[pmd400]

https://www.summitracing.com/int/par...iew/make/dodge

Has anyone used dodge 318 pistons in a 350? The pistons above will be a .055 oversize in a Pontiac. Replacement Pontiac pistons only have a 1.700 comp height where the dodge has a 1.741. The dodge piston will be at around zero deck height where the Pontiac will be .040 in the hole. The dodge also has no valve reliefs so achieving 9.5:1 comp will only require about 80cc chamber heads.

[67drake]

That’s a new one on me. Subscribing

[Steve C.]

Curious, what about the difference in wrist pin size ?




.

[1968GTO421]

^ Piston pin diameter is 0.984 in. -vs- 0..981 in for stock P350.

[ponyakr]

Shouldn't be a problem for a machine shop to hone the rod pin hole .003.

"... Replacement Pontiac pistons only have a 1.700 comp height where the dodge has a 1.741. The dodge piston will be at around zero deck height where the Pontiac will be .040 in the hole..."

Will a 1.741 pin height not put the piston top above the deck ?

Don't think I ever read that before.

Hey, if 1.741 will give you zero deck height, this piston will put the top .004 above the deck, which will provide even more CR. Lots of guys run .005 above the deck, & some even more.

https://www.summitracing.com/parts/s...iew/make/dodge

https://www.ebay.com/itm/SEALED-POWE...kAAOxygj5SemBr

This is assuming you can get by without any valve reliefs. I know the late 350's had no reliefs. But, they also had big chambers, small cams, and pistons down in the hole, maybe .020 +.

[pmd400]

Originally Posted by ponyakr

Shouldn't be a problem for a machine shop to hone the rod pin hole .003.

"... Replacement Pontiac pistons only have a 1.700 comp height where the dodge has a 1.741. The dodge piston will be at around zero deck height where the Pontiac will be .040 in the hole..."

Will a 1.741 pin height not put the piston top above the deck ?

Don't think I ever read that before.

Hey, if 1.741 will give you zero deck height, this piston will put the top .004 above the deck, which will provide even more CR. Lots of guys run .005 above the deck, & some even more.

https://www.summitracing.com/parts/s...iew/make/dodge

https://www.ebay.com/itm/SEALED-POWE...kAAOxygj5SemBr

This is assuming you can get by without any valve reliefs. I know the late 350's had no reliefs. But, they also had big chambers, small cams, and pistons down in the hole, maybe .020 +.

The height of the assembly with the dodge pistons will be, 1.875+6.625+1.741 = 10.241.

I know with a 60919 cam and 1.65 rockers the valves come nowhere near the pistons in a 455 with 6x heads. It actually takes a large cam before piston to valve in an issue. I’d think a 350 with no valve reliefs and a voodoo 702 cam would be fine.

[ponyakr]

"...10.241...."

So, do you know that exact distance, for your block, after square-up & all block machining ?

Or, are you just guessing that you'll end up even with the deck ?

[pmd400]

Originally Posted by ponyakr

"...10.241...."

So, do you know that exact distance, for your block, after square-up & all block machining ?

Or, are you just guessing that you'll end up even with the deck ?

It's an assumption. The pistons could end up .010 out the top. I think the standard felpro head gaskets are .045 compressed thickness.
It's an easy way to build compression in a 350. Pistons at or just above deck, no valve reliefs, low comp small valve heads milled from 90cc to 80cc.

[pmd400]

How much rpm would a cast piston/5140 rod 350 take?

[ponyakr]

Originally Posted by pmd400

How much rpm would a cast piston/5140 rod 350 take?

GOOD cast pistons & rods can easily go 6000 rpm in a 400. Bad cast pistons won't last long, if you beat on 'em a lot. I'm just talkin from my experience. When I had the 1st engine built for our '68 Bird Stocker, NHRA rules required factory replacement pistons only, which of course in a '68 330hp 400, were cast.

But, when I got ready to order pistons, GM did not have any 400 cast pistons in stock, for whatever reason. So, I just bought some from our local NAPA store. Don't have a clue who made 'em. Car ran high 12's, which at that time, was good enuff for TJ to win the 1st 6 races of the season, between 2 local tracks. She shifted it at about 5500 & crossed at about 6000.

After we got that car running, I also had a 400 built for my '69 GTO, to also run Stock. By that time, GM had some cast 400 pistons in stock. Got the car running high 12's. Then the Bird engine started to smoke out one side. Still ran quick enuff to win a race, but obviously had a problem. Upon tear down I discovered that one of the NAPA pistons was cracked, in the ring lands.

So, I pulled the engine out of the Goat, made enuff changes to make it legal for the Bird, and put the Bird back on the track. She won several more races, then at the end of the season, I swapped in a Muncie 4-speed & a rear end with street gears. For little over 2 years TJ used that Bird as her DD. No problems with the factory cast pistons & rods, street or strip.

So, to me, the question is: How good are the cast pistons which are used. I don't know which cast pistons, that will work in a P350, are the best. We raced a well used, original '70 455, for 3 seasons, in 3 different cars. Only new parts were an 041 clone cam, Rhoads lifters, & a TRW replacement timing set. Ran 12.40's & 50's, in 2 different '68 Birds. It was still running good when I gave one of those Birds to the kid that had been driving it. So, apparently, the factory 455 cast pistons were just as strong as the factory 400 pistons.

As for the rods, since the price of the 5140 rods has increased so much, I think some RPM H-beam rods are a MUCH better value, at $400. They are also lighter, which is a plus. These rods should be good to at least 7500, in a 350.

http://www.racingpartsmaximum.com/sa...elhbeam-2.html

[AG]

You need to measure the deck height of your block at the 4 corners before you do anything.

[Jay S]

There are also 318 pistons that come is std bore, 3.91 and .035 over in a 350 and have a 1.72 compression height. More like what you would see in a 3.75 stroke Pontiac. They typically have valve reliefs to, but they would be a little to small to do much good. Another cheap piston option though. The 1972 318’s had free float pins, some pistons for 318s might have provision for that too.

I have machined pistons that had negative deck height and made stepped head pistons. The 1.741 should be close to working though depending on the deck height of the block. We have went -.007 out of the deck before with a .045 gasket in a 455. Close enough you have to not only check the 4 corners, but every single cylinder for clearence.

We have built 2 318 mopars turbo set ups that ran cast pistons in them. One blow throw and a draw throw. Blow through had a dish cut to drop the compression. We abused it a bunch and never broke a piston. I remember one burnt out my brother did with one of those engines I will never for get. The tach went to 7500 and it was buried, speedo went to 150 and it got pegged done into the odometer. It had 3.23s, never made it over 10 mph for about 200 feet with the engine winding like that. The tires started to come apart he let out of it and it spun the car around 1 and a half times after he let out of it. Both back tires went flat when we got home. So I would say a 318 cast piston is at least as tough as a Pontiac piston. Would be a worthy effort to try that, I have a variety of new and used 318 pistons if you want to see something in particular for comparison to Pontiac. I think I have a new set of the 1.72 4vrs, and loads of used 1.741s.

[Formulas]

https://m.facebook.com/groups/401424...2682363834898#

[pmd400]

Just an update. I have a 350 on the stand. It has 89cc 7h1 heads with 1.96/1.77 valves. Pistons are .035 in the hole. No head gasket. I put a cam in with intake lobe of 270@.006, 224@.050 and .470 lift with 1.5 rockers. Intake centreline of 105. Placed playdough on top of the piston the valve didn’t come within a 1/4 inch of the piston. A street hyd flat cam 350 does not need valve reliefs.

[pmd400]

I think iv worked out some parts that will give more compression to a 350.

Dodge 318 3.910 bore dome pistons
https://www.summitracing.com/int/par...-std/overview/

Chevy 6.535 rods
https://www.summitracing.com/int/par...353d/overview/

Stock 3.75 Pontiac crank.

Let’s assume a 10.24 deck height. Pistons will end up 10.24-1.875-6.535-1.81= 0.020 below deck.

The rod is .090 shorter then a stock Pontiac rod so the piston comes closer to the cranks counterweights at bdc. The dodge piston looks to have less material under the wrist pin so that should off set this.

The dodge piston has a .200 dome. I made a dome out of playdough on a 350 piston. A .500 dome really close to the outer edges of the piston doesn’t interfere with the combustion chamber. The valve angle on a 318 is 18* where a pontiacs is 14* so the valve cutouts won’t be in the correct place. I’ve already proven that a street sized hyd flat cam doesn’t even need valve reliefs so this should not be an issue. I think the piston and rod length will fit a Pontiac 350 block/crank/low comp heads.

The problems. The Pontiac rod journey is 2.250. The bbc rod is for a 2.200 journal so .050 will need to be machined.
The bbc wrist pin is .990 and the dodge is .984. Both rod and piston are floating. So rebush and machine the rod for the dodge pin or buy bbc .990 pins and hone the piston pin bore .006 and hope the depth of the retaining clip groove is still deep enough.
Thoughts?

[ponyakr]

The problem is that after you pay all that extra money, you won't be saving a whole lot, by using 318 pistons.

You can buy Auto Tec forged pistons for about $500-$550 or so, with whatever pin size & location you want.

And, if you still wanna use BBC rods, you can go with 6.535, 6.7, or 6.8 length RPM H-beams, for $400.

http://www.racingpartsmaximum.com/sa...elhbeam-2.html

This way you'd have a light, super strong rotating assembly, that should be good to 7500. And you could order a pin height to stick the piston about .010 above the deck, for extra CR. So, you'd get decent CR, but with a flat top & no reliefs.

There are lots of ways to build a 350. But nobody with enuff money to do it right seems to ever wanna do it. They always choose something with more cubes.

The strongest low CR 350 that I know of, which runs a flat tappet cam, iron intake, & 750 Q-jet, is in the GTO Stocker driven by Brad Koivisto. The car runs low 11's. Minimum chamber size is 86.2cc. I assume it takes well over 400hp to go that quick. ???

It ran 11.211 at this race.

https://www.dragracecentral.com/DRCS...r=100#indextop

[Jay S]

I think you were more on the right track using the 1.741 comp height 318 piston rather than the domes. I think you could run a closer quench than on a typical 4.12 bore forged piston Pontiac running a cast type piston that small bore size. Then have the heads machine down to get the rest of the compression your looking for. I think an 80cc head with that 1.741 318 piston would be about 9.5 scr. That would be cutting about .040 off your heads with a .045 head gasket. The quench should be ok if you above 10.230 on deck height. Would have to check every hole for piston to head clearence.

I have had bbc rods bushed for .98 pins. To do that and resize them it was $180-$200 range. Cutting the rods .050 about $125 give of take. If your doing machining anyway it is not that much more to do that stuff. Adds up if your doing recreational machining. Last time I priced Autotec pistons it was closer to $700. It wasn’t for a 350 though, maybe that is cheaper??

[pmd400]

To make it really cost effective you really need a rod manufacturer to change the size of the small end during production at little or no cost.
How much extra would it cost to turn the crank rod journeys .050 under? I’ve got a .020 under crank that need to go .030 anyway?
Where can you buy autotec custom pistons from?

[tom s]

Paul K on this site is a dealer for Autotec I believe.Tom

[ponyakr]

"...Where can you buy autotec custom pistons from? "


I read that members Paul Knippen & Paul Carter can order 'em for you. Don't know what their price would be.

https://www.facebook.com/PaulKnippensMuscleMotors/

A few years ago I called Auto Tec, to inquire about some 350 pistons. They told me that i could by from one of their dealers cheaper than directly from them. So, I asked them for the name of a high volume dealer. The name they gave me was Shannon's Engineering. Here's a quote from my Email; "...a volume dealer with good prices would be Shannon’s Engineering. Get the form I mentioned to him so he can get with us. Phone # 507-445-3235 Tell Shannon I sent you."

After contacting Shannon, he gave me a price of about $460, including pins, if I remember correctly. So, with shipping, the total price would have been just under $500. So, I'm assuming the price would be closer to $550, today.

Ring groove choice could be either stock size, or smaller. He told me that the reason these pistons were cheaper than a custom set, made from scratch, was that these would be machined from shelf blanks, which could be used to make pistons for several different brand engines. I looked up engines with similar bore size. Besides the 318 Mopar, the 283 Chevy & some LS engines had similar bore size. So, they could use the same shelf blanks to make pistons for all these engines, I assume.

In case anybody wants to contact Shannon, here's his contact info.

https://shanonsengineering.com/produ...at-top-pistons