340 dilemma

[bizjetmech]

I just acquired a Dodge Charger that had a transplanted 340, (casting date on block: 9-27-71)......car has been stored since 1991. The plan is to put this 340 in my "H" code Dart Sport, which had a cracked 340 block. Car is currently a driver with a stock 360........but if this thing runs decent with this 340, it will see the local racetrack.

Engine appears to be as advertised by the seller/receipts that came with engine.......bottom end is spotless, appears to have forged steel crank, ARP hardware, Milodon hi-volume pump, etc.

The problem......Engine has TRW L2322 +.030 pistons. After cc-ing the dome and the heads that came with the car, I'm calculating the compression ratio at approx. 11.2-1. (heads cc-d @ 71-72 cc, .028in thick head gasket). I'm guessing that I'm going to have problems running this thing on pump gas.

Engine has been balanced already......ideally, I can find some pistons that weigh the same to drop the compression ratio to 9.5/10 to 1. The current weighs in @ 689.4 grams (w/o pin), which is HEAVY, compared to most of the aftermarket pistons that I can find weights for.

Any inexpensive way to get this thing down to something I can live with?....I just got laid off yesterday, so I have some time (but no money) to mess with this. I have the set of heads that came with the original 73 340 that I'm going to cc check, but I don't think they are any bigger volume than what I have. I don't think anyone makes a thick enough head gasket to get this thing down where I need it. Anyone have any ideas? What kind of fuel am I going to need to be able to drive this thing with no detonation? (if it makes a difference, the local landscape is 1100-1300ft above sea level).

Thanks in advance for any advice/commentary/assistance.

 

[bOb shingler]

did you include the thickness of the head gasket when figuring compression?

 

[bizjetmech]

Calculated C/R using a head gasket thickness of .028

A .040 head gasket would gain a couple of ccs.......according to my calculations, I need to increase the combustion chamber size about 8cc to get it down to about 10-1, or thereabouts. Heads are bone stock.......I was wondering how many cc's I would increase it by polishing out the rough parts in the chambers.

BTW......I've got a set of the 89-92 "308" heads (currently in the car). Anybody know the typical chamber volume (in cc) of those? (From the photo's I've seen of 308s, I'm guessing it's probably under 70).

When you look at 8cc in a syringe, it's a bunch..........

 

[rmchrgr]

Cometic makes a small block gasket that is .040" compressed.

Just throwing it out there - KB 243 is a flat top that they say with 68cc chamber gives you 9.4:1 compression. Weighs 507 and the 984 pin weighs 132 so that's 639 with the pin.

 

[furz4]

You didn't say what cam is in it, but if your going to race it and not street drive it much you might be ok if the cam is large enough. If it's large enough it will bleed off cylinder pressure on low end and help keep you out of trouble on the street. What gear are you going to run? I would think you could run on pump gas with booster for sure if you don't want to tear down right away. That way you would get a chance to evaluate the potential of the combo before starting changes.

 

[bizjetmech]

Car is street-only at this time, and have no plans on going crazy with it.......may go to Heartland Park a few times a year if it runs respectably. The main goal is to show these local "Fast and Furious, Folger's-can-stuck-on-the-tailpipe" ricer boyz what a REAL CAR looks and runs like. 8).

Ideally, it will look and sound like a "stocker" (or close to it). Thinking about locating a good aluminum dual plane, grinding off and blending in the identifying marks, and painting it engine color to look like a stock intake.

Don't know what the current cam is, some kind of HP hydraulic. I'm planning on checking the specs if I can find some kind of I.D. on it. I have a new Lunati Hydraulic that I was thinking about sticking in if I can't find any info on the current cam (Can't remember the Lunati specs off the top of my head; as I recall, it's close to the old "Street Hemi" cam).

Car has 8.25 3.21 Sure-Grip., stock hi-stall converter. Current plan is to go with a fairly stock converter, go a little looser on the converter if it is obviously the weak link in the drivetrain........I want to run it with the stock stuff first, then prioritize revisions/changes.

 

[Tony Fields]

Car is street-only at this time, and have no plans on going crazy with it.......may go to Heartland Park a few times a year if it runs respectably. The main goal is to show these local "Fast and Furious, Folger's-can-stuck-on-the-tailpipe" ricer boyz what a REAL CAR looks and runs like.

Just be very careful if you run into the late '80's early '90's
Turbo Mopars. One of them just might eat your lunch.:-D



Good luck with the build.

 

[sumbitmopar]

Do you have access to a machine shop on the cheap?

 

[70aarcuda]

the dome on the pistons are solid..you can cut the domes off...

fel pro makes a .053 head gasket...

 

[72bluNblu]

The 308's I had reworked for my 340 had a chamber volume of 65 cc's on the dot. The stock 73 340 heads are probably larger than that, even though they're listed at 65 cc's stock I've seen them as large as 68-70.

Also, keep in mind that going to a head gasket as thick as you'd need to drop the compression ratio that much would kill your quench.

 

[1MeanA]

I don't think you'll get much quench with an open chamber anyway. I think you can get copper spacer type gaskets in 1/8" which might work.

 

[oldkimmer]

...............Cometic will make a gasket any thickness u desire.............kim...........

 

[djwhog]

I would go a little longer on the cam duration and or cut the pitons down a little, should be OK!

 

[dstdevl]

jet mech, Try the combination as is with 91-92 or better octane fuel add 104 to it drop your timing back and drive see if you got a ping. check plug burn pattern and add fuel if necessary. hey time it with a vacunm gage go max vac turn back 1 inch check timing marks. BT