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Old 06-17-2013, 12:47 PM
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New 383 Build having issues

Ok I had issues with my old 383 so I tore it down and rebuilt. I put Dart heads 2.02 1.60 180 cc 64cc aluminum. Put new cam shaft in Comp cams extreme 274, 110 degrees lobe separation, .49 lift, 230 duration @.050 lift, lobe lift .327. Carb was speed demon 750 and changed out for street avenger 770. Set timing to 14-30. Idles at 1000 rpm in gear drops to about 700 rpm. This seems to work decent for Arizona in the summer. It is hot here I try to drive in morning or at night when not blazing hot.

My issues are as follows:

Truck idles ok at stop light but after a minute rpm drop to 500 and engine will knock

Truck is flat off the line....not tire roasting power but on freeway it is a rocket.

I have a few basic questions

What the F with the idle dropping and knocking at stop lights?

I do NOT have a torque converter for T400 transmission do I need it and how ill it help?

Is the Cam to loong to make tire ripping power off the line?

Any help will be appreciated. I am a NOVICE builder please keep it simple if you can. Engine sits inside of a 1973 C10 weight aprrox 3500 lbs. Thanks again

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Old 06-17-2013, 02:12 PM
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went from a bad carb to worse?

no idea if the tires should thread,,,,? what is the engine in? what does the car weigh?what is the stock stall speed you are using? what is the rear gear ratio? what intake and exhaust etc.tell more about your static and total timing
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Old 06-17-2013, 02:28 PM
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73 c10

It is a chevy pick up. 1973 C10. Listed weight is 3500 lbs. Rear gears are 3.73. 1 5/8" headers dump into 3" H pipe exhaust. Intake on heads is 180cc exhaust is 64cc. No torque converter is installed right now.
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Old 06-17-2013, 02:29 PM
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The OP will need a stall converter with that cam in that truck..Having a stall converter allows the engine to idle a bit higher getting rid of that knock as the one you have is lugging the engine at the stoplight..a looser converter will give you a better launch as well..

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Old 06-17-2013, 02:38 PM
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I doubt the truck weighs 3500 pounds? you need to post the tune up specs you are using,,,in great detail,IE; initial spark,total advance and when its all in,,,
jet sizes,power valve number, intake manifold,
actual stall speed of the converter thats now in the truck?
Is the truck being used as a truck? or car?
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Old 06-17-2013, 02:43 PM
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Quote:
Originally Posted by RUFF 73 C10 View Post
Set timing to 14-30.
Are you saying 14 at the crank and 30 total initial and mechanical?

Quote:
Originally Posted by RUFF 73 C10 View Post
Truck idles ok at stop light but after a minute rpm drop to 500 and engine will knock
HUH?

Quote:
Originally Posted by RUFF 73 C10 View Post
I do NOT have a torque converter for T400 transmission do I need it and how ill it help?
Most times if you have a rather long cam in the motor, a looser converter will let the motor idle without being tied to the transmission so tightly.

Quote:
Originally Posted by RUFF 73 C10 View Post
Is the Cam to loong to make tire ripping power off the line?
Maybe not. Get the ignition timing sorted out first. Dial in 20 at the crank and 36 total initial and mechanical. You need to make sure though, that the mark on the inertia ring of the damper is valid. Please read this:
http://www.crankshaftcoalition.com/w...op_dead_center
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Old 06-17-2013, 04:00 PM
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Quote:
Originally Posted by RUFF 73 C10 View Post
Ok I had issues with my old 383 so I tore it down and rebuilt. I put Dart heads 2.02 1.60 180 cc 64cc aluminum. Put new cam shaft in Comp cams extreme 274, 110 degrees lobe separation, .49 lift, 230 duration @.050 lift, lobe lift .327. Carb was speed demon 750 and changed out for street avenger 770. Set timing to 14-30. Idles at 1000 rpm in gear drops to about 700 rpm. This seems to work decent for Arizona in the summer. It is hot here I try to drive in morning or at night when not blazing hot.

My issues are as follows:

Truck idles ok at stop light but after a minute rpm drop to 500 and engine will knock

Truck is flat off the line....not tire roasting power but on freeway it is a rocket.

I have a few basic questions

What the F with the idle dropping and knocking at stop lights?

I do NOT have a torque converter for T400 transmission do I need it and how ill it help?

Is the Cam to loong to make tire ripping power off the line?

Any help will be appreciated. I am a NOVICE builder please keep it simple if you can. Engine sits inside of a 1973 C10 weight aprrox 3500 lbs. Thanks again

You say that you do NOT have a torque converter. I think you mean to say that you have a STOCK torque converter. You MUST have a torque converter 2200 + with that cam. This will allow the engine to be up in the power band before it hooks up, and also help with your issue of dropping 300 rpm when you select drive.

I would have thought that you should be able to idle down to 700 or 800 rpm with that cam with correct SCR and tune. What's your static compression ratio ?

Follow what techinspector said with the ignition.

What's wrong with a Holley ?


Duke
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Old 06-17-2013, 04:46 PM
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I have that same cam in my 81 C10, about 3,800 lbs. It is a MANUAL trans though and 3.73 out back, and there is plenty of tire roasting with the cam. Keep in mind this video was made when I had the carb linkage mal-adjusted and the secondaries on the qjet were just barely opening. With all 4 barrels open this motor screams! A 383 should have no trouble off the line. Comp says you need a 2,200 RPM or higher stall converter.

https://www.youtube.com/watch?v=cVUnAddB3tI
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Old 06-18-2013, 08:03 AM
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LS tech I will make sure balancer is correct. You posted a HUH? to one staement. When I am at a stop light the truck will idle at about 7-800 rpm. If it is a long light, the rpm will drop to about 500 rpm and the engine will knock like it is choking. I know Arizona heat isn't the best conditions for a motor but I have no idea why the motor would do that.
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Old 06-18-2013, 08:12 AM
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Quote:
Originally Posted by RUFF 73 C10 View Post
LS tech I will make sure balancer is correct. You posted a HUH? to one staement. When I am at a stop light the truck will idle at about 7-800 rpm. If it is a long light, the rpm will drop to about 500 rpm and the engine will knock like it is choking. I know Arizona heat isn't the best conditions for a motor but I have no idea why the motor would do that.
check your fuel pressure and vacuum before and after this happens.

And you need to get a higher rated stall converter, a 2,500-3,000 stall will HELP A LOT! it'll solve a lot of your idle issues and give you much better power off of a dead stop.

The first thing is fixing your timing though- I would just bump the entinre curve up about 5 degrees and go from there, 19-35 is a pretty safe area for that combo. Also be sure to run the best damn gas you can find until you have everything perfectly tuned, then you may be able to back down to midgrade.
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Old 06-28-2013, 12:33 PM
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Got timing right

Thanks everyone. Got the timing correct, sniffed out a few vacuum leaks, installing Hughes 3,000 stall with stacked plate cooler next week. I will come back again and say thanks when its running.
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