piston questions

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volaredon

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I tried piggybacking this onto another 360 magnum build question and basically got crickets... so Im trying a seperate post.
I have a 30-over 360 magnum on a stand. It needs re rebuilt. (don't ask.... a disaster that started with "out of the box" "ready to run" EQ heads that weren't. Thats all I want to say about that)
I was looking at Summits listings for flat top hypereuctic pistons. This engine is being overhauled for a 3/4 ton truck with a 5 speed NV4500 stick. It will not be a high revving engine, it will be a daily driver/ camper hauler. so I want more of a stump puller than a high revver.
In looking at those Summit listings there are 2 pistons listed that appear VERY similar to each other, even as far as price is concerned. Im looking at Speed Pro H116CP-30 vs KB107KTM-30 ("KTM" means its a kit that includes moly rings) Anyway the first question is this; BOTH list fitment for either an LA or Magnum series 360, which cant be right. Bore x stroke wise, yes. but balance wise, no.
Nether lists a weight in the respective engine families. Is either of these balanced suitably out of the box for either an LA or for a Magnum? Or is paying for a balance job basically required either way when these pistons are used? I was looking for weights of stock pistons vs the weights of these and am coming up empty.
I have access to a set of very short term used, (like 6000 miles) of the Speed pro's. they were run for that 6000 miles in a '76 LA block. (then my son decided he wanted a 408)
I have some summit bucks that expire like, tomorrow. I will be needing some other parts for this engine regardless. Im wondering whether to use them for pistons or for the other goodies Im gonna be needing for this build. The "am I absolutely" going to "have to" have the machine shop balance this engine, if I use these pistons? It will effect the choice I make for other parts, such as balancer and flywheel.
 
No way in HADES would I put a cast or hyper piston in a towing and hauling truck motor. Put a bit more with it and get the Icon forged pistons.
 
I don't know for sure, but it's always been my understanding that unless your getting a stock replacement piston a re balance is a good idea.

Required? I guess that's up to you. Lol
 
I consider balancing a requirement. You've already had what? one failure? two?
 
Well, an oversize piston is going to be heavier than stock anyways, so if you're on your second rebuild (and second overbore, I assume? You didn't mention if you were boring it again...) you should really not even question the rebalance.
 
here's my .02 on it: if you use anything besides stock pistons a rebalance is mandatory.

maybe you don't *really* need it, but i'd rather spend that $325 to find out now rather than find out later.

LA and magnum's have different widths on small ends of the rods, the pistons have corresponding pin bosses. with machine work you can make them work but typically LA pistons on mag rods isn't the way to go. so those speed pros aren't the money saving gambit you think they may be.

depending on the set up, i'd probably be okay with a hyper piston. but if you're straying from stock a forged slug is the way to go. icon, dss and wiesco are all in the same-ish ball park. but if i was really going for it and building a bomb proof bottom end mahle powerpak would be my choice.

but as always, budget dictates a lot of choices...
 
volaredon said:
I tried piggybacking this onto another 360 magnum build question and basically got crickets... so Im trying a seperate post.
I have a 30-over 360 magnum on a stand. It needs re rebuilt. (don't ask.... a disaster that started with "out of the box" "ready to run" EQ heads that weren't. Thats all I want to say about that)
I was looking at Summits listings for flat top hypereuctic pistons. This engine is being overhauled for a 3/4 ton truck with a 5 speed NV4500 stick. It will not be a high revving engine, it will be a daily driver/ camper hauler. so I want more of a stump puller than a high revver.
In looking at those Summit listings there are 2 pistons listed that appear VERY similar to each other, even as far as price is concerned. Im looking at Speed Pro H116CP-30 vs KB107KTM-30 ("KTM" means its a kit that includes moly rings) Anyway the first question is this; BOTH list fitment for either an LA or Magnum series 360, which cant be right. Bore x stroke wise, yes. but balance wise, no.
Nether lists a weight in the respective engine families. Is either of these balanced suitably out of the box for either an LA or for a Magnum? Or is paying for a balance job basically required either way when these pistons are used? I was looking for weights of stock pistons vs the weights of these and am coming up empty.
I have access to a set of very short term used, (like 6000 miles) of the Speed pro's. they were run for that 6000 miles in a '76 LA block. (then my son decided he wanted a 408)
I have some summit bucks that expire like, tomorrow. I will be needing some other parts for this engine regardless. Im wondering whether to use them for pistons or for the other goodies Im gonna be needing for this build. The "am I absolutely" going to "have to" have the machine shop balance this engine, if I use these pistons? It will effect the choice I make for other parts, such as balancer and flywheel.
Click to expand...
i just gotta ask...... is this ^^^ the reason for your multiple times posting 318 over a 360 any day? You've shown very little love to the 360... after reading maybe this is your reason?
 
volaredon said:
I tried piggybacking this onto another 360 magnum build question and basically got crickets... so Im trying a seperate post.
I have a 30-over 360 magnum on a stand. It needs re rebuilt. (don't ask.... a disaster that started with "out of the box" "ready to run" EQ heads that weren't. Thats all I want to say about that)
I was looking at Summits listings for flat top hypereuctic pistons. This engine is being overhauled for a 3/4 ton truck with a 5 speed NV4500 stick. It will not be a high revving engine, it will be a daily driver/ camper hauler. so I want more of a stump puller than a high revver.
In looking at those Summit listings there are 2 pistons listed that appear VERY similar to each other, even as far as price is concerned. Im looking at Speed Pro H116CP-30 vs KB107KTM-30 ("KTM" means its a kit that includes moly rings) Anyway the first question is this; BOTH list fitment for either an LA or Magnum series 360, which cant be right. Bore x stroke wise, yes. but balance wise, no.
Nether lists a weight in the respective engine families. Is either of these balanced suitably out of the box for either an LA or for a Magnum? Or is paying for a balance job basically required either way when these pistons are used? I was looking for weights of stock pistons vs the weights of these and am coming up empty.
I have access to a set of very short term used, (like 6000 miles) of the Speed pro's. they were run for that 6000 miles in a '76 LA block. (then my son decided he wanted a 408)
I have some summit bucks that expire like, tomorrow. I will be needing some other parts for this engine regardless. Im wondering whether to use them for pistons or for the other goodies Im gonna be needing for this build. The "am I absolutely" going to "have to" have the machine shop balance this engine, if I use these pistons? It will effect the choice I make for other parts, such as balancer and flywheel.
Click to expand...

Aftermarket pistons tend to be lighter than OEM, at least for LA engines. Magnum pistons are a bit lighter than LA. But factory balance jobs are just "adequate" from the factory to begin with so a proper balance job should be done anyway. Balance at lower rpm isn't quite as critical as at higher rpms but I've always been nit-picky in that respect. Just because you don't feel an imbalance doesn't mean that there isn't one.

Regardless of what type of piston you go with, follow manufacturers recommendations for ring gaps & piston to wall clearance. It's better to have a little too much clearance than be a little too tight, especially with hypereutectic pistons.
 
volaredon said:
I tried piggybacking this onto another 360 magnum build question and basically got crickets... so Im trying a seperate post.
I have a 30-over 360 magnum on a stand. It needs re rebuilt. (don't ask.... a disaster that started with "out of the box" "ready to run" EQ heads that weren't. Thats all I want to say about that)
I was looking at Summits listings for flat top hypereuctic pistons. This engine is being overhauled for a 3/4 ton truck with a 5 speed NV4500 stick. It will not be a high revving engine, it will be a daily driver/ camper hauler. so I want more of a stump puller than a high revver.
In looking at those Summit listings there are 2 pistons listed that appear VERY similar to each other, even as far as price is concerned. Im looking at Speed Pro H116CP-30 vs KB107KTM-30 ("KTM" means its a kit that includes moly rings) Anyway the first question is this; BOTH list fitment for either an LA or Magnum series 360, which cant be right. Bore x stroke wise, yes. but balance wise, no.
Nether lists a weight in the respective engine families. Is either of these balanced suitably out of the box for either an LA or for a Magnum? Or is paying for a balance job basically required either way when these pistons are used? I was looking for weights of stock pistons vs the weights of these and am coming up empty.
I have access to a set of very short term used, (like 6000 miles) of the Speed pro's. they were run for that 6000 miles in a '76 LA block. (then my son decided he wanted a 408)
I have some summit bucks that expire like, tomorrow. I will be needing some other parts for this engine regardless. Im wondering whether to use them for pistons or for the other goodies Im gonna be needing for this build. The "am I absolutely" going to "have to" have the machine shop balance this engine, if I use these pistons? It will effect the choice I make for other parts, such as balancer and flywheel.
Click to expand...
Both of those are, or at least have been, very good pistons when installed properly. Some of the Mopar crate short blocks even used a version of the H116. There is nothing wrong with using either of these pistons with proper cylinder wall clearance and ring end gap in a towing application either. Both of the pistons will require the rotating assembly to be balanced in either LA or Magnum application.

As for fitment in both LA and Magnum:
The Magnum uses a narrower small end on the rod, and the pistons that are specific to a Magnum application are often narrower there as well, so they won't accept the wider small end of an LA rod unless the LA rod is ground to narrow it.
The pistons that list fitment in both LA and Magnum applications usually accept the wider rod or sometimes the instructions will say something to the effect of "LA rods must narrowed to fit." Summit's website often has the instruction sheets listed for the items so can read through to see what they say, but since yours is a Magnum in this case, you would have the narrower rods and are good to go.
 
I'll just repeat what has been said, and I ballance these things personally all the time. The factory ballance job is not very good, and replacement pistons will NEVER be equal to what you remove weight wise. Not to mention if you weigh 8 factory rods, you will find it takes a bunch of grinding to even get them equal, something the factory doesn't bother to do.
 
RustyRatRod said:
I consider balancing a requirement. You've already had what? one failure? two?
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Just 1. And this engine has been collecting dust ever since. (Those eq heads were bought new right off of their dock in Chicago, I went down and picked them up as it was actually cheaper than shipping)
Professor Fate said:
Well, an oversize piston is going to be heavier than stock anyways, so if you're on your second rebuild (and second overbore, I assume? You didn't mention if you were boring it again...) you should really not even question the rebalance.
Click to expand...
I hope not to have to re bore again. I see no scoring, and that engine had about 3 hours of run time on it from install to take out. But as any, if it calls for it to be bored again , it will be to make it right. Worst case I have another 360 mag short block sitting on the ground right next to this one that's never been apart of this one winds up too bad once apart.
318willrun said:
i just gotta ask...... is this ^^^ the reason for your multiple times posting 318 over a 360 any day? You've shown very little love to the 360... after reading maybe this is your reason?
Click to expand...
No but it adds to it.
My dislike of the 360 goes back to the late 80s, ones I've had and ones dad had, 70s ones that did nothing better than 318s besides more stops for fuel. I've gone 318>360 and 360>318 between fender wells before largely based on what was available at any given time and really didn't get any more out of 360s back then than I did out of 318s in otherwise same cars..... I always considered the dished pistons of the 360 their downfall and always wanted to build a 360 (besides stock rebuild that is, which was what i did to the 360 I currently have on the stand ... )
Dead stock besides an overbore to clean up clearances....
These older 360s were in a Cordoba, a van and a pickup. And the ones that I went 360>318 didn't seem to be any doggier with the smaller engine. The one I went 318>360 with back then didn't seem any more powerful with the bigger engine back then. These were all used engine take outs replaced with lower miles used.
I'm going 360 in this one because it's what I have, and hoping for noticeable improvement over what was in it. . a 318 that my son is still running around with, but now in a c body wagon..and what drives me the most nuts about the 360 is all the people on here that say to drop a 318 in a ditch just because it's a 318, and "you MUST put a 360 in there or your car won't be worth a damn". That is way wrong mentality.
 
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I'll admit most engines I have rebuilt have been pretty much stock, with maybe a 1 or two step over, cam. And before this one I never had a disaster like this one became.
I have put a few together since that disaster and went fine. I have never paid the extra money previously for a balance job, the machine shops I've used have never mentioned it, (and they're in business to make money, plus jobs they've touched that go bad don't do much for repeat business). Ones I don't use no more, I don't use no more because they retired/ closed up after many years in business. Not because of having problems with the work they've done for me.
(Was it here or Moparts) I put up a post asking about the necessity/ advantage of having a 360 neutral balanced.

I will say one thing once this one is done .. I want the best motor I can put together, I want the highest CR at the end of the day I can run 87 with. I'll be damned if I'm paying a buck a gallon more for premium. What ever happened to 10-20¢ a gallon difference between grades? When that went to hell it did so really quickly. I guess these guys don't want to sell much premium pump gas with that scam in place. This isn't going to be a 1000 mile a year build. More like a 10000-15000 a year build.
 
I don't really want to get into it anymore than I have so far in dibbles and dabbles in different posts on here but the problems with the first rebuild have nothing to do with the fact that they happened on a 360 or any other engine.
But this thing was doomed from the start, the reasons it went bad are many. Seems like I made every possible mistake I could, all on this build. It didn't blow up or spin a bearing, or have a cam go flat, so there's hope for it to live again. I may tell the story about everything that went bad about it but not now.
 
Sorry guys. I deleted a couple of posts. . I didn't want to kill my own thread ... but it looks like I might have ...I definitely like reading what you guys have to say....
 
As stated, the factory balance is sub par at best. If you want an engine to live a long life, get the reciprocating components "balanced". This was drilled into me from a very young age by an old time engine builder who helped me into the hot rod industry. Don't get me wrong, I've built a few "grenade" motors from bits and pieces I had laying around, some of them survived for a few thousand miles, others never made a trip down my driveway. The cost of the initial balancing far out weighs starting from scratch when you bring the engine home in peach baskets. Ask me how I know.
 
volaredon said:
Just 1. And this engine has been collecting dust ever since. (Those eq heads were bought new right off of their dock in Chicago, I went down and picked them up as it was actually cheaper than shipping)

I hope not to have to re bore again. I see no scoring, and that engine had about 3 hours of run time on it from install to take out. But as any, if it calls for it to be bored again , it will be to make it right. Worst case I have another 360 mag short block sitting on the ground right next to this one that's never been apart of this one winds up too bad once apart.

No but it adds to it.
My dislike of the 360 goes back to the late 80s, ones I've had and ones dad had, 70s ones that did nothing better than 318s besides more stops for fuel. I've gone 318>360 and 360>318 between fender wells before largely based on what was available at any given time and really didn't get any more out of 360s back then than I did out of 318s in otherwise same cars..... I always considered the dished pistons of the 360 their downfall and always wanted to build a 360 (besides stock rebuild that is, which was what i did to the 360 I currently have on the stand ... )
Dead stock besides an overbore to clean up clearances....
These older 360s were in a Cordoba, a van and a pickup. And the ones that I went 360>318 didn't seem to be any doggier with the smaller engine. The one I went 318>360 with back then didn't seem any more powerful with the bigger engine back then. These were all used engine take outs replaced with lower miles used.
I'm going 360 in this one because it's what I have, and hoping for noticeable improvement over what was in it. . a 318 that my son is still running around with, but now in a c body wagon..and what drives me the most nuts about the 360 is all the people on here that say to drop a 318 in a ditch just because it's a 318, and "you MUST put a 360 in there or your car won't be worth a damn". That is way wrong mentality.
Click to expand...
360 Engines were brought on right at the beginning of the "no smog" ERA. That is the reason people of our age group viewed them differently. We just enjoyed "our" era of all performance engines to the exact opposite approach with the 360. The reality of it is if you get rid off all that crap that was downsized or added to de smog engines of that era you have a small block Mopar with a larger displacement. You would really have to have been a teenager or maybe in your early 20's to remember how disappointing it was that these engines were intentionally having their horsepower reduced by restricting what actually lied beneath all that crap. A bigger small block. Later that stigma went away when people got over it and threw all that added crap in the circle file. If you lived during that time like Volaredon, thousands of others and I did you would remember the history of how all this came about and was viewed at the time.
 
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volaredon said:
My dislike of the 360 goes back to the late 80s, ones I've had and ones dad had, 70s ones that did nothing better than 318s besides more stops for fuel
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Well Don, yur not wrong, below about 3000>3600.
And the reason is that the factory low-compression LA-models both math out to about the same V/P, namely , 112 for the 318 and 114 for the 360.
But, the 360 has a cam that is 12* bigger, with 16* more overlap, so it had the potential to carry power about 400 rpm higher, which is good for some 20/25 hp right there, while still being a 2bbl.
and 360 cars usually carry a one or two gear penalty for lower-rpm cruising.
and whereas a stock 318 will not hardly notice headers, with its modest 20* overlap, the 360 with it's 32 or so, will.
Now; I have installed a 360 2bbl cam into a 318 2bbl engine, which, with a small-port intake and 500AVS, resulted in a lil softer bottom, and a much improved top. Adding 3.23s over 2.76s, more than made up for the loss of bottom end.
So, I can whole-heartedly agree with your LA stock-engine findings.
But
I have also taken a hi-compression 340 short, and bolted an entire 318 top end onto it including the 318 cam, and that was a beast, comparatively speaking.
----------------------------
So, if I had to make a choice, for towing, using factory Magnum parts, I would take a hi-compression 5.9 short any day, with iron Magnum heads, and install a 5.2 cam with a finished SCR around 9.0. The Wallace calculator predicts a pressure of 158psi@900ft, and a V/P of an amazing 150, Perfect for a tow vehicle.
Since you will be running a 5-speed with overdrive, and more than likely
be towing in direct, I think I would like a 5.9, and gear it to tow at a slightly higher rpm with, a lil less ignition timing, then see how that goes. I would for sure run a dash-mounted, dial-back, Timing module, to get her dialed in. With a 5.9, you can put a lot of timing in the VA, during cruise; as much as she wants. So, say you tow at 3000, and bob-tail at 2400 or so; but no less that 2200. Bob-tailing, she will probably like a LOT of VA, into the mid50s would be my guess.

Read about V/P here; V/P Index Calculation
 
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jeff alder said:
360 Engines were brought on right at the beginning of the "no smog" ERA. That is the reason people of our age group viewed them differently. We just enjoyed "our" era of all performance engines to the exact opposite approach with the 360. The reality of it is if you get rid off all that crap that was downsized or added to de smog engines of that era you have a small block Mopar with a larger displacement. You would really have to have been a teenager or maybe in your early 20's to remember how disappointing it was that these engines were intentionally having their horsepower reduced by restricting what actually lied beneath all that crap. A bigger small block. Later that stigma went away when people got over it and threw all that added crap in the circle file. If you lived during that time like Volaredon, thousands of others and I did you would remember the history of how all this came about and was viewed at the time.
Click to expand...
In the late 80s I was in my early 20s... I'm 57 now ..so yeah
But the reality that they dished pistons and put huge chambers on the heads so a double whammy of low compression dogs.
And yeah on the surface that's the first thing is normally think..... Hey bigger engine! But in the 360s case they gave us the bigger engine but castrated them at the same time
 
And AJ.... I've put 360 cams in 318s/ and that makes a 318 of the day definitely run better than a 360 of the day. All stock as built they're about a "draw" other than the fuel thirst.
I've also put 360-2 intake manifolds on otherwise stone stock 318s (but not a 360 cam and 360 carb/intake on any one engine at the same time) and THAT has woken up the 318 "enough to be noticed by the old butt Dyno".
 
volaredon said:
In the late 80s I was in my early 20s... I'm 57 now ..so yeah
But the reality that they dished pistons and put huge chambers on the heads so a double whammy of low compression dogs.
And yeah on the surface that's the first thing is normally think..... Hey bigger engine! But in the 360s case they gave us the bigger engine but castrated them at the same time
Click to expand...
they sure did. They gave you a bigger mold to put good pistons in but then of course you had to do away with the cast crank and all the emissions crap.
 
Ok let's try this again now that I have some wifi...
Jeff definitely gets why I never really cared for a 360.
But I've always wanted to try to build one the way Mopar should have.
And Jeff while you're out there .. you and me run alot of the same section of roads... Who do you know around here that even does balancing?
My last several jobs that I have needed machine shop work have gone to newco performance in kentland. Nice and easy 15 min from work.... I'm not sure they do balance work, I know the last time I had to have a crank ground, they farmed it out somewhere. That's been a few years.
That's the old Larry Young machine shop.
For my usage I don't think the cast crank will hurt me too bad, though I wish they were neutral balance.
Now to figure out which pistons to run whether they're stock replacement, or the ones my kid has or something else. We're the magnums as far off of specs like "advertised CR" as the older engines were?
The last engine I did was a/6. And after much machine work it's right at advertised CR, 8.4:1 as measured out, CC'd, by me. Without 0.100" off between the head and block my particular engine would have been below 8:1 as built by Mopar. Quite a ways off. And how accurate are piston makers' CR estimates with "their" pistons and a given combustion chamber CC size?
 
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I'll be @RustyRatRod 's amen corner for not using Hypereutectic pistons in a truck motor used for pulling. Been there, done that when I didn't know no better and got to do it over! :BangHead: Get you some forged flat top pistons and get your cam reground for a puller motor. Just clean the living daylights out of every single little piece of the motor and put it together. I had an 84 D350 single wheel pickup with a 360/727/4.10 Dana. It would pull my car trailer easy as pie. The longer arm on the 360 crank provides the torque in the right place for a truck that is used as a truck. Like you mentioned, my 84 truck got 12 mpg city, 12 mpg Hwy, 12mpg pushed out of the back of a C130 at 40K feet! Good luck with your project.

:thumbsup:
 
I thought the stock pistons in a magnum engine were hypereutectic? Lots of them did towing and hauling duty for tons of miles .. what's so bad about a hyper piston for towing? I thought they were only bad news if using nitrous?
And I was wrong about those pistons my kid has out of his motor
They're not 116s. They're H405cp. I was just over there for something else and I had him dig them out. So being that they're not what I thought they were.... They ARE speed pro and they are hypereutectic, but not the ones I thought they were. So I guess that's out then.
 
Hyper pistons are fine for towing. The 360 mags were DESIGNED as long runner short cammed truck engines from the factory with those pistons. They’ll be fine. I run hypers on a turbocharged 8.1 in my GM dually and it’s got over 630,000 miles on it, towing its entire life ON BOOST!! Ring gap and skirt clearance are important.

@volaredon I think you should build it stock, the 360 magnums stock are great truck engines. Step up one cam size or so (like 208 @ 050) and send it. Your 87 octane requirement keeps you in the stock long block territory. Use the longest runner dual plane intake you can find (rpm ag) and whatever carb you’re comfortable tuning. And my final thought, BALANCE EVERY ENGINE YOU ASSEMBLE. It’s a non negotiable part of engine building.
 
How inaccurate are the advertised CR on the magnums? If they're like the 70s/80s engines the CR advertised in all the manuals of the day are very ambitious. My last complete rebuild was a /6 and though advertised as 8.4 it measured out well below 8 to 1. I've seen small blocks that actually measured out as less than advertised which means less power than advertised as well.
Are these engines really 9:1 as built, stock from the factory? I want at least that much, but probably a max of around 9.5:1 so I don't have to run premium.
What do you think about running those pistons my kid has, now that I know what number they really are? The truck is an 80s which were still LA engines, basically I'd be building an LA in the confined of a magnum block ..
They said the magnum block is slightly shorter than the LA deck height wise, these 405 pistons are about 20 thou shorter compression height vs the 116s I thought they were. And the 405# are likewise flat top except they have 4 valve reliefs instead of the 2 that the hp116s have.
Even if not needed for a big cam, I would wonder what the valve reliefs did for mixture turbulence, when running especially the 2 that aren't gonna be used for valve clearance in each cylinder?
 
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