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New project 71 Dart
https://slantsix.org/forum/viewtopic.php?t=44769		 Page 1 of 1
Author:  cody'sduster [ Thu Apr 28, 2011 7:30 am ]
Post subject:  New project 71 Dart
Well my son Cody's duster is on rotisserie and we have decided to go with a stroked 360 :wink:
Just purchased a 71 Dart that is in really good shape but it needs more power.
Someone in the past put Clifford intake and headers on it with a Holley 2 bbl.
I don't know if any internal work has been done or not.
How can I tell?

Just took her out and ran through a 1/4 with stop watch in hand. 19.9 :cry:
It was missing a bit at higher rpm. Kind of a cough and catch again.
Without missing, it probably would not do much better than 19.5.

What needs done? I want 15s.
I want to keep the factory air and have good manifold vacuum.
Is this possible with engine only?
Author:  terrylittlejohn [ Thu Apr 28, 2011 8:22 am ]
Post subject: 
sounds like you have some tuning problems with the carb pump shot and jetting , also total adv timing. cam and compression changes will have to be on your parts list.how long ago was there a tune-up on this engine?
Author:  WagonsRcool [ Thu Apr 28, 2011 11:12 am ]
Post subject: 
A general tune is the first step. I'd also look at weak ignition coil (do a HEI conversion?). Could be tight valve lash, sticking valve, weak valve spring. Also look at your ign timing & advance curve.

If you want to know your eng condition, do a compression test, a leakdown test (both on all cyl) . If you have auto trans see what your converter stall speed is. Pop the valve cover off & look at general sludge condition. Turn the eng over by hand & measure valve lift - compare that to factory specs. You may have to do a teardown to see what shape the head & cam are.

I'll assume you have stock 2.76 differential (highway) gears. You want the A/C (= more weight) AND good idle vacuum. I don't drag race but I think you need what, 200-250 HP , more (higher) rear gear, higher stall converter to make your ET. 19's in the 1/4 sounds like a stock eng, so you need to double your HP. There are threads on this stuff, but for more HP a slant needs bigger valves, more compression, more cam, better (more) induction & exhaust.

It's possible (but speed costs, how fast you want to go?) Some people can get that much power out of a slant with a 4bbl carb while keeping good street driveabilty, but for power AND manners it's hard to beat an EFI setup.
Author:  cody'sduster [ Thu Apr 28, 2011 3:58 pm ]
Post subject: 
An HEI setup is my next step. I do need to add a different stall converter but I want to keep the same gears.
I have another slant sitting in the barn. I think I will do a .30 over and massage the head and have the cam reground. Try to end up with 9.5:1. Then I can put it back together with the Clifford stuff and maybe be where I want to be.
Any other suggestions?
Author:  Reed [ Thu Apr 28, 2011 4:03 pm ]
Post subject: 
Dump the Clifford intake and get an aluminum stock two barrel, figure out what cam you have and make sure it is degreed properly, plot out your timing advance curve and make sure it is optimized for the engine combination.
Author:  terrylittlejohn [ Thu Apr 28, 2011 4:26 pm ]
Post subject: 
if going for increased compression take almost everthing off the block and just clean and true the head.
Author:  cody'sduster [ Fri Apr 29, 2011 6:07 am ]
Post subject: 
"figure out what cam you have and make sure it is degreed properly, plot out your timing advance curve"

Sure sounds easy when you say it fast but I have some learning to do.
Is there not an established advanced curve that I should try to attain?
Author:  Reed [ Fri Apr 29, 2011 7:09 am ]
Post subject: 
Not really. Optimal timing curves will vary depending on your cam profile, how your cam is degreed, the weight of your car, your gearing, your induction setup, your altitude, etc... There is a rough baseline that slants like about 12 BTDC base timing and like to have 32 degrees mechanical advance total, usually all in by 2800-3000 RPM, and then you have to play with the vacuum advance amount and timing of when it advances and how fast.
Author:  cody'sduster [ Fri Apr 29, 2011 8:14 am ]
Post subject: 
Right now i am 15 degrees advanced at 750 rpm idle with or without vacuum line hooked up. Something wrong with vacuum pot?
Author:  Doc [ Fri Apr 29, 2011 9:05 am ]
Post subject: 
That's a "red flag" right there...
If you take a factory distributor, designed to run 0 to 4 degrees initial advance, then add 15 degrees more... the high RPM total advance becomes excessive and the engine will "go flat" on power.

In general, a SL6 likes a lot of initial advance but also likes a limited amount of total advance. (28 to 30 degrees)
Sounds like you will need to limit the amount of mechanical advance and test the vacuum advance "pod" to be sure it is working.
Search and read-up on distributor recurving.
DD
Author:  cody'sduster [ Fri Apr 29, 2011 12:18 pm ]
Post subject: 
Thanks Doc!

Wish I had your slant 6 knowledge. I guess I someday could if I keep learning.
I think this 71 has been converted to electronic ignition by some previous owner. It has the ballast resistor and ecu that looks like new.

I am going to install a gm HEI unit and change plugs and while doing all this I will work on distributor. At the same time I am going to take my spare slant and start making it a performance engine.
Author:  WagonsRcool [ Fri Apr 29, 2011 7:35 pm ]
Post subject: 
You can put some vacuum (handheld vac pump) to the dist advance can to check it for leaks & function. The vac source on the carb is ported, so it shouldn't affect ign timing at idle (0" vac). As you open the throttle then vac should increase (10-15") & affect timing vac advance.
Author:  cody'sduster [ Sat Apr 30, 2011 8:16 am ]
Post subject: 
Ok, here is what I have. 13 initial, 23 @3000 rpm with vacuum hose unhooked and 45 with vacuum.
Is this close to correct?
Author:  terrylittlejohn [ Sun May 01, 2011 1:49 am ]
Post subject: 
with no vac you should be in the 30degs range at 3000rpm(mechanical adv).
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