Misc hybrid ramblings

[TiredGXP]

I must have picked up a wild hair somewhere, because I'm seriously considering dusting the iron heads I've been working over and going with 3100/3400 heads on the 3.1.

The 3.1 short block is already assembled with the iron head pistons (12cc dish), so I'd be looking at nearly 11:1 CR. Seems too high for the intended purpose, especially since this will be boosted.

If gen 3 heads can be opened up to about 35cc's then the CR Calculator tells me that the CR drops to 10:1. Might be able to go with 8 lbs boost with proper intercooling and tuning.

Is there enough metal in the head to remove 6.5 cc's from the combustion chamber? Seems like a lot to remove.

The quench looks crappy with the iron head pistons and gen 3 heads. How important is quench in a boosted application? I always thought there would be sufficient combustion chamber turbulence just from boosting, but would a quench distance of .077 cause other issues?

I've got a spare set of rods, so I suppose I could just get a set of gen 3 pistons and move on, but what's the fun in that?

[bszopi]

You might also consider 3500 heads, as they start with a chamber volume of 32.4cc. Be easier to get 2.5cc out of those than 6.5cc from the 3400 heads.

[3400-95-Modified]

You might also consider 3500 heads, as they start with a chamber volume of 32.4cc. Be easier to get 2.5cc out of those than 6.5cc from the 3400 heads.

Yes but he would have to increase the bore of the engine to remove the overlap that a 3.1 bore has on a 3500 chamber. The 3400 headgaskets just barely clear the chamber which makes me wonder if the is still a slight overlap since I now know the bore of the fire ring on a 3400 headgasket is larger than that of the block.

[bszopi]

Yeah, forgot about that issue...

[TiredGXP]

Yeah, too bad about the bore overhang with the 3500 heads.

Since the block and crank machining are all done, I'm pretty much committed to keeping the gen 2 3.1 block.

Found an ultrasonic thickness tester on ebay for ~150, so maybe it's worth grabbing some jy 3100/3400 heads to see where, and how much, metal can be removed without compromising the strength of the combustion chambers.

[2.8/3400 1985 Camaro]

What are your power goals? If you plan to only run 8 lbs of boost you might just try building the engine high CR and RPM instead. As for quench, you can always get a different thickness of HG you know...