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LS3 Springs on Vortec Heads

11K views 22 replies 6 participants last post by  techinspector1 
#1 ·
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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#3 ·
Heres the link to the rotating assembly I'm buying.

http://www.summitracing.com/parts/esp-b13460030/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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#4 ·
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.
 
#5 ·
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.
 
#6 · (Edited)
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.
 
#8 ·
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.
 
#9 ·
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.
 
#12 · (Edited)
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.
 
#19 ·
Didn't mean to imply that DCR calcs are not valuable & critical tool when building an engine.It is when used in conjunction with everything else.More so for the novice or less experienced.It is a valuable tool.I just meant that it shouldn't be solely used.It is an important piece of the puzzle.As far as elevation goes,my thinking is,if I live in a higher altitude & build my engine on the edge of what may work there,then,have to go out of this setting,or,maybe sell the vehicle/engine to someone @ a somewhat lower elevation,you could have issues.I see ppl saying my DCR is XX:1,so,I can run xx octane & it ain't quite that simple.Dcr has to be used along with everything else.
 
#14 ·
So I found a different rotating assembly from scat. Here it is

http://www.summitracing.com/parts/sca-1-90950bi/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?
 
#15 · (Edited)
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.
 
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#18 ·
Thanks guys for the input, I just realized that rotating assembly is with 6" rods vs. 5.7" rods. This was the whole reason I was buying a small base circle cam because of the 5.7" rods. Won't 6" rods cause rod to block clearance issues and cam to rod clearance issues? So with the small base circle cam I would be good with 6" rods, but not on the block side. If it does have clearances issues can I grind the block slightly to make it clear? I almost wish I could buy an assembly with 5.565" rods but they don't even make them anymore :evil:
 
#20 ·
Use longer pushrods to take up the slack left by the smaller diameter base circle cam and clearance the oil pan rail for the big end of the rods. Make certain that there is sufficient clearance between the pin end of the rod and the underside of the piston crown. Clearance flat tappet bores at 0.0015" (one and one half thousandths).

Read and heed......
http://www.crankshaftcoalition.com/wiki/Camshaft_install_tips_and_tricks
 
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