Piston selection

[r15303]

I have a 70 Challenger 440  6 pack with Kieth Black 237 pistons and 6 pack rods.  I want to reduce my compression ratio to about 9.5 or 9.75:1 so I can run on pump gas.  No racing planned.  What pistons do you guys recommend?
Cast vs forged?   

[170cuda]

What heads do you have?

[Tubbed440]

http://www.kb-silvolite.com/performance.php?action=details&P_id=30

With that piston, zero decked, you should be able to run pump gas without too much problems.  If you're running a closed chamber iron head, you might not be able to run more than 32 degrees total advance, but she should still run on pump swill.

If you really feel like you have to change the pistons, then I would personally go with another KB of a different compression height.  If it were me, I'd drive it.   In my book if I changed pistons in a motor, I'd have to tear it all the way down and send the block back to the machin shop, have'm mic the bores and see if the new pistons you've bought would even work.  Most manufacturing specs are pretty tight, but, you might run into a wall clearance issue (too tight / too loose).....but that's the perfectionist in me.

[r15303]

THE HEADS ARE 906

[Tubbed440]

906's are around the 80 cc mark or larger if I'm not mistaken.  So by looking at KB's info, you'd be around 10.2-10.6....which is very pump gas friendly IMO.  Are you having problems with your combo at the moment?

[170cuda]

I think most 906's are around 88cc so it would only be around 9.9. But I could be wrong. Do you run 93 octane in it? If you do it should be ok.

[r15303]

Tubed440 -  The engine is currently torn apart and I want to put it back together but I was having detonation with 93 octane fuel.  I was told I probably have 10:1 + compression which is causing the problem.  Since I don't race I want to solve the detonation problem with a 9.5:1 or so compression.  I dont really need to change the pistons but want to get rid of that detonation.  I read Cryco Psyco's essay (nov. 22, 2005) on engine planning And he thinks holding comp to under 10:1 will run well on pump gas.  Any ideas?

[Tubbed440]

Could have been in your tune.  I ran a similar piston from KB in my 440 with closed chamber heads, zero decked.  Came out to be close to 11.5:1 compression.  I was also running a comp .525 solid cam with around 245 ish @.050 duration too.  Now that I think about it, what cam are you running?  If it's stock cam, then yes, you're going to have to do something different, for sure.  The stocker cam will build more cylinder pressure at lower rpm than the cam that I was running due to less valve overlap, so that would be where the detonation would come in.

[Oldschool]

10:1 should run on pump gas ok.  There could be other factors causing the detonation.  A little too much timing, maybe a little lean on the carb jetting.  Might be as easy as a thicker head gasket and a couple of carb/timing adjustments...       Sure would save you some money.  I run 10.5:1 in my car with no probs on pump gas.  I do have aluminum heads though and that helps a little.  

Or you could just bolt her back together as it was and use this stuff:

http://www.kemcooil.com/product_info.php?pId=61

This stuff is the real deal.  It contains tetrethyl lead, the real McCoy.  A couple of cases would last you for a year or two and at $210.00 you can buy a lot of it before you you get to the amount the new parts and machine work is gonna cost...   I run it in the Beast on days it is above 90* as a precaution.  Never detonates and I am pushing close to 800 HP without power adders...  Also a Be-Cool radiator helps keep it all cooled down..  Just my Old  0.02....        

[r15303]

My cam is a Comp Cam 21-223-4 - apparently a bit hotter than stock.
As far as tune - I'm not sure on timing but when I took the heads off, it looked to me like it was burning rich.  The exhaust valves on the front 6 cylinders were a black color while the two rear cylinder valves looked a brown/tan color like I would expect.  Do you guys think that putting a closer to stock cam in would help detonation??  With the current cam the idle was rough and I want it smoother.  Don't care about racing.  That 440-6 will put out more horses than I'll need!!!   

[170cuda]

A smaller cam will make the detonation worse. The less valve overlap creates more cylinder pressure.

[moper]

What head gaskets were used when you took it apart? The blue Felpros? Or a thin steel one?

[r15303]

The head gaskets were a black color, fairly thin, (not blue) and the only metal was around the perimeter of the cylinders.

[Tubbed440]

They sound like cometics, you'd have to get a part number or a pair of calipers and measure to find out what thickness they are.

[Chryco Psycho]

cometic are all metal this sounds more like a black composition gasket