JimMueller

iTrader: (9)

We got the shortblock built today. Something I'm disappointed with is that my new pistons are in the hole. I tried to use a feeler gauge to get an idea of how much, and it appears to be ~.020. That appears to drop my static compression from 11.5 to 10.7 and SCR from 8.9 to 8.6

The heads are PRC 5.3L which have already been milled ~.021 for a 59cc chamber. If I mill them too much then flow might be compromised. We haven't yet installed the heads because I'm waiting for more parts. So should I consider milling the heads more to get that compression back? I'm concerned we'll go too far and I'll be worse off than I am now, but I want the best combination of flow and compression.

The pistons are flat-tops with 2.2cc valve reliefs, Cometic .040 gaskets, 3.905 piston, 3.910 cometic gasket bore, 6.100 rod, .006 IVC is 63.6ABDC per cam doctor. Although this post (https://ls1tech.com/forums/showpost....8&postcount=10) indicates I should use a calculated 67.05 (277.5 advertised duration, 108.3 ICL per cam doctor) for the IVC field.

http://www.kb-silvolite.com/calc.php?action=comp

Ironically, I bought new pistons because the old ones had a 8cc dome and would have been too high I coulnd't afford new rods, so I chose new pistons which properly mated to my current Eagle rods. I can't replace rods/pistons again, so is my only hope milling more off the heads or decking the block? Decking the block is theoretical feasible, but not practical at this stage.

Even if flow wasn't hurt, I'd have to have about a 54cc chamber to make up for the deck clearance to get back my SCR, but then my DCR would be above 9.0.

mrr23

iTrader: (3)

can call wiseco about it and see what they say. they might send another set. just more waiting.

JimMueller

iTrader: (9)

But even if they did send another set, then wouldn't the rotating assembly need to be re-balanced?

mrr23

iTrader: (3)

so long as they are the same weights, i'd say within 5 grams, i don't see why.

JimMueller

iTrader: (9)

I asked Brian Nutter to chime in, he's the board Wiseco rep OK, looking at their catalog, page 13 (http://www.wiseco.com/PDFs/Catalogs/AB05_chevy.pdf), the standard LS1 deck height is 9.240, and 0 deck with these pistons are 9.213 with a 6.098 rod, and 9.240 with a 6.125 rod. So it looks like it's .017 in the hole assuming the deck height is stock.

mrr23

iTrader: (3)

won't have to wait on him to answer. and you won't like what i found. the reason for it being so low in the hole is because they are made for 6.125 rods. you have 6.100 which gives us the .025" you basically measured.

http://store.summitracing.com/partde...w=32&N=700+115

EDIT: they are made for both rods, just deck heights are different to achieve same compression.

mrr23

iTrader: (3)

CRS6100 rods
http://www.eaglerod.com/products/Che...S1%20rods.html

i hope you told wiseco you had 6.100 rods and not 6.125

JimMueller

iTrader: (9)

See edit above. I ordered the K398A07 pistons based upon e-mail conversation with Wiseco...let me see if I can dig up the messages...

mrr23

iTrader: (3)

on wiseco's site, they say they are for 6.098 and 6.125 rods

http://www.wiseco.com/PDFs/Catalogs/AB05_chevy.pdf

mrr23

iTrader: (3)

you and i were looking at the same page

looks like disassembly and cutting the deck .010" is in order. or buy 6.125" rods, or leave it alone, or cut the heads, or set it on fire.....

JimMueller

iTrader: (9)

No idea. I specifically asked them to compare their K398A07 to a Diamond model, but it doesn't appear anything was mentioned regarding rod length. I'm not sure if the catalog implies the K398A07 can be ordered for different rod lengths. But it was the only aftermarket piston which fit these CRS6100 rods.

mrr23

iTrader: (3)

i made an edit in the post regarding what i found. when you look at the pdf page, the piston is made for both rods. the 6.098 rods are measured with a 9.230 deck height. and the 6.125 rods are measured with a 9.240 deck height to make the compression numbers. so, decking the block will get you where you need to be at. means we get to take the block apart and send it back to the machine shop.

there's a nice big RED HIGHLIGHTED phrase on the pdf. LS1 blocks are 9.240 and the 6.0L blocks are 9.230. they really need to revise their book some.

i need to go back and refigure my compression ratio now. their book doesn't flowchart very well.

JimMueller

iTrader: (9)

I think the combination of least expense and further delay will be cutting the heads depending upon how much airflow would be sacrificed. Does the head need to be completely disassembled to do that (remove seats, guides, etc?).

I'm not terribly keen on delaying this project longer. A custom .035 Cometic with an additional .020 milled off the heads would get me pretty close. But how does the cost and delay associated with that avenue compare to disassembly and decking the block?

I'm also concerned about causing further fitment problems by decking the block too much, then ending up with other extenuating problems. What is the safe range I can deck without causing other problems? Is .010 the limit? Can I safely get the piston .007 out of the hole?

Asmodeus

decking the block can cause the intake manifold and head intake ports to not line up true.. and you might have to re-portmatch them.

JimMueller

iTrader: (9)

Hmm, maybe it isn't as bad as I thought. If the standard deck is 9.24, and the 0 deck on these pistons is 9.213, then it should be in the hole (9.24-9.213)=0.011, no? I don't follow why the .019-.020 feeler felt the most even with the deck surface, though.

If so, then if I can just mill the heads another 2cc (preferably 3cc), on top of the 3cc they've already been milled. But doesn't milling the heads too much also cause alignment problems with the intake ports?

Edit: It look's like you start running into manifold fitment problems around a combined .050-.055 off the bottom of the head. Should inspect the manifold/head intake alignment, though.

https://ls1tech.com/forums/generation-iii-internal-engine/615237-milling-heads-getting-thinner-head-gaskets.html

So I already took off .14 for the gasket, and ~.20 for the mill. That's .34, and another ~.20 (~3cc) would put me on the edge of fitment problems.

I'm leaning towards milling the head another 3cc, and hope that the current clearance is .011 instead of .020.

slow trap

iTrader: (22)

you have a dilemma on your hands. the (best) thing to do would be to get a set of 6.125 rods but definitely not the least expensive.i know if you increase stroke say .250" your piston will only come .125" more out of the hole but i think rod length stays the same so your pistons will be .025" more in the hole than with the 6.125 rod.
imo the right rods will be your best bet even though it will be more $ and waiting.

mrr23

iTrader: (3)

so will cutting the heads too much.

mrr23

iTrader: (3)

honestly, the best course of action is to get the 6.125" rods. the more you cut the heads, the weaker the deck surface becomes. because the surface is thinner, it can lift under high pressures. you aren't running nitrous, so not a big deal. but, if you were to have another rebuild and the heads need resurfacing, they may not be reuseable. i don't know the limits of milling the heads myself. next comes airflow around the cylinder. decking the block preserves this.

xssive

iTrader: (123)

I say you finish the motor. How much are you honestly leaving on the table....?

JimMueller

iTrader: (9)

Supposedly a point of compression is worth a 2-3% increase in power, and probably a bit better fuel economy as well. Although I don't know how to calculate quench, a tighter quench pad should help to fight detonation.

I know my Eagle H-beam ESP's weighed ~644g and I forget the big end weight. How much can this deviate without having to rebalance the rotating assembly? The Scat I-beams are inexpensive at $259, but weigh ~585 grams. So I'm sure that 60 grams would be sufficient enough to re-balance the crank. Does it matter that I want to spin 7200-7500 easily and regularly when picking a rod?