Back From The Track. Where Did My MPH Go?!

[motorhead]

I hit Grand Bend Motorplex yesterday with my boys from XceedSpeed.com... the track was hosted by MoTownMuscle.com and Agostino Racing (those LS1 guys)... and needless to say, outside of the early morning wetness and waiting for the track to be dried, it was a great day. And, boy did my 15 yearold 100,000mile brick show those LS1 cars a thing or two about the darkside!

Well I ran my best ET of all time (3 tenths better):
13.42 @ 101.5mph, but the MPH sucked. In fact it was a 2.5mph drop over my last mid-summer heat run.

I found this to be very odd, since I kept turning up the boost and it wouldn't (according to the gauge) go over 20psi. Is this an indication of a need for a HD WG assy?

I was running on ET Drags this time vs. street Radials the last time out. The air was super cool. I had a mix of 110/114/Toulene in the tank. And the FP was set at 42psi (tweaked it as the day went on)

Yesterday's best:
R/T: 2.561 (hey. I'll go when I am ready!)
60': 2.097 (2.3+ is normal for this thing on radials)
330: 5.701
1/8: 8.68 @ 82.59mph
990: 11.243
1/4: 13.42 @ 101.47mph

Previous best (on radials & race tune like above)
R/T: 1.904 (the call of the TR owner)
60': 2.287
330: 5.988
1/8: 8.98 @ 82.54mph
990: 11.549
1/4: 13.71 @ 103.81mph

End of run numbers on this pass were:

Boost: 21.9psi (23.9psi spike 1 frame earlier) according to the boost sensing harness.. 20psi according to my VDO boost gauge.
RTD: 9.2* (48.7* during 24psi spike... yeah right )
O2s: Start of run--> 844 down to 746 <-- end of run @ 24psi
TPS: 4.49v
MAF: 254 GPS
BLM: 64 (160 during spike)
Batt. Volts: 6.6v
RPM: 4900
Coolant: 176*

Other than the battery voltage dropping off to 6.6v it seems like a solid run. Since I have determined that the RTD readings in the TLink are really unreliable... because if I had hit 49* of retard it would have felt like the car hit a brick wall, and almost shut off. The air and fuel were all there. The O2s seem well within spec, correct?

So, I am guessing that I lost the 2.5mph in the slicks, right UNGN?

Any other opinions as to why this thing didn't take advantage of the cool Canadian air? Track elevation? I dunno.

 

[BUICKTR]

It normally happens when people which from radials to slicks. You will E.T better due to traction but it will slow you mph over radials. Radials spin on take off that is what causes you to mph a little more. What your car did should be correct. You exchanged the spinning (mph) with traction (e.t)

 

[RUQWKNF]

I do agree with what BUICKTR said about the radials vs slicks issue. Just a couple of more thoughts tho.

Ok, first thing first, the voltage issue. You gotta get that fixed ASAP, or else, you'll be picking up pieces.
If the run datalogged that 6.6v voltage, then believe it.
You gotta remember, if the system (IE: C3I, injectors, entire electrical system) doesn't see a minimum of 12volts under WOT, very bad things can and will happen. Not enough v to power the C3I, or injectors. Hence your 9.2* RTD and the spike at 24psi. Sounds like the voltage reg in the alternator is going on the fritz. Also, depending on the condition of the gas, IE: what percent of 110, vs 114, can affect what boost you can run. Also, just because you have race gas in the tank, it won't compensate for an inadequate fuel pump or system. Not saying yours is inadequate, it's just that I have seen some try to run alot of boost with pure race gas, and still slow down because they didn't address the stock fuel system.

- Do you run under drive pulleys? (IMHO, a big no no)
It does three bad things to our cars, kills alternators, kills power steering pumps, and hampers the cooling systems ability to cool properly.

- Is that the factory original alternator? If so, get a new one. Preferrably from a reputable Auto parts. I've always had good luck with a reman Autozone unit, but make sure you get the right one (120amp), plus you also get the warranty.

Next, the TPS could use some tweaking to get it above 4.5v at WOT. It's not bad, but I normally shoot for 4.5 - 4.7 @ WOT. With regaurd to what size injectors are being used, I like to tune for .44 - .46 at idle. Some injectors like lower tps numbers, some like higher at idle.

- What fuel pump do you have?
- Do you have a Hot wire kit on the pump?
- What injectors?
- What size slicks were you running?

- What was tire pressure set at cold? Always set pressures when tires are cold to the touch, never when their hot.

- What suspension mods are you running?
- Still have the front sway bar on?
- How much boost can you foot brake launch with?

- Do you have an external fuel pressure gauge that you can stick under the windshield wiper and watch during a run? With 20psi of boost, and 42psi of fp hose off, then you should see a sustained 62psi at WOT, if watching the fp gauge on the big end, and the pressure starts to drop or fluctuate, then 9 out of 10 times it's a pump issue.

- How are you running your wastegate lines? Using the factory wastegate solenoid? If so, then the chip could be limiting boost to the 20psi level, or the solenoid could be malfunctioning. If running tuner style (line from turbo to wastegate only) then you might be at the wastegates limits. I have been able to get 23psi out of a standard wastegate by trimming off some threads and shortening it up. But if you can't get anymore with this method, then a HD wastegate would be the solution, only thing is, with the HD wastegate, the minimum boost will now be 18psi. So unless the fuel system is addressed and proper bolt ons are used, 18psi can become an issue with true 93 octane. Remember 16-17 is the norm on pump gas. Another thing to remember is, in colder temps, you will see higher boost levels, and need more base fp. When I would run my car on the colder days, I would always have to raise base fp at least a couple of lbs.

Ok, give us somemore info about your combo, and we'll get you straightened out.

Patrick

 

[motorhead]

Originally posted by RUQWKNF

Ok, first thing first, the voltage issue. You gotta get that fixed ASAP, or else, you'll be picking up pieces.
If the run datalogged that 6.6v voltage, then believe it.

...I honestly don't trust the tool entirely, it gives me some funny readings (like drop-out) from time to time. But, I can always investigate the charging system. My question is: How is it possible for the battery voltage... not the charging system voltage, to cut itself in half... and then go right back to normal? The voltage regulator would have turned the dummy light on if the battery had died. Which 6.6v is... a dead battery.

- Do you run under drive pulleys? (IMHO, a big no no)
It does three bad things to our cars, kills alternators, kills power steering pumps, and hampers the cooling systems ability to cool properly.

...Gawd no.


- Is that the factory original alternator? If so, get a new one. Preferrably from a reputable Auto parts. I've always had good luck with a reman Autozone unit, but make sure you get the right one (120amp), plus you also get the warranty.


...Nope. It is a 3 month old rebuild. With the proper 120amp internals. And it does have a warranty. I suppose I can pull it back off and have them re-dyno it.


Next, the TPS could use some tweaking to get it above 4.5v at WOT. It's not bad, but I normally shoot for 4.5 - 4.7 @ WOT. With regaurd to what size injectors are being used, I like to tune for .44 - .46 at idle. Some injectors like lower tps numbers, some like higher at idle.


...Hmm, something to consider.


- What fuel pump do you have?
- Do you have a Hot wire kit on the pump?
- What injectors?
- What size slicks were you running?


1) An ATR double pumper w/ GSS242s.
2) The second pump does. And it is set to come on at 14psi.
3) 36# Ford Blue Tops.
4) 28x10.5x15 ET Drags, the car had 3.73s installed by the previous owner... all passes are made on 28" tall tires.


- What was tire pressure set at cold? Always set pressures when tires are cold to the touch, never when their hot.


...12 psi


- What suspension mods are you running?
- Still have the front sway bar on?
- How much boost can you foot brake launch with?


1 & 2) SSM rear lowers; Adjustable rear uppers; the front has a 12" brake conversion with ~800lb/in springs and the stock swaybars are still on the front and rear (36mm front is coming). MOOG poly endlinks and swaybar bushings. GlobalWest DALs in boxed front lower CAs. Do you want to know my Alignment as well? This thing handles...
3) 5psi


- Do you have an external fuel pressure gauge that you can stick under the windshield wiper and watch during a run? With 20psi of boost, and 42psi of fp hose off, then you should see a sustained 62psi at WOT, if watching the fp gauge on the big end, and the pressure starts to drop or fluctuate, then 9 out of 10 times it's a pump issue.


...Yep. I have never given the fuel system a second thought as it is overkill for the car. And I can't do another 20psi pass now that my race fuel leftovers are mixed with 91 & 94 octane gas. D'oh. Next year.


- How are you running your wastegate lines? Using the factory wastegate solenoid? If so, then the chip could be limiting boost to the 20psi level, or the solenoid could be malfunctioning.

...Yep, the stock setup. The chip is a JC110 racechip, and if it is holding me to 20psi... someone is getting a phone call. I may just have to look into the sillynoid...

HTH,

 

[YGETV8]

Are they 100,000 mile valve springs?

 

[motorhead]

Originally posted by YGETV8
Are they 100,000 mile valve springs?

Nope. 3000km CC980s.

The specs on the car are here:
http://xceedspeed.com/motorhead/T.txt

 

[DonnieShort]

With the parts you have, that should be any easy mid-low 12 combo on slicks. Alot of tuning I foresee in your future . Good luck, it'll come around.




Donnie