Poly 318 buildup

[Gary Pavlovich]

Does anyone know if a 318 Polyhead block can be bore .090 to accept 360 pistons, and if the 360 crank can be modified to mate to the 318 Polyhead block, particularly the rear main seal? I am researching building power in a 318 Poly motor by attempting to bore and or stroke it with the 360 crank and pistons. Are there any speed tips from any of you "old timers" out there regarding a 318 Polyhead buildup? Would like recommendation on carb, cam profile, tuning, etc... Background: Parts I already have; ported & polished heads, Weiand alum. intake, 10:1 forged alum. pistons, (new cam and custom headers are available and will be purchased after I decide on the stroking option). Would like to purchase a dual quad intake if you have one. Thank you, Gary Pavlovich.

[thomasray]

Hi,, I will be watching for your replys as I have a complete motor & transmission that I pulled from a 65 Belevdere. Really not sure what to do with it..

[andrewh]

Well, you should be able to use the 360 crank,but I don't think you want to. The original crank in your 318 should be a forged one. Much stronger than the cast that normally come in 360's. I am not sure how much you can over bore it. You might want to check out the other boards on this, and give this guy a buzz. pquintin@imps0014.us.dg.com

[andrewh]

Well, you should be able to use the 360 crank,but I don't think you want to. The original crank in your 318 should be a forged one. Much stronger than the cast that normally come in 360's. I am not sure how much you can over bore it. You might want to check out the other boards on this, and give this guy a buzz. pquintin@imps0014.us.dg.com Try this board http://www.musclecar.net/dallasmopar/

[karl]

I wouldn't bore it more than .060 over and wouln't do that unless you really have to. The old 318 was a great engine for power and torque. I would agree that you don't want to use the 360 crank for it is as stated a cast crank and not a forged one as in the 318. One other thing to remember is this 318 should have free floating wrist pins and the 360 does not. As for cam selection it totally depended on what you wish to do, are you going to race on the weekends and mainly drive it on the street? I would not go with dual four barrels, unless you want to spend alot of time tuning them for your application. I would go with an aftermarket ingnition and headers. I would beef the torqueflite work on the suspension and make the car run good with what you want to do with it. I beat alot of cars at the drags that had bigger motors, because I could hook up and they couldn't. Butch Leal and I raced a couple of times in the early 70's and he had this problem. We both had modified 340's only he had dual 4's and I had a single. Once he had them tuned he would win, but it was over a year before he did that. So go with what you have and decide what you want and how the vehicle is to be driven. Then go from there. Us old timers will be glad to help any way we can. Good luck

[VoyagerExpresso]

Check out the following site for info re: the poly-head A-series 318 V8 (& related engines). I had a '66 Belvedere with the poly-head 318 for years--great running engine!
http://www.geocities.com/MotorCity/Track/4164/

[musclecarguy]

I don't want to sound like an expert on the ole "poly 318" because I'm not. I had read an article very similiar to what you are wanting to do written by Dick Landy in one of the Mopar mags a while ago. He really didn't believe the 318 was worth sinking any money into for the purpose of running more than normal driving. He believes there is just too much needing to be done to warrant all the money spent. As far as specifics, I just don't remember, but I do know he didn't believe it was worth all the effort. I have one sitting here myself and will probably just leave it together and sell it to someone who needs it one day. I'm sure I didn't help much, but thought I'd pass on what I did read. Good luck with your decision.
Lyle

[debushau]

I also have a poly 318 and was interested to know whether any of your performance items like the Weiand intake, new pistons, cams, etc. worked out. Out of curiosity, would anything be gained by changing the air filter or the carbs? Mine has the stock filter assembly and the Carter AFB 313S 4 barrel.

[glasser]

I don't want to kick ass. I don't want anyone kicking my ass in a Honda accord etc.......... However, how do you rebuild a low buck special 318 wide block without killing yourself at the bank and still be able to drive it daily? I am not a millionaire!

[Dr. Righteous]

Well, as far as I know the old poly 318 is a old design that dates from the 50s. There isn't very much bolt-ons out there for it because at the time it was around just about ANYTHING could be built with less money and make more power. In other words, it was a dog motor.
Someone related it to me comparing it to the chevy 307. Your money was much more wisely invested in a 327 or 350 because it made much more power with the same mods. And it wasn't just cubes, the other motors were better designed and more efficent.

[cruzerjd]

I agree with the others here that in that building a high performance Poly 318 is throwing good money after bad. I built one a few years back withan Edelbrock P 600 manifold and 3 Stromberg type carbs with progressive linkage and still got my ass waxed by Fords and Chevies. Went to a LA 318 and it seemed to have much more power. If you do want to build it, stick with a single 4 barrel, headers should not be neccasary, the stock 318 poly manifolds flow pretty well. A bit of porting and flowing of the heads could open up a few possibilities. As for the carb, I would use a 500 cfm Holley or Edelbrock( Carter). If you plan on driving this car on pump gas, then I wouldn't use the 10:1 pistons. You might be able to mill the head for a little more compression. Be aware that a lot of this stuff costs bucks and it might be more feasible to change over to a LA 318 or 360. There is a lot more performance goodies for these engines and it would ultimately cost you less for better performance. Just my 2 cents worth, cruzerjd

[Gary]

Bone stock and in the same car, a poly 318 will beat a LA 318. The poly was a simplified Hemi designed to be built cheaper and lighter.

Like any engine, the secret to horsepower is to get more air-fuel mixture inside, and get the exhaust gasses outside...faster. Among other things, that means a good intake manifold. Unfortunately, they didn't make such an animal. About the only one you will find is the stock single four barrel, and it's a heavy beast! It has a bore pattern that is meant for the old WFB carb, and a modern spreadbore will only fit with an adapter. The restricted manifold will mean you can't use the full capability of the carb.
You also can not buy headers , so they will have to be custom built.
There are a few mild cams around, but are getting harder to find. You might have to get a custom grind, and use the profiles for the old Fury.

My son and I built a poly with factory duals manifolds and dual exhausts, stock four barrel intake with an adapter and a late model stock carb. The cam was an RV grind from Isky, and we did not make any head modifications. Compression was about 9:1 with cast pistons. It ran low 15's in a heavy B-body with 3.23 gears, which is enough to beat most stock 350 mid-size GMs. The mods we made helped the e.t. by about 1 full second. You can probably get another half second with headers and some head work, but you will need lots of money to make it much quicker because off-the-shelf parts just aren't available.

BTW, I agree with your desire to make the poly run. Anybody can build an engine from a catalog, but it takes an expert to find, modify and create parts to fill the need. That's the way it used to be when I became interested in cars.

[Gary]

FWIW...here is a site with links to suppliers with poly parts.

http://www.geocities.com/MotorCity/Track/4164/

[Brian Mills]

Bone stock Poly beats bone stock LA because Poly has a 0.020" taller piston and full floating rods. I put Polys rods and pistons in my LA in 1977. Just a note, the pistons were TRW, they came with rods attached, the pistons themselves were forged, short skirt with little tabs where the skirt usually is. This is a serious improvement for the daily driver, especially when you add a cam and headers. The difference in acceleration from 4000 to 6200 was worth the price of the slugs alone.

P.S. I didn't get far before my car at the time hit the wrecker. I sold the engine to a dirt track roundy rounder with a Challenger, the local reigning 350 Nova made a nice light snack. The old LA went on to be champ 3 years in a row, driver, mechanic and powder puff. I highly recomend full floating rods, good cam and heads, and a little more compression.

Oh, before I forget, Poly shares water jackets with LA, size and dimension that is. 4" bore would be too much, it's possible, but you would be at the very edge. I wouldn't do it.

[Gary]

Good timing...I just got the new issue of Custom Rodder, and they upgraded a poly 318 with a Holley TB fuel injection, CD ignition and a Weiand single-plane intake. No performance numbers were given, but performance, drivability, and mileage all improved. Too bad the manifold wasn't a dual plane, but apparently it's the only one still made.

[cruzerjd]

I didn't think that the Poly could hold it's own against a later LA, but I might be wrong, all the Poly's I ever worked with were either in large cars or pickups. I guess the lack of performance pieces kind of taints the image. The ones i worked with were in 1, a 1963 Plymouth wagon, 2, a 1966 picckup, and the one we built was in a 1966 Plymouth Belvedere. So in a smaller car I imagine the feeling would be different, I dunno. cruzerjd

[cruzerjd]

Check out the new Car Craft abd look at tech questions. Someone sent a letter asking about building a Poly 318. Most of the stuff that was presented here was there also, but a suprise was that Dick Landy Industries offers a blower system exclusive to the Poly engine, pretty cool. cruzerjd

[1966cuda]

The 318 poly CAN be safely bored .090 over AND stroked to 4" to create a 402 cid polyhead screamer.

LA style pistons won't work tho, unless they are too far down in the hole to do any good. This is due to the latterally opposed valve design in the poly - valve indentions ain't in the right spot.

Talk to Gary Pavlovich in Yahoo Groups 318poly. He's the Guru and has written articles for and has done a 402 build up for mopar mags.

BTW - anyone with 318 polyheads for sale in the vacinity of east Texas - holla at me

1966cuda at g mail dot com

[Dick]

Originally Posted by 1966cuda

The 318 poly CAN be safely bored .090 over AND stroked to 4" to create a 402 cid polyhead screamer.

LA style pistons won't work tho, unless they are too far down in the hole to do any good. This is due to the latterally opposed valve design in the poly - valve indentions ain't in the right spot.

Talk to Gary Pavlovich in Yahoo Groups 318poly. He's the Guru and has written articles for and has done a 402 build up for mopar mags.

BTW - anyone with 318 polyheads for sale in the vacinity of east Texas - holla at me

1966cuda at g mail dot com

You replied to a thread that is 8 years old.

[Ray Bell]

I think, Dick, that despite the age of the thread we should dispel the myth that Polys can routinely be bored 0.090"...

Ben has checked five or six blocks so far, none of them have been capable of being safely that far with the bores still kept in line.

[Dick]

Originally Posted by Ray Bell

I think, Dick, that despite the age of the thread we should dispel the myth that Polys can routinely be bored 0.090"...

Ben has checked five or six blocks so far, none of them have been capable of being safely that far with the bores still kept in line.

The .090 was inflated due to the COLA index accumulating over 8 years.

[1966cuda]

Gary Pavlovich writes:

"There are several ways to go with the Poly and I am experimenting in building one now. You can turn down a 360 crank and nitrite it for surface strength, bore the block .090 (they take it easily) and sonic test for peace of mind, which will yeild a 360cid Poly. Or, order a 4 inch stroker crank (new Mopar Performance offering just out) and bore the block .090 which will yeild about 402cid of Poly. I am going the 402 inch route with 2.02/1.60 stainless valves (Ferria or SI), 10:1 JE or CP pistons, Scheider 288/.480 cam, custom headers by Spitfire Headers...

Initially, I was going to stroke it with the 360 crank along with the .090 overbore to yeild a 360 Poly which is documented by Bill Richardson of RAM Racing Engines, Lynchburg VA (an avid & knowledgeable 318 Poly builder) to produce from 350-500+ HP depending on your intent and budget.

However, after hearing of Mopar Performance's new 318/340 4 inch cast stroker crank (they make a 360 stroker crank also) I got greedy for cubes and thought this combo would be advantageous rather than the 360 because of the 3700lb.+ weight of my 1956 Plymouth 4dr.(my high school "first car" from 1968). I could use the additional torque from the 402 inch big stroker.

The new project will use a 66 Charger rear end with 489 case Sure Grip, starting out w/mild 3:23 gears.

The Poly project would take a 360 size piston because of the 4.0 bore, however the valve reliefs are entirely different on a poly piston. I will have pistons made. After consulting with people more informed than I, a strong case was made for the 3.58 stroke 360 crank: "Years of research indicate the optimum 'bore to stroke' ratio is 90%, which means that with a 4 inch bore, the stroke should be 3.6 inches. The 3.58 inch stroke of the 360 is so close you could spit. In fact a .020 inch offset grind will bring it right on the money." (Don Dulmage).

Sound advice. This science is what Bill Richardson of RAM Racing Engines employs. I have chosen to pioneer the 'gruesome torque' aspect of using the Mopar Performance 4 inch stroker crank for my application."

My desire is that people can learn from my successes and mistakes to help them in building the Poly motor that suits their wants and needs. One thing is for certain, building a Poly motor is a cool way to go, with horsepower to boot. "

[Paul Precht]

I did some flow testing back in the 90s and found the Olds 1.99 intake to be the best for the Poly head. It flowed similar to a Chev 1.94 that was pocket ported, Paul.

[Paul Precht]

I've bored countless sixties Mopar blocks 60 and 70 over without issue. I think a 90 over is possible with a good core, Paul.

[midmomopar]

Originally Posted by Dick

You replied to a thread that is 8 years old.

This seems to be a recurring theme here lately.

[blubele62]

its all us new to the site guys that dont know the ropes yet! like where to find the date and all. please be patient

[rumblefish360]

He he he, it happens, it happens.
My biddy went .090 overbore on his Poly. I think it was hennsley also does this to select cores of "LA" 318's for create engines.

[Ray Bell]

Did they have to offset the bores?

What thickness did they have the walls on the thrust and non-thrust sides?

[midmomopar]

Originally Posted by blubele62

its all us new to the site guys that dont know the ropes yet! like where to find the date and all. please be patient

No sweat, I've been guilty of it myself, searching for something then responding to a post I've found without seeing when it was written. Just seems to be happening a lot in the last week or so, must be a influx or new members. FYI the time and date is at the top left corner of the post.