318 Build

[Davidrad]

I'm going to find a 360 and install a set of domed pistons. Seems like the easiest thing to do. Raising the CR isn't really an issue, I was just hoping for bolt-ons. My normal machine shop only charges me about $150 bucks to mill down the pair of heads if I go that route. It's the fitment issues, springs, rods, rockers that scare me now. Dealing with smog motors and having a piston so far down in the hole is bound to create problems. I've learned a ton by this thread, and been scared a bit by this thread. DCR isn't something you hear about but it makes more sense as a measurement that SCR. You guys are the best and thanks for putting up with me.

 

[rumblefish360]

I haven't read through this whole thread yet but aren't the open chambered 360 heads going backwards? Wouldn't #302 or a closed chamber 273 head be easier to build compression and quench? I think porting small chamber heads is a better idea than milling open chamber heads to get your 9-1 ratio. You mill the heads and the intake won't fit without milling and the two will always have to be used together.

True on the matched Intake and head mill parring. But he will never have any quench since the stock slugs are way in the hole.

 

[j par]

AGAIN- GO FOR IT!!
ad 410 gears and fry tires at will
thank you and please come again....

 

[j par]

Better yet step up to the plate and get a 4-speed fry tires with what you have...

 

[nm9stheham]

I haven't read through this whole thread yet but aren't the open chambered 360 heads going backwards? Wouldn't #302 or a closed chamber 273 head be easier to build compression and quench? I think porting small chamber heads is a better idea than milling open chamber heads to get your 9-1 ratio. You mill the heads and the intake won't fit without milling and the two will always have to be used together.

I was just trying to run with the idea of the OP to use the 308 heads and get the benefit of the better flow of those, since that is what he wanted to do initially. I actually find the idea intriguing, of milling the snot out of some 308's and putting them on a stock 318; there are all sorts of guys wanting to use their 318 short blocks and do what the OP wants.

Milling .090"-.100" from the 308's may be doable. I have read of guys milling that much off of the open chamber heads and it basically takes all of the shallow 'open' section of the open chamber completely out of the head. You still would not get quench.

If it worked, you take out 1 cc of head displacement for something like every .0055" of milling. Then would end up with a TRUE SCR of around 9.1 or 9.2. That is a good step up for the stock 318. You are now where you can hit the upper 7's for DCR with a decent range of cams, and much easier wheel spinning will result. Now you have come quite a ways out of the low compression/big cam non-performance corner.

I am not sure I would not care if the intake and heads had to stay together forever if it worked. An intake is a lot cheaper than a complete 318 bottom end rebuild. (Though that rebuild resets the engine wear to new....)

Edit to add: Oh yeah, I keep forgetting that the pushrods need to be shortened with this much milling....

 

[nm9stheham]

I'm going to find a 360 and install a set of domed pistons. Seems like the easiest thing to do. Raising the CR isn't really an issue, I was just hoping for bolt-ons. My normal machine shop only charges me about $150 bucks to mill down the pair of heads if I go that route. It's the fitment issues, springs, rods, rockers that scare me now. Dealing with smog motors and having a piston so far down in the hole is bound to create problems. I've learned a ton by this thread, and been scared a bit by this thread. DCR isn't something you hear about but it makes more sense as a measurement that SCR. You guys are the best and thanks for putting up with me.

Well, I hope 'scared' is not what you takeout of this. Things just are what they are.... low compression just is hard to make up for with performance engines.
The 360 idea is a surefire way to go for the 'tire-spinning on demand' that you mentioned. Longer stoke, more cubes, and if you start fresh, you can put things where you want.
Since you mentioned the domed pistons, then it is probably time to touch upon the opposite corner of the compression ratio map, where you get it too high in CR. That leads to detonation problems. Every engine ever built since the 50's or earlier would have had 10:1 static CR or more, if this was not an issue. The limit is best expressed in DCR again, where if you get too far past the low 8's then you move closer and closer to possible detonation issues. Some have made things work on the high 8's but you had better be on your tuning game all the time and get consistent gas. Or run race fuel.

So you can see we are always playing the game of upping CR but not so much to stray into detonation-land. It just 'comes with the territory' of using gasoline fueled, spark ignited internal combustion engine technology.

As a side note, some of the newest gasoline engine designs in the world are now using gasoline direct injection (direct into the cylinders, like a diesel) but with diesel-type compression combustion. That gets the SCR's and DCR's up several points, and the torque and combustion efficiencies take a big step up. But you just cannot go there with spark-initiated combustion and gasoline fuel.