392 hemi vs 426 hemi

Discussion of the 331-354-392 HEMIs.

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392 hemi vs 426 hemi

Postby oldngood » Wed Oct 21, 2009 8:29 pm

for the sake of constructive debate, what did they do to make the 426 better than the 392, or why is it better ? here's what I see:

increased bore spacing, which allowed larger 4.25" bore

destroked to 3.75" to allow higher rpms

bigger ports in stock heads

cross bolted 4-bolt mains, stronger

full skirted block, stronger


and that's about it ! I welcome any other info
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Re: 392 hemi vs 426 hemi

Postby handygun » Fri Oct 23, 2009 10:25 am

Well the 426 is based off the B engine, so it picks up the front mounted dist, the external oil pump,5 bolts per cylinder, no separate water crossover etc the 426H was an improvement over the 426W not the 331-392, I think Chrysler would have abandoned Nascar with the MaxWedge before trying to retrofit 392's in their cars, which Nascar is the reason for the 426H, other than some valve angles the 392 probably wasn't much thought of during development of the 426H compared to how to adapt the head to an existing platform and keep that platform together under WOT
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Re: 392 hemi vs 426 hemi

Postby phil » Sat Oct 24, 2009 7:22 am

i am thinking about changing engines in my 34 5w from 331 to 426 ,my question is are the engine mounts / lugs the same , apart from above post differences, are the mounting holes in back of block the same as a 331 / 392
what are the differences i need to look for between the 331 /392 versus the 426 mounts
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Re: 392 hemi vs 426 hemi

Postby oldngood » Sat Oct 24, 2009 8:13 am

handygun wrote:Well the 426 is based off the B engine, so it picks up the front mounted dist, the external oil pump,5 bolts per cylinder, no separate water crossover etc the 426H was an improvement over the 426W not the 331-392, I think Chrysler would have abandoned Nascar with the MaxWedge before trying to retrofit 392's in their cars, which Nascar is the reason for the 426H, other than some valve angles the 392 probably wasn't much thought of during development of the 426H compared to how to adapt the head to an existing platform and keep that platform together under WOT


good points

you mentioned a very critical point that I forgot to post, the 5 bolts per cylinder on the 426- that is a big improvement for holding head gasket seal- the old hemis with only 10 bolts per head/4 per cylinder did not have as much clamping force

and the other issue, the 426 was never meant to be a passenger car engine in the first place, like the early hemi

legend has it the 413w could spank a 392 up to 100 mph- there's no doubt the 426 and RB block in general had a stronger bottom end- one well kept secret seems to be, the fuelers using 392's required a girdle across the mains and oil pan rails, otherwise the bottom of the engine would blow out and drop the crank and main caps- that was rectified with the low skirt cross bolt design of the RB/B engine
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Re: 392 hemi vs 426 hemi

Postby 392heminut » Sat Oct 24, 2009 8:31 am

phil wrote:i am thinking about changing engines in my 34 5w from 331 to 426 ,my question is are the engine mounts / lugs the same , apart from above post differences, are the mounting holes in back of block the same as a 331 / 392
what are the differences i need to look for between the 331 /392 versus the 426 mounts


The motor mounts are a completely different setup, and the early hemi bellhousing had basically the same bolt pattern as the LA engines whereas the 426 has the B/RB bolt pattern. You'll have to change the trans (or bellhousing) and modify the motor mount brackets in the vehicle to do that swap.
Owner of the Poor Man's Hemi Cuda
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Re: 392 hemi vs 426 hemi

Postby Chiz What Is » Sat Dec 05, 2009 9:08 pm

An advantage that the 426 had over the 392 especially in top fuel engines was that you could put more advance in the mag. Anything over 24 degrees in a '92 was very precarious resulting in cracked blocks.
Some days you win, some days you lose and some days you get rained out !
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Re: 392 hemi vs 426 hemi

Postby oldngood » Fri Dec 11, 2009 8:44 am

I had read online where Garlits said the 426 would take a lot more advance than the 392 and still make more power, where the 392 would blow up with that much advance. The question is why ? The most apparent reason would be the stroke on the 392 was longer, 3.92" for the 392, vs 3.75" for the 426- the shorter stroke would mean a faster burn and higher rpm capability- the the hemi chamber on the 426 was also somewhat smaller- it was less of a % of a sphere than the 392 chamber was. That may have led to it having a better detonation resistance than the old 392. Short stroke engines are known for their "fast burn" characteristics, long stroke engines are known to be more knock-prone and octane-sensitive. Digging deep for information, one will find the early Hemi engines were somewhat knock-prone, one reason why they kept the compression ratio rather low until 1958. With no quench pads in the chamber, that would make sense. I've run modern V-6 hemi-type 4-valve engines and can attest to the fact that at 9.6 CR they will ping on anything less than 93 octane premium fuel, even with electronic spark controls, knock sensors, timing retard, aluminum heads, and fuel injection. The hemi chamber is more knock sensitive than most want to admit.

Another issue is the block strength- the 426 was a low skirt design with cross bolted 4-bolt mains, and had more head bolts than the 392 to hold compression and head gaskets easier- the 426 had a lot more beef in the main journal area and cam journal area.

The major trait that keeps coming back to my mind is, the 426 just had much larger intake porting and far better intake manifolds, even in bone stock form. Not only was it stronger structurally, it could make the power with more airflow. Where an early Hemi head flowed maybe 235 cfm at .500" lift, the 426 hemi flowed way over 300 cfm bone stock. The early Hemi had large ports for its time, but they were actually on the small side compared to later Chrysler, Ford, Chevy offerings during the 1960's.
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Re: 392 hemi vs 426 hemi

Postby polyspheric » Fri Dec 11, 2009 11:17 am

The 426 rocker geometry is terrible.
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Re: 392 hemi vs 426 hemi

Postby oldngood » Sat Dec 12, 2009 10:11 am

the bore spacing difference between 392 vs. 426 is huge

4.563" for 392, vs. 4.80" for the 426
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Re: 392 hemi vs 426 hemi

Postby handygun » Mon Dec 14, 2009 6:56 pm

The 426H chamber is much larger than the 392's like 170cc to 107's on my 354 ( i cc'ed mine at 99cc's) the 426 can take more adv because the block is much stronger ie skirted and tied as are the rods,The 426 with its bigger bore also lends itself to being able to flow more air as the cylinders are wider and of course the ports are larger, I dont know how you could make a 4valve Hemi it would be a pentroof, I have held in my hands one of the A-925 heads and it was a pentroof, Hemi's were much more detonation resistant than a comparable wedge head of the same era, motors w/long rods have more dwell time at tdc than a short rod motor this is one reason they can make more power, I am not trying to be a know it all but this much I know
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Re: 392 hemi vs 426 hemi

Postby polyspheric » Mon Dec 21, 2009 3:10 pm

How does an engine dwell at TDC?
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Re: 392 hemi vs 426 hemi

Postby oldngood » Tue Dec 22, 2009 7:50 am

handygun wrote:The 426H chamber is much larger than the 392's like 170cc to 107's on my 354 ( i cc'ed mine at 99cc's) the 426 can take more adv because the block is much stronger ie skirted and tied as are the rods,The 426 with its bigger bore also lends itself to being able to flow more air as the cylinders are wider and of course the ports are larger, I dont know how you could make a 4valve Hemi it would be a pentroof, I have held in my hands one of the A-925 heads and it was a pentroof, Hemi's were much more detonation resistant than a comparable wedge head of the same era, motors w/long rods have more dwell time at tdc than a short rod motor this is one reason they can make more power, I am not trying to be a know it all but this much I know



4 valve pentroof= hybrid hemi= center spark plug- same basic design, just more valves- these are all over the place now, in all the common commuter cars. My wife's Saturn station wagon has a 2.2 DOHC 4-valve.

6.625" length rods- Olds Rocket had them since 1949- Chrysler copied the idea from the first Olds engine, Pontiac also had 6.625" rods since 1955- Olds in 1960's used a 7" rod in their 400 and 425

knock/ping topic: there is a lot of misconception about that on the net for the past 10 years, and one has to read between the lines, and look at the entire history- the 1951-54 era early hemis only had 7.5 CR- they'd run on any crappy gas without pinging- they had a huge 100 cc chamber, flat top piston, and only 331 CID- the resulting compression was very low, which is why they only made 180 HP. To put this in perspective, that's less than a modern GM 3800 Series II V6- which makes 200 HP with short rods and wedge heads, with only 231 CID.

The later high performance 300 letter cars, and especially the 1957-58 10:1 354/392 polys and hemis, were premium fuel engines only. Contrary to what we may read on the net lately about the knock resisting qualities of the hemi chamber, it was a very octane/knock sensitive design- this is a direct quote copy/paste from the Chrysler 300B article, and this engine only had 9:1 CR yet required premium fuel- by the time the 10:1 392 came out, there was 98/100 octane "high test" fuel available at the pump to fuel it. The same goes for any American made V8 of the late 1950's-early 1960's era, the top engine options were designed to run on premium fuel 98-100 octane or better. Personally I've found that the vintage American hi-perf V8 designs, regardless of make- will ping like hell at WOT on today's unleaded pump gas 93 octane- unless steps are taken to reduce compression, use octane booster additives, etc. See below:

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Re: 392 hemi vs 426 hemi

Postby handygun » Fri Dec 25, 2009 8:48 pm

A long rod motor will keep the piston at tdc or closer to tdc longer than a short rod motor hence "dwell time", alot of the older motors had long rods ie flat head fords, olds and pontiac.The Pentroof has two flat sides like a inverted V, if some are saying the 5.7/6.1 Hemi's are not Hemi's because of the two squish bands and not being an uninterrupted sphere then a pentroof definitley is not. laterally opposed valves don't make a Hemi alone, possibly the 300's motor pinged from the combination of small engine, radical cam timing, a heavy car and a 2spd trans, Hemi's can usually get away with a half point more compression than a wedge on the same fuel..all things being equal. I just finished my 354 headed 392 and am hoping to get it in my car soon, being able to run it on pump gas is paramount because it's a heavy (58 Plymouth wagon) street driven car so I kept my comp down and cam pretty timid 280/.485 and Im running a 518/4.10's to help it off the line. I don't want to be dumping additives in the tank to keep it from detonating or turning my timing way back, I have a 10 to 1 472 Hemi in my 65 Coronet that does fine off 93 octane but it's a bigger motor in a lighter car w/alum heads, so we'll see what happens here..hopefully no pinging
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Re: 392 hemi vs 426 hemi

Postby mart » Sat Dec 26, 2009 2:57 pm

handygun wrote:A long rod motor will keep the piston at tdc or closer to tdc longer than a short rod motor hence "dwell time", alot of the older motors had long rods ie flat head fords, olds and pontiac.The Pentroof has two flat sides like a inverted V, if some are saying the 5.7/6.1 Hemi's are not Hemi's because of the two squish bands and not being an uninterrupted sphere then a pentroof definitley is not. laterally opposed valves don't make a Hemi alone, possibly the 300's motor pinged from the combination of small engine, radical cam timing, a heavy car and a 2spd trans, Hemi's can usually get away with a half point more compression than a wedge on the same fuel..all things being equal. I just finished my 354 headed 392 and am hoping to get it in my car soon, being able to run it on pump gas is paramount because it's a heavy (58 Plymouth wagon) street driven car so I kept my comp down and cam pretty timid 280/.485 and Im running a 518/4.10's to help it off the line. I don't want to be dumping additives in the tank to keep it from detonating or turning my timing way back, I have a 10 to 1 472 Hemi in my 65 Coronet that does fine off 93 octane but it's a bigger motor in a lighter car w/alum heads, so we'll see what happens here..hopefully no pinging

------------------
Your cam at 280 degrees duration and .485 inch
lift dosen't actually sound all that mild, so you'll
probably be ok, but your basic supposition that
a mild or conservative cam will help to lower an
engine's octane requirement is wrong. The
opposite is true. A longer duration cam with more
overlap tends to bleed off cylinder pressure at
low and medium speeds, thus reducing an
engine's octane requirement.

mart
=============================
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Re: 392 hemi vs 426 hemi

Postby handygun » Sat Dec 26, 2009 9:36 pm

I agree more overlap bleeds off cylinder pressure, but there are other issues that a big cam creates that can lead to detonation, and I am no cam scientist but with all the cam science that out there, wide lsa's,fast ramps, different lobe shapes, cams installed with adv- straight up- ret. keyways, it can be difficult to make a correct decision. I have seen "bigger" cams installed and with the usual "upgraded" intakes and larger tube headers turn good running setups into no lowend, pinging dogs..maybe there converters were too tight, wasnt it comps high energy series that promoted short overlap events? My personal cam wasnt my choice, I had talked to Jim? at Racer Brown and had been discussing what I was looking for, my machinist unbeknowest to me has a working relationship w/a guy at Erson and ordered a cam thru them, I dont have the card in front of me but it's a little more than what I wanted, these guys build alot of bracket and class motors and have been very good about me building the motor at their shop, using thier burettes etc and this Hemi has been far from routine or easy (8 sleeves) but I'll run it and it's hard to read a fault in them with as generous as they have been with thier facility, so we'll see.
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Re: 392 hemi vs 426 hemi

Postby oldngood » Sun Dec 27, 2009 11:06 am

the pentroof will have similar flame propagation characteristics to the hemi, with the center spark plug. All the modern commuter engines are pentroof hemis to enable the use of 4 valves per hole- but even those are knock sensitive. I ran a 3.4 DOHC with 9.6 CR factory and it was a 93 octane only engine- it would not run well on anything less, and ran lousy on 87 octane, and pinged badly. With 93 it was ok.

8 sleeves is a real gamble for a street motor- ask me how I know, I tried it once and it was a waste of time and money- what happens is the sleeves break the original cast liner when pressed in, and that liner is what holds the deck down- I've tried 8 sleeves before in a Pontiac 455, and the results were a block that would not seal the head gaskets at all- instead of the head bolts pulling the heads down, the bolts pulled small sections of the deck upward only around each bolt hole in the block, leaving gaps between bolts where compression and water leaks through- it's ok with a dry block or filled block, but not with water in the block in a street car- I'd bet Vegas odds you will have head gasket sealing problems with that engine- because the integrity of the original cylinders is what holds the deck down- UNLESS you have a siamesed bore design, which the early hemi is not

even one sleeve will warp the cylinders next to it on either side, and knock the cam bearings out of alignment- I've had sleeved blocks not accept a cam 3 times so far, and then require the cam journal registers to be align honed. On one block 2 sleeves knocked the main bearing alignment out, enough to require it to be aligned honed a second time.

pressing a sleeve in a block is definitely a band aid fix and it doesn't always work, sometimes they leak. By far a better fix is, find another block. If you put 8 sleeves in I'm guessing you were going for a much larger overbore, and there wasn't enough wall thickness there.

putting a big cam in to bleed compression is a band aid of sorts- the right way to build a pump gas engine, is lower the static compression to begin with, and run a torquey cam and make more power in the street rpm driving range of 2000-5500. The biggest mistake most people make is putting too big of a cam in. A 220 duration cam at .050" is plenty big for the street, and a 230 degree cam is actually huge. Bigger cams require progressively looser/higher stall converters and deeper rear axle gears with an automatic. A stock shift is more forgiving, but adapting an early hemi to a stick is a challenge in itself and requires high dollar aftermarket adapters.

some of the engine builders use a big cam to then run 13:1 CR on pump gas, it will putt around at part throttle on the street, and maybe require timing turned back- but then to really race it at the track, the car requires 115 octane racing fuel to live at WOT for any length of time- they just don't want to admit it usually

the best compromise for a pump gas 93 octane engine, is a 9-9.25 CR motor with a 220-230 degree cam @ .050" using solid flat tappets, and as much airflow as you can get from the heads by porting them- then it will run no problem will full advance 34-46 degrees total, and not ping- and make a whole lot more useable power in the critical 2000-5500 rpm street driving range- most cars these engines go in are heavy 3500 lbs. + and require a lot of torque to move them.
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