340 lower end

[KB9GIB]

Good morning and thanks in advance for any information. We are getting ready to put my sons 340 together we purchased a bare 68 block I had It checked out it is std bore but will need bored 30 over so my question is I have seen on EBay crankshaft kits from (Clegg Engine & Machine) has anyone had experience with their Products. Thanks again KB9GIB

 

[rumblefish360]

Are you looking for a stock throw crankshaft?

 

[KB9GIB]

Yes I was looking for a crankshaft. But I just got off the phone with the Machine shop he said the 318 crankshaft and rods would work? It’s just a cruising Car. He also said he could put the bigger valves in the J heads?

 

[rumblefish360]

Yes I was looking for a crankshaft. But I just got off the phone with the Machine shop he said the 318 crankshaft and rods would work? It’s just a cruising Car. He also said he could put the bigger valves in the J heads?

The 318 did use a forged crank early on. Same crank as a he 340. No difference. I forget when it went to a cast crank. For a cruiser, ether crank will do. The cast crank will hold up well past 500hp.

The 318 rods are also forged. The factory used a 4340 material. But they are a little smaller, so, as a big power choice, I wouldn’t go there.
(Big power being N/A over 550hp.)

If you do a 2.02 swap into a 1.88 head, I would continue with a bowl porting. The reason is the 2.02 is bigger but the area under the valve hasn’t increase. So the gain is crap. There is a gain, it’s just a crap gain.

A lot to people **** on a iron head but over all you can grab some really good gains for less money than a new set of iron heads, although not flow as much. A talented porter can have a iron set out flow OOTB Edelbrock heads for less money than the new set.

How big is your cam?
@.050 & lift?

(Another plus is you don’t have extra set of heads to trip over and that are nearly impossible to sell for more than a dozen eggs.

And FWIW

Porter Racing heads has said he did get 280cfm out of those heads. But that’s fully ported.)

 

[KB9GIB]

Thanks you for your information. as for the camshaft don’t know yet? the 3rd member is 355 pos with 727 in a Demon it’s my youngest sons car it was his every day car thought high school he is now 22 and we have put all new body panels on over this passed winter. I do think you for the info. KB9GIB

 

[rumblefish360]

No problem. Does he have PB?

 

[KB9GIB]

No power brakes I think probably like to stay with something that a stall speed is not required. On my old X with a 3500 stall the car runs a bit hotter. Thanks KB9GIB southern Illinois

 

[rumblefish360]

FWIW, that’s a cam duration of 218-220 @.050. Not more.
That will make for an excellent driver and do so in a similar RPM band as the OE muscle cars did.

I used such a cam a ways back. It had a 218@050 in a low compression 318 Duster run the 14’s with 3.23’s, stock converter and stock size tires. Heavy wheel spin. Go wider with the tires. It was a very basic and fun combo that I still got 17/18 on the Hwy.

Good talkin!
Enjoy!

 

[KB9GIB]

Thanks for all your information Rumblefish360

 

[Challenger340]

You have to be careful when mixing/matching 318/340 parts, especially between Forged and Cast pieces. The 340 Pistons can be substantially heavier, the 318 Rods lighter, mismatches can occur throughout, and very tough to locate the early 318-3 Truck Forged Cranks nowadays.
Best bet...
get the parts/Rotating Assembly Balanced.....

And it makes no difference just because "it's just a cruiser" in your mind, then why are you putting 2.02" Valves in the J heads ?
"Cruisers" don't need 2.02" valves either now do they ?
Save the 2.02" Valves money and get it Balanced.

 

[rumblefish360]

Careful?!?! Now that is insane to state! Just down right don’t mix and match parts unless you have them balanced!

 

[KB9GIB]

Thanks for all your input guys. I’m going to just take the parts to the machine shop and let them figure it out. they was the ones that suggested the 318 crankshaft and rods. if I could find 340 parts closer I would go that route. all the 340 crankshaft I see for sale they what around $300 for a crank that might are might not be good and $200 for used rods. That’s why I was thinking of a new crankshaft kit that’s when the machine shop suggested the 318 parts. Thanks again for all your information KB9GIB