2000taalex

iTrader: (1)

I'm doing my best to build a motor correctly (l92 currently at machine shop)
I've been doing my homework on static and dynamic compression ratios, and from what I read from multiple sources is anything over 8.5:1 DCR is a big nono on pump gas without retarding timing.
I have been crunching numbers on some of the very popular camshafts that are available for the LS3, and even without touching shortblock specs (piston dimensions, bore size, etc.) DCR is coming out to be 8.8:1> and above on two popular cams and counting?
Is it too late for me to be messing around and should just get some sleep? Big boys chime in.

I want to build this sucker right.

KW Baraka

iTrader: (7)

8.8:1 DCP ain't gonna hurt much; but still....you're not giving much to work with.

What's your quench coming in at?

For that matter, talk to us more about your block-heads-cam-transmission....and the car it's going in.

KW

2000taalex

iTrader: (1)

For me?
stock 6.2 block, gonna go .005 over. Trying to achieve 11.5:1. Either going to go with a domed piston on a 6.125 rod or just go flat top and mill the heads .030 and run a thinner gasket to bump it up. Stock 823 casting heads, going to run a stock ls3 intake. Coupled with a T56 in a 2000 TA. For quench like I stated above, honestly not sure what it will be yet. Probably will go with a .041 compressed gasket.

I want a kickass streetcar that will hurt feelings on the track as well. I'm fresh when it comes to actually choosing carefully what I need, no more throwing parts together!

KW Baraka

iTrader: (7)

I like what you're doing. If it were my car with worked OEM heads, I'd start looking at something along the lines of 230*/240* duration, 112* + 2* LSA and lift at about .620" to .630".

I would then contact a good cam company like Cam Motion and/or Brian Tooley Racing for additional guidance in tweaking those spec's to get the best cam for my usage for the car.

If you go with domed pistons, you may need to have them cut for valve reliefs.

You are free to do as you please....but this is what I'd do.

Best of luck!!!

KW

KCS

iTrader: (20)

Are you using duration @ .050" to come up with your DCR?

2000taalex

iTrader: (1)

This sounds very uneducated but its the truth - I dont know!
I am punching duration numbers in (lets just say I check a website and its a 228/234 cam) to the cam motion timer program, then using that intake closing time to calculate my DCR. Im assuming this is wrong? I'm sure those numbers are at .050?

KCS

iTrader: (20)

2000taalex

iTrader: (1)

Is there a way to find .002 from duration numbers at .050? Looks like almost every cam I see the numbers must be advertised at .050....

G Atsma

Since .002 is a lot closer to advertised (.000 lift) than .050, use advertised to get a better picture if you can't find .002 specs. Most cams give advertised specs, though I have not seen the ones for TSP or Cam Motion.

Darth_V8r

iTrader: (4)

51 to 55 degrees is pretty common for ramp rates. In the absence of exact measurements, 27 degrees (half of 54) will get you in the ballpark. So if your IVC is 45 degrees, use 72 for your DCR calcs.

2000taalex

iTrader: (1)

All excellent information. This car is going to be equipped with some 4.30 gears and a 27 inch tall tire, so I'm trying to build a motor that makes excellent mid range and top end power. If I can keep my compression up, i would like to get a nice healthy torque curve as well. I am just trying to do the math on which pistons I should use, how much if any I should take off the heads, and then of course what cam. Spin monsters 230/234 looks promising, but maybe even per my application I'll do a custom grind. Any opinions? Remember I am fresh when it comes to actually planning a motor so all input is appreciated!

KCS

iTrader: (20)

Despite the fact that .000" of lift is technically closed and can't be used for a measurement of the duration the valve is open, it takes probably a tenth of a degree to go from .000" to .002" of tappet lift. At operating speeds, more than that is probably eaten up in the "shock absorption" of a hydraulic lifter and deflections within the rest of the valvetrain.

DCR is a foolish thing anyways. Not worth the effort IMO.

KCS

iTrader: (20)

The majority of aftermarket forged pistons will have valve reliefs so you won't have any PTV issues when you mill the heads. You would be better off with a flat top piston and milled heads with smaller chambers to get your compression. Domes add weight to the pistons and are bad for combustion; a double whammy. A 3.2cc flat top and 65cc chambers will get you almost 11:1. If you ask your machine shop to cut the deck of the block, you can get the pistons .010' out of the hole, which will put quench around .042" with GM 6.2L gasket.

Double06

iTrader: (1)

My Comp Cam 243/259 at .050 on a 114 is really a 293/309 at .006 and it has a IVC of 78 degrees. At 12.0 compression it is like 8.5 DCR.

old motorhead

iTrader: (10)

KW Baraka

iTrader: (7)

At 11.5:1 with a 228/234 cam AND if you get quench to .035", you'll be in great shape! The strong mid-range and the strong top end will ABSOLUTELY be where you want it.

I base this on my '95 that has a OEM LS3 rotating assemble, ported and milled LS3 heads (11.4:1 compression) 229*/242* cam and .036" quench.

As stated, your (possibly) DCR shouldn't be a show stopper....as long as you have your quench nice and tight!

KW

2000taalex

iTrader: (1)

Awesome to see someone running something similar to what I run? Did you dyno it? I'm excited!

thanks for all the great info guys.

KW Baraka

iTrader: (7)

Initial dyno was 451HP/400TQ to the wheels.

This was through a set of Hedman Mid-length headers which were barely a step above shorty headers.

I switched to a set of Hedman 1 7/8" longtubes and had a very noticeable power jump....at least 15HP/TQ to the wheels (no new dyno yet). So yeah....I say go with the biggest, long tubes you can fit under your hood!

KW

2000taalex

iTrader: (1)

that's awesome, which cam are you running??
I have some speed engineering 1 3/4 long tubes. should be fine for what I want! I'm hoping.

KW Baraka

iTrader: (7)

Cam's in the sig....Lingenfelter GT1-1....you can Google it. It has a lot of lift so it's not really a 'fan favorite'....but I like it fine.

The 1 3/4" longtubes are good....but hell, if I could do it all over again.....I'd would've ponied up the extra $100 and gone with 2" tubes....

KW