Need to put together a new short block for my 72 Roadrunner. It’s a restored NOM 340 auto car. It’s got some vibration issues, as well as a block issue (busted out transmission dowel) that necessitates at minimum rebalancing the internals and replacing the block. Not looking to diagnose or resolve those problems here.

Not sure what I’ve got to work with internally. The motor is internally balanced (albeit poorly), but I’m not certain if it has a forged or cast crank. No idea what rods or pistons are in it either. At some point before tearing into it, I’ll drop the pan for a peek inside.

Performance-wise, it’s pretty weak, but being a stock 72-spec 340, expectations are modest. Has J-heads, factory T-quad and mild/stock cam. Also has headers installed. I’ve pretty much got it tuned up to its maximum potential in current form. Under other circumstances, I could probably live with it, or just do a cam swap.

It all fits under an Air Grabber. I want the appearance to remain largely stock and keep the Air Grabber fully functional, so I don’t anticipate making any changes with the carburetor or intake. It’s a 100% stock appearing car with the exception of the headers and aftermarket wheels.

Not looking to make it a 12 second car, but if I’m taking it apart, I would like to get the performance a little more in line with its appearance. I’ve had really fast cars previously. I would have bought a big block car if I wanted another. This is a cruiser that I really enjoy driving (think Power Tour). I just want to be able to exert some more authority at the stop light.

So here is the dilemma.

Do I build a 360 based stroker short block, or (re)build a 340 (with more cam and CR)?

I’ve already got a good 360 block to work with. I can get a date code correct 340 block for a few hundred bucks. Not much invested in the 360 block at this point, so I’ve got options but using it over a 340 saves me a couple hundred bucks towards a stroker.

Ultimately, the cost difference between the two is pretty much negligible as long as I reuse my current top end. Buying new forged pistons, and reconditioning the factory parts puts me within a few hundred bucks of a Scat cast crank stroker kit. Obviously, part selection on the rebuild could open or close that gap. Point being, price tag won’t be the sole determining factor on the short block decision.

Things could snow ball pretty quickly building the stroker though. I’ll be very tempted to spring for some better heads and other upgrades. Running 60 more cubic inches with the stock J-heads locks up a lot of performance potential. This would eat at me, so even if I didn’t initially spring for better heads, I’m sure I would eventually.

I’ve already had numerous people tell me I’d regret not building the stroker, but since I don’t currently have that extra performance, I don’t think I’d miss it. Like I stated above, I could live with the current performance level under other circumstances.

Plus keeping that extra 60 cubic inches fed when 93 octane hits $4/gallon will have a psychological impact if not a huge financial impact.

Finally, there is the question of is the car worth more (or less) in the factory 340 configuration than it would be modified with the 360-stroker. If built the way I intend, it will take checking casting numbers to know the difference. Not something terribly important to me, but maybe to a future buyer. (Been watching too much Barret-Jackson)

The hot-rodder in me is wondering why I’m even having this debate. Couple of years ago I’d would have already had the stroker kit ordered by now. I must be getting old.

I know I’m over analyzing the situation, but I’d like to hear some opinions. If nothing else, it’s a debate to kill the time while I wait for my tax refund.

Stroke or not? single choice
	Build a 360-based stroker
	Build a 340
Votes accepted starting: 01/13/11 04:44 PM
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Unless you have your heart set on a smblk, I wouldn't bother,....waste of time,...drop in a BBlk 440-426



Otherwise MP 440 smblk stroker pkg?

340 Stroker, torque to move the b-body and 340 block to complete the stock appearance.

I'd start off with a magnum based 360. if budget is a concern, stock stroke, KB107 pistons, stock rods redone with ARP bolts and redone stock magnum heads redrilled to LA pattern, or if the mag heads are cracked, Enginequest 318B's or RHS X heads.

you can use LA valve covers on magnum heads, I am, and it takes someone to look close and know what he's looking for to realize they aren't stock...

if budget isn't so much of a concern, then add a scat cast stroker crank, scat I beams and diamond dished pistons.

either way, use the stock magnum roller lifters and pick a roller cam in the [Email]220-226@.050[/Email] range (maybe 4-6 degrees more duration for the stroker) and about .530-.550" lift.

there's a dude on here with a mild magnum headed, roller cammed 408 in an orange demon that IIRC gets over 20mpg highway and pulls low 13's in the quarter. IIRC he's using a 700R4 for a tranny.

It's a NOM 340 car; build a stock appearing 360 stroker (because a 360 block is far cheaper) and call it a day.


Dave

The Magnum based thing adds cost quickly unless you find a complete motor to drop in. Cam, lifters, rockers all cost more than LA stuff (most of which I already have). It will mean head work and the whole budget is based on reusing the heads as is.

BTW, just got a call from the machine shop. My 360 block checked out okay, so I'm clear to proceed in that direction if I so choose.

If it's not the original motor, just use the 340 block he has. Other than the block, it's not much different in price to build a 360 LA motor.

I know nuthin bout small blocks but I did take a ride in a 416 stroker that was in a dart and that thing was BAD!

Only you can decide what's best for you. Stroking a 360 would give you the most bang for your buck. That said, I LOVE 340's and have no problem beating the ever loving crap out of mine (sorry resto guys). (psst...big block guys hate getting beat by small blocks.)

Find a 340 T/A block & build a 418. My friend's T/A is a beast, even w/ 3.23 gears. I think the T/A block is a little stronger than the regular 340?

340 block I have is junk. Back corner is broken off from the transmission dowel down.

360 block I have is good. STD bore it'll clean up at 30. Paid $75 for a complete (but seized) short block. Probably could have got it for 50. Point being, 360s are dirt cheap.

340 STD blocks cost $300 and up when you can find them. I've seen 30 over blocks advertised for $400.

340 T/A block... good luck. One of those would probably cost more than my entire short block budget.

So starting with the 360 block, I'm over $200 ahead. Most hardware will transfer off the 340 I've got. Will need a new pan though.

Just to be clear, while cost isn't a deciding factor in this debate, I'm very much restricted to a limited budget.

if you wanna keep the existing top end, just use your 360 or 340 block and keep it stock stroke, etc.....that would at least maintain a reasonable budget.
if you want cost effective stroker, use your 360 block, get a BPE stroker crank and pistons and go from there....then, as you predicted, the $$$ will begin to snowball because everything you don't spend money on will become a psychological bottleneck once you begin piecing the motor together.
hmmm, the more i think about it:
zero deck it, shoot for desired quench, stroke the 360, spring for some closed chamber heads and build the thing to run on 87 octane.....

Id build a 360 and spend the money on gofast goodies verses all the machine work for a stroker.
let the 340 numbers guy keep their high priced block under the work bench.

(1) 360 block (your 340 is hurt) (2)4" crank (what ever level you can afford) (3) Assuming you wanted to keep the J heads so home port the hell of them and mill the recesses to equalize the depths. (4) Get KB hyper pistons & machine for QUENCH (.040") along w the static CR to match your (5) octane and (6) cam choice. (7) Keep the intake/carb (8) rejet/springs the thermoquad