HEMI Tech- PISTONS! rods and related

A new week, so let's add another Hemi subject to the library. Let's talk about those pistons!

1) Pistons...
- What to use for what application?
- What compressions is right for your street, race, or full blown rocket engine to the moon?
- Octane and the pistons you run?
- Forged or cast and for what?
- Where to get them and who makes 'em?

2) Rods...
- When should your stock rods be replaced with billet or similar?
- When is shot peening your stock rods a good idea?
- Should someone really go through the effort of "boxing" a rod?

3) Stroke related items...
- bearings
- pins
- rings to use for the occasion?
- big end caps and bolts to use?

Feel free to add related subjects if I've forgotten anything that should be mentioned as a topic of discussion.

 

stock rods are already shot peened from the factory, pistons can be had from Egge (stock cast) Hot Heads (hypereutectic and forged) and PAW (hypereutectic and forged and stock cast)...for my money there's really not a hell of a lot I'd do to a stock motor other than some 10:1 pistons, cam, intake, and exhaust...the tolerances held on these motors from the factory and the parts they used such as the rods and crank are top quality of the day and in my mind good for a healthy street motor on 90 or 93 pump gas...I'm still curious why you're assembling all of this info since there's already a myriad of good books out there that for the most part already have this info, not to mention allpar.com's history of the motors and the other online resources for parts and building guidelines...

 

Because some people don't know about those good books and some things are not COVERED in those good books. There is a wealth of information on the HAMB from people with tons of tricks, tips and information not available in those books.

If this is a waste of time, someone let me know. I don't understand why someone would ask "why?" unless I'm really wasting time and space on the HAMB.

There's also great books on chop jobs, engine rebuilding, "how to customize your car", etc. etc.... but sometimes having a whole library gets expensive. The HAMB should be a good place to go for information like this for FREE if someone is willing to help put it up.

Still, if this whole "HEMI tech" archive is a waste, let me know.

 

Scooter , Till the Boss bitches about band width keep on keeping on !!

For one thing, if you read all the books he talks about & build an engine like they tell you to, you will have 9 to 15 thousand bucks in a motor!! One "Book Build " I read had 9 GRAND in a Hemi motor for a net gain of THIRTY SIX HORSES!!!
As you say, there is a lot of knowledge among the POH ( People of HAMB)
might as well coax a bit of out into public view.
When I read some of the books that advise every high dollar modification known to man to be used in building your hemi, I can't help but remember the Hot Rod Mag. article of years ago with Rolond Leong the year his Hawiaiaan (sp) Dragster was top fuel winner . They went there with the idea that , being the winner , they were going to learn about building a HIGH Dollar Race motor.
It was really funny to find that the "special crankshaft preparation" Roland used was to switch crank grinders , cause the guy that did them for 20 bucks was a bit sloppy compared to the guy that charged 35 dollars. Or that their "expected race oil system" was not a BIG dry sump oil pan system -- but a stretched releif spring in a 1951 oil pump.
The rods they used were boxed by clamping them between two 3/4 inch "C' shaped plates so they did not warp when they arc welded boxing plates on each side !!
Turned out the engines they built were practically dirt cheap & only won because the team LOVED lots of NITRO!! Happily so do Chrysler Hemis, they like it a LOT!
So keep on with what you are doing.

 

The HAMB is cheaper than buying a shitload of books and I myself don't have the time to search all over the web. I come here for everyting!hahahaha

 

I used arias pistons and are 10:1 compression. Rods are standard hemi they great as is. Pump gas 94 octane.

 

I wasn't trying to put you down man, just asking a question...I know how spendy it can be to buy all those books, and honestly some of the books I have are complete crap...so more power to ya and I'll try to throw in some tricks and such along the way...

 

Kick ass! Keep it coming bro'! No offense taken at all! Wasn't you exactly. No worries.

BTW... I agree. I have a couple books that are WORTHLESS as well!

Thanks for the support guys... NOW BACK TO PISTONS AND RODS!!! Carry on!!

 

Here's my TECH from awhile back about how to convert 426/440 rods for use in a 392. It's a great cost effective alternative for stronger rods:
http://www.jalopyjournal.com/forum/showthread.php?t=5986&highlight=440+rods

 

Boxed and/or aluminum rods are for race, only. They're a waste of $ on the street. I wouldn't put an aluminum rod in ANY street motor for that matter. They don't last. They're throwaways, even in race cars.


Detonation is pretty easy to deal with as the hemi combustion chamber, by virtue of it's design, tends to drastically reduce this phenomenon.

I run a 12.5:1 compression forged piston but a 0.050" head gasket and that lowers my compression quite a bit. I run EIGHTY SEVEN octane fuel ALL of the time and don't get detonation unless I really stand on it off the line. If I ease off the clutch and drive the car off the line it'll take a fair bit of throttle movement to induce a ping. If I stand on the throttle at low rpm, it'll ping. If I floor it going up a hill in 4th gear on the interstate, it simply sets you back in the seat.

Oh, yea, I've been driving it like this for 41 years and it ain't broke itself yet. I'm on the same set of pistons in my third block. First one, cylinders rusted up after an accident in '66 (see pics on my website) and the second one had a bit of cylinder taper after a hunnert thousand miles so, rather than bore the block and buy new pistons, I just bored one of my spares and threw the pistons in it.

 

I've got Venolia forged pistons in my new blower motor.

I bought 'em 'cuz my engine guy was screamin' for parts, Bob Walker was out on the road that week and Ross kinda tee'd me off by treating me like a teenage kid calling to order a decal for my window.

Venolia, on the other hand, required me to fill out an order form and fax it in. Then they called me and went over my specs...they needed my combustion chamber cc's ( no off the shelf stuff here!). They were great to deal with, the price was competitive (but NOT cheap) and I had my slugs in hand in three weeks...good service by any standard.

They are now my supplier of choice...

 

For pistons, my first choice is forged, then cast. I would not use hypereutectic pistons in any motor (my personal opinion, so no need to debate this - again). For rods, stockers are fine for a street motor, just make sure they're checked thoroughly for cracks, twist, etc. I am using Pontiac h-beams from Scat in my 354. They are a direct replacement, and the Pontiac bearings are a lot easier to find and cheaper too. For bearings in general, I prefer tri-metal such as Clevite or Federal Mogul over the King bi-metal bearings.

 

Hemis are dang near perfect out of the box. I have 10:1 Egge cast pistons on stock forged rods in my 392. Other than a warmed up cam, headers, and a tunnel ram, mine is pretty stock. It's an excellent driver on the street. There is no need to over-build them. It's a waste of time and money unless your racing (for real).

 

You can also just use the Pontiac bearings in your stock 331- 354 rods by having the retainer notches reversed when the rods are reconditioned. Or if you are handy with a Dremel, cut your own notches .Pontiac bearings are much less costly, especially in FM or Clevite than Chryslers .

Unless you are building an Elephant motor there is nothing wrong with cast pistons. If cast pistons suit you, then for your 331 , you can bore it to fit a nice clean set of used 354's. By the same token a nice set of 392 slugs will do just dandy in a .0625 overbored 354. In either of these piston swaps one should use clay to check piston-valve clearance if you have changed the cam lift, because the crown height is a .080 to .125 higher --- kind like the high dome compression raiser pistons.
If you want low compression pistons for a blown 331 find a set of 354 industrial pistons , they are flat tops with about 7:1 . ( get a set that ran on propane & you won't even have to clean em--- I had a set -- looked like spanking new!!) If you are not running more than 5 -6 lbs boost the cast piston will hold up just fine--- never mind what all the book writers say.

 

Well in my 354 i run stock rods 8.5-1 comp isky cam head and main studs Blown on Alky runs great on pump gas pings its head off on VP103 motorsport with 8 97,s runs great oh also has MSD 6 with boos retard for pump gas

Now on the con rod front i have heard you can use 455 pontiac rods and bearings the small end is 4 thou too small you can hone that but the big end is on size BTW thats for a 331/354 not a 392

 

Regarding using 354 pistons in a 331 and 392's in a 354....I have read, from several sources, that you will lose 2 points of compression using the "big inch" pistons in the smaller motor.

 

Don't know if anyone will care because this aint street motor stuff but on my top fuel donovan we ordered Venolia custom built pistons, 4.030 bore, top ring .525" down, piston ends up below deck .250". with .100" long 392 Howards aluminum rods. We have a 1.8 rod/stroke ratio. Blown nitro tends to pinch top ring lands so that is why the top ring is further down the piston. It puts the oil ring in the pin but with buttons to keep the wrist pins in place that's no big deal. We have a stock 392 (3.900)stroke Velasco crank and use narrower 426 size rod bearings.

Low compression, high tolerance for pain LOL Brad

 

Many rod options already covered ---> herre is another:

You can use 426 'style' rods in a 392 - though in stock configuration they are approx .100 shorter in length and wider. Like the 440 rods, they need to be narrowed to match the 392 width and the bearings will need to be narrowed as well. The shorter length means you'll need custom pistons --- not usually an issue in a blower motor. (you'll do it anyway in most cases).

Since I'm building a pretty nasty blower motor, with the potential for lots of boost, I tend to over-engineer my bottom ends. It helps me sleep at night . . . and I like not having to worry about losing a rod. My setup is more along the line of a true race motor . . . guess thats the way I like it. Also - I didn't just plunk down a huge wad of $$$ for new parts . . . took my time, looked for special deals, bought some good used stuff, knew what I was looking for, etc..


Many ways to skin a Hemi Cat . . . here is the setup on my coupe motor:

a) RODS: I found a set of used Oliver 426 steel rods . . . bought them for about 40 cents on dollar. ( Oliver makes a great rod - but they are dang expensive if you're buying them new). I modified them to fit the 392 - and ordered pistons to match.

--> 426 H-beams: I also bought a set of CAT 426 rods for another early Hemi - same deal as above, but quite a few $$$ cheaper.

--> 392 H-beams: K1 Technologies produces an H-Beam for the 392 for a very fair price. These are most likely the ones that Hot-Heads sells. You can pickup their H-Beam in stock 392 configuration for roughly $500 - 600. This is a very fair price for a rod of this quality. This is probably the way to go if you want the H-Beam style rods and are spending the $$$.

Couple Links:

http://www.campbellenterprises.com/K1-Technologies/k1-technologies.htm

Sample Price on eGay:

http://cgi.ebay.com/ebaymotors/Chry...ItemQQcategoryZ33623QQihZ019QQitemZ8065027888


b) Oliver 426 Rod Work: I had them narrowed to match the stock 392 crank that I'm running. The crank is .010 -- using FM bearings.

c) Oliver Pin Configuration: They run the larger 426 pin - I believe 1.031

d) Forged Blower Pistons: If you're going to order forged blower pistons -- you're pretty much ordering custom pistons anyway, so you can order them any way you want. I'm using Venolia pistons --> gave them the compression height, ring combination, pin size, etc . . . they make exactly what you want, at a fair price in a pretty short period of time. Lots of guys run Arias as well . . . they'll make what you want.

e) Lower End Insurance: I'm also running Pro Gram M392C4A steel main caps on the center three. For those of you who don't know Pro Gram -- they make a great product. Here is their WEB address:

http://www.pro-gram.com/index.jsp

They make all 5 main caps if you're running a fuel car -- and are worried about the lower end.

f) Oil Pump Setup: I'm running a modified 340 Pump -- available from Hot-Heads, PAW, etc.. There is nothing wrong with a 392 pump -- usually a bit tougher to find.

 

Anybody want to hazzard a guess as to the HP and RPM limits on stock rods, both with and without ARP rod bolts?

 

I've seen comments that it's usually .7-1.0 loss. This came up on Hot Heads new forum & Bob said a slight increase ( forget what combo), guess the jurys still out....

 

That's still a pretty fair loss if you started with a 9.5 piston...if you've got a 331 with eight to one you'll really be hurtin'.....

 

I don't think a well-mannered street motor (daily driver-style) would ever break anything unless you really got stupid with the loud pedal.

I'd bet it would take 7,000 rpm on occasion....and stock rods should be good for 600 HP...anybody else?

 

Loss? as compared to what?

Perhaps as compared to the compression in the 392 but certainly an increase over what was in the engine before boring.
The people who claim a loss are basing that statement on the longer stroke of the 392 . Now consider this, IF an engine has say 8:1 with a stock piston before boring & it is bored .060 & a piston is put in that has a larger diameter ( .060) AND has a crown height that is about .100 HIGHER than the piston it replaces HOW can the compression be reduced?? The new piston is still making the EXACT same travel as did the old piston -- only now there is more volume (.060 overbore) which added to the HIGHER crown will leave LESS space unfilled in the compression chamber ( which has NOT changed any) . Any way you cut it this has to add to the compression ratio of the engine.
While with the longer stroke in the 392 they may have produced 10:1 & now only come out to say--- 9:1 --thats still MORE than the smaller motor has BEFORE the change.

Originally Posted by krooser
Regarding using 354 pistons in a 331 and 392's in a 354....I have read, from several sources, that you will lose 2 points of compression using the "big inch" pistons in the smaller motor

 

OK, I was talking advertised comp ratio of the piston in the proper engine. The usual example is a 10:1 392 piston in a 354 drops to 9.3 & would increase the actual comp ratio of engine.(not saying that is an acurate example, just an example for discussion)

 

OK . So NOWthe key is, we don't want to screw up the factory PR folks hype ? Somehow I thought the idea was to increase the output of an engine that was being built.
I guess boring a 331 .125 AND putting in a HIGHER CROWN 354 piston won't increase the 331 up to the advertised ratio of the 354?? Why Pray tell?

 

It's my understanding that the wrist pin heights are different between the 331, 354, and 392 pistons. That is why compression drops

 

You want to come by & set some side by side to check?? Like I said the piston ends up with the crown ( dome) a bit higher in the cylinder --the champher ( where the piston tops out in the cylinder) is EXACTLY in the same place .
Got to quit believing everything you read -- especially if it's written by somebody with something to sell.

 

The stroke of the 331 & 354 are the same, so things there should work, but...the stroke of a 354 is .281 less than the 392, so the piston isn't moving "the exact same distance" in this case. With less total air volume there would(should) be less than advertised compression. Over on the HH forum a guy asked what the c/r would be putting 10.5 392 pistons into a 354. Bob answerd that 10.0 in a 354 would result in 10.3. If he intended to say 10.5 instead of 10.0, that would go along with the usual reply to the question.

 

A 392 piston in a 354 is moving thru the SAME travel as the 354 did, no one ever said it had the same swept volume, or travel as a 392. So , once again , an oversize piston increases the swept volume of a cylinder, A higher compression dome decreases the amount of volume in the combustion chamber above the piston. Both these factors will increase the compression ratio. You may not end up with as high a compression ratio as the piston did in it's origional home ( 392) but you will have higher compression that the 354 had with its stock piston . The same thing applies to a 331 with 354 pistons.

 

Wait! I have reconsidered & you guys are right it won't help a bit to change pistons fron bigger motors to small ones---- so everybody that has any 354 or 392 used pistons --send them ALL to me . Freight collect even OK?