Need Opinions. Have nothing to compare to.
Here's how I would approach it.
Figuring out the inside.
I'm planning to do a compression check of all the cylinders. I know that won't tell me the compression ratio, but it will tell me how even the motor is from cylinder to cylinder, and tell me how much air I'm moving and if I'm low, like 110psi or doing ok, like 150 - 160psi. .
Compression test will also indicate how radical the set up is. A more radical cam will have lower compression pressures. This is because the cam has the valves open longer to pack in more air at high rpm. But at low rpm it reduces the pressure you'll measure. A higher static compression will offset this somewhat. Bottom line, its a helpful indicator.
You make a good point on degreeing the cam. It wouldn't take me long to get down to that point and then I would at least know what the cam is. I was wondering if there would be markings on the end of the cam listing part# so I could tell what it i
Cool. How far you go just depends how much disassembly you want to get into. If the harmonic damper is stock mopar diameter, the Mopar Performance timing tapes with white lettering on black background are nice to use. That, a dial indicator - and if you really want, a solid lifter, you can measure all of the cams' characteristics. Or you can just try to get .050 intake and exhaust timing and from that look at Compcams catalog.
I believe CC cams are marked. Check with them to verify if you want to go about it that way.
The nice thing about finding out the cam specs is that it will help you ballpark timing curve.
Tuning your hot rodded engine.
Tips - Tuning a modified engine is an iterative process. Its rarely a one shot deal even when things are done in the prefered sequence. Hopefully the journey is part of the enjoyment and satisfaction.
Use a notebook, or some note taking and file system. You'll improve it as time goes on, but start one if you haven't.
It seems you've already got it running OK. I'd start with timing, then return to fueling. However remember they work hand in hand. Besides increasing time needed with increasing rpm; Leaner mix burn slower and so wants more timing.
Timing
Initial:
You collected a lot of useful info>
Timing according to my light is 13 initial (vacuum disconnected), 33 with mechanical advance only (vacuum disconnected) at 2600rpm, 50 at 2600 with vacuum attached to manifold vacuum port.
Perfect. Only suggestions are to note RPM at initial timing, and if to plug the vacuum hose with a golf tee or similar (if you haven't been).
13* at 600 or 800 rpm would be good for a stockish cam.
With a hot cam, the engine will probably like a bit more advance. With a manual transmission, its harder to test idle under load. OTH its not as important. But if its a little 'lazy' or wants to die when you gently slip the clutch, these suggest a little more initial advance would be good.
Try 15* or 16*
Engine vaccum at idle hovers between 12 and 13 (connected to manifold vacuum port).
This suggests to me that the cam is not terribly radical. Hence my suggestion for 15-16* initial. (Manifold vacuum at idle will go up with the increased advance. This is good - it makes tuning easier)
I connected to the ported vacuum and no vacuum at idle. Vacuum jumps when I blip the throttle.
Perfect. This shows the throttle blades are close to their intended position at idle.
Vacuum Advance:
Interestingly, timing at idle with manifold vacuum connected is 17, meaning it is not giving full vacuum advance at idle like I thought it would.
Agreed. This advance canister must be adding 4* at 13" of vacuum. Going to ported vacuum for the advance control as you've done is generally the easier and better approach for a hot rod.
(But in some situations it turns out that it is better to use manifold source. The right way is whatever the engine wants. :) )
Timing at a steady 2600 with vacuum connected to ported vacuum is 37.
Need to know the vacuum as well. Then if you plot out the mechanical advance curve so you have the timing w/o vacuum at 2600, you can figure out the vacuum advance contribution.
Another way is to use a hand operated vacuum pump (eg Mityvac) while the engine is idling.
Vacuum advance has two main purposes.
1. Improve fuel milage by matching the timing to the leaner conditions of part throttle.
2. Keep the engine running cooler.
If the engine pings under part throttle acceleration, reduce the vacuum advance.
Otherwise leave tuning the vacuum advance until after initial and mechanical have been set.
Mopar Performance recommend the following:
a. Driving at a steady highway speed (with rpm between 2000 - 4000) note the max engine vacuum.
b. Back at the shop, set up the timing light and a vacuum pump attached to the vacuum advance. Bring the engine to the 2600 rpm and the vacuum pump to the vacuum found in step a. See what the timing is. For an B or RB engine, they recommend 56*. Adjust the vacuum pod as needed.
Centrifical Advance:
Do you think it may want more initial and less advance?
Yes it may.
Should I try pulling the vacuum advance and going back to straight mechanical, then give it a little more initial?
The secret here is to remove the vacuum advance (and plug it) when working with the mechanical. Just measure the timing (without vacuum) from the lowest rpm through 3000 or so. If your racing, you'll want to check it a little higher, but for now, don't worry about it.
Mopar Performance recommends 38* by 2600 to 2800 rpm for a production headed B/RB engine.
(When gearheads talk about "total" this it, the initial plus mechanical. )
Since you've already been on the dyno, you're ahead of the game. If you check now, you'll know what the best "total" timing was after some experimentation. Then when you change the initial, recheck and if need be, the curve or the total can be adjusted. We're only talking about 2-3* more in the initial, so it shouldn't be more than that at 2600 rpm - depending on the springs in the distributor, it could be less.
Fueling
Its best to tune from idle, then to cruise, then to wide open throttle. Then accerator shot.
However, that's ideal. Many of us don't or can't always do this. :)
I did find it interesting that the book said to start at 1.5 turns out, but carb was set to 3/4 turns out. I adjusted them out approximately 1/4 turn more (1/8 turn at a time each) before vacuum started to drop off. Reset them back to max vacuum where it started to drop.
Absolutely fine. Expect that the mix screws will be further in with four corner idle on a stock or mild cam. The manifold vacuum at idle is stronger (pulls harder) than a more radical engine.
Cruisin'
This is the primary side main jets. When you're feeling bold, try smaller primary jets (1 or 2 sizes at most) and see what happens at a steady 60 or 65 or 70 mph. Somewhere in that range, the main circuits take over. If the engine starts surging and wants to die until you slow down - its too lean. Go richer on the jets.
WOT
First. Check the main throttles fully open when pedal is floored.
Next. Lets look at your runs.
Here is the Dyno screenshot in case anyone wants to see it.
View attachment 1715118408
If that's a steady full throttle pull in 3rd (or 4rth), the fueling doesn't look right to me. It should be much flatter, staying within 12.8 to 13.2 AFR on racing gasoline and probably a little richer on street fuel.
Being that its a dynojet, they should be able to give you the run files. They may or may not be able to give you the reader. If not, you can (or at least used to) be able to get it from Dynojet. Having the reader is nice as you can change what you want to focus on. Most are also set up with a printer, so at least you can get a paper copy.
Can there be gains in increasing the jets if the A/F ratio is already running in the 12-14 range? Wouldn't it go rich if jets are increased?
Yes.
If the air bleed correctors are the right size, changing the jets will move the entire curve up or down.
If the air bleeds and/or "emulsion holes" are not the right size, then what is really needed is to change them. That will flatten the curve. If you're curious whether the problem is more the primaries or the secondaries, my suggestion is disconnect the secondaries during a couple of pulls.
Dyno runs were from about 2000 rpm up to just under 5000 rpm. We didn't push it above 5000 rpm because we didn't know much about the motor yet and didn't want to push it too hard. Out of curiosity,... what is safe redline for these big blocks? I've always heard don't push it over 5500 for very long.
I can't answer this. Depends on how it was built. Most of the time dyno operators take it until rpm stops climbing. Depends on what you are doing. Your choices seem quite reasonable. Its not the max hp you're after. Its whether the changes made are improvements in rpm range you've run it. Perfect.
