Should I be feeling more power?

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Rude72*

Rude72*

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Hello all:

New member here and happy to belong to this forum!

I recently acquired a 1972 Duster 340. It’s a beautiful car in fantastic condition. Nearly everything has been “redone” and the motor is a built 340. I don’t know “jack” about motors and the specifics related to HP and torque, but I feel that this car should be “pulling” more through 2nd gear. Here are the motor’s “specifics”:

  • Correct Vintage 340 block bored .030 over.
  • TRW forged pistons & Speed Pro Piston Rings-Compression 11:1
  • Mopar Performance Purple Shaft Cam P4120235
  • Performance Electronic Ignition with chrome box and Accel Super Coit
  • 340 heads rebuilt with new Valves, hardened valve seats and 3 angle vale job
  • Hooker Comp Headers with Jet Hot coating mated to 2.5" exhaust with cross pipe and Flowmaster Mufflers
  • Holley 750 Carb atop Edelbrock Torker I| Intake manifold with K&N Air Filter
  • Mechanical Holley Fuel Pump on engine as well as secondary Holley Electric
    Fuel pump located near fuel tank and operated by switch in cabin
  • 3 row radiator with overflow bottle and Mopar Performance Viscous
When I punch it from a stop, it initially really wants to go. Once 2nd gear kicks in, the rpm/torque seem to plateau. Once in second, torque seems to diminish and it takes a few seconds (after shifting into 2nd gear) to start gaining more power. I’m not sure if my description makes any sense, but it’s the best I can describe.

Do you think it simply needs a tune up? It’s been roughly 1,500-2,000 miles since the last tune up/oil change. Everything motor-related, including transmission, has recently been rebuilt. Supposedly, all drivetrain components from front to back as well as suspension and electrical additions were rebuilt and/or installed by the Montgomery Race Team. Currently the engine and transmission have roughly 10,000 trouble free mites since their rebuilds. Drivetrain(Engine, trans, rear and suspension) was rebuilt and installed by noted Mopar Super Stock factory backed Mopar racer Ken Montgomery Sr. (verification available from the family if requested). Has been maintained by the same family as well.

Any insight regarding this post would be greatly appreciated!
 
Divenut said:
What gear ratio are you running out back?
Click to expand...
This information was included in the car’s sales description:

B&M shift kit sends power to the 8.75” rear with 3.23 SureGrip gears and Mark Williams axles, (a 489 carrier with 3.91 gears and SureGrip is included).
 
Rude72* said:
Do you think it simply needs a tune up?
Click to expand...
What is meant normally be a "tune up" - spark plugs, cap and rotor, set points, etc. and set timing and idle fuel mix. It wouldn't hurt to change the oil and just check everything (spark plugs, air filter, cap, etc ) at 2000 miles. Looking at the condition of these items will provide some clues as to how the engine is doing.
More likely it needs to be tuned in. Its not factory so adjustments need to be made one at a time.
Rude72* said:
Mechanical Holley Fuel Pump on engine as well as secondary Holley Electric
Fuel pump located near fuel tank and operated by switch in cabin
Click to expand...

Rude72* said:
I’m wondering if it’s a fuel pump issue…
Click to expand...
Not directly. Even if the pump fails entirely, thereisenough fuel in the bowl that the car will run 10-15 seconds at wide open throttle before going dry.
I do wonder why it has two fuel pumps. It was something at one time in the old Direct Connection bulletins but if the mechanical pump is working correctly a stock pump is all that is needed for this engine.

Rude72* said:
Everything motor-related, including transmission, has recently been rebuilt. Supposedly, all drivetrain components from front to back as well as suspension and electrical additions were rebuilt and/or installed by the Montgomery Race Team. Currently the engine and transmission have roughly 10,000 trouble free mites since their rebuilds. Drivetrain(Engine, trans, rear and suspension) was rebuilt and installed by noted Mopar Super Stock factory backed Mopar racer Ken Montgomery Sr. (verification available from the family if requested). Has been maintained by the same family as well.
Click to expand...

Sure. call them.See if the family knows anything about it. Nothing to lose and maybe a little insight into what they did. Ken Montgomery's place was a bit North of Philadelphia. Montgomery Service Center. Was a super nice guy - passed away a few years ago.
 
Sounds like the secondaries are opening a lil too soon, and/or
The stall is too low, but;

The specs on that cam are 284/284/108; and .484 lift
In at 106, the Ica is 68*, and at 700ft elevation, the cylinder pressure is predicted to be ~172psi
Usually this is too high for open-chamber iron heads to run full timing without detonation. SO
More likely,
is that the ignition timing has been pulled and/or is lazy,
Furthermore, the 68* Ica makes the bottom-end nearly as soft as a carbureted 5.2Magnum.

The only cures I know of , depending on which of the 3 or 4 above-items listed are causing it, are;
> Slow the secondaries down, and/or quicken up the Accelerator pumps, or
> get a higher stall, or
> run a higher octane gas so you can put the timing back, or
> reduce the cylinder pressure
>increase the rear gear to 4 series where it shoulddabin from the get-go. This to spool up the rpm to get out of the soft-zone AND, this may allow a lil more Power-Timing before getting into detonation.
>> or some combination
Since you have them, stuff those 3.91s in there, and see how it goes.
 
Rude72* said:
Mopar Performance Purple Shaft Cam P4120235
Click to expand...
That the old 284/284 duration cam for a RB block. But you have a 340?

Rude72* said:
Performance Electronic Ignition with chrome box and Accel Super Coit
Click to expand...
There are several versions of the distributor used by MP. Timing light, timing tape and tach will be needed to find out what timing curve looks like. Search here for a how to do this.
Rude72* said:
Holley 750 Carb
Click to expand...
There's various Holley carbs with nominal 750 cfm ratings. Look at the choke tower for the "list number" or post photos. it will be 4 digits and a dash. eg 33310-4 or 4779-3
Rude72* said:
When I punch it from a stop, it initially really wants to go. Once 2nd gear kicks in, the rpm/torque seem to plateau. Once in second, torque seems to diminish and it takes a few seconds (after shifting into 2nd gear) to start gaining more power.
Click to expand...
My guesses are,
its set up too lean or possibly even too rich to pull the additional load.
timing at the rpm/throttle opening/oad is a little to low.
 
Thanks for all the input and suggestions, guys. Truly appreciated! Like I said, I’m a gearhead “novice” and don’t really know anything about the information you guys provided (thanks again). I’ll probably share this information with my local mechanic and see what he thinks.
 
When I bought my 66 Barracuda, the engine was damn near identical to yours, but set at 10:1.

It even had the same rearend/gear and transmission.

It was lazy out of the gate, but liked rpms, which is what I have been told about 340’s.

I wish I could tell you that I just installed a different rearend gear and everything got better. It probably would have…

I pulled the engine and built a 416…oops

I’d definitely install the 3.91 gears and see what happens. It would be good to know what converter you have.
 
TXOval said:
When I bought my 66 Barracuda, the engine was damn near identical to yours, but set at 10:1.

It even had the same rearend/gear and transmission.

It was lazy out of the gate, but liked rpms, which is what I have been told about 340’s.

I wish I could tell you that I just installed a different rearend gear and everything got better. It probably would have…

I pulled the engine and built a 416…oops

I’d definitely install the 3.91 gears and see what happens. It would be good to know what converter you have.
Click to expand...
Thanks for the info and reply, TXOval. I did a little digging and found this:

3200 RPM Stahl Speed Trans Specialties Converter
 
The small block Torker intake is a turd. Put an rpm air gap on it and it’ll pick up a bunch of low end.
 
It's a really loaded question, as we have zero clue what your opinion is of "more power". We also have zero idea of the car's performance. If we had some zero to 60 or quarter mile times, we'd have something to go on. This type thing is very difficult to get across online.
 
I wouldn't take it to a general mechanic, maybe find a place that does tuning it on a chassis dyno.
 
AJ/FormS said:
Sounds like the secondaries are opening a lil too soon, and/or
The stall is too low, but;

The specs on that cam are 284/284/108; and .484 lift
In at 106, the Ica is 68*, and at 700ft elevation, the cylinder pressure is predicted to be ~172psi
Usually this is too high for open-chamber iron heads to run full timing without detonation. SO
More likely,
is that the ignition timing has been pulled and/or is lazy,
Furthermore, the 68* Ica makes the bottom-end nearly as soft as a carbureted 5.2Magnum.

The only cures I know of , depending on which of the 3 or 4 above-items listed are causing it, are;
> Slow the secondaries down, and/or quicken up the Accelerator pumps, or
> get a higher stall, or
> run a higher octane gas so you can put the timing back, or
> reduce the cylinder pressure
>increase the rear gear to 4 series where it shoulddabin from the get-go. This to spool up the rpm to get out of the soft-zone AND, this may allow a lil more Power-Timing before getting into detonation.
>> or some combination
Since you have them, stuff those 3.91s in there, and see how it goes.
Click to expand...
I like this! ^^^^^^^
The duration @.050 is 241*’s. A 3.23 gear is a good bit to low. 3.91’s at a minimum.
What size tire is in the back?
What ignition do you have?
What is the initial timing at?
Is it a MoPar performance distributor?
What octane are you using?
Do you have a tachometer in the car?
Check the spark plug color. If it’s dark, (black) you’re running rich which is an issue as well. If it’s dark but not black, your still a little rich.

The timing curve suggestion and the secondary opening timing is a very good one.
TT5.9mag said:
The small block Torker intake ————
Put an rpm air gap on it and it’ll pick up a bunch of low end.
Click to expand...
Ditto as well as match the top end.
IMO, it’s worth the expense and time to do it.

I’d also like to know what you have for an exhaust system. Not just muffler brand.
 
The first thing I would do is get rid of one of the fuel pumps. Mech pumps are not designed to pull fuel through another pump. I would keep the elec pump & bypass the mech pump. There is no reason to have two pumps for the HP level of this engine.
 
rumblefish360 said:
I like this! ^^^^^^^
The duration @.050 is 241*’s. A 3.23 gear is a good bit to low. 3.91’s at a minimum.
What size tire is in the back?
What ignition do you have?
What is the initial timing at?
Is it a MoPar performance distributor?
What octane are you using?
Do you have a tachometer in the car?
Check the spark plug color. If it’s dark, (black) you’re running rich which is an issue as well. If it’s dark but not black, your still a little rich.

The timing curve suggestion and the secondary opening timing is a very good one.

Ditto as well as match the top end.
IMO, it’s worth the expense and time to do it.

I’d also like to know what you have for an exhaust system. Not just muffler brand.
Click to expand...
Exhaust system? Manifold? What do you mean, exactly? It has Hooker headers.
 
273 said:
I wouldn't take it to a general mechanic, maybe find a place that does tuning it on a chassis dyno.
Click to expand...
How do I go about finding a place that does this? How much is it (typically speaking) to dyno a car?
 
Last edited:
I truly appreciate all of your guys’ input and suggestions! However, since I am a novice when it comes to motors (and anything motor-related), all of the numbers, gear ratios, etc. are Greek to me. I wish one of you guys lived near by! I’m sure that if you’d drive the car and put it through its paces, you would have a much better idea of what might be the “power” (or lack-there-of) issue.

I guess I’ll start with a tune up and see if my mechanic has any ideas.

Thanks again for all your guidance and suggestions!
 
Rude72* said:
Exhaust system? Manifold? What do you mean, exactly? It has Hooker headers.
Click to expand...
Hooker headers, excellent start.
What I mean is, dual exhaust with an H pipe or X pipe and what size are the pipes? Then muffler brand.

No worries, no that important at the moment.
 
Rude72* said:
I truly appreciate all of your guys’ input and suggestions! However, since I am a novice when it comes to motors (and anything motor-related), all of the numbers, gear ratios, etc. are Greek to me. I wish one of you guys lived near by! I’m sure that if you’d drive the car and put it through its paces, you would have a much better idea of what might be the “power” (or lack-there-of) issue.

I guess I’ll start with a tune up and see if my mechanic has any ideas.

Thanks again for all your guidance and suggestions!
Click to expand...

Where are you in Ohio? There are a bunch of members in that state and surrounding areas.
 
Visit a car meet and find a MoPar club rather than a local mechanic since most are not of an age where they understand a carburetor or the ignition system. Much less one where it’s been altered and upgraded.

If a local shop has an older fella you might be in luck.
 
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