Exactly. That's why I always use the .500 down method. Much more accurate. I've preached it for years but been ignored. So pluck um. lol
340 improvements with dyno numbers
- Thread starter canyncarvr
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Exactly. That's why I always use the .500 down method. Much more accurate. I've preached it for years but been ignored. So pluck um. lol
yellow rose
Overnight Sensation
Yep, whenever I see the statement "I have [compression ratio] with an ISH at the end of it I then KNOW they have NO idea what the CR really is. Example: I have 10:1ish compression.
I don't deal with ish very well. It's simple math. If you are paying for an engine assembly the guy better damn well give you an exact CR and SHOW THE MATH.
But then again, I charge 1K to do the assembly and that's not making hourly. Damn glad I'm retired.
Lustle
Well-Known Member
I've never had the luck to find an original 340. So I've never speced them myself. I've always heard they were 10-10.5 with the pop up pistons. Changing in 1972 to the lower compression. Then again you could probably pull two different motors made on two different days and come up with a different compression ratio. I don't think things were as "exact" back then.
In either case. Building an engine with 9.25:1 compression then putting aluminum heads on it is a waste of time in my books. I figured someone would jump on me saying its 8.25. Yes, its "9.25" with aluminum heads. You don't lose actual compression. I'm saying an aluminum headed engine essentially "acts" like it has 1 less point of compression than an iron engine. It doesn't build the heat like the iron headed engine does. That's the best I can explain it. And I never said dart heads weren't far superior. I'm saying superior depends on your application.
You can put lipstick on a pig, it's still a pig.
In either case. Building an engine with 9.25:1 compression then putting aluminum heads on it is a waste of time in my books. I figured someone would jump on me saying its 8.25. Yes, its "9.25" with aluminum heads. You don't lose actual compression. I'm saying an aluminum headed engine essentially "acts" like it has 1 less point of compression than an iron engine. It doesn't build the heat like the iron headed engine does. That's the best I can explain it. And I never said dart heads weren't far superior. I'm saying superior depends on your application.
You can put lipstick on a pig, it's still a pig.
And both of the magazine engines a have lots of lipstick on them. 
I wish aluminum heads "acted" like they had 1 point less compression. My 10.75:1 ede headed 360 won't run on pump gas to save it's life.
Most 68-71 340's were lucky to have 9.7:1 static compression.
I wish aluminum heads "acted" like they had 1 point less compression. My 10.75:1 ede headed 360 won't run on pump gas to save it's life.
Most 68-71 340's were lucky to have 9.7:1 static compression.
Lustle
Well-Known Member
And both of the magazine engines a have lots of lipstick on them.
I just don't see it man! Haha my buddy rebuilt a 360. Edelbrock 650. 10:1. Iron heads. XE268H. Fairly similar to this magazine. And he made a 385 horse and 420 pound feet of torque if I recall (several years ago now). So I believe they are fairly close to the mark. Although another dyno may disagree completely. That and I have a tendency to wanna trust Dulcich. Guy has been around in the mopar world for years.
ir3333
Well-Known Member
Didn't Dulcich add a cam,intake and headers to a 335 hp 383 and pick up 147 hp?
yellow rose
Overnight Sensation
You keep saying "pop up" piston but they were ALL flat tops. All of them. Just be cause the piston is out of the bore, doesn't make it a pop up. I love the 60's and 70's as much as th next guy but damn, we have got to clean up the lexicon. It took decades to kill off the 3/4 race cam crap and it still hear it now and then.
They all had flat top pistons.
yellow rose
Overnight Sensation
And both of the magazine engines a have lots of lipstick on them.
I wish aluminum heads "acted" like they had 1 point less compression. My 10.75:1 ede headed 360 won't run on pump gas to save it's life.
Most 68-71 340's were lucky to have 9.7:1 static compression.
You must have something else wrong. I run 11:1 on CI on pump gas. Need some quench and anything but an off the shelf cam.
Bummer.
How about the 600+ hp procharger SB engine that MPH'd a mighty 118 in a 3500 pound car? LOL Yep that's it. There is a reason a bunch of these builds never end up in a car. If your buddies engine had even basic bowl clean up, then that's a reasonable number. A XE268 is about a .9-1hp per ci camashaft in a stock headed SB mopar.
I dealt with two engines from that time frame that came off that dyno and made 10-18% less power on another dyno the next day! Neither ran numbers in the car like the higher dyno would indicate they should. IIRC, there was a mea culpa somewhere about the issue later on regarding the "numbers".
It's got a fairly short camshaft in it. Makes pretty good power, just not happy on pump swill. If it was 245+ at 50 it would be ok.
Lustle
Well-Known Member
I never said they didn't. Pop up as in they "pop up" out of the hole because they did. Dome pistons are dome pistons. Dish pistons are dish pistons. Flat top are flat top. And they can all pop up out of the hole.
I don't believe every magazine article of course. Like I mentioned the episode of horsepower tv lol. But I think they are fairly close on with this one. I'm surprised you can't get that engine to run on pump gas. I run 10:1 on iron heads and have no trouble. You mention it's got a short cam, whats the cam specs? With aluminum heads you should shoot for 8.5 DCR. Depending on gas available, elevation, etc etc. of course.
yellow rose
Overnight Sensation
Did you ACTUALLY measure your compression ratio? Did you do a .500 down fill, cc the heads and do the math? If not, you don't know what your CR is.
I hate to be the prick, but just because the piston comes out of the bore doesn't mean it's a pop up. By no stretch of th imagination they ALL had FLAT TOP Pistons. There ain't a swinging Richard in the piston industry that calls a FLAT TOP piston a pop up. No F'ing way. I'm anal about this because this is just another reason how and why guys get jacked up with things. We all need to use the same vernacular or we might as well be speaking different languages. FLAT TOP PISTON was OE in EVERY 340. I've never seen a factory 340 out of the hole that I can remember. In fact, the prick engine builder I used in high school would NOT deck my block on my first rebuild to get the piston out of the hole. That prick is why I became an engine builder. They ain't all chevies.
Lustle
Well-Known Member
I didn't. Engine builder did. Decked pistons, CC'd heads, etc etc, the whole 9 yards. If you want specifics it's actually 10.05:1 static, 7.54 (I think, going off memory) dynamic. It's not a guess. its a known.
As for pop up. That's just what I call it when a piston leaves the hole. Which is why any dome/dish/flat can "pop-up" out of the hole. As far as I understand it. Early 340 pistons leave the hole. That's why you have to watch aftermarket heads and cams and etc on them. For contact. But as I said. I've never had the luxury of actually pulling one apart and speccing it.
It ain't JUST simple math. It's grammar school math. LOL If ya caint do that, then it might be better to take up another hobby. LMAO.
Lustle
Well-Known Member
But don't yah know rusty! They don't teach math in school no more! You won't need it. There's a calculator in every pocket these days!
Lustle
Well-Known Member
Not to get more off track. Just imagine what would happen if all the personal electronics went down tomorrow? No smart phones. No personal computers. No touch screen in your car. Cars with computers still run. But none of the fancy add ons. All those people who wouldn't know where to turn right next without their phone telling them to. Or having to read a book to find something out instead of googling it. Oh what would the world do!
Me? I'd grab a beer and laugh.
Me? I'd grab a beer and laugh.
yellow rose
Overnight Sensation
If that happened I'd be so happy...id be happier than a pig in poo.
67autocross
A new iron curtain drawn across the 49th parallel
Did almost the same build in the mid 90's , made 344 hp I still have the dyno sheet.
Duster3406pck
Member
If anyone was wondering I read an article about the x heads they used if I remember right they flowed 215 cfm
perfacar
Well-Known Member
hi, actually the 72 -73 340, being blueprinted, are 9.32 cr. factory was rated 8.5 cr. do the math.
I have. They always blueprint well below their spec. YOU do the math. I have on several original engines.
The problem is, Chrysler left the deck heights VERY tall. That is the main problem.
Marcohotrod
Well-Known Member
I hope one day I win the lottery so I can test all these rag builds. Just for fun of course!
Lustle
Well-Known Member
This. I would build all the engines and combos you read about. Get actual numbers. Independent test. I would open an engine shop and just build quality engines with known good combos and help guys make power.
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