ez2cdave

Thanks . . . I'll look him up !

Dave

Patrick G

iTrader: (14)

An engine will typically make maximum cylinder pressure at 13 degrees ATDC. To make maximum torque, you want your ignition timing to occur early enough to allow this peak cylinder pressure to occur at 13 degrees. The amount of advance depends on cylinder head port/chamber design/fuel choice and cam timing events. Some combos need more advance, some need less. If your static compression is so high that you can't run enough advance to allow peak cylinder pressure at 13 ATDC, then you will lose power.

Here's an example:
Say you have a very efficient set of heads like a 65cc Trick Flow 215 on a 346 making 10.5:1 SCR running 91 octane. This head likes a 40 degree burn from ignition advance to peak cylinder pressure so that means 27 degrees BTDC ignition advance + the 13 ATDC to achieve peak cylinder pressure.

Now you raise the static compression to 11.5:1 and can only run 23 degrees of ignition advance before you detonate. That means you will be making peak cylinder pressure at 17 degrees ATDC. 4 degrees past ideal. So basically, you will make less power with more compression and less timing in this case.

As a general rule, you will make best power with the static compression and fuel that allows you to make peak cylinder pressure at 13 degrees ATDC.

ez2cdave

Patrick,

Thanks for the great information . . . I am learning a lot here, but this is a much more complicated process than I had imagined !

How does one know how much timing various heads "like" ?

Is there a reference source or is it all just based on personal experience ?

I want to be sure of choosing the right heads and CR . . .

Dave

SSCamaro99_3

iTrader: (1)

Wouldn't you be at 17 degress ATDC? Just want to make sure I am following correctly.

27-40= -13
23-40= -17

Patrick G

iTrader: (14)

Yes, sorry, brain fart. With 23 degrees of ignition advance, the burn would occur 4 degrees past the ideal point of 13 degrees. I'm so used to explaining why nitrous needs its timing retarded (because of a much faster burn), that I got my math transposed. I will correct my previous statement in case anyone else quotes it in error.

ez2cdave

Patrick,

Please don't confuse me any more than I already am . . . LOL !

I want to be sure to be able to make the right choices !

Dave

KCS

iTrader: (20)

I was given a good analogy once in regards to combustion; think of it as a forest fire. The trees represent the oxygen in the atmosphere and the dirt and sand represent the other elements which don't really aid in combustion. The more densely packed the trees (or oxygen molecules) are, the faster the forest fire can spread. Back to the combustion chamber, if you have more oxygen packed into the cylinder, the flame can travel across the cylinder and build pressure quicker.

Conversely, a wildfire won't spread very quickly in a barren desert, so an engine with poor VE may require more spark advance in order to build maximum pressure at that sweet spot Patrick spoke about.

ez2cdave

Guys,

Could anyone please take a look at these specs and see if I have any "conflicts" . . . Do I have the potential of "too much flow" for a "STREET" 427 ?

Please feel to make suggestions for any changes and why they would be needed . . .

The car would be 99% street daily-driven, and I do mean "daily-driven", just like a stock family car would be . . . Traffic, Stop & Go, Freeway, etc.

SPECS :

427cid / 7.0L

LS2 Block - DARTON Dry Sleeves - 4.125" Bore
COMETIC "PHUZION" Gaskets - 051" Compressed Height
WISECO "LS Series" Pistons #K395X130 - 10.9:1 CR (Not 100% chosen-More CR Info Please ?)
F.A.S.T. - LSXr 102mm Intake - Unported
102mm Throttle Body
KOOKS Long-Tube Headers ( 1.875" - 2.00" Primaries / 3.5" Collector, Dual High-Flow Cats, Full 3" Magnaflow Cat-Back Exhaust System

CAMSHAFT : Will Be A CUSTOM Hydraulic-Roller . . . Specs to be determined !!!

West Coast Cylinder Heads - CNC Stage 2 L92/LS3 Heads ( Flow Numbers Below )

INTAKE - 2.160" Valve / EXHAUST 1.600" Valve / 28" of H20 w. a 4.155" Test Bore

LIFT 0.100 0.200 0.300 0 .400 0.500 0.600 0.650 0.700

INT _75.4 _160.0 _226.6 _280.4 _323.0 _353.7 _360.6 _367.6

EXH _57.4 _117.6 _182.4 _222.5 _240.1 _249.0 _251.4 _254.3

http://www.proheads.com/WCCH%20L92.html

Weight - Approx. 3850lb w/Driver
4L80E Transmission - 2.48 1st Gear, 1.48 2nd Gear, 1.00 3rd Gear, .75 4th Gear
YANK 3400 RPM Lock-Up Converter
3.54 Ring & Pinion ( Strange S60 Dana rear )

THANKS !

Dave

Patrick G

iTrader: (14)

If you don't have the heads yet, I think you'd go a lot faster with either some WCCH LS7 heads or some MAST LS7 heads with cathedral ports. While the L92 heads are good, they're not great compared to the LS7 and MAST stuff.

ez2cdave

Hi, Patrick,

I am concerned with the motor getting "lazy / flat / boggy" at low RPM's, since it will be 99% street driven. I am looking for a big-cube motor that has a smooth idle, does not surge or overheat, gets decent MPG, and is a "very nasty surprise" at a stoplight. It would have to "behave" in daily stop & go driving, idle for extended periods in rush-hour traffic, and Pass NC OBD-II Emissions . . . It would be driven just like a "family car", but with a set of "brass *****" !

As it stands, I am concerned about the WCCH LS3 Stage 2 heads being too large for my application.

Since the other heads are even more "aggressive", wouldn't that make things worse for me ?

I haven't chosen a CR yet, but I want to be able to run full timing ( any thoughts on CR with my combo ? ) . . . 91 Octane pump gas . . . No power adders.

Patrick, I am going to have you spec out the cam, once the components are all finalized .

Please forgive the "dumb questions" . . . I am almost 50 and my last "real car" was a 1970 454 Chevelle, almost 25 years ago . . . Being "married" can do things like that to a man, but my wife is a lot more "tolerant" now . . . LOL !

Thanks to you, and everyone else, for your patience and very helpful information !

Dave

WKMCD

iTrader: (2)

Not an expert but...

I would go straight to the Stage 3 WCCH L92's. Richard has them flowing right with LS7 heads. Run as much compression as you can and still get 28-29 degrees of timing. That seems to be about 11.3 11.4:1 The sweet spot on the intake side of the cam seems to be 230-234 and 8-10 degrees of split. The heads like lift so .640 or better is good.

Just my $.02

Good luck!

Kevin

ez2cdave

Kevin,

Thanks for your input on my combination . . .

I need and welcome all the help I can get !

Dave

TwoValveKid

iTrader: (1)

Ended up doing something similar. Picked out pretty much the entire drivetrain and did cam/pushrods last. LS3 stroker from Scoggin Dickey with Mast Medium bore LS3s and a patrick G spec'd cam. What really sold me on the Mast stuff is that they outflow just about every ported LS3 on the market...with a much smaller runner.

87silverbullet

iTrader: (11)

That usually happens when you have an aftermarket casting. They were able to tweak the port the way they wanted to.

TwoValveKid

iTrader: (1)

Yep. But still. I was really waiting for the TSP Small Bore LS7's but parts started showing up and i got a nice deal on a set of Mast Medium Bores through Scoggin Dickey. Even got harland sharp to supply some rockers.