GRNcamaro

Im gona buy one of the kits from victory racing for my lt1. im gona run le2 heads on it.

this is the kit
EAG-12111 Eagle 383ci Competition Stroker Kit, Eagle 4340 3.750" Crankshaft, Eagle 6.000" H-Beam Rods, -5cc SRP Forged Pistons, File-Fit Rings $1499.99

their saying the compression will come out to about 11:3 and i wanted 11:1 they said no problem i could buy some custom pistons.

im having a hard time making the decision do you guys think this set up is good enough for my le2 or should i go for the custom pistons and go for 11:1 compression.

for some reason im having a hard time figuring out how much of a difference the 11:1 to 11:3 will make.

RealQuick

Do you mean 11.1 to 1 (11.1:1) versus 11.3 to 1 (11.3:1). There is virtually no difference between them.

GRNcamaro

yes im sorry 11.1 to 11.3

RealQuick

If the custom pistons are more $$, then I'd just get the 11.3:1's. Still pump gas friendly and you wouldnt notice a difference by .2 CR.

chief455

I agree with the above posts, but how are you getting the ratio?
With these specs:
bore = 4.030"
stroke = 3.75"
gasket = .039"
dish = 5cc
deck = .014"
chamber = 58cc
I have ratio at 11.58:1
with zero deck = 12.01:1

not that bad, but different..

GRNcamaro

eric from victory gave me this

4.030 Bore
3.750" Stroke
6.000 Rod
9.010" Deck
.039 Gasket
-5cc Flat Top
54cc Cylinder Heads
12.1:1

sbs

Unfortunate that they'd rather make money on custom pistons rather than telling the customer that he's wrong.

rskrause

If you use these numbers:

4.030 Bore
3.750" Stroke
6.000 Rod
9.010" Deck
.039 Gasket
-5cc Flat Top
54cc Cylinder Heads

And you assume that 9.010" deck means 10 in the hole, the CR calculates out to 12.15. If the chambers are 58cc, it is 11.55. Small difference in the CC size make big difference in CR which makes sense of you consider it is a ratio. Increased bore and/or stroke raises CR, all else being equal. Which also makes sense, 'cause it's a ratio.

Rich

GRNcamaro

so really where the diffrence in numbers is comeing in is the cylinder heads they thought they were 54cc and there 58cc. im sending my heads out to Loyd Eliot for le2 set up.

okay so what pistons should i run to come up with the correct ratio i want?

rskrause

If your compression height is chosen to make the piston 10 in the hole and everything else is the same, you need a piston with ~8.3cc negative volume. Off the shelf pistons for a 3.75" stroke/6" rod combo usually have a 1.125" compression height. If your rods are 6.00", stroke is 3.75" and deckheight is 9.010", such a piston will be 10 in the hole, as I stated earlier. All you need is to get an off the shelf piston with a 1.125" CH and have the valve reliefs fly cut to take out the extra material needed. Verify with the piston manufacturer that such a cut will not make the crown too thin. If it is a standard or heavy duty piston, it will usually not be a problem. While you do not need a "custom piston", depending on the resources available to you, it may be easier to make a custom order than to have the work done locally.

Clear?

Disclaimer: I am relying on the info you have provided and have not verified it. Don't be mad at me if something doesn't fit or produce the desired CR. I also have no idea if 11.1:1 is the correct CR for your combo, etc.

One other thing: some people would want a "zero deck" with an 0.039" gasket to tighten up the quench. I don't think with what you are building that would make a rat's *** of difference, but some of the Internet "experts" will make it seem like the sky is falling with a quench of 0.049", which is what you will have. The numbers change if you decide to zero deck it (by having another 0.010" milled off the block deck). In that case, you would need a -10.4cc volume for the pistons.

Rich

GRNcamaro

well im just gona run it with the -5cc pistons that would be a safe bet right?

chief455

Don't get chased away from your project - I'm sure you can figure it out real quick.
In your first post you left out a few pieces of info you/we/they need to figure the static compression ratio.
head gasket thickness = usually 039"
head chamber volume = stock = 58cc, call Lloyd and ask if when you get your heads done, he can set them between 52-58cc by milling or opening the chamber a little. Most porters I know end up with more volume after porting and mill the gasket surface to get the desired volume for compression ratio agreed on before starting work.
Last thing you need to know is the block deck height.
It is ~ 9.010" stock - but when machinists bore/hone they usually like to deck/square a block to insure it is all in alignment and gasket surfaces are flat. As Rich said - most insist in a zero deck (cylinder top even with the piston top - piston NOT down in the cylinder .010" like stock).
It is a negligable difference regarding performance on a mild street motor - but since they are machining your block, you may want that done just to give you a solid number to go by AND a flat/square surface. Zero deck may cause problems for some guys by putting the valves too close to the pistons - but that's an entire different topic. You should be fine with a mild street cam. Again - ask Lloyd about your cam lift.
So - decide if you will have your block machined to 9.00" (zero deck) or leave it stock at ~9.010"
Find out how many cc chamber volume your heads may range when ported and use .039" for your gasket. NOW you can select the piston top cc volume. Go with something offered off the shelf if possible. It's a very common combination you're doing - go with the piston cc that will put your compression ratio right at what you decide - or a little lower. Yes you can fly cut the piston tops to raise the ratio a little but if you are within ~ .2 points either way, why bother and pay $. Play it safe in this portion of your build.

As for desired ratio to use pump gas - play it safe and stay at 11.5:1 or less. Just my unprofessional board member advice - not a God given fact. Going higher gains so little in power but risks much in detonation and difficulty to tune on pump gas.
You'll have the power from good head porting, cam selection, headers/intake, etc. and the ability to use more ignition timing for crisp response. Too high a ratio with pump gas most times makes you be conservative with timing to avoid detonation and/or power loss - or damaging the motor. Too high compression can hurt the motor - too low compresion can hurt peak power.
You can still drive, enjoy and tweak for peak power - you can't drive and enjoy or tweak damage.

Use this calculator - change head cc's, deck height, piston volume - watch what the ratio changes are like.
That will give you a feel for which specs make the most change

http://www.rbracing-rsr.com/compstaticcalc.html

GRNcamaro

i havent sent the heads out to loyd yet im going to give him a call in another month and send them out before spring. the block hasn't gone to the machine shop im going to talk to my machinist this week . interms of a cam im still up in the air i have no idea i want something a little on the agressive side but i might just go with an le2 cam
this is the first engine im building performance wise by self my dad refuses to help me on it so i feel a little lost on the numbers

if you guys want to throw in a cam suggestion feel free to. the car is gona be a weekend warrior sorta just cruise and take it to the strip. my cobalt and my truck are my dds. the vett is just a garage queen. the 383 in that my dad put all the parts together for and i assembled.

chief455

you're way too far from enough information to give cam suggestions.
Once you know what you really want to drive the car for - street or strip, auto or manual trans, how much power can the trans and rear end handle, what rpm can the motor handle, what heads/intake/compression do you really have - THEN you can discuss cam choices.

Start where you are - pump gas or race gas?
expensive block or budget build? LE2 package with LE3 cam? - talk to those people and give them a consistant guide as to what you want when you're done.
if you keep leaving choices - nobody can really help you decide what YOU want.

GRNcamaro

well ill answer what you have given me so far.

pump gas

i dont mind spending a few bucks but im not dont want to go insane on the engine. i know there are people here who have over 10g into the motor.

im gona be running le2 head

im trying to decide on compression now and what engine set up im gona run. mostly the point of this thread.

the trans is a auto and gona be rebuilt

the rear is either going to be rebuilt or replace with a 12bolt i havent made up my mind yet.

i have no idea what rpm the engine can handle.

the car is gona be a street/strip car

i rather leave the rear and tranny strength out of the equation because there gona be dealt with after the engine is assembled and i know where ill be at hp wise.