even if you use a magnum crank?
LA 318 advice
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junkyardhero
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Baggs
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HiJack away.
junkyardhero
Well-Known Member
uhhh... depends?
i know that the mag rods are lighter. so i guess it would come down to what the bob weight was with the mag pistons if you were trying to keep the LA rods.
but then you're into a whole: why would you use LA rods with mag pistons and crank...
junkyardhero
Well-Known Member
oh... my friend... not who you want to give carte blanche to on a thread....HiJack away.
yeah, people pay for lighter rods. magnum rods and pistons on a LA crank? I"ve not mixed and matched the internals of the LA/Mag
junkyardhero
Well-Known Member
you can install rod and piston assemblies on either. but, again rebalance (to do it right).
you can do a bottom end boogie mag to LA straight across even.
the difference is the pinboss in the pistons and the small end of the rod-- LA wider, mag narrower. so it's keep it matchy-matchy or skinny up LA rods to fit mag pistons.
if you change components, you change the bobweight and it needs a rebalance.
totally not confusing at all, right?
oh, and don't forget... the rings are different too...
i've always kept LA, LA and Mag, Mag when it comes to the inside. I like the Magnum blocks and cylinder walls
Baggs
Well-Known Member
I get ya, if shooting for 1HP/CI or more.
But as I mentioned before, 200 for the block cut, same for the intake (both assumptions) and run it
Vs 500 for pistons, still square the block up, balance it.
I’ll take a 400 $$ route if it’s doable, vs say a 900$$ route on a 235/240 HP engine.
The truck it’s going in weighs 2525 with the L6 it had in it, so should be similar.
As was mentioned, if the block will take .100 (I’ll sonic test it and compare to a SBC block I have) and see. But if .080 is okay to do, then a proper HG will bring it to about 9-1 SCR.
The reason for me to compare to the SBC in regards to the decking, in my younger days, I can recall folks doing .060 on them. But I’ve no idea of the difference yet. But Amazon will deliver the tool I need, next week to compare thickness of each as-is.
Baggs
Well-Known Member
I tried to message you, but you box is full.
The .1, .2 and .3 numbers you listed, how did you find this information, or by sonic testing decks?
Thanks
“With bows of Holley- falls-la-la-la?”
Get them out of used engines.
I have a set of good used 9.2:1 pistons out of a 1968 318 with the stock valve reliefs, slated for a 1974 stock bore 318 that I have set aside for building, with a melling 340 cam.
The '69 318s also had the good 9.2:1 pistons too.
☆☆☆☆☆
^^^
☆☆☆☆☆
☆☆☆☆☆
"Not shooting for 300 HP here....." Your words. So here's my advice. Have the block deck skimmed to just clean it up and level it parallel with the crank center line. Get the heads milled .025". Then, just do a basic rebuild. Bore if needed, but if not, reuse your pistons. You're talking about buying KB pistons and your goal isn't over 300 HP? Ridiculous. You can make a low compression engine run great by advancing the cam some and putting a good loose curve in the distributor. With a decent intake like a Weiand Action Plus, a good carburetor like a 650 AVS2, a nice mild camshaft maybe one step down from the Comp 268 and headers, you'll probably be all over 300 HP and you may not even need to bore it.
junkyardhero
Well-Known Member
you're worried to death about a point or so of compression but haven't addressed the cam what so ever.
are you keeping what's in there? if so, what is it?
if you aren't, then there's a whole wide world of options to wade thru. there are a bunch of key factors that would weigh heavily on cam choice: vehicle weight (from my understanding it's in a 32 pickup?), transmission, gears, use/driving style.
you can build a mean little ripper with so called dog water compression and the right cam, intake and carb (and headers). it'd be no fun in a big ol' boat but in something light it'd do just fine and dandy.
are you keeping what's in there? if so, what is it?
if you aren't, then there's a whole wide world of options to wade thru. there are a bunch of key factors that would weigh heavily on cam choice: vehicle weight (from my understanding it's in a 32 pickup?), transmission, gears, use/driving style.
you can build a mean little ripper with so called dog water compression and the right cam, intake and carb (and headers). it'd be no fun in a big ol' boat but in something light it'd do just fine and dandy.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Here is just some math. for a 3.91 bore/ with a swept of 652cc
The cv (combustion chamber Volume) is assumed to be;
open chambers; 70heads/6.8 gasket/no eyes=76.8=A
Closed chambers; 60cc /6.8 gasket/no eyes =66.8cc=B
Below is a table
that compares the Scrs at the above cvs, at four various deck hts .
decks at .... cc are... ScrA ...... ScrB
.100 deck = 17.7cc = 7.9 ..........8.7
.075 deck=13.28=8.24 ...... 9.14
.050 deck = 9.84cc= 8.5 ........ 9.51
Zero deck=zero cc = 9.5 ........ 10.76
>For your application as long as you are on the primaries, power is hardly gonna matter. and
>As to fuel economy, at a particular speed with a given gear combination, you adjust the throttle opening, to get the power you need to cruise at that speed. Whether your Scr is high or low is of no concern, because Scr has NOTHING TO DO with cruising. Instead, it is EFFECTIVE Pressure that gets you the power....... which you adjust with the gas pedal. While it is true that a larger throttle opening usually means the engine will be less frugal, that is only true if you do not set the tune correctly.
>The point is, that not a chance would I spend money on pumping the Scr UP to get fuel economy that only requires a 5/1 Scr in the first place..
> a High Scr only comes into play as more power is required of a particular engine combination; ie, if you run out of power, or the bottom end gets soft, more CYLINDER PRESSURE is required. You can get that pressure in several ways;
1) a higher Scr
2) an earlier closing intake valve
3) more head flow
4) super-charging
--------------------------------------------
But, I gotta tell ya, swapping in a higher stall TC, say a 2800 versus an 1800, with no other changes, is gonna climb to near double the power out the crank, not by some miracle of physics, but by virtue of the additional rpm.
As an example; say your 318 is able to, at WOT, achieve 200ftlbs at the crank @1800rpm, which is 68hp. Whereas
the same 200ftlbs@2800 is 107hp. But whereas,
your 318 will not stall out at the same torque. More likely
it will have climbed to ~ 240@2800 with a 4bbl, which is then 128hp; and 128/68=plus 88%
There is nothing that you can do to a given engine, as regards cylinder pressure, short of supercharging it, that can make this huge a kick-in-the-keyster.
Therefore,
if you are not changing the ICA of your cam,
I see no good reason to destroy a perfectly good short block to get up to, a point and a half of compression, which barely makes a difference in your application.
If you keep going in the direction this thread is headed, your gonna spend a ton of money, only to find that for some 90% of the time, say from stall to 3500, you're only using less than 50% of the available power.
Wellchit, the highstall is gonna cover that no problem.
How so, you may ask?
Well, if the 318 gets up to 250 hp at WOT@ 4500pm, which is maybe 130hp@ 2800, and 68hp@ 1800; and has say the typical 2.76 gears for 2800=32mph; Suppose
the TC launched you at 128 hp right at Zero mph, and kept ripping at minimum 128hp all the way to 32mph,
Guess which one is getting up to 32 mph sooner!
I mean that's an over-simplification NOT favoring the TC, but you get the idea.
-------------------------------
Just so you know, I have done it both ways, and when I made this amazing TC discovery, many decades ago, I bought a couple of more 2800s, soon afterwards, Just to put on the shelf for the next A-body, and for many decades, every 318Mopar I bought, got one, as the first mod; and then, rear gears soon afterwards. I never again messed with the 318s except they almost always got a 4bbl, and dual exhaust. And I never again installed a 340 cam, I think I have about 3>4 of those, still stored in the attic.
In any case, whatever you decide to do;
Happy HotRodding.
The cv (combustion chamber Volume) is assumed to be;
open chambers; 70heads/6.8 gasket/no eyes=76.8=A
Closed chambers; 60cc /6.8 gasket/no eyes =66.8cc=B
Below is a table
that compares the Scrs at the above cvs, at four various deck hts .
decks at .... cc are... ScrA ...... ScrB
.100 deck = 17.7cc = 7.9 ..........8.7
.075 deck=13.28=8.24 ...... 9.14
.050 deck = 9.84cc= 8.5 ........ 9.51
Zero deck=zero cc = 9.5 ........ 10.76
>For your application as long as you are on the primaries, power is hardly gonna matter. and
>As to fuel economy, at a particular speed with a given gear combination, you adjust the throttle opening, to get the power you need to cruise at that speed. Whether your Scr is high or low is of no concern, because Scr has NOTHING TO DO with cruising. Instead, it is EFFECTIVE Pressure that gets you the power....... which you adjust with the gas pedal. While it is true that a larger throttle opening usually means the engine will be less frugal, that is only true if you do not set the tune correctly.
>The point is, that not a chance would I spend money on pumping the Scr UP to get fuel economy that only requires a 5/1 Scr in the first place..
> a High Scr only comes into play as more power is required of a particular engine combination; ie, if you run out of power, or the bottom end gets soft, more CYLINDER PRESSURE is required. You can get that pressure in several ways;
1) a higher Scr
2) an earlier closing intake valve
3) more head flow
4) super-charging
--------------------------------------------
But, I gotta tell ya, swapping in a higher stall TC, say a 2800 versus an 1800, with no other changes, is gonna climb to near double the power out the crank, not by some miracle of physics, but by virtue of the additional rpm.
As an example; say your 318 is able to, at WOT, achieve 200ftlbs at the crank @1800rpm, which is 68hp. Whereas
the same 200ftlbs@2800 is 107hp. But whereas,
your 318 will not stall out at the same torque. More likely
it will have climbed to ~ 240@2800 with a 4bbl, which is then 128hp; and 128/68=plus 88%
There is nothing that you can do to a given engine, as regards cylinder pressure, short of supercharging it, that can make this huge a kick-in-the-keyster.
Therefore,
if you are not changing the ICA of your cam,
I see no good reason to destroy a perfectly good short block to get up to, a point and a half of compression, which barely makes a difference in your application.
If you keep going in the direction this thread is headed, your gonna spend a ton of money, only to find that for some 90% of the time, say from stall to 3500, you're only using less than 50% of the available power.
Wellchit, the highstall is gonna cover that no problem.
How so, you may ask?
Well, if the 318 gets up to 250 hp at WOT@ 4500pm, which is maybe 130hp@ 2800, and 68hp@ 1800; and has say the typical 2.76 gears for 2800=32mph; Suppose
the TC launched you at 128 hp right at Zero mph, and kept ripping at minimum 128hp all the way to 32mph,
Guess which one is getting up to 32 mph sooner!
I mean that's an over-simplification NOT favoring the TC, but you get the idea.
-------------------------------
Just so you know, I have done it both ways, and when I made this amazing TC discovery, many decades ago, I bought a couple of more 2800s, soon afterwards, Just to put on the shelf for the next A-body, and for many decades, every 318Mopar I bought, got one, as the first mod; and then, rear gears soon afterwards. I never again messed with the 318s except they almost always got a 4bbl, and dual exhaust. And I never again installed a 340 cam, I think I have about 3>4 of those, still stored in the attic.
In any case, whatever you decide to do;
Happy HotRodding.
You simply cannot tell some folks how insignificant a change in compression will make by itself. They just will not listen.
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Newbomb Turk
Well-Known Member
I know this because it's in the Chrysler engine book and I've done it many times. Well, the amount to mill off isn't but the deck thicknesses are.
The OE passenger car stuff has about .500 thick decks. You can take .100 off of that. If you take more yo can compromise head gasket sealing but the Chrysler stuff can go a bit thinner than a Chevy deck because Chrysler used blind head bolt holes and the head bolt holes are supported by bracing under the deck. Bracing for lack of a better term.
The X blocks have a .750 thick deck and the R blocks are 1.00 thick.
I disagree with the argument that compression ratio changes make little difference. It might not make much difference on a dyno, but in the car it's a big difference in drivability. You don't see that on most engine dyno's. Compression ratio increases also increases expansion ratio. That's also a big deal because it affects blowdown and helps reduce pumping losses.
Cause the CR, VE, Cid etc.. police always come along to scare them off.
Just buy pistons. No headaches with the intake. Been there. First picture we also had to cut the timing cover look at the difference. And look at the thickness of the intake flange compared to the second picture. Both were aluminum headed.
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One other thing to think of which I ran into. anything bolted to the heads drops down and in , . Headers hit, alternator bolt was low on the head.
I'd just get the deck squared with the minimum cut. Hone with torque plates and buy good rings and pistons and be done. The high octane gas of the 60's is only available in 55 gal drums.
That, plus I feel some get super focus on only one/two pieces of the puzzle but don't/can't look at the overall picture. And the 2 puzzle pieces most seem to over worry about is cr and velocity not that there not important pieces but seem to paralyze people from building generally decent mild low budget engines.
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