Moparts

318 Poly question

Posted By: 6PakBee

318 Poly question - 10/22/21 02:32 PM

Anyone know off hand what the piston height is on a stock 318 poly? Thinking about what it would take to build a zero deck motor for quench.
Posted By: Sniper

Re: 318 Poly question - 10/22/21 05:19 PM

Can't answer the question, but that combustion chamber might make quench tricky.

[Linked Image]
Posted By: HotRodDave

Re: 318 Poly question - 10/22/21 08:28 PM

Zero deck is easy, about .035 ought to do that but quench? Even max milling the head will give no meaningful quench pad, you would have to weld em up and mill them flat again. Another option would be to use an end mill and machine some flat areas in there and get custom pistons with a matching raised area... I love what quench does for an engine but even I wouldn't bother with it for the gain you would get on that engine.
Posted By: 6PakBee

Re: 318 Poly question - 10/22/21 09:15 PM

Okay, so trying to get quench is a stupid idea. No problem, I'll move on. Thanks for the frank comments, saves me continuing to pursue something that is questionable with this design.

Unfortunately it's been 50 years since I was inside a poly and I can't remember anything about it other than if you miss a gear and you see the tach going past 6500, you will bend a lot of pushrods.
Posted By: Sniper

Re: 318 Poly question - 10/22/21 09:47 PM

Originally Posted by 6PakBee
Okay, so trying to get quench is a stupid idea.


I believe it's the Marines that say if it works it ain't stupid. Not a stupid idea you have, might be tricky to implement and the gains may not make it worthwhile, but if you did it and it worked as you hope it's not stupid. Expensive, that is another story there.
Posted By: Cab_Burge

Re: 318 Poly question - 10/23/21 01:34 AM

Mopar stop making those motors for a reason, they weren't efficient or powerful down work twocents
The 273 L.A. motors made more power and got better mileage than any of the 305, 318,325, 331 or 354 C.I. poly motor in any of the Mopar cars or trucks scope
Posted By: poorboy

Re: 318 Poly question - 10/23/21 01:46 AM

Originally Posted by Cab_Burge
Mopar stop making those motors for a reason, they weren't efficient or powerful down work twocents
The 273 L.A. motors made more power and got better mileage than any of the 305, 318,325, 331 or 354 C.I. poly motor in any of the Mopar cars or trucks scope


You are talking about the early 60s here, Mopar put dual quads on those A motors and they made almost as much HP as the early Hemi's did. The reason Mopar quit making them was because they were too big for the downsized engine compartments, and because they were too expensive to make. Mopar (and most everyone else) wasn't too concerned about efficiency until the mid 70s gas shortages..
Posted By: 6PakBee

Re: 318 Poly question - 10/23/21 05:21 AM

Originally Posted by Cab_Burge
Mopar stop making those motors for a reason, they weren't efficient or powerful down work twocents
The 273 L.A. motors made more power and got better mileage than any of the 305, 318,325, 331 or 354 C.I. poly motor in any of the Mopar cars or trucks scope


It would be interesting to see how the poly heads flow compared to an LA or Magnum. I would think that would be the major difference between the engine families. And just looking at the heads, one would think, and I know this is an assumption, that the poly heads would flow better.
Posted By: Cab_Burge

Re: 318 Poly question - 10/23/21 06:30 AM

I should have included the two barrel L.A. 273 compared to the two barrel Poly motor made more power per C.I. and got better mileage than any of the Poly motors made.
I've owned and driven cars with both motors, the L.A. motors are way better than any of the those early Poly motors that Mopar stop making in 1966 twocents
As far as the size of those Poly motors compared to the L.A. motors how can they be bigger if they both can use the same timing sets as well as those timing sets fitting on the 1957 and 1958 392 Hemi motors? work scope up
I'm almost positive that the 1962 and later 318 Poly motors and 318 L.A. motors have the same blocks and crankshafts scope
BTW, the Poly motors where NOT L.A. motors tsk whistling shruggy
Posted By: Guitar Jones

Re: 318 Poly question - 10/23/21 07:20 AM

I've seen flow numbers for the poly heads in the past and even ported versions. Unimpressive to say the least but not horrible. You can use the LA stroker cranks in them and you might be able to bore some blocks .100 over. Unless you just want to do something different they probably aren't worth the effort.
Posted By: earlymopar

Re: 318 Poly question - 10/23/21 11:40 AM

Crankshafts yes but the LA block design is a lighter weight "thin-wall" casting. Poly blocks also have deeper reliefs on the intake side of the deck to clear the straighter pushrod angle required by the Poly heads.
Posted By: Sniper

Re: 318 Poly question - 10/23/21 11:53 AM

https://www.motortrend.com/how-to/426-cube-318-poly-can-outgun-hemis
Posted By: Gtxxjon

Re: 318 Poly question - 10/23/21 01:41 PM

Nothing wrong with Poly questions.

Semi-hemi engines don’t squench like wedgie engines.
Stroking is the easiest way to ‘up Poly compression’ methinks!

Folks have been spoilt with LA engines for over 50 years!

But the lowly 318 Poly can be made to work...

The old trick was to overbore to 4 inch and turn down a 360 crank.

But now we have high compression 402 kits for the serious Poly Folks.

400 horses not beyond a stout Poly build.

We are moving on to a 500 horse Poly build now, with a blower...

Dare I say it?

Chevrolet intakes and headers from the LS range... whistling
Posted By: Sniper

Re: 318 Poly question - 10/23/21 01:43 PM

Originally Posted by Gtxxjon
Nothing wrong with Poly questions.

Semi-hemi engines don’t squench like wedgie engines.
Stroking is the easiest way to ‘up Poly compression’ methinks!

Folks have been spoilt with LA engines for over 50 years!

But the lowly 318 Poly can be made to work...

The old trick was to overbore to 4 inch and turn down a 360 crank.

But now we have high compression 402 kits for the serious Poly Folks.

400 horses not beyond a stout Poly build.

We are moving on to a 500 horse Poly build now, with a blower...


Read the link I posted, 551 hp no blower needed.
Posted By: Gtxxjon

Re: 318 Poly question - 10/23/21 01:45 PM

Read it many times and those parts are way too exotic for ‘shade tree’ mechanics like me. drinking

I have contacted these folks for help and advice, but no luck.

Biggest problem was a trick roller camshaft, they are rarer then Unicorn tusks... fan

Compcams have made them for the selected few, the rest of us have only flat tappets.

Biggest we have found is a 'Custom ground' Schneider with a 0.525.
This stuff is so rare you have to 'GO IN PERSON' and BEG!!!
Its a long way from London Town to the West Coast... penguinwalk

So it’s an ‘old school’ blower for us now to find another 100 horses... drive

Attached picture Schneider.jpg
Posted By: Gtxxjon

Re: 318 Poly question - 10/23/21 02:01 PM

By a strange coincidence the fat intake flange method of port raising was done to my race engine in the 80’s.

Back before aluminium heads were available for 440 engines it was the only way forward.

The Ovalport intake was developed by Mother Mopar in the 60’s too.

I have here a set of Big block heads with that same design for a Nascar development engine.

Ovalport IN, D-port OUT... beer

All that is Old is NEW again... iagree

Attached picture D-port exhaust Weslake 426 D5ish.jpg
Attached picture 440 ovalports.jpg
Posted By: Gtxxjon

Re: 318 Poly question - 10/23/21 02:18 PM

My Rob Loring 452ci engine had the 'raised ports back in the 80's.

5/8 inch flanges and the ports raised by 1/2 inch with directional runners.

Engine made 550 hp and ran in the nines with a street Dart.

Very trick stuff indeed for the ERA!

Attached picture 440 ICE engine.jpg
Attached picture Ice head with flange.jpg
Attached picture Rob Loring ICE ports.JPG
Posted By: Gtxxjon

Re: 318 Poly question - 10/23/21 02:40 PM

The wonderful Gary Pavlovich has been the Poly Guru, for as long as I have known!

He supplied all the knowledge and the parts for our 402ci Poly stroker build.

Work underway for the new Schneider camshaft and better valve seals.

The biggest Poly flat tappet ever made @ 0.525'' with old school Crane dual valve springs...

Gary's custom made valves at 2.02'' and 1.60'' with 11/32'' stems.

Sure look much more exotic than a LA head lol... stirthepot

Attached picture 402ci Poly heads.jpg
Attached picture Roo poly head work.jpg
Attached picture Schneider.jpg
Posted By: Gtxxjon

Re: 318 Poly question - 10/23/21 02:48 PM

Facebook and ''62 to 65'' sites for Poly POWER!

Some crazy OLD folks take POLY very seriously indeed... drive

Me I'm just a DYNO-SNORE dino

ps. the 2 bolt POLY caps were a little suspect so the last job I did before my retirement was a 340 cap conversion! (just in case we hit the 500hp) lol... fan

Attached picture GP POLY.jpg
Attached picture 340 caps.jpg
Posted By: 6PakBee

Re: 318 Poly question - 10/23/21 05:22 PM

I sure appreciate all the replies. I think I'm going to add this to the already bulging project list simply because you just don't see many polys any more. It's the original engine in a '65 Belvedere II I have and I think I'll keep it that way. Thanks again.
Posted By: topside

Re: 318 Poly question - 10/23/21 05:56 PM

Anyone contemplating building a Poly should pick up Victory Library's "Chrysler Poly Performance" - I think a member here wrote it but can't recall his name.
It's a great resource & delves into a lot of stuff.
I've had a few - '63, '64 & '65 318s - and they didn't seem very octane-sensitive to me, they'd run on anything. Not sure I'd worry much about improving quench.
Then again, they were stockers, never pushed the CR, just drove them. Decent street motors, and not everything needs to make 600HP.
They used heavier castings than LA is what I've heard, and metal costs money. Chrysler would do anything to save a buck.
It's tempting to think "BBC" when looking at the valve arrangement, but ported Poly heads seem to max out at around 250/200 CFM I/E.
Subtract about 50CFM each side for stock.
Posted By: Cab_Burge

Re: 318 Poly question - 10/23/21 06:45 PM

For those that don't know why Mopar designed and built the Poly motors was for using a single rocker arm shaft to save money over using the hemi motors heads with dual rocker shafts and rocker arm spacers and spring on the same designed blocks on the Chrysler, De Soto and Dodge cars scope shruggy
Posted By: 6PakBee

Re: 318 Poly question - 10/23/21 07:13 PM

Originally Posted by topside
Anyone contemplating building a Poly should pick up Victory Library's "Chrysler Poly Performance" - I think a member here wrote it but can't recall his name.
It's a great resource & delves into a lot of stuff.
I've had a few - '63, '64 & '65 318s - and they didn't seem very octane-sensitive to me, they'd run on anything. Not sure I'd worry much about improving quench.
Then again, they were stockers, never pushed the CR, just drove them. Decent street motors, and not everything needs to make 600HP.
They used heavier castings than LA is what I've heard, and metal costs money. Chrysler would do anything to save a buck.
It's tempting to think "BBC" when looking at the valve arrangement, but ported Poly heads seem to max out at around 250/200 CFM I/E.
Subtract about 50CFM each side for stock.


Thanks for the tip, just ordered the booklet. up
Posted By: Rhinodart

Re: 318 Poly question - 10/23/21 10:37 PM

I just picked up a low mile 66 318 poly and 727 trans, my first ride was a 66 Satellite with a poly and I was always intrigued with it...
Posted By: Gtxxjon

Re: 318 Poly question - 10/24/21 10:21 AM

Huge commitment building a stroker Poly!

A few (pre 66) friends have started and baled out, but one fine Moparmate has carried on through 'thick and thin'...
Divorce, baliffs, forced to move house and no money for beer and Mopar Mags... spank

Once you begin the POLY Project its for life, not just for Christmas...(10 years and counting)
He laughs in the face of WEDGE heads now... realcrazy

But a trip to San Diego to see 'Gary Pavlovich' in person and he was struck dumb, with POLY POWER!!! drive

It was a revelation and Epiphany all in one moment!

He couldn't believe how folks has dissed the lowly Poly and how the head design was being used in modern V8 engines...

Its like Betamax and VHS, the best product doesn't always win out?

Its all about 'supply and demand'... drumhit

400 cfm Chev-head, can't be bad... ozbbq

Attached picture 400 cfm.jpg
Posted By: moparx

Re: 318 Poly question - 10/24/21 04:46 PM

Bruce Toth from down around Emlenton Pa. has been working with poly engines over the last several years, and has had several articles published in Chrysler Power magazine.
pretty impressive hp and torque numbers from these engines.
they are worthwhile reading if one wants to build a poly. just be aware, these non mainstream engines cost way more than the typical small block chebby, but can be a real surprise to a lot of them if built right ! drive
beer
Posted By: earlymopar

Re: 318 Poly question - 10/25/21 11:54 AM

I didn't find the cost of building a poly to be any different than building an LA. The only problems are part availability / fewer options which often forces the builder to get creative on adapting other parts. As usual, it really depends on what the build is.
Posted By: HotRodDave

Re: 318 Poly question - 10/28/21 07:54 PM

318 poly head is much better than a 318 2bbl head any day of the week, they flowed more and everything, the engine were just bigger, heavier and more expensive to make, the wedge design was a compromise. Boring away .100 in 8 cylinders took out a lot of weight...
Posted By: earlymopar

Re: 318 Poly question - 10/29/21 11:50 AM

Agreed on all points Dave. A comparison of the Poly head to the current generation Hemi head underscores the Poly head design is sound. They called the Poly a "semi-hemi" for a reason.
Posted By: 6PakBee

Re: 318 Poly question - 10/29/21 01:53 PM

Thanks to topside up for the tip about Victory Library's "Chrysler Poly Performance". I ordered a copy and it is an excellent read. Going through it the only problem I foresee is getting a hydraulic roller camshaft. Everything else seems to be doable....at least at this point. grin
Posted By: 6PakBee

Re: 318 Poly question - 10/30/21 01:31 PM

Have read the entire "Poly Performance" booklet over three times and there is one dimension I can't find. Is the center-center lifter bore spacing for a cylinder the same for the 318 poly as it is for an LA engine? Thanks!
Posted By: Twostick

Re: 318 Poly question - 10/30/21 03:25 PM

Originally Posted by 6PakBee
Have read the entire "Poly Performance" booklet over three times and there is one dimension I can't find. Is the center-center lifter bore spacing for a cylinder the same for the 318 poly as it is for an LA engine? Thanks!


Yes.

The reason the push rod angle for an LA is less than ideal is because the lifter location and angle was not changed.

A Poly head can be run on an LA block with some minor modifications, external oil drains from the heads and pushrod clearancing the block.

Kevin
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