Extra hp out of my 340.

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hux340

hux340

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Hi All,
I've got a 71 Dodge Demon 340. Don't know what's been done to the motor as it was rebuilt before I bought it. Seems very strong though & with maybe 10,000 miles on it. We put it on the dyno recently & it's getting 340 hp at the flywheel. I would like to get some extra hp without tearing down the motor. Has no after market mods on it besides a 670 holley street avenger. Was looking at doing the following -
1. Alloy Heads
2. Dual plane alloy intake manifold &
3. Headers (or as we call them here in Aust. extractors).
Not sure about a cam change as I don't want to sacrifice torque which it's got plenty of.
With the alloy heads I would like them to fit under the factory rocker covers. I will also paint the inlet manifold the hemi orange. Trying to keep the engine bay as original as possible.
If I do the above what hp increase would I see?
Cheers,
Glenn.

Dodge at Norieal Park July 15 010.JPG
 
hux340 said:
Hi All,
I've got a 71 Dodge Demon 340. Don't know what's been done to the motor as it was rebuilt before I bought it. Seems very strong though & with maybe 10,000 miles on it. We put it on the dyno recently & it's getting 340 hp at the flywheel. I would like to get some extra hp without tearing down the motor. Has no after market mods on it besides a 670 holley street avenger. Was looking at doing the following -
1. Alloy Heads
2. Dual plane alloy intake manifold &
3. Headers (or as we call them here in Aust. extractors).
Not sure about a cam change as I don't want to sacrifice torque which it's got plenty of.
With the alloy heads I would like them to fit under the factory rocker covers. I will also paint the inlet manifold the hemi orange. Trying to keep the engine bay as original as possible.
If I do the above what hp increase would I see?
Cheers,
Glenn.

View attachment 1715137914
Click to expand...
We here also call alloy, aluminum.

Is your car an automatic trans?
What gears does the rear have and your current tire size? A cam change would need these known factors before a cam is purchased as well as IF your willing to swap a converter to a higher stall unit.

A good and properly done converter will allow a bigger sizeable cam to be used without a loss of drivability. A lack of low end torque is well covered by a good converter.

Generally speaking without much fan care or issue, a basic swap of parts is the first and easiest upgrades to do.

Holley or Edelbrock carb, Edelbrock intake and prepped Edelbrock heads make an excellent first step.

Knowing of your pistons pop up out of the block is the first BIG question as this dictates which heads to purchase. Edelbrock makes a head for this stock positive deck height piston.

The best Extractors (or headers) are ether Doug’s or tti. Expensive but OH! So very worth it.



72Dart6pack said:
E3 spark plugs add a easy 20 hp. Just a thought? :poke:
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LMAO... stop it all ready!!! LMAO!!!
 
Gotta throw that out there every once in a while. :rolleyes: Also those electric turbo chargers you put before your Air Cleaner I heard add gobs of power.
 
When this is a genuine 340 it will probably have a very decent dual plane intake on it already, so
I would do, in this order: extractors (love that word :) ), Edelbrock or other aluminum heads, cam, rear end.
 
Do the cam change last, and be very carefull on picking a cam that will maintain best torque where you want it. ANY duration increase will soften the bottom rpms torque, in an attempt to make more power higher up. So focusing on increasing total lift, as well as rate of lift while keeping seat to seat timing close to stock would be the direction i would go. Obviously you can put in a higher stall converter, but get familiar with them before making this choice. They don't feel the same, and you may or may not like the difference.
 
In the US 1971 340 motors came with a thermoquad carb and intake that was pretty good to start with. Putting a set of good heads on it, or working with what you already have might be an effective way to up the power on the cheap. Find out what your current heads flow as is, and find out what could be done to improve them before throwing money at other heads that may not increase power without work done to them. Also check things like the timing curve, cam (stock? Not stock?) Is the heat riser passages blocked?
 
Pretty much agree with the suggestions to leave the cam alone - depending of course on your real objective.
340 Hp is very respectible for a stock engine -
The one item that will help power for the entire rpm range will be extractors.
Even changing the intake manifold will likely somewhat compromise the bottom end - although you can easily cover that with converter, or make up for some it with extractors and carb (idle circuit) tuning.
See this post for a dyno comparison graph:
Edelbrock LD4B
There's a much more recent magazine test of a stock 340 with similar results, although higher numbers.
I'm going to presume by your Hp that there was no falling off at the top end due to valve float. You may pick up some high rpm power with a Mopar Performance "tach drive" distributor - but it has no vacuum advance so it will hurt fuel milage.
So my suggestion is spend the time and money on the extractors first. Intake depending on what you want.

If there aren't any extractors down under for the left hand drive models, then either Doug's or TTI's from here (stateside) are probably the best of the mass produced headers. If you have someone do custom, especial in stainless, that's a great option even though expensive. Take the time to match the top and sides of the ports.
 
Do you have the dyno sheet so we can look at the power curve?
 
These little motors need to breathe, I'd put at least a 750DP on it, a good set of headers and change the gears. If it didn't see a bunch of interstate speeds I'd go with 3.91's.
 
Surprised nobody said "stroke it" make it at least 418 cubes. LOL.

As mentioned , don't touch the cam unless you are VERY sure. J.Rob
 
Ohhhhh boyyyyyy, RAMM stirring the pot!!!!!
:rofl:
 
hux340 said:
Demons a A833 4 speed with 3.23 LSD.
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Oh yea! Loving those words!
Manual trans!!!!! Gotta live the
“Man Pedal!!!!”

Since you have a clutch car, any cam you decide to put in is complemented by a gear ratio that matches. This is why combinations with manual trans cars include a higher than normal gear ratio in place of the higher stall converter.

It is IMO. Since I have been a manual trans car driver for decades, that to take advantage of a manual trans car in a performance application that you move to a mechanical cam. The solid cam rpms better and higher than a Hyd. cam does. You will need more duration to equal the Hyd. cam, but you will out power it and rpm it.

IF in the future you want to increase the cars performance and flexibility, look at an overdrive trans. A 5 spd manual trans is what I would look for.
 
rumblefish360 said:
Good mention!!!!
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Yes. That's the more recent magazine tests I was thinking of.
Note that the first jump in power came from installing a carb that wasn't "stuck" with whatever calibrations it had.

I think general lessons from these two magazine tests are valid, even if taking the absolute numbers with a couple grains of salt.
 
Mattax said:
Yes. That's the more recent magazine tests I was thinking of.
Note that the first jump in power came from installing a carb that wasn't "stuck" with whatever calibrations it had.

I think general lessons from these two magazine tests are valid, even if taking the absolute numbers with a couple grains of salt.
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Yes but also the whole package as it came together! While the bigger carb let’s it breath, which all MoPars suffer from in stock configuration, the intake (RPM) in test 4 is about what most people can expect from just bolt on parts (not to shabby IMO) the additional HP with the cam is really cool since it is still a small streetable Hyd grind that won’t hit you in the backside on around the block egg and milk runs.
All together a 43 hp gain with a 28 ft. lbs. gain in torque at peak. And it’s a gain from bottom to top. No loss.

And we (they) didn’t get to porting or swapping heads yet.

Hummmmmmmm..........
 
Mattax said:
Yes. That's the more recent magazine tests I was thinking of.
Note that the first jump in power came from installing a carb that wasn't "stuck" with whatever calibrations it had.

I think general lessons from these two magazine tests are valid, even if taking the absolute numbers with a couple grains of salt.
Click to expand...


Right that's why the +40hp/+40trq gain I mentioned from the Headers and intake was AFTER they already fixed the carb issues with a new Edlebrock 800.


I graphed the difference & the gains are through out the ENTIRE curve not just peak.
New Stock(new 800cfm) vs 340(Carb +Headers+Intake)

lol,,no cam yet and for damn sure no new aluminum heads.

upload_2018-2-3_11-48-32.png
 
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Nice graph. Thanks.

With the addition of some well prepared aluminum heads (not ported) power should really pick up nicely.

It should really be nice with taking advantage of the available extra flow of the ports with some high lift.
 
if you're driving it on the street...leave it alone!
If you're going to race it you'll need many changes that will compliment each other.
 
myduster360 said:
1-5/8 Extractors and an Alloy Performer RPM added up to 40hp and 40ftlb on this stock cammed 340. HUGE Bang for the Buck and just an afternoon's work

1970 340 High Performance Mill Dyno - Mopar Muscle Magazine

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Total BS HP claims in that article. No way does a stock headed 340 and an xe268H camshaft make 390hp... LOL NO WAY, NO HOW!!! 350hp if it's lucky!

Been beat to death in here so many times and I'll say it every time that POS article comes up. Much like many of the HP claims that have been pushed by that mag over the years... 600+ HP 3500 pound cars running 120mph... yep that's about right. :) Get the F outta here.
 
I agree with Ir3333, leave it alone. The power you have is nice and the engine compartment is even nicer. However, we all want more and so do you. Problem is, neither of us know exactly what you’re dealing with as far as modified engine internals and parts that are already in it. You could possibly open up a huge problem and then make it worse by mismatching parts because we don’t know what you have.

If I had to modify an unknown engine, the first thing I would ever do is a compression/leakdown test. This will uncover any problems or shortcomings you currently may have. Then I would install an air fuel ratio meter and tune the fuel system as much as possible, simultaneously with ignition timing. You can gain 20 ft.lb easily from a better tune. You’ll have to tune ignition and fuel anyways after bolting on any aftermarket part.
 
crackedback said:
Total BS HP claims in that article. No way does a stock headed 340 and an xe268H camshaft make 390hp... LOL NO WAY, NO HOW!!! 350hp if it's lucky!

Been beat to death in here so many times and I'll say it every time that POS article comes up. Much like many of the HP claims that have been pushed by that mag over the years... 600+ HP 3500 pound cars running 120mph... yep that's about right. :) Get the F outta here.
Click to expand...



LOL,,, So a stock 340 gaining 40Hp/40Trq from headers and good intake, is just OUT OF THIS WORLD UNBELIEVABLE?? lol!! FAKE NEWS!!! lol

Quick lesson on racing Dynos. Dynos can vary in their accuracy and its correction factors manipulated to get whatever # makes you feel good about your crap build,,big whoop. So freaking out about an absolute value of the Hp being too high or too low is just over the top silly.

Key lesson is a Dyno will vary far less in their precision. So once you Baseline, REGARDLESS OF THE ABSOLUTE VALUE YOU'RE LOOKING AT. So you do SOMETHING to create an extra 40HP,,you better believe that engine just Gained 40hp over the Baseline.

That's the whole reason I didnt say squat about the values only that the STOCK 340 gained 40HP/40lft from a Intake and Headers.
 
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