My encounter with 16psi w/stock fuel system.
09-08-03, 03:19 AM
#1
s4 for life
Thread Starter
My encounter with 16psi w/stock fuel system.
I recently ported my wastegate and installed a downpipe/midpipe combo on my car. This solved 90% of my boost creep problem. 
A few days later I was crusing to the record store with my friend and had the opportiunity to see what she could do uphill. When getting onto an uphill onramp to I5, I downshifted from 40mph in 4th gear too 3rd gear and floored it. .2324 seconds later I get thrown back into my seat and look over to my boost gauge to see 16psi @ about 4,000rpms. *** soon as my brain could tell my foot what to do, I let off the gas. "What the #$%# was that?" my friend asks. I was at a loss for words. Wasnt' boost creep, wasnt' spike (I didn't think).
After brainstorming with my brother we concluded that the twin-scroll flapper door (which is closed before ~2700rpms and opens after) which is used to help spool the turbo at lower rpms, was closed when I was in 4th gear and when I downshifted the flapper actuator didn't react fast enough. The flapper door closed+4000rpms+WOT=16psi in .2324 seconds. Spooling up so fast was also much more than the WG could react too so it didn't help the matter.
Well, my engine survived. I don't know HOW lean I ran because my o2 sensor broke when I put my downpipe on so my A/F gauge isn't working. I think the low intake temps that my cold-air box and fresh air headlight cover might have helped deter detonation.
Normally My car boosts to 1st=7 2nd=8 3&4th=9 5th=8
16 was quiet a suprise.
Has this Twin-scroll boost spike happened to anyone else?
Steve
A few days later I was crusing to the record store with my friend and had the opportiunity to see what she could do uphill. When getting onto an uphill onramp to I5, I downshifted from 40mph in 4th gear too 3rd gear and floored it. .2324 seconds later I get thrown back into my seat and look over to my boost gauge to see 16psi @ about 4,000rpms. *** soon as my brain could tell my foot what to do, I let off the gas. "What the #$%# was that?" my friend asks. I was at a loss for words. Wasnt' boost creep, wasnt' spike (I didn't think).
After brainstorming with my brother we concluded that the twin-scroll flapper door (which is closed before ~2700rpms and opens after) which is used to help spool the turbo at lower rpms, was closed when I was in 4th gear and when I downshifted the flapper actuator didn't react fast enough. The flapper door closed+4000rpms+WOT=16psi in .2324 seconds. Spooling up so fast was also much more than the WG could react too so it didn't help the matter.
Well, my engine survived. I don't know HOW lean I ran because my o2 sensor broke when I put my downpipe on so my A/F gauge isn't working. I think the low intake temps that my cold-air box and fresh air headlight cover might have helped deter detonation.
Normally My car boosts to 1st=7 2nd=8 3&4th=9 5th=8
16 was quiet a suprise.
Has this Twin-scroll boost spike happened to anyone else?
Steve
Last edited by 13bpower; 09-08-03 at 03:21 AM.
09-08-03, 02:47 PM
#4
s4 for life
Thread Starter
Originally posted by NZConvertible
Fuel requirements at 4000rpm are a lot less than at 7000rpm. Since you lifted off straight away, it's unlikely any detonation occured.
Fuel requirements at 4000rpm are a lot less than at 7000rpm. Since you lifted off straight away, it's unlikely any detonation occured.
Anyone else experienced this?
R-rat, did you get the twin-scroll creep? Is that why you wired it open? Notice any difference in boost response?
Last edited by 13bpower; 09-08-03 at 03:04 PM.
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