depends on how aggressive your tune is, i reckon. if you've got enough timing to require 93, then a 1/3pt would be noticeable... but if them heads are simply making up for any dynamic compression lost by the cam (vs stock cam + 317s), i doubt it'd make a heap of difference for an 87/89 friendly tune.


...but i've been wrong a time or two in my life.

 

It’s making low 20*s in the top end on the high octane table, I pulled 4* out across the board for the low table and it acts fine the few times I put 87 in it just as a test.

Screw it, ill go with the cometics that way the comparison between the heads will be all flow and port velocity no change in CR.

 

just make sure your pushrod length still works with the milled surface & gasket thickness change.

 

I have 7.350, 7.400, and 7.450 on hand hopefully I don’t need something crazier then those.

 

Getting the chambers measured on the heads today and might start motor tear down this weekend. I think I'm gonna go ahead and replace the oil pump since it's a mystery and I've had low OP on below 32* startups and after I added the oil cooler I lost 5-10psi on warm idle. Just gonna get an M295 and open it up to see if it could use some light porting or not, clean the oil pan and pickup tube and replace the pickup tube gasket while adding one of those little pickup girdle dudes.

Is it worth doing something with the timing chain? IIRC it's a stock gear and chain with no tensioner.

 

Me personally, leave the 3.42s - install a smaller cam more suited for a 5000+ lb vehicle, mill your 862s if you haven't already and treat them to a really good valve job. When you buy tires next time, get a 31" tall tire instead of 33s. If you're stuck on that cam, installing ported 243s, and keeping 3 42s - put a longer arm in that engine. (4" stroke crankshaft)

Or, change nothing and merely add BOOST. There's more than one way to accomplish the same thing.

 

I actually just switched from a 31" tire to the 33"s a few weeks ago and the ride quality is worth the minor performance loss. I also had a smaller 212/218 cam in it before and although it got a tad better mpg this one definitely pulls a little harder up top although I think it's suffering from the 862s lack of top-end flow even though they have 2" valves cut in. Disclaimer this is all butt dyno speculation. So ported 243s and keeping it above 4k is the plan! When it blows up a stroker will be considered or a low mile 6.2, a Trick T6 setup would solve all the slowness but that would cost me as much as I paid for the truck and as a daily that sees 18-20k a year IDK how wise that would be.

 

a cam with more duration & lift pulling harder up top? whoda thunk?

 

Same lift more duration, but yeah pretty obvious, and that's what I'm hoping to gain with these heads. Which, I just had the chambers checked and they are 63cc which is what I thought after having them milled .010, so with a.041 gasket I will be at 10.4:1CR and .033-.037 quench depending on deck clearance. Might need to get a set of .045s.

 

I would go with an aftermarket chain & gear set. The Rollmaster "Red" has the 2nd best chain just behind the Katech C5-R chain, and has billet gears. The sloppiness of factory LS timing chains bothers me for some reason. I know that's just how they are... but they don't have to be. I guess because I've assembled a lot of different makes of domestic V8's through the years and not a single one had a sloppy timing set like the OEM LS

I see you've figured out your quench and gasket thickness.