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318 Poly question #2977166
10/22/21 09:32 AM
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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.


Wife says too many cars, liquidation coming soon......
Re: 318 Poly question [Re: 6PakBee] #2977243
10/22/21 12:19 PM
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Can't answer the question, but that combustion chamber might make quench tricky.

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Re: 318 Poly question [Re: 6PakBee] #2977314
10/22/21 03:28 PM
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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.


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Re: 318 Poly question [Re: HotRodDave] #2977324
10/22/21 04:15 PM
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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.


Wife says too many cars, liquidation coming soon......
Re: 318 Poly question [Re: 6PakBee] #2977331
10/22/21 04:47 PM
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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.

Re: 318 Poly question [Re: 6PakBee] #2977391
10/22/21 08:34 PM
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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


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: 318 Poly question [Re: Cab_Burge] #2977404
10/22/21 08:46 PM
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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..

Re: 318 Poly question [Re: Cab_Burge] #2977451
10/23/21 12:21 AM
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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.


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Re: 318 Poly question [Re: poorboy] #2977454
10/23/21 01:30 AM
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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


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: 318 Poly question [Re: 6PakBee] #2977460
10/23/21 02:20 AM
10/23/21 02:20 AM
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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.


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Re: 318 Poly question [Re: Cab_Burge] #2977472
10/23/21 06:40 AM
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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.

Re: 318 Poly question [Re: earlymopar] #2977476
10/23/21 06:53 AM
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Re: 318 Poly question [Re: Sniper] #2977511
10/23/21 08:41 AM
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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

Last edited by Gtxxjon; 10/23/21 08:44 AM.

Carpe diem, quam minimum credula postero, thanx Horace!

There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
Re: 318 Poly question [Re: Gtxxjon] #2977512
10/23/21 08:43 AM
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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.

Re: 318 Poly question [Re: Sniper] #2977515
10/23/21 08:45 AM
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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

Schneider.jpg
Last edited by Gtxxjon; 10/23/21 10:09 AM.

Carpe diem, quam minimum credula postero, thanx Horace!

There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
Re: 318 Poly question [Re: Gtxxjon] #2977521
10/23/21 09:01 AM
10/23/21 09:01 AM
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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

D-port exhaust Weslake 426 D5ish.jpg440 ovalports.jpg
Last edited by Gtxxjon; 10/23/21 09:21 AM.

Carpe diem, quam minimum credula postero, thanx Horace!

There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
Re: 318 Poly question [Re: Gtxxjon] #2977525
10/23/21 09:18 AM
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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!

440 ICE engine.jpgIce head with flange.jpgRob Loring ICE ports.JPG
Last edited by Gtxxjon; 10/23/21 09:20 AM.

Carpe diem, quam minimum credula postero, thanx Horace!

There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
Re: 318 Poly question [Re: Gtxxjon] #2977532
10/23/21 09:40 AM
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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

402ci Poly heads.jpgRoo poly head work.jpgSchneider.jpg
Last edited by Gtxxjon; 10/23/21 10:05 AM.

Carpe diem, quam minimum credula postero, thanx Horace!

There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
Re: 318 Poly question [Re: Gtxxjon] #2977533
10/23/21 09:48 AM
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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

GP POLY.jpg340 caps.jpg
Last edited by Gtxxjon; 10/23/21 10:03 AM.

Carpe diem, quam minimum credula postero, thanx Horace!

There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
Re: 318 Poly question [Re: Gtxxjon] #2977576
10/23/21 12:22 PM
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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.


Wife says too many cars, liquidation coming soon......
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