Monday, February 15, 2010

The 318 poly engine

The 1957 - 1967 Mopar 318 Poly (Semi-Hemi) 'A' engine used in Myrtle has a partial hemispherical head. It is a mostly different engine from the modern 1967+ Mopar 318- 340 - 360 small block 'LA' motor which has a wedge head.

A decent history of the Poly engines:

While we originally toyed with dropping in a new Mopar crate engine (maybe even a Viper crate), the idea of having a cool retro engine just became too tempting.

Often Overshadowed By Their Hemi Brethren, They Might Be The New Cool:

Some of the parts on the lower part of the 'LA' block are interchangeable, but almost everything from the cam up is different (excluding the ignition).

The 318 Poly was not a popular performance motor, so often the parts are harder to find, or there won't be as great of selection. However, you can get everything you need to rebuild an 'A' engine here:

The Travco probably weighs 14,000+ lbs. With a 318 Poly stock engine it keeps up; but that's about it. Don't worry... you can add a little bit of performance to this engine; The 318 Poly heads produce excellent torque for the engines relatively small displacement. This isn't a bad thing in a motorhome like a Travco.

Performance gains can be found with a cast iron OEM 4 barrel dual plane intake, or even the aluminum 6 barrel dual plane intake (Edelbrock P600). You do not want the Weiand single plane intake. A single plane will reduce torque at lower RPMs. You are driving a motorhome. You want torque at low RPMs.

Myrtle is upgrading to the Edelbrock P600 with 3 x 2 barrel Rochester carbs configured with progressive linkage. We will set this up so that most of the driving is done with only the centre carb (providing decent gas mileage), with the outboard carbs opening for extra power when you floor it. That's the plan anyway...

Carbs and stuff can be found here:

You'll have to scrounge for the intake.

Headers for your Travco? TTI makes the only Poly headers I am aware of. We have some TTI "LA" headers on the Dodge Dart and they are very good quality. I have no idea if the Poly headers will fit on a Travco. There is a lot of room under there, so they might be OK, but you would need to modify where they connect into the rest of the exhaust.

Here are some forums to ask any questions you might have.

Performance Poly Forum

Yahoo Poly Forum. This group knows there stuff.


3 comments:

1966 Travco 270 said...

I might be getting a Mahal with a 318 in it. Just depends on if he can find the title or not. I am curious to see what kind of mileage I get.

VoyageVixen said...

You are thinking of a 2nd travco? what will you do with 2? :)

Jeremy Filipenko said...

Stan's headers makes headers specifically for trick applications see http://www.stans-headers.com/chrysler_headers.htm Part number 318y-13 Unfortunately they are similar in price to the TTI headers (not cheap!), I am considering getting a set for the Caveman and for my 64 Fargo 1/2ton.