LT1 performance

John Nechiporchik · 07-29-2015, 06:17 PM

Over the past month, I have been flogging my 98 Firebird LT1 since freshening the engine and installing the FAST XFI 2.0.
After several iterations to the VE table, we have a consistent A/F result with maximum correction at 3% at one point.
Overall, the performance of the car has been sub par with a best of 10.95 @121MPH in 2800'DA.
Additional info:
A/F target is set at 12.9-1.
converter flash is 5400...ATI 8"
shifting at 7000....RPM drops to 5800 on gear changes
Converter slip is 4% in high gear ( at end of run)
5.14 gear with 30x9 Hoosier bias tires (3 years old)
vehicle weight is 3240#
60' at Milan is 1.43-1.46 on Test and tune night (marginal track)
Just checked valve springs (PAC 1409X....170# on seat)
checked compression.....185PSI all holes
initial timing is set at 40degrees until coming off two step at 3300rpm....then pulling timing back to 36.

Questions:
Based on this info, thoughts on A/F ratio at 12.9???. I have been told the LT1's like to run fat....but I'd like to hear from someone who has experience ...preferably that runs a FAST system.
Next, I have rec'd mixed signals on the timing for this combo. Again, can someone with an LT1 stocker help me out here?
Lastly, I believe the converter is too tight based on my review of the racepak data. Again, would appreciate input based on the data presented.
BTW, I did replace the rear tires yesterday with Hoosier 18212 Lightweight radials (30x9) on a 10 inch rim...but no test results yet.
Any input is appreciated. Gotta wake this thing up !!
Thanks,
John

countrypuppy4865 · 07-29-2015, 07:47 PM

12.9-13.2 should be pretty good. If the air fuel is within .5 of the target you shouldn't have much left in the tune(you may be chasing .02-.03 at that point). Radial tires will pick you up .10 or more. With 121 mph it seems like it's way down on power.

russellauto1 · 07-29-2015, 07:55 PM

GIve Ed Wright at Fastchips a call. Very Knowledgable on lt1 Tuning.

Ed Wright · 07-29-2015, 10:16 PM

Your timing and air/fuel sound close enough, I'm with Cooter. Doesn't sound like there is much left there. I did tune one good running LT1 Stocker that liked 12.5-1 air/fuel, but only one. My car likes 12.8-1 to 13.0-1, depending on RPM. Sometimes you get a wide band that's calibration is shifted a little, so the numbers you see at peak torque may look a little different than somebody else's. Most LT1s I have worked with like 35 to 37 degrees, so 36 should be very close. Not likely much ET there, if you are at 36 now.
Sounds like your just down on power.
You have verified your timing with a light, right?

John Nechiporchik · 07-30-2015, 08:21 AM

Yes, Verified timing with light.

Dan Fahey · 07-30-2015, 02:32 PM

Interesting comment about Radial Slicks

Why are Radials Better than Bias Ply Slicks?

D

Tony Goodman · 07-30-2015, 04:06 PM

John, Have you tried leaving off the footbrake 3000 rpm. If it's to rich on the 2 step it can make the car sluggish. Start up, idle, burnout need to be lean and clean on these cars. Tony

John Nechiporchik · 07-30-2015, 06:25 PM

I will try that approach.

Ed Wright · 07-30-2015, 07:44 PM

Quote:

Originally Posted by Dan Fahey

Interesting comment about Radial Slicks

Why are Radials Better than Bias Ply Slicks?

D

Often the easiest one tenth or more you can bolt on an automatic car.

Dan Fahey · 07-31-2015, 12:43 PM

Quote:

Originally Posted by Ed Wright

Often the easiest one tenth or more you can bolt on an automatic car.

Ed... I keep hearing that?
Why does it do that..?

One race said because the tie does not grow.
I think it is more about the structure of the tire.
Think it is about less parasitic drag and does not wiggle like a Bias Ply.

Dan

07-29-2015, 06:17 PM	#1
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 315 Likes: 74 Liked 12 Times in 6 Posts	LT1 performance Over the past month, I have been flogging my 98 Firebird LT1 since freshening the engine and installing the FAST XFI 2.0. After several iterations to the VE table, we have a consistent A/F result with maximum correction at 3% at one point. Overall, the performance of the car has been sub par with a best of 10.95 @121MPH in 2800'DA. Additional info: A/F target is set at 12.9-1. converter flash is 5400...ATI 8" shifting at 7000....RPM drops to 5800 on gear changes Converter slip is 4% in high gear ( at end of run) 5.14 gear with 30x9 Hoosier bias tires (3 years old) vehicle weight is 3240# 60' at Milan is 1.43-1.46 on Test and tune night (marginal track) Just checked valve springs (PAC 1409X....170# on seat) checked compression.....185PSI all holes initial timing is set at 40degrees until coming off two step at 3300rpm....then pulling timing back to 36. Questions: Based on this info, thoughts on A/F ratio at 12.9???. I have been told the LT1's like to run fat....but I'd like to hear from someone who has experience ...preferably that runs a FAST system. Next, I have rec'd mixed signals on the timing for this combo. Again, can someone with an LT1 stocker help me out here? Lastly, I believe the converter is too tight based on my review of the racepak data. Again, would appreciate input based on the data presented. BTW, I did replace the rear tires yesterday with Hoosier 18212 Lightweight radials (30x9) on a 10 inch rim...but no test results yet. Any input is appreciated. Gotta wake this thing up !! Thanks, John

07-29-2015, 07:47 PM	#2
countrypuppy4865 Senior Member Join Date: Nov 2003 Location: Donaldsonville, LA Posts: 966 Likes: 8 Liked 183 Times in 62 Posts	Re: LT1 performance 12.9-13.2 should be pretty good. If the air fuel is within .5 of the target you shouldn't have much left in the tune(you may be chasing .02-.03 at that point). Radial tires will pick you up .10 or more. With 121 mph it seems like it's way down on power. __________________ Jimmy "Cooter" Hidalgo, Jr. 4865 E/SA '04 GTO 4865 SS/GA '99 Firebird

07-29-2015, 07:55 PM	#3
russellauto1 Member Join Date: Oct 2008 Posts: 146 Likes: 2 Liked 40 Times in 6 Posts	Re: LT1 performance GIve Ed Wright at Fastchips a call. Very Knowledgable on lt1 Tuning.

07-29-2015, 10:16 PM	#4
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 389 Times in 168 Posts	Re: LT1 performance Your timing and air/fuel sound close enough, I'm with Cooter. Doesn't sound like there is much left there. I did tune one good running LT1 Stocker that liked 12.5-1 air/fuel, but only one. My car likes 12.8-1 to 13.0-1, depending on RPM. Sometimes you get a wide band that's calibration is shifted a little, so the numbers you see at peak torque may look a little different than somebody else's. Most LT1s I have worked with like 35 to 37 degrees, so 36 should be very close. Not likely much ET there, if you are at 36 now. Sounds like your just down on power. You have verified your timing with a light, right? __________________ Ed Wright 4156 SS/JA

07-30-2015, 08:21 AM	#5
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 315 Likes: 74 Liked 12 Times in 6 Posts	Re: LT1 performance Yes, Verified timing with light.

07-30-2015, 02:32 PM	#6
Dan Fahey VIP Member Join Date: Oct 2008 Posts: 2,114 Likes: 1,078 Liked 180 Times in 110 Posts	Re: LT1 performance Interesting comment about Radial Slicks Why are Radials Better than Bias Ply Slicks? D

07-30-2015, 04:06 PM	#7
Tony Goodman Junior Member Join Date: Jan 2006 Location: Zeeland, MI Posts: 98 Likes: 128 Liked 18 Times in 4 Posts	Re: LT1 performance John, Have you tried leaving off the footbrake 3000 rpm. If it's to rich on the 2 step it can make the car sluggish. Start up, idle, burnout need to be lean and clean on these cars. Tony

07-30-2015, 06:25 PM	#8
John Nechiporchik Member Join Date: Mar 2007 Location: Grosse Ile Mi. Posts: 315 Likes: 74 Liked 12 Times in 6 Posts	Re: LT1 performance I will try that approach.