Comp cams xe268h for 318

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dartfreak75 said:
If I get the money before the engine gets put together I will probably go with the xe256 or xe262. I have a lot of work to do to get the body brakes suspension and steering up to par if I have money after that ( or a better cam falls in my lap) I will upgrade If not I will use what I have and then say yall told me so Haha. Lol I also want to upgrade my carb and I'd like to upgrade pistons but once again the money is up. I would like to find a set of 273/318 floating pinned rods and attached a set of higher cr pistons but unless I find a deal on a used set I dont see it being doable.
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Typing at the same time....

Thank you... it restores my faith in humankind LOL. I appreciate your listening.

There is a set of those rods up in Strasburg VA advertised on FABO that might be had at a fair price. I am trying to think of a set of pistons with higher CR that are the same weight as stock, so that you can avoid the price of re-balancing but am drawing a blank. That is the chronic parts problem with the 318; cheap high compression piston options with stock weights.

The other ones that could be considered are very early 318 LA pistons like '68-'69 that have been reported to have a much higher compression height; they should balance out fine. But finding those would be a challenge; the standard replacements are not that, even if they are listed to cover '67-'69.
 
BTW, you asked about lower CR's for trucks. IIRC those are listed in the Silvolite catalog; you can see the lower compression heights listed.

Trucks spend most all of their operating time at low RPM's near the peak of the torque curve with small cams. The small cams increase the DCR at low RPM's to optimize this. But the RPM being around the torque peak puts you the closest to detonation.... add in some poor octane fuel from a fuel pump in the 60's in the middle of no-where and it wants to go 'ka-boom'. So I presume that is why the CR was lowered in those uses.
 
nm9stheham said:
Typing at the same time....

Thank you... it restores my faith in humankind LOL. I appreciate your listening.

There is a set of those rods up in Strasburg VA advertised on FABO that might be had at a fair price. I am trying to think of a set of pistons with higher CR that are the same weight as stock, so that you can avoid the price of re-balancing but am drawing a blank. That is the chronic parts problem with the 318; cheap high compression piston options with stock weights.

The other ones that could be considered are very early 318 LA pistons like '68-'69 that have been reported to have a much higher compression height; they should balance out fine. But finding those would be a challenge; the standard replacements are not that, even if they are listed to cover '67-'69.
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nm9stheham said:
BTW, you asked about lower CR's for trucks. IIRC those are listed in the Silvolite catalog; you can see the lower compression heights listed.

Trucks spend most all of their operating time at low RPM's near the peak of the torque curve with small cams. The small cams increase the DCR at low RPM's to optimize this. But the RPM being around the torque peak puts you the closest to detonation.... add in some poor octane fuel from a fuel pump in the 60's in the middle of no-where and it wants to go 'ka-boom'. So I presume that is why the CR was lowered in those uses.
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Yes I absolutely listen and respect everything you and all the other members here have to say. If I could afford to I would listen and do every bit of advice you all give lol but with my budget I have to do what I gotta do lol after our PM conversation I had every intention of saleing the cam and buying the one you (and others) recommended. But the cam was (is) on Ebay never sold after a couple months now it's almost time to start assembling the engine and it still hasn't sold so and i just dont have the funds for a new one. I had a 67 318 with new speedpro pistons i sold with my barracuda I wish I would have kept it now! Are the early 318s higher compression height than the later ones?
 
The pistons in the early ones have a larger compression distance but it ain't by much.
Here are some specs I found, in; HPBbooks how to rebuild your SMALL BLOCK MOPAR.
Piston compression distances: 1967 to [email protected], 70/[email protected], 72 to [email protected]
>>so these are about 1.97cc per change-up. The KB167 are advertised at 1.810 and 5cc eyebrows. This alone maths out to a difference of 8.77cc on the low-compression slugs.
Heads: 1967@57cc, 68 to 74@60cc, 75 to 86@63cc, 85/86 #302fastburns at 62.3cc, and the big-port police heads at 75.1
>>So these are about 3cc per change-up, not including the big valve heads
Boy it just cracks me up when I hear somebody say they have police heads,lol.

All SBM rods, up to and including 1973 had bushed rods.
The lighter weight 71 and older rods were forging #1318699.
The heavier 1972/73 rods,forging#2899496 came in 72/73 318s,and 68 to 73 340s; There must be a bazillion of these kicking around.
 
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dartfreak75 said:
Yes I absolutely listen and respect everything you and all the other members here have to say. If I could afford to I would listen and do every bit of advice you all give lol but with my budget I have to do what I gotta do lol after our PM conversation I had every intention of saleing the cam and buying the one you (and others) recommended. But the cam was (is) on Ebay never sold after a couple months now it's almost time to start assembling the engine and it still hasn't sold so and i just dont have the funds for a new one. I had a 67 318 with new speedpro pistons i sold with my barracuda I wish I would have kept it now! Are the early 318s higher compression height than the later ones?
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.
What do you want for it?
 
If you can bear up to another long post.....just some brain-storming here.

Which heads are you planning to use? The reason I ask is your mention of higher compression pistons. That appeals more and more to me as possibly the lowest cost improvement as you:
  • Can keep that cam and still achieve much improved low RPM torque. The engine low end RPM range is going to shift down and that is a better match for a stock TC, low rear gears, and smaller breathing heads. You get to keep the larger cam in case you ever switch to milled 360 heads.... food for thought there.
  • Example: If you are still using the 675 type 318 heads, I'd look at the KB399 pistons and that cam. DCR ends up in the 7.5-7.7 range with the least expensive head gaskets (Felpro 8553PT). That is getting pretty good and a far cry above the low 6 range where things are heading now.
  • It may be good enough that you can run fine with the stock TC and save that cost and effort, and will work much better with the present rear gear.
  • The unhappy cost is the balance issue. But wait.... there may be an easy solution. The KB399 pistons weigh 40 grams less than stock 318 pistons (552 grams vs 592 grams for stock ones). However, there are some cheap piston pins that will bring up the total piston + pin weight back to the stock 318 levels of 753 grams. These cheap pins are stock 2 bbl 273 pins, which weigh a massive 220 grams. (I bet someone here has some they'll give away.) Take those and drill them out a bit on the inside to get to 200 grams even, and there you are, right where it needs to be. The drilling can be done on a drill press as the inside ID is not critical; you just need to not nick the surfaces when holding them.
  • If you do the above, then let me know so we can work in more detail on weights. I have just taken a quick run through this info and would like to double-check. If you have the bottom end apart, and can borrow a precision gram scale, that would help to settle the final question I have.
  • Here is some actual measured 318 piston weight data for background info: 273 & 318 Connecting rod weights
Of course, if the bores are too worn, and you don't have the money to re-bore it, then I guess just throw it together and run it. That is something we just don't have info on at this point, unless you posted it before. IMHO, it would be a waste to buy new pistons and not have them properly fit; the increased compression just would not happen.

Switching topics: Higher compression with will be better for fuel mileage than the present setup but still not great with the present cam. Considering fuel mileage, if you change cams, to something 2-3 steps smaller I bet you are going to more than pay for the cam change in < 5000 miles of driving. For example, if you go from 13 mpg to 15 mpg (and I think it would improve at least that much), then you save over $150 in 5000 miles. The price of a Lunati Voodoo 701 cam from Summit is $137, shipped. However, DCR will only go from 6 something like 6.1 up to 6.4, so not nearly as great an improvement for low RPM range operation as with the piston change.
 
AJ/FormS said:
The pistons in the early ones have a larger compression distance but it ain't by much.
Here are some specs I found, in; HPBbooks how to rebuild your SMALL BLOCK MOPAR.
Piston compression distances: 1967 to [email protected], 70/[email protected], 72 to [email protected]
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Well now I am confused AJ. We had a recent post here on FABO where some said that they had actually measured some early 318 pistons with the piston tops <.010" below the deck.

I do know that I have some '68 273 pistons with a measured compression height of around 1.820" (confirmed by another poster) so that info on the early 318's being way up in the bores made sense. Now I just don't know.... Regardless, finding those early pistons in a usable condition with the OP's unknown bore wear is probably just about impossible.

AJ/FormS said:
Heads: 1967@57cc, 68 to 74@60cc, 75 to 86@63cc, 85/86 #302fastburns at 62.3cc, and the big-port police heads at 75.1
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FWIW.... Those mostly look like NHRA competition chambers volumes not typical production volumes. Example: 675 heads reportedly measure out around 68 cc's + or - (as did mine at 68 cc's).
 
dartfreak75 said:
I had a 67 318 with new speedpro pistons i sold with my barracuda I wish I would have kept it now!
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No huge loss so don't beat yourself up over it one bit ... those are still pretty low in the bores and not really much higher CR..... maybe 0.1 point. They would not change the large-ish cam challenge in any significant way.
 
I dont mind the long posts I enjoy them actually I like soaking in the knowledge. The heads I'm using are 302 heads its the original heads off the engine (86) it was a lean burn engine it had the lean burn distributor and a ecu controller on the firewall. I am gonna try and pull the heads off this week and measure the deck height so we know exactly what we are working with. I'm assuming it's around .100 down the hole that along with 65cc heads and +3cc for the eyebrows in the pistons (just in case) .027 head gaskets gives me exactly 8:1
 
OK, I forgot on the heads. In that case, the KB167's would make more sense; the domes on the 399's wont work with the closed chamber heads as far as I know. Using those and the .028" thick head gaskets (Mr Gasket 1121G) would give SCR of 9.4 and DCR of 7.3 with the cam. Much better than the low 6's and better than a stock 318 (which is in the high 6's for DCR).

But at a piston weight of 526 grams the balance problem rears it's ugly head again. Even the heavy 2 bbl 273 pins are not quite enough weight added to get back to stock piston + pin weights; they would end up at 746 grams, versus the stock 753 grams. For a po' boy build, that might be close enough to not have any serious vibration. (Heck, I'd be tempted to thread the pin ID and thread and lock in some added weight in those heavy 273 pins...... despite the 'uproarious laughter' and 'eye-roll' emoticons that are no doubt on their way LOL.)

Going back to the KB399 pistons and bit more brainstorming... is there any thought of using those 360 heads or, are they in too rough a shape to use? Just some quick numbers... typical 360 heads, unmilled, with the .028" thick head gaskets and KB399's ends up at a DCR of 7.4 with your cam, and you could bump it to 7.6 with cam advance of an additional 4 degrees to and ICL of 104.... hmmm.
 
dartfreak75 said:
I dont mind the long posts I enjoy them actually I like soaking in the knowledge. The heads I'm using are 302 heads its the original heads off the engine (86) it was a lean burn engine it had the lean burn distributor and a ecu controller on the firewall. I am gonna try and pull the heads off this week and measure the deck height so we know exactly what we are working with. I'm assuming it's around .100 down the hole that along with 65cc heads and +3cc for the eyebrows in the pistons (just in case) .027 head gaskets gives me exactly 8:1
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I think you are about right on the eyebrows; I use that + 1 more cc for the gap down to the top rings. I get your identical SCR if I use your numbers.... good to see that both our numbers are on the same page! That means that the DCR numbers will agree too as long as we use the same intake closing angle.
 
nm9stheham said:
I think you are about right on the eyebrows; I use that + 1 more cc for the gap down to the top rings. I get your identical SCR if I use your numbers.... good to see that both our numbers are on the same page! That means that the DCR numbers will agree too as long as we use the same intake closing angle.
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Ok I did 4cc for the eyebrows and that puts us at 7.92:1 do all 318 have the eyebrows ? Is there a chance mine dont? Just curious we will find out soon lol.
 
AFAIK factory teener pistons don't have eyebrows.
I had a nice 73ish Duster back in the day with a 318. I bought it cheap, and checked out for a quick flip. I sold that car for about 350, and always with the statement that I would buy it back for 50 no questions asked.
One time it came back, and the guy said it wouldn't start. No biggie I gave him his 50 and he was happy. So I cranked it over and could tell instantly it had no compression........ which I quickly traced to the valves. I pulled a head and it had 4 bent valves. And same on the other side. And the witness marks were on the tops of every piston. No eyebrows. So I smoothed the crowns,No biggie, and slapped a different set of heads on her and put her up for sale again.
Then, I just had to know how a teener could do this, so I contacted the previous owner. The story I got, was him and some buds were at a beer-drinking bush-party and decided it would be cool to see a teener blow up revved right up, with a brick on the gas pedal. Well, as I recall, the PO said that after 20 minutes it was still revving to the moon so one brave soul dared to reach in and turn the key off. ...... and after that, it wouldn't restart.
So my guess is the valves floated, the lifters pumped up and the valves kissed the pistons. And as long as the thing was wound up, it continued to run.
I made some good coin on that car, selling it several times.
I still have the heads; they're the ones in the stack with 4 missing valves.lol.
 
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Here is some more brainstorming if you do the math 3.31/2=1.655 + 6.123 for the rods - 9.6 for the deck that puts us at 1.822 (max compression height at top of the block) so if I am .1 under the block then that leaves us a piston height of 1.722. The largest c h piston i can find in the cheap range (ie speed pro etc) is 1.755 with no eyebrows. That will put me at 8.78 then if I could mill my heads a little let's say .020 that that will put me at 9.18. That Is about where I want to be. That is still gonna run me about 140 for the pistons plus machine shop labor for getting the pins pressed and heads milled. But this would be a better bottom end. If the bores are good and not wore
 
It would be nice if I could find some already on rods and could just rering them and attach them to my crank. Been looking on Ebay no luck yet
 
AFAIK; as far as I know.
The early rods are lighter than the 73 ups, maybe as much as 100 grams.
Therefore to maintain balance, you would need the matching pistons and crank.

9.6 is a nominal figure. It only exists on paper and in the imaginations of men..... unless someone has cut it to 9.6,lol.
 
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Ok thanks I hope you are correct if they dont have the reliefs that will put me at 8.22 starting out . So a quick .033 off my heads will put be at 9:1 I can always do that later. That assuming I'm .1 in the hole if I'm less than that the higher the cr will be.
I hope you are right haha
 
Oh yea I did my head cc at 65 if your number (AJ) is 63 it will be a little better also.
 
AJ/FormS said:
Let me rephrase that;
AFAIK; 73 and up factory teener pistons don't have eyebrows. And I think neither do the 71/72s. But I have no knowledge of the high-compression 318s of 69 and older
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Mine is a 86 so that means it shouldn't
 
Ok so I dont know why i didnt think of this before but I looked in my part info book and for 85-86 318 pistons the comp height is listed at 1.76 so with that number it puts me .062 in the hole instead of .100 if I put that on the calculator it gives me a cr of 8.87 that's no eyebrows either. That's is not as low as I thought. A quick and easy .015 off the heads will put me over 9:1 that is very doable. Of course I really know until I pull the heads and measure my pistons and cc my heads.
 
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