340 Piston to valve clearance w/RHS heads

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The hyper pistons don't run hotter, the top ring is up higher so it gets hotter hence the larger ring gap. If it were my engine I would run the lightest pistons I could find hyper or not. And yes lighter pistons will make a very noticable difference in how it runs, how fast it revs, how it feel behind the wheel. If you can swing it the Scat I-beams are very light and very strong. Those and some light pistons that would be one heck of a reving engine. With hyper pistons that engine will last over 100k hard miles easily as long as you get that ring gap right.

All other things being equal, an engine with lighter pistons will out excellerate an engine with heavier pistons. It will out last it too.
 
Hypereutectic pistons deflect heat towards the chamber and they grow less=require less skirt clearance.
I've used them off and on for years with great success and have not blown a hole through one yet.fwiw



Seems to me there are a lot of knowledgeable people here giving sound advice, some however is not.

None the less...most of it is falling on deaf ears.
 
The factory doesn't use KB pistons with the top ring so high up. Only KB makes its pistons like that.

U have to be careful with any sbm the intake seals top and bottom. I now use only fel-pro intake print o seal gaskets with a seal core. In the past I had gaskets split, lucky just on the intake ports and not water ports.

Don't believe those factory 12 second numbers. these new cars aren't tough like the old cars. U got a great rear end, 7 1/4 rear ends break with any power long term.

I would just build the engine with hypers, maybe skipping decking, etc. A good balance job is whats needed. My engine came out fine doing it that way.

A bit more weight, a bit more stroke does add to more stress on the parts for the same rpm's. Forget how the factory do things today. They use smaller pistons and longer strokes for emissions not longevity. The light wheels, low profile tires weigh less and the sports cars have less drag today.

U get that 340 running and stick in 4.10 gears--which is a bad idea with $5 gas coming--and it fly pass these new cars, believe me
 
I said the rings run hotter just to clarify...and they do, which IS the reason for the larger gap because when they expand, and if you used the standard gap, the rings would butt and then it would seize the piston in the hole AND then the piston would explode due to its brittleness.

Again, you'll save roughly 800kg (roughly 2 lbs) of rotating weight by using the lighter pistons. The difference is modest when you think of the weight of the whole thing. There's at least 120 lbs of metal flying around in there just in the bottom end+flywheel+balancer.

Speed Pro says:
"Piston weight has recently become a very high profile topic in the performance media. Realistically, a reduction in piston weight has only a modest impact on horsepower or vehicle accelleration. The true value of reduced weight lies in the potential for higher RPM as a result of the reduced loads on components such as connecting rods and bearings. Optimisting the engine combination for these higher RPM levels will certainly carry the potential for more power."

And talking about Hypereutectic pistons: "...This quiet operation, along with a lower cost are the primary advantages over a comparable forged piston."

So lets recap:

Hypereutectic Pistons:
Pro's:
Lighter weight
Quieter when cold
Cheaper (not by much)

Cons:
Brittle (failure mode is exploding)
Not as durable as forged
Special ring gap

Forged:
Pros:
Most Durable
Ductility
Standard gaps

Cons:
Price (again, not much)
heavier
might rattle a bit when cold.

Bottom line is: The Hypereutectic pistons don't have a different compression height than the forged...so I still have the same original problem. So, in my original question, it does not help. I'm not trying to turn this thing 9 grand or anything. I would, however, like to run this engine a bit on the lean side in cruise, and while doing so, I may detonate it during the tuning process as I also run a LOT of timing. Forged pistons hold up better in these conditions. I'm also not worried about the weights cause of stress on the crank and rods. These have been around for a while and they're not known for flying apart. I have NEVER read anything about these particular pistons that were bad other than the weight. 440 pistons are even heavier yet. I could really care less about the extra rpm I could have or the incrementally small hp gain I would get. I'm also not worried about high RPM...actually I'd like to reach my HP goal at the lowest RPM possible...and achieve a large area under the curve (good torque).

Also, who knows, down the road I may want a turbo...

And furthermore...if I bought exactly the same parts in that kit but used the KB's instead of the L2316F's, it would cost $577.13 instead of 632.99...a whole $55.84. A price I am willing to pay. So yes, the hypers may be fine, plain cast pistons might be fine too...I'll leave that for you guys to find out....and I'll stick with the forged.
 
Mad Dart said:
On my 410 the pistons stuck out of the hole .016-.018 Just like yours. I am using RHS Heads from Brian at IMM. I have all forged internals with H Beam Rods. I used the SD Felpro gaskets that are .054 Compressed, 4.172 Bore. The reason I used the Felpro 519SD is I was gunna hit it with some NOS and at the time Cometic did not make gaskets for the RHS Heads. Now they do!

Quench was about .036. I have bounced this engine off 7200 RPM a few times. I usually shift it at 6500. Rev Chip is set at 6800 Rpm

The Fire Ring is a little wider on the SD gaskets. FYI
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I always liked the headgasket to be able to fail before a piston when using nitrous, just for the reason that no matter how we all think we know everything, and how many things we check, sometimes we screw up and we pay the price in the biggest way.:iconbigg:
 
The kb243 .030 hypers I last used weighed 574grams w/o pin, w/pin weighed 693 and cost $27 each, or around $240
You can lighten the pins easily and get them lighter.
I tune cruise to surge then back 2 jets and pinged'em to find max total, they'll handle a pinging.

The trw .030 stock replace forged pistons weigh over 700 grams, I have 2 sets.

I would only use trw's in stock class or where rule mandated, they are titanic in weight.
 
POS Dakota said:
I always liked the headgasket to be able to fail before a piston when using nitrous, just for the reason that no matter how we all think we know everything, and how many things we check, sometimes we screw up and we pay the price in the biggest way.:iconbigg:
Click to expand...

I hear that, been there done that and paid the price in the biggest way more than once!
haaaaaaaaaa:burnout:
 
I would just mill the TRW pistons, they have a lot of material on the top . You could mill them .010 easy. should take care of any piston to head issue as long as U go with those gaskets U mentioned. Then you can rev rev rev. (course, need to check with actual mic jus to be safe.)
 
Just buy the right thickness head gasket for the build... it's that simple.

.015-.020 out of the hole, get a .055-.060 gasket.
 
That extra weight is at the very end, it does add up. Speed pro pistons are heavy, yeah their web page might say no biggie, they want you to buy their stuff, lol

U forgot the engine might smoke the first few mins with the forged pistons. I'm old enough to recall when many fast cars on the street all smoked at wot, lol The 1970 cars were 10-12 years old, it was great for $500 U could get a real car and beat on it--till the fame cracked , ha ha. Winter driving when streets were dry were a blast, U missed so much...

I got this feeling those trw/speed pros are now made in China, my KB hypers were made in Mexico, does it matter, IDK

I do know my engine builder was all for hypers if no nitrous was being used. He said thou some people just can't get it in to their heads hypers are better all around. They will not break and no need for "too much timing".

That and loose bearing clearances, like .0025 min, looser is "better". Too tight they heat up and spin but some folks just think .001 is the way to go

That engine shop is in Westland, he-Doug--is really in to Mopars, he isn't no kid either and not some old fart. They built my engine just fine and didn't sell me stuff like decking cause it didn't need it. If U got some time stop on up there and chat with him, he will remember me and my car. Won't hurt to speak with him before U pull the trigger. Its Am Car on Hix rd, cool guys, cool shop. I put 2,500 miles on that engine since July and long trips where just east i-75 and to westland. The rest was stop and go traffic driving and short blasts down the freeways. Its just fine, good oil pressures also 30 lbs min when hot. I could had spent more but got little extra. Its coming out mid March, rain, snow or sun
 
The speed pro pistons are almost exactly the same weight as the original CAST pistons....yes, they were cast. There's no reason why the piston material will cause it to smoke...more like the rings being warn. Lubricants were different then. Ever seen what the stock shortblock will take on an 88-92 5.0 Mustang? Those have forged pistons from the factory.

I saw that both the KB & Speed Pro pistons are either made in Mexico or India depending on what their application is. The interesting thing about that is I'm MUCH more likely to trust a forging made in a 3rd world country than a casting. Grain structure is way better on any forging...and its easy to have porosity problems on a casting.

I have absolutely NO interest in the hypereutectic pistons...plain and simple..even old topics on this site where people were having problems with wearing out/burning rings. I'm not worried about saving the very small amount of money...especially when this deal will probably be 4-5 grand by the time its done. Forged pistons do not explode, they do not crack down the center, and the ring lands don't break off at anywhere near the rate of hypereutectic pistons if ever. If someone could quantify the power gain from using lighter pistons (have never seen/cant find such a test...they probably haven't done it because its less of a difference than you think OR they know you should use forged at any high power level where you would care), then I would call Diamond up and get a nice custom lightweight forged set made....btw Diamond's 0.030 over forged piston is 566g....that is a shorter compression height but still, adding 0.020" will add maybe 40-60g.

My junk cast crank 77 360 that's a .040 over rebuilder special and has a zillion miles on it and FM cast pistons hasn't blown up either. Detonation & running too lean (don't ask), way too hot (230 degrees for 45 minutes the night before the dream cruise), not much oil pressure, overrev in gear before I had a limiter (6700rpm)...the ductility may have helped in these cases. These things are tough anyway, but I spent the extra money to get a 340 so I could have forged everything....so I'm going with my wishes.

My friend has an all forged 468 big block chevy with iron LS6 heads, stock crank, rods, and some heavy dome pistons and it turns 7400rpm....and was built in the 80s...goes 10.0's. Doesn't break either. Street car....and doesn't smoke.

For a lot of people...better=cheap...I'm not willing to do so on this build. Take a metallurgy class and then tell me if you still like cast hypereutectic pistons. The difference in process alone is kind of eye opening. Pretty hard to screw up a forging as long as they did a decent job machining.
 
Folks who think heavy pistons don't matter; those are the type of guys I want in the lane next to me.
 
340sFastback said:
Folks who think heavy pistons don't matter; those are the type of guys I want in the lane next to me.
Click to expand...

Ok fine...but where's the quantifiable proof much you loose in an application like this? Engineering calcs? Dyno tests? Science it out for me if you're so worried about it.

Considering the old MM build where they used stock x heads with a good valve job, headers, comp xe 268, air gap, and a 750 edelbrock and got 391hp...with the heavy *** pistons. You guys make it sound like the difference would be 25-50hp in 400hp...when in reality I'm sure its well below that...probably closer to 5hp at high rpm.
 
goldduster318 said:
Ok fine...but where's the quantifiable proof much you loose in an application like this? Engineering calcs? Dyno tests? Science it out for me if you're so worried about it.

Considering the old MM build where they used stock x heads with a good valve job, headers, comp xe 268, air gap, and a 750 edelbrock and got 391hp...with the heavy *** pistons. You guys make it sound like the difference would be 25-50hp in 400hp...when in reality I'm sure its well below that...probably closer to 5hp at high rpm.
Click to expand...

I just want to share this...I built an exact engine like that MM engine for a kid, who wanted good power. At the time, I didn't even know that build was done by a mag.
We used a 750 Holley, but everything else was the same....it made 358HP on our dyno. If I change the DTS dyno calibration to match Superflow, it would be about 374HP. Now every engine will make more or less HP even if built exactly the same but I thought the near 400HP was a bit of a stretch with stock heads.

You could mill .005 off the KB's and get the better piston too. Just a thought....
 
goldduster318 said:
I said the rings run hotter just to clarify...and they do, which IS the reason for the larger gap because when they expand, and if you used the standard gap, the rings would butt and then it would seize the piston in the hole AND then the piston would explode due to its brittleness.

Again, you'll save roughly 800kg (roughly 2 lbs) of rotating weight by using the lighter pistons. The difference is modest when you think of the weight of the whole thing. There's at least 120 lbs of metal flying around in there just in the bottom end+flywheel+balancer.

Speed Pro says:
"Piston weight has recently become a very high profile topic in the performance media. Realistically, a reduction in piston weight has only a modest impact on horsepower or vehicle accelleration. The true value of reduced weight lies in the potential for higher RPM as a result of the reduced loads on components such as connecting rods and bearings. Optimisting the engine combination for these higher RPM levels will certainly carry the potential for more power."

And talking about Hypereutectic pistons: "...This quiet operation, along with a lower cost are the primary advantages over a comparable forged piston."

So lets recap:

Hypereutectic Pistons:
Pro's:
Lighter weight
Quieter when cold
Cheaper (not by much)

Cons:
Brittle (failure mode is exploding)
Not as durable as forged
Special ring gap

Forged:
Pros:
Most Durable
Ductility
Standard gaps

Cons:
Price (again, not much)
heavier
might rattle a bit when cold.

Bottom line is: The Hypereutectic pistons don't have a different compression height than the forged...so I still have the same original problem. So, in my original question, it does not help. I'm not trying to turn this thing 9 grand or anything. I would, however, like to run this engine a bit on the lean side in cruise, and while doing so, I may detonate it during the tuning process as I also run a LOT of timing. Forged pistons hold up better in these conditions. I'm also not worried about the weights cause of stress on the crank and rods. These have been around for a while and they're not known for flying apart. I have NEVER read anything about these particular pistons that were bad other than the weight. 440 pistons are even heavier yet. I could really care less about the extra rpm I could have or the incrementally small hp gain I would get. I'm also not worried about high RPM...actually I'd like to reach my HP goal at the lowest RPM possible...and achieve a large area under the curve (good torque).

Also, who knows, down the road I may want a turbo...

And furthermore...if I bought exactly the same parts in that kit but used the KB's instead of the L2316F's, it would cost $577.13 instead of 632.99...a whole $55.84. A price I am willing to pay. So yes, the hypers may be fine, plain cast pistons might be fine too...I'll leave that for you guys to find out....and I'll stick with the forged.
Click to expand...
any well built engine will or should have a (special)ring gap.i have kbs best low cost piston,got $$$ buy custom forged.i'm poor so i have kbs.like brian said tune it right it will live...sheesh sombody get me a doctor!!!!
 
We are just trying to help.

If the piston rocks when cold its more likely not to seal as well, the rings rock with the pistons and wear out quicker.

Putting just 1,000 miles a year on the engine is nothing, any pistons will last. I'm more worry about high fuel prices than those hyper pistons breaking. $20 in gas was going too fast last year.
 
There been times when one hour is about it and its not funny!

I did not keep track of how much fuel I brought last year but think I been sick if I knew

The way I see it thou is if I'm going to limp around town, I might as well do it in a nice comfy newer Buick car
 
I already had trws so I ran them in my 340,but instead of spending money on stock rods I got a set of lighter/stronger aftermarket ones,something to think about as everything helps.
 
lead69 said:
I already had trws so I ran them in my 340,but instead of spending money on stock rods I got a set of lighter/stronger aftermarket ones,something to think about as everything helps.
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Thats the thing...
neither you or I, without blowing something up or trying our darndest to do so, can prove wether the seasoned better steel of the 60's/70's is better or worse than the chinese more meat in specific locations rods.

I have seen them both break.

history behind used sets bought at swaps is a mystery.
american faith is fair weather when it comes to chinese made steel/stuff.

Whats interesting...is that when it comes to chinese rods, all are sold that they are better...
BUT....when it comes to rocker arms.....get out the holy water and start praying...ha ha ....nothing but fear from most.

It's almost comical! :tongue1:
 
Yeah I had thought about buying aftermarket rods too...I think the only Chinese made (but US machined) rods I couldn't find anything bad about were the K1's. Seems like they are good. I'm still going to at least get a price on custom diamond pistons that would be zero deck and allow me to use the Fel-Pro 1008's at 0.039" thick...and be light.
 
TurdFerguson said:
Thats the thing...
neither you or I, without blowing something up or trying our darndest to do so, can prove wether the seasoned better steel of the 60's/70's is better or worse than the chinese more meat in specific locations rods.

I have seen them both break.

history behind used sets bought at swaps is a mystery.
american faith is fair weather when it comes to chinese made steel/stuff.

Whats interesting...is that when it comes to chinese rods, all are sold that they are better...
BUT....when it comes to rocker arms.....get out the holy water and start praying...ha ha ....nothing but fear from most.

It's almost comical! :tongue1:
Click to expand...

I would ask what brand have you seen break?,I have run cat h-beams (about the cheapest rod out there on e-bay) in a ton of engines with no issues,alot of high end pontiacs run them,just have them honed and they are good to go.I have only heard of failures with eagle I beams where scats etc. seem to have a good rep,I have never ran an I-beam personally but have built a few successful engines with them.I will say there is not an h-beam on the market that would break in his engine.
 
lead69 said:
I would ask what brand have you seen break?,I have run cat h-beams (about the cheapest rod out there on e-bay) in a ton of engines with no issues,alot of high end pontiacs run them,just have them honed and they are good to go.I have only heard of failures with eagle I beams where scats etc. seem to have a good rep,I have never ran an I-beam personally but have built a few successful engines with them.I will say there is not an h-beam on the market that would break in his engine.
Click to expand...

I bought a set of the Falcon H Beams for SBM that I am using on my TT Build.
I got them for $298.00, they look exactly the same as the EAGLE H Beams to me. The small end needed to be honed though cause they didn't finish machine them. I called them on it and they gave me a $80.00 Refund on the spot, no questions asked. Brian at IMM took care of the final honing.

Here they are, price went up a little. http://cgi.ebay.com/ebaymotors/H-be...rQ5fTruckQ5fPartsQ5fAccessories#ht_2659wt_941
 
Some of those higher compression engines got beat up in the late 70's early 80's by the cheap gas and us high school kids driving the cars cause they were so cheap back then.

So a piston might have crack due to the bad gasoline and the rods were reused Then many years later another owner throws a rod out and says its old factory stuff and the cheap China stuff is better.

Yeah get a price and let us know, I'm guessing its $800 plus, too much for me, I need gas money cause I'm drive my car alot, life is short you will see.
 
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