Ok this might be a stupid question I recently read in a power block online magazine that the 318-360 Mopars used the same stroke and bore and got the different displacements by changing the height of the pistons ( no clue what thats means I think they mean the wrist pin). Anyone know what the hell this all means? also i have a 318 that if thats all true i want to put a set of 340 or 360 pistons into it, so if theres any one that has ever tried it I appreciate your input.
Wrong. 318 bore and stroke is 3.91 x 3.31. 340 bore and stroke is 4.04 x 3.31. 360 bore and stroke is 4 x 3.58.
And if your feeling really peppy, 4.03" bore 4" stroke will give you a 408. (Stroker crank in a .030" over 360 block) From expierence I can tell you, they are torque monsters! Changing pistons without changing the bore and stroke will really only affect your compression ratio, theyre still going up and down the same ammount, in a hole of the same size. Volume displaced wont change one bit. It will only be compressed more or less.
"Torque Monsters" is an under statement .The 408 in my Dart is a freaking animal to be a 10 to 1 ,hyd. cam , motor .Someone hit the nail on the head when they came up with the idea to make a stroker crank for these LA motors ...
273/318/340 have the same stroke. 360s are scarce in Australia so they cut the mains on a 360 crank & put em in 318s to get 349s.
Yes you can but when the stroke is a great as or greater than the bore the engine develops different charcteristics. Ideally when stoke is 90% of bore everything works the best. that is where i like to be . Piston speed is lower in feet per second so engine has a bit more safety factor. HP is not much different as the heads really control that. Besides I was doing these before Mopar made the 4 inch stroke. In fact i was receiving a verbal whipping (behind my back)From R E of Mopar Action right at the very week the 4 inch cranks were introduced. Mopar also at that time intro-ed a small main journal 3.58 stroke crank. We were reworking a stock 360 crank and then offest grinding the rod journals 020 to get the 3.6 stroke. There we were ahead of the curve again. I have one of the first ones done still. Don
used 340 pistons in a 360 machined cylinder heads for clearance because the deck height is +.?? lots of compression pulled big time out of the corner.
Sounds like some Mopar knowlageble folks her. I've got a question regaurding the intake and heads on a 273. I've got a '64 Barracuda with a cracked head. I know that the intakes and heads are uniqe to this engine. Are the later parts interchangeable with this short block? Am I reading right, the difference between the two is the angle of the intake mating surface, or the angle of the intake mounting bolts? Most info I've found is vauge on this. I would like to know what would be my best course of action short of replacing the whole engine.
I don't know a whole lot about the early 273's, but I'll just about guarantee somebody over at www.forabodiesonly.com would know the answer. I do believe that you can bolt on the top end from a 318/340/360 though.
Big time torque monster. My 360 is .060" with 4" stroke (414") mediocre heads, intake, 30 year old design juice cam put out over 500 lb/ft on the first pull before we even ran the timing loop. got another 20 lb/ft out of it through some tuning. torque peaked at 3800 and graph was flat as western kansas
Yeh, this is OT, but here it is anyway. Overbored a 300 Ford six - shaved .060 off the tops of six used 340 pistons - honed the pin end of the Ford rods to fit the Dodge pins. Put it all together with a stock cam (that was a mistake - it really needed a cam with a bunch more overlap to soften the increase in compression). Best cold starting engine I ever owned, BUT once it warmed up, 92 octane gas even with 108 boost could not keep the "rattles" away. Why? Why did the bear go over the mountain? Here is a Mopar question: has anyone made a 340 out of a 360 by installing a 318 truck crank (using main bearing spacers) and stock bore 340 pistons in a .040" overbore?
------------------------------------- Wrong. Displacement is determined *solely* by the bore and stroke. You can't change displacement simply by altering rod length, piston height, block deck height. etc. And just for information, regarding small block Mopars, the bore and stoke for the four LA- block sizes are as follows: 273 - 3.63 bore X 3.31 stroke 318 - 3.91 bore X 331 stroke 340 - 4.04 bore X 3.31 stroke 360 - 4.00 bore X 3.58 stroke As far as boring and.or swapping stock pistons and cranks a**** these four "similar but different" engines to create different sizes, there's not much that would be reasonably do-able or practical ,at least on a common mans budget!, First, even though the 273, 318 and 340 use a conmon crank with a 3.31 inch stroke, you can't bore bore a 273 out to create a 318, nor can you bore a 318 out to create a 340.. There's simply not enough meat in the cylinder walls for this.The only real swap possibility at all here to build a bigger engine, using even semi-stock parts would be to *possibly* turn down the bigger main journals of the 3.58 stroke 360 crank to a 273-318-340 journal size and install that crank into one of these engines. But then you'd need high-dollar custom pin-height pistons and/or custom length rods to make it work Plus the 360 crank was only available in cast iron, (3.31 stroke cranks came in both cast iron and steel) so. cutting the journals down to the smaller 3.31 crank journal size would likely weaken it excessively. In the end you'd get very little gain for a lot of money in custom parts and machine work, when you could simply build a 360 with common 'off-the-t******lf replacement parts. Mart3406 ============================
If it's doable some one probably has, but little demand for destroked 360s. On the 300 you obviuosly upped the compression w/o putting in a cam matched to the higher mech comp ratio, or you have some sharp edges on the pistons causing hot spots.
------------------------ I'm not sure why you'd bother messing with custom bearing spacers and the like, just to end up with 20 fewer cubic inches. Destroking does not make a more powerful engine. It may result in an engine than can theoretlcly rev higher , but as long as the bore size remains the same, you merely end up with an engine that has to rev higher, just to make the same power as an otherwise identcly built, larger displacement, longer stroke engine. Unless you're building a race engine for a cl*** that limits engine size to a particular displacement and destroking is the only way to get down to that size, I don't see any purpose in building a destroker, just to lose 20 cubic inches. Mart3406 ===============================
Your least cost option may be to replace the damaged head. Try these guys: www.wildcatmopars.com That being said, you can probably find a complete 360 for the same money. .
The early 273 did use 2 types of heads. You are correct on the manifold angle, but they also used 5/16 manifold bolts. You can use the later heads, you just have to match the manifold. Ran into this with a 66 273 years ago.
In response to George, all sharp edges on the pistons were deburred. The only reason for doing the 340 dodge piston into a 300 Ford 6 was to satisfy the curiosity of "what if?" BTW, I've also adapted 389 Pontiac pistons to the 300 Ford but it was in a racing engine. I've also built up a 300 running 390 Ford V8 flat tops on .050" overbore - it's waiting for a car to put it in and time from me to do the project. For Mart3406, there are reasons why some would like a 340 under the hood! The main bearing spacers are $300 - expensive, but so are 340 blocks if you can find a rebuildable. Is big torque and horsepower everything there is in this automotive hobby we on the HAMB all enjoy? Not in every case. Different strokes for different folks......uh, 'nuf said.
As an owner of a stroker 408 im a little biased ,but that still doesnt change the facts.If you want to build a small block Mopar that will make big power and live along time ,build a stroker.Sure a little motor can make big power ,but it will lack the lowend grunt out of the hole over the stroker 408 -414.The stroker will make great power at or below 6000 rpm and allow it to last longer than the smaller motor spinning high to make the same .The way it is now ,it doesnt cost much more to buy a '4 stroker crank kit than to build the smaller 340 - 360 with new stuff ,so why do it ? This is true on any make not just the LA motors . "Theres no replacement for displacement" ...
the early 273 heads were closed chamber heads with different angles for the intake bolts. you can swap the '67 up 318 heads and intake, but will lose some compression because the 318 heads are open chamber.
The 302 casting 318 heads(late 80's) are a popular choice. I have them on my 273. Going with later model heads gives you more intake options if you want to go with an aluminum intake. You can even use magnum heads, but the intake options are somewhat limited there.You can shave the heads to bring back the compression, just make sure they do both the block sides and the intake sides. You will have to cap of the smog ports on the 302's, but that is a simple fix.
The '64-65 273 heads/manifold are unique in the manifold to head mounting bolts, being nearly vertical. As stated above, you can use '68/up 318 heads, but they are open chamber and you will loose compression and power. The '66/67 273 heads are still closed chamber heads, but with the 90' intake manifold bolt configuration to all other LA engines. Also as stated above, the '302 castings are a very viable option, also closed chamber, and stock flow just a little better than the 273 heads. With either of these heads, you have more intake options than just the little flat single plane intake (2bbl or 4bbl) that is on your early 273. The two that most quiclky come to mind aree the Edelbrock RPM (273/318 sized ports, not the Performer RPM) and the RPM Air Gap, though many more current and older options out there. The best stock small block head is the '92/up Magnum head, BUT with anything larger than the 1.78" intake valve common to the 273/318, you WILL NEED to notch the cylinder bore. (360's had 1.88", 340's had 2.02" and 1.88" and Magnums had 1.92" intake valves.) On the other hand, the stock 318 bore will accomodate all these valve sizes. Some time back, Steve Dulchic built a 318 with 302 heads ported to 340/360 intake port sizes, with Edelbrock RPM Performer intake, etc... and made over 400hp. Last item is the stock iron Magnum heads actually outflow stock Chevy LS1 heads. Hope it helps, Mike Bynum
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