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Old 03-31-2013, 09:51 AM
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choosing cam for mild 355?

I was looking for help choosing a cam for a mild 355 motor in a heavy c10 truck, as Its abundntly clean I can't do it haha. Motor is a 355 with a set of 195 runner, 64cc heads, rpm intake, 3.73 gears, 700r4 trans and 2600 summit racing stall. Comp lifters, pushrods and mutha thumpr cam 235/249 @50, double roller timming chain, summit racing 1.5 roller tip rockers, Edelbrock 1406 carb. Motor is a dog down low but comes to life after 2500ish rpm. As it sets now it won't even foot brake a burnout or spin the tires off the line with bald tires. I might add that I truly like the rough sounding idle. Truck primary use is street/strip. But its not oftin that it gets on public roads. Thanks for the help.

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Old 03-31-2013, 10:20 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
You need to recurve the distributor for that cam..
its in the wiki on distributors. That cam is best with a 3500 stall. ( the converter you have is not the right converter.
(these 2600 stall chap converters are junk. All they do is bend the fins inside. Very inefficient)
Get a real high stall lock up converter. 3200-3500stall based on a small 245MM case size.

Will be a whole different truck once the distributor advance curve is properly modified.

24-26deg at idle 34-36degt at max advance (10deg advance curve)
You cannot get the right curve by just swapping adv springs.
Thanks fbird. You always seem to have the answer. With age comes wisdom right? I do have a question on the stall speed. When I contacted comp about the stall they said that the cam I had I needed a 2500rpm stall and 9.0.1 compression. I might be wrong but dosent a factory 86 sbc had close to the compression? I bought the 2600rpm on there recomendation.
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Old 03-31-2013, 10:26 AM
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what times are you turning with the truck now?
Have you weighed the truck?
What fbird said is a very good starting point for your tune.One thing at a time,starting with the timing.What ignition system are you using?
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Old 03-31-2013, 10:37 AM
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I have not run the truck yet. No local tracks within a 100 miles. Need to get to one. I haven't weighed the truck but assume itit's in the 4000 mark. The distribitor is a summit brand hei and taylor wires ac delco plugs.
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Old 03-31-2013, 10:46 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
Stock low perf base engines are 8.5:1 or less.

That cam and any other hyd cam that has 235 deg duration @.050" needs a 3500 stall converter.
The idiot that gave you the converter stall recommendation has obviously never used such a cam.

That cam really wants 10-10.5: cr (92 octane)

Summit does not sell the right converters for h this job. All their Summit th700r4 converters are junk tweeked stock GM converters.
You need a true 9" 10" hi stall. 3000+++stall with lock up ATI , Precision, Yank, etc.

The 600cfm carb is TOO SMALL if you were after horsepower.

Get a 750-800cfm carb. More power.
Fbird, do you recommend changing out the cam to better suit the cr of the motor and the stall I have. Or recurving the distribitor and later changing out the stall. I say later sue to just having a child and not being able to drop 400+ on a quality stall.

I can swing a quality cam at this time.
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Old 03-31-2013, 10:51 AM
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tune what ya got for now.even with not enough converter and carb,the truck should still launch hard.even if you change the cam,you still need to do the proper tune,get it done first.
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Old 03-31-2013, 11:32 AM
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Quote:
Originally Posted by F-BIRD'88 View Post
Fix the distributor, first. it will be a whole different truck ..


if you want a milder cam get one with 218@.050" or less for that truck.
I recomend Isky Cams or Crane Cams.

EG: Isky 264/271 Mega cam #201264-27112
Quote:
Originally Posted by vinniekq2 View Post
tune what ya got for now.even with not enough converter and carb,the truck should still launch hard.even if you change the cam,you still need to do the proper tune,get it done first.
Is it fairly simple to recurve one? I've never done one so its sorta intimidating to me. Do yall have a recomdation on a brand recurve kit?
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Old 03-31-2013, 01:18 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
With that cam and the lame converter I would just lock out the distributor.
read the wiki
I googled for it and read the wiki. Didnt see it, I will reread it. Thank for all the help fbird. Really wish there was local individual here that new how to do a lot of stuff like this. Living in a small down starts to buf me sometimes. .
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Old 03-31-2013, 02:49 PM
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I agree that you can improve the characteristics of the motor with proper spark advance and improve the characteristics of performance of the vehicle with a looser converter, but the fact remains that you have used too much cam timing for the available static compression ratio of the motor and nothing can fix that, short of using less cam or more static compression ratio. Anything else if just a crutch. Please refer to this wiki article to get an idea of what cam should be used with what static compression ratio.....
http://www.crankshaftcoalition.com/w..._compatibility

Don't feel like the Lone Ranger though, the majority of fellows who change cams will use too much cam for the available SCR. It takes a while and a few engine builds to understand that each part you use to build a motor has to compliment all the other parts to make a good COMBINATION. No single part stands alone, they all have to work together toward a final goal.

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Old 03-31-2013, 02:58 PM
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And to think that aid in choosing the right parts has been all along................................Just incredible!!!!.

You taught me awhile ago two things,don't sweat the small stuff and you can only teach the willing.
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Old 03-31-2013, 03:20 PM
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Originally Posted by techinspector1 View Post
I agree that you can improve the characteristics of the motor with proper spark advance and improve the characteristics of performance of the vehicle with a looser converter, but the fact remains that you have used too much cam timing for the available static compression ratio of the motor and nothing can fix that, short of using less cam or more static compression ratio. Anything else if just a crutch. Please refer to this wiki article to get an idea of what cam should be used with what static compression ratio.....
http://www.crankshaftcoalition.com/w..._compatibility

Don't feel like the Lone Ranger though, the majority of fellows who change cams will use too much cam for the available SCR. It takes a while and a few engine builds to understand that each part you use to build a motor has to compliment all the other parts to make a good COMBINATION. No single part stands alone, they all have to work together toward a final goal.
Thanks for the link Tech. I will read it thoroughly and change out the cam down the road.

I did want to ask Fbird a question. While i have your attention. At what RPM do i set the timing? 34-36 deg at idle? 3000 rpm? Im printing off the link you gave me and heading to my shop after typing this. Going to try and get this squared away.
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Old 03-31-2013, 03:43 PM
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FBird is suggesting that you eliminate the centrifugal advance altogether and lock the spark advance in at 34-36 degrees, depending on the combustion chamber design in your heads, so that you put all the advance in at the crank and have 34-36 at idle and all the way through the rpm range. The only other variable would be vacuum advance needed at cruise (light load) to raise total timing to 40-50 (or whatever) total degrees of advance for fuel mileage improvements.

This much ignition timing will cause the motor to fight against the starter when cranking to start, so some means of freeing up the system will have to be used. Down and dirty, cheap and simple is to interrupt the coil wire and install a (normally-on) momentary-off push button switch in the line with the switch mounted in a convenient location in the driver's compartment so you can push the switch while keying the starter. (Normally-on) means there will be an electrical connection through the switch except when the button is pushed to interrupt the current flow to the coil. When you hold the button and stop current to the coil, this will allow the starter to spin the motor free of firing the spark plugs when cranking it over. Once the motor is spinning, let go of the momentary switch to restore current to the coil and fire the plugs and you're off and running. There are electronic devices which will do the same thing, but suffice to say they are not as cheap as a plain old momentary-off push button switch and some 12 gauge wire.

This operation assumes that you have verified TDC at the crank and that you know positively that the mark on your damper is correct.

Last edited by techinspector1; 03-31-2013 at 04:00 PM.
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Old 03-31-2013, 05:28 PM
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Well I locked out the dizzy and stabed it back in after finding tdc and pointing the rotor to number one cylinder. I had to spin the cap has far counter clock wise as it would go to get it to fire and idle. I check it wirh a light and it shows 8 btdc. I guess my question is how do I get it to 34-36 with out anymore adjustment in the dizzy? Do I need to restab the distibutor closer to say 15-20 deg mark to start? It sure starts easy where its at but has a very slow and laggy rev, and will spit through the carb if revreved higher then abiut 3 grand
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Old 03-31-2013, 05:32 PM
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the timing at idle needs to be set at 36
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Old 03-31-2013, 05:33 PM
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I'm sorry I just checked and had the vacuum advance hooked up with trying to time it. After unpluging and capping it I just rechecked and had 2 btdc. I might have not got true tdc after all. That still dosent tell me if there is that much adjustment in the dizzy. I'm at my shop right now, so anything yall recomend I will try while I'm here.
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