Did the machine shop sonic test the cylinder walls for thickness? .040 my be pushing it.
340 for Cruising and Fun 1/4 mile Passes
- Thread starter Siksty7 Dart 270
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That's in the plan before proceeding. Bore measurements conveyed to me on the phone ranged from 4.071 to 4.075.
Hone it out to the largest cylinder and get some custom light pistons made? Cost more but save the block some cylinder thickness and be rev happy.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Just so you know;
When I built my 367, the machine shop refused to install my KB107s at the KB recommended skirt clearance of .0015>.0020.
I got the block back measuring .0035skirt clearance.
Ok fine, I said, you guys build race motors so, it is what it is now.
I gapped the rings to KB ringfactor of .0065, which was .026
That first summer, I had nothing but hot-running issues .
I didn't dare drive it in traffic.
Coming off the hiway, pulling in for gas, when I would shut it off, the engine would lock up, and it could be 15>20 minutes before the starter could crank it back to life.
I tried all the usual things; HO-starter, Hi-Flo-waterpump, rodded out the rad, Big steel fan. etcetera.
So when winter came, as I would for the next five winters, I installed a 318/auto; she was my DD. Winter was for freshening the 367.
So then;
I pulled the 367 apart, sent the block out for a lil more skirt clearance. It came back at .0040 skirt clearance.
Next I opened up the top ring gap to .0080 factor, which was .032, and second went in at "a lil less".
Next spring, when I installed it, she was a completely different engine. I took off that big bastard steel fan, and installed a Thermostatic clutched slightly smaller steel fan, and a 195 Hi-flo. Engine now warms up very fast, and she runs at 207*F exactly. No more hot-running.
With a 223/230/110 Hughes hi-lift cam and 1.6 arms, she popped off a 106@12.9 on 245/60-14s, spinning for a long, loooong way, on the only run it ever made.
I was expecting piston slap, and on cold mornings, I think I hear it; but, by the time I have backed out of the car port and idled past my neighbors homes, it's all quiet under the hood.
The question is;
Which change made the difference? was it the skirt clearance? or the gap-increase? Cuz those were the only changes I made that winter. Well, besides catching and fixing a wrist-pin bushing migrating sideways.
Answer;
IDK, but since there was no damage to the skirts of any kind, I suspect it was just the top-ring gap. A few years later,
that 223 cam dropped lobes, and I took the opportunity to up -am,
to a 230/237/110, which promptly ripped off an Eighth-mile of 93mph@7.92 , spinning 325/50-15 BFG-Drag Radials a long way. Some say still hazing the tires thru the traps; yes I know, crappy old airport runway. This engine now has over 100,000 miles on it, a lot of them pretty hard.
The First point is this;
If you install Hyper-Eutectics (mine were at 028>032Q), I wouldn't be afraid of a lil extra gap nor skirt.
The Second point is;
Those alloy heads nearly broke me to buy, but as it turns out, they paid for themselves in just a couple/few years, in fuel savings alone. That 223 cam was a real fuel-sipper on the hiway, and since I live in the country, it's all hiway to anywhere I want to go.
The Third point is;
I'll never go back to a low-pressure engine.
I will make a lotta sacrifices to be able to run at least 185 with a 4-speed, closer to 200 with an auto. The difference is that with a manual trans it's a little harder to drive really slow at a really low rpm. With the current 230* cam, I have to retard the Idle timing down to 5*advance, in order to tame her, for parading with 3.55s, at sub 4mph.
BTW-1
that 223* cam got me into the 30s mpg, with a dedicated carb, a manual-trans, and geared at 75=1840rpm in overdrive; and, with alloy heads, Tight-Q, running 195psi, she's always burned nothing but 87E10.
This combo has evolved over the years so, those days are gone.
and yes!, I really miss that 223* cam.
BTW-2
I'm 72 now, and so, if I was to build a hotrod today, It would likely have a Mopar overdrive automatic, 3.73/3.91s, and stall around 2800/3200, for 65=2200 in Lock-up.
At that point, I wouldn't really care what engine is under the hood...... but;
since I have this early 340 short block, and
some old closed-chamber 318 heads, and
this Offenhauser Dual-Port taking up shelfspace, and
a selection of spreadbore to feed it.........
Ima thinking to connect it all together with a really small Solid lifter cam, and
I'd paint it turquoise, cuz turquoise looks pretty.
Like I said, just so you know.
Happy HotRodding.
Last edited:
Swinger 340
Well-Known Member
Crain Cams were a block from my home in Hallandale, Florida, before they moved to Daytona. Several of my friends worked there and I was given Fireball cams for my 340's to play with. I tossed them when I moved five years ago. I run the DC Purple cams now, but wish I kept the Fireballs, for a rainy day. I didn't think the parts of today were so crappy made. These cams were from the 70's.
If you have pistons in the 4.070 bore size, hone the block to 4.078 for all the holes.
Send your pistons to Line2Line coatings and have your pistons coated. They will end up running at .0015-.0020 clearance and they won’t stick or rock.
Last set of pistons I had coated were 320 plus shipping.
I’d rather run used, coated pistons than uncoated new pistons.
mopowers
Well-Known Member
I'm curious your thoughts on the OP's proposed combo. Any concern about the 8.23:1 dynamic compression ratio with iron heads and a pretty wide quench distance (0.051") on pump gas?
I’d rather he had .040 quench and let the compression ratio end up where it is. You can tune for it and the tune up window will be a bit wider with tighter quench.
I’m with Tim. Better to run a typical .038 head gasket for the quench then tune it up. Carb and distributor. Run the 91/93 octane and be good with it. It’s a good combo. Stab it with the cam for the rpm range you want to be in and let it rip. It’ll be just absolutely fine.
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