The forums name is for A bodies. The forum this thread is in is "Small Block Mopar Engine" which is what we are talking about. If you don't like the 318 discussion here you are free to check out a 340 thread.Well rename it the 318 slant 6 forum then
Yeah I'm good my mistake is and has always been getting involved in discussions here. Ill just stick with the classifieds LOL!
I've never measured "down in the hole" height, but my favorite combination is a 1968 or 1969 shortblock, which had an advertised CR of 9.25:1 with open chamber heads, floating pins, and lighter weight rods than 71 up teens. Add a pair of the 302 casting heads, or a pair of 1967 273 or 318 heads, either one is closed chamber, although the 67s are a few CCs smaller chamber. Port match the heads to as close to a 340 intake gasket as prudently possible, blending in about an inch and a half. Put a cam that is reasonable for the car weight, gearing, and intended use in it. Top it with a decent intake and either 68 to 70 340 manifolds, 95 and up Magnum manifolds, or a set of headers. The 95 and later Magnum manifolds are slightly larger than the earlier Magnum manifolds, and have larger outlets. Timing might need to be conservative for 89 octane, but dialing in the amount and rate of both vacuum and mechanical advance will get you there. These engines really wake up with some compression, more so in my opinion than flow. We put together a similar combination for a friend's 86 M body Gran Fury. This friend had owned more than a dozen 340 A bodies over the years, and his exact words were "that damn thing is amazing! It runs as strong as any 340 car I've ever owned"
All he likes to do is troll, start 318 strawman arguments and if there's no active 318 thread he'll dig some up lol, then play victim when people argue back.
I've got a 318 with Enginetech pistons that measured 10 thou down after the block came to me heavily decked. Compression height for those pistons is 1.741 so if you calculate the distance with with the piston(1.741), rod(6.123) and crank stroke (3.31/2= 1.655) you get 9.519. If you go by Chrysler stated Deck height of 9.600 that leaves you with anywhere between 0 and .080 distance you could have. Measure twice and cut once as the saying goes if you want to know and be accurate. Pull the heads measure and just sit them back on.
Yeah but I have few different manifolds I can put on so I managed to find one to fit (portosonic) but the heads have been milled a bit to get from memory about 58 to 60 cc from the 302 closed chamber heads.
I made it a more accurate representation of you.
The best thing You can do is warm it up then do a cranking compression test. Fresh battery w/a charger hooked up, all plugs out, throttle held wide open, ign. disabled.
I measured mine last week, it was almost .060 in the hole which would be in the ballpark of what your book says. My engine was made in mid or so of 1972, BUT, I do have stockish replacement .030 over pistons.
By 72 emissions were kicking in and the CRs dropped into the outhouse basement. Between either dish pistons or 0.040" to 0.100" down and combined with open chamber heads the combustion was terrible and prone to detonation. Best bet would be figure new pistons to zero deck it with modern rings with 1.2mm width. This reduces friction. You want pistons with 2 valve reliefs not 4 and flat top. Also plan on in the future getting heads like the Edelbrock closed chamber for good quench which is high mixture motion. Good for efficient combustion.
Yup. More than one way to skin the cat.
Well, sorta. While it is true that compression dropped, it's also true that horse power ratings changed from gross to net. So that makes it appear that engines lost a ton of power from 72 onward, when in fact, they did not. That'a always a part of the equation people sometimes forget. With all else aqual, a 10:1 engine for example, will make only about 6% more power than an 8:1 engine. Compression alone isn't the end all be all a lot of people think it is.
One thing to remember is that factory ratings were just that, ratings. Not actual measurements. 68 and 69 318s have an advertised 230 horsepower, and an advertised 9.25 ratio with open chamber heads. A 70 318 is still advertised as 230 horsepower, with an advertised 8.8 ratio. A 71 318 still advertised 230 horses, but ratio is now 8.6. So the math says half a point less compression, at a theoretical 3 percent per point, should be a minimum of four less horsepower.
Very true Rusty. The open chamber heads did have more tendency to detonation. Other factors in the emissions systems of the day caused drivability issues. The eengineers were having fits trying to figure out how to lower all the pollutants and be able to have reasonable drivability. The VW diesel emissions scandal is just another phase of the same thing. People that had their VW diesels reprogrammed to be emissions compliant all cocomplain power and fuel economy went down the outhouse hole. I used to wonder when you would end up following one of those cars, how they possibly met emissions. As a licensed automotive and heavy duty mechanic my nose said they did not. Nose was right.
There could be a number of other factors involved that the factories could have used beside fudging the numbers. Camshaft profiles could be one. Lower intake lift but longer duration is one I found in the TRW cam catalogue. This applied to Mopar, Chev and Ford bread and butter engines of the day. That was 30 years ago I found that, so it may be difficult to track down now.
