1972 Demon 340 engine mods

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Miszny

Miszny

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Hi

A friend of mine has a 1972 Dodge Demon numbers matching car with 3 speed manual.
Car was fully restored to all original specs. Its from August 1972 which means low compression, cast crank and 245hp.

His idea is to add some more power to make it more fun to drive, but all work needs to be done so that he can go back to stock specs whenever he wants to.

We were kind of debating what to do here not to go too crazy.
The most radical idea included swapping heads, cam, intake and carb...

Since many of you guys helped me out a lot before and directed me to the right path in doing things, I am really curious on what would you do?

Thank you!
 
Guess it depends how much more he wants out of it.

Raise the compression a bit, little more cam and gear. should still look all original with those simple mods
 
Throw some gears in it.
Pistons are the next change I would make.
 
Not the cheapest option but...

Why not just pull that motor and put a different one in? Wrap the numbers matching engine up and store it in the garage. And drop another motor in that you can rag on and not worry about blowing up. That's the safest way to save a numbers matching setup.
 
If he likes it, I'd just replace the camshaft, maybe build a 2nd 8 3/4 chuck for it with a lower gear, and call it a day. With a cam that's a prety fun package.
 
Well...

Motor swap is not easy as we are talking about a car that is in Europe, so access to everything is limited.
The idea was to use bolt ons, adding 100-150hp would be great.

I've seen some powerful low compression builds and was thinking that this might be the best option.
Looks are not the most important, there can be a compromise like new valve covers, intake, air filter, carb and stuff... Just non permanent mods.

I saw a set of ported, used iron heads with 270ish flows at .600 lift and was curios what cam/intake/carb could I use to make the most of it?

Rear end swap is also an option.
 
moper said:
If he likes it, I'd just replace the camshaft, maybe build a 2nd 8 3/4 chuck for it with a lower gear, and call it a day. With a cam that's a prety fun package.
Click to expand...

Here is a recipe for a car just like this from back in the day....

Mopar 280 Purple Camshaft
273 Adjustable Rockers
Mild shift kit
4:30 gear

Everything else was left stock including factory exhaust to the tips. Car ran 12.90's with a sticky on the back. I am sure there are plenty of other recipes but I saw this one for myself and it flat worked....

It boils down to what the owners expectations are. Personally the original drivetrain would go in the corner and I would go over 400ci but then you will be changing other aspects of the car and once that train starts moving everything changes lol.... Post some pictures of it if the car is all original. Hard to find a demon like that these days lol...

JW
 
Check you balancer on that crank. They changed in '72. Pretty sure by August it will be cast. My '72 is a steel crank, but it was built late in '71. According to Allpar they changed in April
 
'73red-duster said:
Check you balancer on that crank. They changed in '72. Pretty sure by August it will be cast. My '72 is a steel crank, but it was built late in '71. According to Allpar they changed in April
Click to expand...

I did not know that...... Interesting.....

JW
 
Do you think 72's were built in August of 72? I thought production would stop in July and then start building 73's in August for September introduction.
 
Miszny said:
His idea is to add some more power to make it more fun to drive, but all work needs to be done so that he can go back to stock specs whenever he wants to.

We were kind of debating what to do here not to go too crazy.
The most radical idea included swapping heads, cam, intake and carb...
Click to expand...
Going back to original means not changing the pistons. so the idea of swapping out the top end parts is the ticket IMHO.

Is this for drag racing or for brisk cruising or what? That will decide the cam and that will guide the top end changes. If 'twer me, and I had the $$, and it was for street, I would be looking into swapping out the heads for Edelbrocks, with an Air Gap or Performer intake and then choose the cam and carb for what I I wanted to do. The breathing of those heads and intakes will get you easily up into or past the mid 300 HP range, even with stock manifolds. Headers would be even better.

I'd have to run the numbers on the resulting compression ratio to be sure, but off the cuff, I would expect the real static CR to be in the low to mid 9's with 63 cc head chambers with those lower CR 340 pistons. So low RPM torque will be pretty darned good, and the torque band can be made wider. That will help with the wider RPM range needed with that 3 speed.

It appears that Edelbrock has removed their restrictions on the dealers and distributors marking down the price on the Edelbrock heads. I see that all sorts of dealers are selling the 60779's for $683 each, fully loaded with valves and springs. That is down $130 apiece form not so long ago.

You'll always be able to easily sell such heads and the intake, etc., later.

Now, he needs to do something about that 3 speed....
 
Here are some photos taken today. You can see my Duster there too.

I checked the balancer and this car has forged crank for sure so it's not that terrible aferall.

IMG_0404.JPG


IMG_0407.JPG


IMG_0408.JPG


IMG_0406.JPG
 
nm9stheham said:
Going back to original means not changing the pistons. so the idea of swapping out the top end parts is the ticket IMHO.

Is this for drag racing or for brisk cruising or what? That will decide the cam and that will guide the top end changes. If 'twer me, and I had the $$, and it was for street, I would be looking into swapping out the heads for Edelbrocks, with an Air Gap or Performer intake and then choose the cam and carb for what I I wanted to do. The breathing of those heads and intakes will get you easily up into or past the mid 300 HP range, even with stock manifolds. Headers would be even better.

I'd have to run the numbers on the resulting compression ratio to be sure, but off the cuff, I would expect the real static CR to be in the low to mid 9's with 63 cc head chambers with those lower CR 340 pistons. So low RPM torque will be pretty darned good, and the torque band can be made wider. That will help with the wider RPM range needed with that 3 speed.

It appears that Edelbrock has removed their restrictions on the dealers and distributors marking down the price on the Edelbrock heads. I see that all sorts of dealers are selling the 60779's for $683 each, fully loaded with valves and springs. That is down $130 apiece form not so long ago.

You'll always be able to easily sell such heads and the intake, etc., later.

Now, he needs to do something about that 3 speed....
Click to expand...

Idea is to make it move better on the street but not too crazy. Also to keep good cruising speed so rear gears swap is probably not a good idea.
Car is really great as you can see, it's a true time capsule and head turner.

Thanks for the tip with Edelbrock heads price drop, there heads were high on the list with Performer intake and 750cfm Holley double pumper.

Solid cam with adjustable rockers also were the idea. I was thinking about solid roller setup but perhaps solid flat tappet would do the trick also. Question on what would be good choice given rear gears and manual trans?
 
I had a 72 Demon. I was the second owner. Wish I still had that car.

Anyway, it came with a steel crank and 2.02 valves. I've even heard from reputable sources that some early 73's came with steel cranks.

Chrysler used up what they had. If there was leftover cranks and heads and things they'd use them.

I wish I'd have kept that car.
 
I ran some numbers with the later, low compression 340 pistons, and even with a .028" thick head gasket, and the 63 cc chambers in the 60779 Edelbrocks, the engine is still going to be in the low 8.3-8.5 range for static CR. That is not high CR, and you're gonna have to stay small on the cam to avoid dumping the low end torque into the toilet. That is where the issue with a solid is going to crop up..... finding a short duration solid that will not dump the dynamic CR too low is a challenge. Finding a hydraulic is easier.

I'd be looking at something like the 2 smallest VooDoo hydraulic flat tappet cams, or similar, and not be afraid to put the ICL at 106 or even 104 degrees, to help keep the low end torque good. Stepping up through the gears with that 3 speed is gonna need low RPM torque unless you want to wind it way up in RPM's before each upshift. Using the smallest VooDoo hydraulic flat tappet cam and installing at an ICL of 106 would put the DCR in the low 7's..... that is not a high DCR for the street but you are not going to do much better with those pistons.

Looking at a hydraulic roller like the smallest VooDoo Retro-fit hydraulic roller is interesting. You can keep the duration down and get considerably more lift to help high RPM breathing and HP. It would try that before looking at a solid flat tappet. But it is still dropping the DCR below 7.

I would seriously be tempted to mill the new Edelbrocks about .030" to get about 5 more cc's out of the chambers. Then you would get the DCR up to the mid-7 range. You could mill even more off, and then the cam possibilities open up even more.

By the way, I see you are in the Warsaw.... it is great to hear from owners outside of the US and Canada.
 
Milling the heads is no problem, I have access to professional shop so all is up to deciding where to go with this, gather funds and stick to the plan.
What would be the best way? How much to mill down the Edelbrocks?
Perhaps some custom grind cam would be the way to go and still stay with solid cam idea?
With hydraulic high lift cams and hard springs there are often lifter collapse problems and it would be best to avoid it.
What would be the maximum duration that could work?
With VooDoo cams it looks like this:
- smallest hydraulic flat tappet is 213/220 @.050" .454/.475 lift LSA/ICL 112/108
- smallest solid roller is 231/237 @.050" .555/.566 lift LSA/ICL 110/106
- smallest solid flat tappet is 235/243 @.050" .525/.546 lift LSA/ICL 110/106

With solid roller above Lunati says 9:1+ compression so I was thinking that it could be run with Edelbrock heads as they are.

Also basic Howards solid roller cam:
- 229/237 @.050" .555/.555 lift LSA/ICL 110/106 (9.5:1+ compression recommended)


Yup we are far away with really bad access of parts and all needs to be planned well so when the parts arrive nothing is missing. Shipping is very expensive and waiting time is also pretty bad like 7 to 21 days... At least there is no problem with good machine shops.

I could open Summit store in Europe, this could make things so much better for people like me over here ;-)
 
nm9stheham said:
I ran some numbers with the later, low compression 340 pistons, and even with a .028" thick head gasket, and the 63 cc chambers in the 60779 Edelbrocks, the engine is still going to be in the low 8.3-8.5 range for static CR.
Click to expand...

I was sure that as is it makes 8.5:1 compression and with Edelbrocks it would be in 9ish range?
You wrote before that it would be mid 9 with 63cc heads right?
 
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Summit in Warsaw.... that sounds good! LOL

I would go with the durations you list in first cam, the Voodoo hydraulic flat tappet, or one size larger in that type of cam. Your compression ratio is not very high and that is the problem with the solid cams that you list; with the low static compression ratio and the larger cams, the dynamic compression ratio will be very low (in the 6 range), and the low RPM torque will be like a worn out Trabant engine.

That is a BIG problem with a 3 speed manual transmission; if you have low torque at low RPM's, then you will have to rev the engine very high and slip the clutch a LOT to start off. And then when you make the 1-2 or 2-3 upshifts, and you release the clutch and the RPM's drop, the engine may again act like that worn out Trabant until the RPM's increase.

I had a 250* at .050" cam, low compression Opel 1.9L Ascona that I rallied for many years, and it had exactly that problem: it was WORSE than a worn out Trabant engine below 3800 RPM; and the 2-3 gear step was very bad when rallying in hills and mountains. The only thing that saved that engine was that I could rev it to 8000 RPM. But a smaller cam and higher compression would have been much better for rallying. The important thing to have is a large RPM range; your torque needs to be good from 2000 RPM to 5000 or 5500 RPM.

Solid cams hardly ever come in small durations, and when they do, the lift is low and that does not take full advantage of the good heads. The only one that I like for this use may be the ST-2 made by Racer Brown. It is 218* at .050" and .450" lift. The roller types would be better as you can get more lift, like the Howards cam that you list, but the duration is just too long for the compression ratio that you have with the 3 speed manual transmission.

One thing that WOULD help you with a non-roller cam is to change from the stock 1.5 rocker ratio to a 1.6 rocker ratio. This would change the the .450" lift of the Racer Brown or Lunati cams to around .480". This is a very good change to make with the limited cam duration that you need. There are 2-3 good choices for 1.6 rockers IMHO. Your may also want to look into the B3RE geometry correction kit to make sure the rocker geometry is optimized.

Since you are so far away with the shipping delays and costs, one thing I would advise you to do is to pull the heads immediately and make sure what pistons that you have. All my thinking is based upon the later low compression 340 pistons. If your engine has been rebuilt with higher compression pistons, then all of this thinking changes.

Also, be aware that the bearings in these engines are over 40 years old and the bearing surface materials will sometimes flake of. So you may want to get new bearings with this order and be ready to replace them.

I would also get a new oil pump and be ready to replace that. They are not expensive.
 
I agree with finding another engine, especially if that is the numbers matching engine for your car. It would hold its value much better if you have the original engine in original condition.

Whether you're in another country or not, that's the idea I would shoot for. Just bide your time. Is there really a need for a rush? More often than not, rushed projects don't turn out as good as they could.

Also, I cannot believe the crankshaft argument. Who cares which crank is in it? If you decide to use it, just make sure of which it is and use the correct corresponding parts. A cast crank will support 600 HP with everything balanced properly and using a good quality balancer. People seem to forget that when bench racing.

Weigh it all out and do what's best for YOU. Don't rely on anyone else (including me) to make your decision. No one knows your situation better than you.

I know if I were in your place, I would do everything in my power to preserve that original engine. JMHO.
 
nm9stheham said:
Summit in Warsaw.... that sounds good! LOL

I would go with the durations you list in first cam, the Voodoo hydraulic flat tappet, or one size larger in that type of cam. Your compression ratio is not very high and that is the problem with the solid cams that you list; with the low static compression ratio and the larger cams, the dynamic compression ratio will be very low (in the 6 range), and the low RPM torque will be like a worn out Trabant engine.

That is a BIG problem with a 3 speed manual transmission; if you have low torque at low RPM's, then you will have to rev the engine very high and slip the clutch a LOT to start off. And then when you make the 1-2 or 2-3 upshifts, and you release the clutch and the RPM's drop, the engine may again act like that worn out Trabant until the RPM's increase.

I had a 250* at .050" cam, low compression Opel 1.9L Ascona that I rallied for many years, and it had exactly that problem: it was WORSE than a worn out Trabant engine below 3800 RPM; and the 2-3 gear step was very bad when rallying in hills and mountains. The only thing that saved that engine was that I could rev it to 8000 RPM. But a smaller cam and higher compression would have been much better for rallying. The important thing to have is a large RPM range; your torque needs to be good from 2000 RPM to 5000 or 5500 RPM.

Solid cams hardly ever come in small durations, and when they do, the lift is low and that does not take full advantage of the good heads. The only one that I like for this use may be the ST-2 made by Racer Brown. It is 218* at .050" and .450" lift. The roller types would be better as you can get more lift, like the Howards cam that you list, but the duration is just too long for the compression ratio that you have with the 3 speed manual transmission.

One thing that WOULD help you with a non-roller cam is to change from the stock 1.5 rocker ratio to a 1.6 rocker ratio. This would change the the .450" lift of the Racer Brown or Lunati cams to around .480". This is a very good change to make with the limited cam duration that you need. There are 2-3 good choices for 1.6 rockers IMHO. Your may also want to look into the B3RE geometry correction kit to make sure the rocker geometry is optimized.

Since you are so far away with the shipping delays and costs, one thing I would advise you to do is to pull the heads immediately and make sure what pistons that you have. All my thinking is based upon the later low compression 340 pistons. If your engine has been rebuilt with higher compression pistons, then all of this thinking changes.

Also, be aware that the bearings in these engines are over 40 years old and the bearing surface materials will sometimes flake of. So you may want to get new bearings with this order and be ready to replace them.

I would also get a new oil pump and be ready to replace that. They are not expensive.
Click to expand...

Worn out Trabant engine, that's a good one :)

I guess you are right with checking compression first. I will pull one plig and use endoscopic camerato look inside. Question is how do I distinguish low compression pistons from hp pistons?

This car was fully restored a few years back and purchased thru RK Motors Charlotte.
This is it: 1972 Dodge Demon For Sale | Collector and Classic Cars For Sale | RK Motors Charlotte
I talked to them and they claim its a 275hp high compression engine but then they say it was rebuilt according to factory specs... There is N2R code there and for me it means 240hp...
Don't know what to think, so will check.
Previous owner of this car did some changes added rear wing, some hood stickers, pistol grip shifter... which were totally not needed, but I guess it made the car look as he wanted.
Car runs great but its impossible for me to say what it is just by driving. I have a big block car and power difference is huge so its hard to say.

The ST2 cam seems like a good way out.

Also Summit in Warsaw is the best idea ever, located in center of Europe I could supply everybody around Europe quickly :) I should talk to them I guess ;-)
 
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RustyRatRod said:
I agree with finding another engine, especially if that is the numbers matching engine for your car. It would hold its value much better if you have the original engine in original condition.

Whether you're in another country or not, that's the idea I would shoot for. Just bide your time. Is there really a need for a rush? More often than not, rushed projects don't turn out as good as they could.

Also, I cannot believe the crankshaft argument. Who cares which crank is in it? If you decide to use it, just make sure of which it is and use the correct corresponding parts. A cast crank will support 600 HP with everything balanced properly and using a good quality balancer. People seem to forget that when bench racing.

Weigh it all out and do what's best for YOU. Don't rely on anyone else (including me) to make your decision. No one knows your situation better than you.

I know if I were in your place, I would do everything in my power to preserve that original engine. JMHO.
Click to expand...

I am totally for preserving it as close to stock as possible, its just great car, but if the owner wants some more power, then I think its good to advice him to do it right not to go too far and to avoid mistakes on the way. He understands its a #s matching car and he will not go crazy.
I think motor swap is too much for him... Seems like a much bigger task.

My first idea was built 318, there are guys here running 400-450hp motors like this, but its much bigger than just cam/heads/intake/carb swap. These are cheap and very underestimated motors.
Here is a perfect example of my buddy's 318 Challenger (its .030" over, 410+hp):


We will see how things go, I have not given up on the 318 idea yet.
 
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