Trying to wrap my head around boost decreasing as Rpms increase?

[monster50iii]

At 2800rpms I'm around 38-40psi of boost. By 3800rpms boost drops to 32-33psi. I recently checked for boost leaks and had none. Is it just a situation where the engine uses that much more air volume with the increasing rpms, and the compressor just can't keep up? Fueling stays constant the entire time. Curious what other fixed vane guys have experienced. Thanks

 

[Chevy1925]

Without seeing drive pressure, yes. The engine is now eating more air than the turbo can produce and boost is falling off. You are outside the map of the turbo above 3k

 

[monster50iii]

I've been considering sending it off and getting a 66 wheel put on it, but is 1.5mm really going to make that big of a difference? Wondering if a guy just goes to the 69

 

[Chevy1925]

Why are you wanting the extra rpm? Can you put a pic up of the dyno graph? What is plies width at 2800 and pulse width at 3800?

I don’t believe throwing a wheel at it will get you what you want, that’s a lot of rpm on a little charger

 

[Hate2Looz]

Sounds like you're over speeding the turbo, to me.

 

[Yngdmax92]

I have a 3794 with modded vanes in it as well from Danville. Mine holds 41 psi to 3500 rpm with Danville remote tunes. Yours seems odd to me

 

[monster50iii]

I've got the 1.0 housing on now as I had a feeling the turbine was holding things back. I may get a do gauge on it shortly.

Pulse stays right near 2250us the entire time. Fuel is constant, never changes.

I believe I have enough fuel right now for nearly 700hp, but the turbo just isn't quite up to the challenge. I feel like I could make 650hp on a 2100us tune with a more properly sized turbo. I think the 1.0 housing was a good move, but im thinking a bit larger compressor wheel may compliment the 1.0 housing?

 

[Dozerboy]

What do you have an S364.5? I would think you should be higher, but that’s just a guess without more trouble shooting.

I have a 3794 with modded vanes in it as well from Danville. Mine holds 41 psi to 3500 rpm with Danville remote tunes. Yours seems odd to me

That one of the things you can do with a VVT. Doesn’t mean your making more power then if you where only at 35psi.

 

[monster50iii]

I gained 30hp going from 38psi to 33psi with my old 3794

 

[Yngdmax92]

I gained 30hp going from 38psi to 33psi with my old 3794

Lol, well that doesn't make me feel good . Hmm there's no smoke, and all my parameters are within check. I guess some day I'll have to go over there and have him live tune it.

 

[monster50iii]

So, in the past, I did my wot pulls in 4th gear.. I learned that must not load the truck very much. Pretty sure that's been why I've seen boost decrease. A bit embarrassing lol.

Source: https://youtu.be/Pbx2hjnmVM8