273 Pins are shorter than 318, 340, and 360.
302 casting on a set of 318 heads
- Thread starter 63spf
- Start date
-
273 Pins are shorter than 318, 340, and 360.
moparmat2000
Well-Known Member
How about these. Not cheap compared to the sealed power slugs but may be closer to zero cylinder side CCs. However forged and comes w rings, but out of stock at this place. $369 doesnt seem too bad for what you get, including floating pins Look at CR with 64 and 62 CC heads. Not sure what an average 302 head chamber measures.
Slantsix64
Well-Known Member
You can buy flat top roller motor pistons off rock auto they are taller will give you a great CR true 9:1 roller motors have the pistons .040 in the hole, taller piston closer deck height. 302 heads are 64ccs
Last edited:
moparmat2000
Well-Known Member
I may just say **** it, just rering whats there, do a valve job on what I have, new bearings and gaskets odds n ends and thats it.
Slantsix64
Well-Known Member
I had a stock compression 318 best of 10-12 mpg compression ratio of 8:1 and that was after I added 302 heads pumping out a weak 120psi, I built a 9:2 roller with the same 302 heads pumping out 155 psi cold test way different beast more power and overall better mpg lots of torque 15 city with 3.55 the bump in compression was worth it more compression you can Get away with more camshaft and not turn the motor into a dog. The extra effort was worth it.
nm9stheham
Well-Known Member
By about 0.2" so not any issue for overall length. They'll bear in the pin bosses a length of around 0.7" which is plenty to spread the pressure. 2BBL 273 pins weight around 211 grams, vs 154 for the 318/340/360 pins.
Probably H814's...still .067" in the hole in an LA block, and around .050" in the hole in a later block
Yep easy to get to that point. Those Wiseco's....I can't find the weights in their catalogs or anywhere but being forged (rather than hypers like the KB's) might make them heavy enough. You could deck the block and change pushrods to make the stockish pistons work at a higher SCR.
nm9stheham
Well-Known Member
Can't get a better testimonial for this type of change than that. For street use, the added low RPM torque works for you in many ways.
Here is a Stock 1969 230 hp 318 with the factory 9.2:1 pistons in it yet and factory stock heads, intake and exhaust manifolds. Added an Edelbrock 1406 600 cfm carb with an adapter.
727 Trans, 2.94 rear gears in a 69 Satellite. Performs very well, fun playing with the secondaries, definate seat of the pants improvemnet and best of all gets 20 mpg.
Get the right combination of factory parts and keep the port flow good, you will be surprized what these 318s will do.
One other indirect performance gain was swapping to the much lighter Torq Thrust All Aluminum wheels. 80 lbs less of rotating mass to spin up every time you start and stop.
So Happy with this setup, great low end torque engines, 1800 rpm at 60 mph. Great freeway cruising with power to pass any one you want.
727 Trans, 2.94 rear gears in a 69 Satellite. Performs very well, fun playing with the secondaries, definate seat of the pants improvemnet and best of all gets 20 mpg.
Get the right combination of factory parts and keep the port flow good, you will be surprized what these 318s will do.
One other indirect performance gain was swapping to the much lighter Torq Thrust All Aluminum wheels. 80 lbs less of rotating mass to spin up every time you start and stop.
So Happy with this setup, great low end torque engines, 1800 rpm at 60 mph. Great freeway cruising with power to pass any one you want.
moparmat2000
Well-Known Member
So since the 69 teener factory slugs are no longer obtainable and it seems aftermarket cast slugs are below deck height which one is closer to zero deck height?
moparmat2000
Well-Known Member
When you say roller motor piston, are you talking about a 1991 318 or magnum engine?
Slantsix64
Well-Known Member
Yes the 318 roller la block premagnum I think 1985-1991 , I'm also going to due a magnum 318 build which does have a true 9:1 betterheads stock camshaft 251/261 .432 1.624 ex 1.780in better rings.
nm9stheham
Well-Known Member
H814CP is the taller stock cast type out there right now. Same aftermarket pistons as for the 5.2 Magnum. A tad taller than waht slantsix is referring to. Around 8.9 SCR with .028" head gaskets and 62 cc chamber heads on an LA. No eyebrows is part of that CR..... so keep an eye on P-V clearance; that cam you linked probably is a slow ramp cam and does not have a ton of lift or duration, so that helps.
Looking on Rock here H814CP piston for 1993 D150 318 is showing 1.755 CH Flat Top. Without the valve reliefs, this should help bring up the compression closer to the 69 318 pistons 1.772 CH that has valve reliefs.
Tallest CH 318 aftermarket piston so far: H814CP at 1.755 CH flat tops.
nm9stheham
Well-Known Member
BTW, a .030" mill on heads will bump up SCR about .45 points on the open heads, and about .35 points on the closed chamber heads. Fresh, flat head surfaces is a + if you put in the thinner head gaskets.
Thanks Everyone for all the great info on heads, compression heights, pistons, and compression ratios. Have been trying to come up with the Perfect Mopar Replacement Pistons for our 318s to stay head to head with the 69 9.2:1 pistons. I was close but now I am much better informed and know what to go after and why.
Thank You . . .
On the hunt now for duplicate smaller diameter 69 318 head gaskets to keep the compression up like it should be.
Pictured here are the standard Felpro 318/360 universal head gaskets on the 302 head. As you can see these are leaving some much needed compression on the table and I want to put that to work.
Thank You . . .
On the hunt now for duplicate smaller diameter 69 318 head gaskets to keep the compression up like it should be.
Pictured here are the standard Felpro 318/360 universal head gaskets on the 302 head. As you can see these are leaving some much needed compression on the table and I want to put that to work.
nm9stheham
Well-Known Member
FWIW.... I stopped worrying over that factor quite a while back. For a .039" thick head gasket, going from the standard Felpro 4.18" diameter down to 4.00" (you can't go to the exact bore due to misregistrations of gaskets and holes) raises SCR by 0.07 points. The numbers are similarly tiny with .028" or .050" head gaskets thicknesses.
DODGE 5.2L/318 Mopar small block LA Head Gaskets -
All lined up on a row. 4.040 looks to be the smallest and .027 thickness. Cometic has them. Not cheap though.
All lined up on a row. 4.040 looks to be the smallest and .027 thickness. Cometic has them. Not cheap though.
Like the size and specs on this one
Mr. Gasket Head Gaskets 1121G
Made for the LA 318s 4.140 in. Gasket Bore; 0.028 in. Compressed Thickness
Liking these specs a lot, wish they can keep them from leaking. Probably have to make sure surfaces are machined straight and clean.
That's what I used on my 273.
moparmat2000
Well-Known Member
Took a break from this and poring over pistons online yesterday. Had a bit of a headache from all the bench racing. Still in the hunt though. Not writing off the 302s yet as they are still really plentiful and cheap in my local boneyards.
It's looking like the right piston (flat top close to TDC as possible) is needed to make em work.
What exactly is the typical CC of a 302 head?
Also if the runners are similar to an open chambered mid 70s 318 head, am I assuming correctly that adding larger 1.88" sized intake valves will help it a lot.
Question, what is the CC of the 69 318 heads?
I ask this because if on the 69 318, the 69 pistons are at zero deck height at TDC, and the heads are an open chamber type giving X total chamber volume between head, gasket, and piston. Then is it possible with the 302 head closed chamber volume, gasket volume, and piston volume lower in the hole than the 69 setup that X can be duplicated just slightly lower in the cylinder.
I would think that zero deck height flat tops, along with a .028" headgasket and closed chambered 302 heads would yield too high of a compression for pump gas street use.
Anybody have actual numbers on the 302 head CC volume, and piston to deck CC volume of say the H84CP in a standard bore. I can run them from there.
Not sure if this combination will give a decent amount of quench.
Also I still think if the 302 is similar to the old open chambered 70s heads with the exception of it being a closed chamber with smaller intake valves and hardened seats then i think it would benefit by hogging them out to fit larger 1.88" intake valves.
It's looking like the right piston (flat top close to TDC as possible) is needed to make em work.
What exactly is the typical CC of a 302 head?
Also if the runners are similar to an open chambered mid 70s 318 head, am I assuming correctly that adding larger 1.88" sized intake valves will help it a lot.
Question, what is the CC of the 69 318 heads?
I ask this because if on the 69 318, the 69 pistons are at zero deck height at TDC, and the heads are an open chamber type giving X total chamber volume between head, gasket, and piston. Then is it possible with the 302 head closed chamber volume, gasket volume, and piston volume lower in the hole than the 69 setup that X can be duplicated just slightly lower in the cylinder.
I would think that zero deck height flat tops, along with a .028" headgasket and closed chambered 302 heads would yield too high of a compression for pump gas street use.
Anybody have actual numbers on the 302 head CC volume, and piston to deck CC volume of say the H84CP in a standard bore. I can run them from there.
Not sure if this combination will give a decent amount of quench.
Also I still think if the 302 is similar to the old open chambered 70s heads with the exception of it being a closed chamber with smaller intake valves and hardened seats then i think it would benefit by hogging them out to fit larger 1.88" intake valves.
Last edited:
nm9stheham
Well-Known Member
I've been using 62 cc for the 302 chambers. Have seen numbers around that and up to 64.
The 675 heads for the '69 (early) 318's and late 273's are around 68 cc.... mine measure right on that number.
No quench/squish possible with these pistons down in the bore. Some would say that there is actually an increased detonation chance by putting the the piston to head in the range of .095" + or -. IDK how true that is and you're not pushing things with 9:1-ish SCR anyway. The early pistons near zero-deck with the open chambered heads would be about .120-.130" from piston to the flat part of the chamber. So not all that different IMHO.
Cylinder volume for .067 in the hole for an LA deck (like the 814's) is 13 cc's. Here is a volume calculator; enter the numbers in inches (318 standard bore radius is 1.955") , and multiply the output by 16.1 to get cc's.
Volume Calculator
Your proposed setup of true zero deck with .028" head gasket and 5 cc standard eyebrows for typical performance pistons would be 9.7 SCR. Not bad at all IMHO for pump premium and paying attention to timing etc., but you would be pushing the quench gap too tight without precice machining. So you would use a .039" head gasket and end up with 9.5. Or simply put the KB167's in at standard deck height ( nominally .012" below deck) and the .028" head gasket and be at 9.5 with a good quench gap around .040"....easy. BTW, piston-to-block deck variations need to be checked when you push things this close; the block deck height variations, rod lengths, and crank machining can all play into that piston-to-head clearance.
Yes on the 1.88" valves.... no need to worry over port volume (mass) IMHO.
The 675 heads for the '69 (early) 318's and late 273's are around 68 cc.... mine measure right on that number.
No quench/squish possible with these pistons down in the bore. Some would say that there is actually an increased detonation chance by putting the the piston to head in the range of .095" + or -. IDK how true that is and you're not pushing things with 9:1-ish SCR anyway. The early pistons near zero-deck with the open chambered heads would be about .120-.130" from piston to the flat part of the chamber. So not all that different IMHO.
Cylinder volume for .067 in the hole for an LA deck (like the 814's) is 13 cc's. Here is a volume calculator; enter the numbers in inches (318 standard bore radius is 1.955") , and multiply the output by 16.1 to get cc's.
Volume Calculator
Your proposed setup of true zero deck with .028" head gasket and 5 cc standard eyebrows for typical performance pistons would be 9.7 SCR. Not bad at all IMHO for pump premium and paying attention to timing etc., but you would be pushing the quench gap too tight without precice machining. So you would use a .039" head gasket and end up with 9.5. Or simply put the KB167's in at standard deck height ( nominally .012" below deck) and the .028" head gasket and be at 9.5 with a good quench gap around .040"....easy. BTW, piston-to-block deck variations need to be checked when you push things this close; the block deck height variations, rod lengths, and crank machining can all play into that piston-to-head clearance.
Yes on the 1.88" valves.... no need to worry over port volume (mass) IMHO.
moparmat2000
Well-Known Member
Asking about runner design compared to 70s open chambered heads as I have a set. If these are similar in design to the 70s heads, except for smaller intake valves which are easily remedied, and of course the closed chambers, then this is a win. Having a mopar buddy trying to convince me to run the 74 heads because I have them. This is why I am asking. Trying to build this engine on the cheap.
Will elaborate more later in the day.
64 cc on stock 302 heads chamber volume.
69 318 9.2:1 stock pistons.
.050 down in hole
1.772 CH
The other 93 D100 318 flat tops are
1.755CH
302 valves are fine as is for great port flow, you want to keep the speed up not slow it down when it hits the larger valve opening.
The 302 heads have hardened seats, improved ports and port flow over the stock 318 heads of the 70s.
Here is the magic: LD4B Dual Plane aluminum intake, the port runners match factory 318 heads. So no turbulance there as long as you port match the gaskets and if any casting edges are sticking out debur them. Same with heads to the stock exhaust manifolds.
Then you want to open up your full exhaust system to 2.25 or 2.5".
The reasoning is you have hot compressed exhaust gasses leaving the stock manifolds at the exit looking for a place to expand out all the way out to the back. Literally drawing the hot gases out of the engine as they are expanding all the way out to the back of the car.
318 Magic: Smooth Port Flow and Port Speed in and out of the engine. Ma Mopar designed the manifolds with this in mind.
You can put headers on but then you are changing the engineer's dynamics, that can create lesser performance.
We have hit on a layout that works very very well, and other can choose to differ.
I always like hanging close to Ma Mopar. Those engineers ate Steak and Eggs for breakfast and could not wait to get into work for the day.
Good luck on your build. We are all learing along the way.
64 cc on stock 302 heads chamber volume.
69 318 9.2:1 stock pistons.
.050 down in hole
1.772 CH
The other 93 D100 318 flat tops are
1.755CH
302 valves are fine as is for great port flow, you want to keep the speed up not slow it down when it hits the larger valve opening.
The 302 heads have hardened seats, improved ports and port flow over the stock 318 heads of the 70s.
Here is the magic: LD4B Dual Plane aluminum intake, the port runners match factory 318 heads. So no turbulance there as long as you port match the gaskets and if any casting edges are sticking out debur them. Same with heads to the stock exhaust manifolds.
Then you want to open up your full exhaust system to 2.25 or 2.5".
The reasoning is you have hot compressed exhaust gasses leaving the stock manifolds at the exit looking for a place to expand out all the way out to the back. Literally drawing the hot gases out of the engine as they are expanding all the way out to the back of the car.
318 Magic: Smooth Port Flow and Port Speed in and out of the engine. Ma Mopar designed the manifolds with this in mind.
You can put headers on but then you are changing the engineer's dynamics, that can create lesser performance.
We have hit on a layout that works very very well, and other can choose to differ.
I always like hanging close to Ma Mopar. Those engineers ate Steak and Eggs for breakfast and could not wait to get into work for the day.
Good luck on your build. We are all learing along the way.
moparmat2000
Well-Known Member
Sounds great Looking at using 1968 340 exhaust manifolds with this combination
318, 340 Comparison
-
