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Intake centerline question

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Curt
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Intake centerline question - Page 2 Empty Re: Intake centerline question

Post  Rickybobby85 January 4th 2015, 3:17 pm

Curt wrote:
Rickybobby85 wrote:
Thank you for the reply. I apologize if we may have gotten off on the wrong foot.

That is the only foot to get off with when being spoken to by Randy. No need to apologize to him. He's almost like an "Ed", except with knowledge.


WELCOME!  pirat

Lol that's certainly good to know. I wish I had started this stuff earlier so I had even a fraction of that knowledge lol. And thank you for the welcome!

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Post  manofmerc January 6th 2015, 7:56 am

Is there some way to contact the engine builder? I imagine not .Before changing cams or anything radical you need to see if the pistons have been notched for your larger 2.19 valves .If the engine isn't in the car I would pull a head off and look at the pistons to see if they have been cut for your bigger valves .This way you will know for sure .And at the same time you can look at the heads and see what was done to them .Another possibility is a bore scope .You can remove a sparkplug and look inside the cylinder with the piston at tdc to see if has notches added they would be easy to see .Personally I would want to know what was in my engine .The cost of gaskets ($100) would go a long way towards having more confidence in my engine even if you don't change cams .And If it runs good I would leave that cam in there for now .If you change cams then you have you break the new one in check piston to valve clearance valve spring retainer to top of valve guide clearance etc. etc..Find out what you got before you change anything .Doug Cool

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Post  DaveMcLain January 6th 2015, 8:56 am

Rickybobby85 wrote:
DaveMcLain wrote:Most of the time the closest valve to piston event does NOT happen at overlap but about 10 or so degrees before TDC for the exhaust and 10 or so degrees after TDC for the intake valve more or less just depending on the cam as well as its installed centerline(a very big factor).  Going to a cam with more duration can greatly reduce the valve to piston clearance even if the maximum lift is the same or less.  The same goes for advancing the cam to a lower intake center line value in other words, moving from an ICL of 110 to 102 with the same cam would GREATLY reduce the valve to piston clearance so let's just say that your engine was put together using the 8 degree retard factory timing set your intake centerline could be 114 not 106 and that could be why the current cam could be clearing right now.




Thank you for the reply. That is certainly an interesting theory. I guess since all this is new to me it's absolutely mind boggling that 8 degrees has that big of an effect on clearance. Right about now I'm definitely feeling a bit "in over my head" with this so I feel like some educational material is in the near future for me. I guess at this point since the cam is in there, it runs good and makes good power I'm going to leave it alone until I get a good grasp on this and can make educated decisions instead of seat of the pants guesses. Lol

Yours or really any engine sitting on a stand where you can see things a degree wheel and a dial indicator can become a great learning tool. It can be very interesting to actually see where the piston really is in the bore when various valve events actually happen. A long time ago I was helping a friend build a blown alcohol 350 Chevy engine for his S-10. We worked on it every Wednesday over a winter and learned a lot. When we installed the cam and degree'ed it in he was astounded at the position of the piston on the power stroke when the exhaust valve was well off of its seat and dumping the cylinder pressure. It was only about an inch or so down from the deck and he felt that couldn't be right. Yet it agreed with the cam card information. "But we have a 3.48 stroke"! "We go through all of these gyrations to fill the cylinder and compress it yet we only get power for about an inch of that movement"! The engine ran good though, 8.81 in a 3200lb pickup.

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Post  capri-sun January 7th 2015, 9:53 pm

I like a bullet cam ,, 590/610 ,,,,272/292 110 cl ,, sounds good in a STOCK 460 factory rebuild crate motor ,, dove c heads,, jmo
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Post  IDT-572 January 8th 2015, 10:02 am

Just clay up what you have now and check the radial clearance on the valve notch and report back. We will be happy to help you.

Myself I would probably pull the separation back to a 106 installed on a 104, same .050 numbers you picked for the second cam, if all works out on clearance, and if the rough idle wont bother you.
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Post  gt350hr January 8th 2015, 2:30 pm

A C8 head with a 2.19 valve should have the intake valve about .100 below the deck so a cam with .180 (ish) lift with a .040 gasket would have the pist .040 below the gasket. At that point the standard cast piston valve relief would be ok. Most aftermarket pistons are designed for an intake opening at .050 number of 30. Certainly a less I.O number would result in more piston to valve especially on flat tappet cams .
(the other) Randy

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Post  rmcomprandy January 8th 2015, 8:15 pm

IDT-572 wrote:Just clay up what you have now and check the radial clearance on the valve notch and report back. We will be happy to help you.

Myself I would probably pull the separation back to a 106 installed on a 104, same .050 numbers you picked for the second cam, if all works out on clearance, and if the rough idle wont bother you.

YES ... radial clearance is usually the problem with a big valve and OEM replacement pistons ... not depth.

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Post  Rickybobby85 January 10th 2015, 9:26 am

Fellas it'll be a while before I can pull the heads to actually clay it up (like spring actually). These single digit temps make it unbearable to do anything really. So in the meantime I'm just going to leave it be and focus on rewiring the whole car when temps are bearable to do so. Putting it on an arc switch panel while attempting to keep the headlights on the factory switches while discarding any and all parts of the factory harness that dont contribute to anything. Fun times.

So does anyone have any reccomendations to any educational material regarding cams/valvetrain geometry and all that stuff? When it comes to rebuilding/replacing parts it's not so much of a task, but learning why and when to use certain parts and making them work in harmony is a foreign concept for me. I figure a person's greatest weapon is knowledge and if I plan on keeping this car and going faster and faster, knowledge is key.

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