1973 340, want more power.

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Richard McLaughlin

Richard McLaughlin

1974 Duster 340
Joined
Oct 10, 2016
Messages
338
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35
Location
New Brunswick
Hello!
I am new to the vintage car game.
I have a 73 340 in my 74 duster.
I am looking to get upwards of 450 hp with it.
What do you recommend?
Stroker pretty much the only option? 416 seems like a reasonable choice but not sure.
Thanks!
 
No, you can get well over 450 HP without stroking. Head flow and camming up properly are the keys, with other breathing improvements; intake, carb, headers and exhaust. It has been done a million times before so that number is very doable.

How are you going to be using the car/engine? Drag strip only? Street/strip and not a daily driver? Cruiser and daily driver only?

Be careful in chasing an HP number; you can get there several ways, but the torque curve that goes with a certain approach to 450 HP may not fit what you normally want to do with the car.
 
How did you arrive at 450hp?
Read Rusty Rat Rods' guide to hot rod bliss.You can probably make your stock 340 much faster fairly economically....
 
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I always question when people toss out a pure HP number. If you define what you are really looking for, people on here can give you better guidance.

For example, do you simply want 450 hp or do you want a street-able 11 second car?

For that matter, do street manners even matter? We don't know from your post.

Chassis improvements are an important part of building a fast car? Does that matter to you or do you just want a pure HP number?
 
It is a street car. I would like to be able to do a few 1/4 mile runs. But 99% street car. I want to make it just as powerful as a 6.4l srt basically. Or around there. Maybe that is not realistic.
 
Richard McLaughlin said:
It is a street car. I would like to be able to do a few 1/4 mile runs. But 99% street car. I want to make it just as powerful as a 6.4l srt basically. Or around there. Maybe that is not realistic.
Click to expand...


So from my quick google search, it looks like you want a very street friendly ("99% street car") mid/low 12s.
 
Ba
Richard McLaughlin said:
That sounds right! So, what is the best way to get there?
Click to expand...
Balance

Make sure everything works together, the rotating assembly, the cam, the intake, the converter and the gears

A stroker may not be the only way to go but I like mine
I can get more torque to the wheels then I can get to the ground, and I don't need to rev her to the moon

Now, it could be you like a high revving small blocks, I don't know
 
Don't need 450 hp to go low 12's in a Duster. You should get to low 12's and have money left over from the 3 grand, means you've already got the 340. Need more info such as to what you have now.
Gears?
manual or auto? converter?
exhaust (headers? manifolds?)
Is the 340 healthy right now (oil pressure, overall a good running motor??)
 
318willrun said:
Don't need 450 hp to go low 12's in a Duster. You should get to low 12's and have money left over from the 3 grand, means you've already got the 340. Need more info such as to what you have now.
Gears?
manual or auto? converter?
exhaust (headers? manifolds?)
Is the 340 healthy right now (oil pressure, overall a good running motor??)
Click to expand...
Gears not sure. Oil pressure fine, dual exhaust newer and good, has headers, runs great, automatic 3 speed
How do I find my gears? Can't really eh? Guy I bought it from said it had gears good for the highway and driving. Not low low gears.
 
Richard McLaughlin said:
Gears not sure. Oil pressure fine, dual exhaust newer and good, has headers, runs great, automatic 3 speed
How do I find my gears? Can't really eh? Guy I bought it from said it had gears good for the highway and driving. Not low low gears.
Click to expand...
I'd say some head work, the right cam, and you might want to spend some on a good quality converter, and you'll be about there. Not sure what intake and carb you have sitting on top....
 
IMG_0892.JPG
IMG_0892.JPG
 
A discussion of how to get there and meet the 450 HP goal will follow (I am sure), and will involve pistons, heads, combustion chambers, etc. I know you may just want a list of parts; you might get that. But this is one thought process laid out if you want to understand how you are getting there.

If it's 99% street, then you will be happier (I am fairly sure) with an engine that does not need to be revved way high to just get moving. So maintaining a decent low end torque curve would be a good objective. Whatever mods you do, make sure it does not sacrifice too much of what is called DCR - dynamic compression ratio. A DCR in the low 8's or high 7's will keep torque up but still allow you to run pump premium up your way. Discussing/computing the DCR for various piston, combustion chamber, and cam choices as you go along can be part of this thread.

With the lower compression ratios that came in the '73 340, then pistons should be on the list to select to get the DCR (and static CR, or SCR).

Then head breathing capacity to get to the 450 HP mark. Look at the below linked site for some head flow info; you will be targeting something a bit more than the unmodified port flows of Edelbrock RPM Performer LA heads. There are a few ways to get to these numbers. #1---Head Flow Charts & Comparisons

Then cam selection will need to match that and allow the head flow to work for that HP level. If you want to keep a broader torque curve (for street use), then getting a cam with a high lift to duration ratio will help, and not going wild on duration. Roller cams also allow better lift to duration ratios, as does using 1.6:1 ratio rockers.

Then an intake, carb and headers to match; those selections are fairly easy.

Your budget is realistic IMHO.

And just know that a normally aspirated, carbed small block will not have the same broad torque curve of that FI 6.4L SRT engine. There are some major differences in fuel delivery and air delivery between the 2 engine types that result in some big differences in behavior. So it won't be exactly the same. But it WILL be fun!
 
Richard McLaughlin said:
650 holly, not sure on I take.
Click to expand...
Your intake is a factory cast. I'd want a 750 dp Holley. Sell the 650. Looks like it's a 650 spreadbore. To match the square bore carb, I'd get a square bore aluminum intake. The Edelbrock RPM is a good one, but not the only one that would work.
 
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First I'll address the stroker issue. Stroker's really don't make much HP over non-strokers. Stroke = torque. When you stroke an engine. It helps it make more torque, maybe a tad more HP. The biggest benefit to a stroker is that you move the entire power band down, which is a function of the new torque. So while a 340 and a 416 might both make 450 horse. The 416 will make it lower in the RPM range, and with more torque. While the 340 will make it higher up and with less torque in the bottom end. Strokers emulate big blocks. Because of this, the stroker is also an easier street engine. It will make power where you are more often (under 4k rpm), and you won't have to crazy cam it to make it run. Eliminating vacuum problems, high idle problems, gearing, etc etc. That come with a big cam small block.

Now, for a 450 horse 340, it's really not that difficult. I run a (aprox) 420 horse 340. And it's a seriously simple build.

340 - .040 over bore
Keith black 243 pistons
10.05:1 SCR (static compression ratio) - 7.45 DCR (dynamic compression ratio)
J heads, opened to 2.02 int valves, light bowl/turn work
RPM Air gap
Holley 670 Street avenger (soon to be FItech EFI)
Comp XE274H cam
Rev-n-ator ignition
Hooker 1-5/8 headers, into 3" exhaust with dynomax bullets

Nothing special at all. When it was built the builder rated it 400 horse with the 340 hi-performance exhaust manifolds. It had a 2-1/4" exhaust on it. I figure headers and 3" exhaust gotta be worth 20 horse. This is enough to motivate my 3400lb scamp into the mid 12's. This winter I will be doing the following.

Full port work - looking to get 260cfm
Solid roller cam - probably in the high 230/low 240's - around .575-600 lift
1.6 hughes rockers
Increase DCR to 8:1 maybe a little higher (my elevation is 3000ft).

With that, I am aiming for 475 horse. If I saw 500 I'd be excited. Building a high horsepower small block is not a HUGE undertaking. But it takes time. The most important thing is to sit down, figure a plan out. Then go for it. The components must match (as others have mentioned).

I'll also say this. Figure out what your car can do right now. Have you raced it? Do you know how fast it is? Why do you want more power right after you got it? Is it not powerful enough now? Why aim for the same power as a 6.4l srt? What car is the 6.4 in that you want to be as quick as? Remember, A bodies are very light (low 3,000 pound). 420 horse in my scamp has absolutely made my friends **** their pants on several occasions. Figure out your car, before you change your car. You don't even know your rear gear ratio. If you suddenly drop a 450 horse 340 and it's got highway gears? That's the best way to make a turd. Figure out what is in your engine. Heck, for all we know a cam change and a little head work might make 450 horse. Or maybe it already makes 450 horse, and you just don't see it cause it's got a junk converter.

Learn your car inside and out. THEN you can know where to focus to make the changes you want.
 
nm9stheham said:
A discussion of how to get there and meet the 450 HP goal will follow (I am sure), and will involve pistons, heads, combustion chambers, etc. I know you may just want a list of parts; you might get that. But this is one thought process laid out if you want to understand how you are getting there.

If it's 99% street, then you will be happier (I am fairly sure) with an engine that does not need to be revved way high to just get moving. So maintaining a decent low end torque curve would be a good objective. Whatever mods you do, make sure it does not sacrifice too much of what is called DCR - dynamic compression ratio. A DCR in the low 8's or high 7's will keep torque up but still allow you to run pump premium up your way. Discussing/computing the DCR for various piston, combustion chamber, and cam choices as you go along can be part of this thread.

With the lower compression ratios that came in the '73 340, then pistons should be on the list to select to get the DCR (and static CR, or SCR).

Then head breathing capacity to get to the 450 HP mark. Look at the below linked site for some head flow info; you will be targeting something a bit more than the unmodified port flows of Edelbrock RPM Performer LA heads. There are a few ways to get to these numbers. #1---Head Flow Charts & Comparisons

Then cam selection will need to match that and allow the head flow to work for that HP level. If you want to keep a broader torque curve (for street use), then getting a cam with a high lift to duration ratio will help, and not going wild on duration. Roller cams also allow better lift to duration ratios, as does using 1.6:1 ratio rockers.

Then an intake, carb and headers to match; those selections are fairly easy.

Your budget is realistic IMHO.

And just know that a normally aspirated, carbed small block will not have the same broad torque curve of that FI 6.4L SRT engine. There are some major differences in fuel delivery and air delivery between the 2 engine types that result in some big differences in behavior. So it won't be exactly the same. But it WILL be fun!
Click to expand...


His goal isn't 450 HP. His goal is low 12s in a street friendly, pump gas combo.
 
Lustle said:
First I'll address the stroker issue. Stroker's really don't make much HP over non-strokers. Stroke = torque. When you stroke an engine. It helps it make more torque, maybe a tad more HP. The biggest benefit to a stroker is that you move the entire power band down, which is a function of the new torque. So while a 340 and a 416 might both make 450 horse. The 416 will make it lower in the RPM range, and with more torque. While the 340 will make it higher up and with less torque in the bottom end. Strokers emulate big blocks. Because of this, the stroker is also an easier street engine. It will make power where you are more often (under 4k rpm), and you won't have to crazy cam it to make it run. Eliminating vacuum problems, high idle problems, gearing, etc etc. That come with a big cam small block.

Now, for a 450 horse 340, it's really not that difficult. I run a (aprox) 420 horse 340. And it's a seriously simple build.

340 - .040 over bore
Keith black 243 pistons
10.05:1 SCR (static compression ratio) - 7.45 DCR (dynamic compression ratio)
J heads, opened to 2.02 int valves, light bowl/turn work
RPM Air gap
Holley 670 Street avenger (soon to be FItech EFI)
Comp XE274H cam
Rev-n-ator ignition
Hooker 1-5/8 headers, into 3" exhaust with dynomax bullets

Nothing special at all. When it was built the builder rated it 400 horse with the 340 hi-performance exhaust manifolds. It had a 2-1/4" exhaust on it. I figure headers and 3" exhaust gotta be worth 20 horse. This is enough to motivate my 3400lb scamp into the mid 12's. This winter I will be doing the following.

Full port work - looking to get 260cfm
Solid roller cam - probably in the high 230/low 240's - around .575-600 lift
1.6 hughes rockers
Increase DCR to 8:1 maybe a little higher (my elevation is 3000ft).

With that, I am aiming for 475 horse. If I saw 500 I'd be excited. Building a high horsepower small block is not a HUGE undertaking. But it takes time. The most important thing is to sit down, figure a plan out. Then go for it. The components must match (as others have mentioned).

I'll also say this. Figure out what your car can do right now. Have you raced it? Do you know how fast it is? Why do you want more power right after you got it? Is it not powerful enough now? Why aim for the same power as a 6.4l srt? What car is the 6.4 in that you want to be as quick as? Remember, A bodies are very light (low 3,000 pound). 420 horse in my scamp has absolutely made my friends **** their pants on several occasions. Figure out your car, before you change your car. You don't even know your rear gear ratio. If you suddenly drop a 450 horse 340 and it's got highway gears? That's the best way to make a turd. Figure out what is in your engine. Heck, for all we know a cam change and a little head work might make 450 horse. Or maybe it already makes 450 horse, and you just don't see it cause it's got a junk converter.

Learn your car inside and out. THEN you can know where to focus to make the changes you want.
Click to expand...
Thank you very much!!
 
I really like the idea of the stroker moving the power band lower in the rpm range making it more street able. Makes sense to me anyway, maybe others have different opionions on it.
 
You could get mid to low 12's another way.... :D 2500 dollars would buy you a 360 mag and get your EQ heads, custom cam, intake blah blah blah = 400 hp and more low end torque..... have a roller cam for todays oils, sell the 340 for 1200 and you'd get your goals for +1300.
:lol:
 
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