340 Magnum

[johndarling]

Hello. It's been a long time since I've been here but I'm builing a new project so I'm back.

What I have;
- 1972 340 block standard bore but needs to be bored 0.030 or 0.040 over. Block and main caps only.
- 1996 5.2L Mangum complete engine minus the intake.

I want to put all the magnum components in the 340 block. To be used as a daily driver in a 4-speed pick-up. I'm thinking around a 5500 RPM red line. I know a 340 can twist alot harder than that, I used to have a 340 Dart with fully ported x heads and balanced bottom end that would pull HARD to 7000. That was a toy with 430 gears that ran 12's, this will be my daily driver.

I'm building on a budget so please don't go into a bunch of expensive aftermarket parts. I have access to a machine shop, so I'm going to do the head work myself. I will however have the block bored by someone that knows much more that I.

Things I know (or think?)
- The heads will bolt on using AMC lifters and melling MPR-89 push rods. I will need a magnum intake (or I may opt for going with the fuel injection, I'm not sure yet)
- The mag camshaft will NOT work. I'm thinking of a cam around a 440 lift and 210 duration. ????? I know with the mag 1.6 rockers that will bump the cam some.
- The crankshaft, balancer, and rods should work and I'll get light weight 4.070 pistons.
- I'll use an LA front cover, water pump and pulleys

Questions I Have
1. What pistons would be best, cast or forged? I would normally say forged but I want them light so I think the case would be better and cheeper.
2. What effect does the closed chamber mag heads have on compression? I was going to use a 9.5:1 piston but I want to be able to run on pump gas and I'm not sure how much the heads will raise the ratio from stock J or X heads.
3. I know all 318's, and forged crank 340's were balanced internal and the cast crank 340's and 360's were balanced external because the crank couldn't make up for the weight of the rods and pistons. On cast 318's this isn't a problem because the weight of the piston's and rods are lighter. SO for my next question if I go with a light weight 340 piston will the magnum (cast) crank be able to be used in my 340? I think it will.
4. Are the mag rods strong enough for 5500 RPM?

Thanks

John

[dwc43]

Cast is fine for a street engine.
2. Doesn't really matter cause the pour flow of the 318 head on your 340 will kill the power it has the potential to make. Find a good set of 360 heads. You'll come out way ahead.
3.Rebalance the whole thing.
4. The mag rods should be fine to 6000. I'd get set of '68 or '69 cast rods. They have a full floating pin and are much lighter and stronger.

[johndarling]

Originally Posted by dwc43

2. Doesn't really matter cause the pour flow of the 318 head on your 340 will kill the power it has the potential to make. Find a good set of 360 heads. You'll come out way ahead.

dwc43,

Thanks for the input.

I thought the 5.2 and 5.9 magnum heads were the same and they should flow better that the old "stock" 340 - 360 J heads?

Thanks

John

[73scamp318]

Originally Posted by dwc43

Cast is fine for a street engine.
2. Doesn't really matter cause the pour flow of the 318 head on your 340 will kill the power it has the potential to make. Find a good set of 360 heads. You'll come out way ahead.
3.Rebalance the whole thing.
4. The mag rods should be fine to 6000. I'd get set of '68 or '69 cast rods. They have a full floating pin and are much lighter and stronger.

HAHAHAHAHAH. Don't belive anything this fool has to say.
The magnum rods are forged use those, and the mag heads out flow the x or j heads with no effort, plus they have way better quench. dw don't even start on this magnum verse x head agian.

Just search for your self, or talk to ryan at shadydellspeedshop.com.

And the 318 heads are the same as the 360 heads, also they head flow isn't differnt with differnet castings. (mag)

Even if the rocker gear isn't as good, he will never see that at the rpms that he is turning, even 8000rpms it wouldn't matter.

Do a mild clean up on the heads (mostly bowl work) you will see great gains.

Take this from a guy who has magnum heads!!
and is building a 340 magnum now. (well kind of i thas magnum heads with an r3 blocka and turbo)

Steve

[rumblefish360]

Welcome. This is the deal as I see it.

What I have;- 1972 340 block standard bore but needs to be bored 0.030 or 0.040 over. Block and main caps only.
- 1996 5.2L Mangum complete engine minus the intake.

Keep the bore down to the min. This will keep the cyl. walls strong and straight. This is the way to go for power and long life. Bore & hone with a torque plate. This reduces blow by and of course, better cyl sealing. This equals more power.
The Magnum components here, the crank, along with the rods which are way strong enuff, should be mated to Magnum pistons since your useing the magnum heads. If it isn't possible to get them in the desired bore size, carefullly look at the piston manufactures ratios @ the heads total cc area.
If you must, it is easy to call up a speed shop like Hughe racing or the piston maker like Keith Black to find what you need. 9.5-1 ratio is fine. I myself would not go more.
Speaking of pistons, should you decided on a hyperutecic piston, follow the makers recomendations very carfully. There strong pistons but can break due to poor ring clearances.
The pistons should not be closer than .039 for safe operation. It's possible to run closer, but, I have run KB hyperu's with a Fel-Pro gasket @ .040 and all was fine.
Quench should be investagated. It's a vs. comp. ratio thing. More than a .050 distance between piston and head, you start to loose the bennifits of the quench area.
There are comp. ratio calcs online. someone should post one for us.
The pistons are around or at least under $250 a set. Rings are less than a $100 and a balance job should be about $300 or less. Bearings are under the buck mark as well as smal part. For less than $750, you should have a drop in set up. Boreing the engine extra.

The pushrods listed are a unknown to me. But if you did the homework on hollow pushrods to use, your in. Yes, AMC liffters.
Use standard LA-340 cams. The new lift works like this.
Example; cam lift minus rocker ratio times new rocker ratio or
.500 / 1.5 X 1.6 = .5333333333333333333333333333
Select cam duration for the RPm cruise speed. Power should fall in there. The extra lift should be looked after. It also doesn't make the cam bigger, just more aggresive. And not much, just a tad.

The balancer and torque conveter should come from the extarnal balanced 340 as a unit, or together. OR use both the Magnum 318 components together. Do not mix and match them. This could create a problem

Everything else looks fine. Skip the 68-69 rods, waste of time looking for old parts is what it is. 360 heads are fine also, but I would prefur the Magnums. A search for older J heads is a waste of time when you could be driving instead of looking and rebuilding. The X or J heads can rock, but the magnums are in hand and flow very well with a smaller valve and higher velocity for better air and fuel mixing and resulting in a better burn for feul efficent power to make them a better choice in a truck.

[rumblefish360]

I can't seem to get Ryans link to work. I get some crap sh^&*) instead.
Anyone have the sheadydell speed shop link
http://hughesengines.com/

[LA360Dart]

Despite what dwc43 says the Magnum heads are a better balanced head with better port velocity. This will help torque for a 340 in a truck. If you look at the new catalog the magnum head is the replacement casting.

As for pistons cast piston, they will be ok. Magnum rod will be fine (small end is 1") the rpm being only 5000 to 5500. Magnum heads have 60cc chamber raises compression from about 9.5 to 10.5 over the LA 360 castings. Also will only need 34* total timing as chamber is more efficient.

Hope this helps

I'm running LA 360 with Magnum heads works very well. Just check push rod to head clearance with cam and lifters of your choice. The parting line was close on mine a little clean up was all it took...

Denny

[dave571]

Originally Posted by johndarling

Hello
1. What pistons would be best, cast or forged? I would normally say forged but I want them light so I think the case would be better and cheeper.
2. What effect does the closed chamber mag heads have on compression? I was going to use a 9.5:1 piston but I want to be able to run on pump gas and I'm not sure how much the heads will raise the ratio from stock J or X heads.
3. I know all 318's, and forged crank 340's were balanced internal and the cast crank 340's and 360's were balanced external because the crank couldn't make up for the weight of the rods and pistons. On cast 318's this isn't a problem because the weight of the piston's and rods are lighter. SO for my next question if I go with a light weight 340 piston will the magnum (cast) crank be able to be used in my 340? I think it will.
4. Are the mag rods strong enough for 5500 RPM?

Thanks

John

A Good forged piston will be lighter and stronger than a cast one. This will make balancing cheaper, and may help ofsett the cost of the better piston.\

I recently worked on a cast 340 with forged slugs that were light enough that it was balanced internally.

As for heads, there is no question the modern magnum heads will provide good street manners. Better than any of the old iron. I've heard it's hard to find magnum heads that aren't cracked, but I'm not a SB guy, so I don't know first hand.

[dwc43]

Originally Posted by rumblefish360

Welcome.
Everything else looks fine. Skip the 68-69 rods, waste of time looking for old parts is what it is.


No need to look for old parts. We buy ours new from a speed shop.


360 heads are fine also, but I would prefur the Magnums. A search for older J heads is a waste of time

THat's just not so. I'll take everyone you find since you think it's a waste of time.


The X or J heads can rock, but the magnums are in hand and flow very well with a smaller valve and higher velocity for better air and fuel mixing and resulting in a better burn for feul efficent power to make them a better choice in a truck.

I'd increase the intake valve on either head for better flow. Work the exhuast side for more flow and balance.

[dwc43]

[QUOTE=73scamp318]HAHAHAHAHAH. Don't belive anything this fool has to say.
Like you have any room to talk.

The magnum rods are forged use those,
Too heavy compared to the ones I told him about. Weight hampers acceleration as well as longevity.


Even if the rocker gear isn't as good, he will never see that at the rpms that he is turning, even 8000rpms it wouldn't matter.

That's totally incorrect. 1st off we only run 6000. The mag head wont support 8000, opnly a W series head will. And the roker gear stinks. It's an exact chevy clone and they stink. That's why they need guide plates and stub girdles and such. Put one on a spintron and see for yourself, even at low lifts they stink,period.

Do a mild clean up on the heads (mostly bowl work) you will see great gains.
Also work on the exhuast side too.

Take this from a guy who has magnum heads!!
and is building a 340 magnum now. (well kind of i thas magnum heads with an r3 blocka and turbo)

Watch the rocker gear if you ever get such an engine built. Without mods, high rpm will kill it.

Steve

[johndarling]

Thanks for all the input. I hope to have this engine built and installed by next spring. I'm doing the body now before it gets to cold. The engine I can do in my garage after it gets cold.

Who has the best bang for the buck as far as the parts? I will need to buy the pistons, cam, lifters and all the basic engine rebuild stuff.

One more thing. Can anyone tell me what the HP limit is for a A535 5 speed. I have a 833 OD in it now but the wide ratio kind of sucks. It is also getting worn out and needs to be rebuilt. I would like to switch to the close ratio A535 but don't know how strong it is. Or I was thinking of going to the 833 non-OD. It has a much closer ratio but with a 391 gear my milage would be killed.

[rumblefish360]

Originally Posted by dwc43

I'd increase the intake valve on either head for better flow. Work the exhuast side for more flow and balance.

Being in a truck, I wouldn't increase valve size. It will slow down port velocity. Best to keep it up. Even more so in a truck and small cid's.
Working the exhaust side of the head is a good idea for single pattern cams. But, I think a split duration cam would be cheaper and better to use IMO.
Love my 2.02 J heads, but there used in a different manor.

Dave 571. I heard the same thing about Magnum heads. New ones are cheap enuff to purchase though.

[73scamp318]

Why is the rocker gear so crappy? You think that the shaft is bad? How much harmoncis travel through that? The shaft flexing? You need split shafts for it to be good. And you don't need w series heads for 8000. Anyways jesel came out with there magnum series rockers, ain't cheap.

Steve

[dwc43]

Originally Posted by rumblefish360

Being in a truck, I wouldn't increase valve size. It will slow down port velocity. Best to keep it up. Even more so in a truck and small cid's.
Working the exhaust side of the head is a good idea for single pattern cams. But, I think a split duration cam would be cheaper and better to use IMO.
Love my 2.02 J heads, but there used in a different manor.

Dave 571. I heard the same thing about Magnum heads. New ones are cheap enuff to purchase though.

I agree. I use dual pattern cams almost all the time. A change in exhaust rocker arm ratio works well too for certain things or a combo of both. As for a truck, put more gear in it ... LOL!!

[dwc43]

Originally Posted by 73scamp318

Why is the rocker gear so crappy? You think that the shaft is bad? How much harmoncis travel through that? The shaft flexing? You need split shafts for it to be good. And you don't need w series heads for 8000. Anyways jesel came out with there magnum series rockers, ain't cheap.

Steve

Well the 5/15 rocker studs flex like hell. That's why chebby needs a stud girdle. Even switching to a 3/8 stud won't help it that much. HArland sharp has a shaft that wont flex. None travel through the shaft. And yes, split shafts allow even higher valve spring pressures without flexing the shaft for a roller cams. You might get it to turn 8000 r's with enough gear, but it wont make more power unless you put some W heads on it. Yes, they have some shaft rockers and that will help some if you could afford them. Lot cheaper to build up an X,J, or U head and make more power on the cheap and not have to worry about wasting all that money.

[Tarrbabe]

But name calling is not productive and can cause a lot of trouble even to the point of splitting a group to the point that they take sides. This is not productive as different sides spend time on fighting each other instead of working on a positive plane.
Some think that speed is a defined thing but there are many ways to reach a goal. It is up to us as individuals to glean through the information and decide what approach we want to take. For every advantage, their is a draw back of some sort. That is what makes the chase worth it.
The old saying is: Speed cost money, how fast do you want to go?
One might speed $15000.00 to go 10.00's. Show me the one that does it for $2000.00 and I will accept that he is ( DA MAN! ).
Lets all work together and see what we can come up with. Who knows, we might even put the Chebbies and Furds to shame and enjoy it even more.


By the way, I'm re-doing my 340 now. I bought Ross forged 9.8 pistons for $495.oo plus tax and using stock rods reworked for strength. This combo will be lighter than the stock pistons by 300 grams per cy. and require rebalance. I have to disagree with the statement that heavy rods will last less than lite.

Just thinking out loud.

[rumblefish360]

Originally Posted by dwc43

power on the cheap

Thats the thing . Cheaply makin it. I understand the bennies of new heads, better flowing heads, but whats in hand? How well will they work? Did you learn how to port yet.
I'll tell ya now, it's amazing how well ported 318 heads will work.
All you need is a gasket set to max out the port size and make that bowl look preety.
If you take the time to destroy a few practice heads, you could be doing your freinds on the cheap for some side cash or to recoupe your pratice costs.

What you have hanging around isn't junk. Only if you let it sit it will become junk.

[dwc43]

I've ported some before RUmble, just don't have the time or the patience for it. It just takes so damned long, but the gains are worth it I guess. I usually hand that off to someone else if I can get away with it.

[johndarling]

I have cleaned up and polished heads before. Should I polish the exhaust side and just do a clean up on the intake side. I was planning on match porting the intake and heads. To "clean up to bowls" is that just taking out the rough castings?

Thanks

John

[dwc43]

I'd gasket match it on both sides if you like. Work mostly on the exhuast side and clean it up and open it up a bit as well as polish it. Pull the valves and polish and clean it up underneath. Shapping and reducing the guide below the valves will help too.

[Crank]

open the bowls ,clean up the ruff castings on both intake and exhaust, clean up around the valve seat in the chambers, scribe the bore on the heads and deshroud as much around the intake valves as you can polish the chambers then cc the chambers and to even them out .