Big Block vs Poly

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JGC403

JGC403

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Over the past several issues Chrysler Power mag has really been trying to revive the Poly Engines. I have been following along and think that the articles have been interesting. At the very least it is different.

My goal for my 1968 Barracuda is around 550hp. What I wanted to do was build a 400 block with a 440 crank, using as much aluminum components to get the weight down. So aluminum intake, water pump housing, heads. Also headers to help get the weight down.

The Poly motor. Looks like a LA or Magnum block could be modified for the Poly heads to work. To get to the power level I would like a 318 or 360 would have to have a 4" crank. So we would be looking at 390c.i. using the 318 block or 408c.i. with the 360 block. But I'm stuck using cast iron heads. I'm not sure how much the poly heads weight, but would it be lighter than my proposed BB above?

What do you think Big Block or Stroked Poly? The Poly would be different.

I guess what it comes down to is weight and power. Would the LA with Poly heads and aluminum intake, be lighter than 400/440 with aluminum intake, water pump housing, and heads?

The 550hp goal would probably be maxing out what the proposed Poly motor would be capable of making. While the 400/440 could still have some hp left in it? Am I correct in what I'm thinking there?

The reason I asked this now is I found a set of Poly heads in the Junk Yard. So if I do go the Poly route I can start collecting some parts.
 
I'd go big block. More cubes, you don't have to wind the pee out of it, better availability of parts. Plus, there is nothing cooler than an A body car with a big block.
 
No way in hell a poly will touch weighing in at BB levels,even w/aluminum
heads.BB heads are lighter than small block ones,so you aren't saving as much weight as
you'd think.I love the poly,and was always a fan of the head design,I acquired a dual quad
intake & WCFB's. I also love Gary P.'s commitment to developing the promise of the "original
twisted wedge",which definitely has it's advantages,and yes you can convert w/some effort
to them. But if all out performance and weight savings is the primary,I can't see one reason
not to just go stroked SB w/alum. heads. No BB is going to come within 200lbs. of that eng.
w/o some serious effort,and for what,20-30 cubes?Most good SB heads flow as well as the
BB ones unless you're stepping up to Indy/B1 type stuff,and to still lug&lift the extra iron,I
won't start mentioning the space logistics.
Either way,the choice is yours,if you want different poly up.If you want to brag,
go big block.If you want to go fast in a light car that meets your goals,small block all the
way baby! If you get a set of heads that flow260, w/a modest roller or .904 specific cam &
1.6 rockers,you'll kill that goal,no problemo. Try talking to MRL about this???
 
I figure the place for the poly is within the early B body crowd. C P has been involved with the poly for many years. a great engine with definite power stashed in there, but costs $$$ to play with. in that cuda I would check out 400 stroker or S B stroker. as with anything, all depends on your goals. IMO
 
I agree with the "for early B's" statement. Up to 66 or so.
But not enough that I would go out of my way to
own one.
If a car came to you with a good running poly engine then why not up the power some if you got the time and money to track down the obsolete.
 
Cracker want a poly???

I mean...

Poly want a cracker???
 
I am a big fan of both engines.A budget stroker 400 will give you 451 cubes. A stroker poly 318 gives you 390.Both short blocks will cost about the same to build,,BUT you are at a + 61 cubes with the stroked 400.11 years ago we did the 451 stroker with Edelbrock heads and a mild 490 lift hyd cam.Drove the car on the street(65 Belvedere tremic 5 speed 4.10 gears) put 30,000 miles on it in 2 years,put a 727 in it and went drag racing,3800+ lbs ran 11.90's in street trim. That engine was transplanted into a 73 'Cuda in 2007 and is living happy ever since.
Now the poly 318 would require much more money to build with the intake costing over $600 alone. You may be able to find something used.Poly head work may surpass the price of aluminum BB heads. Doubt if the early B TTI headers will fit in a A body,,,But it sure would be different when raising the hood.I have a friend doing a no expense spared Poly now to put in his 64 Dodge "B" wagon.Why ? He has had just about every Ma Mopar engine combo in different cars and Poly is the last on his list to do.So bang for the buck the 400 stroker wins for me. Just thinking out loud....
 
I found some numbers on engine weight, for the Poly, LA and B Engine.

273-318-340 LA - 525lbs
360 - 550lbs
B Engine - 620 lbs
RB Engine - 670lbs

B Engine with aluminum heads, intake, water pump housing about -530lbs
Poly with LA block and aluminum intake - 530lbs
LA with aluminum head and intake - 455lbs

So with the Poly/LA hybrid, and the B engine the same weight or so, the B engine has the advantage with the extra cubic inches.

I already have a Small Block Stroker in another vehicle. So I don't want to build another one for this project. I can get the weight of a B Engine down to about the same weight as a production Small block, so that shouldn't be to bad. Along with moving the battery to the trunk and a set of fiberglass fenders I picked up for a couple of bucks. I think I can get a Big Block to handle just fine.
 
HOLD ON! GRAND ERRORS TAKING PLACE HERE!!!!!


jerry6 said:
Big block , ply is heavy , parts are not easy to find .
Click to expand...

No so! Major error! SOME parts is more correct. Let me list what is hard.

Cam. Few companies still have a Poly cam listing. Allow me to list the 2 worthy.
Racer Brown
Crane Cams

Gaskets, look up Detroit gaskets

Pistons may get into custom territory depending on your needs for your goal. Forged slugs are almost always a custom item. Figure on a !1,000 set of slugs if you go outside the box.

Bigger than stock valves MAY be a custom order.

Killer6 said:
No way in hell a poly will touch weighing in at BB levels,even w/aluminum heads.
Click to expand...

You have this reversed. Even with aluminum heads and intake. The Poly has not a aluminum head. But does so on the intake.

I acquired a dual quad intake & WCFB's.
Click to expand...

I have said intake and they will use 2 - 500 AFB/AVS - Carter or Edelbrock. 600's require intake carb pad mods.


JGC403 said:
I found some numbers on engine weight, for the Poly, LA and B Engine.

273-318-340 LA - 525lbs
360 - 550lbs
B Engine - 620 lbs
RB Engine - 670lbs

B Engine with aluminum heads, intake, water pump housing about -530lbs
Poly with LA block and aluminum intake - 530lbs
LA with aluminum head and intake - 455lbs

So with the Poly/LA hybrid, and the B engine the same weight or so, the B engine has the advantage with the extra cubic inches.
Click to expand...

Thank you for the engine weights. The in bold text quoted from you has an issue that the OE poster MUST be made aware of.

There is no way in high heaven or the depths of hades that a LA block and Poly heads can work together OR a Poly block and LA heads work together UNLESS YOUR ONE HECK OF A GOOD WELDER AND CAN SERIOUSLY THINK OUTSIDE THE BOX.

I have in the past show the 2 blocks side by side with each of the engines heads mounted on each other's block to show why this can not be done unless, UNLESS YOU ARE ONE HECK OF A DYNOMITE WELDER AND CAN THINK OUTSIDE THE BOX TO MAKE THIS HAPPEN.

And I'd love to see this ****!

The Poly valve layout is EI EI EI EI
The L.A. valve layout is EI IE EI IE

Now think how that cam goes on each engine and let me know how you plan to work it.
LMAO!!!!!! "Z" pushrods? Drill and tube the head with pushrods in a "X" fashion?

The Poly block has a water passage inboard the engine in the valley area that feeds the intake cross ways to the otherwise of the engine.


To the OE poster, IF, IF you want to do a Poly engine, be prepped for a bigger expense than an LA. With less bang for the buck. While there is a fella CNCing Poly heads, there max flow falls short of the LA head in a similar state of work done to it.

Be in known, I personally know a Poly that has gone .060 with plenty of wall left. I have read .100 over bored. Some LA 318's have gone .090. (4.00 bore)
 
Contact Gary P. For serious information and how to do your poly.
And then tell'em rumbledish360 sends his best.
You'll not regret it, if you do a Poly.
 
There was an article in on of the Chrysler Power Mags that show what had to be modified to an LA block to put Poly heads on. The valve layout doesn't matter because you put a poly camshaft into the LA block so you would have the correct EI EI EI EI

I'll go look for the Chrysler Power mag now. October 2014 issue. They don't mention much, just state that they are getting a 0.030" over 360 with a 4" crank ready for Poly heads. and a picture with a caption where the pushrods area in the blcok had to be given some clearance.
 
...and on his farm, he had a poly - EI EI O


(couldn't resist - been reading nursery rhymes with my 4 yr old little girl...)
 
This guy is building 3 stroked polys as we speak one is going to the engine masters challenge and has contributed to the chrysler power article,block cam heads intake are all custom..Hekimianracing.com
 
JGC403 said:
There was an article in on of the Chrysler Power Mags that show what had to be modified to an LA block to put Poly heads on. The valve layout doesn't matter because you put a poly camshaft into the LA block so you would have the correct EI EI EI EI
Click to expand...

BING! GO! Have fun with that.

There's a fella on FABO that cnc's the Poly head. Mills the stand down and has T&D rockers.
 
rumblefish360 said:
Thank you for the engine weights. The in bold text quoted from you has an issue that the OE poster MUST be made aware of.

There is no way in high heaven or the depths of hades that a LA block and Poly heads can work together
Click to expand...
First,I'm not buyin' the 90# reduction in the "B" eng. An alum. int. will
save you 25# 383 TQ vs. Eddy DP,iron heads 88#/pair vs. Stage VI Al. 48#/pair. is 40# saved.
There ain't 25# to start with when you get to the H2O housing,just sayin.And a SB TQ
intake weighs 14# more than the 383 TQ. 52#vs.38#,as well as the heads 97#/pair.And
I'm supposed to believe the poly heads WITH an Al. intake weigh in 5# more on an LA?
Bullshit!!!! Second, um yes,just like every guy running Stage V engineering
Hemi conversion heads,or the unfortunately lost Covalt 32V heads, you just change the
cam......... no welding needed.Yes polys work on LA's w/no more work than any other hot
rod effort,changes are made & mods are performed and SHAZAAM!!!
 
The only reason to go with a Poly based build is because you do it either because you want a talking point, or you want to further the engineering and have the tools and talent to do so. If you watn a talking point, stick with simplicity and drop the power requriements. If you want the power, the goal will be a struggle to meet given the Poly parts market, and will not be a struggle at all given the B wedge parts market. All you have to do is make the choices as to what is important to you.
 
using the poly falls into the category of " a mopar guy loves to be a little different".
loves to build something that is not cookie cutter?
the poly 318 is a great proven engine and yes more power can be achieved.
that big wide sucker with a set of duals is just cool!???
the best fit for this engine is the home base 62-5 b body IMO
 
JGC403 said:
http://www.bigblockdart.com/techpages/weight.shtml

Aluminum Heads save 50lbs/set
intake save 25lbs
water pump & housing save 15lbs

90lbs weight savings
Click to expand...

The Stage VI bare casting weight came from mopar at 48lbs./pair, I have
personally weighed every other thing above,bare 452 castings 88lbs/pair incl., valvtrain of
course being equal so....... call ma mopar a liar. My friend had a set of Al. Stage VI's, but
didn't get to weigh them.You will save more weight on a SB switching heads&int. to alum.
than on a BB,that was the main point,and I'm still not buyin' the poly heads are 30lbs/pair
heavier than J/X castings. I need me some poly heads to weigh :) .
The logical thing is the SB,the coolest is the poly,the BB offers the most
HP potential since you're going Al. heads you can get the airflow to nix the extra mass.
Sounds like you prefer something different, and it's a stretch,but poss. in
polywood so I say go for it!! :glasses7:
 
RustyRatRod said:
http://www.1962to1965mopar.ornocar.com/poly318.html
Click to expand...

I do remember seeing that website a ways back. That fueled my interest in the Poly, even on a 402, they are pretty much maxed out at a little over 400hp. I see on the sight where is says that it should be good for 500+ HP, but nothin to back it up.


Killer6 said:
The Stage VI bare casting weight came from mopar at 48lbs./pair, I have
personally weighed every other thing above,bare 452 castings 88lbs/pair incl., valvtrain of
course being equal so....... call ma mopar a liar. My friend had a set of Al. Stage VI's, but
didn't get to weigh them.You will save more weight on a SB switching heads&int. to alum.
than on a BB,that was the main point,and I'm still not buyin' the poly heads are 30lbs/pair
heavier than J/X castings. I need me some poly heads to weigh :) .
The logical thing is the SB,the coolest is the poly,the BB offers the most
HP potential since you're going Al. heads you can get the airflow to nix the extra mass.
Sounds like you prefer something different, and it's a stretch,but poss. in
polywood so I say go for it!! :glasses7:
Click to expand...


So your talkin a difference of 10lbs. Still saving 80lbs on the BB and that is still a lot. Along with an aluminum master cylinder, battery relocate to the trunk, headers. Still will have a better weight distribution than a stock 440 Cuda and closer to a stock Small Block, so it should go around corners.

Poly Heads weight 51lbs each with out rockers arms. Actually over estimated the Poly, should be closer to 511lbs with aluminum intake
.
http://www.moparchat.com/forums/showthread.php?t=117690

Anyways always wanted to build a 451 or maybe a 470, Poly was just something new and different I discovered since I read about it in Chrysler Power. Probably would look out of place in an A-body and more at home in a B-body. Maybe could get away with it in an Early-A if it would fit.

More expense with a Poly, one extra expense that comes to mind would be custom headers.

I think I'm settled on a stroked 400.
 
JGC403 said:
I do remember seeing that website a ways back. That fueled my interest in the Poly, even on a 402, they are pretty much maxed out at a little over 400hp. I see on the sight where is says that it should be good for 500+ HP, but nothin to back it up.





So your talkin a difference of 10lbs. Still saving 80lbs on the BB and that is still a lot. Along with an aluminum master cylinder, battery relocate to the trunk, headers. Still will have a better weight distribution than a stock 440 Cuda and closer to a stock Small Block, so it should go around corners.

Poly Heads weight 51lbs each with out rockers arms. Actually over estimated the Poly, should be closer to 511lbs with aluminum intake
.
http://www.moparchat.com/forums/showthread.php?t=117690

More expense with a Poly, one extra expense that comes to mind would be custom headers.

I think I'm settled on a stroked 400.
Click to expand...

More expense in pollywood for certain,tho' until 440 source came
out with 'em, the H2O housing was $168,and I still doubt a true 15# savings on the BB,for
that $ i'd skip a few meals instead!! Anyway, I am a fan of the 451, and hp/$ is a much
better choice. Good luck & keep us posted :coffee2:
 
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