1974 Dart 440 tuning help

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NoahSewal

NoahSewal

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I finally got this car dialed in good with lots of troubleshooting and help from you guys. locked my timing in at 36 degrees and it runs smooth all the way up to 6500rpm. and i've got exhaust put on with a air fuel gauge and even with my tight love separation it's helped me sort out idling and wot tuning. i appreciate everyone's help a lot. now that im here i just want to discuss what a/f ratio would sound right for my engine. it's a stock stroke 440 with 2355f pistons. stock cast heads with isky 505 cam with 108 lobe seperation and lots of duration. ive got an 800dp on it now and it seems happiest out of all the carbs. this is the only carb i've used where the engine reacts to the idle a/f screws lol. 3500 stall converter and 4.56 gears. at idle i've got around 13.2 a/f ratio, about the same at cruise, but WOT it goes leaner to 15- 15.5. i've got a 3.5 power valve in the primaries and 5.5 in the secondaries and 72/74 jets in the carb. 10lbs of vacuum at idle. should i just jet up the secondaries to get a more rich WOT? i'm sure im leaving some useful information out but i just want to get it tuned in as best as i can before i run the track again. my goal is to run better than my 9.1s 1/8th and 2.0s 60' from last time ha.
 
12.6 to 13.2 WOT. I have never run a pv on the secondary. This is what I would do. 6.5 pv in the front only, 72 jet front,80 in the rear then test.
 
What list number carb do you have. Don't remember the 4780 having a secd PV. Regardless, your way light on the secd jet.
 
Before you do anything else, get a curve of some kind in your distributor. You're pissing away power and torque with the distributor locked out.

As for what your A/F ratio should be...needs to be worked out on a dyno or at the track. Not all sensors read the same. don't tune to a specific ratio. The engine will tell you what it wants if you let it.
 
Newbomb Turk said:
Before you do anything else, get a curve of some kind in your distributor. You're pissing away power and torque with the distributor locked out.

As for what your A/F ratio should be...needs to be worked out on a dyno or at the track. Not all sensors read the same. don't tune to a specific ratio. The engine will tell you what it wants if you let it.
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I agree, but wasn't going there. And vacuum advance...
 
I’d stop immediately making full throttle runs if you’re seeing AFRs in the 15s. If you roll into it wide open and it goes more than 14 for a second or more, abort the run. You can damage stuff running that lean. Get it too rich (like 11.0) and then tune it leaner till it slows down, then go back rich slightly.
 
Your cruise afr is ok, could possibly be a little leaner, but it’s ok for now so don’t change the main jet. Plug the secondary power valve, and go up about 12 sizes on the secondary jets. That’s where I’d start tuning it. Measure your vacuum at light throttle cruise and cut it in half, use that to select your power valve in the primary as a start.
 
Newbomb Turk said:
Before you do anything else, get a curve of some kind in your distributor. You're pissing away power and torque with the distributor locked out.
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I wouldn't lock a street car down either, but run a MPP dizzy and see what the curve is. It might as well be locked. His car is never even under any significant driving load under 3500 RPM. If it's not detonating and it isn't pushing back on the starter, where's the issue?
 
roccodart440 said:
I wouldn't lock a street car down either, but run a MPP dizzy and see what the curve is. It might as well be locked. His car is never even under any significant driving load under 3500 RPM. If it's not detonating and it isn't pushing back on the starter, where's the issue?
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Yeah, those all in by 2500 deals may as well be locked out.

My issue is how much power it costs by locking out the timing. It’s HUGE. If for example I put a curve on a distributor that was locked out and gain 20/20 or 30/30 torque and power that tells me that’s how many horsepower the engine was unhappy.

I used to be a lock it out guy. Then I got an education and I almost won’t do it any more.
 
Newbomb Turk said:
Yeah, those all in by 2500 deals may as well be locked out.

My issue is how much power it costs by locking out the timing. It’s HUGE. If for example I put a curve on a distributor that was locked out and gain 20/20 or 30/30 totiming would be rque and power that tells me that’s how many horsepower the engine was unhappy.

I used to be a lock it out guy. Then I got an education and I almost won’t do it any more.
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What RPM's would you be seeing these increased numbers? What RPM are you starting these pulls at? Obviously the numbers you are seeing improved are under the curve, since timing would be all in by peak HP RPM, maybe not at peak TQ RPM.

Usually on a dyno I start my pulls between 2500 and 3000 and end them 250-500 past peak HP. I'm curious wat you are doing
 
roccodart440 said:
What RPM's would you be seeing these increased numbers? What RPM are you starting these pulls at? Obviously the numbers you are seeing improved are under the curve, since timing would be all in by peak HP RPM, maybe not at peak TQ RPM.

Usually on a dyno I start my pulls between 2500 and 3000 and end them 250-500 past peak HP. I'm curious wat you are doing
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I believe he is advancing the timing all through the rpm range to compensate for the slew rate of the electronics. He’s done some pretty extensive testing on this stuff.
 
roccodart440 said:
What RPM's would you be seeing these increased numbers? What RPM are you starting these pulls at? Obviously the numbers you are seeing improved are under the curve, since timing would be all in by peak HP RPM, maybe not at peak TQ RPM.

Usually on a dyno I start my pulls between 2500 and 3000 and end them 250-500 past peak HP. I'm curious wat you are doing
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I start at about the same as you do, but when testing for timing I don't usually make a pull when doing it.

When sorting out timing curves I start at 2500 (maybe a skosh lower depending on what it is) and load the engine to different vacuum and throttle positions and let that tell me what the timing needs to be.

I have a 3 stage retard at the desk so i get the engine at say 2500 and start loading it down until I get the engine stable and then I add or remove timing until it makes the most vacuum.

Then I move up 500 RPM and do it again. Once you get to max RPM you can see what the curve needs to be at about any RPM and load.

The trick is getting the distributor to match what the engine wants.
 
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