I've been collecting parts for my 416 LS3 build and have gathered nearly everything. I've actually picked up the short block earlier this week from the machine shop and realized I've overlooked a couple key things.

One, dynamic compression. However, the cam spec'd to me by Pat G stated I would have around 8.3:1 DCR. When I run the numbers in the calculators I find online, I'm getting around 10:1! Yikes!!! Can someone run the numbers and see who's correct?

Cam...IVC is 46.5 @ ABDC
Pistons...11.3:1 with 70cc heads

Two, I never calculated piston quench. I'm using Wiseco pistons K464X7 -3cc piston volume. Pistons are level with the deck, but the dome is out of the deck. What thickness head gasket? Cometic .040? Block deck was squared at 9.235. Heads are Mast Motorsports 245 Cathedral port heads with 70cc chambers.

I'm kind of rambling, but you all get the gist.
Thanks!

 

What are you hoping to have?

 

I'd prefer to the DCR to be around what Pat G told me it would be and to have the tightest quench I can possibly have and still be able to safely run 93 octane fuel

 

I'm getting 11.9:1 SCR with http://www.csgnetwork.com/compcalc.html.

 

You're using an IVC @ .050" to calculate DCR. Usually it's calculated with an IVC @ .006" or "as advertised" lift which will give you a lower ratio.

 

This.

 

And you’ll have to measure your piston height. May look flush but most often LS pistons are out of the hole .005. Most guys say to run quench in the .035 range minimum. Mine right now is in the .035 range

 

Hi Jeb, IS THIS what you state, a LS-416 @ ZERO DECK, a 70cc head chamber, .040" gasket.

YES you ramble, I want to be of help, just to get the "spec" correct.

Then you state a 3cc dome piston ?

That STATIC = 12.27 C.R. >

Then you state a -3cc dome piston ?

That STATIC = 11.44 C.R. >

I have never heard of a "G" camshaft, could you provide the camshaft information ?

I would be concerned with the STATIC FIRST.

Do you have "offset" piston pins ?
I run 12:1 with a 416, pump fuel, wide LC camshaft AND Offset flat top pin pistons. (4cc with valve pockets)

Lance

 

That piston does have offset pins as do most Wiseco LS specific pistons. Wiseco has this weird thing with - or + volumes in their catalog but usually a - number is a valve relief/dish volume. Their catalog also shows a compression ratio with those pistons and 70cc heads to be at 11.2:1.

 

All the calculators I have run for the static compression show me with a 11.44 compression. I'm ok with that. It's the DCR I'm concerned with. However, I have been measuring it @.050 and not .006. I don't have those numbers and do not know how to convert if you can. Wiseco says 11.3 with 70cc heads, but they never state with what size gasket. I've tried calling them, but can't get the information I want from them.

My cam specs are as follows @ .050:

Intake 233 duration .629 lift Exhaust 240 duration .615 lift
LSA is 114
ICL is 110

Intake valve opens 6.5 BTDC
Intake valve closes 46.5 ABDC
Exhaust valve opens 55 BBDC
Exhaust valve closes 2 ATDC
ECL 118
Cam overlap is 8.5

Piston is zero out of the deck. However, the dome is above deck. Is the dome calculated too? Part of the piston, right?

I gave the piston part number for anyone interested enough to calculate. Wiseco states total piston volume, which includes both valve reliefs and dome volume to total -3cc. Piston compression height is 110. With a deck height of 9.235, that measures to a 0 deck piston height, calculating stroke and rod length.

Yes, these are offset pin pistons. They are made for a 4" stroke LS3 with 6.125 rods. The cam is a custom camshaft ground by Texas Speed, but spec'd by Pat G.

 

TSP or Patrick might have the lobe info for you. I know TSP doesn't put that info on their cam cards, so you may just have to call one of them.

Don't sweat the dome, it will be in the chamber and not in the quench area. If the piston is not above or below the deck, the whatever your gasket thickness is will be what your quench distance will be. Simple.

 

Thanks KCS...

I just got off the phone with Texas Speed. They converted the numbers for me and IVC ABDC is 73. I just plugged that new info into the DCR calculator and got a 8.54:1. A lot better than 10:1! However, it is still a little higher than I wanted it to be. I'm not really getting any wiggle room here. My tune, I suppose, is going to have to be spot on. That's another area I'm going to have to tackle next.

 

Hi KCS, I agree though the OP stated a >040" HG.

THE GREAT CONCERN for Dynamic Compression Ratio DEBATE, sure I understand.

THOSE who "praise" this have LITTLE/NO knowledge with concern to Pin OFFSET, (including direction) a MAJOR factor in DCR.

Lance

 

.040 is the thickness head gasket I intend to run. That is the thickness I've used in all my calculations. Everything seems to be checking out, unless you can find otherwise. I've provided all the information needed.

 

With .040" quench.....you'll be fine.

If Pat is gonna do your tune, he'll get it right.....way easy for him!

KW

 

Hi Jeb, VERY good news that your piston pin is OFFSET.
My guess is that they were installed in the OEM style. (notch forward)

This effect of "offset pins" ALLOWS for the piston to move FASTER away from combustion pressure when at the OEM offset side.

The OTHER great fact for your build, a MAJOR DCR FACT, is your R/L of 1.53 OR the Rod Length/Crankshaft Stroke ratio.

These TWO ITEMS have MORE EFFECT with concern to DCR than IVCP.

THESE two items EFFECT the piston position away from the top of the cylinder vs Cam Timing
THESE two items EFFECT the piston speed as it moves away from the top of the cylinder.

YES, choose the .040" HG, you will be fine AND have a better Quench.

Lance

 

Add 27 to your IVC and that should get you very close to the .006" IVC.

Most stroker kits available are .000" or .005" down the hole.