Power falling off at 5500rpms
03-07-2005, 02:47 PM
#1
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Join Date: Oct 2003
Location: GA
Posts: 71
Power falling off at 5500rpms
My mods are 383 P-1SC with 15psi pulley/ twin high flow cooler showing 10psi
Ported Lt1 intake to match heads
Ported Trickflow heads with valve job
224/236 114lsa cam .530/550 lift
1.6 com cam roller rockers/ with harden pushrods
FLP's Longtube headers
Borla catback
Racetronix 57lbs injectors with the fuel pump and wire harness kit
52mm throttle body (holley)
Msd 6a with msd wires and autolite 3923 plugs gapped @ .030
I was doing some tunning with my tunercatt on my 383 with P-1sc @ 10 psi and did logins with my datamaster software and notice that after 5500rpms that the power drops off very steadly. My Injectors (Racetronix 57lbs) d/c are around 87/91% at 5500 and up to 6300. On the AFR fuel verses RPM fuel inrichment tunnercatt running 28% @ 5600rmp up to 34% @ 6300. The timing is set a 24* timming but showing 27 up to 5100 and then goes up to 28* on up to 6300. The Maf maxes out @ 5100rmp (on the pressure side.)
On the Dynomaster the Peak horsepower it made in third gear was 524hp@ 5500rpm and 535tq @ 4100rpm the torque band drops off steadly at 4900rpm. The cam 224/236 114lsa .530/550 using a 1.6 comp cam mag roller rockers should make power up to 6200rpms unless the blower is maxing out at 5500rpm. Unless im running out of fuel at 5500. (Useless info) the stock o2 were showing 888/893 up to 6300 and peaks at 901/905 at 5000rmp.
Ported Lt1 intake to match heads
Ported Trickflow heads with valve job
224/236 114lsa cam .530/550 lift
1.6 com cam roller rockers/ with harden pushrods
FLP's Longtube headers
Borla catback
Racetronix 57lbs injectors with the fuel pump and wire harness kit
52mm throttle body (holley)
Msd 6a with msd wires and autolite 3923 plugs gapped @ .030
I was doing some tunning with my tunercatt on my 383 with P-1sc @ 10 psi and did logins with my datamaster software and notice that after 5500rpms that the power drops off very steadly. My Injectors (Racetronix 57lbs) d/c are around 87/91% at 5500 and up to 6300. On the AFR fuel verses RPM fuel inrichment tunnercatt running 28% @ 5600rmp up to 34% @ 6300. The timing is set a 24* timming but showing 27 up to 5100 and then goes up to 28* on up to 6300. The Maf maxes out @ 5100rmp (on the pressure side.)
On the Dynomaster the Peak horsepower it made in third gear was 524hp@ 5500rpm and 535tq @ 4100rpm the torque band drops off steadly at 4900rpm. The cam 224/236 114lsa .530/550 using a 1.6 comp cam mag roller rockers should make power up to 6200rpms unless the blower is maxing out at 5500rpm. Unless im running out of fuel at 5500. (Useless info) the stock o2 were showing 888/893 up to 6300 and peaks at 901/905 at 5000rmp.
03-07-2005, 07:40 PM
#2
Registered User
Join Date: Oct 2001
Location: Bay Area, CA, USA
Posts: 311
Re: Power falling off at 5500rpms
What year LT1?
Is it using an OBDI or OBDII computer? What did Brian at PCMFORLESS say.
Can you confirm that the fuel pressure was not dropping. What was your fuel pressure?
Is it using an OBDI or OBDII computer? What did Brian at PCMFORLESS say.
Can you confirm that the fuel pressure was not dropping. What was your fuel pressure?
03-07-2005, 09:27 PM
#5
Registered User
Join Date: Aug 2004
Location: SE PA
Posts: 93
Re: Power falling off at 5500rpms
You could be out of blower. you could be out of fuel also with those injectors.My buddy has pretty much the same combo except with a D1-SC and 85lb injectors. His makes power right up to 5800. Another thing a lot of people overlook is the boost on the back side of the valve. Do you have a rev kit? good spring pressure? What did your dyno curve look like when the power dropped of?
You could be at the max of your blower/injector combo. I do know his car made 550 to the wheels when his 55lb injectors went static so we put 85's in. No wide band?
You could be at the max of your blower/injector combo. I do know his car made 550 to the wheels when his 55lb injectors went static so we put 85's in. No wide band?
03-08-2005, 06:28 PM
#8
Registered User
Join Date: Jul 2004
Location: MI
Posts: 1,174
Re: Power falling off at 5500rpms
I had the same symptoms. Running 383/D1 @ 12 psi the engine power would starve @ 5K rpm. I had a Walbro 255 lph with a K-bell. So, I went to two Walbros and the K-bell on pump #1. The stock plumbing lines from the tank are very small. I used -6 socketless Aeroquip hose. Now no starve. I think I went over the top with two pumps, but the pluming was key.
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