you need to re-read my #9 post. its all about the combination. leave out one ingredient and your motor will not perform well at all.
13:1 Compression Pistons in 340 Small Block
- Thread starter DodgeMoparV2
- Start date
-
Oldiron440
Well-Known Member
This, "excellent flowing heads" is very true I built a 292 cube W Ford for a project of mine with 200cc heads a large head for the little motor, you would think a 175 is what would work. A 248 @ .050 street cam and 600 dp, 445 tq 455 hp. There plenty of big blocks that can't post those numbers.
nm9stheham
Well-Known Member
Very good point on the e85... I'd put e85 and 12.5 SCR roughly on par with 93 gas and 10 SCR.
The e85 idea ought to tempered with the OP's availability. Not as hard to find around bigger cities, along interstates and in the cornbelt. Not the case here, I have 1 station within a 30 mile radius and 5 stations within a 70 mile radius. It goes to 0 stations if you head west into the mountains of VA and WV. And in the Rockies, it is 100-200 between stations in most areas. Not a good choice for a higher consumption rate fuel and a not-great-fuel-mileage engine to start with.
I dunno exactly where in OH the OP lives to see; in the southern part of OH, e85 availability looks darned poor.
The e85 idea ought to tempered with the OP's availability. Not as hard to find around bigger cities, along interstates and in the cornbelt. Not the case here, I have 1 station within a 30 mile radius and 5 stations within a 70 mile radius. It goes to 0 stations if you head west into the mountains of VA and WV. And in the Rockies, it is 100-200 between stations in most areas. Not a good choice for a higher consumption rate fuel and a not-great-fuel-mileage engine to start with.
I dunno exactly where in OH the OP lives to see; in the southern part of OH, e85 availability looks darned poor.
Oldiron440
Well-Known Member
One more thing on e85,
I had the opportunity to run my 12.5 440 on race gas for the camshaft break in and we made four pulls setting up timing and carb then we switched the carb and fuel to e85. What we saw was the peak numbers go up 18 tq and 15 hp that was expected but the torque down low went up 20 ftlb.
I had the opportunity to run my 12.5 440 on race gas for the camshaft break in and we made four pulls setting up timing and carb then we switched the carb and fuel to e85. What we saw was the peak numbers go up 18 tq and 15 hp that was expected but the torque down low went up 20 ftlb.
I agree. And want to reiterate the point that availability of E-85 in the midwest (corn country.) Is decent. May not be true everywhere around the country. And on a final note. Exhaust will smell different. I think it smells a little like french fries mixed with petro. And fuel efficiency certainly falls. I'm not sure how much at WOT. But could be as high as 40%. You get less BTU of energy from alcohol than gas. But you can compress alcohol alot farther before auto detention.
I love listening to the younger "Tuner" kids speak that higher octane and race gas increases power in and of itself. It doesn't. In fact it produces a little less energy. But higher octane can be compressed more than low. So in the end? You want to use the lowest octane fuel your build will accept before detonation issues occur.
Sell these pistons to somebody building a drag race engine and buy the proper ones for your needs.
Best answer yet! A set of lightweight pistons and a longer stroke crank (3.58-3.79 with J heads) makes a whole lot more sense and will live a whole lot longer. It will also do it without making you have to grab your ankles and smile in maintenance and fuel costs. The overkill street builds are fun for a while but are pretty useless as any kind of driver. It will grow old quickly and you’ll be looking to detune it to make more of a driver out of it. Seen it many times.
agreed. those pistons must weigh 850 to 1000 grams each, so old school. there are better ways to get high compression. sell them to a museum. get that 3.79 stroker crank and some flyweight pistons with the pin height so high they look like a super model waif.
and get rid of those j heads. Aluminum heads already have hardened seats and you don't have to worry about detonation as much. or if you want to worry about it get a set of 308's.
Last edited:
yellow rose
Overnight Sensation
The OP didn't want a Stroker. You guys can spend money for nothing right quick.
Bob weight is overrated. By a long ways. He can get a different piston, but it will be hell to get quench. I'd have to pull my bob weight card, but I don't think my Pistons were anywhere near 850 grams.
The point is...the OP has the Pistons. There is nothing wrong with them. In fact, I can make the argument that he may be going backwards buying a newer piston. Especially if that new piston isn't designed to come out of the deck.
Old doesn't mean bad. New doesn't mean good.
yellow rose
Overnight Sensation
Well, no argument about those pistons for an all out race engine. But most people tire of a 13 to 1 all out race engine on the street fairly quickly. However, I'm not saying I wouldn't enjoy this kind of a build way too much myself! When the fuel is race gas or your burning 40 percent plus more e85 than you would gasoline, things become costly quickly, hence a pump gas build is cheaper to operate long term. I mentioned maintenance but I was thinking more of breakage. But if you get the domes milled for a reasonable compression ratio and maintain quench, nothing wrong with them in a street build if they measure out okay.
To the OP, I would take a step back and decide on a clear goal for the car (horse power number or ET goal, or drivability goal). From what I've read, it sounds like you want to use the domed "13:1" pistons, want 8mpg or better, want to beat on big blocks, want to use J heads....These goals don't really go together. Those heads won't support big power (no big block killer), those pistons belong with fully ported aftermarket heads (no J heads), and 8mpg won't happen if you have the engine make big power (generally, the bigger the power, the lower the mpg)...does that make sense?
If your goal is a fast street/strip car, just remember it takes way more work (and $$$) to make a car walk that thin line of race and street.
If your goal is a fast street/strip car, just remember it takes way more work (and $$$) to make a car walk that thin line of race and street.
yellow rose
Overnight Sensation
I don't think anyone told the OP to use them as 13:1 Pistons. I'm saying use them as 11:1 Pistons. Done correctly, he can do that on pump gas, get .040 quench and have a very low dome. Then the piston will be lighter, he won't be through the roof on compression and he can use what he has.
BTW, to get 13:1 out of those Pistons isn't easy. They still have to be out of the deck .040-.050 to do it.
Can't tell you how many engines came through the shop that were some claimed compression ratio and when it came apart, it wasn't even close.
Especially the MoPar stuff with open chamber heads and a zero deck. Even with the piston out .017 like some books call for, you are nowhere near the claimed CR.
yellow rose
Overnight Sensation
Depends on the shop, but it takes about an hour to do it. So whatever the hourly rate is.
my last post guaranteed, yeaaaaaa!!!!!!!!!!
money for nothing and the chicks for free. any money spent on the combination of his current direction is a waste.
the idea for a stroker crank is a light piston with a reduced pin height. bob weight is NOT overrated. ok I exaggerated a bit there on piston weight but they are heavy.
hell to get quench? with those j heads for sure. like I said GET RID OF THEM duh.
and while old school is cool and nostalgic, new technology wins races at the track and on the street. it produces more enjoyable power on the street and new cars are proof of that.
Oldiron440
Well-Known Member
If you bracket racing it doesn't matter if you have a 400 hp LS or a 400 hp LA motor you can win or lose with either. New technology doesn't have a thing to do with it.
furrystump
Well-Known Member
- Joined
- Nov 13, 2004
- Messages
- 2,083
- Reaction score
- 1,688
The question that needs to be answered is, is this a user friendly tried and true recipe for a person with somewhat limited experience? Lets get comfortable working inside the box before we go thinking outside it. Outside the box is where money goes to die!
beanhead
Well-Known Member
Intake valve closing point is what bleeds off compression, not overlap. Keep that in mind if you do use these pistons, when spec'ing out your camshaft. And, as Rumblefish pointed out somewhere along the way, once RPMs get going the pressure builds again anyway..things to consider. If you do build for 13-1, post up a video with good sound quality!
James Clews
Well-Known Member
I would run them but I am a tight arse that does not like waste.I rqan a set of these in the mid seventies that I took to a machinist and said here is a set of 10 to ones and these are 13.1s so just shave about two thirds of the dome off and we will be right to go. They ran real good in my little 340 and would rev to 7500. do not know what compression ratio they were but they did not detonate on the fuel of the day.
Wyrmrider
Well-Known Member
I have no problems with those pistons
as YR said
not at 13:1
Will NOT work with aftermarket closed chamber heads without even more work
and I'd check with clearance with more modern than X-J combustion chambers
They are heavy so not for a high rpm build today
(back then High RPM is not what it is today)
as said theheads limit power so no reason to shoot for high compression
As YR says you have to build for some quench on the back side of the chamber (OUT OF THE DECK) and cut/ mill the domes for whatever compression you want
as YR said
not at 13:1
Will NOT work with aftermarket closed chamber heads without even more work
and I'd check with clearance with more modern than X-J combustion chambers
They are heavy so not for a high rpm build today
(back then High RPM is not what it is today)
as said theheads limit power so no reason to shoot for high compression
As YR says you have to build for some quench on the back side of the chamber (OUT OF THE DECK) and cut/ mill the domes for whatever compression you want
Duane
Well-Known Member
I agree with yellow rose. I have a set of those Pistons from years ago. I had mine cut for a little extra valve clearance, but as assembled on a typical 68-70 cc head they only actually came out to 10.9:1 compression. I believe those Pistons were advertised as 13:1
at a chamber volume that is much smaller than the typical x or j or w2 head. One of the things I learned with my new stroker build is that because of the addition swept volume of a stroker crank, it is much easier to get a really high compression ratio without a heavy domed piston. I think the op should assemble one cylinder assembly and do some ccing and see what he actually has for compression.
Bet you it is not a true 13:1. My new 410 build with a 69cc w2 head has 12.7:1
Compression with a .005 out of the hole .100 thou thick flat piston that is a least 200 grams lighter than that trw piston.
Last edited:
Duane
Well-Known Member
The most significant improvement in new cars are, they come standard with high flowing race heads as standard equipment on a stroker engine, with the super charger as an option lol.
MOPAROFFICIAL
Oogliboogli
He could always get a 6-inch belt n wheel sander like Ryan J and just sand his pistons down hahaha
Sorry, couldn't resist.
Seriously , these guys got you on the right track in regards to how to run them.
Sorry, couldn't resist.
Seriously , these guys got you on the right track in regards to how to run them.
-
