Piston selection

[moper]

Sounds like Victor/Detroit, which are also thick like Fel Pro's. I think the detonation issue is because the cylinder pressure is too high. You're right in wanting it to be detonation free, but I'd suggest going about it differently. Your cam choice is a grind that is primarilyl designed to make cylinder pressure in an engine that may not have enough static ratio. The fix here IMO is swapping the cam, but not with a stock one like your other post. But with a slightly bigger performance grind. Something that will bleed off some pressure at lower engine speeds. I've had good results using the Comp Cams Magnum 292 on mild 440s. It will idle decent, but will require you to tune the six pack center carb a bit to get a good idle. If you have power brakes, they will be affected by that negatively tho. As an alternative, you can alse have your heads' chambers polished and slightly enlarged. That will help reduce the detonation and static ratio. And I would definately run the Felpro gaskets. Cometics can solve the issue too, but you will need to have the block and heads milled to the right surface finish for them.

[r15303]

Thanks Moper - I do want to use Felpro gaskets when I put it back together.  I do notice the brake problem with my current cam - one of the reasons I want to change cams and since I'm changing, I want to correct the brake issue and improve the idle, and the detonation too.  Yes - I want it all!!!  If I reduce the comperssion and change to a "stock" cam, like the comp cam 21-215-4, do you think that will solve the brake, detonation, idle problems??

[moper]

Well, the cam you have should not have any power brake issues, or a ragged idle. For comparison, a 383 project form 4 years ago has KB flat tops, decently milled 906s and measured compression is 9.8:1. With the XE268, it idles at 650 rpm silky smooth, and pulls 13" of vaccum. That's plenty for power brakes. A 440 would pull more vaccum, and be smoother due to the inches. If you have over 10:1, you will get better idle, better power brakes, and more tendancy to detonate. The trick is getting the balance of all 3. Best case scenario witha  stock cam, it may not detonate as much because the cam's design isnt as modern, but will give up a little power over the XE. I'd also suggest you seriously look at your igition. If the curve is not set properly, you will get detonation and ping. And once it starts, it's very hard to get it to stop. I have modified several distributors simply to delay the ignition advance because of lower stalls or mild gearing combined with a high cylinder pressure and pump fuel.

[r15303]

Thanks Moper  I'm beginning to get the concept now.  Just read a good article in the latest Engine Masters magazine dealing with getting the most power from pump gas.  It goes into many of the same issues you are talking about.  I'm learning - slowly 

[moper]

fast or slow doesnt amtter, so long as we all learn...lol. for me, I alwyas have to "take the less traveled path" the first time. Then when I'm doing it over, I can say I "learned" ...lol