When someone looks at my 1/4 mile times and my mods they say they have run that with nothing more than cai & muffler upgrades. What i am looking for is something that can be causing this low of performance from what everyone think i should be at. The car runs flawless but i would put the horsepower at 300-315 comparing to others and there 1/4 mile times. The stock car is 275 and the Sc unit sould add 40% to 50% more hp making in theory around 400. So what could be an issue causing the lower that expected numbers? The car ran a 14.75 before the mods so they have done a lot to improve them so something was wrong before. I was thinking new injectors or something like that because 108K miles may have worn something out.

 

Do you have a boost gauge? I'd bet you're not making 6.5 psi if I had to guess. My car ran 14.5 on the stock motor and pulled a 13.1 with a powerdyne 4.5, long tubes, and a tune. It's an A4 car with 2.73 gears and made that pass with 175,000 miles on it. Also take a look at your 60 foot time, you should be shooting for 2.0 maximum. With 315's you could do much better I'm sure. Keep in mind if you're running at a high density altitude then your times will be significantly lower than someone running at sea level on a cold day. Launching techniques might help the 60 foot time, but judging by the mile an hour at the traps I'd say you're loosing power from something. Try a compression test to see if you're loosing compression. If you're not making 6.5 psi then check the belt tension and all the pressure tubes for cracks. I was making about 3lbs till I replaced the belt and pressure tubes, then it made 5 consistently. Hope this helps.

-Pete-

 

After thought: whats your plug gap? Going from .050 to .035 I noticed a bump in power and engine smoothness. Did you get it professionally tuned?

-Pete-

 

What does your exhaust consist of, other than "flow master"? Is that a complete catback, or just a muffler? Which one? Blowers need big exhaust. You're cramming extra air into the cylinders, you have to get the increased combustion products out.

What is the elevation of the track you run at? Running a 14.75 at sea level would indicate the engine was way down on power before you put the blower on it, maybe in the low 200's.... definitely not 275HP. What was the MPH with that 14.75? Doing some quick math using the ET and assuming a 3,600# race weight, you picked up about 44 HP if you dropped the ET from 14.75 to 13.92.

You can't make 50% more power with 6.5psi of boost. 6.5/14.7 = 1.44 That's the theoretical max power gain (44%), but the S/C uses up some of that power to turn the compressor.... might be using as much as 4-5HP per psi to turn it, depending on the efficiency of the blower.

The Granatelli MAF could be a major liability. It makes its extra HP (if you are lucky) because it is intentionally miscalibrated to lean out the top end. That's good for stock tuning, but not useful for a 'power adder' setup. The MAF and the FMU are fighting each other. Have you ever inspected the plugs after a hard pull? Have you ever data logged it to see if its leaning out and you are getting knock retard at WOT? Have you ever had a wide-band on it to verify the tune? Have you ever actually had it tuned?

What gears do you have?

 

Boost gauge reads 5 to 6 on average. The plug gap is .035. The header mids go to a 3" high flow cat and then to the stock pipe and Flowmaster. It looks like 2 or 2 1/2" from the cat back. I think the elevation is just over 2000ft and the runs were all made on very warm nights when it was muggy. My gears are 3:23. I have the stuff to datalog but have no idea what to do. There are no instructions and i played with it some and nothing worked. Anyone want to give me crash course that would be great. Thanks in advance. I planned to get 3:73 or 4:11 and bigger injectors so i was holding off on the tune till i finished the mods. Can you check the injectors to see if they are running at full power since they are so old?