440 Head Scratcher

[Hanover Mopar]

Just took the car out for a quick spin. It is a some what built 440 about 550 HP. Ran great until until it warmed up good, about 190. It started popping intermittently at all steady speeds. Single small backfires that go right away under acceleration. No problem at all under acceleration.

Spark or fuel???

Anybody have any guesses where to start.

Thanks in advance
Jack

 

[moparnation74]

Sounds like a fuel problem...The car is running lean at high rpm's....

 

[moparnation74]

If not a float/pressure issue....Second guess would be weak valve springs, floating valves...

 

[Hanover Mopar]

Only does it at steady lower rpm it seems. Letting it cool down to see if the problem still happens. Very stout valve train so I don't think it's valve float but you never know

 

[khryslerkid]

Check plug wires for looseness, burnt through on a header tube...

 

[Hanover Mopar]

i have socks on them but will still check. thanks

 

[miller]

If the answer doesn't come out at ya, I'd suggest a compression check. Could tell you if your valves are closing all the way. Admit, could be a handful of different things.

 

[69 GTX]

Maybe a tight valve?

 

[Yatzee]

Just took the car out for a quick spin. It is a some what built 440 about 550 HP. Ran great until until it warmed up good, about 190. It started popping intermittently at all steady speeds. Single small backfires that go right away under acceleration. No problem at all under acceleration.

Spark or fuel???

Anybody have any guesses where to start.

Thanks in advance
Jack

High vacuum occurs at steady speeds and when you accelerate vacuum drops. Sounds a bit like a timing issue with the vacuum advance applying too much timing or static timing is way off. Regardless, if your firing a piston at the wrong time you will get pops because the valve timing doesn't match ignition timing. How is it at idle and can you actually feel the misfires or just hear them?

 

[Hanover Mopar]

Just checked plug wires. Had #1 out for TDC yesterday and adjusted valves (again). The plug wire was very loose and I think it wasn't supplying spark at lower steady rpm then picking it at full power. Thanks you Khryslerkid and I should have looked there there first (it's usually the last thing you touched my father used to say).

The verdict is Moroso plug wire suck as others have said.

If Firecore the way to go??

 

[Billccm]

If Firecore the way to go??

I'm waiting for my Firecore set. Hopefully delivered Friday. Lots of consensus here for Firecore. My car currently has MSD plug wires. It runs great, but for whatever reason, I have cracked insulation on two particular wires. Actually, it's not even cracked, its falling off.
The MSD replacement set did not fit at all. The Taylor set I ordered was even worse in that two wires were way too short. Both went back to Summit.
I spoke with 'Firecore Rick', texted some pictures, and discussed options. He claims his custom set will fit better than factory. We will see.

 

[khryslerkid]

Just checked plug wires. Had #1 out for TDC yesterday and adjusted valves (again). The plug wire was very loose and I think it wasn't supplying spark at lower steady rpm then picking it at full power. Thanks you Khryslerkid and I should have looked there there first (it's usually the last thing you touched my father used to say).

The verdict is Moroso plug wire suck as others have said.

If Firecore the way to go??

Well reading your original post it sounded like what happened to me during my 20 min break-in.

About 15 min into it, running @2,000 rpm, it starts popping. Runs ok for a bit then starts popping. MSD wires, two of them had backed off. Crap!

Glad you found it. I've always said, "try the simplest thing you can think of first". 9 out of 10 that's your problem.

 

[Bigal75]

I run Firecores on a Hemi. They definitely clip on to the plug tightly lol. I would recommend them.

 

[Ironbuilt]

I run 10.4mm Taylor's on my built 440. Definitely worth the extra money. Don't forget the boots or the headers will eat them up.