318" poli build.

[Walter R. Malik]

Is that exhaust valve really as shrouded as it looks to be in that cutaway and cylinder head photo? I'm thinking Mopar abandoned the Poly in around 1966 for good reason.

ABANDONED ...?
The modern designed Chrysler/Jeep "PowerTech" 4.7L V8 and "EKG" 3.7L V6 have pretty much the same type valve set-up in the chamber but, with the spark plug in a different location.

[Carnut1]

000_0008a.jpg

[/quote] I thought the same thing when I got a good look at the poly chamber. Add some quench and a heart shape with a different plug location and it is a pretty good modern chamber. I am a fan of the 4.7l h.o.. Thanks, Charlie

[Truckedup]

The Poly engine isn't bad compared to other engines of it's time...and applying known hot rod tricks you can get reasonable power .There's info from guys saying some or all the cranks will crack eventually at higher power levels so that may be a limitation..It's like running a Ford Y block, if you like it, do it.....
I used to modify 50's Chevy and GMC inline 6's....it's a fun challenge to a point until reaching a certain power level, always less than desired, and then it's big money after that...Same for the vintage Triumph bike engines I race...

[novadude]

Is that exhaust valve really as shrouded as it looks to be in that cutaway and cylinder head photo? I'm thinking Mopar abandoned the Poly in around 1966 for good reason.

ABANDONED ...?
The modern designed Chrysler/Jeep "PowerTech" 4.7L V8 and "EKG" 3.7L V6 have pretty much the same type valve set-up in the chamber but, with the spark plug in a different location.

Really? With no quench I wouldn't have thought that the poly design would be a good "active" combustion chamber. There is a good side by side drawing from Chrysler in Obert's "internal combustion engines" textbook showing the '66 318 poly chamber and the "new" '67 318 chamber. Can't recall the details, but the text discusses reduced emissions with the new chamber design.

[Truckedup]

Really? With no quench I wouldn't have thought that the poly design would be a good "active" combustion chamber. There is a good side by side drawing from Chrysler in Obert's "internal combustion engines" textbook showing the '66 318 poly chamber and the "new" '67 318 chamber. Can't recall the details, but the text discusses reduced emissions with the new chamber design.

And didn't Mopar change the B block from a closed wedge chamber to an open chamber in 68 to reduce emissions?

[DaveMcLain]

000_0008a.jpg

I thought the same thing when I got a good look at the poly chamber. Add some quench and a heart shape with a different plug location and it is a pretty good modern chamber. I am a fan of the 4.7l h.o.. Thanks, Charlie[/quote]

Its sort of a shame that the 3.7 and 4.7 got such a bad reputation for durability because the design itself is probably quite high performance. I've never driven one but I've sure worked on a lot of the heads.

[Diodedog]

The Poly engine isn't bad compared to other engines of it's time...and applying known hot rod tricks you can get reasonable power .There's info from guys saying some or all the cranks will crack eventually at higher power levels so that may be a limitation..It's like running a Ford Y block, if you like it, do it.....
I used to modify 50's Chevy and GMC inline 6's....it's a fun challenge to a point until reaching a certain power level, always less than desired, and then it's big money after that...Same for the vintage Triumph bike engines I race...

Here's some links to all the Poly Hi Po stuff available http://www.hotrod.com/articles/426-cube ... gun-hemis/ https://www.facebook.com/polysuperpac/? ... 1&__md__=1 The Poly cranks are basically the same and as strong as any 340 crank, the company listed has stroker kits that are quite affordable. Back in the 90s I did a mild port job on a Poly port using an Olds 1.99 intake and it flowed very similar to a mildly ported 1.94 Chev head. What kind of Triumph engines are you running, I have a 70 650 Tiger and a 72 Norton Commando.

[Diodedog]

https://www.facebook.com/polysuperpac/? ... 1&__md__=1

[Walter R. Malik]

The Poly engine isn't bad compared to other engines of it's time...and applying known hot rod tricks you can get reasonable power .There's info from guys saying some or all the cranks will crack eventually at higher power levels so that may be a limitation...

ALL Poly 318 engines had forged steel crankshafts.
Actually, the same steel crankshaft as the early 273/318 wedge or 318-3 truck crankshafts.

[Truckedup]

What kind of Triumph engines are you running, I have a 70 650 Tiger and a 72 Norton Commando.

I run land speed racing....74 frame with a 70 650 in modified production push rod gas class, a current record holder with speeds of 125-128 MPH on one mile and mile and a half mile paved tracks. The new build is a dual Triumph 650 pre unit engines in a custom frame open class 1350 cc ...I managed to fry a piston in trial runs...it'll be ready to race again shortly...60-65 hp from 40 cubic inches built in a home shop is not too difficult with a pile of money ...

On the crankshafts is this from Allpar website. Some hot rod site also mention crank breakage but who knows if it was common or not

The weakest part of the V8 engine was (at least in early years) the crankshaft. Even though the cranks are forgings, they are prone to breakage. Mine broke between the number four main bearing journal and the number seven and eight connecting rod journal. I know of at least seven other 1955 Dodge owners who have experienced similar problems. My car, however, gave me a warning of impending trouble with low oil pressure. There were no noises until it cut loose, and then there were plenty of new audio sensations. The crank looks structurally sound; I believe that the trouble is in the Dodge bearing materials. A good aftermarket bearing should be used during a rebuild. The cranks can be welded back together and made into interesting lamps.

[Brian P]

I believe this is a Fiat Firefly head... Looks like a Poly head mated with an LS Chevy head....I assume the head is a compromise of power, fuel mileage and low emissions...

More info: https://www.allpar.com/forums/threads/n ... es.165833/

In one of the pics, you can see right out through the intake port. The short side of the intake port is pretty straight. That plus the offset valve arrangement looks like they are aiming for high swirl.

I am thinking that someone at Fiat established (correctly) that the intake ports on the existing 1.4 FIRE (4-valve pentroof) were too big. My rough calcs suggest that an engine of this size (333cc per cylinder) and RPM (peak power around 6000 rpm) should have intake ports around 26mm in diameter. That's pretty easy to do with a 2-valve configuration with a bore size of 70mm.

I like the long intake runners, too. And the variable valve timing that shifts intake and exhaust timing together.

This certainly won't be a high-performance engine, but it does look like a good example of keep-it-simple economical design.

[pdq67]

I didn't know the Chrysler 392" hemi engine was also a poli-head engine?? 354" engine, sure....

If I was to design the poli- head, I would have put the intake valve in the chamber and left the exhaust valve flat like the old MEL and "W" engine heads. Like they are...

Raised the exhaust ports as well as the intakes and had at it!!

pdq67

[Geoff2]

The Chrysler Poly 313-318 engines were great engines. They felt more like 418 cubes than 318. My 1960 Dodge Phoenix with a Poly 318 could easily beat my mate's 390 Galaxie, both cars similar weight.

[Nick Campagna]

While in High School and College, I looked real hard at my Dad's 1956 Chrysler Windsor. It had the 331 Spitfire motor. The New Yorker had the 354 Hemi. The '56 Spitfire was a single rocker shaft motor with valves on opposite sides of the shaft. That was the Chrysler Spitfire. The block could accept the Hemi heads with minor relieving at the push rod holes in the block deck surface.

[Geoff2]

There is a poly engine in the EMC, results in HR magazine Mar 2017. Stroked to 402 cubes, made 602 hp @ 6000 rpm with a relatively small cam 234/238 @ 050 & a whopping 617 ft/lbs of tq. Most all engines in the EMC use aftermarket alum heads, which makes the the result so remarkable because it used 50+ year old FACTORY heads.
Contrast this to a 375 ci Ferd Y block block entry, aftermarket alum heads, 22 degrees more cam duration with a 256/260 @ 050 cam, it made 603 hp but only 565 ft/lbs of tq.