My old school 340 upgrades and results.

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340dartley

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I have a couple of other threads here but they were subject specific. This thread will touch on some of the issues but will hopefully be able to grow with the evolution of the motor and car.

First off here are the specs on my car and motor.
1969 Dodge Dart Swinger. 340 automatic
.030 340 with forged 10.5 to 1 pistons
X heads with some bowl work and port matching.
Stock rocker arms and push rods.
Stock intake
750 dp carb
Mopar purple cam .508 lift 292 [email protected] duration
Bottom end was lightened and balanced

I drove the car to a 12.0 quarter mile time at Bakersfield back in the early 90s. I was not the owner of the car at the time.
I purchased the car back in Oct of last year. I have yet to make a pass with it as life sometimes gets in the way. The previous owner told me to shift at 5200 rpm as it pops at any higher rpm.
I was told it should probably have new valve springs installed.
I also just purchased an Edelbrock performer rpm manifold and would like to get a bit more high rpm performance.

I started looking for valve springs and found the options limited in my budget.
Well tonight I removed the valve cover to see what I had to work with. I was surprised to find a double valve spring with a damper already installed.
This brought up 2 things. If I upgrade the springs I already have the keepers and machine work done so I can just put them in. The other thing is wouldn't double spring even if worn be able to control the valve train past 5500 rpm. Maybe there is another issue.
 
Could have cam going flat, MP specs for that cam call for a MP single spring, but someone may have put dual springs with similar specs. Or you have sunken seats. I would measure installed height to see where they are at. Have the heads had any work done recently? Hardened seats put in? Could have sunken seats making installed height too tall. Or could be just weak springs.
 
Yes you can replace springs of the same intalled height.

Springs could be the issue, or yes...it could be something else. If it were me, I will start with the basics:

Compression test
Leak down test
Pull a few springs and check open and closed pressure.

Don't worry about more top end until it runs right as is.



340dartley said:
I have a couple of other threads here but they were subject specific. This thread will touch on some of the issues but will hopefully be able to grow with the evolution of the motor and car.

First off here are the specs on my car and motor.
1969 Dodge Dart Swinger. 340 automatic
.030 340 with forged 10.5 to 1 pistons
X heads with some bowl work and port matching.
Stock rocker arms and push rods.
Stock intake
750 dp carb
Mopar purple cam .508 lift 292 [email protected] duration
Bottom end was lightened and balanced

I drove the car to a 12.0 quarter mile time at Bakersfield back in the early 90s. I was not the owner of the car at the time.
I purchased the car back in Oct of last year. I have yet to make a pass with it as life sometimes gets in the way. The previous owner told me to shift at 5200 rpm as it pops at any higher rpm.
I was told it should probably have new valve springs installed.
I also just purchased an Edelbrock performer rpm manifold and would like to get a bit more high rpm performance.

I started looking for valve springs and found the options limited in my budget.
Well tonight I removed the valve cover to see what I had to work with. I was surprised to find a double valve spring with a damper already installed.
This brought up 2 things. If I upgrade the springs I already have the keepers and machine work done so I can just put them in. The other thing is wouldn't double spring even if worn be able to control the valve train past 5500 rpm. Maybe there is another issue.
Click to expand...
 
What is everyone's thoughts on spring pressures? My thoughts for a motor turning over 6000 would be 150 seat pressure with 350 open pressure.

It runs well up till it pops. I would think that a flat cam would show up earlier in the rpm range. Leaking valve more so at idle. Granted it has a lopey idle at 1300 rpm so that may hide any problems there.
 
No work has been done recently. The engine has been untouched for 20 years or so. Same complaint was stated back then. This is a full drag car. Not street legal so it has not been driven in several years.
 
Bad ignition ? Wires ? rotor? Cap?
Wow, it's been popping @5200 for 20 years!?!
A drag car !?!
 
What kind of popping? Ignition? Valve float?

If you're running electronic ignition. I know the stock black box is supposedly no good above 5000 or so rpm.
 
I am running a Chrysler electronic distributer with 34 degree advance locked. Msd7al box. Msd blaster coil
 
You mention the previous owner said it pops. Have you yourself made it pop?
 
j par said:
Bad ignition ? Wires ? rotor? Cap?
Wow, it's been popping @5200 for 20 years!?!
A drag car !?!
Click to expand...
Yes it was always shifted right at 5 and ran low 12s . My thinking is the cam is just s just hitting the sweet spot when you shift. The dragstrip it used to run at closed down in 2005. Hasn't been rn down the track since then.
 
I also have some parts in my garage that I have collected over the years that I might potentially use.

I have a performer rpm manifold
273 adjustable rockers with push rods for hydraulic lifters
Was also going to put a 1 inch spacer under the carb
 
A 508 hyd cam should pull to 6K easily in a 340.

I'd check lifter preload as well as other basic diagnostics to determine why it's popping.
 
you can turn 6000 rpm's with stock 340 springs. a 340 with that cam should sleep walk to 6k. you could have electrical break-up causing the popping. I also think you might want a little more timing than 34. just my 2 cents
 
318willrun said:
you can turn 6000 rpm's with stock 340 springs. a 340 with that cam should sleep walk to 6k. you could have electrical break-up causing the popping. I also think you might want a little more timing than 34. just my 2 cents
Click to expand...
Thanks for the reply. That is exactly what I was thinking. I know several ignition components have been upgraded over the years with no real change in how it runs. Not sure if they were upgraded for the purpose of repair or just to upgrade. The one thing that was not upgraded was the distributer and pick up. It still uses a stock style Chrysler electronic pick up. Watching the tach for signs of needle bouncing or anything does not help as the tach is cable driven.
 
Just to ramble on the subject a bit more. When I used to run the car in the 90s it had a Chrysler ignition box and no msd7al . We used to run no alternator. At some point someone decided that it needed a 7al box. This had issues with running with no alternator. They eventually added the alternator so the 7al box would not cut out. All this and the et of the car did not change at all. For the record it has a single wire GM style alternator
 
That's about all I've used is the factory Dizzy's. I've even spun stock single points to 6k. That's what I had in a Duster 340 I use to have. electronic or points? What ECU? factory? orange or chrome box? MSD? Is the tach accurate??? Ha! there is a big one! I had a tach that said 6000 and was really turning about 7200... lol. Just lots of places to start, you'll get it with pursuit :)
 
ahh,... just read your last post. Yeah, I think if it were mine, I'd just install the mopar electronic conversion kit. less than 200 and I bet your chasing would be done
 
j par said:
Bad ignition ? Wires ? rotor? Cap?
Wow, it's been popping @5200 for 20 years!?!
A drag car !?!
Click to expand...
LOL......
you know what, though? Here is an old school build pumping 12.0's in the 1/4 with a serious issue... wasn't a few folks arguing about those old skool cams.... never mind..... :rofl:

factory cast intake, cast heads, all kinds of hug bush here..... get'n her done
 
At what RPM are you spinning it during your burnouts? Above 5200? No popping?

If so, I'd look at the fuel system.
 
Honestly during that burnout I was being egged on by my neighbors to do it and I was not even watching the tach. Was shifting by the seat of my pants. Lol
 
From the angle of that driveway if you got a running start from inside the garage and hit that sucker just about as fast as you can I bet you can clear the neighbor across the streets house! LOL car sounds good....
 
That's not a driveway. That's a sweet ramp.

As for your issue at above 5000 rpm. I assume you're running a mechanical pump? Pull it and check the arm and push rod. A recent roadkill garage episode they had the same problem. Car fell on its face above a certain rpm. Turned out the push rod was worn bad. Simple check!
 
That is a great sounding engine in an really cool car!!!

Jake
 
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