Kevin, you're probably right - there is a direct and linear correlation between what I see as free length and seat pressure at the installed height spec. Also, the factory does give both a free length standard and minimum spec, but only provides the one rate spec of 74 lbs at installed height.

I'm pretty sure that heat trashed these. I measured one spring from a Diamante head and found it a lot closer to standard spec. Among all of the heads I have here, I might even be able to come up with a decent set and avoid buying new ones.

I just looked closely at the heads and found a bump on an area that I "thought" was just inside the fire ring. I sanded on it a bit, then grabbed the dremel to level it and promptly dug into the quench pad a little too much - particularly when I put the gasket on it and found it was under the fire ring. <img src="/forums/images/graemlins/scared.gif" alt="" />

So, I'll dig out a reserve set of heads and start porting again. <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

I had some trouble getting the cams where I want them on these heads with the new block. The offset bushings work about as they should on the 0,4,5 and 6? bushings, but the 7 and 8? bushings go whacky and roll the cams forward too much. Perhaps it's a difference in geometry of the Chevy pin location offset from cam center. Maybe if I have a set of full-thickness heads, I can get the cam timing closer to what I want to see.

Frank

I'm getting a little aggravated at the "session expired" message since this is the second time today - perhaps it's just me. <img src="/forums/images/graemlins/rolleyes.gif" alt="" />

The Diamante heads are back from the machine shop. The fellow did a decent finish job, but not great - and certainly not nearly as good as he did on the Galant head I put on the Mighty Max. Anyway, the valves have been ground/seats dressed and the heads have been cut .003" - which puts me a little over the factory spec limit on total cut for block + heads:



I'm not so concerned about the extra .001" on the total cut as what I see on the combustion chambers. The OE heads CC'd at 46cc combustion chamber. I just measured one of these and find a 44cc chamber. The loss of 2cc is just enough to throw off the entire calculation set and put me at ~9.4:1 static CR and ~7.8:1 dynamic CR..... too high to run the cams where I want them with the blower.

I can use a $65 standard .020" head shim set and get to 8.9:1 SCR and 7.4:1 DCR - or have a .016" custom shim set made for $150 that will put me at the original target of 9.0:1 SCR and 7.5:1 DCR with the cams set to close the inlet valves at 59? ABDC.

I'm tempted to buy the custom set, but I think I'll save the money, play it a little safer, order the standard set and call it good.

I really don't know what the added shims will do to the quench action, but probably not much difference from not having the shims with these pistons, since the pistons have a round dish and not the triangular shape of the combustion chamber.

Frank

I've brought it up again Frank.

Frnak, I have you had a chance to check out compressed head gasket thickness from differant sources? You might get lucky and find one that has a higher compressed thickness.

I have dealt with this a couple of ways.

1: Shims , and like you I was concerned about loosing quench. On the 2.6 there really isnt any so it was not a deal breaker. Your motor has a real Squish region so there may be somthing to lose.

2: removing material from the chambers. Depending on the desing its can be hard or easy. Yours look to have a pretty decent finish. 2 cc's is a fair amount of material. to take out, but it can be done.

3: Dish the pistons. I have always like this option. You can easily leave the outer squish region intact. The pistons usually have a bit of margin. This can affect your ballance. On a 4 cyl not a problem. And it should not be an issue on your 6 but its worth considering before you do it.

4: Head shim. Your two options seem good. In my experiance your better to have to low a CR than too high. The percentage lost in efficancy from a 1/2 point to low is small compared to how much you lose from having to retard the timing if your too high.

What is your current squish? For fun google "Singh's Grooves" That might be an interesting way to get some CR out. <img src="/forums/images/graemlins/rodent.gif" alt="" />

Kevin

Kevin -

No, I haven't measured any gaskets other than the OE composition gasket - it's right at .050", even after it's been torqued down with ARP head studs. There might be another gasket that's thicker, but I don't want to experiment with that, since the OE gasket does such a nice job of sealing - even with a little boost.

I don't really want to grind the chambers by hand for fear of changing the flame direction. It could be done by machine, but I don't want to spend time looking for a machinist who is comfortable doing it and I'm not anxious to spend the money for it.

Same on the pistons - they're already in the block and I'm taking so long to build this engine already, I don't want to back up - or spend the money to put more dish in them.

Current clearance at .037" is more than I had on the last engine at .032" IIRC, so .020" more would give me .057", admittedly a lot.... and maybe questionable. The flip side is the circular piston dish on the Wisecos that negates any available OE-designed squish except at the outer 1/4" of the piston.

The combustion chamber grooves are sort of a whacky idea and go against everything I've learned, but there do seem to be some positive results reported from some of the experimenters. I saw some pictures of combustion chambers that appeared to be getting excellent burn patterns, but some others that didn't look so good. It seems to matter how and where you cut the grooves, so I should probably try that as a last resort. It sure is an interesting idea, though.

I couldn't get the Diamante cams to roll far enough forward with the Chevy eccentric bushings, so I'm going to go back to the Montero cams and try the .020" head shims first to see what happens. One thing I considered was that with the Diamante cams being retarded and running a little more overlap, I might not have been seeing as much boost pressure as I might get with the intake closing sooner and less overlap. So, I might get even more dynamic cylinder pressure than just what is suggested by the mathematical calculation models.

I guess the old "build it, run it and see what happens" is still the rule..... but I'll sneak up on it. Next time (if there is one) I'll have the pistons cut with 2cc more dish.

I have a Gen1 Montero in the yard that I could take the heads from and check the combustion chambers, but that would cost more time and money. I had planned to use the cams from that engine, so I guess I'll pull the heads as well and save them for "just-in-case".

Frank

I finally got some time to work on the engine - .020" head shims are in with spray Hylomar.... it might hold pressure better than Copper Spray-A-Gasket, but it's not quite as easy to work with and I don't think it goes on as thin...... anyway, the shims and heads are torqued down.

The Diamante heads are mildly ported, with new valve stem seals, new valve springs and a 3 angle valve grind..... OE composition head gaskets, ARP head studs torqued to 87 lb-ft w/ARP moly lube - about 130 lb-ft equivalent w/oil.... should hold some pressure.

I was just about to make a set of adjustable cam sprockets, but first I put the Diamante cams in just to see if the head shims gave me back enough deck height to make it easier to use the eccentric cam bushings..... in combination with the new block and different heads, they made quite a difference and moved the base setting about 3? more advanced than the previous engine, so I will try the Diamante cams once more.

Both cams are now degreed with the intake C/Ls at 107.5? ATDC, a 7.5? advance from OE Diamante. That should give me back the bottom end torque and raise cylinder pressure some.... we'll see what happens..... hope it's not too much. It won't be as long now as it has been:



Frank

As sexy as that picture is, I figured the forum would have edited it out as porn....

Looks real good Frank <img src="/forums/images/graemlins/kewl.gif" alt="" />

Replaced the transmission input pump seal and bolted the engine in this morning:



Frank

Awww, yeah!

John B.

When are you coming to ATL so I can break it again...