Valve to piston clearance?

[dartfreak75]

My goal would simply be to have fun.

Very true!! I'm having fun just learning about it. Knowledge is power. I cant wait to have that knowledge pay off behind the wheel. ;)

 

[RustyRatRod]

Thanks rusty!! I appreciate your help that is a huge relief. Iv been up reading and studying about this since about 5 am lol
Do you think that will be a pretty combo?

It's a mild cam so it should run well in a 318. I would still verify like crackedback said, because the last thing you want is disaster. But if I had to sling it together without checking, I wouldn't lose any sleep. lol

 

[nm9stheham]

You gotta be a bit more careful with fast ramp camps like a VooDoo... it gets the valve open a lot faster. At the .050" lobe lift points, a 262 fast ramp cam will be more like a 272 or 275 for a medium rate cam, and like an even higher duration for a really slooow ramp cam.

(But eyebrows are easy to cut into cast pistons....!)

 

[70aarcuda]

on the kb 846 the valve notches are .243 deep

I have a set of 847 dish....got all the parts including a block that is ready to go...need to balance the end and it cane be assembled...

dam rings are expensive

 

[stumblinhorse]

I will give you stuff that I have learned. Your 302 stock springs are prolly a little light for that cam.

 

[dartfreak75]

I will give you stuff that I have learned. Your 302 stock springs are prolly a little light for that cam.

That's already taken care of my friend!! Thanks for the heads up tho.

 

[AJ/FormS]

OK just asking, but
302 heads are the fast-burns right?
If that's right, then you are so close to having a tight-Q situation, all you need to do is get the pistons a little closer to the top of the bores and run the .028 gasket.
IIRC the KB 167s will get you close to -.012. That plus the .028s will get you .040 about as good as it gets.
With the tight-Q comes a more efficient design,. Usually followed by a snappier engine and a little more low-rpm torque. This is usually followed by more mpgs, because you cn run a little less gear and not so much TC..
Now your Q-situation totals .030 plus .039=.069; Which with closed-chamber heads, I have read/heard , is possibly inviting detonation.
If it was my project, I concentrate on the either more Q or less but , I have heard that the troublesome zone is .050 to .080, and at .069 you would be right in the middle of it.

 

[dartfreak75]

OK just asking, but
302 heads are the fast-burns right?
If that's right, then you are so close to having a tight-Q situation, all you need to do is get the pistons a little closer to the top of the bores and run the .028 gasket.
IIRC the KB 167s will get you close to -.012. That plus the .028s will get you .040 about as good as it gets.
With the tight-Q comes a more efficient design,. Usually followed by a snappier engine and a little more low-rpm torque. This is usually followed by more mpgs, because you cn run a little less gear and not so much TC..
Now your Q-situation totals .030 plus .039=.069; Which with closed-chamber heads, I have read/heard , is possibly inviting detonation.
If it was my project, I concentrate on the either more Q or less but , I have heard that the troublesome zone is .050 to .080, and at .069 you would be right in the middle of it.

This is good info!!
So getting the piston closer to the head would reduce the risk of detonation?? You lost me there. I'm sorry I dont know much about quench and detonation yet. I'm just shooting for a 9:5 scr and the combo above is how I got there.
You are correct about the 167s and as much as I'd love to go that route they are out of my price range.

 

[RustyRatRod]

This is good info!!
So getting the piston closer to the head would reduce the risk of detonation?? You lost me there. I'm sorry I dont know much about quench and detonation yet. I'm just shooting for a 9:5 scr and the combo above is how I got there.
You are correct about the 167s and as much as I'd love to go that route they are out of my price range.

Yes, as quench increases, the risk for detonation goes down. The added turbulence from quench has a cooling effect on combustion and lower temperatures, thereby reducing detonation.

But IMHO, with your combo, it's splitting hairs, because that cam with 9.5 SCR will not build enough cylinder pressure to worry about. With 220 and 226 degrees duration, even with a 112 LSA, I think you'll be fine. The stock cam was what? like 190 or so degrees duration @.050? Maybe less. Even though it is a small cam, it's still a big increase from stock. I am sure AJ can pull out his computer and give you some cylinder pressure numbers.

In short, what I am getting at is, you will likely not need quench to get to where you want. Yes, you can go to the trouble to make it happen, but IMO it will not really garner you a thing.

 

[dartfreak75]

The dcr with that cam would be 7.96 with a dynamic cranking pressure of 151.85. If that is the cylinder pressure that you are referring to

 

[AJ/FormS]

This is good info!!
So getting the piston closer to the head would reduce the risk of detonation?? You lost me there. I'm sorry I dont know much about quench and detonation yet. I'm just shooting for a 9:5 scr and the combo above is how I got there.
You are correct about the 167s and as much as I'd love to go that route they are out of my price range.

So is race gas mixed in every tank, then.
And if you have to choke the timing she will become a dog.
The 167s have a compression distance of 1.810. Any other flat-top with at least that much, to perhaps 1.930 would be good.
Again, if it was mine, I would try very hard to keep the Q out of the .050 to .080 zone. And try very hard to get it into the .035 to .045 zone.
Just so you know, I adjusted my 367 to .039Q, and with a Hughes 270/276/110/53overlap cam (223/230@.050) and a final drive ratio of 1.97, she returned 32mpg,point-to-point, traveling at speeds between 65 and 85; for 600 miles.
At 9.5 Scr you will be pushing 160psi at sealevel. IMO, you can't afford to push your luck with Q in that zone.
Quench doesn't care how you get it. It can be zero-deck and .039 gasket or pistons down .011 and .028 gasket.
Once the final compression ratio is known, you may have to re-adjust the cam's Ica to reduce the cylinder pressure to run on pumpgas. You may have to run the next bigger size cam, or a cam with slower ramps, re-time the 262, get the same cam on a 108Lsa, or shave the pistons a bit on the sparkplug side.
Or you can bolt it all together with the pistons down .030 and run a superfat gasket .050, or thicker. That will solve your Q, while simultaneously dropping your Scr.......to about 9.2 and cylinder pressure falling to 154psi. Now you are out of the danger zone......... But it kindof defeats the purpose of those heads,lol

 

[dartfreak75]

So is race gas mixed in every tank, then.
And if you have to choke the timing she will become a dog.
The 167s have a compression distance of 1.810. Any other flat-top with at least that much, to perhaps 1.930 would be good.
Again, if it was mine, I would try very hard to keep the Q out of the .050 to .080 zone. And try very hard to get it into the .035 to .045 zone.
Just so you know, I adjusted my 367 to .039Q, and with a Hughes 270/276/110/53overlap cam (223/230@.050) and a final drive ratio of 1.97, she returned 32mpg,point-to-point, traveling at speeds between 65 and 85; for 600 miles.

Wouldn't that create more valve clearance issues?
So your saying I would need to run race fuel with a 9.5 compression engine? But not with what your talking about? I ran the numbers with the 167 pistons and it put me a ways about 10:1 and high 8s to 9s dcr that sounds more like a pump gas issue that a 7.9 dcr. I'm I wrong?

 

[dartfreak75]

The build combo in mind is a 318 bored .040 over with h814cp speed pro piston it's a true flat top no relief cuts the block will be cut .037 to get the piston. 030 in the hole. I will be using a regular felpro blue gasket (.04-.045) the heads will be cut around .005-.01 just enough to clean them and make sure they are flat.
The heads are 302 heads with std sized valves and this cam. And the cam will be set straight up dot to dot. No additional advance

View attachment 1715252312

After further research I may be better off with the 526 pistons they have the exact same listed weight as the factory pistons and they are less expensive than the 814s and they only have a compression height difference of .01 that's like a .2 change in my scr. They are 180 dollars cheaper. That's a huge difference in my tight of a budget.

 

[RustyRatRod]

Damn. I am done. Good luck. I sure hope it comes together good for you.

 

[AJ/FormS]

IMO you are concentrating too hard on Scr, and not paying enough attention to Quench and Dcr. Scr is just a means to an end. Cylinder pressure is the target. With tight-Q you can run about 5 psi more than on the loose end of the scale. If your Q runs into the dangerzone, you will have to drop another 5psi. Therefore, you can run;160psi with tight-Q, 155 with loose-Q, and 150 with the Q in the dangerzone. All other things being equal, the absolute power difference, from 150 to 160, ain't all that much. But, the part-throttle difference and fuel efficiency can be remarkable.
Better IMO, to be tight on the Q, and adjust the pressure by other means; principally the ICA or the piston crown shape.
ICa is first chosen by your cam specs, and then adjusted by the installed centerline.
Cheaper pistons, if .010 deeper in the hole, could get you to .079Q, with the .039 gaskets. This is at the bottom of the out-of-danger zone., as to detonation.
But I see an opportunity here; if you can get the decks cut to zero or near zero, with the cash savings,then you get your Q back into the zone.
Your target Dcr is no more than 8/1 @160psi,with tight-Q
10.2Scr will not work with the 262 cam as the cylinder pressure, depending on your altitude, is creeping up over 170psi; you would need an Ica of 66* or a bit more, to bring it down to 160pi depending on the installed centerline. You might be able to hit that with a 268 to 272 cam.
However, if the pistons come without eyebrows, you may spend the savings on putting them in later.

I have had good success with the .039FelPros. I like those gaskets and would strive to use them. That means my pistons could be no deeper than .011. I would do whatever it took to get them at least that high. If I had to cut the decks, then I would target zero. If the 262 Voodoo wouldn't work then for a few bucks more, I would get a custom cam.Or I would reshape the crowns.
If I had to fit into .500 lift for those heads then a custom cam would get me there. If I cut the decks, then there will be more machining required
P/V clearance is checked last.
If the pistons do not have eyebrows, then they will likely need them...... if not today, then for the next cam. You might as well plan ahead. You can cut the eyebrows, one atta time, with the heads mounted, snugged, but not torqued.
If your pistons already have the eyebrows, you may be money ahead, but I can almost guarantee they will be bigger than they need to be for the 262 Voodoo.
Sometimes more is less.
Sometimes a little more money spent on an exact-fit piston, will save you a lotta money on various machinings, therefore actually costing you less.
I think KB performance actually has a teener piston on the books with an .050 Quench-pad on them.I don't see them in my ancient catalog. These will pop up above the deck and you will have to custom fit them. These are the ones I would get. No block machining, no head machining, no intake machining,pre-cut eyebrows, and all the chunks fit together like stock.

 

[nm9stheham]

Wouldn't that create more valve clearance issues?
So your saying I would need to run race fuel with a 9.5 compression engine? But not with what your talking about? I ran the numbers with the 167 pistons and it put me a ways about 10:1 and high 8s to 9s dcr that sounds more like a pump gas issue that a 7.9 dcr. I'm I wrong?

Yes, that DCR number is incorrect. You're using the .050" ICA fo 38 degrees , not the advertised ICA of 59 degrees. Lunati does not list the advertised ICA on their cam card, you have to figure it out..... I think someone already helped with that.
Use the 59 degree ICA, and your DCR will come in where it should... right at 8.0. That is with no block decking and just a clean up shave on the heads.

Sometimes more is less.
Sometimes a little more money spent on an exact-fit piston, will save you a lotta money on various machinings, therefore actually costing you less.
I think KB performance actually has a teener piston on the books with an .050 Quench-pad on them.I don't see them in my ancient catalog. These will pop up above the deck and you will have to custom fit them. These are the ones I would get. No block machining, no head machining, no intake machining,pre-cut eyebrows, and all the chunks fit together like stock.

A lot of good info above, and a plan that I advocate for this case. The issue is the re-balance cost. Working on solving that with 273 pins.....

 

[nm9stheham]

FWIW, I worked out the pistons to valve clearance for the OP's combination at TDC; that is easy to figure since the .050" intake opening angle occurs right at TDC. I won't go over all the numbers (unless someone wants to see them), but basically, with that cam and that combination and using a 675 head as an example head, the valve-to-piston clearance is going to be in the .075-.085" range at TDC.

Since the valve is moving faster than the piston for the first 5 degrees or so past TDC, then that small clearance gap is going close up tighter after passing TDC. They might even touch. So it looks to me like eyebrows are 100% necessary here. They probably can be only .100" deep, but still needed.

 

[dartfreak75]

FWIW, I worked out the pistons to valve clearance for the OP's combination at TDC; that is easy to figure since the .050" intake opening angle occurs right at TDC. I won't go over all the numbers (unless someone wants to see them), but basically, with that cam and that combination and using a 675 head as an example head, the valve-to-piston clearance is going to be in the .075-.085" range at TDC.

Since the valve is moving faster than the piston for the first 5 degrees or so past TDC, then that small clearance gap is going close up tighter after passing TDC. They might even touch. So it looks to me like eyebrows are 100% necessary here. They probably can be only .100" deep, but still needed.

Thanks nm9stheham I appreciate all your work in this topic.

 

[nm9stheham]

Your'e welcome! Tryin' to do it as well as I can to help out.

 

[Marcohotrod]

I think we need to add in how far the valve is recessed in the head from the deck surface of the head. calculating .075-.085 is assuming all the valves backs are even with the surface of the head-are they?

 

[nm9stheham]

I think we need to add in how far the valve is recessed in the head from the deck surface of the head. calculating .075-.085 is assuming all the valves backs are even with the surface of the head-are they?

Actually, I worked all that in.

1. I started with how far the lowest edge of the intake valve sets above the head surface when closed; measured that on a 675 head to get a starting number.
2. Then used .075" valve lift since the lobe lift at .050" occurs within a couple of degrees of TDC. Then reduced that .075" by the cosine of the valve angle.
3. Subtract 2 from 1 to get the approximate intake valve-to-head- surface distance at TDC.
4. Then work in how far below the head surface the piston top is.

If the .050" lobe lift number was not conveniently right at TDC, then this gets hard/impossible to work out on paper without knowing the exact cam lift vs crank angles.

 

[Marcohotrod]

cool info, are 302 and 675 heads about the same? and so the intake back is above the head deck by about how much? and dot to dot is within a range, then there is checking that by degreeing measuring

 

[nm9stheham]

I truly appreciate your interest in making this accurate, MH. The closed intake valve minimum distance relative to the surface of a 675 head was .090". I asked for the same measurement for the 302 heads but did not get an answer. I THINK the valve position is pretty consistent head type to head type for the same sized valves. But, yes that is a variable that I can't answer without a similar measurement from the 302 head.

What I tried to do was get an answer good enough to see the valves were going to clear the piston heads in the OP's proposed setup by quite a bit, or was it going to be close. If it is <.100" at TDC, I would expect it to be much too close at some number of crank degrees after that. Cam timing can make it better or worse, but I think some eyebrows are needed here. Does not surprise me.... my '68 273 2 BBL pistons that set right at zero-deck had shallow eyebrows, and that was for the stock cam with significantly lower lift and duration.

Best I can do on paper with my parts on hand, and a few other anecdotal references. If I had the actual detailed cam profile, then this would be a snap to accurately compute the clearances at all crank angles in a spreadsheet.

 

[AJ/FormS]

I can tell you one thing;
If you put a brick on the gas pedal of a 74 Duster with a 318; it will rev up, float the valves, and send all 8 exhaust valves into the crowns. It will sit there like that for 20 minutes or so they said, until one brave soul plucked the brick off. The revs came down, it stalled, and would not restart.
I got the car back for the promised $50. I pulled the heads and put a good set on, that I had kicking around, then I took it for a spin. That was 1978.
With the heads off, I could clearly see the fresh divots in the pistons.
I still have those heads, but I threw those bent valves away.
So, they say those Mopar lifters have a range of .135 IIRC.
I guess it was too much range or not enough deck clearance,lol

FWI
many years later(2000) I took that engine apart for inspection, with an eye towards making it my winter engine. There was nothing else wrong with it, so into my Barracuda it went in winter of 2001. Five winters later, I installed into my sons D-100. About 8 years later it came back to me....... again. Anybody need a high-mileage, lo-compression teener, that just won't die?
Be advised, I installed 360 springs on those heads and shimmed them up some. She has been to 5500 many many many times. Yes with the factory cam it was born with, but with the big TQ, TTIs, and 3 inch full-length duals. She liked the 2800TC too. She's my fourth favorite all-time engine, meh;maybe third

 

[BigBlockMopar]

The heads are 302 heads with std sized valves and this cam. And the cam will be set straight up dot to dot. No additional advance

Are you still planning on installing it this way?