I recently had my stock HX-35 with a 16 cm non wastegated exhaust housing uprgraded with a bigger compresor wheel and housing. I still am only able to push 35-40 lbs of boost, the same as stock, what can i do to get alittle more boost?

 

bigger wheel = more flow. just because the boost number is the same as stock doesnt means its not flowing more than stock.

 

You can try a boost elbow in your compressor housing if it'll accept one but like stateted your getting more volume of air at the same pressure which is a good thing, but you might gain some with a lil more PSI

 

no boost elbow for him..... what are you EGT's? you prolly don't have enough fuel to make more boost.....

 

Keep in mind that you're still using the same turbine section. That turbine can only extract so much power.

The larger compressor wheel takes more power to spin. The fact that you went to a larger compressor and STILL have good boost is a good thing.

Taken to the extreme, you'd lose boost because the turbine just can't extract enough power to drive the compressor hard enough to make the boost numbers. In this case, you'll see really high drive pressure and low boost pressure-- the opposite of what you want.

Personally, I'm in favor of larger, more efficient turbines that can drive the compressor to certain levels more efficiently.

It's all about balance. If the turbine is too big, you add a lot of inertia and slow down the spoolup. It also inefficient-- like flyswatting with a shotgun.

 

Someone explain to me how more flow can be had with the same boost. If the head is the real restriction in the process, I don't see how a larger wheel is going to produce more airflow at the same boost. I do see and understand that when you push say 40 psi with an HX 35 that it is hot boost and thus has less air molecules than 40 psi with a Htt 62 that is at a lower temp. But in my mind 35 psi with an HX 35 and 35 psi with a larger wheel both being on the compressor map and not past the choke point will net the same airflow if temp of boosted air is the same. Now I would believe that a larger wheel will have lower temps at 45 psi boost but at 35 psi I wonder.

 

It depends what you mean by "on the map". If the edge of the map is 55% efficiency and the compressor is near the edge of the map, it's obviously making hotter air than a slightly bigger compressor that's also "on the map", but at 74% efficiency.

I'm not entirely convinced of the benefits of an HX40 wheel though (even though I have one). It seems to me their map would extend farther to the right, but not necessarily to higher pressure ratios...

 

so if I went back to a 12 cm housing would that increase boost and still lower egt's? I do not want hight drive pressure because i do not want to blow a head gasket. egt's do not exceed 1400 now but before they would under the same boost conditions, i have removed the afc and fuel plate so i think i am pushing enough fuel to have a higher boost number

 

Increased boost may or may not lower EGTs. If you're on the ragged edge of the compressor's range, it might be a step backwards.

Also, if that increased boost causes turbine power to skyrocket, then your drivepressure will go way up with a tiny increase in boost-- definitely NOT what you want.

Keep in mind that a turbine can only extract a certain amount of power relatively efficiently. Let's say the efficiency range of the factory turbine is 70shp. If raising the boost a couple 3-5psi more drives the required shp from 70hp to 85hp, then you've definitely taken a step backwards.

An intake temp gauge is useful to tell you where you are at. Once you get off the map, or at least towards the edges, you'll see 50-100 degree temp increases for just a couple psi more boost.

 

So what we are really saying is that at a certain boost number, a larger compressor wheel is more efficient and thus has a lower temp and or more mass of air at the same boost pressure. But, down at the lower psi like high 20's low 30's where a stock charger is reasonable efficient, a bigger compressor wheel does not push more mass of air at the same boost pressure.

 

schaef 12, hey what are your egt temps now that you have the 16cm housing? Also how is your spool up time with the 16cm? How much lower do they run than with the 12cm over all?

 

Basically yes.

The temps will tell the story.

 

So basically the same boost with a bigger compressor is a good thing, drive pressure not to much higher and cooler denser air?

 

With a bigger wheel and housing it's like going from a 1" watering hose to a 2" watering hose, get alot more volume of water and the same pressure maybe a lil less. It's one way to relate to it.