Doing some baseline runs with my new setup and am running into some boost fade issues. PTE 3431E .63 A/R on an 89mm H22. ~9.5:1 compression, SFP manifold with Tial MVR and 3" turbo-back exhaust. ~10psi springs in the wastegate, boost reference straight off the compressor housing.

Haven't messed with my PWM control yet because I'd rather fix this issue than try and tune it out. The fade is very consistent and happens every single time. @ this boost/torque (if it would hold flat) I should be making close to 290-300whp, not 220.




Ideas? Exhaust side of the turbo too small for such a large displacement engine? I disconnected the wastegate line and it has no problem building a ton of boost with zero [audible] wastegate opening

 

youre losing boost somewhere..



or you miraculously have one of the only engines out there with massive blowby that still runs..

 

I'll check for boost leaks then I guess. I wouldn't think a boost leak would be so linear though

 

turn the controller on and set it to 10psi and see if it holds. ive seen some cars drop a little in the higher rpms, but that is way earlier than anything ive seen. mine dropped a pound or two from 7k to 9k with no boost controller

 

Peak boost is 10psi, correct? what does it drop to by redline?

 

~10.5 down to a little under 9. This was an early run, the most it ever dropped was from 11 to 8

 

I recently redid my wastegate reference line from the compressor housing to the manifold now and it completely eliminated the problem for me. Also, when using the boost solenoid I get immensely better 'resolution' now with the duty cycle.

Do you have a recirculating wastegate dump back into the downpipe?

 

I have a similar issue with my setup, boost peaks out to about 21.5 on mine @ 7600 and is down to about 16 by 8500. I pushed the turbo to past its efficiency range.

40mm inducer with a .60 a/r on intake side
56mm exducer with a .69 a/r on exhaust side

 

Could have really high backpressure too. Do you have a flex in the exhaust anywhere? I'd check that to see if it has collapsed. You have to look at the inside.

 

Thanks for all the input guys, figured I'd update this. Relocating the wastegate reference line to the vacuum block "solved" the issue! Must be a boost leak somewhere between the turbo and TB I guess. Haven't had much time to work on the car lately, will continue to search for the final answer

 

i hadnt considered that. but it makes sense that the vacuum sourcing for the wastegate would potentially cause such an issue.