As stated in my last thread, I'm gonna be picking up my 96 vortec 350 REALLY soon and I'm gonna need to start ordering the few things it needs. One of the things it needs is a complete gasket kit. Now while I was looking through my Jegs catalog, I was thinking....cant I get thinner head gaskets and bump the compression up a bit? Isn't the stock CR something like 9.4:1?

Could I get a head gasket that would bring it to maybe 9.9:1, or would that be too much? OR, would it just not be worth it at all?

The motor is gonna stay pretty much stock. I'm not gonna touch the heads as they only have 5k on them. The motor has roughly 130k and doesn't smoke or burn one drop of oil, so I'm gonna leave it be. I AM gonna change the cam to a 96 (Z28) LT1 cam I have, get a nice single plane intake, and slap some headers on it. And I figured a nice .5 bump in compression would yeild a few extra ponies...

Good Idea, or NO?

 

I've been trying to find out a few things about the vortec truck motors myself. Most specifically, what the CR is on those from the factory.
Have you taken off the heads yet? Are they dished pistons or flat?
If you don't mind taking your block apart, milling the deck is a way of raising the CR. Milling the heads is too. A thinner gasket would have some effect, but possibly unnoticable.
Hope this helps, Good luck.

 

The thinner gasket would raise compression a noticable amount. I think theres a formula for CR on the formulas page. If not just email me and i can send it to you. Also with the setup you have, you will proabably make more power with a dual plane manifold.

 

Or you can use this one.

http://www.kb-silvolite.com/temp/calc.php?action=comp

 

According to that site, stock CR on the vortec 350 IS 9.4:1 with a .045" gasket.

I put in .032" for the gasket and it says it'll be 9.7:1. So I figure with a .035" gasket and a LITTLE bit of milling on the heads will bring me to my desired 10.0:1.

Is that too much CR for a stock iron vortec motor?

 

Are your pistons flattops?

 

too much for far to little gain..


you might even get some loss because of timing you have to pull out.



if the motor is going to remain mostly stock, like you said, doing this will make you need premium gas..... and with no gain..

id leave the compression alone.. 9.4:1 is plenty for a iron headded performance street motor.

you're better off getting a diff cam or searching elsewhere for power.

 

Mr Dude is right. That's too much IF you're keeping the stock cam.

One thing about short lift/duration cams is they build cylinder pressure rather quickly (high dynamic compression ratio, or "DCR"). That's why they build good low RPM torque.

A long duration cam looses some low RPM cylinder pressure and trades it for higher RPM cylinder fill (not the same as cylinder pressure). The normal method to make up for the loss in DCR is to raise the static compression ratio (the one on paper).

Right around 8:1 DCR on a street engine is acceptable for high octane gas. If you want to run lower octane you have to lower the DCR a little. You can actually do that by putting in a larger cam... OK, I'm starting to stray off.

Use this download to find out what the approx DCR is on that engine. Then you can play with the SCR and the cams to get the DCR around 8:1

Don't take that program as gospel either. It's to be used as a GUIDE.

Read the page first, then download the program.
http://members.uia.net/pkelley2/DynamicCR.html

 

he said hes using the LT1 cam... thats not going to really bleed off enough to let him get away with the higher compression

 

It hardly makes sense to try to calc the CR based on what the claimed factory CR is, and then subtracting .010" in gasket thickness. Because the claimed CR is always off to begin with.
It'll raise the CR alright, but if you really want to know you have to measure all the values used in the CR calculation.
A camaro can use more CR than a truck.
I think some guys are using something like 9.75:1 with vortecs, possibly more. It depends on piston design too. Some of those factory dished pistons are next to worthless when it comes to closing up the quench clearance.
That's howcome I was wondering about the piston design.

 

supposidly, the vortechs kidney chamber is suppost to be efficent enough to get away with a lil more, but i wouldnt go over 9.5:1 still on a street car... since its already suppost to be at 9.4:1 i wouldnt change anything for that .1 point.... it would make no diff in power, but a diff in octane tolerance and timing...

 

Oh yea...I must have missed that.

And again you're right. When GM used that cam in the LT1 with IIRC, 10.1 comp., they had to use aluminum heads, reverse flow cooling, knock sensors, and SFI to get it to run on 87 octane, and said in the owner's manual that 91 or higher is recommended in the summer.

 

Whats the lift on that year lt1 cam? I only ask because youll have to change the valve springs if its any more than .460. I hear you can run up to a .480 lift but I wouldnt go past .460 with out changing the valve springs. Just thought I would throw that in there I am building a vortec motor myself right now. Good Luck.

 

The LT1 cam in the 96 Z28's were .449/.462 and I figure that I should be alright with the stock valve springs.

I'll leave the compression ratio alone after hearing all this

Thanks guys!

 

I'd still recommend installing a stronger spring. The lift of the LT1 cam is .035" higher than the biggest Vortec cam (.427" on the exhaust). The factory springs suck butt.

I'm not gonna say which ones exactly, but Comp Cams recommends 981-16 with a roller cam of their's that has similar specs to the LT1 cam, just a little more aggressive. Hint, hint.

http://store.summitracing.com/partde...%2D8&view=2047

You'll have to remove the damper to run them without having the spring locator on the valve guide boss cut smaller.

Just to be sure, I'd call them at 1-800-999-0853 and see what they say.