Doggy engine, what to check next?

[AKcharger]

Stock 383 4bbl (HP) Runs great just feels more like a 318
What it is:
- Original 383 HP one rebuild in 90s stock cast iron intake and exhaust dual exhaust
- edelbrock 4bbl, electric ignition

Other stuff
- again runs great EXCEPT it will spark knock when underload and I accelerate
- compression good, I think all at least 100psi
- I was thinking a worn cam but no miss or backfires
-13MPH highway with AC, thought it would do better

I'm gonna have the springs swapped out in the distributor and hope that helps but after that, I'm kinda stumped?
Suggestions???

[metallicareload99]

Usual questions: Rear gear ratio? What's the timing set @ now? Idle and total and @ what RPM? Compression test or leak down numbers? I've heard a cam problem could make a low RPM miss, so you should be ok there

[Kern Dog]

I have a 383 that I rebuilt to 9.3 compression, lightly ported '346 heads, a 280/474 Mopar Performance cam, recurved distributor, Holley 750 and 1 7/8" headers. It ran fine but with a 3.23, it felt slow. With 3.91s, it really runs strong. The 383 has a shorter stroke than a 360 so it may lack torque but should make more power at the top end.
Smooth running means that it is not misfiring. Spark knock indicates detonation, maybe due to low octane fuel or the ignition timing is too far advanced.

[70 sublime]

My 383 was from a 71 Chrysler Newport
Bone stock with the 2 barrel carb set up still on it
Engine only had 50 000 miles on it so left it as is
I put the HP exhaust mainfolds on it with 2 1/2 " dual exhaust
Car had 2.92 rear end gears
Totally gutless around town
Loved the open road
50 to 90 mph was great
Lots of zip to pull out to pass anyone in front of you
Longest trip I ever did was about 3 hours each way and got 24 mpg out of it

[b5blue]

Check the air filter, wires and plugs. What oil do you use? Mufflers not blocked? Timing set at? Well tuned 383 were whipping the shit out of lots back in the day. 

[Kern Dog]

Again, the 383 has a stroke length similar to a 318 or 340.
They need more axle gear to get them moving from a dead stop.

[496polara]

Check timing,plugs,wires,etc. Check for the carb opening all the way at full throttle.
Compression test ? "All cylinders at least 100" ? My 8.5-1 440 has 145psi with a comp xe 274 cam. That is "low" for what I would like to see but it runs too good to tear it apart.

That low compression motor should tolerate lots of timing without detonation even with 89 octane.

[b5blue]

Pull timing till no pinging right away. 

[AKcharger]

Hi guys thanks for the response. More data
Metallicare - 3:23, I think I'm at 10° but its retarded af far as possible to avoid pinging. af for Compression I did it when I got car a few years ago, remember it was in the 100's but don't recall exactly
Kern dog - copy on gear but my last '70 had a 383 and I put 2:76's in it and it had more guts.
B5 - Fire core wires, air filter has been blown out (oh! maybe I should flip the air clean lid upside down!) and timing is retarded as much as reasonable possible
496 Polara - so 100 is Low? huh, I thought that was kinda middle of the road?

Well I was told by "Halifax Hops" a Mopar distributor guy at Carlise that the Mopar Performance Electronic ignition distributor have weak springs, hence they over advance and spark knock. so I'm gonna send that off for repair that way I can set the timing properly and go from there

[metallicareload99]

The Mopar Performance distributor does have weak springs. I had a lot of the same problems, when I finally recurved mine, it helped a bunch.

Advancing the idle should pep it up. Slowing the advance and limiting total timing "should" help with the pinging

[Kern Dog]

Hi guys thanks for the response. More data
Metallicare - 3:23, I think I'm at 10° but its retarded af far as possible to avoid pinging. af for Compression I did it when I got car a few years ago, remember it was in the 100's but don't recall exactly
Kern dog - copy on gear but my last '70 had a 383 and I put 2:76's in it and it had more guts.
B5 - Fire core wires, air filter has been blown out (oh! maybe I should flip the air clean lid upside down!) and timing is retarded as much as reasonable possible
496 Polara - so 100 is Low? huh, I thought that was kinda middle of the road?

Well I was told by "Halifax Hops" a Mopar distributor guy at Carlise that the Mopar Performance Electronic ignition distributor have weak springs, hence they over advance and spark knock. so I'm gonna send that off for repair that way I can set the timing properly and go from there

Halifax guy seems pretty knowledgeable.
There are also those that are strongly critical of the entire design of the MP distributors built from the early 2000s to approximately the 2015 era. I have one in my Charger and can attest to their faults. Weak springs, weights too small and light leading to unstable timing.

[metallicareload99]

IMO the only actual issue with them is the lack of service parts for em. I don't know why they were sold with such an aggressive timing curve, with so much mechanical advance. Including a recurve kit would have been nice to include with the electronic conversion kits

[b5blue]

Consider an MSD dist.

[AKcharger]

Copy all guys...yeah place to start is Distributor. The Halifax guy said $190 for spring change plus shipping back, I thought that was a bit steep just to change springs. So I looked and I can get a new Fire Core® Distributor for $175! I have one on my '72 and happy so I'm just gonna go that route.
Will update when I get that in!

[b5blue]

FYI my old Firecore dumped so switched to MSD.

[Dano 1]

Might be worth getting a wideband air fuel ratio gauge to see how well your carburetor is tuned. I'm not good enough to tune based on the butt dyno and looking at plugs so my wideband has helped a ton to get my car running well. We're also in the heat of the summer which means hot, humid air which will rob power and greatly effect your tune.

[b5blue]

I had to swap to aluminum heads to lose ping. (Sidewinders)

[metallicareload99]

I have @ least 1 point MORE compression with aluminum heads than I did with iron heads and almost all pinging has gone away.

$190 seems steep, especially if it's just a spring change? Nice thing about the old (early 2000ish?) Mopar Performance distributors is changing the curve was easy IF you had the kit. MSD is nice cause it's even easier and they include all the parts, but no vacuum advance. How is the Firecore curve modified?

[Kern Dog]

Aside from flow improvements, the aluminum heads discharge heat faster than cast iron does. That helps reduce detonation sometimes just by itself.
I've read for years the practice of choosing a cam to reduce detonation. That may work at low rpms where detonation can occur but the bigger camshaft usually is less efficient at cylinder filling at LOW rpms but makes up for it at higher rpms. Because of this, the detonation issue still exists but now it will be at a higher rpm point where it may be harder to hear. One thinks the pinging is gone so he hammers the engine at full throttle.....unaware that he is abusing the engine until it starts to show evidence of damage.