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

[Sixt8Chrgr]

My goal is to drive this car to work occassionaly with the factory A/C operational. Cruise to the local cruise ins, do a burnout every so often but this car is basically a cruiser with a little bit of a choppy idle. Should I throw out the brand new cast pistons with new rings for a set of forged pistons and moly rings? Here is the build.

Here is the build
440 .030
Comp cam 268 H
Chrysler Electronic ignition with chrome box
750 Holley
Headers and H pipe
Steel Crank
452 heads with the valves back cut and the heads with a three angle valve job
3.23 rear gears
Automatic tranny
Eddy performer RPM intake

The only reason that I can think of to do the above is if I want to change out the heads and build the motor more aggressively, and to get more horepoer now. My motor builder tells me that I can get about 30 more hp with better pistons. The cost is around $500...does not seem like a good payback. Another good reason to do this now is because the motor is apart. Any advice is appreciated.

[b5blue]

Are the pistons 9 or 9.5 to 1 or so? If so keep and use them you'll be fine.   

[Sixt8Chrgr]

I dont know to be honest.

Another note that I did not mention...the pistons and rings came with the motor and head when I bought it all. So I have very little in the pistons and rings.

The reason I was thinking about replacing them is if I wanted to put Eddy heads on the car sometime in the future and "hop" it up some. But probably will not.

Thanks

[BSB67]

You first need to find out what the compression height is of the cast pistons.  There are some very low compression pistons out there that you don't want to use.

[Sixt8Chrgr]

ok

[Challenger340]

I do not know of any stock Cast rebuilder Pistons, that have sufficient Comp Distance for ANY performance whatsoever.

Get the Forged slugs !

[Sixt8Chrgr]

Just talked to the motor builder and the cast pistons will deliver a compression ratio of 8.5:1. I told him to order the forged pistons and get the cr to 9.5:1 or close. Is this correct for my build? I want to burn pump gas.

Thanks,

[BSB67]

The devil is in the details.  I think with that cam you'll be close with to 9.5:1.  You'll need a good quench, 93 octane, and everything else right.  Getting good quench with an open chamber head, flat top piston and standard stroke 440 is difficult if not impossible.  I think you'll need a dish or reverse dome piston.  Either you need to trust your engine builder, our you will need to get into the weeds on this.

[Sixt8Chrgr]

I will get into some of the weeds on this, but not many. Will have to trust him somewhat.

Thanks

[1Bad70Charger]

Just talked to the motor builder and the cast pistons will deliver a compression ratio of 8.5:1. I told him to order the forged pistons and get the cr to 9.5:1 or close. Is this correct for my build? I want to burn pump gas.

Thanks,

If your engine builder knows what he is doing running 10 to 1 compression on your 440 engine is a no brainer and yes, 9:5 to 1 will allow you to run pump gas (stick with 93 if you have it).

I would tell him to order the proper forged pistons to get you as close to 10 to 1 compression as that is where you really want to be on a decent pump gas performance street engine. 

[Sixt8Chrgr]

That is what I told him to do.

He knows what he is doing. He builds race engines for dirt track cars in Mooresville NC and also street engines for Lee Hodge of Hodge Restorations out of Inman SC.

The guy has a dyno at his shop along with all the machines to do all the work to the heads, block etc. I am not worried about his capabilities. I have been just trying to use as many parts from my original engine purchase as possible. If i would have left it up to him he would have built a real nice roller motor, but I just did not want to spend that much money.

Thanks for all the help and I will keep everyone posted. Once we have the dyno sheets I will post them up here.

Lawrence

[BSB67]

I don't think that you can get away with 10:1 CR, iron head and that small camshaft running on pump gas

[b5blue]

Agree, you will need to pull a lot of timing out and that costs power. Fuel is only getting worse! (Pinging/knocking is the problem) I can run 89-93 @ 9.5 to one with iron (346's) heads but you have to adjust the dist. for it.   

[Sixt8Chrgr]

So are you recommending building to a less CR? I don't understand what you are saying.

[1Bad70Charger]

So are you recommending building to a less CR? I don't understand what you are saying.

The other poster can confirm what his opinion is but i think its clear that he does not think with your iron heads and small cam, etc., that he would not consider running more that 9:5 to 1 compression on pump gas, and I can tell you from his other posts he CERTAINLY is more knowledgeable than me when it comes to the issue at hand.

I just know that 10 to 1 is always a no brainer for a pump gas performance engine, but that is on an engine that is built with the purpose of being able to handle that compression on pump gas, and your engine is not being built that way, like at 10 to 1 crate engine would be.  As your doing I would just follow your engine builders advice as he seems like he really knows what he is doing and best of luck with everything!  

[b5blue]

The Mopar B/RB book explained that compression is determined (limited) buy fuel octane, it is effected by iron or aluminum heads as they move heat away from the combustion chamber at different rates. So 10 to 1 is fine for aluminum (with today's fuel) but high for iron.

[Sixt8Chrgr]

I was wondering why aluminum heads can handle more compression as compared to iron heads now I know.

I will confirm that the builder is moving towards 9.5:1. Thanks for the clarifications.

[BSB67]

So are you recommending building to a less CR? I don't understand what you are saying.

The other poster can confirm what his opinion is but i think its clear that he does not think with your iron heads and small cam, etc., that he would not consider running more that 9:5 to 1 compression on pump gas, and I can tell you from his other posts he CERTAINLY is more knowledgeable than me when it comes to the issue at hand.

I just know that 10 to 1 is always a no brainer for a pump gas performance engine, but that is on an engine that is built with the purpose of being able to handle that compression on pump gas, and your engine is not being built that way, like at 10 to 1 crate engine would be.  As your doing I would just follow your engine builders advice as he seems like he really knows what he is doing and best of luck with everything!  

Its the early intake valve closing that will drive the cylinder pressure up.  I would guess that it will have a cranking cylinder pressure of 160 psi + which is on the edger with iron head and pump gas in my experience.  Plus if it is a true flat top, it won't have the help of good quench.  Put a MP 509 cam in it and you would be fine (on detonation) but might not like the drivability.

[Sixt8Chrgr]

So are you recommending building to a less CR? I don't understand what you are saying.

The other poster can confirm what his opinion is but i think its clear that he does not think with your iron heads and small cam, etc., that he would not consider running more that 9:5 to 1 compression on pump gas, and I can tell you from his other posts he CERTAINLY is more knowledgeable than me when it comes to the issue at hand.

I just know that 10 to 1 is always a no brainer for a pump gas performance engine, but that is on an engine that is built with the purpose of being able to handle that compression on pump gas, and your engine is not being built that way, like at 10 to 1 crate engine would be.  As your doing I would just follow your engine builders advice as he seems like he really knows what he is doing and best of luck with everything!  

Its the early intake valve closing that will drive the cylinder pressure up.  I would guess that it will have a cranking cylinder pressure of 160 psi + which is on the edger with iron head and pump gas in my experience.  Plus if it is a true flat top, it won't have the help of good quench.  Put a MP 509 cam in it and you would be fine (on detonation) but might not like the drivability.

I have alrady bought the cam and motor is not far from being finished. We will see what I have shortly.

[b5blue]

My car being a drag racer had a 509 in a bone stock 69 short block with closed chamber heads (heavy ported) and it was a cantankerous beast under 2k RPM, pulling the TM7 high rise off and using a six-pack helped a lot but idle was epileptic at best. With a 3.23 rear gear I owned anything over 60 mph though, I routinely spanked high end autos trying to mess with me on the interstate (my kids called it "warping") up to 110-120MPH. It was very fussy about who I bought gas from and after 5-6 years I grew very tired of the dryer full of coffee cans idle. I like my easy to live with 268/284 cam much better with 9.5 and open chamber 346 heads, still plenty of bottom end and power for the street.  

[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?

[b5blue]

I'm going by and built my engine using Mopar Performance B/RB Big Block book. The cam I have is the old Road Runner grind. Until I got a dist curved and adjusted for my build I chased knock/ping, with bone stock barely "surfaced" (not cut) 346 heads and .060 over-boar pistons spec. @ 9.5 to one. (speed pro's)   

[Sixt8Chrgr]

Ron (Firefighter) helped me pick out this 268H cam. It is slightly larger than the stock 440 cam but best I can tell it is just a more modern grind. Similar thought process as the modern L-79 grind in my Corvette. Very similar to the old style but just some technology added for better driveability with today's gas.

I don't want a idle that is going to shake the fenders off the car and I don't want to be adding octane booster. This car is a street cruiser with factory A/C that I intend on using frequently. I did want some choppy idle but nothing crazy. I THINK I have what I want but will tell soon.

Thanks

[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

[b5blue]

That is perfection in my book, should handle mid grade @ 89 octane if needed. 

[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.