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Old 07-26-2012, 06:54 PM
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Valve clearance

I have a stock SBC 350 bottom end. I am going to be putting some aluminum heads, roller cam, intake etc.

My question is how much valve lift can I get away with before running into valve to piston issues??

Stock flat tops with with 4 eyebrow valve relief, .025 deck heigth, .015 head gasket.

I heard you can run into issues with the eyebrows being to small to accomodate 2.02 valves??

Any input would be great. Thanks in advance.

PS: cam I wont to use has following lift......int .54 / exh .562

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Old 07-26-2012, 07:58 PM
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That cam though not high lift,likely wont fit.depends also on duration and lobe angle.always check clearances
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Old 07-26-2012, 08:16 PM
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There's no way to know and nobody can tell you rather or not your going to have clearance issues you have to check it and there's no way around it.
A cheap method we use is play dough with talcum powder to prevent the valve from sticking.
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Old 07-26-2012, 09:39 PM
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Hmmmm. I was planning on checking clearances but I'm worried about buying a $300 cam and not being able to use it.
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Old 07-26-2012, 10:05 PM
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Do you hav another similar cam to mock up with?

Similar duration @.050" and LSA. The lift has little to do with VTP clearance
as the piston is way down the bore when the valves are at full lift.

The duration and overlap has more to do with it.
valve opening at near TDC.

You don't give any info on the heads Non stock valve location etc.
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Old 07-26-2012, 11:01 PM
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I'm going to use either AFR 180 street or patriot freedom series 185. I was hoping to use a comp XE288 or XE 294 hydraulic roller. I would attach the link on the cams but I'm posting from my phone so I hope that helps. The only cam I have is a flat tappet magum 270. its 224 at .50
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Old 07-26-2012, 11:12 PM
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Either should fit.

The larger XR294r-10 cam I would definatly mock up with the heads and Check VTP clearance.
All part of the joys of building Hi performance motors.
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Old 07-27-2012, 01:29 AM
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safer is better

when i doubt go to a place like howards cams or elgin or something and buy a cheap solid cam with close to the same numbers...may be impossible when comparing to a roller but its worth a try. most solid lifter stuff is 90 bucks from them. Or as an alternative. check with some local dirt track guys and see if they have a comparable one laying around you could use to test. Us dirt guys never get rid of anything.
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Old 07-27-2012, 04:32 AM
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Quote:
Originally Posted by prostcelica View Post
I have a stock SBC 350 bottom end. I am going to be putting some aluminum heads, roller cam, intake etc.

My question is how much valve lift can I get away with before running into valve to piston issues??

Stock flat tops with with 4 eyebrow valve relief, .025 deck heigth, .015 head gasket.

I heard you can run into issues with the eyebrows being to small to accomodate 2.02 valves??

Any input would be great. Thanks in advance.

PS: cam I wont to use has following lift......int .54 / exh .562
Besides the raw lift, the cam timing and additional advance/retard has an effect as well. There are so many variables that it is hard to guarantee anything when it comes to valve to piston clearance. I would definitely mock this up first and check the p to v.

Here is a page on things to check.

Stock piston valve reliefs need to be checked and clearanced if needed w/2.02" intakes. Aftermarket pistons tend to have more generous reliefs.
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Old 07-27-2012, 06:44 AM
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Agreed, can't really tell anything without mocking it up. Too many variables.

However, it's not THAT big a "deal" to have the valve reliefs "fly-cut" (type of cutter used for the operation). Any automotive machine shop that has a "piston vise" and a mill can do it. This is the procedure to be used when cams and pistons not "stock" are used. Common practice.

Jim
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Old 07-27-2012, 08:26 PM
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That seems like a lot of cam for a stock bottom end.
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Old 07-27-2012, 09:29 PM
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If you were willing to mock up the motor w the heads, using the cam you got now (with solid lifters)
degree the cam in accuratly and then make some very precise valve to piston clearance and valve open at TDC measurements, you can interpolate what the new cams VTP clearance will be.

VTP clearance is usually closest at around 10deg BTDC and 10deg after TDC.
The exhaust side is the critical spec as the piston and valve chase each other.

May people have notched the piston valve relief deeper and larger radius by hand using a die grinder and 3M discs on a assembled motor with some creative house keeping and masking.
Its not that hard to do.
Any amount of hand releiving needed to get good VTP clearance will be small.
Again the exhaust is the critical factor. You can move the new cam around a bit too to gain clearance.
You need not sweat over this.

When looking at cams this big (duration) you should strongly consider running a mechanical street roller cam.
More power, easy lash setting maintenance. More rpm. These street roller cams are low noise and easy to keep set.
and always out perform a hyd roller.

Last edited by F-BIRD'88; 07-27-2012 at 09:38 PM.
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Old 07-28-2012, 01:40 AM
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Thanks F-bird

Thats great info. That is a good plan. Is it super critical to use a solid lifter for mock up?? I guess I can probaly just buy a couple of solids instead of a hole set. Also what is minimum VTP clearance?
Is there a cam manufacture in particular that sells a "street" solid roller and lifters??
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Old 07-28-2012, 01:54 AM
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Quote:
Originally Posted by prostcelica View Post
Thanks F-bird

Thats great info. That is a good plan. Is it super critical to use a solid lifter for mock up?? I guess I can probaly just buy a couple of solids instead of a hole set. Also what is minimum VTP clearance?
Is there a cam manufacture in particular that sells a "street" solid roller and lifters??
You can buy single lifters. I have used a hydraulic lifter and taken it apart and filled it up w/small washers to make it solid. Either way, just so the lifter cannot collapse. You can reuse it when you check/set the geometry.

0.080" on the intake and 0.100" on the exhaust is considered by many to be a good safe clearance. You will probably find the closest near-miss at the exhaust valve on overlap, when the piston is chasing the exhaust valve back onto its seat.
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