which gear to use for accurate HP and torque numbers.

But still wondering about my other questions... .....