Hi,

Newbie from Sweden here.

I drive a Plymouth Barracuda, Cuda 340 -72. This winter I did a major overhaul on my engine.

I have some concerns though regarding my new built engine; it is not at all as powerful as expected.

Here is the recipe:

340” + 0.030, honed and decked. Stock (forged) crank and stock rods. New KB Hyper pistons (CR ~ 10:1). Summit damper. All balanced.

Comp cam 1,5:1 roller rockers. Edelbrock Performance RPM camshaft. Edelbrock Performer RPM heads (63cc). Edelbrock performer RPM Air-Gap intake. Carburator – Edelbrock 600 performer. KN air filter.

MSD 6AL ignition. Pro billet distributor (no vacuum). Initial timing 12 degrees.

Hooker Super Comp headers (1 ¾”) connected to a double 2,5” exhaust system.

Transmission: 727 with a 2500 rpm converter.

The car runs great above 3000rpm but under 2500 rpm it is too slow/weak. Even with the 2500 stall converter it won’t spin the tires (8 3/4" 3,42:1). The idle is poor. It idles at 1000-1100rpm in park but when I shift to D the idle drops to 700rpm and it starts to idle poor.

Could I have done something wrong when I installed my new parts?

Wrong combination? Adjust the ignition/carburator? Change converter to higher stall? Advance/retard the camshaft?


Thanks in advance.


Kristoffer  

The 340 is a great motor it just isn't a torque monster.  When you removed the factory vac. advance dist. you basically gave the engine a handicap. The Non Vac. advance unit is ment for one thing, Drag RAcing a quarter mile at a time. Before doing anything reinstall the factory vac. advance unit. it will give you improved drivabilty by giving the engine an extra 10+ degrees of timing under normal driving conditions. Plus you will pick up about 5-8 miles per gallon with this increased timing. If you are still not fully satisfied with the performance then call Dynamic converter, They will be able to advise how much stall you need, likely 3500 to 3800. This will certainly wake up your sleepy small block.
I just installed a 4000 stall dynamic in my 360 b-body and picked up 4 tenths.
Also when you go this route you should consider upping the carb to a 700 double pumper holley. A 600 is way to small for the combo in your engine, plus a stock 340 came with more than a 600.  

Thanks for your inputs.

Even though the Non vac will give me a handicap in drivability it should work well in a quarter mile as you say, but my car can't even perfome a burnout... It runs ok during normal driving.

Do you think that I need as much as 3500-3800 rpm stall? Sounds alot to me, but I have very little experience.

I had a Holley 700 DP and the result was the same in the low end. Maybe it run better at higher rpm's with the Holley, but my concern now is the off the line performance. I had to swap the Holley cause of the problems I had when the engine was hot, it wouldn't idle at all...

BR
Kristoffer  

A taller gear will will wake it up. You probably have a 8-3/4 rear with the stock gear. You can put a 3:91 gear in it and wake it up but it will drink gas like crazy because you will be turning 3000 rpm at 60MPH. I would up the carb to a 750 with the combo you have its probably starving for fuel.The down side about E bodies is they are pretty heavy I have a challenger with a 360 built similar to yours and it runs 14s in the 1/4 with a 3:91 gear and 2500 stall im thinking about going with a Hughes 3500.  

Did you degree the cam 4*adv , or straight up?
You need to raise the initial timing to around 22*-26*  Or basically the most timing your starter can turn over [fully warmed up].
Then your gonna have to limit the mech advance to like 32*-34* total at 1800-2200 RPM
I have a 340 with those pistons, heads that flow the same/better similar cam and such and thats what I had to do and RECOMMEND you'll be able to lower the throttle blade position and correct it in relation to the idle orifice/transfer slot which will better you idle quality, improve response ect.  

BTW Vacuum advance is for gas mileage.

In order to limit the advance I ground down a small nut to just a lil bigger than the largest bushing that comes with the distributor then flattend the sides so that it would fit and not spin in the slot, causing inconsistent timing, then trial and error testing to get the need mech advance.  

You can't even do a burn out because you have to little timing at part throttle, thats right, the vac. advance unit works in all but full throttle operations. I suggested the 700 d.p. if you were to up the stall converter. You will need all of the 3500 stall speed I suggested, possibly more.
Someone suggested a set of gears, good idea, I just am not sure how far you wanted to take this from a street driven car.
My street driven 67 b-body Satellite weighs 3600 lbs and has a low comp 360, it runs 12.60's all day, and yes it has the factory electronic vaccum advance dist.  

Timing is everything, setting a car up with 22-26 degrees initial timing is asking for nothing but starter troubles down the road.
There seems to be a group of back yard mechanics that think the factory had zero clue when building cars. No doubt the Vac. unit helps with gas mileage, it helps with driveability, that goes hand in hand. This is why it is needed on a street driven car.
Initial timing simple, 12 degrees with vac. advance disconnected.
Total timing 34-36 degrees at 3000 rpm, vac. advance disconnected.
After setting your timing install the vac. advance line, now you can set up the carb, and not before the timing is set properly.
You will think you have a new car once this is done.  

I blame most of it on the cam shaft. the Eddy cams are not that good, there are much better cams out there. For your set-up, I would use a Comp 228. You will see BIG gains in power all thru the rpm band.

Everyone I know that has used a Eddy cam ended up changing it for the same problems your having. The suck.  

There were two edelbrock cams for the 340 motors. Neither one will give the problems your having.
The first one is basically a stock cam and performs from idle to 5500 rpm and the second one is a dual pattern cam rated at 1500-6500 rpm. The dual pattern cam tend to be for high compression engines, which you have. Their main flaw is a slight drop in power in the 4000-5000 rpm range, which you do not appear to be having so I highly doubt the cam is the problem.  

Thank you for the valuable inputs.

I installed the cm straight up.
Initial timing around 22-26 sounds alot! But I was reading the same on another forum so you are probably right. I will try your recommendations as soon as I got the time and post the result here.

What carburator are you running?  

3404spdvaliant.:
Did you degree the cam 4*adv , or straight up?
You need to raise the initial timing to around 22*-26*  Or basically the most timing your starter can turn over [fully warmed up].
Then your gonna have to limit the mech advance to like 32*-34* total at 1800-2200 RPM
I have a 340 with those pistons, heads that flow the same/better similar cam and such and thats what I had to do and RECOMMEND you'll be able to lower the throttle blade position and correct it in relation to the idle orifice/transfer slot which will better you idle quality, improve response ect.  

BTW Vacuum advance is for gas mileage.

In order to limit the advance I ground down a small nut to just a lil bigger than the largest bushing that comes with the distributor then flattend the sides so that it would fit and not spin in the slot, causing inconsistent timing, then trial and error testing to get the need mech advance.

Thank you for the valuable inputs.

I installed the cm straight up.
Initial timing around 22-26 sounds alot! But I was reading the same on another forum so you are probably right. I will try your recommendations as soon as I got the time and post the result here.

What carburator are you running?  

67dodge:
I blame most of it on the cam shaft. the Eddy cams are not that good, there are much better cams out there. For your set-up, I would use a Comp 228. You will see BIG gains in power all thru the rpm band.

Everyone I know that has used a Eddy cam ended up changing it for the same problems your having. The suck.


I hope that I will be able to solve my problems without changing the cam.
I talked to a guy here in Sweden that drives a 340 with the same setup as I have and his experience is the same as your and he recommends me to change the cam.  

drmopar:
You can't even do a burn out because you have to little timing at part throttle, thats right, the vac. advance unit works in all but full throttle operations. I suggested the 700 d.p. if you were to up the stall converter. You will need all of the 3500 stall speed I suggested, possibly more.
Someone suggested a set of gears, good idea, I just am not sure how far you wanted to take this from a street driven car.
My street driven 67 b-body Satellite weighs 3600 lbs and has a low comp 360, it runs 12.60's all day, and yes it has the factory electronic vaccum advance dist.

At first I used a Holley 700 DP but it wouldn't idle at all when hot. From a performance point of view there was no difference compared to now, that I could feel...
3500 stall or even more sounds alot on a street driven car? I have no experience of high stall converters so please fill in.
3,91 gear is a bit tough. I like to be able to drive my car more than just up and down the strip...

Would be intereting to know more about your setup.  

Check under readers rides, you will see my 67 satellite under most commented. A complete discription of my car is there for all to see if interested. It is the White with Black roof and scoop.
Some pictures of the car in action as well, along with a history of wins.
There was a time when driving a high stall converter on the street was not a good idea, however the new Dynamic 9 1/2 units are so tight until you throttle it you would think your driving with a stock converter.
Let me know how you make out.  

Hey Dr,

You just triggered a question I'm interested in knowing the reasons behind technically.  I recently wondered why a distributor has both vacuum advance and mechanical advance in it.  I had the 440 cuda I have posted a number of times about and had blocked off the vacuum and set timing to 12 adv at idle and checked it at high rpm (saturated advance) and found about 36 deg advance.  I never connected up the vacuum since it appeared that I had mechanical advance and having vacuum at the same time did not seem to add any value.  Ok, so what value would it add and why is there both mechanical and vacuum advance?  I've not found this described or written about anywhere and it certainly is a mystery to me (and a buddy with a 70 340 challenger with the same disty setup).  Does not seem to make sense.  Now mine is pretty hard to start after a weekend of no use...any connection to keeping the disty blocked off?