273 302 318 340 build

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I could go that route, but Im still thinking that with the factory 2bbl pistons I will be over camming it.
I was wanting to budget build a sb and still enjoy the cuda(if rain ever stops here LOL)

So I borrowed a dial indicator to help figure out compression ratios on 85 318 stock bore and appears stock pistons. Engine #2 is a 70 318 with .030" over TRW L2373. Heads are 302, not sure on comb chamber volume but I put 60 in. I will CC the heads and looking at milling them what I can without having to change from my stock adjustable valve train. I put 60 CC in there until I get more accurate numbers.
I used verniers to get how far in the hole.
Compression Ratio formula I got from net
Swept Vol +Deck Height Vol + Head Gasket Vol +Combustion Chamber Vol
Divided by Deck Height Vol + Head Gasket Vol + Combustion Chamber Vol
85 318 70 318
Bore 3.91 3.94
Stroke 3.31 3.31
Compression Height 1.72 1.67(DAMMIT!!)
Head gasket thk/vol (1121G) 0.028"/6.1763CC same
Comb chamber volume 60CC 60CC
DeckHeight Volume (averaged) 17.289CC 33.06598CC(OUCH! twice as much)
Swept Volume 651.779CC 661.3164(not looking good lol)
Constant Volume 83.465 99.242
All these numbers give me a comp ratio of 8.8:1 on the 83 318 and a horrible compression ratio of
6.7:1 on the 70 318.
My measuring techniques may be hokey at best, but it gives me an idea as to where I am at and it helps me wrap my head around the “science” of it.
As I mentioned the 302 heads will get cc’d and Im going to ask machine shop the safest amount to mill without having to change from stock adjustable valve train.
Besides being horrible numbers on 70 318, anyone see errors that I may have made? Or numbers I am leaving out?
Thanks all.
Here is link to compression ratio formula
How to Calculate Compression Ratios
 
you said you were trying to add about 50 hp and more low end torque???
Here is my 40 year old 318 (1976), short block never taken apart. Home ported the worst smog 318 heads on earth, and didn't even have them cut. Threw in the cheapest summit cam kit (109 bucks cam & lifters), and put on a spreadbore cast intake with a squarebore 670 holley. No headers, 2.76 gears, stock converter.... Low end no problem with me... I found the best traction road (chip seal) we have for street tires... still no dice, still spinning up to 50 mph and backing off just a tad to get it to quit :D
 
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Nicely done! Sounds good and pulls good too.
318willrun said:
you said you were trying to add about 50 hp and more low end torque???
Here is my 40 year old 318 (1976), short block never taken apart. Home ported the worst smog 318 heads on earth, and didn't even have them cut. Threw in the cheapest summit cam kit (109 bucks cam & lifters), and put on a spreadbore cast intake with a squarebore 670 holley. No headers, 2.76 gears, stock converter.... Low end no problem with me... I found the best traction road (chip seal) we have for street tires... still no dice, still spinning up to 50 mph and backing off just a tad to get it to quit :D
Click to expand...
 
4spdragtop said:
Nicely done! Sounds good and pulls good too.
Click to expand...
Also, I'm using the Fel pro head gaskets that are .050 thick! I have worse compression than a factory 318 that's never been apart. If I cut the heads .040, it would be a healthier. and no, if I cut the heads .040, I will not be cutting anything else. It will be just fine. Of the times I've done it, never an issue.... ever.
 
Did you cut intake side as well? My machinist says yes but he doesn't have to mill the intake.
Thanks!
318willrun said:
Also, I'm using the Fel pro head gaskets that are .050 thick! I have worse compression than a factory 318 that's never been apart. If I cut the heads .040, it would be a healthier. and no, if I cut the heads .040, I will not be cutting anything else. It will be just fine. Of the times I've done it, never an issue.... ever.
Click to expand...
 
4spdragtop said:
Did you cut intake side as well? My machinist says yes but he doesn't have to mill the intake.
Thanks!
Click to expand...
No. I've never cut anything but the head-to-block surface. Ever. I've never had an issue. Even if you use a .039 thick head gasket, your giving up about .014 to the original head gasket. So your .040 becomes only .026 of a gain, follow??? Like I said, I didn't cut the heads on the 318 I now have in my car because I was keeping the cost under 500 bucks. And i did keep the cost to 497.00 :)
 
The E-4 won't overcam the 273 with 2 barrel pistons. I've built plenty of them. 273's don't have the compression problem that later engines have. As 318willrun said, he has given you a blueprint for a 318. It is all about air flow, matching components, and tuning your combination. And getting it to run where the car lives, or how you drive it. Don't get hung up on compression, and getting every .001 of an inch. Things are not that critical on the street. If you are racing in class, that's different.
 
So thanks to Mike/ 2darts, I picked up the 302 heads today. He made the purchase for me(3 hours away from me) and then also had a friend bring them closer to me!
When I picked up the heads he had a surprise waiting for me..an absolutely awesome Tshirt from Moparfest. And an autographed Mr Norms placard!! Very very cool!
The heads appear to be pretty clean. Valves are 1.78 and 1.50. Looks like the intake ports were smoothed out a bit. Mainly flash removal. Doesnt appear to be any work in the bowl area.
Machinist quoted me $80 per head to mill them. He said that he generally goes .030" without an issue. Im going to clean up the valves, then relap, then cc and then take them into shop to see what we will do.
I have done some reading/research on valve "shrouding"? Can anyone provide more info on this??
I figger the investment in these will help no matter what shortblock I end up going with.
Seller also threw in a Streetmaster, couldnt go wrong on the deal. Probably go with LD4B tho
So I noticed 2 spots in the combustion chamber that appear to be "zits"?? I circled them in yellow. Should these be a concern?
Also how far has anyone milled the 302's? And did they do intake side as well as block side?
Thanks all, and thanks again Mike!!

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As long as the zits are protrusions I would grab a Dremel tool and a small grindstone and remove them. Why mill the heads.
 
4spdragtop said:
Did you cut intake side as well? My machinist says yes but he doesn't have to mill the intake.
Thanks!
Click to expand...
If you mill the heads .030 you should probably take some off the intake surface too. That way the heads can be swapped to another engine and any intake can be used.
 
Not protrusions Mike. They are "pits/craters" small ones.
Im going to cc heads before milling. Then play with numbers to chk/compare ompression numbers
toolmanmike said:
As long as the zits are protrusions I would grab a Dremel tool and a small grindstone and remove them. Why mill the heads.
Click to expand...
 
4spdragtop said:
Not protrusions Mike. They are "pits/craters" small ones.
Im going to cc heads before milling. Then play with numbers to chk/compare ompression numbers
Click to expand...
If they are pits have the machine shop look at them before they do any machining. They could cause hot spots and preignition/detonation.
 
There is a chart somewhere in one of the mopar sb engine books that gives you the amounts to take off both sides. I'll see what it says. My memory. ...
Im not going to do anything that requires milling the intake.
Thanks again!
toolmanmike said:
If you mill the heads .030 you should probably take some off the intake surface too. That way the heads can be swapped to another engine and any intake can be used.
Click to expand...
 
With the 302's, I personally wouldn't mill them at all. Maybe .010 to make sure they are true flat.
 
4spdragtop said:
I could go that route, but Im still thinking that with the factory 2bbl pistons I will be over camming it.
I was wanting to budget build a sb and still enjoy the cuda(if rain ever stops here LOL)

So I borrowed a dial indicator to help figure out compression ratios on 85 318 stock bore and appears stock pistons. Engine #2 is a 70 318 with .030" over TRW L2373. Heads are 302, not sure on comb chamber volume but I put 60 in. I will CC the heads and looking at milling them what I can without having to change from my stock adjustable valve train. I put 60 CC in there until I get more accurate numbers.
I used verniers to get how far in the hole.
Compression Ratio formula I got from net
Swept Vol +Deck Height Vol + Head Gasket Vol +Combustion Chamber Vol
Divided by Deck Height Vol + Head Gasket Vol + Combustion Chamber Vol
85 318 70 318
Bore 3.91 3.94
Stroke 3.31 3.31
Compression Height 1.72 1.67(DAMMIT!!)
Head gasket thk/vol (1121G) 0.028"/6.1763CC same
Comb chamber volume 60CC 60CC
DeckHeight Volume (averaged) 17.289CC 33.06598CC(OUCH! twice as much)
Swept Volume 651.779CC 661.3164(not looking good lol)
Constant Volume 83.465 99.242
All these numbers give me a comp ratio of 8.8:1 on the 83 318 and a horrible compression ratio of
6.7:1 on the 70 318.
My measuring techniques may be hokey at best, but it gives me an idea as to where I am at and it helps me wrap my head around the “science” of it.
As I mentioned the 302 heads will get cc’d and Im going to ask machine shop the safest amount to mill without having to change from stock adjustable valve train.
Besides being horrible numbers on 70 318, anyone see errors that I may have made? Or numbers I am leaving out?
Thanks all.
Here is link to compression ratio formula
How to Calculate Compression Ratios
Click to expand...
how far in the hole were the stock 85 318 pistons with stock deck height??
 
4spdragtop said:
I dont have the #'s in front of me but I believe .085 average for 83 318 and 0.155 for the .030 over 70 318
Click to expand...
so .085 in hole with .28 gasket wounder how much quench distance it have with a 302 head? anybody? i come up with .365 is this right? that tight from factory,..humm
 
Thanks DWB, Im not sure what relationship quench plays in this? Can anyone elaborate? Always trying to learn
So I played with numbers a bit. I substituted new pistons in the 70 block. The new pistons I was looking at were these Sealed Power from Summit
https://www.summitracing.com/int/parts/slp-526ap30
The compression comes out pretty much the same. 8.8:1
With the 70 block I get the steel crank, and its already bored .030" over.
So when compared with the 83 318(stock bore) the extra .030 doesnt gain me much as mentioned earlier.
Also with the new Sealed Power pistons, the compressed height is 1.745". So Im gaining on the TRWL2373 which is 1.672.
I wonder if there is a weight difference between the SP pistons and the TRW? I dont want to get into a balancing issue. Which means more machining/$$$
Thanks all
dirty white boy said:
so .085 in hole with .28 gasket wounder how much quench distance it have with a 302 head? anybody? i come up with .365 is this right? that tight from factory,..humm
Click to expand...
 
So Ive muddled/confused things with my still unknown avenue that Im going. Ive been searching looking at piston options. One factor Im trying to research is the.piston weights and how much total weight difference is allowable before needing to balance the rotating assembly??
I sent Fed Mogul an email about the TRW L2373.030
Said that it was discontinued years ago but still had prints. Weight was 595 grams +/ 10 grams.
He had no info on the pin.
Factory 84 318 stock and 69 318 stock from my factory service manuals is 592 grams.
So 3 grams difference +/- tolerances.
Summit website has no weights that I could see for any of their piston choices.
Anyone know how much difference between all 8 pistons before a rebalance is required?
Thanks

I emailed tech thru Summit site. The KB Silvolite1266C 030. Weighs 778-805 grams. Thats quite a bit heavier than stock (592 ish)
 
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Don't take that data from Summit...I have found plenty of errors on their data.

Stock weight is 592 gr and the pin is 161 gr.

If you are not running hard, I would go up to 5 grams if I was not caring, but I'd like closer. Google 'piston weight change for rebalance' and you will get answers higher than that.

It is not hard to drill some material out of the underside of the pin bosses to get them close to what you had. Or, since the pin walls are REALLY thick on these pins, just drill or grind some material out evenly through the pin's interior length.

You're not going to get a quench effect with any of these pistons....! Piston to head clearance is around .110" with the .028" head gasket and the taller 526 pistons.


You're getting there on CR IMHO! I am getting around 9.2 Static CR with:
- 302 heads milled .030", assuming the chambers are 64 cc's to start with before milling
- .028" head gasket
- The Sealed Power 526 AP pistons. These are around .077" in the hole and are the tallest stock type pistons around these days.
 
Thanks for the heads up on Summit tech, KB were the ones that answered the email thru Summit site? That is where they mentioned weights vary from 778-805 grams. Quite the variance AND difference from stock (592)
When I called I spoke to KB tech, Daniel was helpful. Steered me towards the 1266C, same one I emailed about.
Stupid me I never asked Daniel to confirm the weight dammit!
The advertised compressed distance is 1.745". So thats a gain over stock(1.720) of .025" where that now puts the piston about 0.064 down (my redneck measurement was .089 avg)
Im hoping to finish lapping the valves tomorrow as well as play with more numbers. Once the lapping is done I'll cc the chambers.
Ive checked rockauto jegs mancini but it looks like Summit has the best selection/variety. Any other places?
I can see how this is so time consuming lol, but I enjoy it.
nm9stheham said:
Don't take that data from Summit...I have found plenty of errors on their data.

Stock weight is 592 gr and the pin is 161 gr.

If you are not running hard, I would go up to 5 grams if I was not caring, but I'd like closer. Google 'piston weight change for rebalance' and you will get answers higher than that.

It is not hard to drill some material out of the underside of the pin bosses to get them close to what you had. Or, since the pin walls are REALLY thick on these pins, just drill or grind some material out evenly through the pin's interior length.

You're not going to get a quench effect with any of these pistons....! Piston to head clearance is around .110" with the .028" head gasket and the taller 526 pistons.


You're getting there on CR IMHO! I am getting around 9.2 Static CR with:
- 302 heads milled .030", assuming the chambers are 64 cc's to start with before milling
- .028" head gasket
- The Sealed Power 526 AP pistons. These are around .077" in the hole and are the tallest stock type pistons around these days.
Click to expand...

I heard around the same volume, thats why I went with 60cc.
I will cc them after lapping.
Lelo Dart said:
I have heard 58-62cc but have not measured myself. I do have a pair though.
Click to expand...
 
The 1266C has 4 valve reliefs; it is not a flat top. It crosses over to the Sealed Power 285. So you will add 6-8 cc's of valve relief volume in to the equation and go back downwards on CR.

Stick with the 526AP's, IMHO.

Silvolite catalog is here; look at the top of page 22 for the 1226 valve relief pattern:
https://www.uempistons.com/catalogs/silvolite_catalog.pdf

That weight range of 778-805 grams that you were given does not make sense...... Even adding 161 pin weight to 592 gives 753 grams... Typical ring pack weight would be around 58 grams and adding that in does make sense either. Maybe they are including the carton weight? LOL
 
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