451 running great

[Garys1969RR]

Finally got a nice day at the track (Bandimere 1/4 mile strip) to test out my 69 Road Runner with the 451 engine. Best 2 passes 12.95 ET @ 107 MPH. Not bad for 5400 feet elevation. Still bogs off the line unless I bring the RPMs up alot against the torque converter. Running 915 ported heads, and 13.3 to 1 C/R. Holley street dominator intake, Holley 780. Car weighs right at 3600 lbs, 3.91 posi. Does anyone have any suggestions to eliminate the bog when the throttle is opened up quickly? I am thinking about a Reo accelerator pump, and larger primary main jets. Currently have 72 primary, and 80 secondary. Thanks.

 

[Meep-Meep]

Did you try different timing settings? Some engines with big cams can benefit from a locked advance set at the total number. Take a bunch out of the dizzy and replace it with more initial. I had to do this on my old 383.

Or I wonder if the elevation has something to do with it? The ATM pressure is lower and that might affect how the carb circuits work. I'd try a smaller carb like a 650 just to see how it responds. My opinion is if you have to do such major changes to a carb you probably have the wrong carb for the application. I.E. a REO pump solving the apparent problem of a bog on an otherwise nearly stock configuration engine might mean you are not truly solving the problem. REO pumps are typically used when the carb is pretty far away from the valves like on a tunnel ram. Are you running a dual plane or short and direct runner single plane? Then you likely don't need a REO pump. Your problem might be a velocity issue and the inability to provide a high delta pressure between the boosters and the float chamber. Remember, it's the ATM pressure that pushes the fuel out based on a lower than ATM at the booster (delta P). Maybe call Rusty and get one of his TQ's? I have a feeling you are in for some research and development. And remember.....

“Basic research is what I’m doing when I don’t know what I am doing.”
― Wernher Von Braun

 

[RustyRatRod]

Do you feel like the bog is on the primary or secondary side? Maybe try a heavier secondary spring.

 

[Garys1969RR]

I am running a single plane Holley street dominator intake with a 1 inch spacer. And Rusty, I went from a yellow sec spring to a purple, and that helped alot. But now, the motor doesn't really open up strong until a little after it leaves the line. Like the sec are opening late. So I will continue to change settings, and test. Next step is 76 main jets in the primary. Then once the initial bog is fixed, then will go back to the yellow sec spring to open the sec sooner.

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Basically I believe the air is rushing in quicker than the fuel, then when the fuel catches up it takes off. Thats why I was thinking a bigger accelerator pump. Or maybe bigger squirter size would help. Single plane intake.

 

[RustyRatRod]

I gotchya. You certainly make it sound like a lean condition. You'll get it ironed out.

 

[lewtot184]

I am running a single plane Holley street dominator intake with a 1 inch spacer. And Rusty, I went from a yellow sec spring to a purple, and that helped alot. But now, the motor doesn't really open up strong until a little after it leaves the line. Like the sec are opening late. So I will continue to change settings, and test. Next step is 76 main jets in the primary. Then once the initial bog is fixed, then will go back to the yellow sec spring to open the sec sooner.

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Basically I believe the air is rushing in quicker than the fuel, then when the fuel catches up it takes off. Thats why I was thinking a bigger accelerator pump. Or maybe bigger squirter size would help. Single plane intake.

going to bigger jets at that elevation is probably the wrong direction. check float level and fuel pressure/volume. try a blue 417 pump cam with the 30cc pump. ignition curve could be an issue.

 

[Garys1969RR]

I have limited the advance in the distributor to 18 degrees of centrifugal advance. And I am using 20 degrees initial. For a total of 38. Not sure if the bog when opening the throttle is caused by too small of accelerator pump shot, or too small of primary jets. It would seem that the accel pump shot isn't enough, as this is what is supposed to cover the fuel lag when the throttle is opened rapidly. I plan to read the plug color before I do any jet change.

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What size accel pumps do the old Holley 3310 carbs come with? I believe there is a 30 cc and a 50 cc available , but is there one smaller than the 30, Such as a 15 cc?

 

[MarPar]

switch the posi for a sure-grip, that will take care of it...lol

sorry Gary, i couldn't resist...:toothy4:

good luck gettin' her figgered out

Mario

 

[Garys1969RR]

Found out the carb choke pull off hole to the vacumn was leaking air, so plugged it. Also acc pump wasn't working right. Also needed a new sec diaphragm.

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Working great now. Just haven't made it back to the track yet!

 

[62 Dart Convertible]

Found out the carb choke pull off hole to the vacumn was leaking air, so plugged it. Also acc pump wasn't working right. Also needed a new sec diaphragm.

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Working great now. Just haven't made it back to the track yet!

Looking forward to reading about your results!!