My trip to the track...

Hello all,

I have been dodging a date with destiny for well over a year. There were all kinds of excuses from "it's too hot" to "but my car is leaking oil like a sieve". The excuse last week was rain....no they really did cancel the test and tune for rain. I got home from work late and gave the car a quick once over trying to remember what all needed to be done before it was ready to race.

I noticed there was no battery hold down so I grabbed my old aluminum hold down and bolted that down. I kept thinking I was forgetting something, but oh well, I grabbed a small tool bag and my helmet bag and tossed them into the back seat. As I started out I began to notice the skies darkening. There were spot rain showers in the area, but it was relatively clear when I came home 30 minutes earlier.

When I was about a mile from the Mississippi river the first drops of rain began the slow pitter patter on the windshield. The roads around me still looked dry so I wasn't worried. As I crossed the river the rain began to fall a little faster and I had to turn on the windshield wipers. The highway across the river was wet like it had been raining here for a while. OK, now I was worried. Oh well, It would still make for a nice test drive. As I closed in on Gateway Motorsports Park, the rain stopped and the roads dried out. It was a relief to see cars in the pit and staging lanes as the track came into view from the highway.

Should I have been worried when the lady in the ticket booth asked if I was with the Camaro club? "Hummm no...should I be?" They sold me a tech card regardless and I headed to tech. Nice guys in tech...."just print your name there and sign there"...."by the way, where is your radiator over flow bottle?" DOH!!! I knew I forgot something. "Just get yourself a plastic bottle and zip tie it in there." Thanks, so off I went to the concession stand to grab a water bottle and chug the contents. The tool bag contained the needed strapping material and within a minute the bottle was strapped into place and connected to the radiator.

Off to the staging lanes for my first pass.
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The first pass resulted in a 13.48.
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A second pass improved slightly to a 13.44.

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The car flattened out on the top end as reflected in the MPH. Either too much timing or not enough fuel. I made a third pass, but got too aggressive on the starting line and blew away the tires. The only good thing about the last pass was the MPH which finally topped 100.

The car felt like it was laying down from about the 1000' mark. It didn't hear it misfire, so I assume I have a fuel delivery issue. Here are some more details on the setup:

78 360 shortblock with the piston .088 down the hole at TDC
EQ Magnum heads with 2.02 intake and 1.625 exhaust
Mild roller cam with 224/230 degrees at .050" on 110 LSA
MOPAR M1 dual plane intake with 1/2 plastic spacer
750 Holley Vac sec with purple spring
1 5/8" Summit Racing long tube headers with 2 1/2" dual exhaust to the back bumper.
Timing is set for 16 deg initial with 36-37 total

904 Trans with mild shift kit
3200 stall 9.5" converter
742 case 8 3/4 with 3.91 gears
27" tall Ripkin Raptors on the back 255R-50-17s

The fuel pump is a new stock unit.
The fuel filter is a few years old but the car has moved less then 500 miles in that time.
Gas tank is original

What should I check first?

If you haven't replaced the rubber lines, I'd start there, especially the one at the tank.

I know mine needs those replaced.

I would check Fuel Pressure first. I would guess your running out of fuel since it is laying over.

If it slows down at the top of 3rd gear, it is running out of fuel. Need to upgrade the fuel system.

3310 750 carbs are notoriously lean at high RPM. You may have to update that carb with a rear metering block with jets.

Mad Dart said:

I would check Fuel Pressure first. I would guess your running out of fuel since it is laying over.

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The gauge on the dual feed line shows 6-7 PSI at idle.

nerd racing said:

If you haven't replaced the rubber lines, I'd start there, especially the one at the tank.

I know mine needs those replaced.

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I am pretty sure all the fuel lines up to the fuel pump are original. Do you think the rubber lines are getting soft and collapsing? If the rubber was breaking down wouldn't I see remnants in the fuel filter?

sledger46 said:

The gauge on the dual feed line shows 6-7 PSI at idle.

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At idle don't mean much when you are 6500 RPM at WOT, that is where the demand is. That is where you can tell if your Fuel Pump has NUTZZZ or not.

To check it. Run a line somehow out to your cowl area and zip tie it so you can see it. Take the car out and Let it rip while watching the gauge. You will know if it is good or not right away.

Check your float levels too! Do you have Jet Extensions in the rear bowl? If not get some.

I'm glad to hear you enjoyed your trip. There's nothing else like it! Once you fix the running lean issue, you'll be able to tell it ;)

If it slows down at the top of 3rd gear, it is running out of fuel. Need to upgrade the fuel system.

Mad Dart said:

At idle don't mean much when you are 6500 RPM at WOT, that is where the demand is. That is where you can tell if your Fuel Pump has NUTZZZ or not.

To check it. Run a line somehow out to your cowl area and zip tie it so you can see it. Take the car out and Let it rip while watching the gauge. You will know if it is good or not right away.

Check your float levels too! Do you have Jet Extensions in the rear bowl? If not get some.

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Getting the fuel pressure gauge mounted where I can see it at WOT will be interesting. I will have to check the float levels and see where the rear level is. I know I checked it when I originally installed the carb, but that was years ago. The carb uses a metering plate on the secondary side, so I don't have any jet extensions.

Nice wheels!

There are a bunch of things you could try.

Change preload on lifters
Fuel system upgrades, fresh lines, fresh filters.
Metering block in rear of carb and jetting
A lighter vacuum sec spring. Softest until it bogs at WOT application, then up one in stiffness.
A 750dp carb would really make a difference
Timing curve - all in by 2500ish and keep feeding more total timing. With pistons that far in the hole, it's more like an open chambered head. Open heads usually run more timing. You may get into the low 40's. Test test test!

It appears soft on MPH for what the set up has in it. The ET at each incremental point doesn't appear that far off, that's soft most of the way through. Strangely, the MPH at 660 is strong for the ET. Those are some confusing timeslips.

Some where I read that the MPH from the 1/8 to the 1/4 mile should increase 25%. So if we take 81 MPH in the 1/8 times 1.25 we get 101.25 MPH in the 1/4 mile. I seem to remember a conversion factor for 1/8 mile to 1/4 mile ETs of 1.57 which would result in the 8.53 from the 1/8 mile generating a 13.39 1/4 ET

What we got versus theory

8.53 8.53
81.04 81.04
13.44 13.39
98.24 101.25 MPH

If I believe the 1/8 mile times/MPH then the 1/4 mile number don't really seem that far off.

Nice solid combination, you had fun at the track. You didn't list what fuel pump you have. CrackedBack,said it best.etails are everything.....

I would lean more towards timing too, go up a few degrees at a time at full advance and test . With the fuel we run today they like alot more timing.

Ok, we have a good starting place. I think your 1/8 mile times is off as well. Your gears and stall are giving you the 60' time, but you are not pulling like you should from then on. I think your combination should be 12.70's at approx. 105 mph. For example, I ran 12.9's at almost 105 with a 360 with 340 heads and a street mp cam, 3000 stall and 3.91's in 100 % street form. I would put a 750 double pumper on it. I would be running your total advance timing between 37-40 degrees. You could try a new HP mechanical fuel pump, they make them that pump a lot of gph. I almost get the feeling your vacuum secondary's are not coming all the way open.....?????

Abodybomber said:

Nice solid combination, you had fun at the track. You didn't list what fuel pump you have. CrackedBack,said it best.etails are everything.....

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Fuel pump is stock. It is only a few years old. The car was originally a /6 car so it is bound to have small fuel line throughout. I will have to dig through my stuff. Back in the day I had a Sun test kit with a remote fuel pressure gauge.

I question the vacuum secondary as well. I put the lightest purple spring in, but didn't notice any change in performance. I will have to tie a bread tie on the vacuum secondary rod and see if it moves during a run. I think I can get my hands on a 650 DP, but with it being used I am sure it will have a different set of problems.

Checked the float levels over the weekend and found the rear float level set so low the adjuster nut wouldn't turn the needle assembly to raise the float level. Got the float level set where it should be. The front float level was close but just a little bit too low so I raised it slightly. Hopefully it will stop raining before the test and tune on Wednesday.

The rear float level could explain the "running out of fuel" problem. This could change the E.T and the mph dramatically. Keep us posted....

318willrun said:

The rear float level could explain the "running out of fuel" problem. This could change the E.T and the mph dramatically. Keep us posted....

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I wouldn't expect much change in ET, but the MPH in the 1/4 should go up 1-2 MPH. Bolting on a set of drag radials would have more impact on ET ;-) Hopefully the rain will stop long enough to find out on Wednesday evening.

You could easily drop 3-4 tenths if you are running out of fuel in the secondaries over the last 1/8 mile. Yes, traction always lowers your E.T.

wallace calculator for 1/8 to 1/4...says

Your ET computed from your vehicle ET of 8.569 seconds is 13.42 seconds in Quarter Mile.

you are only a few hundreds off ....

70aarcuda said:

wallace calculator for 1/8 to 1/4...says

Your ET computed from your vehicle ET of 8.569 seconds is 13.42 seconds in Quarter Mile.

you are only a few hundreds off ....

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I agree with your statement. The float level change on it's own will only result in 1-2 MPH and few hundredths of a second difference. If the weather is close to the same then I would think it would run 13.39 @ 100.5 in the 1/4. The additional fuel on the top end will allow me to safely test adding in additional timing which might result in a .1 or more change in ET.

As someone mentioned earlier, only change one thing at a time and test, test , test...

It will be interesting to see! I love test and tuning! I dropped 4 tenths once on a high 13 second car by going from a 750 vacuum secondary (without the rear metering plate) to a 750 holley double pumper. If you are lean from the 60', your whole ET and mph suffer.... This time of year, heat and humidity in the St Louis area will rob E.T. and mph too.. Keep her cool...

318willrun said:

It will be interesting to see! I love test and tuning! I dropped 4 tenths once on a high 13 second car by going from a 750 vacuum secondary (without the rear metering plate) to a 750 holley double pumper. If you are lean from the 60', your whole ET and mph suffer.... This time of year, heat and humidity in the St Louis area will rob E.T. and mph too.. Keep her cool...

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I may get lucky as the weathermen are predicting partly cloudy skies for tomorrow with a high of only 79 F and a low of 61 F with only a 20% chance of rain. The weather might be good for a couple hundredths. I plan to make a couple of baseline passes with the float change and then try upping the timing a few degrees.