capncrunch

Okay,
I am piecing together a '97 LT1. I need to know what the maximum lift is for the stock springs, and (separate question) what head-gaskets I should use with new 'stock' pistons and .010" off the heads?

The cam I have is only .480/.488" lift and Comp said it should work fine with stock springs. However, I am considering using 1.6 Rockers and didn't know if that would be too much lift? I would like to save as much money as possible, as we are looking at buying a house, too. Any input?

I have found several different specs on-line for the stock head-gasket thickness (anywhere from .040" to .050") and have decided that I would rather err to the side of too thick, than too thin, as I'm going to run a 6lb supercharger with it. Because of the supercharger, and the .010" milling, I don't want to get too thin (increased compression), nor do I want a 'weak' gasket.
What do you guys suggest?

ACE1252

You are going to run a supercharger and are worried about using stock springs?

In my opinion, the valvetrain is not an area to skimp on....

I'm not trying to be be mean, but do protect your investment.

Bersaglieri

I have what I actually measured somewhere, but from my book I have 85lbs @ 1.780 and a solid height of 1.260. That shows .520 installed to bind, but you're going to need clearance, typically .050-.060" meaning you should only put them to around .470 lift max. That's assuming all installed heights are 1.780, which typically they are not. Lift isn't the only thing you need to consider when choosing valve springs, they must control the valve as well.

Choosing head gaskets is something you need to decide on after calculating what you're finally compression needs to be. Wallace Racing is somewhere I use to calculate engine specs.

PS Comp is wrong. It's unfortunate, but most of the tech line guys are clueless. Do you think the smartest people who work there answer calls all day or get paid more to do something worthwhile?

-Dustin-

capncrunch

Wow! you guys both make really good points!
So, what then, Comp Beehives? Maybe I could up the rockers to 1.6 too then? (I haven't bought any yet...)

Also, I tried to use one of those compression-calculators, but couldn't decipher their symbols!

Here:
CR = [{(B/2)^2 * S*Pi}+Vcc+Vp+{(B/2)^2*Pi*(DH+TG)}]
[{(B/2)^2*Pi*(DH+TG)}+Vcc+Vp]
Where:

CR= Compression Ratio
B = Cylinder bore (Stock LT1 = 4.00 in)
S = Stroke (Stock LT1 = 3.48 in)
Vcc= Combustion Chamber Volume (Stock LT1 = 58cc = 3.539 in3)
Vp= Piston Volume (Stock LT1 = 4.5cc = 0.274606 in3)
DH = Deck Height (Stock LT1 = 0.015 in)
TG = Head Gasket Crush Thickness (Stock LT1 = 0.050 in)
Pi = 3.1415

I KNOW that MOST of these numbers will match my 'stock' rebuilt motor, with polished crank, 'stock' sealed power pistons, 'stock' heads (except for .010" head-milling.)-Anyone know if I can take that amount off of the deck height and be 'even'?

BUT I don't know how to read the symbols in this equation... (What are the ^, * symbols supposed to mean?)

BTW- Ace, I ran ALL stock internals with 4.5lbs of boost for almost 80,000 miles (from 36K to 115K) before I blew a head-gasket and overheated the motor on the way to work one morning.
So, I wasn't just acting without any basis, BUT you are right about skimping and protecting our investments!

Bersaglieri

I prefer not to use beehives, that's just personal preference. Plus with .480 or even .500 lift they are hardly worth the money. There are many replacements that would work. LT4/Hotcam springs [.525 lift] and Isky 235D [.550 lift] could handle the lift and mild camshafts. Show us the camshaft and we can give you the lift with 1.6's and what springs can handle that lift.

^ = to the power of. So 4^2 = 16.

Regardless I'm not a fan of doing compression calculations long hand.

http://www.wallaceracing.com/Calculators.htm

Compression one is on the left hand side.

With supercharging you typically want to lower the compression below the stock amount. Play with that calculator and see what you end up with. Decking you're stock heads aren't doing you any favors since that will bump compression.

-Dustin-

capncrunch

Camshaft is a Comp 07-500-8 (Xtreme Energy 258HR-12)
Specs: Duration .258I /.264E
Lift .480I / .488E
112* LSA

The engine compression calc said 10.71 (assuming that subtracting .010" from the head-gaskets is the same as milling them .010"). So, in theory, I should be able to get some .060" gaskets and be back to 10.4 or 10.5 to one?And NO, I didn't want to mill them, but had to to get a good flat surface for the rebuild.

BTW- I was not sure about this cam being the best for the SC. Is there one that would be better?

ACE1252

The general consensus around here is if you change the cam then you need to upgrade the springs. Plus, it does not make much sense to me to reinstall tired stock springs on a freshen up.

I didn't know you already had the supercharger for so long. I figured you had just dropped some nice coin for it and my thinking was why not for a set if springs.

Good to hear it lasted such a long time with the LT1's high compression numbers.

I've got a set of PAC's 1518's, but I have read of the beehives giving up pressure early....so far mine seem fine. I ran across a good recommendation for a dual spring, but can't remember what it was. Hopefully, others will chime in on a good spring for supercharged apps.

Bersaglieri

That XE500 is barely bigger than stock. The @ .050 numbers are 206/212, stock is 202/207 with .450/.470 on a 116LSA. Not a horrible thing, but if you're going in there you'll see good gains without sacrificing much low end if you go a little larger on the camshaft. That means more power before adding boost. Thunder Racing, a site sponsor, has some nice boost oriented camshaft. In my opinion, something like their Comp 218/230 .495/.510 [.528/.544 1.6 rockers] on a 114LSA would be great for your setup. Driving characteristics and all motor power of a Hotcam or CC305 but tweaked a little for boost.

.010 off the deck or head gasket is not the same at .010 off the head. .010 off the head means a smaller combustion chamber. Best way to do things would be to have the head CC'ed by a shop unless you can do it yourself.

Even if it isn't accurate 10.71 is a little higher than ideal for a boost rebuild. If you can do anything to get it lower, I'd try to get it down. Dish pistons would be the typical way, but your options seem limited.

Not sure what you use for a tune, fuel pump, and/or injectors, but those may need addressed with the added power from this rebuild. Just something else to consider.

-Dustin-

capncrunch

Thanks guys!
I agree (Ace) with the new springs being the best idea, and will get some for sure
Bersaglieri, I will change tune, I have a 255lph fuel pump and 30lb injectors. Also, since I aready have the reciprocating-assembly balanced, I AM limited in options...
COULD a thicker head-gasket get me where I want to be on CR? I know this time I'll have the layered steel with cylinder-ring gaskets.
I appreciate the input on the camshaft, too. I wasn't sure about thie one I bought, but Comp seemed to think it was good for the app.
I wonder how they are on returns?

Bersaglieri

A thicker head gasket would help lower the static compression, however, cylinder pressure is going to be exerted on more gasket area than when using a thinner one.

If the camshaft is unused, [not sure if you bought it straight from Comp], but I'd ask to do an exchange at the very least. I don't see why they wouldn't return it if it's within a reasonable time frame. Let em know they are still getting your business, just in the form of a S/C camshaft.

-Dustin-