Hey all. A couple of Saturdays ago I took my '96 Z28 to Speedworld drag strip, outside of Phoenix. Daytime temps were mid 70's and cooled off to mid 60's, perfect weather. My car is the one with the Jasper upgrade LT1 and it pulls hard. Trans is auto, 3.23 in the diff. I run prem unleaded and
put a couple gallons of 100 proof at the track. I really thought this car would throw down a 12.99 or so time.
First run: .296 reaction, 2.25 60', 14.23 et @ 99.43 WTH ?
First run was against a cool older dude in an '07 Vette with an LS3 , 6 speed. He was throwin' down mid 12's @ 116 mph
Second run: .187 reaction, 2.168 60', 14.035 @ 99.39 I left the trans in
3rd to make sure no overdrive action. Car pulls hard, shifts at 6,000 rpm,
no stumble anywhere. There were alot of people and cars there, I might have gotten into the 13's with one more run but each run was taking 45 minutes or so. Probably have to get the 60' times down, better diff gear
ratio ? The car has CAI, Jasper LT 1 with comp cam and reflashed prom,
aftercat flowmaster. I really thought it would run quicker.

 

traction traction traction! get some DR's dude!

 

traction or not .....your mph looks low....why 100 octane...doesnt need it...

What does your car look like?....go to speedworld all the time

 

I was there 3 weeks ago this coming Saturday, 3/15. My car is a '96 Z28,
Mystic Teal in color with American Racing 5 spoke wheels, pretty dark
window tint. I really thought this car pulled harder than low 14's, but
I think I could have gotten a real, real high 13 with one more try. Something I do not understand, before the original LT1 blew a head gasket I took it to Speedworld about 2 1/2 years ago. The weather was great that night too and I ran a 13.10 @ 101 mph. Now I'm starting to wonder if they had a problem with their timing equipment that night. The car feels stronger now, so what the hell ?
They are having some old F/X cars and stuff race this Saturday, I'm trying to work it out to go.

 

What are the cam specs? You will have to do a little more modding if you want to see a very low 13/high 12 run. As noted, better tires and improved sixty foot times will help with your goal as well. Might want to look into doing some more exhaust work, headers would really make a big difference.

 

I would definitely chk the opti or if you,ve got kr ,b/c your not seeing much improvements from your mods!Also we need more info. about your car On my car i did cheap mods @the beginning and then spent more money later and didn,t see as much improvements from more expensive mods!

 

x2 that is a little low mph for a modded car

 

That is exactly what I was thinking, the LT1 has about 5,000 miles on it
now, should be broken it. The tires are Toyo Proxes, 245/50 R16. The cam is a Comp cams part # 07-502-8, specs are : gross lift I=.495,E=.503 duration @.050 is I=218 E=224. Lobe seperation is 112.00
lobe lift @ .050 is I = .3300 E = .3350
The car has a K&N CAI and Flowmaster dual 2 1/2 outlet aftercat exhaust. When the motor was put in all vaccumm lines, battery, battery
cables, alt., etc. were replaced. Everything I could afford.
At the dragstrip: I do a small burnout to help clean the tires, because they are'nt slicks I don't sit there and really heat them up. With the auto trans I put one foot on the brake and one on the gas, once pre stage and stage lights are on I bring the rpm's up to about 1,500 so I don't leave the line at idle. Soon as the last yellow blinks out I'm gone, stage deep and don't red light. I don't just mash the gas pedal down, that would cause major traction issues. I put the pedal down as quick as I can with a minimum of tire spin. Trans shifts @ 6,000 rpm and feels great. The 2nd run was 35 hundredths from a 13 second time slip, but I agree it should be faster. Motor and computer reflash were from Jasper. For a street car it is real fun to drive, if I can't have a 12 second car low 13's would be , ok.

 

The red text above is your problem. That exhaust is choking your motor mods.
ditch the cats or get high flow replacements then put a cutout in the I-pipe. The Flowmaster catback has been found to choke an LT1 to the tune of 2-3mph.

 

x2 on the chokemaster, and you have to get a better launch. sticky tires. You would do alot better if you could mash the pedal immediately. You do not have a package that is working together.

 

As I re-read my discription of my launch, I have to agree. I get the gas
pedal to the floor in probably just over a second, which is slowing my
60 foot times and costing mph on the top. My first thought was steeper
gears in the diff, maybe 3.55 or so. The reality is my '96 cats are 12
years old now, and combined with the flowmaster probably slowing
the car down. I spent such a boatload of $$$$$$$$$ already it will
take time to correct the exhaust. Good thing even for a 14.035 car
it is still fun to drive. At a steady 70 mph it gets about 21 mpg
too. I appreciate the replys and the insight.

 

I really do not think that is the source of the problem. I understand the general consensus on this board is that flowmaster sucks, however I have yet to see any data that supports this theory. Last fall I ran back to back passes on the dyno. One pass was with open cutouts (one behind each header) and another with the cutouts closed (exhaust running through the catback). There was a negligible difference between the two passes for both average and peak horsepower (roughly 3-5 hp).
Last fall I also ran at Milan with and without the cutouts open (on the same day) and the trap speeds varied by roughly 0.8 mph.

I am open to other data but from my experience a flowmaster system provides adequate flow for a street/strip car. Were the OP to change catbacks I do not think much difference, other than sound, would be experienced. IMO the OP should focus on traction, driving technique and making sure the car is in good running order.

 

I may just take it back without any changes and hit the go pedal harder, find out for sure how big a problem traction or lack of is. In the bleach box I don't have to push the gas pedal down very far for them to go up in smoke, I guess that is the idea. The car does'nt feel strangled for air either coming in or going out, goes up to 6,000 rpm pretty well. The reason I modulate the gas pedal is I had a '70 Chevelle that was a 14 second car, 300 hp 350 ci. I would floor it on launch, tires spinning for 20 feet or more, oops, there goes a second. Fastest time for me with it was 15.10, I did'nt understand the concept of minimal tire spin. I need to go the other way now, find out what is too much tire spin.

 

was DA taken into consideration?
isn't phoenix at a fairly high altitude?

 

.8mph is almost 10 hp, people pay money for mods that get them 10hp.
I never suggested that he buy a new catback, I said add a cutout.
And your dyno tests are appreciated but somewhat tainted as you darastically changed the backpressure without giving the computer any time to adjust afr.
The only imperical data that I have is a buddy of mine with a 95 had the Flowmaster catback and when he opened the cutout in the I-pipe at the track he gained 2mph.