S-10 Forum banner

1 - 20 of 53 Posts

·
Registered
Joined
·
1,561 Posts
Discussion Starter #1
Does anyone know for SURE the stock compression on a '99 4.3l? Its pulled from a zr2 if that makes a difference. Im taking the heads to the speed shop this week and im gonna throw some money at them. What do these heads respond well to? Im already planning decking them to increase compression, and probably larger valves and a port job. What else should I get done? I got quite a bit of money to work with here so give me some ideas. Thanks
 

·
2nd place is the1st loser
Joined
·
238 Posts
The compression ratio is 9.2:1.As for what to do to the heads.Your already going good with a port and polish with bigger valves.Since your wanting to spend the money buy some good quality valves.I would also have a 3 angle valve job done to them.Some good strong valve guides and valve seals.If your gonna put a different cam in get better springs.While your at it buy some full roller rockers.That should make a stock set of heads happy.:headbang:
 

·
Registered
Joined
·
1,561 Posts
Discussion Starter #3
I heard somewhere that polishing should only be done on the exhaust side?? Is it okay to run 2.02 valves or is that too big for the street?
 

·
2nd place is the1st loser
Joined
·
238 Posts
You wont see great gains for the most part.But it will provide better flow.You can just have a porting only on both sides if that what you want.
 

·
Road Race/Auto X S10
Joined
·
3,828 Posts
I recently had my heads done by mach. I ordered the stage 3 porting, along with machined valve guides for my new cam, and bigger valve springs. I stayed with the same size valves since the lift of the cam was alot higher than stock, I didnt want to risk any valve to piston clearance issues. I beleive you can run 2.20 intake and 1.60 ex valves.
 

·
2nd place is the1st loser
Joined
·
238 Posts
I wouldnt run any higher than 2.02-1.60.Any bigger wont show much of a difference on your engine.And your probably safe on clearance with just a decent cam and stock pistons.
 

·
Road Race/Auto X S10
Joined
·
3,828 Posts
Thats what I ment 2.02 duh. I'd definately look into it before running a .500+ lift cam with those valves. Theres only one person that I know can give a for sure answer and thats bill so give him a call. www.machperformance.com
 

·
Registered
Joined
·
940 Posts
mcgruff1 said:
Will those 2.02/1.60's clear with a cam w/.500 lift?
just cuase the valve are larger doesn t mean they won t clear, but i m running 2.02 and 1.60 valves with a .500 + lift cam and i have plenty of clearance, as long as your heads are setup to handle a cam that big you ll be fine, a good machine shop should be able to tell you what will work and what won't.
 

·
2nd place is the1st loser
Joined
·
238 Posts
He was concerned with clearance because he is having the heads milled down.Not because of the valves.
 

·
Registered
Joined
·
263 Posts
im not trying to be an ass, but isnt there a better way to raise compression without decking?
 

·
2nd place is the1st loser
Joined
·
238 Posts
You can change the pistons or a head with a smaller cc.
 

·
Registered
Joined
·
1,561 Posts
Discussion Starter #14
The short block is in awesome shape and I dont want to pay for new pistons+install, and I dont even think they make performance heads for the vortec 4.3. Whats wrong with milling the heads? They were gonna be milled down to get between 9.75 and 10:1 compression, I'm not sure yet about how everythings gonna clear but I'm talking to my speedshop tomorrow and I'll see what they say.
 

·
Registered
Joined
·
561 Posts
The only problem with milling the heads is running into sand pockets within the casting. If you don't your all good and there isn't much difference when compared to pistons or smaller chamber heads accept that higher compression pistons have deeper valve relifes for clearance. Decking the head moves the valves that much closer to the stock piston.
Example
Stock piston/head has say .085" valve to piston clearance.
If you cut .120" off the head you slam a valve into the piston.
If you cut .075" you risk doing the same thing should you suffer from any valve float.

To avoid this
Take a piece of plasticine modeling clay
Stick it to the top of a piston
lay and old allready compressed head gasket on the block
Lay a head on top of it and bolt it down snug (torque to spec is not required)
With the timing and cam and rods etc... all in there turn the crank by hand 2 full revolutions.
Take the head back off
Cut the clay with a sharp knife at the thinnest part of it where the valve made and impression
Measure it's thickness.

That's how much clearance you have
Don't have your head cut more than would move the valve within .015" of the piston.

If the clay is .095"
Shave the head .080" MAXIMUM!
If you are going to install a cam larger than the one you tested with include it's difference in overall valve lift in your calculations.
Same goes for 1.6:1 rockers.
 

·
Blown ex ***
Joined
·
5,710 Posts
this taken from another site. VERY reliable.
keep in mind this is V8 info. but helpfull none the less. enjoy.

(1) open throat to 85%-90% of valve size
(2)cut a 4 angle seat with 45 degree angle .065-.075 wide where the valve seats and about .100 at 60 degrees below and a .030 wide 30 degree cut above and a 20 degree cut above that rolled and blended into the combustion chamber
(3)blend the spark plug boss slightly and lay back the combustion chamber walls near the valves
(4)narrow but dont shorten the valve guide
(5) open and straiten and blend the upper two port corner edges along the port roof
(6) gasket match to/with intake and raise the port roof slightly
(7) back cut valves at 30 degrees
(8) polish valve face and round outer edges slightly
(9)polish combustion chamber surface and blend edges slightly
(10) remove and smooth away all casting flash , keep the floor of the port slightly rough but the roof and walls smoothed but not polished.
(11) use a head gasket to see the max you can open the combustion chamber walls
(12) blend but don,t grind away the short side radias

(13) have a local machine shop clearance the retainer to valve guide distance and add aftermarket springs and valve seals
(14) there are valve keepers available that add .050 extra clearance(USE THEM) but make sure the valve springs you use and the rocker/valve train geometry are set up correctly to work with the larger valve spring height and clearance!
(15) use the CORRECT matching rockers
(16) adding, machining for, screw in rocker studs is a good idea!
(17) your wasteing time and money runing a vortec head engine with an extreme high rpm cam,and intake, especially on a larger 383-427 displacement engine, the heads are designed to make massive torque in the 2000rpm-5500rpm range on a 350 displacement engine, they will not efficiently feed a 7000rpm combo on a larger engine so build your engine with that in mind

.............................


Too add, this is a direct quote by "gary at GMPP" from team chevelle. He is extremly well versed in vortec heads:


Quote:
--------------------------------------------------------------------------------

Two years ago we undertook an exhaustive (no pun intended) study of the Vortec head in numerous modified states with different valve sizes, throat cuts, valve jobs, port mods, guide mods, etc. We used up about 10 heads, numerous valves, and about $50,000 worth of labor. The study generated 100+ pages of flow and swirl data,which I have at my desk.

Here is the short version. Out of the box, .480 valve lift, 350-400 HP dependant on the CR, cam, ring seal, oil control, blah, blah, blah.

More than .480 lift, cut the guides down to clear the retainers.

Straight mill up to .060 safely, .080 with low CR of 10 to 1 or less. 0.100 is living on borrowed time.Always use flat top or dished pistons to enhance flame travel and intake swirl.

Angle mill up to 1 degree (about .110 off the exhaust side, .000 off intake side) safely for about 12 to 1 CR with flat pistons with little valve relief. Angle mill to 2 degrees (about .200 off exhaust side)if you like to live on the edge, it has been done.

Larger valves increase flow, chamber mods not needed, trade off between shrouded verses unshrouded valves not worth the decrease in laminar flow and swirl.

Throat cutting behind larger valves compliments the larger valves. Open the throat to the seat, remove the edge left by the cutter in the port.

Blend the seats into the chamber, you don't want an edge here to disrupt flow and create turbulence.

"Bowl blend" and shortened guide in port also improves flow. Taper and blend the iron boss.

Minumal porting increases flow, too much increase in port size or loss of the benefits of the shape of the stock port will decrease efficiency.

Vortec heads (and most others) like straight stemmed valves. Undercut valves create unwanted turbulence and a decrease in intake charge velocity (they add volume (slowing the gases)to the overall "port" volume just behind the valve where max velocity is required.)

Generally speaking, Vortec's stall at between .500 and .550 valve lift. This is where flow actually begins to decrease. But their true strength is low lift flow which gives more area under the total flow curve. And if you think about it how long are your valves at peak lift? They spend much more time at .400 and below, where the Vortecs outperform most other heads. This combined with high velocity, lack of turbulence and superior combustion chamber design are where the Vortecs stand out.

Unported, with all the other tricks in place, the Vortecs will flow about 235-240 CFM at .500 I and 165-170 cfm at .500 E, on a 4" bore at 28" H2O, with clay radiused port opening. With some careful porting there is another 5-10 CFM or so to be had. But again the low lift numbers are unsurpassed at .100, .200, .300, etc. lift. For example the Vortecs flow as much air at .400 as .500 and no 23 degree head that I'm aware of can match them at .200-.300 lift for the combination of flow and swirl. Even the Fast Burn head can't touch them at low lift, it's ports are too big (flow is similar, swirl is less), it does of course out perform them at lift over .500.

Unported Vortecs with the "tricks" can produce 500 HP on well built, high CR, drag race short block. 425-450 HP is more realistic for a killer street engine running on pump gas.


--------------------------------------------------------------------------------
 

·
2nd place is the1st loser
Joined
·
238 Posts
That last post was about as good to the point as you can get.Mcgruff I wasnt telling you to not mill the heads.The other guy's ? was other ways to raise compression.That is why I gave those awnsers.I think if done right milling the heads is the better way for a street driven car to raise compression.Your on the right track stay with your plan.
 

·
Registered
Joined
·
1,561 Posts
Discussion Starter #18
Can you tell me the stock piston to valve clearance? The heads are gonna be milled down .040" as of now, with a .500 lift cam and 1.6 exhaust valves, stock intake valves, blended bowls, deburred, and a few other things. Can anyone tell me if it will work or at least tell me the stock piston to valve clearance? Oh ya stock valvetrain too.
 

·
2nd place is the1st loser
Joined
·
238 Posts
The best people to ask will be your machine shop.If they cant tell you what it is you should find another machine shop.I am not 100% sure but i would bet with that mill you should be fine.I wouldnt have went with that big a lift cam.Its almost over kill for a daily driver.but call your machine shop up about your concerns and get a 2nd opinion if you have doubts about them.
 

·
Registered
Joined
·
1,561 Posts
Discussion Starter #20 (Edited)
Its a pretty reputable machine/dyno shop, but they cant tell me the piston to valve clearance for this engine. They almost exclusively work v8's. The guy says the cam should be good (comp 270hr) in the engine, but Im definitely gonna get a second and 3rd opinion. I read above:
.Straight mill up to .060 safely , .080 with low CR of 10 to 1 or less. 0.100 is living on borrowed time.Always use flat top or dished pistons to enhance flame travel and intake swirl.
That would mean .040" milling + .020" extra lift would = .060" which should work in theory, right?
This is for the vortec v8 heads, is this the same for my engine too?

Thanks again for all your help
 
1 - 20 of 53 Posts
Top