Stroking the 392?

Discussion of the 331-354-392 HEMIs.

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Stroking the 392?

Postby NE57 » Fri Mar 27, 2009 1:34 pm

Hello all, New member here with a question or three.

I just bought a 57 392 basket case and have been researching stroking it online. I think I have a fair understanding of the process but I haven't found any hard info on clearancing.
At this point anyway, I think my main concerns are what is safe, reliable and doable welded stroke length? I'm also wondering about clearancing the block, particularly under the cylinders. Just how thick or thin is the casting in this area and what is the danger of busting thru to the water jacket? Will sonic testing give me the answer?

I will ofcourse have the crank done professionally but I'd like to do as much other work myself, hell that's the point, to do it just to do it, for the enjoyment of the work.

Also I've been researching rods. For budget reasons I'd like to stay with either stock 392 rods or if they will work with a stroker, 440 rods for added strength. But I don't fully understand rod/stroke ratios. Would the shorter 440 rod be a problem with a longer stroke? How would they fit in the block? I know they have to be machined to fit the journal. Do they require more clearancing(I'm assuming they are wider at the big end than 392 rods)? As I said I'm looking for safety and reliability as well as torque.

This will be for a street car with maybe the occasion weekend warrior bit. Not shooting for high RPMs. Target power is under 500 HP but if I can teak some more without killing the motor or my checkbook so much the better. This will be the third early hemi I've had, plus I built a nitrous sbc awhile back, so I'm not a complete novice around engines. Not a wizard for sure but I'm up to the task, given the right info.

well, thanks in advance for your thoughts,
Neil
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Re: Stroking the 392?

Postby George » Fri Mar 27, 2009 3:50 pm

Basic stroking comment. If you increase the stroke you have to shorten the rod or move the wrist pin higher up the piston.If you're using custom pistons anyway, moving might be the best bet, as long as you don't move it so high that it interfears with the ring seal.
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Re: Stroking the 392?

Postby DblAdigger » Fri Mar 27, 2009 10:38 pm

Clearance grinding for strokers depends on: 1) the stroke, of course, and the configuration(bulk) of the rod big end. It WAS generally considered that a 3/8ths arm was OK, a 1/2 arm required some grinding, and a 5/8 arm would usually hit water. This was with M/T aluminum rods with the bolts set down .100. That was with standard Chrysler rod size. Now a days, with the smaller BBC rod journals and hence smaller big ends things would change.
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Re: Stroking the 392?

Postby NE57 » Sat Mar 28, 2009 10:17 am

Thanks for those replies. I'm going to 'try' to resist going for max cubes and lean a little to having thicker material remaining after clearancing. By my calculations looks like the 1/2 is worth just 13 cubes more then the 3/8 arm. I'm not certain yet what the finished bore will be, they are already 30 over but rusted, hopefully going to 40 over will be enough to clean them up, but we'll see. I'd like to leave room for another freshening up in years to come, or in the case of some cylinder/piston failure.

That is, If you think there is not a real significant advantage for a street motor to go 1/2 instead the 3/8? Would there be enough extra leverage on the 1/2 to make it worthwhile, aside from the additional displacement?

So if I did go with the 3/8 that would mean the pin has to go 3/16 higher in the piston, correct? (assuming stock 392 rods). That doesn't sound like it will pack the ring spacing too much, I think a thicker top ring land would be a distinct advantage? I'm thinking something like 11:1 compression but I need to speak with the piston maker about that in detail.

Ok I should mention...part of the reason I'm considering a stroker is the heads. When I got them they already had 2.125 intakes and 1.945 exhaust valves installed. Yeah they sound big for the street, My thinking is building in extra bottom end torque will maybe offset the loss from overly large valves(I'm just assuming there will be some vacuum loss with these big valves). Or is my thinking not correct? The heads are what they are, I have to work with them.

While I might like the sound and performance of a solid lifter cam, for the issue I just mentioned I'm wondering if a hydraulic with modified Rhodes lifters might be the ticket?

Well, sorry to get all convaluted but this is not the usual build because of the valves, so I have to plan this thing down to a T.

Thanks again
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Re: Stroking the 392?

Postby TrWaters » Sun Mar 29, 2009 2:56 pm

You need to remember that when using stock rods with a stroked crank that, while moving the rod journal away from the crank centerline will extend the rod out farther on up stroke, it will make the rod "short" on the down stroke. i.e.,piston pin closer to the counterweights, often times where even a short skirted piston will not be enough to clear.
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Re: Stroking the 392?

Postby NE57 » Sun Mar 29, 2009 7:36 pm

>it will make the rod "short" on the down stroke.

yeah I was wondering about that. Since I have all of the internals including the old bearings I was going to re-assemble the short block in a trial run. Take a close look at the relationship of the various moving parts to each other and the block. How much clearance exists now and how much might be gained where and by what method. Get thoroughly comfortable with what is 'really' involved as oppossed to what I 'read' is involved before committing the crank to the welder.

I've heard that 392 rods are among the longest rods. If a longer rod is indeed required, what do people use? I've read about really long strokes for the 92 so its doable, but with how much effort and $? My feeling is that while a very mild stroker might be easy the gain may not be worth the cost involved. If I do it the gain has to be substantial.

I haven't gotten quotes yet but just from looking at various sites I think the bare minium will be $3K for welding/grinding and pistons(really unsure about how much custom pistons will cost), then add in all the usual machine work and parts. If I need to get uber exotic rods it might be a project buster.

I guess critical factors are how much can the piston bottoms be cut and frankly, what's the cost to turn down the counterweights if need be, and would balancing become overly complicated at that point.

Its a bit more confusing than just ordering a stroker kit for a more popular engine where somebody already did the homework. But then there's not so much a challenge in that.

Thanks again, all input is appreciated.
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Re: Stroking the 392?

Postby DblAdigger » Mon Mar 30, 2009 9:30 pm

Having built and run many 392's with 5/8 arms in them, with stock length (aluminum) rods in them, I think you're over thinking the, non existent, problem. Stroker pistons are made to clear the crank.
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Re: Stroking the 392?

Postby dan miller » Wed Apr 08, 2009 7:11 am

A nifty way to accomplish this is to offset grind the crank to BBC (2.200") and utilize Eagle 7.100" rods with a set of aftermarket pistons. We utilize Ross, and a call to Pat O'Neil will get you all squared away. Ross makes a beautiful and very light piston for this application. You'll end up having around $1500 in a killer rotating assembly that you can lean on as hard as you want, without any fear whatsoever.

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Re: Stroking the 392?

Postby NE57 » Tue Apr 14, 2009 11:50 am

Should the cylinder bottoms be clearanced before or after the block gets rebored? I'd hate to slip and nick a fresh wall, but maybe a clearance notch would cause a problem for the machinist?
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Re: Stroking the 392?

Postby DblAdigger » Wed Apr 15, 2009 9:44 pm

We used to grind after boring as it was hard to get the pistons and rods in before.
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Re: Stroking the 392?

Postby NE57 » Thu Apr 16, 2009 10:02 am

haha yeah ofcourse it would be hard to put a too big piston in :lol: . I have a set of pistons that fit the present bore so I thought a mock up beforehand might work. Even though the piston would pop above deck the main cylinder clearance problem would in the general area of about +/-90 degrees b/atdc??? Was unsure if notching beforehand might cause a problem for boring tool, didn't know if it might jump or jam when it hit the face of the notch.

But I'm thinking I should be a bit conservative on the stroke, since this will be my first time at stroking. Earlier you said a 3/8 stroke was usually ok with alum rods. I'll be using stock rods, I assume they are less bulky at the big end.

Thanks
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Re: Stroking the 392?

Postby wayfarer » Thu Apr 16, 2009 11:33 pm

I might suggest talking with your chosen piston supplier to determine the highest position you can have for the pin, then back into the rod length. With all things being equal, if you want a ½' arm can you move the pin by ¼"? Perhaps you can even have the pin higher, but do the math before spending money. There are many high quality rods available, both in 2.2 and 2.5 diameters, with equal numbers of folks claiming that one is better than the other. I do not recommend using the stock 392 rod. They have a fairly small cross section under the pin and they will pull apart at that point. If you want to save some money by using an OEM rod then use the standard 440 piece (6.75"), and since it is 0.2" shorter than the 392 the pin does not have to move far. Also, if you get lucky, you may find some long 426 rods, like the old 7.06" NASCAR piece.
Good Luck, and keep us posted.
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Re: Stroking the 392?

Postby NE57 » Fri Apr 17, 2009 11:18 am

I'll tell ya its hard to know what to do. You don't like the stock rods, other sources suggest they are fine for my power level. (In no way am I discounting your expertise or experience, you certainly seem to know what you're doing) Experts disagree.

I'll tell ya another thing..I don't think there's a single component in this pile of parts that doesn't involve more investment. I'm not complaining, I knew it would cost actual money. But its too easy to fall into the 'might as wells'... Then again my basic belief is that overkill can be a good thing sometimes. I've already abandoned the idea of 4 webers. If this economy turns around maybe I'll revisit that. I have to keep in mind that after I get this puppy built I still have to go out and buy a car to put it in. I see online that 65 darts and 55 plymouths are often in the 5-10K range for something presentable.

You might call it bang for the buck or being cheap where it doesn't hurt. I'm trying to distill just the right combination of mods and money. I feel a stroker is the basic building block for great streetable torque, but I have to actually accomplish it all.

Believe it or not and this might be funny...this project started out with exploring power options for a Mercury Grand Marquis. I'm reading this, hearing that about what people are doing(and they ARE doing it). Then it hit me...WHY would anyone go thru all that trouble and expense and deal with state emissions inspections just to have a 300hp 4000lb comfy couch? So I remembered the first rod I built when I was 20(and a bit moto-ignorant)...64 Polara with a 354 4spd 4.56. THAT was fun. Till it met an untimely death by spun bearing and lack of funds.

oops, looks like I rambled too much for this thread subject, sorry. Anyway, all opinions are great and will be considered as to how they fit the project. Thanks much again.
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Re: Stroking the 392?

Postby wayfarer » Fri Apr 17, 2009 12:07 pm

Yeah, you're right, opinions are like...well, you know. We have used the stock 392 rod in many rebuilds, but only when we are satisified that they meet the minimum requirements for the particular project; blown engines and big strokers tend to put alot of stress on internals and we will go to great lengths to try and keep a fresh engine alive. Whether the economy is up or down, the EarlyHemi is still an expensive rebuild and no one wants to do it twice...we want to be sure that the right parts are used. It is not just our reputation, it is usually someones hard earned money.
With a welded stroker, the additional cost of the 440 rod is simply the cost of the rod. You already have the journal work covered and the wrist pin placement is covered with the new pistons. And, as before, you have a fair bit of room to play with the stroke based on pin location and rod length. Check out some of the RB type forums, you may find that long rod that fits your package. Mopar used several long rods in the 426.
Many years ago we built a stroker using stock replacement Hy-Duty pistons (they were bought out years ago) with 0.984 pins, then bushed the small end of the 440 rod ( FM # 4-67314Y) for the 'smaller' pin and matched the new stroke to the piston/rod combo. With a 0.030 bore we had 415 inches and 10:1 compression. Not a real radical package but with a very agressive solid lifter cam and 4-speed we knew how the car would be driven.

Looking for the car to use can be alot of fun, and you old 64 is a perferct example of what can be used. Like you, I am also fond of the 55-56 models, but as you note, something like a decent #2 can go $10k. Of course then I look aroud at what $20k will buy and the old car looks like a good investment. Certainly better than my '101K'...lol If I can help out at all just send a PM.

Gary
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Re: Stroking the 392?

Postby NE57 » Fri Apr 17, 2009 3:18 pm

I had heard about the 440 rod as an alternate. My concern was that it being shorter it would reduce dwell time at tdc and reduce torque, and torque would be my target with a stroker, aside from extra CID. But really some of that theory goes a little over my head. Like 'how much' shorter before it actually reduces torque? I have found no hard info on that. Maybe I'm too concerned about what's not a big deal?

I see that there is a BBC rod at 7.100" that's described as for use in strokers. If I wind up changing rods anyway i think i should consider the BBC's too. How does the over width(across bolt to bolt, not journal width) of the big end compare? Would the BBCs mean more grinding in the bores for clearance? But at 7.100 rod length I might have more difficulty packing the rings? I dunno, its hard to think about something I don't have in my hands to look at.

My boss is getting mad at me being online all day researching hemis when there's work to do. Good thing the boss is me. He can't fire me. Although he can dock my pay. Well, I've confused myself enough for today.
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Re: Stroking the 392?

Postby wayfarer » Fri Apr 17, 2009 8:03 pm

You are correct, the longer the rod the more dwell time at TDC and BDC. This is part of what makes a 392 a big torque engine, but remember that the 440 is not exactly a wimp with the 6.75 rod.
As I recall, the width of the bbc rod is similar to the 392 and 440, but since you are welding it up you can / will make the journal the correct size and as a bonus you get to dictate side clearance. Also, since the bbc journal is smaller diameter than the Mopar then it might allow a bit more clearance to the pan rail and bottom of the cylinder.

Cheers
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Re: Stroking the 392?

Postby DblAdigger » Fri Apr 17, 2009 10:17 pm

While I agree that there can be some gains/losses in the long rod/ short rod debate,,,it brings to mind what my old crew chief used to say: "You'll never see it in the lights". IMHO, chasing a few HP, EXCEPT in something like EMC, is not worth the time OR expense. Myself, I like the long rod/lighter piston route.
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Re: Stroking the 392?

Postby polyspheric » Sat Apr 18, 2009 5:20 pm

.
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Re: Stroking the 392?

Postby wayfarer » Sat Apr 18, 2009 6:04 pm

Assuming that all of the rods are the same length, then the piston will spend as much time on the bottom as it does at the top. The crank will cover the same number of degrees rotation, it does not know, or care, whether the piston is at top or bottom.
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Re: Stroking the 392?

Postby polyspheric » Sun Apr 19, 2009 5:19 pm

.
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Re: Stroking the 392?

Postby wayfarer » Sun Apr 19, 2009 8:27 pm

...and all this time I thought that the laws of physics had been throughly vetted...
perchance you are a tenured professor somewhere ? Naw, I didn't think so.
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Re: Stroking the 392?

Postby NE57 » Mon Apr 20, 2009 6:52 am

>longer the rod the more dwell time at TDC, less dwell time at BDC

Could you explain why?
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Re: Stroking the 392?

Postby NE57 » Tue Apr 21, 2009 11:00 am

Ok, one other issue comes to mind. Regarding rod ratio...shorter rod(440sixpack for example), longer stroke means more piston side loading, correct?

My particular concern here is that I may have to go to an 060 overbore because of a few scored cylinders. Which may mean if the piston side loading is severe enough I might expect a shorter cylinder life but at 060 the next rebuild might have to include sleeving or a new block. Seems logical to me.

In real world terms am I concerned over nothing? Is the extra wear just theoretical? Considering the expense of everything I'd like to get reasonable life out of the motor.
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Re: Stroking the 392?

Postby wayfarer » Tue Apr 21, 2009 11:46 am

Good questions. First, a word of caution regarding large overbores in the 392. Be sure to sonic check each hole to verify that an .060 will not leave a thin spot. The 392 is well known for core shift.

As for the r/s ratio, here a couple of examples to ponder:
392...4.25 stroke with 440 rod (6.76) = 1.6
392...4.25 with 7" rod = 1.65
392...4.5 with 7" rod = 1.55
392...4.5 with 6.76" rod = 1.51
stock 392 = 1.78
340 small block = 1.85
350 chev = 1.63
454 chev = 1.53
428 ford = 1.63

Although you have concerns about side loading, I do not believe that your suggested packages should be any less reliable than some of the examples. Some of the theoretical wear may be reduced with a light weight piston (less inertia).

Keep us posted on your progress.
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Re: Stroking the 392?

Postby NE57 » Tue Apr 21, 2009 1:23 pm

>Be sure to sonic check each hole to verify that an .060 will not leave a thin spot.<

Oyyy! more $!!!

So I spent the last hour or so searching the cost of sonic testing. Found things like, "While its expensive its worth it" etc, which sounded ominous. I found only one website that lists that as a line item with price. $85. Whew, not so bad after all. Is that about the going rate?

But what if I find the block does indeed have some thin spots. I read something about block fill. If the block is thin but filled at the bottom, would abandoning the stroker idea work? Will the lower stresses of stock stroke allow me to still use the block if its filled partially, maybe rethink my power level? Don't really want to pop for another block. An article says water temps would be Ok but oil temps would go up. An oil cooler could handle that Ok, right?

looks like sleeving the block gets costly...$850ish. But i read sometimes there are disastrous problem with that, he didn't elaborate.

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