Author Topic: 340 with no power (Read 7135 times)

SwedeFish · « **on:** August 27, 2008 - 07:24:46 AM »

Hi,

A newbie from Sweden here. I have a Plymouth Barracuda, Cuda 340 -72. This winter I did a major overhaul on my engine and transmission (727).

I have some concerns though regarding my new built engine; it is not at all as powerful as I 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 ��) 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 its got no power. Even with the 2500 stall converter it won�t spin the tires. (3,42? axle) The idle is poor. It idles good at 1000-1100rpm in park but when I shift to D it drops to 700rpm and idles 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

Bullitt- · « **Reply #1 on:** August 27, 2008 - 09:12:02 AM »

Hi Kristoffer Welcome to C-C.Com....Sounds like you have all of the ingredients to make good power. Someone here will surely give you some good pointers. I would look at the carburetor 1st as that is an area that requires a bit of adjustment to get right. Have you measured the vacuum of the motor & used that information to tune your carburetor?

Wade

SwedeFish · « **Reply #2 on:** August 27, 2008 - 09:33:07 AM »

Quote from: bullitt99 on August 27, 2008 - 09:12:02 AM

Hi Kristoffer Welcome to C-C.Com....Sounds like you have all of the ingredients to make good power. Someone here will surely give you some good pointers. I would look at the carburetor 1st as that is an area that requires a bit of adjustment to get right. Have you measured the vacuum of the motor & used that information to tune your carburetor?

Wade

Thank you for the warm welcome and a prompt reply.

I agree with you regarding the ingredients, I had great expectations. I choose to go with a package to eliminate my own guess work (just as the say in the add

).
I haven't measured the vacuum, I have no equipment to do that. Maybe I should get some... I know that I can do better on the tuning of the carburator, I didn't read the instructions good enough the first time

But I doubt that some minor adjustments on the carburator will make my engine much more powerful. At first I ran a Holley 700 DP and it was still lacking power in the lower prm's. I had to swap the Holley cause it didn't work at all when the engine was hot.

BR

Moparal · « **Reply #3 on:** August 27, 2008 - 09:52:47 AM »

2 things I think about.

timing might could use more advance
timing chain , did you centerline the cam?
What springs are in the msd distributer?

Bullitt- · « **Reply #4 on:** August 27, 2008 - 09:58:24 AM »

Low end power is very much effected by carburetion.. I have tinkered with carbs all my life but only till recently was I enlightened as to how they really work. The Elelbrock is not so different from my Thermoquad in that it relies on vacuum, springs & metering rods to supply proper fuel ratios. Your instructions would give you the steps to follow, for a general understanding of carburetion this article explains a lot.

http://www.chevyhiperformance.com/techarticles/83118_carburetor_basics/index.html

SwedeFish · « **Reply #5 on:** August 27, 2008 - 10:16:51 AM »

Quote from: Moparal on August 27, 2008 - 09:52:47 AM

2 things I think about.

timing might could use more advance
timing chain , did you centerline the cam?
What springs are in the msd distributer?

How much more advance would you suggest?
I think I centerlined the cam, I used a degree wheel (is that the proper word for it?) but I had some trouble finding the proper position.
I changed the spring the other day, from factory setting to one heavy silver and one light silver, curve C wich is the middle curve. I use the blue bushing (factory setting, 21 degrees)

SwedeFish · « **Reply #6 on:** August 27, 2008 - 10:25:30 AM »

Quote from: bullitt99 on August 27, 2008 - 09:58:24 AM

Low end power is very much effected by carburetion.. I have tinkered with carbs all my life but only till recently was I enlightened as to how they really work. The Elelbrock is not so different from my Thermoquad in that it relies on vacuum, springs & metering rods to supply proper fuel ratios. Your instructions would give you the steps to follow, for a general understanding of carburetion this article explains a lot.

http://www.chevyhiperformance.com/techarticles/83118_carburetor_basics/index.html

As soon as I get back to my garage I will study my manual carefully

The reason I went with a 600 cfm is that I wanted good low end response, but no luck so far...

Thanks for the link and the comments.

422STROKER · « **Reply #7 on:** August 27, 2008 - 03:30:04 PM »

What kind of initial timing are you running?

Get a vacuum guage less than 10 bucks and will help in tuning the carb.

That is a large drop in rpms to work out. Should be closer to 100 rpms drop.

Tom

71chally416 · « **Reply #8 on:** August 27, 2008 - 03:43:38 PM »

As long as you guys insist on relying on your initial timing figure you will continue to roll the dice as to what your real ignition timing is. For all we know you could have a screwed up mechanical advance mechanism and be running 25 degrees total. 1 degree off can be 10 hp on a small block, so you can imagine what 10 degrees off will do to your power, especially down low.

If the dampner you bought is degreed than ignore the initial figure and just set it at 35/36 degrees total with the vac hose unhooked. If like most you neglected to either buy a degreed dampner or mark it before you installed it, that's about 2 3/8" from zero.

SwedeFish · « **Reply #9 on:** August 27, 2008 - 04:42:04 PM »

Quote from: 72challorange on August 27, 2008 - 03:30:04 PM

What kind of initial timing are you running?

Get a vacuum guage less than 10 bucks and will help in tuning the carb.

That is a large drop in rpms to work out. Should be closer to 100 rpms drop.

Tom

I run 12 degrees initial timing. (approximately, it is a bit hard to read cause the damper is degreed on the opposite side from the pointer...)
Any ideas why I have this large drop in rpm from P to D?

SwedeFish · « **Reply #10 on:** August 27, 2008 - 04:47:01 PM »

Quote from: 71chally416 on August 27, 2008 - 03:43:38 PM

As long as you guys insist on relying on your initial timing figure you will continue to roll the dice as to what your real ignition timing is. For all we know you could have a screwed up mechanical advance mechanism and be running 25 degrees total. 1 degree off can be 10 hp on a small block, so you can imagine what 10 degrees off will do to your power, especially down low.

If the dampner you bought is degreed than ignore the initial figure and just set it at 35/36 degrees total with the vac hose unhooked. If like most you neglected to either buy a degreed dampner or mark it before you installed it, that's about 2 3/8" from zero.

The damper is degreed and I marked it before installation but the tape fell off

. No vacuum, only mechanical advance. I wil try to set it at 35/36 degrees total. That should be close to what I run today.

Thanks

71chally416 · « **Reply #11 on:** August 27, 2008 - 04:54:44 PM »

That's what it sounds like to me is your problem. Lack of advance will just kill your low end.

And just a thought, make sure you're getting full throttle. Get somebody to push the gas pedal to the floor in the car and make sure the carb is fully opening. If you still have the stock throttle bracket you'll find just clamping the cable in it's stock location will not be right...

SwedeFish · « **Reply #12 on:** August 27, 2008 - 05:21:44 PM »

Quote from: 71chally416 on August 27, 2008 - 04:54:44 PM

That's what it sounds like to me is your problem. Lack of advance will just kill your low end.

And just a thought, make sure you're getting full throttle. Get somebody to push the gas pedal to the floor in the car and make sure the carb is fully opening. If you still have the stock throttle bracket you'll find just clamping the cable in it's stock location will not be right...

I have Lokar throttle and kickdown cable and bracket. I will check the WOT again just to make sure.

If I use more advance on the low rpm I assume that I will have to make sure that the total timing doesn't get too high, but stay at 35 degrees? In the MSD kit followed different bushings to stop the advance at different degrees. For example; factory setting is a bushing that allows the timing to advance 21 degrees plus the initial advance. The smallest bushing will give you like 32 degrees plus initial timing. The biggest bushing (smallest advance) is rated 18 degrees plus initial timing. Maybe I should go with the 18 degrees and run more initial timing with a total timing of 35 degrees?

One more thing... My 727 changes gear too early when in D. The cam and intake should rev to 6500 but my tranny change gear at 4500 (approx.). Maybe its got something to do with my other problem?

71chally416 · « **Reply #13 on:** August 27, 2008 - 06:31:04 PM »

You can experiment to see which bushing works best with your combo of parts but make sure you have 35/36* max at 2,500/3,000 rpm with your timing light. If you just set the initial without checking the total, then you are just guessing.

If you have a high reving 340 with good heads and cam and it's short shifting at 4,500 and then falling below that on the shift it will be a slug
much like many bikes that need RPM to run good. 340's don't have a lot of low rpm TQ but theylove RPM and make their HP upstairs. It's a short stroke big bore motor and it should be shifted at 6,000rpm and maybe even higher. That should be determined at the race track with a shifting loop test. I.E. - make a few runs shifting at different RPM's to see where it ET's the best. If it shifts too quick when it's in drive you probably need to adjust your kickdown linkage. It also should be all the way back on the tranny lever @ full throttle. If it still shifts too quick just shift it manually at 6K. I think you'll see a big difference when you keep the motor in it's power band

422STROKER · « **Reply #14 on:** August 27, 2008 - 10:49:41 PM »

I mentioned the initial to help with his idle quality, I saw that he had a MSD dist which can be tailored to achieve both good initial along with proper total.

I figure if he can bump the inital up it will clean up his idle issues, that along with a good tune on the carb.

Tom

Author Topic: 340 with no power (Read 7135 times)

SwedeFish

340 with no power

Bullitt-

Re: 340 with no power

SwedeFish

Re: 340 with no power

Moparal

Re: 340 with no power

Bullitt-

Re: 340 with no power

SwedeFish

Re: 340 with no power

SwedeFish

Re: 340 with no power

422STROKER

Re: 340 with no power

71chally416

Re: 340 with no power

SwedeFish

Re: 340 with no power

SwedeFish

Re: 340 with no power

71chally416

Re: 340 with no power

SwedeFish

Re: 340 with no power

71chally416

Re: 340 with no power

422STROKER

Re: 340 with no power