73 Challenger 340 AT doesn't seem to have the power I think it should

[moparleo]

Never, ever, ever, ever assume anything especially when automotive related. When you buy an unknown, before you start to change or adjust things, you need to verify and know what exactly you are working with. Some red flags are "looks to be 10.2:1 compression " Is the what has been measured , shown with a receipt or a guess ? Aluminum heads with a stock spread bore intake, with a square based carb& base adapter.
original, stock ignition. Should have been at least a higher performance ignition to fire the plugs an a high compression engine and a performance curve. A matched intake and carb setup for the aluminum performance heads. You didn't say what type of exhaust. A good quality set of headers, exhaust system. The engine package has to work together. Not unlike cooking a recipe without all of the proper ingredients. Looks like a rebuilt long block completed with stock parts. Not even close to a proper performance build. The guy builds race cars ? Who does his tuning. Who assembled this motor him? How do you know what parts were actually used ? His word? Receipts ? Photos during the build ? Like said earlier, need to verify the cam specs, preferably with the paperwork that came with the cam. Degree the cam, this will also allow you to verify that a new timing gear/chain were installed. You can never ,ever, assume/trust what you haven't seen for your self. Verify compression. The more information that you have, the better the decisions that you will make when choosing other parts to enhance performance of your package. Looks to be only half way done. I would put it on a stand and do a teardown to see what I have and go from there. JMO Get a degree wheel, accurate torque wrench, dial indicator, vacuum gauge, good quality basic tool wrench/socket set. A clean place to work where you can cover and store your work. Patience, a service manual and a good friend to help and motivate you. Hopefully with some experience with automotive tools and prior repair experience.

 

[Sparkey]

Never, ever, ever, ever assume anything especially when automotive related. When you buy an unknown, before you start to change or adjust things, you need to verify and know what exactly you are working with. Some red flags are "looks to be 10.2:1 compression " Is the what has been measured , shown with a receipt or a guess ? Aluminum heads with a stock spread bore intake, with a square based carb& base adapter.
original, stock ignition. Should have been at least a higher performance ignition to fire the plugs an a high compression engine and a performance curve. A matched intake and carb setup for the aluminum performance heads. You didn't say what type of exhaust. A good quality set of headers, exhaust system. The engine package has to work together. Not unlike cooking a recipe without all of the proper ingredients. Looks like a rebuilt long block completed with stock parts. Not even close to a proper performance build. The guy builds race cars ? Who does his tuning. Who assembled this motor him? How do you know what parts were actually used ? His word? Receipts ? Photos during the build ? Like said earlier, need to verify the cam specs, preferably with the paperwork that came with the cam. Degree the cam, this will also allow you to verify that a new timing gear/chain were installed. You can never ,ever, assume/trust what you haven't seen for your self. Verify compression. The more information that you have, the better the decisions that you will make when choosing other parts to enhance performance of your package. Looks to be only half way done. I would put it on a stand and do a teardown to see what I have and go from there. JMO Get a degree wheel, accurate torque wrench, dial indicator, vacuum gauge, good quality basic tool wrench/socket set. A clean place to work where you can cover and store your work. Patience, a service manual and a good friend to help and motivate you. Hopefully with some experience with automotive tools and prior repair experience.

I do have receipts for all the parts he installed. I only said "looks to be 10.2:1 compression" because that is what the Silv-o-lite web site said but I thought that the block & or heads might change that number.
He changed to aluminum heads only because one of the oem heads was cracked. So his performance build was basically a cam with the lift & duration listed in my original post (from the manufacturer). He did install a new double roller timing chain & gear set & timing case cover. Also rings, bearings, oil pump, oil pan, lifters, vacuum canister & 12pt head stud kit. There is also more but these are the big items when I scanned thru the stack of receipts.
The exhaust is stock exhaust manifolds with 2 1/4" pipes that went straight back to the rear mufflers but it was way to loud for my liking so I added straight thru glass packs in front of the rear axle. It is still louder than I like.
I am just looking for a driver car. I don't plan on doing any racing. I just think this doesn't go as well as I remember my other E body did 45 years ago. Maybe it is just my memory.

 

[Mastertech]

Hi, just a few comments on this thread. I had a 72 Challenger early production with a forged crank and rods which was my daily driver for 10 years. 8.5 to 1 compression with the 1.88 intakes. As a tune up professional for 40 years I have set up many of these over the years. Step one is set your initial timing to 10 degrees before TDC. Mopar used to sell a quick advance curve kit that would give you full advance by about 2800 to 3000 rpm. The stock springs are a light one and a very heavy one. The light ones often break and then the weights are partly swung out so that when you think your setting the initial timing properly you actually have it retarded. Second is to restore the heart of your 340 by putting back the Thermoquad. It is matched to your factory intake and will work better than any other carb.
Setting it up is not really very difficult and the jetting, metering rods and power piston spring are fine for your application. Three things on the TQ that are important.
First step is always to set the choke lever hole to the correct height from the bottom the base plate. This must be right as it affects the secondary air valve opening and this where most guys go wrong. Next is to set the air valve spring. The factory setting is to light and this causes a bog. The special little wrench for the lock ring is no longer available but it can be done with two screw drivers, a small one for the spring adjustment and a larger one for th outer lock ring. Adjust the valve so that when you tap it with your finger it opens and then closes with a bit of a snap, usually about 12 to 3/4 turn from just closing. Last you need to set the metering rod height. Back in the begining of the emission era Detroit thought all smog was caused by Hydrocarbons so they leaned everything to the point that they barely ran and ended up with lean misfires and incomplete combustion actually resulting in higher HC and Nox both. It took them untill the mid 80's before they figured that one out.

On the top of the power piston there is a small set screw. Block your throttle at 2100 rpm and then turn the screw in (clockwise) a little bit at a time.As you do you should here the engine increase in speed. Keep turning untill ther is no more increase then back it off a little bit. This will give you a seat of the pants setting. I actually set this by using my gas analyzer and adjusting untill get about 1 to 1.5 % HC with the PCV out. Finally adjust your idle mixture screws by turning them in one at a time untill you get a lean misfire and then back them out 1/2 turn. Re insert the PCV valve,wait a couple of minutes and set your idle speed to about 700 to 750 rpm.

The last performance step is to have a transmission shop set the line pressure in transmission to 75 psi. No need for a shift kit. Also set your transmission kickdown so that you have about 1/16 inch clearance or freeplay in the linkage when the throttle is wide open. Also as a last thought check to make sure you are actually getting wide open throttle, if not the cable can be adjusted on the bracket untill you do.
Last step try not to crack your face grinning when those big 2 1/4 inch secondaries roar and tires break loose when you put your foot into it and then again when it upshifts from first to second. Have fun!

 

[halifaxhop]

Post the tag number on the distributor, and also check that the mechanical and vac advance is working. To check the mechanical just take the cap off and make sure the rotor can turn a bit somewhat freely a bit, they seize pretty easy if they have not been oiled over the years. Makes a world of difference also the curve should be different than stock as noted before.

 

[Sparkey]

Post the tag number on the distributor, and also check that the mechanical and vac advance is working. To check the mechanical just take the cap off and make sure the rotor can turn a bit somewhat freely a bit, they seize pretty easy if they have not been oiled over the years. Makes a world of difference also the curve should be different than stock as noted before.

The tag number is: 37 2
3656771
The rotor does turn pretty freely and when I plugged the vacuum advance hose back on the carb the rpm's picked up so I think that means the vacuum advance is working.
When you say the curve should be different than stock does that mean timing degrees?

 

[halifaxhop]

Here is what you have 73 MT/AT Mech at the crank 17-27 @ 2000 rpm, vac @ 12.5 at the crank 14-20. Set it at factory should be close to what you want.

 

[halifaxhop]

The tag number is: 37 2
3656771
The rotor does turn pretty freely and when I plugged the vacuum advance hose back on the carb the rpm's picked up so I think that means the vacuum advance is working.
When you say the curve should be different than stock does that mean timing degrees?

View attachment 52685

You have a cam so it changes things. That one should be pretty close if everything is working. Did you put a timing light on it with the vacuum advance hose off and did the timing advance to the factory specs at the Rpms?

 

[Sparkey]

You have a cam so it changes things. That one should be pretty close if everything is working. Did you put a timing light on it with the vacuum advance hose off and did the timing advance to the factory specs at the Rpms?

Yes I did put the timing light on it with the vacuum hose disconnected. It was set at approximately 12 degrees when I got it & I tried going up to approximately 15 degrees as recommended by one member. That seemed worse than the 12 or so. I set it back to 12 for the time being as I couldn't remember the other recommended settings at that time.
I don't know how to check the advance beyond idle as I can't see the timing mark much beyond 12 degrees or so because it disappears behind the water pump.

 

[halifaxhop]

Hate to say thisyou might want to get a timing tape for the balance to see exactly what it is doing. It should be close to the numbers I posted.

 

[Sparkey]

I will try to find a tape for a small block & check all 3 of the numbers. I looked yesterday & could only find tapes for big blocks.