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  #16 (permalink)  
Old 10-31-2011, 12:32 PM
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Quote:
Originally Posted by ap72
change that -10 to a -08. 1.6 rockers will help on your intake but won't do much on the exhaust.

Its another area where you have to consider the cost/benefit, you could possibly pick up 10hp by running 1.6 rockers but you'd also need valvesprings that can handle that lift and last.
So would doing a 1.6 on the Int and 1.5 on the Ex be more beneficial?

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Old 10-31-2011, 12:55 PM
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Originally Posted by zildjian4life218
So would doing a 1.6 on the Int and 1.5 on the Ex be more beneficial?
yes, but again make sure your valvetrain can handle the extra lift.
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Old 10-31-2011, 12:57 PM
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Originally Posted by ap72
yes, but again make sure your valvetrain can handle the extra lift.
I will make sure I get valve springs that will match whichever cam I end up choosing.
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Old 10-31-2011, 01:11 PM
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Originally Posted by zildjian4life218
Hey I was wondering if someone could give me a couple pointers on what to look for when picking out a cam to best suite a given set of cylinder heads and power goals. I know cylinder pressure, head flow, converter stall, gearing, and weight all matter a lot when choosing a camshaft. I was hoping you guys could give me some insight on what determining factors will effect my power goals.

I currently have a 355ci late model sbc with hypeurtectic pistons and eagle rods. It also has vortec heads that i ported a little. On top of that is a performer rpm vortec intake with a 650cfm edelbrock carb. The current cam is a performer rpm hyd flat tappet has gone flat. multiple lifters are scored and lost their convex shape. So I would like to take the winter months here and pull the cam out and replace it with a hydraulic roller. I have a complete setup from a vortec engine, wishbone, hardware, and lifters that I could use but I heard that too much lift will cause the lifter to rotate in the bore which would not be good. I have also heard of people buying GMPP lifters because they handle rpm better or something? http://www.summitracing.com/parts/NA...5&autoview=sku
Is there any fix to the lift issue? I imagine not running a small base circle cam would be the first and obvious answer but idk if cams grinders do take the base circle down even a little to cause the lifter issue.

One thing I noticed about the vortec heads is the intake flows best at .5 and the exhaust flows better at .6 so should i get a cam where the intake lift is close to .500" and the exhaust lift will be close to .600 or maybe run 1.6 rocker arms on the exhaust? I also plan on buying a set of full roller self aligning rocker arms for this motor over the winter so I can go with whatever ratio will best suite my needs.

My end goals are I would like to get my car in the 12s for sure....... faster is always better. Drive train will hold. The title says it weights 3200ish with the original v6. So at least 320whp will get me there but the more the better right? lol Please any and all input is appreciated. I am still learning from all you guys on here so like i said any input is well appreciated. Thanks!
320 hp out of a 350 is not difficult and with Vortec heads is a no brainer. It certainlya cam over a half inch of lift isn't required. These kind of lifts get you into a parade of engineering problems to where valve to piston clearance, rocker to stud, pushrods to guide, springs to coil bind, spring rate and strength, and retainer to upper guide clearance all become additional problems to be worked out; often not inexpensively.

Lets talk ports and their relationship to the cam as it seems a lot of non-sense is out there. A port, any and all ports, has a maximum flow potential. Once that's hit adding lift at the valve is of no further help. What will help a maxed port is more duration because that adds time. But excess duration adds a lot of overlap and offers a late closing intake. At RPMs in the off idle to the torque peak range this causes the mixture velocity in the port to slow and even reverse at some lift points, this drops bottom end power and pushes the torque limit higher in the RPM range. A partial solution lies in raising the compression ratio, but in the end you are limited by the fuel's detonation limit. Gearing can help some reducing the load on the crankshaft either through stiffer gears, high stall converter, or a lighter vehicle all reduce the detonation sensitivity.

The issue of lifter's is not rotation in their bore, for Chevy, Chrysler, or Ford engines this is a non issue, the dog bone and spider is fine. Where very high lifts are used the aftermarket provides other solutions. The problem is the rate of lift that can be applied to a roller lifter, sudden lifts, especially in the ramp transition to the lobe flank if done to suddenly pushes the lifter sideways in its bore causing it to bind, this is one thing a flat tappet especially a large diameter flat tappet does better, it is the reason why, where the rules allow it, Chevy engines use Ford or Chrysler tappets which are larger and muy larger in diameter.

The SBC has been known to need more exhaust help compared to the intake, that's not to say the exhaust is poor compared to other engines, it just isn't as good as the intake on a ratio of flow for the port and valve sizes for this engine. The aftermarket has long used a little more timing and or lift on the exhaust side of the SBC.

But all of these issues are not a concern for a 320 hp 350, they're not even an issue at getting 380 to 400 horses out of a 350. A 350 with Vortec heads having a compression ratio from 9 to 9.5 with a cam that has about 225 degrees of duration and about .48 inch lift. With a good intake like the Edlebrock Performer RPM and a carb with about 700 to 750 CFM capacity, a decent ignition and long tube headers will pull 400 horses on an engine dyno without sweating and do it under 6000 RPM with a fat and flat torque curve.
I'd expect 380 with circular dish pistons where the squish/quench clearance is rather deep and as a result insufficient. With a D dish or flat top piston, a deck and head gasket combo that nets out about .040 to .055 inch of crown to deck clearance which with a 12 cc D cup will deliver an SCR of 9.6 or 9.3 respectively. You can diddle a few more ponies by using 1.6 rockers, back cutting the exhaust valves at 30 degrees and polishing the back side of the intakes with your home ported Vortecs.

That's all it takes to get some impressive numbers out of a 350, no crazy involved, just attention to the details and careful parts selection which sounds like something you've already done much of.

Bogie
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Old 10-31-2011, 01:18 PM
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Awesome post bogie. I just changed the lift in my desktop dyno from .560 to .5 and it only lost 4hp! I guess maybe ill consider keeping the lift down because like you said im gonna run into issues rocker to stud, pushrods to guide, springs to coil bind, spring rate and strength
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Old 10-31-2011, 01:32 PM
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Quote:
Originally Posted by zildjian4life218
Awesome post bogie. I just changed the lift in my desktop dyno from .560 to .5 and it only lost 4hp! I guess maybe ill consider keeping the lift down because like you said im gonna run into issues rocker to stud, pushrods to guide, springs to coil bind, spring rate and strength

be careful with those "dexktop dynos" they don't take into account the entire lift curve (as they usually can't), not only will your peak lift be higher but you'll have more duration above every lift point, which adds up. For 320fwhp a mild flat tappet cam can work, but if you want to get into the 425fwhp+ range you're going to need some lift. accounting for 20% drievetrain loss you'll need AT LEAST 400hp, the more the better. Also consider the additional cost of running the hotter cam over the mild cam is about $100 extra on valvetrain expense- cheap hp in my book.

Again, it all depends on what you want, if you want to just build something mild and cheap or max out what you have- MOST of what I have built has been mild and cheap as it is cheap. But when you do your homework and spend a little extra it can make a big difference.

Basically the same reasoning that applies to a 383vs a 350 applies to one cam vs another, the costs aren't that much more and the output is higher.
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Old 10-31-2011, 01:50 PM
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Nowhere in this thread has anyone mentioned matching up the cam with the static compression ratio. That's one of the first questions the tech at the cam grinder will be asking if you call for a recommendation.

I got lambasted when I introduced this chart a few months ago, but if you're not paying attention to the SCR/cam timing, you're shooting yourself in the foot. It's always tough getting wrapped around an idea that you never thought about before.

I contend that's why there are so many over-cammed and under-cammed combinations out there trying to make power, because the builder failed to take SCR/cam timing into consideration.

Another thing, please stop talking about stratospheric lift figures with these heads. As mentioned by AP72, the heads will only flow to a modest rpm where they will stall. The only thing you'll be doing after that point is wearing out valve springs and guides. 0.500" lift should be a God's plenty. If you want more hp, get some better heads that will support more power rather than these production units with restricted runner size. And don't tell me that they will make more power because you ported them. If you don't have multi-years of hands-on experience porting cylinder heads, you could have hurt flow more than you helped it.

How would I do it?
1. Strip the block.
2. Align-hone or align-bore the main bearing bore.
3. Cut the block decks to 0.015" piston deck height using a flat-top piston with 7 cc's of valve relief. This will square the block so that the heads sit properly to seal up the intake manifold.
4. Use brushes to clean every nook and cranny and remove all the shrapnel from the roached cam and lifters. If you don't get that junk out of the motor, you're just asking to do this all over again.
5. Use a GM 10105117 composition gasket that compresses to 0.028". This will yield a 9.99:1 SCR assuming 65cc heads that will work well with the cam timing you want to use. See here....
http://www.crankshaftcoalition.com/w..._compatibility
6. Use the 110325-08 cam and lifters as a kit. The 108 LSA will be a little lumpier than the 110. Make provision at the retainer/seal junction to allow full lift plus 0.060" play.
7. With the 0.043" squish, you should be able to use plenty of ignition timing and make good power on pump gas. Here's a table from Barry Grant with recommendations for spark lead with certain cam durations....
http://barrygrant.com/demon/default.aspx?page=5

And finally, there's the question about how much lift to use with stock GM production roller lifters. It depends on the cam grind. If the lift is excessive, then the grinder will cut the cam on a reduced base circle which moves the nose of the lobe closer to the centerline of the camshaft. If this reduction is excessive, the lobe can allow the lifter to drop out of the dogbone and rotate. Complete engine failure follows soon after. You fellows who plan to use GM lifters should counsel with your favorite cam grinder about this problem. Also, you fellows who want to know if you can use GM lifters in an early flat tappet block.....No. Not without machining the tops of the lifter bores so that the dogbones have a level and flat place to sit. It's much simpler to use aftermarket retrofit roller cams in a flat tappet block.
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  #23 (permalink)  
Old 10-31-2011, 02:41 PM
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Originally Posted by techinspector1
Nowhere in this thread has anyone mentioned matching up the cam with the static compression ratio. That's one of the first questions the tech at the cam grinder will be asking if you call for a recommendation.

I got lambasted when I introduced this chart a few months ago, but if you're not paying attention to the SCR/cam timing, you're shooting yourself in the foot. It's always tough getting wrapped around an idea that you never thought about before.

I contend that's why there are so many over-cammed and under-cammed combinations out there trying to make power, because the builder failed to take SCR/cam timing into consideration.

Another thing, please stop talking about stratospheric lift figures with these heads. As mentioned by AP72, the heads will only flow to a modest rpm where they will stall. The only thing you'll be doing after that point is wearing out valve springs and guides. 0.500" lift should be a God's plenty. If you want more hp, get some better heads that will support more power rather than these production units with restricted runner size. And don't tell me that they will make more power because you ported them. If you don't have multi-years of hands-on experience porting cylinder heads, you could have hurt flow more than you helped it.

How would I do it?
1. Strip the block.
2. Align-hone or align-bore the main bearing bore.
3. Cut the block decks to 0.015" piston deck height using a flat-top piston with 7 cc's of valve relief. This will square the block so that the heads sit properly to seal up the intake manifold.
4. Use brushes to clean every nook and cranny and remove all the shrapnel from the roached cam and lifters. If you don't get that junk out of the motor, you're just asking to do this all over again.
5. Use a GM 10105117 composition gasket that compresses to 0.028". This will yield a 9.99:1 SCR assuming 65cc heads that will work well with the cam timing you want to use. See here....
http://www.crankshaftcoalition.com/w..._compatibility
6. Use the 110325-08 cam and lifters as a kit. The 108 LSA will be a little lumpier than the 110. Make provision at the retainer/seal junction to allow full lift plus 0.060" play.
7. With the 0.043" squish, you should be able to use plenty of ignition timing and make good power on pump gas. Here's a table from Barry Grant with recommendations for spark lead with certain cam durations....
http://barrygrant.com/demon/default.aspx?page=5

And finally, there's the question about how much lift to use with stock GM production roller lifters. It depends on the cam grind. If the lift is excessive, then the grinder will cut the cam on a reduced base circle which moves the nose of the lobe closer to the centerline of the camshaft. If this reduction is excessive, the lobe can allow the lifter to drop out of the dogbone and rotate. Complete engine failure follows soon after. You fellows who plan to use GM lifters should counsel with your favorite cam grinder about this problem. Also, you fellows who want to know if you can use GM lifters in an early flat tappet block.....No. Not without machining the tops of the lifter bores so that the dogbones have a level and flat place to sit. It's much simpler to use aftermarket retrofit roller cams in a flat tappet block.
FWIW, Vortec heads stall at about .530" lift

And the cam mentioned would work from 9:1 to 10:1, but the fuel type you use would change from 87 to 91.

Running 1.6 rockers is NOT needed and will lead to increased wear if the proper parts are not used and set up properly, its a give and take like everything else. 1.6 rockers would really shine if the vortecs had a good valve job that opened up the bowl and was blended into the port though, as your stall moves up closer to .575" lift- the runner still restricts it though.
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Old 10-31-2011, 03:33 PM
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Quote:
Originally Posted by ap72
FWIW, Vortec heads stall at about .530" lift
Be careful here. Intake runner stall is dependent on RPM's also. For example, you wouldn't be able to stall the heads at 3500 rpm's with a 0.530" lift.
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Old 10-31-2011, 06:01 PM
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Thanks for the input everyone. I like the idea of sticking with just 1.5 ratio rocker arms. What does everyone think my current setup is making hp wise approximately. I want to get an idea of the increase I'll be making. Thanks again for all the input!
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Old 11-01-2011, 06:32 AM
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Be careful here. Intake runner stall is dependent on RPM's also. For example, you wouldn't be able to stall the heads at 3500 rpm's with a 0.530" lift.
and displacement, the rest of the engine combination, etc. My point was that you won't need to lift the valve much past that to achieve peak flow, how long you are at peak flow (in cam degrees) becomes another issue though.
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Old 11-02-2011, 06:37 PM
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So would everyone agree that the howards cam I suggested be ideal for my application and power goals? Also 110 or 108 LSA? I care more for power than I do the lumpy idle sound.
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Old 11-03-2011, 10:34 AM
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I just thought do I need to get a new timing cover with a cam button?
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Old 11-03-2011, 01:32 PM
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So would everyone agree that the howards cam I suggested be ideal for my application and power goals? Also 110 or 108 LSA? I care more for power than I do the lumpy idle sound.
108.
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Old 11-03-2011, 01:37 PM
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Originally Posted by ap72
108.
Awesome Thx AP for the help! What kind of power increase do you think im looking at? Maybe around 50hp
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