Engine build

[wage92]

Alright guys, getting ready to order my rotating assembly to build my 406 small block. Found a kit that is pretty stout, good for my needs. My question is, the kit will leave me with about 10:1 compression with a .039" gasket. Think this is too high for 93 octane? I have heard all kinds of things and im pretty sure its at the upper end of pump gas but it should be fine...any input?

 

[paratrooper307]

10:1 is generally fine for pump gas, provided that you run good quality fuel and dial in ignition timing properly. Proper timing gives you some leeway. For instance, my Corvette has 11:1 compression and can run regular unleaded if premium is unavailable, but it has computer controlled ignition timing and knock sensors. General wisdom says to run lower compression in heavy, hardworking vehicles like trucks, but 10:1 should be doable. You'll find a variety of opinions either way.

 

[3MAX]

My engine shop set me up with 10.2:1 on my 383. Said I would be fine on 93 octane.

 

[bailey9r]

Lot of variables involved to make it ping or not, as mentioned timing control, the computers retard it way back to get by but at great cost to performance (power and MPG) but the controlling end to pressure is cam timing. overlap bleeds off lots of pressure (centerline and duration) so a torque cam would make a setup self destruct that would have been fine with a "lumpy" rpm cam. Even rear gear adds to the package. A 342 will make more effective cyl pressure than a 411.
I would rather a proper set up 9-1 than a retarded 10-1, and a proper set up 10-1 than a 9-1. if that makes sense to you.

 

[1BEATK5]

Aluminum or iron heads?

 

[wage92]

aluminum heads.

 

[Deuling]

Pics, gimme pics . I think you will like this motor. What rotating assy you going with? Ive heard you should take your crank, flexplate, and harmonic balancer into a shop and have it all balanced together.

 

[wage92]

pics will be up soon, and yes the rotating assembly im getting will be fully balanced. Scat cast crank, probe forged pistons, scat stroker clearanced forged rods, and balancer and flexplate. Found a comp cams cam that will work, and i should have 10:1 compression, with about 8:1 dynamic compression so should run great on 93 octane.

WIll be buying the rotating assembly once i get some more cash, week or two probably.

 

[Deuling]

Bitchin

 

[dyeager535]

If my conventional thinking is right, modern chambered aluminum heads should run fine on 87 Octane right around 10.5:1

I know we have some true engine builders here, but my understanding is that aluminum heads will take/need about a full point of compression over cast iron heads with the same general design (and same octane).

9.5:1 with Vortec heads/chambers on 87 octane is easily done.

As mentioned cam will factor, as will quench. "Deck height" (compression height) + compressed gasket thickness should not exceed .040" optimally. Too much space and combustion efficiency is compromised, which can lead to further problems. Any compromises are just going to require higher octane to "band aid" the real problem, which is inefficiency.

 

[Smokinthehippies]

we need scott to the rescue