Mopar guys, I need help tuning a 340.

My dad's buddy has an OT mid-70's Dart Swinger (cool little car) that he recently installed a 340 in, to replace the original leaning tower of power slant 6. It's an auto with a mild convertor, but I'm not sure of the specs. I love that he put a 340 in it, and not a crate 360 or the like.

From what I could see, it has stock appearing iron heads, Hedman mid-length headers, a Edelbrock Torker 340 manifold, a mild cam, and a Holley Street Avenger 670 VS, which I told him to upgrade, citing my own struggles with 2 different Street Avengers. I recommended a Street HP, as this is what I put on my SBC and it made a world of difference. It also sports a full MSD ignition setup. I know the Torker is probably too much for stock heads and a smallish carb, so I'll recommend a good dual plane unit next time I see him.

Anyway, he had it by the house yesterday and was telling me about how the idle tends to trail off and it acts like it wants to die, but doesn't. Without getting too into detail, he said timing is currently 33* at 3000rpm, but he's unsure of the base timing at idle. I did see the vacuum advance hooked up. He started it, and while it sounds OK, it revs really slowly. The first things I suspect are base timing is off, and I'm pretty sure the carb was just dropped in. It also looked like an adjustable advance can on the distributor (hex shaped, not round), so I'm not sure how quickly it's advancing. So I need to know where to start with the timing. I'm not terribly familiar with Mopars, but I know 33* all in is a bit low for a performance SBC. I'm also going to pull plugs and see where the jetting needs to go, but I can handle that. I'll check the springs in the mechanical advance, and I can almost see them being 2 heavy springs in there.

So, any other advice or pointers would be greatly appreciated!!

 

This is going to sound nuts but I am digging through an old manual and it is showing 5degrees advance for the 340 in a cuda or a dart sport either one.

I do know that they run real well with a carter thermoquad, . The Avenger series carb is a crap carb, they seem to come with problems built in and at first blush I am going to guess that the most of your problems with tuneup is the carb. It would do better with a stock out of the box 4150 would be your better choice.

 

After dicking with my 360 for the last two decades, I have found a couple of thing to be true with small Chrysler engines. Most important, timing is critical. I would dial in about 14-16 degrees initial, and no more than 36 total at about 2500 or there abouts. My 360, with just over 10:1 compression and Edlebrock aluminum heads uses 18 degrees initial quite happily.

 

modified motors with an auto transmission like a lot more initial advance.

 

I'd look in the dist. Put it at 15-17* initial and about 35* total at about 2400 rpm. Unhook the vac advance until you have the mechanical advance tuned properly. Also look at the carb. Get that jetted right.

Any idea what gear is in the car?

 

Thanks guys.

beaner: Oh I broke it all down to him. It's amazing how much better my car's manners are after swapping for an HP. The street avengers are cheaply made, poor quality garbage, period. I had 2, both had serious problems.

abodyjoe: the owner doesn't even know. He's still running the factory slant 6 rear, if that's any indication. The car doesn't have a tach on it, so I can't even guesstimate.

The guy is a good dude, but he has pretty much no mechanical knowledge as far as cars are concerned. The first time he brought the car by, he was having stalling problems. As it turned out, he tried adjusting the float to the point that the float fell off the adjustment screw. I'm willing to bet that with some simple tuning, this car should run pretty well.

 

One of the fellas got a real deal on an avenger a year or so back and he could not get the engine to hold a steady idle or pull at low RPMs. This being the 5th or 6th that I had screwed with I completely removed the idle screws and it didn't change a thing.

So I walked over to the shelf in my garage and snagged a 600 vac secondary Holley, blew it off and bolted it on. He took his truck for a spin and it run like a scaled ape. He asked me two questions, one was how much he owed me and the other was what should he do with the avenger.

Well the holley I bolted on was a 5 dollar you-pull it carb. My first answer was to hand him a 4 pound hammer and a piece of 3" H beam. He beat his fancy schmancy carb flat. The second answer was nutin. It was worth 5 bucks to watch him beat that carb.

 

From the tech archives at Mopar Action -

Timing should be at 33-35 deg BTDC at 3,000 RPM w/vacuum advance disconnected, then reconnect it. This should result in around 10-18 deg BTDC at idle.

http://www.moparaction.com/Tech/index.html

 

This is exactly what my manual says and is what I did. Set at 5 degrees advance, with the vacume advance off. Motor is in a 340 Duster, Edlebrock Air gap, Holley 750, Mild comp cam, factory X heads and headman headers car runs and starts great.

 

He said he's got 33* at 3k now. I'll have to double check everything. For all I know, he set the timing with the vacuum connected.

 

X2, and the 340 torker is a dog turd. An LD-340 or (and it pains me to say this) Performer RPM will run away and hide from the torker, top to bottom. The LA Mopar torker sucked the fat one from day one, no-where near as good an all-round performer as the SBC torker. I used to build LOTS of LA mopars, always avoided that intake like the plague. Personally, I would use a stock cast iron thermoquad intake over the torker.

 

So you're saying lose the Torker...........

 

The older Wieand dual plane is a good piece as well. But uh yea, the LA torker pretty well sucks the fat one. The cast iron TQ intake is actually a REALLY good piece, but TQ's are tricky to set up if you have never worked with them before, and parts can be difficult to get. Personally I like them, EXCELLENT carb, but you need to be used to thier "quirks". And I'll re-iterate, 36 degrees is pretty much the magic number. I've had a couple here and there that liked 38-40, but they were more race type motors.

 

I'll most likely tell him to look for a Performer intake.
I'll try 36* and see how it feels.

 

Actually, step for the performer RPM air gap if you have the hood clearance to do so. I have had the Torker, Performer, Mopar performance's version of the same, and the RPM air gap on mine and LOVE the latter. These engines have a bad habit (at least here in the desert) of being super hot on the upper end of things and boiling carbs. The air gap has gone a long way to prevent that along with a phenolic spacer below the carb.

 

No on the performer, its sized for the 318 ports. LD340 or Perf. RPM.

 

A couple of points for a Chevy guy working on a Mopar.
1. Set total with vacuum disconnected to 36 as said. Now check at idle. Factory is around zero, which stinks. It really should be 10 with a very mild cam, 15-18 with a rumpity cam. You will have to deal with brazing up slots after disassembling the dist. It isn't on top like a SBC.
2. The vacuum advance does have a hex on the end, but that's NOT how to adjust it. There is a small allen INSIDE the vacuum fitting that can limit the vacuum advance. Look it up online once you get the carb, intake and initial timing sorted.

Here's the deal in tuning
http://www.sweptline.com/tech/engine2.html
and talking about the vacuum advance adjustment
http://moparforums.com/forums/f7/tuning-tips-case-you-missed-6393/
and another showing the mechanical advance slots...
http://www.moparmusclemagazine.com/...mopar_electronic_ignition_system/viewall.html

 

RPM Air Gap, got it.
I run the Air Gap RPM on my SBC, and have only good things to say about it.

 

I know ALL about the vacuum advance cans, lol. I had issues with my timing until I fabbed a limiter plate for controlling the amount of vacuum advance, including trying the adjustable cans. Can't say I'm a big fan, I'd rather play with weights and springs.

 

did you dads buddy buy the 340 off the hambs classifieds? sounds like an engine i saw for sale a few weekes ago, it had the j heads but was missing the dual plane intake so i passed.

 

If the car is an automatic a good dual plane will work if it is a stick I would keep the torker.

 

No, he's had the block and internals for a few years, just finally got it put in.

 

Yup, auto.

 

Re timing the guys already got it right.

Re the intake/carb either find a nice Edelbrock LD340 intake or run the Airgap intake.

Both are almost identical in performance but the LD340 is a killer early 70s vintage /period piece that is just as good as the Airgap.

With the LD340, I ran a 1" 4 hole phenolic spacer (mine liked the 4 hole better) or an open 1" spacer which will increase the plenum volume/air speed and allow that 340 wind out and breathe DEEP. Wont hurt the low down TQ either.

Also, a 750 HP DP carb dialled in properly will allow that 340 to ROAST the treads easily

Boogie....

 

^^I used to just mill the divider out of the LD340. If you want a single plane, strip dominator will WALK all over the torker top to bottom. As far as that goes, so will either of the dual-planes, stick, auto or clutchflite.

 

factory specs mean little when performance cam and parts are added.use a vacuum gauge to get best vacuum at idle ,then check advance ,drivability,and adjust.listen to the engine.

 

So as it turned out, all it needed was a little more advance. He said a local shop tuned the car initially. When I went to take the distributor hold down loose, there was little resistance, so the timing may have walked on him. Now it starts in half a crank, idles strong in neutral and gear, and the engine is really smooth and responsive. The plugs looked good, so I didn't touch the carb outside of dropping the idle a bit after bumping the timing. Felt good on the road with no pings. I can definitely feel the Torker holding it back down low, but I was afraid to really crank it up, because the car needs an alignment BADLY. It's very darty (see what I did there???) and the steering is really loose feeling. He's getting that addressed today.
I passed along the RPM Air Gap recommendations as well. I told him with the way it feels now, he should notice a nice bump in useable power with the intake swap.

Thanks for all the input!!

 

My Son is a Mopar nut. He doesn't have much time anymore. He has a '70 340/ with 2/ 4's and won't sell. I have some speed parts for B B Mopars, still brand new in box. He Runs the Mechanical End at International Truck in Cinn. I have some other used B B's + 727 Trannys. I am cutting back, getting to old to do any more, Spine issues.

 

My only 2 cents is to make sure he doesn't have a Chrysler dual point dizzy. I know you said it had MSD, but if it's not a complete system and has a dual point check the bushing in the dizzy,they wear out causing a wobble and erratic ign. timing.

 

wow all the teck i used a street avg and loved it no problems running a purple cam hyd gring. i used a vac gage to set the timmimg, I know laff but it got 16 MPG and would run 14s all day long and start everytime never ran higher then 195 or close to.