• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Why does my boost drop off?

I should have asked what turbo also. Did you ever keep 24 psi? the springs get whooped up sometimes and stretching it may help
 
Too small of a turbo, too small of a turbine housing/wheel, or the cylinder head doesn't flow.

You have MS, post a MSQ and MSL.
 
Last edited:
Ah, ok. I'm slowly backing away cause I know nothing about turbocharging Kjet, my B21 runs on Megasquirt. Just curious tho, do you put boost through the CIS plate?!? That thing is tiny. But it sounds like tryingbe is right about something being too small, especially the wastegate, that's asking a lot from an internal wastegate. Also from that thread it seems this is not a new problem, it hasn't ever pushed 24 psi consistently. Isn't that out of the compressor efficiency range?
 
Ah, ok. I'm slowly backing away cause I know nothing about turbocharging Kjet, my B21 runs on Megasquirt. Just curious tho, do you put boost through the CIS plate?!? That thing is tiny. But it sounds like tryingbe is right about something being too small, especially the wastegate, that's asking a lot from an internal wastegate. Also from that thread it seems this is not a new problem, it hasn't ever pushed 24 psi consistently. Isn't that out of the compressor efficiency range?

No, just the K-jet intake manifold, 2" compressor discharge up to 2.5" ebay intercooler to 2.5" piping to K-jet intake. Siemens 72's stuck in the k-jet holes on the head. Here's a link to a datalog from tonight. I'll post up the msq from my phone in a minute
https://drive.google.com/file/d/10z6yZBsimyYwH6EgOByEV9Zx8h4qh96X/view?usp=sharing
 
I really think that is too much exhaust flow for the internal wastegate, they just aren't that good, that's for stock applications, that being said I did constantly put 20 psi through a ported 15g for a couple years, but it didn't like it, turbo hot side coked up with white **** and cooked the bearings. Idk, if you have to run that much boost to get the power level you want, I would run a bigger turbo with less boost. Also you haven't said if it ever consistently ran 24 psi, is this a new problem or it just doesn't do what you want. Maybe someone else has some ideas..
 
I don't follow your logic, maybe if it was over boosting, then the waste gate hole would be too small. This is a China Bay td05-20g supposed to be good for 400-500hp with their waste gate actuator and waste gate port. Maybe with my gearing it just won't hold the boost? It boosts 21psi in first, 23-24 in second 24psi in the third then drops off as I accelerate, it holds 24 a little longer in 4th then I run out of road.
 
How is the return pressure on the actuator? The 15g ones are pretty sad, so even with an MBC they would still creep down since the actuator couldn't keep the gate closed at higher rpm. You could try a helper spring on the gate just for testing, see if that helps.

Also what Harry suggested, could be the exhaust side is too small and becoming a restriction.
 
The MSL you gave only shows 22PSI max and it also said you didn't stay in WOT long enough. Stop letting off at 5000RPM

RMP1.jpg


RMP2.jpg
 
But it sure seems like it drops off in the car.

That's just mean your top end is not setup for flow, ie. head, cam, turbo, etc.


Get an adjustable cam gear, put it on the dyno, get a baseline, then retard the cam gear couple of degree, make another pull, repeat until you like where you have power band.
 
Back
Top