70 BARRACUDA INAUGURAL TEST DRIVE, RUNS ROUGH......**HELP**!

[70 Grand Coupe]

Let me begin with a little back story. I purchase my 70 BH in July/15. It had no interior, just the dash, steering wheel. I did not drive the car except to load and unload it.  It has the original 318, 650 4bbl Holley with NO CHOKE, 904 AT, 8 3/4 rear. I am not sure what the rear gear ratio is yet.........that is one of my questions. I had the car painted and I have about 98% of the interior complete. The car had its bodywork complete in 2008 and sat in the sellers heated shop with (2) other Cudas until I bought her.

The 318 is original to the car. The seller told me he installed a larger cam, aluminum heads, 650 4bbl Holley in 08 when the car was getting the bodywork done. The bottom end was in excellent shape so they didn't touch it. The 904 was rebuilt at that time as well.

Today, I took her for her inaugural drive around the industrial park. Of course with no choke it was a rough start. It idles at about 800rpm at normal operating temp. Once in gear, it idles around 4-500 rpm. I have to feather the accelerator to get her going. The engine bogs down and sputters at 3000rpm at 60mph. 

I installed a new fuel pump and sender unit as well.

Q1: What would you recommend to do 1st?
Q2: How do I determine what size of gears I have in the rear?
Q3: What is a good gear ratio for Hwy driving. I would like to be at 60-70 mph at about 2000 RPM, not 60 MPH @ 3000 RPM.
Q4: There are some rods coming from the transmission to the intake near the base of the intake. What are these for? Mine are not connected to anything but is clamping the accelerator cable.
Q5: Is it possible that the new sending unit is too small in diameter and might be impeding the flow of fuel?

Well that enough questions for now. I appreciate y'alls feedback and advise and would like to thank you in advance.

Darcy

 

[Chryco Psycho]

Tune the carb I have a Holley tuning guide in the archives .
 Make sure the timing is advanced enough .
 3.23 gear ratio will get you close to where you want to be or a better trans like the 833 OD or 518 auto to drop rpm in high gear .
 An accurate tach rpm @ Mph will give you gear ratio or turning the drive shaft x turns to a full rotation of the tires will work too but bith tires have to turn evenly  or allow only one wheel to turn & count the rotations for 2 tire revolutions .
 The rods are the throttle pressure system / kickdown linkage , these have to be connected or the trans is dead real quick , these are conneted to the carb throttle lever & move as the throttle is opened to increase pressure in the trans as more power is going through the trans .
 The tank fuel sender no matter which size will be adequate for a 318

[sassygreen]

q1 new carburetor. q2 Jack up rear end , place car in neutral, spin driveshaft and count how many times the tires turn in comparison to the drive shaft. If the drive shaft spins 3 revolutions to one revolution  of the rear tire = 3.00 to one, or 3.00 If it spins a little over 4 to one turn of tires it will be 4.11 to one or 4.11's.    q3  I like 273 ratio behind an automatic.  60 70mph = 2100, 2300rpm.  q4 passing gear linkage. This determines line pressure for automatic transmissions. Needs to be hooked up correctly or a new transmission will be in your future. q5 not likely Hope this helps.

[70 Grand Coupe]

With your advice I figured out my gear ratio to be 1.34:1., 8 3/4 non sure grip. Sassygreen recommends 2.73:1 and Chryco Psycho suggests a 3.23:1 ratio. Just to confirm the higher the ratio, I will gain in cruising speed, but will loose the get up and go off the line correct?

Just a friendly reminder the car has a moderately modified 318 with 340/360 cam, Edelbrock Performance RPM Heads, RPM Air Gap intake and Thunder 650 cfm carb (new). The 904 TF was rebuilt before I bought the car so I would like to continue using it for now. I am quite impressed with the power the SB is making. Of course, I dream of stroking out the 440 I have on my engine stand, but that will come later.

In the interim, I would like to know the most cost effective way to gain a little cruising speed on the Hwy cuz right now I am at approx 60MPH at 3000rpm.

Q1: is more cost effective to change out gears or transmission as suggested prior?
Q2: If I was to change gears, do I have to change out axles? Any other hidden parts, costs?
Q3: Is it easy or difficult to convert to a sure grip while I am at it?

Thanks.

Darcy

 

[Bullitt-]

Has the CAM been broken in?   

[734406pk]

With your advice I figured out my gear ratio to be 1.34:1., 8 3/4 non sure grip. Sassygreen recommends 2.73:1 and Chryco Psycho suggests a 3.23:1 ratio. Just to confirm the higher the ratio, I will gain in cruising speed, but will loose the get up and go off the line correct?

Just a friendly reminder the car has a moderately modified 318 with 340/360 cam, Edelbrock Performance RPM Heads, RPM Air Gap intake and Thunder 650 cfm carb (new). The 904 TF was rebuilt before I bought the car so I would like to continue using it for now. I am quite impressed with the power the SB is making. Of course, I dream of stroking out the 440 I have on my engine stand, but that will come later.

In the interim, I would like to know the most cost effective way to gain a little cruising speed on the Hwy cuz right now I am at approx 60MPH at 3000rpm.

Q1: is more cost effective to change out gears or transmission as suggested prior?
Q2: If I was to change gears, do I have to change out axles? Any other hidden parts, costs?
Q3: Is it easy or difficult to convert to a sure grip while I am at it?

Thanks.

Darcy

 

It seems you have a 3.91:1 rear axle ratio based on the RPM to MPH ratio. This assumes that your speed and RPM figures are accurate.
-It is more cost effective to change the ring and pinion gears in the rear axle to get where you want to be.
- You do not need to change axle shafts. However, you may want to replace axle bearings and oil seals at this time. (Rear brake condition ??)
- Easy to convert to "Sure Grip"? I guess it depends on what you compare it to... The diff carrier is replaced with a "Sure Grip" type, so all the carrier bearings would be replaced and needing pre load adjustment etc. It isn't difficult., though... You should read up on this before deciding to go this route.