My Turn for a Cam question - 318 Build

[MOPAROFFICIAL]

They are indeed .030 in the hole. They are not stock pistons. They were replaced the first time I built this engine about 17 years ago. At the time, I let the machine shop get all the parts, they told me they couldn't find a "mopar" piston the right size, with full floating pins. So what they put in it is pistons that have 2 valve reliefs, but they are in the wrong place to actually do any good as valve reliefs. I don't know if the're chevy pistons or what. I'll post a pic later to show what I mean.

View attachment 1714986753

Poly pistons. HEAVY

 

[rumblefish360]

Those look like Poly pistons with valve reliefs for high lifting camshaft lives.

 

[318willrun]

This won't make much power with those cams and compression, at 5200ft. The big thing is the heads and compression.
unless a decent throat cut is made and you really know how to port, the heads are going to be weak in low/mid lift flow and probably would be better off porting with stock valve sizes with such small cam and limited porting ability, and if you do use the 1.88...open the runner to 360 sized port window. You are gonna be foot deep in iron dust fyi

I get everything your saying, except what you didn't say. What is "much power"? The op is looking for a driver, not a 12 second car. I agree, I would cut the heads in that altitude. However, I think the op will be happy for what he is expecting.
Oh, by the way, I did a throw together 318 for my brothers Demon in Loveland, Colo (about the same altitude) a few years ago. I did the MP .474 cam, cut .040 360 heads that were home ported, and 4bbl with hedman headers. Short block was never taken apart. He out ran a mid - nineties corvette (4 exhaust pipes in the center), along with some other stuff. He had 3.55's and an 11" TCI breakaway converter. All used parts, including the 318 2bbl we started with. He was happy for the few cents he threw into it. I think the op will be happy also.

 

[nm9stheham]

They are indeed .030 in the hole. They are not stock pistons. They were replaced the first time I built this engine about 17 years ago. At the time, I let the machine shop get all the parts, they told me they couldn't find a "mopar" piston the right size, with full floating pins. So what they put in it is pistons that have 2 valve reliefs, but they are in the wrong place to actually do any good as valve reliefs. I don't know if the're chevy pistons or what. I'll post a pic later to show what I mean.

Cool... at least the shop was creative in getting the CR up. Per what I can find on the Egge version of these (L2050), these pistons should actually be about .010" below the stock 318 LA deck. So you might want to check again. The reliefs look a mite bigger than 5-6 cc's....I'll guess maybe 8 cc's total? Now you're up a tenth or so more for SCR. But still could use some CR help for the altitude.

Now for sure I would be checking the piston to valve clearance with a new cam and those pistons! Hmmm, are the cam and timing chain still on? If you tossed one head back on and lightly bolted it down, with clay on the top half of one piston, and put together a set of the pushrods and a pair of good lifters and the rocker set for that cylinder, you could rotate the engine by hand and see what you have for piston-to-valve clearance now with the present cam lift. (You may have to fill the lifters with some oil to get them to open up the valves right.) Then you would at least have some idea on the clearance you might have with a new cam. Durations and timing will have an effect on it too, but at least you will have a starting point for understanding the clearance.

Poly pistons. HEAVY

Do you have a weight on those babies, MO?

 

[MileHighDart]

Cool... at least the shop was creative in getting the CR up. Per what I can find on the Egge version of these (L2050), these pistons should actually be about .010" below the stock 318 LA deck. So you might want to check again. The reliefs look a mite bigger than 5-6 cc's....I'll guess maybe 8 cc's total? Now you're up a tenth or so more for SCR. But still could use some CR help for the altitude.

Now for sure I would be checking the piston to valve clearance with a new cam and those pistons! Hmmm, are the cam and timing chain still on? If you tossed one head back on and lightly bolted it down, with clay on the top half of one piston, and put together a set of the pushrods and a pair of good lifters and the rocker set for that cylinder, you could rotate the engine by hand and see what you have for piston-to-valve clearance now with the present cam lift. (You may have to fill the lifters with some oil to get them to open up the valves right.) Then you would at least have some idea on the clearance you might have with a new cam. Durations and timing will have an effect on it too, but at least you will have a starting point for understanding the clearance.

Do you have a weight on those babies, MO?

No unfortunately I've already tossed the old cam and lifters. Old cam was a stock 340 grind so I think it was .430 / .444 lift. So the comp 252H would be a little less at .425/.425, and the 256H would be a little more lift at .447/.455 So I'm thinking I'd be ok with either, unless I start shaving .040 off the heads to raise compression, then I might have to start worrying about piston to valve issues. Plus it had .050 head gaskets on it before and I'd be going with the .028 gaskets this time.

 

[MOPAROFFICIAL]

I get everything your saying, except what you didn't say. What is "much power"? The op is looking for a driver, not a 12 second car. I agree, I would cut the heads in that altitude. However, I think the op will be happy for what he is expecting.
Oh, by the way, I did a throw together 318 for my brothers Demon in Loveland, Colo (about the same altitude) a few years ago. I did the MP .474 cam, cut .040 360 heads that were home ported, and 4bbl with hedman headers. Short block was never taken apart. He out ran a mid - nineties corvette (4 exhaust pipes in the center), along with some other stuff. He had 3.55's and an 11" TCI breakaway converter. All used parts, including the 318 2bbl we started with. He was happy for the few cents he threw into it. I think the op will be happy also.

You had a very different build, 360 heads 160cc intake port as cast plus your "porting" and some camshaft, He has 318 heads 124cc intake port as cast once 68cc chambers now filled with 1.88 valves making them "65cc".
Your heads probably flowed at least close to stock at worse or at best 10cfm over let's say, not a knock on you, maybe they were gods gift to modified iron heads, regardless ...his without the right work flow 40cfm behind yours.

 

[MileHighDart]

Well, I went ahead and ordered the XE256H, complete kit, cam, lifters, 901-16 springs, retainers, keepers, and timing gear set. Ordered from Summit, they price matched the price from Comp cams website, and I had a $25 discount code so got a pretty good deal.

 

[Dartboy52]

Well, I went ahead and ordered the XE256H, complete kit, cam, lifters, 901-16 springs, retainers, keepers, and timing gear set. Ordered from Summit, they price matched the price from Comp cams website, and I had a $25 discount code so got a pretty good deal.

Cool, I think you will be happy.