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Old 12-14-2012, 02:55 PM
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sbc build

Hey y'all,
I am building a 350 for my rat rod, 1953 3 window chevy pickup, and I have a question on cam selection. I have the short block built. I have had the motor bored .040 over, new crank and .040 speed pro flat top pistons. The heads I have are 906 vortec heads. I had them worked, new springs and the heads cut to allow for .550 lift. valve job and the heads were decked. I am trying to figure out what cam to run. I plan on having a 3.08 rear end and the trans is manual. I want it to sound rough at idle and I want it to run well from at least 2000-6500. I dont have an intake or carb yet. Thanks for the help.
Shaun

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Old 12-14-2012, 03:27 PM
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Old 12-14-2012, 03:30 PM
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static 9.7 by the calculator I am using online! I would like to make good power through the power band. I am not looking to make 500 hp at 7500 rpms and have it cruise like garbage
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Old 12-14-2012, 04:03 PM
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Quote:
Originally Posted by southernculture View Post
Hey y'all,
I am building a 350 for my rat rod, 1953 3 window chevy pickup, and I have a question on cam selection. I have the short block built. I have had the motor bored .040 over, new crank and .040 speed pro flat top pistons. The heads I have are 906 vortec heads. I had them worked, new springs and the heads cut to allow for .550 lift. valve job and the heads were decked. I am trying to figure out what cam to run. I plan on having a 3.08 rear end and the trans is manual. I want it to sound rough at idle and I want it to run well from at least 2000-6500. I dont have an intake or carb yet. Thanks for the help.
Shaun
Shaun, here we go again. You cannot intelligently choose a camshaft for a motor until you know the static compression ratio. We can sort of figure most of the volumes because we've done it so many times, but we have no idea of the piston deck height on your motor. (the distance from the crown of the piston to the block deck where the heads bolt on). If you'll do a little work for us, we can figure it mathematically. Assuming you have a short block and have not bolted the heads on yet, turn the crank so that ANY piston is at the top of its bore. Using a steel rule, turn it on edge and lay it across the bore about a half inch from the edge of the bore on either side of the piston (looking at the piston as a clock face and standing at the side of the block, place the rule at 3 O'Clock or 9 O'Clock to prevent the piston from rocking on its pin and giving you an erroneous reading. Using a pack of feeler gauges, stack gauges together until you fill the gap between the underside of the steel rule and the piston crown. Turn the crank a little clockwise and counter-clockwise to make sure you have the piston at top dead center. Depending on the piston compression height and piston deck height, this could be anywhere from -0.020" (minus twenty thousandths) to about +0.055" (plus fifty five thousandths). Post whatever the figure is. Also, how much was taken off the heads? Each 0.007" (seven thousandths of an inch) cut equals about 1 cc.

Last edited by techinspector1; 12-14-2012 at 04:19 PM.
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Old 12-14-2012, 04:15 PM
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That is a tough order. A cam that idles rough due to a lot of valve duration and valve overlap usually does not allow the engine to produce much cylinder pressure and torque a low RPM and therefore you need a lower rear gear ratio to bring the engine RPM up quicker. The rougher the idle, the worst that condition will be.

Sealed Power CS-113R, solid flat tappet cam will fill that request. It would have a bad (meaning good) idle and produce good low end torque and high end horsepower. Cam range is from 2000 to 5500 RPM.

Sealed power CS-113R solid lifter camshaft specifications:
228 degrees I / 230 degree E valve duration
110 deg. LSA
.395" I / .401" E valve lift with 1.5:1 rocker arms
.421" I / .428" E valve lift with 1.6:1 rocker arms (350 CI engine)
Use with 9.5:1 to 10.0:1 static compression ratio.
Comp Cams 813-16 solid lifters

Last edited by MouseFink; 12-14-2012 at 04:22 PM. Reason: spelling
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Old 12-14-2012, 04:25 PM
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Quote:
Originally Posted by MouseFink View Post
That is a tough order. A cam that idles rough due to a lot of valve duration and valve overlap usually does not allow the engine to produce much cylinder pressure and torque a low RPM and therefore you need a lower rear gear ratio to bring the engine RPM up quicker. The rougher the idle, the worst that condition will be.

Sealed Power CS-113R, solid flat tappet cam will fill that request. It would have a bad (meaning good) idle and produce good low end torque and high end horsepower. Cam range is from 2000 to 5500 RPM.

Sealed power CS-113R solid lifter camshaft specifications:
228 degrees I / 230 degree E valve duration
110 deg. LSA
.395" I / .401" E valve lift with 1.5:1 rocker arms
.421" I / .428" E valve lift with 1.6:1 rocker arms (350 CI engine)
Use with 9.5:1 to 10.0:1 static compression ratio.
Comp Cams 813-16 solid lifters
Ouch! that is a tiny cam. it'll run on garbage springs and last forever but don't expect spectacular power.

The 401A3 will be a better match for your goals, provided you run good springs. I'd advise supplementing the cam oiling somehow too, either grooving or face oiling lifters.
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Old 12-14-2012, 04:27 PM
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sbc build

I have a question for you. What type of gas do you plan on using in this rat rod. I see you have a problem. You are going to use Vortec heads which are 64cc chamber heads. In your short block measure the distance from the top of the block to the top of the piston at TDC. You probably will have .025. This area from the bottom of the head to the top of the piston at TDC is call Quench. The recommended Quench is .040. So if you have .025 you will need a .015 head gasket. This setup will give you around 10.425 compression ratio which is too high for pump gas. If you use a .040 thick head gasket to bring the compression down the engine probably will ping under load. You need to talk to your machinist and motor assembler. The 12cc dish piston should have been recommended for using Vortec heads.
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Old 12-14-2012, 04:44 PM
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Quote:
Originally Posted by cdminter59 View Post
In your short block measure the distance from the top of the block to the top of the piston at TDC. You probably will have .025. This area from the bottom of the head to the top of the piston at TDC is call Quench.
Ummm, not altogether correct. The distance from the crown of the piston to the block deck where the heads bolt on, with the piston at top dead center, is called Piston Deck Height, not to be confused with Block Deck Height, which is the measurement from the centerline of the main bearing bore to the block deck where the heads bolt on.

Quench, also called Squish, is the distance from the piston crown to the underside of the cylinder head WITH THE HEAD GASKET IN PLACE and the piston at TDC. It is the sum of the piston deck height and the gasket thickness.

Quote:
Originally Posted by cdminter59 View Post
The recommended Quench is .040.
Ummm, actually, 0.035" to 0.045" is acceptable to most builders. I believe David Vizard found the limit at around 0.027", where he encountered a piston/head collision. I have no idea what the weight of components was, so that is another variable.

Not trying to give you a hard time CD, just trying to keep the nomenclature correct so that those who are learning from reading these threads will get it correct.
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Old 12-14-2012, 04:46 PM
How fast is fast enough?
 
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Quote:
Originally Posted by cdminter59 View Post
I have a question for you. What type of gas do you plan on using in this rat rod. I see you have a problem. You are going to use Vortec heads which are 64cc chamber heads. In your short block measure the distance from the top of the block to the top of the piston at TDC. You probably will have .025. This area from the bottom of the head to the top of the piston at TDC is call Quench. The recommended Quench is .040. So if you have .025 you will need a .015 head gasket. This setup will give you around 10.425 compression ratio which is too high for pump gas. If you use a .040 thick head gasket to bring the compression down the engine probably will ping under load. You need to talk to your machinist and motor assembler. The 12cc dish piston should have been recommended for using Vortec heads.
It's actually closer to 9.5-9.9:1 with 64cc chambers.

flat top pistons and vortec heads are probably one of the most popular combos in the past 15 years- it'll work just fine.
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Old 12-14-2012, 05:07 PM
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the gap from the top of the piston is .024 to the top of the block. I am the engine assembler. I have not changed the rear gear yet but was planning on a 3.07. The trans I have now is a saginaw 3 speed. I plan on getting a m21. but that is much later. I would rather have rough idle and more power than perfect drive ability it is a rat rod. I am fine with running it higher in rpms, I will be running roller rockers and upgraded pushrods. I dont have a head gasket yet so that gap is still open to arguement, when I did the calculation on the cr it was with a .40 head gasket. I will run pump gas!
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Old 12-14-2012, 05:15 PM
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I am not sure how much was taken off of the heads, by looking at them there is only raw metal on the corner of both of them.
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Old 12-14-2012, 05:22 PM
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btw the springs that were installed were comp, I am not sure of the specs however the heads were machined to allow .550 lift with these springs. New seats cut and new retainers.
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Old 12-14-2012, 05:34 PM
How fast is fast enough?
 
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Quote:
Originally Posted by southernculture View Post
the gap from the top of the piston is .024 to the top of the block. I am the engine assembler. I have not changed the rear gear yet but was planning on a 3.07. The trans I have now is a saginaw 3 speed. I plan on getting a m21. but that is much later. I would rather have rough idle and more power than perfect drive ability it is a rat rod. I am fine with running it higher in rpms, I will be running roller rockers and upgraded pushrods. I dont have a head gasket yet so that gap is still open to arguement, when I did the calculation on the cr it was with a .40 head gasket. I will run pump gas!
DO NOT USE A .040" GASKET! The .015" spec'ed will be the best match for your combo.
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Old 12-14-2012, 05:52 PM
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Use the comp cams small hyd thumpr cam it will sound good and make pretty good power. But not real smooth at idle it will lope pretty good.

They make good power and sound good dont work on all engines but it sounds like you could run the small thumpr without it any issues. Sep for maybe some carb tuning. Alos most dyno resluts put the thumpr above other cams inhp because the thumpr design produces good peak hp number other cams can produce more average hp. Which is better for truck build with 3.08s

You can hear them on youtube alot of people have vids of the sound.
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Old 12-17-2012, 05:03 PM
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I think I am sold on the mother thumper 12-601-4 looks like it will be a good fit spec wise for my motor and I do like the sound at idle! Thanks for the help.
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