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Old 02-16-2011, 07:19 PM
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compression ratio of a stock 96-00 vortec engine??

Hey All,

I need to find out the compression ratio of my 96-00 stock 350 5.7 vortec engine w/std bore. I'v been getting different answers. I'm about to purchase one of the two cams for my build..but I'm using stock pistons and need to make sure my compression will be fine. The cams below is what I will be using. Also..I've heard that a switch to 1.6 will be benificial using over .480 lift with my vortec heads...?? what do you all think? 3.42 rear gears..stock converter..700r4 tranny...28 inch tires
http://www.compcams.com/Company/CC/c...?csid=187&sb=0
http://www.compcams.com/Company/CC/c...?csid=199&sb=0

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Old 02-16-2011, 07:38 PM
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i have a 97 C1500 with a 5.7 vortec engine, compression ratio in that is 9.5:1
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Old 02-16-2011, 07:50 PM
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thanks jamyz, so do you have 64cc vortec heads?
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Old 02-16-2011, 08:02 PM
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sorry about that, yeah, i believe the stock iron vortec heads are 64cc and thats what i still have intalled, the engine is still stock except for exhaust and ignition
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Old 02-16-2011, 09:07 PM
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I thought it was lower, like 8.5, but i could be wrong.
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Old 02-16-2011, 09:13 PM
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Somewhere I saw 9.52:1 for the '99 'Burb 5.7L Vortec engine. The actual CR could be a tenth or so lower.
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Old 02-16-2011, 10:44 PM
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as far as i know, all TBI and Vortec 350's are about 9.3:1
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Old 02-16-2011, 10:47 PM
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Quote:
Originally Posted by redfish211
Hey All,

I need to find out the compression ratio of my 96-00 stock 350 5.7 vortec engine w/std bore. I'v been getting different answers. I'm about to purchase one of the two cams for my build..but I'm using stock pistons and need to make sure my compression will be fine. The cams below is what I will be using. Also..I've heard that a switch to 1.6 will be benificial using over .480 lift with my vortec heads...?? what do you all think? 3.42 rear gears..stock converter..700r4 tranny...28 inch tires
http://www.compcams.com/Company/CC/c...?csid=187&sb=0
http://www.compcams.com/Company/CC/c...?csid=199&sb=0
what are done ot the heads? Vortecs cant handle over .480 stock, they need to have springs changed over to a beehive setup. The second cam would work great with 1.5:1's. I would recommend Scorpion 1.5:1 Roller Rockers, 1.6's are NOT needed.
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Old 02-17-2011, 10:32 PM
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Quote:
Originally Posted by FastOrange
what are done ot the heads? Vortecs cant handle over .480 stock, they need to have springs changed over to a beehive setup. The second cam would work great with 1.5:1's. I would recommend Scorpion 1.5:1 Roller Rockers, 1.6's are NOT needed.
I've had a great valve job and switched out the valve springs. I purchased the Scoggin Dickey Z28 springs..and had my machine shop install them. I've heard that no matter what Vortec heads do not flow well with over .500 lift. Is that true?
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Old 02-17-2011, 10:51 PM
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Quote:
Originally Posted by redfish211
I've had a great valve job and switched out the valve springs. I purchased the Scoggin Dickey Z28 springs..and had my machine shop install them. I've heard that no matter what Vortec heads do not flow well with over .500 lift. Is that true?
From what I've read (I do not own a flow bench), if the ports are stock/unported, the flow levels out at 0.450"-0.500", but doesn't fall off much at lifts out to =/> 0.600".

So while flow doesn't increase, it also doesn't seem that the ports go into a stall or choke at higher lifts the way some heads tend to do.

That said, there's not enough port volume on a stock Vortec head (~170cc intake) to make me want to go overboard w/the cam specs, anyway.
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Old 02-17-2011, 10:57 PM
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Thanks for the lift info Cobalt. So I should stay under the .500 lift if I can using vortec heads. Everything I'm using in the build is pretty much stock except for the intake, cam and carb.
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Old 02-17-2011, 11:23 PM
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Quote:
Originally Posted by redfish211
Thanks for the lift info Cobalt. So I should stay under the .500 lift if I can using vortec heads. Everything I'm using in the build is pretty much stock except for the intake, cam and carb.
Yes, if for no other reason that the duration you'll want to run will usually have lift figures at or below 0.500" or so, anyway.

If you're using an OEM roller cam set up, the duration can usually be a little less than a FT cam, using the same lift figures.

I like to choose the cam specs using 1.5 rockers, too. That gives you the choice to increase the ratio later on, for the intake, exhaust, or both- if needed.

I sure hope headers, dual exhaust and low restriction mufflers w/an "H" or "X" connecting the two sides is in the plans, too!
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Old 02-17-2011, 11:29 PM
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thanks Cobalt... I'm narrowing my cam down for sure. I've been talking to the tech crew over at Comp..and I've gotten about 4 cam recommendations. I a bit confused.. cause this is my first performance build. I just need to make sure the cam can run well with a stock convt.
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Old 02-18-2011, 12:11 AM
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While I don't usually recommend cams, THIS thread has some info on cams. There must be a thousand others w/info on cams for engines w/Vortec heads, too.

Basically, I'd use a hydraulic roller split pattern cam w/something like 220-224 degrees (max) intake duration, 224-228 degrees exhaust duration, lift below 0.500", on a 110 degree LSA.

A little bowl work and a good three angle valve job would really wake this type cam up. But even w/stock heads w/o any special work, it should perform well.
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Old 02-18-2011, 10:23 AM
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Vortec heads solve flow problems. The idea of .6 lift and these heads is not congruent. Everything has a purpose and place, and these, are Vortecs. The budget 906 head can keep up with the RPM head package using milder components, like Comps Mag270.

2 awesome GM beehive springs/ tiny retainers to look for that work well with vortecs.

Shorter 1.875" free length, 330lb/in, the installed height will be ~1.6". so seat pressure should be 91 lbs, and .5" lift will be or 256lb.

Longer ones free length of 1.94" , 10166343 for the valvesprings, and 10166344 for the retainer, these springs are 315lb/in w/105lb seat pressure installed at 1.8". spring rate open of 365lb/in, 1.6" IH measured with the 3100 retainers. A .5 pressure of 306

coil bind was measured at .81" lift on the 343 springs, and .5" lift measured IH would only leave you .035" before coil bind.

To get more than .450" safe lift the guides need to addressed. If the only prep you take is the springs and retainers, you will get pressure, but there are other obsticles easily cleared.

Last edited by spinn; 02-18-2011 at 10:36 AM.
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