340 Set Up Help!

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calgee

calgee

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A few questions for you guys. I have a 1970 Dart with a 340 bored .30 over, running a comp cams thumpr 227/241(part CL20-600-4), 800 cfm eddy, 2300-2500 stall , 3.55 gears and 40 series flow masters. I have the timing rolled back to 15 degrees BTD. The car runs strong, gets horrible gas mileage and is super loud and shakes while stopped (it idles great while in park) . The family (including me) want something a little more mellow. Where do I start? The cam to me is fairly rough and when you are at a dead stop the car shakes quite a bit which the wife and kids are tired of. I know I want to change the 40 series flow masters to something more mellow. Any recommendations? The 40's are sooo loud. I want something more of a deep rumble. As far as cam I was thinking of putting a purple cam in but wasn't sure which way to go to get a smoother idle,better MPG and still have response as well as be able to use my converter. Also carb CFM recommendation would be a big help to. I don't want to put it back to stock but maybe a step or two above. Thanks!
 

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650 AVS or a Holley, your choice.
Comp XE262 Hyd. cam
Dynomax turbo mufflers

Now you have a nicer driver that gets decent mileage.
 
What heads and pistons?
Changing the mufflers may do what you are looking for.
Flow masters resonate real bad.
I have not much luck with gas milage with Eddy carbs.
 
rumblefish360 said:
650 AVS or a Holley, your choice.
Comp XE262 Hyd. cam
Dynomax turbo mufflers

Now you have a nicer driver that gets decent mileage.
Click to expand...

I mostly agree with rumblefish but I would use the XE268 if using a compcam.
 
Wow! She's a beauty. I almost hate to see you mess with it as your combo is pretty nice as is, although I do understand where your coming from.

As far as the rear gear and converter, you're fine, even going milder with the engine combo. Matter of fact, it's probably the mild converter that's giving you that roughness at idle that's annoying.

I like Rumble's assessment as far as a nice drivable combo. But, you may get by with the 800 carb for mileage/performance, as long as you keep your right foot out of it. I know, not easy...lol.

Sireland brought up a point about compression? If this is a factory "low comp" 340, you should try and push your initial timing as far as you can...maybe even to the 20/24* range. With a cam like that, it would really help to smooth out the idle in gear.

As far as the exhaust, I'm old...lol. I still prefer stock replacement (Walker) type mufflers. :D

Good luck, and again, nice Dart...:thumleft:
 
initial timing...not total timing...and check the metering rods in the carb to see if they are bouncing up and down while the engine idles....timing first...
 
the carb is a bit on the large side , get the timing up will help a bunch
 
duster360 said:
I mostly agree with rumblefish but I would use the XE268 if using a compcam.
Click to expand...

I did write tha cam first but I figured I would back it down for mileage issues.

I also about wrote that the 800 carb was ridiculously big.

I have gotten better than 20 MPG's with a Carter 625, but the engine was stock enhanced, stock cam for starters.
 
I can't keep up with the "mullions" of new tech cams out there, but it used to be pretty hard to beat a stock 340 cam for all around just plain street/ performance

I know some of the modern grinds are better yet if you figure out which one.

First thing you need to do (unless you have already) is to forget this nonsense of a "thumper." Do you want it to perform, or sound nasty?

So far as loud, what do you have for AFTER the mufflers? tail pipes out the rear? That is mandatory to get the sound in the cab under control
 
Increase the initial timing to 20* and recurve the dizzy so you're at 36* all in on the mechanical. My stock-ish 318 in my challenger runs best at 18* advanced at idle, and it's just a low compression mild cam build. The 340 in my duster with 9.8:1 compression and a Lunati 60404 does best at 20-22* advanced at idle so far.

That may not be enough though, that cam has a ton of duration. I don't understand those thumpr cams. Too much duration and not enough lift. Either way, that's a big cam.

And get rid of the flowmaster 40's. Worst muffler ever. Even flowmaster makes better mufflers than the 40 series. The 40's flow awful and drone like crazy. I'm pretty happy with just the plain old summit turbos on my Duster, I may change them out for something louder, but I might just keep them too.
 
Just tune it up correctly, initial and all in like mentioned first... Then move onto the carb. I can't see why that cam would be that radicle, shaking the car real bad? Sounds to me like it's not running right is all or you got some busted motor mounts.
 
calgee said:
. As far as cam I was thinking of putting a purple cam in but wasn't sure which way to go to get a smoother idle,better MPG and still have response as well as be able to use my converter. Thanks!
Click to expand...


Try rhoades lifters, they will help with all these issues, no matter which cam you use. They will make it idle smoother, more low end and mid range torque and power, better fuel economy.
 
I should clarify the shaking part. It doesn't really shake bad, but lets say its not a smooth idle once in gear. Its not shaking to the point that its unbearable or to the point where its coming apart. My buddy tells me its normal for that size cam. The car right now def wants to move when you hit the gas and I have lost the *** end numerous times from a dead stop at a light getting on her to hard. I can be doing 55-60 mph on the highway and hit the gas and she takes off. Maybe I'm just an old 35 year old and just want a nice quiet ride (what has happened to me?)! I think I would rather have it perform well and be easy to drive than sound nasty. I calculated a few fuel stops ,miles driven, gallons put in, etc and I think I am getting about 10mpg using premium grade. As far as after the mufflers its just straight pipes out the back. I have posted before regarding carb size. I have a 600 cfm Holley and a 600 eddy. I have swapped them both onto the car and could never get it to run right. Is it the cam or overall combo?? The pistons are just forged sealed power , stock x heads with a mild valve job, comp springs. Again appreciate all the help and feed back!
 
The smaller carbs should be easier to tune. Are the smaller carbs used/old/sitting around for a while?

You mention you jus want a quite ride? Then I suggest the Summit mufflers. I did there exhaust kit system on my Duster. Very nice and mello sound. It'll get aomly a little loud when your on it hard. It is louder to the outside spectator than it is in the cars cabin.
 
Yeah the carbs were old. I bought rebuild kits for both of them and did the rebuild which seemed fairly easy. I made sure I cleaned everything out well with carb cleaner and the air compressor. Floats are adjusted as well. I think using the paper gasket was a big part of the problem but I haven't gotten around to trying them out with a thicker gasket. Do you think 600 CFM is to small of a carb? I know the 340 likes a big carb from what I hear.
 
calgee said:
i should clarify the shaking part. It doesn't really shake bad, but lets say its not a smooth idle once in gear. Its not shaking to the point that its unbearable or to the point where its coming apart. My buddy tells me its normal for that size cam. The car right now def wants to move when you hit the gas and i have lost the *** end numerous times from a dead stop at a light getting on her to hard. I can be doing 55-60 mph on the highway and hit the gas and she takes off. Maybe i'm just an old 35 year old and just want a nice quiet ride (what has happened to me?)! I think i would rather have it perform well and be easy to drive than sound nasty. I calculated a few fuel stops ,miles driven, gallons put in, etc and i think i am getting about 10mpg using premium grade. As far as after the mufflers its just straight pipes out the back. I have posted before regarding carb size. I have a 600 cfm holley and a 600 eddy. I have swapped them both onto the car and could never get it to run right. Is it the cam or overall combo?? The pistons are just forged sealed power , stock x heads with a mild valve job, comp springs. Again appreciate all the help and feed back!
Click to expand...

View attachment phpeqizjiAM.jpg
 
CL20-600-4

Basic Operating RPM Range:2,000-5,800
Intake Duration at 050 inch Lift:227
Exhaust Duration at 050 inch Lift:241
Duration at 050 inch Lift:227 int./241 exh.
Advertised Intake Duration:279
Advertised Exhaust Duration:296
Advertised Duration:279 int./296 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.486 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.473 in.
Lobe Separation (degrees):107

With that cam and decent compression I don't see you being able to run a 600 cfm carb. I tried to run a 670 Street Avenger on mine with a Lunati 60404, which has more lift and similar duration at 050, and couldn't even get it to idle below 1,200 rpm- too lean. Went up to a 770 cfm SA and had no issues with idle, although I'm still full rich on the idle screws with the out of the box jets. And that's at almost 22* advanced on the timing at idle, still only pulling about 10mmHG of vacuum around 900 rpm.

That cam is not going to idle smooth either, so you will have some vibration at idle. I know I do. Basically that cam is not for a mellow street cruiser, so if that's what you want you may have to change the cam. Or use the Rhoades lifters to bleed off a little cam at idle.

As I mentioned I have the Summit 2.5" turbos and Summit's 2.5" dual system on my car, its pretty reasonable for volume. I'll probably even go to something louder, but I also have FatMat throughout my entire car to isolate the cabin, and it makes a big difference.

Here's a short video of my Duster with its 340 at idle and some revs, gives you an idea of the Lunati and what the exhaust sounds like...

Here are specs on the Lunati 60404, you can see the similarities...

Basic Operating RPM Range:2,200-6,400
Intake Duration at 050 inch Lift:234
Exhaust Duration at 050 inch Lift:242
Duration at 050 inch Lift:234 int./242 exh.
Advertised Intake Duration:276
Advertised Exhaust Duration:284
Advertised Duration:276 int./284 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.513 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.533 in.
Lobe Separation (degrees):110

[ame]http://youtu.be/C_P8H2aLYPU[/ame]
 
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