Alrighty... this is my first aluminum headed SBC build. It's a 1988 L98 from a 88 Z51, 4+3 manual, 3.07 rear, stock 113 heads, [URL=http://www.summitracing.com/parts/CCA-K08-423-8/]THIS CAM[/URL], 24lb injectors, hedman headers, air pump removed, no egr, a little port work on the heads will be done to smooth them out, valve job, al light mill. swapping to the short runner style Miniram intake manifold instead of the long tube L98. Block is getting tanked, likely .030 over and decked. Light polish on the crank, and obviously new bearings/pistons/etc with oil pump.
Car is mostly an auto-x/trackday/toy. AC will be functional in this plastic EZ-bake oven.
Now, what compression ratio should I bump to and still be on pump gas? I was considering 10.5:1 to 11:1 should be fairly "safe" and still handle 92 octane gas.
Thoughts?
10.5:1 would be my limit and still have power on the pump juice. You can go 12 or 13:1 but you have to run so little timing and bleeding off cylinder pressure, that you are down on power compared to something with less compression. Unless you want to run corn fuel.
Ranger, i don't know much about these motors, but why is that limit so low?
10.5 isn't low. It's a good aluminum head, but a big bore. A lot different than a small modern OHC motor.
11:1 on good pump premium is fine if you've got good knock compensation. You won't be pulling timing most of the time.
that and the 113 heads are small chamber IIRC, like 58cc.
92CelicaHalfTrac wrote:
Ranger, i don't know much about these motors, but why is that limit so low?
The limit isn't low given you are still playing with 50-60's technology today....
Ranger50 wrote:
92CelicaHalfTrac wrote:
Ranger, i don't know much about these motors, but why is that limit so low?
The limit isn't low given you are still playing with 50-60's technology today....
Thanks for the ammo to razz Bob with from now on. 
there's also the metallurgy aspect as well. It's a fat cast iron block unlike most of the modern 4 cyl cars with aluminum blocks. Not only is there less cylinders creating heat/pressure, the metal cools down qquicker. They dissipate heat faster allowing higher compression ratios without getting pre-ignition. When you have 8 cylinders, with 4" bores going bang, they create a lot of heat and that big cast iron heat sink holds it in.
Bobzilla wrote:
there's also the metallurgy aspect as well. It's a fat cast iron block unlike most of the modern 4 cyl cars with aluminum blocks. Not only is there less cylinders creating heat/pressure, the metal cools down qquicker. They dissipate heat faster allowing higher compression ratios without getting pre-ignition. When you have 8 cylinders, with 4" bores going bang, they create a lot of heat and that big cast iron heat sink holds it in.
That makes sense to a point. Didn't think of that. There's a flaw or two in there, but the initial theory certainly applies.
This is why i ask these questions! 
Add to that the "Squish area" is not ideal in a wedge V8.
Proper squish can realy help keep detionation at bay.
If I may.... do some research into Dynamic Compression Ratio. If you follow the procedures and formulas for DCR, your cam choice will calculate out and supply you with an appropriate compression choice
Bobzilla wrote:
44Dwarf wrote:
Add to that the "Squish area" is not ideal in a wedge V8.
Proper squish can realy help keep detionation at bay.
and there's this.
Ah gotcha... this is what i was asking about this morning when you first asked. Wasn't sure if it sucked or not, but now i know.
oldeskewltoy wrote:
If I may.... do some research into Dynamic Compression Ratio. If you follow the procedures and formulas for DCR, your cam choice will calculate out and supply you with an appropriate compression choice
according to the caluclator I found, the cam likes 10.5:1, and a flat top piston with 4 valve reliefs would make it 10.46:1. That's pretty darn close.
Bobzilla wrote:
oldeskewltoy wrote:
If I may.... do some research into Dynamic Compression Ratio. If you follow the procedures and formulas for DCR, your cam choice will calculate out and supply you with an appropriate compression choice
according to the caluclator I found, the cam likes 10.5:1, and a flat top piston with 4 valve reliefs would make it 10.46:1. That's pretty darn close.
If your chambers are hot spot free, you might be able to bump that 10.46, upto about 10.75. Don't forget you can do some tricks on the ignition side as well. You just don't want to have a DCR so high that you are stuck using av gas
How much worse could the head be than an M20 BMW?
11:1 on pump gas is very common.
Isn't an M20 aluminum block and head, OHC? Not cast iron block, aluminum head, pushrod/cam in block/OHV? So like comparing apples to concrete blocks?
It's iron block aluminum head.
Just pointing that with proper tuning, a 30+ year old head design handles it just fine.
Still overhead cam, right? So quench area is shaped a lot differently. that and I'm dealing with 65 year old head design. 
Dropped it off this morning. All said and done it's going to cost me $400 in labor and another 350-400 in parts. God this is cheap compared to the swift.
My Swift is a lot faster than yours was, and I don't have that kind of money in it
yeah, but mine was in a lot worse shape IIRC when I got it... that and some learning errors. Like NEVER believe a seller. Oil pumps ARE different for SOHC and DOHC etc...
There's still time to screw up this build too 
lol Hopefully not. got a call last night, the intake valves are a little ... worn. The keepers are so sloppy in the grooves he's suprised I hadn't already dropped a valve. Pistons/rings/bearings should be there today so He's going to bore the block today and will probnably be done by tomorrow.
