Intake centerline question

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Intake centerline question

Post  Rickybobby85 on January 3rd 2015, 2:09 pm

I have a 70 lincoln 460 rebuild stock bottom. C8 heads ported to death with 2.19in/1.76ex valves. Currently running a comp magnum 280h. 530/530 lift, 280/289 duration 110 lobe separation and a 106 intake centerline.
I'm looking at swapping cams because, honestly, I hate the way this cam sounds at idle. Yes, I realize I'm doing this for all the wrong reasons, but I would like the car to not sound like a boat.

I realize with the stock heads im limited in lift options so I was looking at the comp big mutha thumpr 295th7. 530/515 lift, 294/312 duration, 107 libe separation, but a 102 intake centerline.

With that 102 centerline is this thing going to fall on its face in the upper rom reaches or will I be ok? Is this even a cam I should consider for a street strip fox or are these things a gimmick just to get the choppy idle? I know I'm looking at changing for the wrong reasons but I really would like to retain my performance level. Figured it couldnt hurt to ask. Any insight would greatly be appreciated.

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Re: Intake centerline question

Post  rmcomprandy on January 3rd 2015, 6:02 pm

Rickybobby85 wrote:I have a 70 lincoln 460 rebuild stock bottom. C8 heads ported to death with 2.19in/1.76ex valves. Currently running a comp magnum 280h. 530/530 lift, 280/289 duration 110 lobe separation and a 106 intake centerline.
I'm looking at swapping cams because, honestly, I hate the way this cam sounds at idle. Yes, I realize I'm doing this for all the wrong reasons, but I would like the car to not sound like a boat.

I realize with the stock heads im limited in lift options so I was looking at the comp big mutha thumpr 295th7. 530/515 lift, 294/312 duration, 107 libe separation, but a 102 intake centerline.

With that 102 centerline is this thing going to fall on its face in the upper rom reaches or will I be ok? Is this even a cam I should consider for a street strip fox or are these things a gimmick just to get the choppy idle? I know I'm looking at changing for the wrong reasons but I really would like to retain my performance level. Figured it couldnt hurt to ask. Any insight would greatly be appreciated.

70 Lincoln huh...?  242/257 @.050" is way, WAY to big.

The 230 @.050" that you have is way to big so, I know you have absolutely no priority for performance.
I am really surprised that the 2.19" intake valves are not contacting the stock OEM type pistons unless it has a retarded timing set; but, who knows ... certainly I must not.

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Re: Intake centerline question

Post  Rickybobby85 on January 3rd 2015, 7:07 pm

Why thank you for that ever so tongue in cheek-esque reply. Here's the thing, I didn't build the motor. It is the way is was when I bought the car. Car seems to run fine to me. Has great compression all across the board so I'm fairly sure it hasn't had any piston to valve problems. It's my first big block (or carbed motor for that matter) so I assumed, being as strong as it was (feels strong to me) it was well within its limits on camshaft selection. So myyyyyy bad.

I ask these things because I flat out don't know and had assumed I was in the ballpark. Judging by your reply, I suppose I'm not. And that's ok because I'm still learning.

So I respectfully ask your opinion as to what camshaft selection would you reccomend for this car? That's why I'm here is to get help. I mean that's what these sites are for right? If I can't ask the people who eat, sleep, and breath this stuff without getting flamed, then who does one ask?

Thank you

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Re: Intake centerline question

Post  gmsmkr on January 3rd 2015, 7:21 pm

Hi man welcome to the forums lots of great people here.... If there is any more about your combo that you can think of let us know.

What type of pistons.... I assume stock replacement type?

How much port work? Just cause it has it does not mean it is right (port work)

What kind of intake?

Size of carb?

What size tire and rear gear?

Edit: what do you not like about the magnum cam?
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Re: Intake centerline question

Post  butterbean on January 3rd 2015, 7:32 pm

first off Hello Ricky, its sounds like to me that your car runs pretty good with that cam and you have had no issues with piston to valve clearance, so with that said do you know if the pistons have been clearanced for the larger valves?? if you know that then you can go a little bit bigger on cam lift and duration, I know you said that you don't care about performance and you hate the motorboat sound (i hate it to) so let us know more about your combo like carb intake tranny stall ect ect ect
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Re: Intake centerline question

Post  cool40 on January 3rd 2015, 7:40 pm

If you want it to sound good look for more lift too. Be real sure you check valve to piston clearance. This 460 is in a fox body? Lots of good info in the builds section too. Cool
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Re: Intake centerline question

Post  Rickybobby85 on January 3rd 2015, 7:55 pm

Hey guys, thanks. Glad to be here. Here's everythingni have on it. Weiand stealth intake. Holley hp 850 built by aed performance. I sent john dickey everything on the motor and this is what he recommended. Yes factory replacement Pistons. Car rods. Stock crank. Msd pro billet dizzy. Hooker super comp long tubes. Harland sharp rockers, comp guide plates, springs, lifters, and rods. I really cannot elaborate on the port work that was done. All I seen was a receipt for the work. Nor can I speak on if the Pistons were fly cut for the valves. I was just assured they were "ported to death". I haven't had it apart as I'm house hunting and don't have a proper place for a tear down. It really sucks buying stuff second hand fellas. C6 trans w 3500 stall. Rear gear is a 3.55.....for now. All this is in an 87 fox hatch. Of course cam specs are above.

There's nothing inherently wrong with the magnum. It performs just fine by tell of my butt dyno. I really would like to keep the car performing as well as it does or better but the magnum is just too much of a vegetable cam. "Potato potato potato potato" lol. Like I said earlier I was seeking out a cam for the wrong reasons (which is to find one more audibly pleasing), but I mean I would still like the car to run like a raped ape.

Thanks fellas

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Re: Intake centerline question

Post  butterbean on January 3rd 2015, 8:27 pm

Rickybobby85 wrote:Hey guys, thanks. Glad to be here. Here's everythingni have on it. Weiand stealth intake. Holley hp 850 built by aed performance. I sent john dickey everything on the motor and this is what he recommended. Yes factory replacement Pistons. Car rods. Stock crank. Msd pro billet dizzy. Hooker super comp long tubes. Harland sharp rockers, comp guide plates, springs, lifters, and rods. I really cannot elaborate on the port work that was done. All I seen was a receipt for the work. Nor can I speak on if the Pistons were fly cut for the valves. I was just assured they were "ported to death". I haven't had it apart as I'm house hunting and don't have a proper place for a tear down. It really sucks buying stuff second hand fellas. C6 trans w 3500 stall. Rear gear is a 3.55.....for now. All this is in an 87 fox hatch. Of course cam specs are above.

There's nothing inherently wrong with the magnum. It performs just fine by tell of my butt dyno. I really would like to keep the car performing as well as it does or better but the magnum is just too much of a vegetable cam. "Potato potato potato potato" lol. Like I said earlier I was seeking out a cam for the wrong reasons (which is to find one more audibly pleasing), but I mean I would still like the car to run like a raped ape.

Thanks fellas
well I think I would ask if the pistons are stock replacement or aftermarket with or without dish or flat top, do you have to use fuel additive? or just pump gas? sometimes the valve relief's are a little different so you may have enough room to put a bigger cam in it, I've used grinds like .550/.575 and 240/245 @ .050 on the street with good results, looks like you have enough stall and gears for it as well, but it may be to big for the piston to valve clearance, maybe Randy or Scotty can help with this as well but I know them and they are about making the most power and not about the sound of the cam, good luck
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Re: Intake centerline question

Post  gmsmkr on January 3rd 2015, 8:29 pm

A split dur and lift can sounds to me what you are looking for I would get something in the 240 rang on dur and 550+ on lift with a 106CL and it will have the sound you want and still work ok.. I would check piston to valve clearance before I jump to much on the cam.

Beat me to it bean Razz
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Re: Intake centerline question

Post  Rickybobby85 on January 3rd 2015, 9:05 pm

Fellas I guess I'll just pull it apart and see what's going on with it before I buy anything for it. Id be perfectly fine going for max performance with it as long as it sounds at least better than a vegetable cam lol.

Just out of curiosity though, if I wanted to go for max performance for this setup, does anybody have a reccomendation or a part # that has worked for you or maybe been tried and true? If I can't run as nasty a cam as I want, I want it to be as fast as it can be then.

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Re: Intake centerline question

Post  rmcomprandy on January 3rd 2015, 9:12 pm

What you have said in your third post is a whole lot different than the original post which leads one to believe this is simply a REGULAR REBUILT 460 in an everyday street vehicle  but, with a bigger cam ... which it certainly is not simply that.

If you don't know the piston to valve clearance you now have, then anything you use with larger intake opening at 8 degrees after top dead center than what you have is taking a chance.  No one on here wants to take that chance for you but, giving a solid recommendation is not gonna happen without taking a chance.

Here is what is involved:
A 280H lobe, (230/230 @.050"), will have a lobe lift at TDC of .077" installed at 106 centerline or about .133" valve lift with a 1.73/1 rocker arm ratio of which you really don't know you have. If the ramp velocity remains near the same it will lift about .003.5" per degree at the lobe or near .006" at the valve.  About .181" valve lift at 8 degrees after TDC; (about where the valve is closest to the piston).
The pistons HAVE been notched appropriately or contact would happen with a 2.19" diameter intake valve in a C8, C9 or D0 head.

The "Mutha Thumper", (234//249 @.050"), of one size smaller than the "Big Mutha Thumper", (242/257 @.050"), has a valve lift of about .197" at 8 degrees after TDC when installed at 106 intake centerline which puts it closer to the piston.
Without knowing the piston to valve clearance your engine presently has, it is impossible to give you a solid recommendation, other than to keep the intake lobe size near what you have now.
The "Mutha Thumper" will certainly sound rougher because the overlap is much greater and the "Big Muther Thumper", (though maybe bending valves or holing pistons), rougher yet.

We can all make GUESSES if you aren't bothered at all about fixing bent valves.

Something custom IS your best alternative.

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Re: Intake centerline question

Post  Rickybobby85 on January 3rd 2015, 9:46 pm

rmcomprandy wrote:What you have said in your third post is a whole lot different than the original post which leads one to believe this is simply a REGULAR REBUILT 460 in an everyday street vehicle  but, with a bigger cam ... which it certainly is not simply that.

If you don't know the piston to valve clearance you now have, then anything you use with larger intake opening at 8 degrees after top dead center than what you have is taking a chance.  No one on here wants to take that chance for you but, giving a solid recommendation is not gonna happen without taking a chance.

Here is what is involved:
A 280H lobe, (230/230 @.050"), will have a lobe lift at TDC of .077" installed at 106 centerline or about .133" valve lift with a 1.73/1 rocker arm ratio of which you really don't know you have. If the ramp velocity remains near the same it will lift about .003.5" per degree at the lobe or near .006" at the valve.  About .181" valve lift at 8 degrees after TDC; (about where the valve is closest to the piston).
The pistons HAVE been notched appropriately or contact would happen with a 2.19" diameter intake valve in a C8, C9 or D0 head.

The "Mutha Thumper", (234//249 @.050"), of one size smaller than the "Big Mutha Thumper", (242/257 @.050"), has a valve lift of about .197" at 8 degrees after TDC when installed at 106 intake centerline which puts it closer to the piston.
Without knowing the piston to valve clearance your engine presently has, it is impossible to give you a solid recommendation, other than to keep the intake lobe size near what you have now.
The "Mutha Thumper" will certainly sound rougher because the overlap is much greater and the "Big Muther Thumper", (though maybe bending valves or holing pistons), rougher yet.

We can all make GUESSES if you aren't bothered at all about fixing bent valves.

Something custom IS your best alternative.



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

I understand how the first post could be misleading. The top end was worked over but I was told the bottom end was basically a stock rebuild. It sucks buying stuff second hand. And I completely understand about the "guesses". I would certainly clay the top of the piston before I just threw it in and ran it. I might be new to the world of go fast parts but I'm definitely not going to run something before checking it. I had just figured i had enough clearance to run a cam of that nature. Still learning my friend.

So as I understand it, piston to valve clearance is measured at the point of overlap, correct? Is that measurement all that is required, besides all the other engine specs to have a cam custom ground? Or can a cam be ground based off of the specs I have on the 280h just not to exceed the specs of that cam? I'm guessing it would be a smarter play to go ahead and get the clearance but I figured I'd ask.

Thank you


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Re: Intake centerline question

Post  DaveMcLain on January 4th 2015, 10:56 am

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.



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Re: Intake centerline question

Post  Curt on January 4th 2015, 11:41 am

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
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Re: Intake centerline question

Post  Rickybobby85 on January 4th 2015, 2:16 pm

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

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Re: Intake centerline question

Post  Rickybobby85 on January 4th 2015, 2:17 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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You need more info about your engine

Post  manofmerc on January 6th 2015, 6:56 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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Re: Intake centerline question

Post  DaveMcLain on January 6th 2015, 7:56 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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Re: Intake centerline question

Post  capri-sun on January 7th 2015, 8:53 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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Re: Intake centerline question

Post  IDT-572 on January 8th 2015, 9:02 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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Re: Intake centerline question

Post  gt350hr on January 8th 2015, 1:30 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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Re: Intake centerline question

Post  rmcomprandy on January 8th 2015, 7:15 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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Re: Intake centerline question

Post  Rickybobby85 on January 10th 2015, 8:26 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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