skinny z

I'd like to build a data base about iron heads and workable SCR/DCR for pump gas. I tried this at the beginning of the year and it turned into a tuning thread.
The key here, (and something I neglected to ask last time) besides the usual specifications of static compression and camshaft timing are the results from a compression test. It surprises me how many engines get built and tuned but this little scrap of information is never measured. Without that number the SCR is sort of assumed to be whatever.
Before this off-season tear-down, compression pressures in this 355 were solidly around the 200 psi mark. I couldn't keep it out of detonation.
Trust me, I've tried every angle to keep it out of spark knock but it wasn't happening.
Now I'm looking for info from others.

skinny z

Here are my specs:
Bore and stroke: 4.03 x 3.48
Head cc (measured not assumed). 64cc
Piston relief. 5cc (from piston mfr. data)
Piston to deck. .014" (measured all cylinders)
Gasket. .026" x 4.100"
SCR 10.38:1
DCR 8.4:1
Compression test. 195-200 psi cold.

1gary

I'll try to not stray too far off your question.What was the running temp on your engine??.

And the ignition timing??. Was it locked??.

Did you check the machined decking of the block to insure it was done correctly?. If not you could be chasing it forever driving you crazy.

skinny z

At the risk of this turning into another tuning thread, which I don't want:
160 stat. Engine temps seldom exceeded 180 degrees.
Timing was everything you could imagine however even with a 12 degree initial setting, advance starting at 2000 rpm and not all in until 4000 with a max total of 30, it still rattles. That pretty much kills any performance potential.
Block decked and squared, crank indexed and rod resized. All pisons measure .014" down.
With the timing compromised this much, it's plain to see that in this case the running compression is too much.
I've already taken steps to reduce this and keep my target quench range which now will be somewhat more at .050" (.014" + .036" gasket).

Looking for others with data to support their builds rather than tuning help. Despite everyone's best efforts in the old thread, nothing made any real difference in the performance. Plugs, A/F ratios, timing.....

86LG4Bird

iTrader: (1)

Engine #1: Stock L31 shortblock, uncut Vortec heads, ZZ4 cam (208/221/112, 107ICL).
Stock L31 intake/injection. 180 tstat. .015" head gasket.
Head cc's not measured. Cranking compression not measured. Cam not degreed.
Pistons were .025" in the hole. 9.6:1 CR if I assume 64cc chambers.
87 octane. No detonation.

Engine #2: A duplicate of the above engine, but running under a E4ME QJ and Edelbrock performer manifold. Base timing 15 deg. L69 chip in ECU.
87 octane. No detonation.

1gary

In the big picture of things,in a build as many eyes the check the machine work done that are not connected to each other,is the best check and balance method to use.

My guide lines have been 9.5 SCR and 8.5 DCR with a range of .035 to .040 quench using D-cup reverse dome pistons.Also using the stacked parts method to determine what is what.Then checking what it should be against what it measures on multi bores.If you really wanted to get detailed,you add in the top ring measurement to the volume.

1gary

Also I have used over the yrs three calculators:

http://www.rbracing-rsr.com/compstaticcalc.html

http://www.csgnetwork.com/automotiveconverters.html


http://www.wallaceracing.com/Calculators.htm

There are times you find variances between them.

And you see me ref's these two links alot because they do work:

http://www.crankshaftcoalition.com/w..._compatibility

http://www.crankshaftcoalition.com/wiki/Quench

skinny z

.

skinny z

Very interesting stuff. Especially the Crankshaft Coalition Cam and Compression Ratio calculator.
It supports my thinking (and calculations) regarding my over-zealous build.
The yellow highlight shows roughly were I was at. In between the yellow and blue more precisely and the 224º of cam timing I’m running is a little on the short side. What’s even more interesting is that I’m leaning towards a 10:1 SCR. As indicated by the red highlight, it’s a little undercammed at that point.
Now to get 10:1, a slightly larger combustion chamber (up to 66cc from 64cc) means a head gasket in the .036” range. That opens up my quench to .050”, something I didn’t want to do.
I may have to rethink that although the spark knock was so intense on the last build that I can’t believe that 2/10ths of a reduction in SCR is going to improve things a whole lot.
I’d like to know if this chart refers to aluminum or cast iron as a head material.

1gary

Anything above 9.5 is aluminum heads.

I am waiting for Delta,57,Alky,Sofa,etc to chime in to see their thinking on this topic.I am kind of in a hurt because of my carpal tunnel hands and in the middle of a semi serious E85 research.

Come on guys,alittle help here!!.