[burch]

Hello Everyone,

I went to Carlsbad Saturday to try to re-claim some of the performance I've "tuned" out of the car since last year.

For those of you that don't know (and haven't heard my complaining), the combination I was running last year:

.040" over 400 w/TRW Pistons, Eagle Rods, Ported #670 heads, Crower 60311 Camshaft (247/252@0.050)

Last year this combination ran 12.40@108 in my 3800lbs Firebird (race weight), and consistently ran 12.45-12.60's.

This year I've made the following changes:

1. Holley Street Dominator Intake replaced Performer RPM (both gasket matched)--I'm running a 1/4" or 1/2" (can't remember off the top of my head) spacer on the Street Dominator.
2. 830cfm 4150HP replaced 750cfm 4150HP
3. Holley Black fuel pump/-8AN lines/sumped tank replaced stock fuel lines/Carter Mechanical pump

At the PDD race at LACR two weeks ago, the car was SLOOOOOOW. Ran 13.40's@100mph all day long. Tuning wise, I dropped the jets 3 sizes from the "out of the box" (84/84) setup (so I was running 81/81) and set the timing to 36 degrees, and just drove it (not very well either )

First pass of the day at Carlsbad was with the exact same setup... ran somewhere around 13.00 @ low 100mph, and the WBO2 said the A/F mixture was about 14.5:1 at the top of 3rd (OUCH!).

2nd pass, went to 84/84 jets: ~14.0:1, 12.981@102.79
3rd pass, went to 88/88 jets: ~13.9:1, 12.869@104.26
5th pass, went to 92/92 jets: ~13.5:1 ,12.839@105.19

Now, I'm pleased that I've found 5 of my lost MPH already, without doing any playing around with the timing whatsoever, but 92/92 Jets?!?!? I'm running TWO powervalves too!

And the kicker is that it STILL isn't rich enough... I'd like it to be in the 12.8/12.9:1 range at the top of 3rd. It's looking like I'm gonna need something outrageous like #98 jets all the way around to get there!

Does this sound slightly out of whack to anyone else? Tom V?

FYI I was running stock jetting in the 750 on the 12.40 pass... 73/73 jets and two powervalves. Also the new carb is an 80511-1.

[burch]

Hello Everyone,

I went to Carlsbad Saturday to try to re-claim some of the performance I've "tuned" out of the car since last year.

For those of you that don't know (and haven't heard my complaining), the combination I was running last year:

.040" over 400 w/TRW Pistons, Eagle Rods, Ported #670 heads, Crower 60311 Camshaft (247/252@0.050)

Last year this combination ran 12.40@108 in my 3800lbs Firebird (race weight), and consistently ran 12.45-12.60's.

This year I've made the following changes:

1. Holley Street Dominator Intake replaced Performer RPM (both gasket matched)--I'm running a 1/4" or 1/2" (can't remember off the top of my head) spacer on the Street Dominator.
2. 830cfm 4150HP replaced 750cfm 4150HP
3. Holley Black fuel pump/-8AN lines/sumped tank replaced stock fuel lines/Carter Mechanical pump

At the PDD race at LACR two weeks ago, the car was SLOOOOOOW. Ran 13.40's@100mph all day long. Tuning wise, I dropped the jets 3 sizes from the "out of the box" (84/84) setup (so I was running 81/81) and set the timing to 36 degrees, and just drove it (not very well either )

First pass of the day at Carlsbad was with the exact same setup... ran somewhere around 13.00 @ low 100mph, and the WBO2 said the A/F mixture was about 14.5:1 at the top of 3rd (OUCH!).

2nd pass, went to 84/84 jets: ~14.0:1, 12.981@102.79
3rd pass, went to 88/88 jets: ~13.9:1, 12.869@104.26
5th pass, went to 92/92 jets: ~13.5:1 ,12.839@105.19

Now, I'm pleased that I've found 5 of my lost MPH already, without doing any playing around with the timing whatsoever, but 92/92 Jets?!?!? I'm running TWO powervalves too!

And the kicker is that it STILL isn't rich enough... I'd like it to be in the 12.8/12.9:1 range at the top of 3rd. It's looking like I'm gonna need something outrageous like #98 jets all the way around to get there!

Does this sound slightly out of whack to anyone else? Tom V?

FYI I was running stock jetting in the 750 on the 12.40 pass... 73/73 jets and two powervalves. Also the new carb is an 80511-1.

[SCOTT ESTERLE]

Sure does. Block the secondary power valve & try something like 80's primary & 84's secondary. I would think that would still be to much for your combo. Give it a try & see what happens.

[PMDRACER]

First thing that came to my mind was a vacuum leak. You're not using one of those 'hollow' carb studs, are you? 8^)

TIGER EFI - Electronic Fuel Injection for the Traditional Pontiac Engine. bill@tigerefi.com

[johnta1]

Sounds like low fuel pump pressure,or power valve wrong size.

First thing first.

Carb throttle plates opening all the way?
Float level correct?
What's the fuel pressure? at idle and on a pass?
Fuel filter clogged/restrictive?
What's the power valve numbers?


I'm also assuming this is a new carb,so should be clean inside.No clogged passages,etc.

johnta1
Pontiac Power RULES !!!
www.wallaceracing.com

[tempest455]

What was the barometric pressure, humidity and temp???

Tempest455
http://www.wauknet.com/douthitt/

[Classic Performance]

Recently had the same problems. Since you changed the fuel system,double check your pressure and volume. You may be trying to jet out of a lean condition due to lack of delivery.

Have you changed your spark plug heat range? Does the motor miss at all? You may be trying to use fuel to cool to hot a plug.

Hope this helps!

PONTIAC MOTORSPORTS - Fuel for the soul!

[Old Man Taylor]

Average environment on that day was 82 degrees, baro of 29.79, humidity too low for my computer to read, relative altitude of 1750'. Can you tell that I was there too? There was also a 10 mph head wind.

http://www.jimspontiac.homestead.com/Index.html

[burch]

Spark plugs are AC R45S's .. I've run colder plugs in the past and didn't notice any difference.

Power valves are 6.5 F/R.

No vacuum leaks I'm aware of... I've had a vacuum gauge on it recently and it was pulling the same idle vacuum as always (11-12"). Carb is tight, gaskets are good, etc...

The throttle plates are definately opening all the way (tested more than once).

Float level hasn't been set recently, so I'll re-check it next time out, but it was good the last time I checked.

Fuel pressure SHOULD be around 7psi, set with the car idling. I was unable to check it going down the track because (like an idiot) I forgot my mechanical FP gauge, and the datalogging portion of my WB is currently broken (otherwise it would have logged fuel pressure).

I'll pull both filters off and check them--they're the Earl's inline style: one is a screen-type, and the other is a sintered bronze element. Screen type is before the pump, bronze one is right before the regulator. Both filters are rated at 4-5gpm (240-300gph) so they exceed the flow rate of my pump, which is rated at 130gph @ 7psi.

The carb is relatively new, and is clean.

I'm gonna try to head back to the track this weekend to do some additional testing. If I can't get the datalogger working I'll make SURE to take the mechanical gauge so I can duct-tape it to the windshield and see what's going on pressure wise.

The car isn't behaving as if there's a delivery problem though... with the Carter mechanical pump I'd see absolutely NO effect from upping jet sizes, because the pump wasn't able to keep up much pass 2nd gear. Also, the wideband would show the A/F shooting for the moon (15:1 or so) once you got to the top of 2nd gear.

Now the A/F is fairly flat all the way across the gears, although it's definately richer in 1st/2nd than it is in 3rd (probably because the engine is less loaded in the lower gears).

[Half-Inch Stud]

.

[Half-Inch Stud]

...try a Q-Jet and see if the problem goes away.

HIS

"tbdET/1xxMPH/1.xx 60foot/28"/3.54:1/10"/469 #48/Flat HYD/DualQ-Jets/Offyl/3xx0Lbs
11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/469 #48/FlatHYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/469 #48/FlatHYD/Q-Jet/Torker/3650Lbs
12.70/103MPH/1.71 60foot/28"/4.10:1/12"/469 #48/FlatHYD/Q-Jet/Torker/3950Lbs"

[Classic Performance]

Had the same problem with AC R45TS's. Take a set of R43S to the track. NGK heat range #7 or #8 would also work.

PONTIAC MOTORSPORTS - Fuel for the soul!

[tempest455]

Regarding the weather conditions, I have seen .40 from bad to worst conditions on the same combo/tune up.

Tempest455
http://www.wauknet.com/douthitt/

[Tom Vaught]

Quote:

"Sure does. Block the secondary power valve & try something like 80's primary & 84's secondary. I would think that would still be to much for your combo. Give it a try & see what happens."

Agree with Scott, ditch the rear powervalve as you may very well be uncovering it during part of the run. If it gets uncovered your fuel curve
will go lean and then come back as the fuel equalizes in the bowl. Tom V.

ps Always block the rear PV on a drag car and
jet up accordingly.

[tempest455]

Sorry, I meant best to worst......

Tempest455
http://www.wauknet.com/douthitt/

[burch]

Well, I checked & cleaned both filters today.. minor debris, but certainly nothing out of the ordinary. Actually less than I expected after installing all new lines and a new tank.

I'll do the rest of the checks on Saturday. Wish I could have made it to the Pontiac Heaven drags but things aren't going very well at work so we couldn't swing it financially.

[burch]

Well, Saturday was fun. Got 9 passes in and could probably have done 15 if I wanted.

Car ran mostly 12.70's all day long in the 106.5 range, with a best of 12.59@107.5 on a single pass when I actually managed to get it through the 1/8th mile pretty well (but still only a 1.799 60').

I found and fixed two problems:

1. Fuel pressure was set incorrectly. Re-set to 7psi, held steady for all runs

2. I was building vacuum inside the gas tank. Removed the pressure check valve from the gas cap and it seemed to solve the problem. I'm not sure if it made any difference as the fuel pressure during runs didn't change at all with/without the check valve but the tank didn't go "pop" when I loosened the cap after I removed the valve.

I ran Champion J12YC plugs @ .045" gap (nobody had AC R43S). 36 degrees timing (locked advance) on all passes.

BUT: It still went fastest with the 92/92 jets! It ran 3 107+MPH passes with those jets, and the best I could do with leaner jets was 106.5, with a bunch of 105 and low 106mph passes.

Any ideas? I will probably go back to the track next weekend and try swapping the 750cfm carb just to verify that there isn't something wrong with the 830.

-Jon

P.S. HiS, I don't have any QuadraJets, so I can't try one.