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Old 05-29-2013, 09:26 AM
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Need advice on cam selection for 383 Vortec 4x4

FNG here lol... Anyhow I'm needing a little help on cam selection for my 383 Vortec project that is going in my z71. My setup is 10.5:1 383 with stock 64cc Vortec heads with ls6 valve spring, matching retaines, keepers, and umbrella valve seals (supposed to make the stocker Vortecs good up to .550 lift with this combination). I have 4.56 gears, a reworked stall which is supposed to have a stall speed of 1500 with a 4l80e behind it. Going to a carburetor so I have a Summit Racing stage 2 dual plane intake manifold 1500-6500 and vac 750 holley. Also have long tube hedders. My z71 is pretty big, 6 inch lift and 35" tires and I also pull a 19' bass boat a lot with it so I'm really needing some extra torque down low to get this big joker moving. I've looked at some Comp 4x4 cams as well as a few of the Howard's cams but I can honest with myself, I'm not a cam guru... I was kinda thinking maybe something around .500 lift, a low LSA, and keep a decent idle as well but I do like that lope Any idea guys? I trust y'all more than my friends and summit tech line on cam selection. Thanks

RR

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Last edited by RyanR; 05-29-2013 at 09:43 AM.
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Old 05-29-2013, 09:54 AM
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I don't have any specifit recomendations, but I can offer a few tips.
  • Check the installed height and geometry.
  • Be sure to use only ONE method of guiding the p-rods (no guide plates w/SA rockers, etc.).
  • Don't go too small on the duration, else the dynamic compression ratio could be too high for pump gas.
  • Match stall speed and gear ratio to camshaft.

Some links to info on the above:
• Valve train points to check
• Valve train geometry
• Valve spring installed height
• Adjusting hydraulic lifters
• Cam duration vs. compression ratio
• Comp cams CamQuest software program- useful for comparing cam estimated output @ rpm to one another
• How to choose a cam
• Various calculators from Wallace Racing, including gear ratio vs. tire size, etc.

A couple calculators for static and dynamic compression ratio:
• Static compression ratio calculator
• Kelly DCR calculator
• Wallace Racing DCR calculator
• KB/Silvolite DCR calculator
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Old 05-29-2013, 11:33 AM
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Your compression is too high for your intended use.

The cam that matches your compression will not match your intended use. Cobalt was hinting at that but I'll just lay it out nice and simple.

For towing a boat you want around 9.5:1 compression and with your set up I would say around a 215/220 duration cam.
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Old 05-29-2013, 12:02 PM
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Quote:
Originally Posted by ap72 View Post
Your compression is too high for your intended use.

The cam that matches your compression will not match your intended use. Cobalt was hinting at that but I'll just lay it out nice and simple.

For towing a boat you want around 9.5:1 compression and with your set up I would say around a 215/220 duration cam.
U can be blunt guys... I dont want no one to be a jerk, call me stupid, or anything like that but thats why I'm here and asked. I want honest opinions and honest answers. I haven't bought my rotating assembly yet so no big deal at all. I almost did this morning but I'm glad I held off and talked to a few people first... so lower the compression a touch to around 9.5 and 215/220 duration cam... thanks for the links as well. Any thoughts on lift or lsa?
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Old 05-29-2013, 12:27 PM
How fast is fast enough?
 
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Quote:
Originally Posted by RyanR View Post
U can be blunt guys... I dont want no one to be a jerk, call me stupid, or anything like that but thats why I'm here and asked. I want honest opinions and honest answers. I haven't bought my rotating assembly yet so no big deal at all. I almost did this morning but I'm glad I held off and talked to a few people first... so lower the compression a touch to around 9.5 and 215/220 duration cam... thanks for the links as well. Any thoughts on lift or lsa?
go with a hyd roller cam and all the lift you can get in that short duration.

the 262/270 voodoo hyd roller cam moved to a 108 LSA would pull pretty damn hard, something along those lines will be great for towing.

The duration is a little shorter than I recommended but that just means you'll have even more low end torque. Fair warning though, that cam and those heads will stop making power around 5,000 RPM- which is probably higher than you plan on revving it anyway.
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Old 05-29-2013, 12:41 PM
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Originally Posted by ap72 View Post
go with a hyd roller cam and all the lift you can get in that short duration.

the 262/270 voodoo hyd roller cam moved to a 108 LSA would pull pretty damn hard, something along those lines will be great for towing.

The duration is a little shorter than I recommended but that just means you'll have even more low end torque. Fair warning though, that cam and those heads will stop making power around 5,000 RPM- which is probably higher than you plan on revving it anyway.
I'm using a 4 bolt new style block so its going to be hydraulic roller.And yes as big as my truck is, it will be very rare for it to ever see past 5, 000 rpms. But yea man that sounds good, guess its time to get on summit's site and do some looking. Y'all dont think a 108 lsa will make it have a hard time idling do u?
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Old 05-29-2013, 12:58 PM
How fast is fast enough?
 
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Quote:
Originally Posted by RyanR View Post
I'm using a 4 bolt new style block so its going to be hydraulic roller.And yes as big as my truck is, it will be very rare for it to ever see past 5, 000 rpms. But yea man that sounds good, guess its time to get on summit's site and do some looking. Y'all dont think a 108 lsa will make it have a hard time idling do u?
LOL, no that thing will idle pretty mildly. and you can't buy that from summit, have to call Lunati directly.
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Old 05-29-2013, 01:01 PM
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RyanR, been down this road with a 10.25 to 1 sbc. Heavy truck and used to pull my 6x14 enclosed trailer. You seem to have the gears and trans to support it with tall truck tires.

If this was mine and I was more concerned about grunt and drivablity to pull the trailer I would go with a roller hydraulic cam in the neighborhood of 218-220 @.050, no more than .475-.500 lift and LSA around 110-112 with intake lobe at 106-107. The cam might have a slight and I mean slight lope to it. It would more than likely just rumble. Be meticulous with valve train geometry with a shaft system being the best, make sure it is correct! Make sure you get a good timing curve to the ignition (36-38 total@2800-3000rpm, even 2600) because you will be using more initial timing. Build a quick curve coming off idle then limit it to use more initial. Even if you have to use 18-20 initial and 18 total in advance. Be careful to keep it out of detonation, your capturing a lot of compression down low for todays gas quality. Any little stumble you get off idle on light accel correct it with jets, power valve, IFR and main air bleeds. Make sure your cooling system up to the task. Take it for what it's worth, I have done close to this combo and it took some time and work to iron out the ignition curve and fuel curve. Just my 2 cents.
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Old 05-29-2013, 01:44 PM
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AP72 and I don't always agree, but we're pretty close this time.
First thing I like to do in these situations is to find out what the gear would be with standard 28" tires. In other words, you may think you have enough gear under the truck to warrant quite a lot of cam. That may not be true. If you figure the final drive, taking the tire size into consideration, your 4.56/35" tire combination is the same as running a 28" tire with a 3.64:1 gear, probably not enough gear to warrant any kind of hot camshaft and therefore not enough gear to warrant high static compression ratio which would require a hot cam.

The other thing to take into consideration is the heads. They are nice heads, designed for a 350 cubic inch motor. On a larger motor, they will run out of steam early in the ballgame, being pretty much all done in at around 5000/5300 (this is just my opinion). So, that's another reason for a shorter cam. Any cylinder head out there will have a "stall" point, where the heads will taper off and just will not flow any more air. As nice as they are, the L-31 heads were designed to haul folks to the grocery store and grandma to bingo and back. They were not designed for an offroad truck. Just be aware that they are PRODUCTION heads and don't expect miracles.

I'd check the main bearing bore for being round and parallel. Align-hone or align-bore to correct any misalignment. Register the block on the mains and cut the decks to zero based on your stack of parts. Use a 0.040" composition gasket. Pay close attention to the cooling system and have it working up to snuff. If these heads get hot, they're toast. (cracks).

I'd build the motor at 9.00:1 static compression ratio and use the first cam on the list in Crane's catalog, or a similar grind from another manufacturer.
Grind number HR-260-2-12 IG
Part number 119811
Brute low end torque and HP, smooth idle, daily usage, towing, economy, also mild turbocharged.
2200-3000 cruise RPM
8.0:1 to 9.5:1 static compression ratio advised.
1000-5200 rpm operating range.
Advertised duration 260/270
0.050" tappet lift duration 204/214
112 degree lobe separation angle
Gross valve lift 0.429"/0.452"
Install 4 degrees retarded for 350 hp @5000, 440 ft/lbs torque @3500.

With all due respect to steeny, I don't think I'd run more than 34 degrees total initial and centrifugal spark lead with those heads. They're pretty fast in the chambers.

Last edited by techinspector1; 05-29-2013 at 02:09 PM.
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Old 05-29-2013, 02:40 PM
How fast is fast enough?
 
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Quote:
Originally Posted by techinspector1 View Post

With all due respect to steeny, I don't think I'd run more than 34 degrees total initial and centrifugal spark lead with those heads. They're pretty fast in the chambers.
especially while towing and with a longer stroke...
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Old 05-29-2013, 02:46 PM
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techinspector, hey no problem with me. I appreciate the respect and same back to you! Although it would not scare me to go with at least a cam with 210-215 @.050. stiil would not go over .500 if that. You could be correct on the total timing but no way would I set the cam in retarded. Maybe....maybe a cam without any advance ground in, set straight up. If it needs to be set up retarded it is the wrong cam grind to install. Just one of my rules of thumb.
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Old 05-29-2013, 02:55 PM
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These are the cams I had been eyeballing

http://www.summitracing.com/parts/cc...make/chevrolet

http://www.summitracing.com/parts/hr...make/chevrolet

http://www.summitracing.com/parts/cr...make/chevrolet

And like you guys have mentioned already, I've read over and over that 34* total timing is the sweet spot for Vortecs so I guess that correct.

Techinspector1, yeah I'm definitly not expecting anything spectacular out of the Vortecs, their decent factory heads but factory is the key word there. In the future I may step up to some Eliminators but for now I'm just using what I have. And you think drop the compression down even further to 9:1 instead of 9.5:1? And this truck isn't my DD, it's more of a weekend warrior, bass boat hauler. Don't get me wrong I am concerned about mileage to an extent and do want it driver friendly but I'd still like a cam to sound pretty serious but not so much that it won't hardly idle on its own, ill matched to my setup, and unpractical.

I've been seeing alot of post about maybe my 3310 750 Holley is going to be too big for a lifted, big truck such as mine and it would prefer a 600-650 cfm better because of the small bores / better throttle response.. Any truth to this?

You guys are great on this forum... Some of the other forums I've been on in the past take forever to get responses and sometimes the newbie's never get answered at all. Thanks guys
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Old 05-29-2013, 03:01 PM
How fast is fast enough?
 
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For a more aggressive sound run 2.5" dual pipes into thrush welded mufflers.

For the cam out of the 3 you picked I would go with the crower cam and 1.6 rockers.

Or call lunati for the cam I spec'ed and run 1.5 rockers.
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Old 05-29-2013, 03:03 PM
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RyanR, If I may..the 750 is too much that you will never use if it is to be driven as you say. Not that the carb won't work..you are going to have to work at it to make it right for the app. If you don't feel comfortable diving deeper into carburetion other than a jet change and a power valve, get a 600-650.
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Old 05-29-2013, 03:04 PM
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I agree with AP72. The crower grind looks good.
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