Meep-Meep
дворянин
On my own car, the 69 RR with a 426MW short block, 915 heads and an OEM iron 6BBL setup, I have logged about 10,000 miles so far and not so much have turned a screw once I sorted out the center carb. For anyone interested, my combo is mild but it makes very good power for a street car that can be driven daily. Average fuel economy is 13 MPG tested with a speedometer head that has been calibrated with correct gear used. I bet it can pull 16 MPG on a flat steady cruise. For those who have a mild build and think 8 MPG is normal (not driving at WOT all the time) need to keep reading. You are likely damaging your engine by washing the rings. The extra fuel over time dilutes the oil and will drastically shorten the life of the block, rings and pistons. This is true for any engine.
The engine is as stated, a 62 413 MW bored to .030" 426. Why? Because I had it lying around and have a long history with this very block dating back to my street racing days in the 80s. Right now I'm running a set of (good swap meet deal) Ross pistons that I cut down to zero deck flat tops. Compression is CC'd at 9.5:1. The cam is a MoPar .455 / 272. Timing at 12 I with about 35 total all in by 2500-ish. Hooker 2" headers. 4 speed with 3.23 gears. 3" TTI H pipe into Accurate 2.5" tails with 20" Thrush Hush mufflers. Car weighs 3970 with me in it. Call it 4000 lbs.
When this first got running I noticed on the O2 sensor that it was very rich at tip in. Also the outboard carbs came in way too soon. The rich condition was puzzling because I could get the idle to 14.5:1 but at tip in I would see 10.5-11:1. Even at cruise (3.55 gears at the time) it would be 11.5:1. The first step was to disconnect the outboard carbs and run on the center. I did this for about 2 months. WOT AFR was damn near perfect at 12.5:1 on the center carb. PV is a 5.5 based on my idle vacuum of 12" HG. After some thinking I came to the conclusion that the idle feed restriction was to big causing the rich condition on tip in and cruise. Not main jets. Those remain stock. So I got a QF metering block, and after a few tries, I settled on a .025 IFR with OEM sized air bleeds. While I had the carb off I took the opportunity to drill and tap for replaceable air bleeds. The result is a very consistent AFR between 14 and 14.5:1 from idle all the way to freeway cruise. There is a noticeable flat spot just at the clutch friction point depending on how hard you leave. This is due to the leaner IFR but expected to be covered up with a different pump cam. Using the white 218 cam now and stock squirter so I think there is a little room for improvement.
Once the center carb was happy I began to look at the outboards. WOT was and still is a tad lean depending on the weather but seems to run OK. Though I might get a bit more power going from 13:1 to 12.5:1. The main issue with the outboards was they were opening too quickly because there is no check ball in the diaphragm body to meter / delay the signal. The new repo cabs do not come with this ball nor is the ball seat configured to accept it. The true OEM ball seat has four very fine grooves that create a small leak around the ball to meter the air flow. I can't over emphasize how important it is to delay the signal to the carbs using a factory intake. And everyone who thinks the yellow spring must be used because that's what the DC manual says is missing a very important point. I have the plain OEM springs and it's perfect. Even the black spring can't delay the opening without the check ball but it will prevent the outboards from opening all the way. These are observations I made watching this setup on a chassis dyno. For those who think vacuum secondaries don't open fast enouigh need to stick their head in the air cleaner and watch. Spoiler alert. The opening rate is not linear. It's nearly instant to about 1/2 throttle with no ball.
Track performance on street tires in complete street trim is low 14 sec 1/4 mile (yes that sucks). But street radials, 3.23s with a 4 speed with an engine that has incredibly good response is not a recipe for a hard launch. Plus I'm out of practice in peddling out of the hole. Used to do much better. However, the MPH is 105. It pulls hard all the way to the point my clutch no longer holds shifting from 3rd to 4th right at the end. That cost me some MPH and a little ET. With slicks, gears and a clutch that holds, this is a high 12 second car through the restrictive and quiet mufflers.
I hope the above provides some useful information and answers some questions that many have about the 6BBL set up. While my setup still has a few areas that need work, its a long way from what it was. The simple center carb mod solved 95% of my drivability issues.
The engine is as stated, a 62 413 MW bored to .030" 426. Why? Because I had it lying around and have a long history with this very block dating back to my street racing days in the 80s. Right now I'm running a set of (good swap meet deal) Ross pistons that I cut down to zero deck flat tops. Compression is CC'd at 9.5:1. The cam is a MoPar .455 / 272. Timing at 12 I with about 35 total all in by 2500-ish. Hooker 2" headers. 4 speed with 3.23 gears. 3" TTI H pipe into Accurate 2.5" tails with 20" Thrush Hush mufflers. Car weighs 3970 with me in it. Call it 4000 lbs.
When this first got running I noticed on the O2 sensor that it was very rich at tip in. Also the outboard carbs came in way too soon. The rich condition was puzzling because I could get the idle to 14.5:1 but at tip in I would see 10.5-11:1. Even at cruise (3.55 gears at the time) it would be 11.5:1. The first step was to disconnect the outboard carbs and run on the center. I did this for about 2 months. WOT AFR was damn near perfect at 12.5:1 on the center carb. PV is a 5.5 based on my idle vacuum of 12" HG. After some thinking I came to the conclusion that the idle feed restriction was to big causing the rich condition on tip in and cruise. Not main jets. Those remain stock. So I got a QF metering block, and after a few tries, I settled on a .025 IFR with OEM sized air bleeds. While I had the carb off I took the opportunity to drill and tap for replaceable air bleeds. The result is a very consistent AFR between 14 and 14.5:1 from idle all the way to freeway cruise. There is a noticeable flat spot just at the clutch friction point depending on how hard you leave. This is due to the leaner IFR but expected to be covered up with a different pump cam. Using the white 218 cam now and stock squirter so I think there is a little room for improvement.
Once the center carb was happy I began to look at the outboards. WOT was and still is a tad lean depending on the weather but seems to run OK. Though I might get a bit more power going from 13:1 to 12.5:1. The main issue with the outboards was they were opening too quickly because there is no check ball in the diaphragm body to meter / delay the signal. The new repo cabs do not come with this ball nor is the ball seat configured to accept it. The true OEM ball seat has four very fine grooves that create a small leak around the ball to meter the air flow. I can't over emphasize how important it is to delay the signal to the carbs using a factory intake. And everyone who thinks the yellow spring must be used because that's what the DC manual says is missing a very important point. I have the plain OEM springs and it's perfect. Even the black spring can't delay the opening without the check ball but it will prevent the outboards from opening all the way. These are observations I made watching this setup on a chassis dyno. For those who think vacuum secondaries don't open fast enouigh need to stick their head in the air cleaner and watch. Spoiler alert. The opening rate is not linear. It's nearly instant to about 1/2 throttle with no ball.
Track performance on street tires in complete street trim is low 14 sec 1/4 mile (yes that sucks). But street radials, 3.23s with a 4 speed with an engine that has incredibly good response is not a recipe for a hard launch. Plus I'm out of practice in peddling out of the hole. Used to do much better. However, the MPH is 105. It pulls hard all the way to the point my clutch no longer holds shifting from 3rd to 4th right at the end. That cost me some MPH and a little ET. With slicks, gears and a clutch that holds, this is a high 12 second car through the restrictive and quiet mufflers.
I hope the above provides some useful information and answers some questions that many have about the 6BBL set up. While my setup still has a few areas that need work, its a long way from what it was. The simple center carb mod solved 95% of my drivability issues.
