Upgrading a 72 - 340.

[swing69]

Looking for cost effective way to get the most out of this 340. It was a running motor (so said the previous owner), but I never heard it run.

The eddy manifold was removed, and I actually found this stock, 72 340/4 intake on another core motor (go figure!). The mains look pretty good, as do the journals. The heads look good too. The bores are a little 'ridged'. I'm thinking a block clean, bore/pistons and rings. New bearings and call it a day. check out the spreadbore / squarebore adapter! Oh, I also have a new cam for it. Summit kit: 6901 (http://store.summitracing.com/partdetail.asp?part=SUM-K6901&autoview=sku).
Is the stock intake worth keeping? or ditch it for a eddy? any suggestions about using this cam? I used the 6900 kit...and liked it. I just was looking for allittle "more" umph. Should I look for higher compression pistons for use with this cam? are they available?
Side question: Were windage trays stock in all 340s? this one had one. Comments?

 

[rumblefish360]

Is the stock intake worth keeping?

yes

or ditch it for a eddy?

the performer? No!

any suggestions about using this cam?

install it straight up.

I used the 6900 kit...and liked it. I just was looking for allittle "more" umph.

not over a stock 340 cam

Should I look for higher compression pistons for use with this cam?

no

are they available?

pistons? are you kidding me? You must be a young fella. They most certainly are!

Side question: Were windage trays stock in all 340s? this one had one.

yes

Comments?

Your a young fella aren't ya? I think a few books are in order for you starting with "How to rebuild my small block MoPar" and the "Hpw top hot rod my small block MoPar."

You also need a plan and stick to it. Your gaggle of questions are disorganized and most basic without direction. The books will help you get squared away.

 

[66dartgt]

72 340's will have lower cr pistons around 8 or 8.5:1, smaller intake valve heads 1.88/1.60's, possibly a cast crank, (check the vibration damper for a bell crank weight built into it - if it does - its cast), (asymetric appearing). Heads will have larger intake and exhaust ports. Should have full floater rods (good), and windage tray, double row timing chain, stock 340 performance cam if original.

What to do with it ? Depends on what you want to accomplish. If it were me and I wanted to keep the stock size motor (not stroked ?):

Source a forged crank and matched damper, balance the bottom end, redo or replace the rods with eagles, higher cr pistons 68-70 style, bowl port the heads, stick a modern style cam in it (comp extreme or vudoo maybe), along with headers, maybe add stainless 2.02 intake and exh valves. Plop a modern 2 plane intake on it with a holley 4 bbl and call it a day.

The stock intake is actually a pretty good piece depending on what you want to do with the motor, the adapter plate is needed to put a square bore holley on it, otherwise a spreadbore will bolt directly on. TQ's were stock on 72+ 4 bbl motors.

Tell us more about your intentions !

 

[swing69]

Young? I wish. I've also rebuilt 3 other small block Mopars (318s). Yes, I've been through the 2 mopar books on the rebuilds. I'm just not familiar with the 340s, and how they were set up stock. I just got the motor opened today, and didn't read up on the 340s. But with only 3 motors built, yeah...I'm pretty new. Yahooo! I"m young again!

To the motor: The cam may or may not be the original, but its pretty pitted anyhow. so that's coming out. the heads? I'm keeping stock. The intake? if it flows similar to the eddy performer, I also don't know about the 6901 cam and how it compares to "stock". I was also curious if the stock piston CR was compatible with the 6901 cam. I have that cam on hand, and would like to use it.

The questions are thin, vague, I agree. Its only because that's where the holes in my thinking are! lol. If I read my post, first, I'd think the same thing! don't worry...I know pretty much whats going on. I do NOT pretend to be an engine builder, as a prof. engine builder has MUCH more experience and knowledge with engine internals than I do. I'm not making an engine plan yet...I'm just trolling for some info!

The vehicle?? The car that will be getting this motor is a 73 Dart sport. The 340s mating to a 727 and 8.25 (or 8.75) with 3.55 gears. this is HS auto shop project car and will be sold in June when done.

Machine work and final paint are done "outside". assy work, bodywork and mechanicals are done in house. here are a few status picts.

 

[rumblefish360]

LOL , "I'm young again."

The 340 is just like the 318 minus the bigger bore and larger cam they came with. The windage tray is a nice free-be bonus.
The cranks are fordged except in 1973. (Some say late '72 they came in.)
Also the '73 - 340 is extrenaly balanced and not the same balancer or weights as a 360.

The cam you have is by whom? Sorry, I do not know the number by it's self.

 

[rumblefish360]

OH, the stock cam is a split that you can still get from MoPar and they also have a updated version that makes some more power without really increasing the spec on it.

With the stock intake, I'd keep the cam on the mello side not in excess of 230* duration. I'd also make it a split pattern cam so it will help the engine breath better, weather through exhaust manifolds or headers, the split cam pattern will help.

 

[340sFastback]

Put some positive deck pistons in there like the earlier 340s had to get the compression up. You don't want to put '72 spec pistons back in there. Pay attention to the weight of the piston, the lighter the better. KB makes some good pistons to put in there http://kb-silvolite.com/index2.php . Someone here can give you the part number.

 

[340sFastback]

Here is a good article on building a slightly hotter then stock 340:

http://www.compcams.com/Community/Articles/Details.asp?ID=-738676943

 

[Tarr]

With a car that nice, don't short circuit the deal. You can have the block mic'ed and see if it needs boring. If it does, I'd suggest the Ross 9.7 cp 514 gram pistons. They are about 200/250 more than cheap replacement pistons but are about 300 grams lighter than the stock pistons. Don't forget to get everything balanced. I live in Mid-Tennessee and the entire machine shop out lay was just over $1000. But I suspect I got a good deal as it was a friend.
That was to bore block to match pistons, install valves and valve job on J heads with 2.02s that I supplied, Rebuilt rods both ends with new bushing on small end, Check and square block and heads, grind crank to .10 under, and of course tank block, heads and install new cam bearings, gring rings to fit, install Arp studs and alighn crank bore and balance everything. I still don't have mine put together because I'm waithing to get the car back from the body shop. But I won't have any regrets when I get there.
Good luck.

Buy the way, My 340 is a 72 model with steel crank. The reason I recommend the forged pistons is that I feel they will take more abuse and I'm thinking of NOS later.

 

[rumblefish360]

I like the KB107's. They'll deliver an excellent quench area @ zero deck height and 9.8-1 with a stock head and a Fel-Pro .039 thick gasket.

(Oh, gooootta love the 40+ HP jump in the cam change from that write up! )

 

[70aarcuda]

kb243 is the 340 piston....kb107 is a 360 piston the compression height is way to short to be used with a 3.31 crank..

kb243 weight in at 585 grams..a good 100 grams lighter then the factory ones..

 

[dusterdon]

You have a cast crank motor there. For what you're planning, the cast crank is plenty strong for you inteded usage. A normal rebuild with the higher comp. KB pistons and you'll be in business.

 

[rumblefish360]

UGH!

Tony, thanks for correcting me. I hate when I do that mistake.