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Old 10-11-2013, 12:20 PM
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LS3 Springs on Vortec Heads

Hi, currently building a 406 sbc with 062 vortec heads. The valve guides have not been machined down. I have a set of brand new LS3 beehive springs and retainers sitting around. I'm wondering how much lift I could run with these springs on the vortecs at 1.698-1.708" install height. I believe at 1.800" install height LS3 springs are good to .570" lift. I would think the first cam would be better for my build news, but it has .008" more lift. The two cams I'm looking at are:

Lobe center 108
Advertised Duration: Intake / Exhaust 296 / 308
Duration @ .050" Lift: Intake / Exhaust 232 / 242
Lobe Lift: Intake / Exhaust .333 / .345
Rocker Ratio: Intake / Exhaust 1.5 / 1.5
Gross Valve Lift: Intake / Exhaust .500 / .518

OR:

Lobe center 108
Advertised Duration: Intake / Exhaust 300 / 308
Duration @ .050" Lift: Intake / Exhaust 240 / 248
Lobe Lift: Intake / Exhaust .328 / .340
Rocker Ratio: Intake / Exhaust 1.5 / 1.5
Gross Valve Lift: Intake / Exhaust .492 / .510

Looking to rev the engine to 6000-6500 MAX...

Any help would be appreciated,

Thanks

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Old 10-11-2013, 12:40 PM
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What pistons are you using. Please be specific with part number.
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Old 10-11-2013, 03:12 PM
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Heres the link to the rotating assembly I'm buying.

http://www.summitracing.com/parts/es...0030/overview/

Why can't I use the stock LS3 retainers? I assume there the same thickness as the comp retainers. I measured the LS3 retainer vs the stock vortec retainer and the LS3 are about .100" smaller. Do you recommend the second cam, because it it will make better overall better? I just figured the first would be better for a street car.
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Old 10-11-2013, 04:50 PM
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Quote:
Originally Posted by F-BIRD'88 View Post
Stock LS3 retainers and locks do not fit a gen 1 SBC valve.
The comps do.
Your cr will be very high with flat tops and 64cc heads on a 400SBC.
Better to use a kit that has the -18cc or -22cc D dished 400 piston.

Either cam is fine. the second one will make more power.
If these are both used cams buy new.
You are going to spend more on getting those springs to fit the vortec heads (retainers locks shims seals) than if you just bought the spring seat and guide boss cutter and did the heads correctly.
Yea my static compression is going to be around 11.2:1. I calculated with the second cam my dynamic will be around 8.1:1 so I'll be fine with 91 octane. Both cams are NEW and I guess I could just buy the springs and retainers from comp cams that they recommend for a vortec head to achieve .550" lift. They say no machining required with them I was just trying to see if my LS3 springs would work since I already owned them. Plus I was going to use the LS3 spring,retainer, and VORTEC locks for the SBC valve.
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Old 10-11-2013, 06:48 PM
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400's soak up cam duration like a sponge... when looking at cam spec's, don't be fooled by the catalog's given rpm powerband recommendations - as they are based around the most common SBC size of 350 cubic inches.

The 400/406 cube actual powerband will be 400-500 rpm lower than what it would be in the common 350 sized engine if both have the same cam.

Another reason for you to go with more duration is you have rather small head flow for an engine as big as 406...so you need to crutch it by getting the valve open for a longer period.

I don't like dynamic compression calc's either - there are too many little variables in each specific build than can influence how high a compression ratio you can get away with. The tuning skill of the owner/operator can play a big part also.

But I do agree, your compression ratio with the current list of planned parts is too high for pump gas. Either grind the head chambers to a bigger 68-69cc, or plan to use a dished piston. 10.85-1 is the most I've tried to get away with in a 400 on pump gas... for it to work the timing and carb tune have to be spot on, you have to control underhood heat with things like carb shields and coated headers, and feed the carb cool air from a scoop or cold air ducting.
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Old 10-11-2013, 08:10 PM
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You cannot use LS3 spring retainers and locks because they are designed for 8mm O.D. LS valve stems and SB Chevy valve stems are 11/32" O.D. You must use Comp Cams SB Chevy retainers and locks designed for 11/32" O.D. valve stems that are designed for beehive valve springs. Comp Cams 795 retainers and 613 locks are 10 degree and are a perfect fit on the LS3 beehive valve springs.

The LS3 beehive valve springs coil bind at 1.085". That means if you set up the LS3 valve springs at 1.700 @ 128 lb. seat pressure using SB Chevy valves, the maximum valve lift will be is .555" with a .060" safety margin. You must have at least .600" clearance between the bottom of the SB Chevy retainers and the valve seals with the valves on the seats. Mock up each valve with only a retainer and locks and measure them during the valve job. That will tell you how much material you must machine from the top of the valve guide boss when you machine each boss for the positive stop Viton seals. You must machine each valve guide boss diameter approximately .065" or to .835" O.D. The LS3 valve springs are .845" I.D. The valve guide boss serves as a valve spring register in order to prevent spring oscilation. If you allow beehive valve springs dance around on the seats, you will have broken beehive valve springs just below the retainers.

Last edited by MouseFink; 10-11-2013 at 08:17 PM.
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Old 10-11-2013, 10:49 PM
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Your static compression will be 11.5:1, not 11.2. Please identify the cams by part number so I can figure the DCR myself.
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Old 10-12-2013, 12:48 AM
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Quote:
Originally Posted by techinspector1 View Post
Your static compression will be 11.5:1, not 11.2. Please identify the cams by part number so I can figure the DCR myself.
I think the part number was 00212s or 00211s through crower cams. I was figuring a .050" quench for the 11.2:1. I can only find the eagle kits with -6cc, -7cc, and -30cc pistons. The -30cc pistons would put me way down to around 8.8:1. I some what believe in DCR... my other engine runs 10.8:1 scr with 8.5:1 dcr and runs 91 octane no problems, but that may also be because of my aluminum heads.
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Old 10-12-2013, 08:57 AM
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DCR is not the be all do all & absolute.It is a helpful tool tho to be used in combination with other tools,including common sense, to help determine a combination of parts & help you make good decisions about a certain combination of parts & what their effect may have.It's just 1 tool to be used in conjunction with others.You can't build an engine with just a pair of slipjoint pliers & you can't determine everything just from DCR,but'it can be 1 helpful tool when used along with others.
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Old 10-12-2013, 09:04 AM
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I'm glad I'm not the only one who knows compression and IVC are not everything, not by a LONG shot.
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Old 10-12-2013, 09:33 AM
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There are too many variables to say a certain DCR will or won't work.Use of motor,available fuel,tuners ability,carb or EFI,type of engine mgmt.Some say elevation.I don't put alotta faith in elevation & usually won't even consider it a variable.
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Old 10-12-2013, 10:34 AM
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Personally, I put quite a lot of credence in DCR. It gives you an indication of what the cylinder pressure will be for a given camshaft intake valve closing point and my opinion is that those of you who poo-poo DCR just have not taken the time to get your mind wrapped around the concept.

Gearhead346 has figured it out. The rest of you should be able to figure it out too.

As far as elevation, air density decreases to the tune of about 3% for each 1,000 ft. elevation, so at 5,000 ft., the motor can be down on cylinder pressure by 15%. If you aren't taking this into consideration on your build, then you are not using all the tools available to you and the motor could turn out to be a pooch.

Last edited by techinspector1; 10-12-2013 at 10:39 AM.
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Old 10-12-2013, 11:02 AM
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Quote:
Originally Posted by Gearhead346 View Post
I think the part number was 00212s or 00211s through crower cams. I was figuring a .050" quench for the 11.2:1. I can only find the eagle kits with -6cc, -7cc, and -30cc pistons. The -30cc pistons would put me way down to around 8.8:1. I some what believe in DCR... my other engine runs 10.8:1 scr with 8.5:1 dcr and runs 91 octane no problems, but that may also be because of my aluminum heads.
I don't know what calculator you use, but I have become accustomed to the one on Keith Black Pistons site. I've used it long enough to be able to figure out whether a combination will work or not.

What I'm seeing with the SCR at 11.50:1 and using the Crower 00212 cam timing, the DCR figures to 9.33:1. This motor will not run on pump gas. You need to be nearly a full point lower on DCR.

With an SCR of 10.50:1 and using the Crower 00212s, the DCR on the KB calculator is 8.54:1, a number that is perfectly acceptable for pump gas in my experience, particularly with using aluminum heads.
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Old 10-12-2013, 11:16 AM
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So I found a different rotating assembly from scat. Here it is

http://www.summitracing.com/parts/sc...50bi/overview/

This will give me -18cc pistons and put me at 10.16:1 SCR with 64 cc heads and .040" quench. DCR at 7.27:1. Will this be more reasonable and still make decent power? Also if I check the clearances and buy Comp cams 787-16 retainers will the LS3 springs handle that .492/.510 cam?
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Old 10-12-2013, 11:30 AM
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A bore of 4.155 (+0.030") and a stroke of 3.750" will yield a 408 cubic inch motor. Using a 64cc chamber and 16cc piston will produce an SCR of 10.3:1. Using the Crower 00212s (intake closes at 48 degrees after bottom dead center @0.050" tappet lift) and installing it straight up will produce a DCR of 8.38:1 on the KB calculator.

Same motor, using the Crower 00211s, (intake closes at 44 degrees ABDC) will produce a DCR of 8.62:1, a perfectly acceptable figure for pump gas. This cam has nice, easy ramps and will make power from 2500 to 6400 in a 408 cubic inch motor.

Gearhead, you can specify the piston crown displacement when ordering the kit. They'll include any piston that you tell them to. Use the 16cc piston.

Last edited by techinspector1; 10-12-2013 at 11:38 AM.
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