When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Just spitballing here.
I'm putting together a 360 for a guy with a custom-built vehicle and it's not ever going to do any work or pull anything. For what it's going to do, I can't justify wasting a good 390 crank and set of rods on it..... but I am also having a hard time convincing myself that a standard rebuild of a 360 would be very much fun.
The block is in good shape, but not .010" overbore good shape. 352s run a lot better than 360s given that the piston comes a bit closer than .100" to the deck like a 360 but finding .070" or .080" -over 352 pistons ain't happening.
Humor me, if you will.......
Certain Dodge 340 pistons in a .040" size will allow me a .030" overbore (4.080") on the block and get me a .050" deck clearance with a 1.830" compression height on a standard 10.17 deck height block (.015" higher than even a standard 352 piston). The wrist pins in the 340s are floating just like an FE but are slightly bigger and would be compensated with just .009" more rod bushing honing (.984" vs the FE's .975")
The valve reliefs look darn similar on some of the offerings too. Just changing the deck clearance on a simple calculator with all else being the same yeilds a difference in compression ratio of 0.8:1 doing this (7.79 to 8.5).
Wow....I damn near plagiarized your posts word for word. I should have searched first.
I see nothing wrong with trying. The piston prices aren't too out of line of the 360 pistons. I will talkto the guy tomorrow and see if he's game for trying something unique. The only added cost would be balancing. The rods are already getting new bushings and the block is already being bored. I just worry that the 340 pistons might be too heavy.....and adding weight to a crankshaft is $$$.
The reason for not going to a 390 is that this is a <3000 lb. "buggy" and it won't be used for anything but bombing around gravel roads. I'm not wasting any of my good 390 parts on it.
I got the "ok" from the customer. He's down to try something different. I think the only thing that might make this not happen is piston weight. If the 340 pistons weigh much more than the 360 pistons (not able to shave enough metal off of them to make them similar in weight), I'm not paying the balancer for heavy metal in the crankshaft.
"That thing got a Hemi?" Nope, just some Durrrrge pistons.
340 pistons came in. Some preliminary math says that:
1. 340 piston weight is 27 grams heavier than 360 piston. Going to use a 352 crankshaft as those counterweights have less weight removed as 352 pistons are 50g heavier than 360 pistons. This gives more material to be removed (or don't have to try to add to the 360 crank...expensive).
2. Piston skirts clear crank counterweights.
3. Decking block and heads .010" will give 0.012" deck clearance. Math says that's 1/8th of the deck clearance of the 360.
4. Wrist pin bores on rods are 1.040" and there is plenty of material to open up the bushings an extra .009".
Already pulled a C4AE-something 352 crank out of another engine to compare to the 70's 360 crank. There were a couple of extra drill holes in the 360 crank that the 352 crank didn't have so I'll use the 352 crank as there's more material to remove (if need be) for the slightly heavier pistons.
The weight of the piston matters 1/2 as much as mass that's rotating. I don't know what the typical variability on the rods is in a 352 or 360 but from set to set it wouldn't surprise me to see 30-50 grams of total difference so that in itself could swamp out any real difference caused by using a piston that's a little heavier or lighter. The amount of weight that is available to remove from the crank is pretty much impossible to tell by looking at the existing holes in the counter weights. Cranks vary a lot when it comes to where their weight is distributed with some having throws or counterweights which are heavier or lighter.
Many times when I'm working on a balancing job and I have to add a little weight say 15 - 20 grams I'll just weld inside of one of the existing holes. It isn't a big deal and it doesn't add to the cost.
Got the call from the machine shop today so I picked up the heads, block, crank, and rods. Plenty of meat in the wrist pin bushings so I'm not worried at all.
I'll get the crank bearings ordered (10/20) and get the stuff off to the balancing joint! Then I have to figure out a cam to use once I get final numbers on deck clearance.
I got the rotating and reciprocating parts back today.
The pistons sit .028" in the hole while the 360 pistons are now at .112 " after decking so I lost .084" of wasted space for combustion. It's not super-tight, but it's way better for the same money spent!
If a 390 4V is any indication, the valve reliefs in these pistons is a bit overkill. I'm twice the deck clearance than the 390 and the reliefs are bigger with these. I probably could have gotten away with flat tops since I'm running a stock cam.....but I couldn't find any.
352 pistons have shallow reliefs and about .012" less deck height and they do ok with certain cams in the .512"-.533" lift range.
If a 390 4V is any indication, the valve reliefs in these pistons is a bit overkill. I'm twice the deck clearance than the 390 and the reliefs are bigger with these. I probably could have gotten away with flat tops since I'm running a stock cam.....but I couldn't find any.
352 pistons have shallow reliefs and about .012" less deck height and they do ok with certain cams in the .512"-.533" lift range.
With a stock cam it might have been ok with no relief because the duration is short. Keep in mind that duration is what uses up the relief and peak lift isn't really a factor.
With a stock cam it might have been ok with no relief because the duration is short. Keep in mind that duration is what uses up the relief and peak lift isn't really a factor.
There's so little duration that I stuffed the cam in there at 4 degrees advanced to close the intake sooner and keep the pressure in the cylinder and I STILL have a metric ton of piston-to-valve clearance. I'm not surprised though. Gonna say I will have no issues with this engine other than sounding like a derby car due to the stock cam.
It's together short of tin. It should be on the run stand by early afternoon.
Got it on the run stand yesterday and had the break-in done by noon. Runs good albeit "sounding stock" since it's the first one in a while with a stock camshaft . Before taking it back off I thought I'd do a compression test....just for poops and laughs. A healthy stock 360 at this elevation (almost 5000 feet) will put up between 85-95 PSI with all plugs in (so not really cranking blisteringly fast) and this one, lukewarm, with all plugs in and 30 minutes of total runtime was at 135 PSI. Gonna call it a win.
Rezvani's Latest Post-Apocalytic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.
