LA 340 Intake Manifold

[340inabbody]

Hi I thought I would post a new thread on some specific questions I have regarding intake manifold for the 340.

My 340 is in a 1970 Sport Satellite. The engine has an unknown cam and 12:1 forged TRW’s and I believe is solid lifter. I plan to rebuild it for the street. I do want around town performance and just want to have fun with it and be able to do a burnout and sound good (which it does as it has long tube headers).

It currently has a nice M1 and Holley 4150 650 double pumper non vacuum. With an ESD dizzy.

I am trying to plan for the future but do what needs to be done now as I go. It’s an automatic and the converter is unknown as well and probably needs to be changed.

That leads me to the intake manifold. Not sure the M1 is the right manifold for this setup/car? Will it be ok at lower rpms around town or am I sacrificing that?

Also I need to add a vacuum port as I have power brakes and need one for my PCV. I would have to drill a port. Also height is critical as I am installing an Air Grabber hood and it may be an issue not sure right now.

So wondering if I should fork over and buy a different Intake Manifold that would generaly be a better solution or is the M1 just good enough and save the money and drill and tap a port and hope the hood fits……

Thanks for reading and taking the time to reply.

 

[rumblefish360]

The M1 single plane is designed for 3000 - 6500 and then some.
For cruising around town, I suggest a RPM-AG. I’m not sure if the power you’re looking for so a cam duration can float in between a 224@050 to a 248@050 which is pretty healthy for a street cam.
Do you know your gear ratio and are you happy or OK with the current cruise rpm?

 

[340inabbody]

The M1 single plane is designed for 3000 - 6500 and then some.
For cruising around town, I suggest a RPM-AG. I’m not sure if the power you’re looking for so a cam duration can float in between a 224@050 to a 248@050 which is pretty healthy for a street cam.
Do you know your gear ratio and are you happy or OK with the current cruise rpm?

Hi RF thank you for taking the time to read and teply!

I installed a Suregrip 355 rear gears and its fine. Wish I actually put a 410 in it. But its not for long highway cruises.

Power wise I honestly could use some guidance on a configuration/combination that would make sense including cam and type of carburetor (if my mechanical 650 1450 double pumper mech adv isn't ideal) what cam and converter. Stroke de-stroke leave stroke etc.

At a minimum it sounds like the M1 wouldn’t be all that great 1500-2500 RPM where the around town cruise speeds would be used often.

 

[12many]

Not sure the M1 is the right manifold for this setup/car? Will it be ok at lower rpms around town or am I sacrificing that?

in a nut shell:

The M1 single plane is designed for 3000 - 6500 and then some.
For cruising around town, I suggest a RPM-AG

Sounds like you have a stout motor and for what you want to do with it is you might need to de-tune it some. Aside from the high CR, (what fuel are you running atm?) unknown cam and converter but knowing the gear you have, the weight of the car and how you want to run it, for intakes an RPM variant or dual plane of some sort would be a much better choice. Perspectives from street, street/strip, and pure race guys will vary. That M1 is a race piece, that can be made to work great on a street/strip setup but the whole package has to be really matched and complimentary. (Like anything)

An intake change to a dual plane, dial in the carb and timing see how it performs, go from there. That’d be my approach.

 

[Syleng1]

1) I agree with above.
2) with out knowing the cam, converter and gears (sounds like you got that gear ratio covered) you are really shooting fish in a barrel.
3) rear tire height also effect final gear ratio.
4) what the heck more pics of the car please!
Syleng1

 

[340inabbody]

1) I agree with above.
2) with out knowing the cam, converter and gears (sounds like you got that gear ratio covered) you are really shooting fish in a barrel.
3) rear tire height also effect final gear ratio.
4) what the heck more pics of the car please!
Syleng1

I just finished the bodywork and paint. Took a long time as the car needed every panel done. Now I have to do all the assembly work. It’s been 116 all week slowing progress.

 

[Bobzilla]

Since you're mentioning a height issue to the hood, figure that out first before wasting time on the pcv setup. Sometimes the accelerator pump of a Holley carb will contact the outside top of an M1 single plane intake runner if used without any spacer. Check that first. If the carb will not sit flat on the intake without a spacer then you can skip drilling holes for pcv stuff and get a different intake.

The performance of that intake will be fine on the street when everything is properly tuned. The operating range is the "sweet spot" and does not mean it won't drive or idle decent at lower speeds. That being said, I did notice a tiny reduction in idle quality on my 360 when I removed a chinese dual plane and installed an M1 single plane, both completely stock with no modifications.

 

[Bobzilla]

Also a side note.

That intake is an LA head pattern intake but has the Magnum bypass hose and thermostat housing locations. Nothing wrong or better about that, just an interesting intake.

 

[Professor Fate]

For the amount of work you need to do to the 340 to make it happy on the street, I would just find a good 5.9 Magnum, have the cam reground (Oregon Cam Regrinders), throw a Chinese AG clone manifold on it, and rock it.
By the time you rip down the 340, change out those 12:1s to something more street-friendly- and possibly have to re-balance (do you really want to hunt down AV/race gas every time you want to run to the ice cream parlor?), change the cam to something that generates enough vacuum to operate those power brakes, change out the manifold to something with a more street-friendly RPM range, you're basically doing an engine rebuild anyway.
The added stroke of the 5.9 will help build torque for that B body, and the stock pistons are pump-gas friendly. Normally, good 5.9s require nothing more than a touch-up hone to the bores when refreshing the bottom end.

 

[rumblefish360]

Hi RF thank you for taking the time to read and teply!

No worries. Everyone here likes to help.

I installed a Suregrip 355 rear gears and its fine. Wish I actually put a 410 in it. But its not for long highway cruises.

3.55’s aren’t exactly a Hwy. gear ether, but they’ll do.tire size has a roll in this.

Power wise I honestly could use some guidance on a configuration/combination that would make sense including cam and type of carburetor (if my mechanical 650 1450 double pumper mech adv isn't ideal) what cam and converter. Stroke de-stroke leave stroke etc.

Stroke/destroke… whoa, hood on a second. Let’s not put the bourse before the cart a second. Normal thinking of the more concerned around here will ask this; Are you prepared to though bags of money at this engine build?

As noted above, a wise man did say an inexpensive route is a junk yard 5.9 Magnum. I did this in my ‘79 Dodge Magnum. I added 1-3/4 headers from Hooker, which fit your car, a Edelbrock RPM-AG and a 750 AFB. (Also due to the year of the car and not a bad option for yourself ether is an) added upgraded ignition. My trans is a 727 and the 9-1/4 rear has 3.55’s on 245/60/15’s.

The engine combo is a known 300HP combo if not a tick more power. The Magnum is a little heavy at just under 3600lbs. It has all the creature comforts minus T tops or moon roof.

All in all it is a good street performer and a excellent driver.

At a minimum it sounds like the M1 wouldn’t be all that great 1500-2500 RPM where the around town cruise speeds would be used often.

In order to get the single plane to act nicely on the street, it will normally need a high gear ratio and a reasonable converter to match the camshaft. It can be done, but, most people ***** about it.

 

[340inabbody]

Guys I really appreciate your comments and help on this! I don’t have a lot of money and don’t want to throw any more than I need to at this. I AM looking to just getting it assembled and running again. A rebuild is the future but here and now maybe a manifold will help.

With being said was wondering if this is what you were referring to as Chinese manifold knock off or clone? I was trying not to spend $475 on an intake manifold and these are a cheap alternative IF they run fairly well. Any comments on these? What are they and if ok how do I choose the right one?

 

[rumblefish360]

I installed a Suregrip 355 rear gears and its fine.

Power wise I honestly could use some guidance on a configuration/combination that would make sense including cam and type of carburetor (if my mechanical 650 1450 double pumper mech adv isn't ideal) what cam and converter. Stroke de-stroke leave stroke etc.

I re quoted you for a reason. Allow me to tell you about my wife’s car, a ‘67 Cúda. While it weighs a good bit less, this may be of use to you. In a FWIW, IF the car was mine and I was constructing it with your above guide lines as my goal, this is what I would do myself.

The wife’s car is a .030 overbored 360 roller block (not a Magnum block) stuffed with Federal Mougal/Speed Pro Hyperutecic C116HP pistons set at zero deck. (Zero deck need not be)
The cam is a Hyd. roller (actual type of lifter is your call) with the specs pictured below.
It has a 750 cfm carb (recommended!) RPM-AG, Trickflow cylinder heads, 1.6 rockers, TTI headers and exhaust and a MSD - RTR distributor. (You’ll need to go to 4secondsflat.com for timing bushings to get it where it needs to be)

The converter is the OEM odd splines unit (which is a huge problem since there’s zero aftermarket support) which was custom stalled at ProTorque for the car. The car runs 3.55’s on 26 X 10 Mickey’s.

While this is not a fast off the line combination, it does run really well and has a good long top end pull. Frying tires is not a problem and I can do it for days.

I used to notch parts for a no nonsense approach and best results for the parts used as cast and OOTB. The use of the 1.6 rockers on the Hydraulic roller and cylinder head combination allow this to rev a little beyond the cams listed rpm range. I haven’t found top end speed yet. I threw in the towel at 130 mph with about a 1,000 rpm left in it.

 

[rumblefish360]

When setting up your engine, do the math and find a calculator to keep a pump gas friendly ratio that suites your local octane limits. IDK if 93 is available to you. The small TF changers can raise the compression up real quick.

The above can be done in a Magnum 5.9 for quicker results in a pump gas friendly ratio. As the Magnums are a 9.0-1 to start with.

If you don’t mind throwing bags of money at a stroker, that’s your call and I’d run right to a 4.00 crank and not look back. You could increase the cam duration by 6*’s without batting an eye & have no ill effects. Though if you you change your gear to a 4.10, then a cam can jump in duration like crazy, but be reminded the bigger the cam the higher the operating rpm is.

 

[Professor Fate]

Guys I really appreciate your comments and help on this! I don’t have a lot of money and don’t want to throw any more than I need to at this. I AM looking to just getting it assembled and running again. A rebuild is the future but here and now maybe a manifold will help.

With being said was wondering if this is what you were referring to as Chinese manifold knock off or clone? I was trying not to spend $475 on an intake manifold and these are a cheap alternative IF they run fairly well. Any comments on these? What are they and if ok how do I choose the right one?

View attachment 1716116723

View attachment 1716116724

Those are the generic Chinese Air Gap manifolds that I spoke of- they are sold under a number of different names and vendors- search for your best price. They fit both LA and Magnum heads, so if you do go the Magnum route down the road, you don't have to hunt down another manifold.
They work well, but aren't anything special other than what you'd imagine they are: a decent performing, low cost street-oriented option.
If you're not in a hurry, Speedmaster usually offers "Black Friday" deals of up to 50% off, otherwise these guys have a respectable daily price:
For 1967-2003 Small Block Chrysler/Mopar 318 340 360 Air Gap Intake Manifold | eBay
Oops- I just noticed that the one you showed was even cheaper by a few bucks- good find!

 

[pittsburghracer]

40% off but you were close.

 

[340inabbody]

So what does “Air Gap” mean when describing an intake manifold? I thought that was a registered trademark of Eddy?

 

[rumblefish360]

Figure out what your compression is now or at least where the piston sits in the bore. Know for sure where everything is at. Know for sure if it is the 12-1 domed piston or not.

I don’t think Edelbrock has it as a Reggie trade mark.
For an example, ALL a Chrysler big block intakes are of this design from the day they were born.

 

[toolmanmike]

So what does “Air Gap” mean when describing an intake manifold? I thought that was a registered trademark of Eddy?

The plenum and runners are separated from the base. Air can circulate through the gap making for a cooler air/fuel charge.

 

[rumblefish360]

Crap…. I hit send/post….

There are options for head gaskets by Cometic (very expensive but….) that they will custom make in any thickness and bore size you spec. So… if n an example, you can tell them you have a 4.07 340, gasket size will be custom at 4.09 X .120 thick. That’ll drop your compression ratio.

Be ready for sticker shock! But it’s cheaper than a full rebuild.
This may not be the way to go though as some hi compression pistons will have the engine acting terrible with a lot of space that a thick head gasket produces.

Let’s wait and see what exact pistons you have in the engine and where they sit at. Also there health state.

 

[340inabbody]

Crap…. I hit send/post….

There are options for head gaskets by Cometic (very expensive but….) that they will custom make in any thickness and bore size you spec. So… if n an example, you can tell them you have a 4.07 340, gasket size will be custom at 4.09 X .120 thick. That’ll drop your compression ratio.

Be ready for sticker shock! But it’s cheaper than a full rebuild.
This may not be the way to go though as some hi compression pistons will have the engine acting terrible with a lot of space that a thick head gasket produces.

Let’s wait and see what exact pistons you have in the engine and where they sit at. Also there health state.

I bore scoped them and positively identified them as TRW 12:1 yup.

 

[340inabbody]

So what is the difference between an LA manifold and a magnum manifold and how can one manifold work for both applications if the ports are different or is it just the bolt pattern? Thanks.

 

[rumblefish360]

OK, cool. Do you know the dome size and dimensions?
Do you know what head you want to run?
Sorry, recap what head you have now please.

 

[rumblefish360]

So what is the difference between an LA manifold and a magnum manifold and how can one manifold work for both applications if the ports are different or is it just the bolt pattern? Thanks.

So what is the difference between an LA manifold and a magnum manifold and how can one manifold work for both applications if the ports are different or is it just the bolt pattern? Thanks.

The LA attaching hardware is on an angle while the Magnum is straight up and down.

The he above intake pictured has both holes drilled/cast in to use on ether head. Port are close to the same. Problem is, port sizes vary slightly on every engine, every head, every year every casting series. An “X” head has a listed port size but you may find only 1 or 2 matching exactly that size on any single head never mind the run of millions.

 

[toolmanmike]

Yep, your engine sounds like a hot rod piece. Overbuilt for most street cruisin'. Pull it and sell it. Like mentioned, a Magnum is a goid choice.

 

[340inabbody]

OK, cool. Do you know the dome size and dimensions?
Do you know what head you want to run?
Sorry, recap what head you have now please.

I’ll have to get back to you on the specs as I don’t have this Info handy right now. Was wondering can you stack head gaskets? Or is that unreliable? Never heard of it being done before.