Keep my cast pistons and rings or go with forged and moly rings?

[375instroke]

So my motor doesn't ping because it's old?

[BSB67]

A flattop piston even at zero deck with a 452 casting is going to yield a low 9 static compression number.  Nothing to worry about with the XE268 cam. It'll have some rumble at idle yet pull descent vacuum and work fine with a stock tq converter & 3.23 gears.   

The last set of 452's i had measured out at 92cc....that's a lot of chamber volume. 



Ron

Ron - flat top at zero deck w/ 92 cc and a .040 gasket is over 9.8:1.

[firefighter3931]

A flattop piston even at zero deck with a 452 casting is going to yield a low 9 static compression number.   Nothing to worry about with the XE268 cam. It'll have some rumble at idle yet pull descent vacuum and work fine with a stock tq converter & 3.23 gears.  

The last set of 452's i had measured out at 92cc....that's a lot of chamber volume.  



Ron

Ron - flat top at zero deck w/ 92 cc and a .040 gasket is over 9.8:1.

Did you account for the valve reliefs ? Those are usually good for 5-6cc. Most off the shelf "performance" slugs will be at least .015 below deck at their advertised compression height. There's allways the option of going to a thicker head gasket to pull some static compression out of the motor. I'm sure his machinist can figure it out once it's all mocked up. If not, we can do it for him.  


Ron

[firefighter3931]

Some engine math to chew on 

basic combo ; 3.75 stroke x 4.35 bore with 5cc valve relief volume (flat top piston)

(1) 92cc chamber/.040 head gasket/undecked block (.015 in the hole) = 9.27:1
(2) same specs but with a zero deck = 9.55:1
(3) 92cc chamber/.050 head gasket/zero deck = 9.36:1
 
*Any of these combinations would be fine with pump premium fuel, inmo.


Ron

[BSB67]

My original 440HP runs fine on pump gas with full timing and no pinging.  Now is this because the motor has 100,000 miles on it?  The compression is stated as 10.1:1, and it's got the original HP cam and 906 heads.  If I was to rebuild the motor, would it ping then?  I don't get it.  Isn't the 268H cam bigger than the stock HP cam?

Its a couple of reasons.  1) The actual CR is probably 9.6:1.  The few true unaltered 440 hp's that I've measured ranged from 9.5:1 to 9.7:1.  2) The factory cam  builds less cylinder pressure based on intake closing.

The comp cam has faster ramps so the duration at 0.050" is larger.  It is fair to call this a bigger cam.   But cylinder pressure is effected by the intake seat timing, and they are both 268 degrees.  If you assume that the two 268s actually measure the same for both cams, and compare the intake closing (IC) based on their specified intake centerline (ICL) they are considerably different. If you throw in a little chain stretch and wear, the difference in the factory IC is 8 to 10 degrees greater than the comp cam.  Therefore, the factory cam will result in a noticeably lower cylinder pressure than the comp cam with everything else being equal.

The 100,000 miles might make some difference as well.  Altitude and gas quality have an effect too.

My all original 440 hp had an actual 9.65 CR, and with a high performance timing curve and J12Y plugs, it would rattle pretty bad.  That was with Sunoco 94 Ultra at about 700 ft above sea level.

I am curious, do you know for a fact that the cylinder heads have never been removed for a valve grind?  What is you cranking cylinder pressure?

[BSB67]

Some engine math to chew on  

basic combo ; 3.75 stroke x 4.35 bore with 5cc valve relief volume (flat top piston)

(1) 92cc chamber/.040 head gasket/undecked block (.015 in the hole) = 9.27:1
(2) same specs but with a zero deck = 9.55:1
(3) 92cc chamber/.050 head gasket/zero deck = 9.36:1
 
*Any of these combinations would be fine with pump premium fuel, inmo.


Ron

Ron - I'm simply responding to what you stated.  I agree to your numbers w/ 5cc reliefs.  5cc is 0.40 in CR.

[firefighter3931]

Some engine math to chew on  

basic combo ; 3.75 stroke x 4.35 bore with 5cc valve relief volume (flat top piston)

(1) 92cc chamber/.040 head gasket/undecked block (.015 in the hole) = 9.27:1
(2) same specs but with a zero deck = 9.55:1
(3) 92cc chamber/.050 head gasket/zero deck = 9.36:1
 
*Any of these combinations would be fine with pump premium fuel, inmo.


Ron

Ron - I'm simply responding to what you stated.  I agree to your numbers w/ 5cc reliefs.  5cc is 0.40 in CR.

I should have been clearer when i originally made that stement...so technically your estimate is correct. Most performance slug with a 2.065-2.067 compression height will come with aset of valve reliefs. My 446 with the uncut deck had the 2355 speedpro slugs at .020 below deck. We had to square deck it to get it to zero. 

Point taken on the intake closing. The factory roadrunner cam closes the intake valve at 67* ABDC while the XE268 has a closing point of 60* so there is a bit of difference.

My old engine combo with the 2355's at -.020 below deck/92cc 452's/.040 felpro gasket and small crower hyd flat tappet (HDP282) with less than 60* intake closing ran fine on pump premium with 16* initial 36* total timing all in at 2800 rpm.

We just installed the smaller Crower HDP 271 in a similar build 440 and it runs great. No ping and snappy throttle response.  It's a heavy 66 charger with stock converter & 2.76 gears....soon to be upgraded to an 11in 2400 stall and 3.23 suregrip. 



Ron

[BSB67]

Ron - how did you get less than 60 ABDC for the Crower cams?

[firefighter3931]

Ron - how did you get less than 60 ABDC for the Crower cams?

I remember mapping it out many years ago and from my recolection it was just shy of 60*  I had the cam advanced on a 106 icl and it made ~160 psi on a dynamic compression test. With the right AFR & timing curve it ran great. 

The cam card is showing 42* for the i/c event but that is at .050 tappet lift.

http://www.crower.com/misc/cam_spec/cam_finder.php?part_num=32243&x=50&y=10



Ron

[BSB67]

The 282 installed at 106 (i.e. 6 degrees advanced) puts it at 68 ABDC.  I also think the L2355 reliefs are 7 cc, and with them 0.020" in the hole, put it at about 9:1 CR.  That cam and CR would of course be very pump gas friendly.

Your original point is well taken, it is almost impossible to get into trouble with CR/detonation with any flat top stocking piston and 92 cc chamber heads. 

[firefighter3931]

The 282 installed at 106 (i.e. 6 degrees advanced) puts it at 68 ABDC.  I also think the L2355 reliefs are 7 cc, and with them 0.020" in the hole, put it at about 9:1 CR.  That cam and CR would of course be very pump gas friendly.

Your original point is well taken, it is almost impossible to get into trouble with CR/detonation with any flat top stocking piston and 92 cc chamber heads. 

I'll take your word for it on the math (it was many years ago) and yes you're correct...it ran great and had no sign (audible or visual) of detonation. 


Ron

[375instroke]

My original 440HP runs fine on pump gas with full timing and no pinging.  Now is this because the motor has 100,000 miles on it?  The compression is stated as 10.1:1, and it's got the original HP cam and 906 heads.  If I was to rebuild the motor, would it ping then?  I don't get it.  Isn't the 268H cam bigger than the stock HP cam?

I am curious, do you know for a fact that the cylinder heads have never been removed for a valve grind?  What is you cranking cylinder pressure?

The previous owner had no information for me, and told me some things that I know for sure are untrue, like the car has the original Sure-Grip.  It isn't coded for one, and doesn't have one now.  The odometer showed 88,000 miles when I got it, and the car looked like that was true.  It came from back east, and they drove it in Summer only.  The left valve cover isn't right.  It has the spark plug clip for number 7.  The manifolds have been off, and a new exhaust system installed.  The carb was a tiny Edelbrock AFB, the vapor separator and fuel pump were gone, and a tiny electric fuel pump was installed.  The motor was fogged over with a rattle can, but of the right color.  It doesn't look like the motor was apart.  The head gaskets are steel shim.  The motor and trans numbers do match.  This is all I know.