I am currently building a vortec headed 350 for my 89 RS....I am using the EAGB13402L rolling assembly from Competition Products, and would like some suggestions on deck height for this setup....The heads are 96 vortecs, which have been shave 20 thousands, the block is also a 96 and as yet has not been decked...Did a search but did not come up with much...The pistons are the Speed Pro Hypers .40 over..Would like to get optimal quench, and compression......Thanks, Tom

 

Deck it to 9.010 which should leave pistons in hole .010" and run a .030-.032 gasket. This will leave enough deck for another rebuild if you ever need to bore and resurface

Else 0 deck it and run a .039-.041 gasket which is pretty standard size. Dont overhang gasket into chambers and it will run great.

 

Of those two options Orr gave you, I'd prefer the 9.010, only because it leaves you the option of cleaning up the deck on a possible subsequent rebuild. And use an .026" gasket : GM part no. 3830711 or Mr.Gasket 5716
No sense in shooting for more than .036" quench clearance.
I'm not sure how true that rotating assembly will be though. You might want to have it in hand and either measure each part ACCURATELY before cutting the block. If they really square up the block well, you can go tighter than .036". Shoot for a MINIMUM of .032" There is no such thing as too tight on quench! as long as pistons and heads don't meet Everything about the motor improves as you tighten that clearance.
What cam do you plan to run?

 

Thanks for the replies guys....The 9.010 sounds good...Cam is as yet undetermined...As it sits the car has a 2700 rpm stall, 700r4, 3.23 gears and a weight of 2900 lbs without me in it...Defiantly going to change the gears as soon as possible..Forgot to mention the guides have been cut, and springs selected for up to .560 lift..The car is not going to be a daily driver....Am open to any suggestions, once again thanks...

 

It sounds like you're gonna have about 11:1 CR, so it will need a big cam to run on pump fuel. Something like a Comp XR288.

 

That kit still a 3.48 stroke right? Shouldnt be near 11:1 with that piston unless i got the wrong specs from trying to look up that part number

 

Yeah, those pistons have 7cc valve reliefs.
I actually ran the numbers this time:
assumed chambers of 60cc (guessing about 1 cc per .006" milled?)
deck clearance .010"
gasket .026"


SCR = 10.78
DCR with a 282 cam at 106 ICL = 8.45
Right about where I'd want things with iron heads and premium pump gas.

 

Thanks guys, it sounds like this setup should work out well for a little track fun...Those are the 7cc, four brow pistons...Have had the 89 since 2004, and am ready to cut loose with it......Anyone have personal experience with a setup similar to this as a whole???

 

Seen that similar combo with a vic jr carb intake and comp 288hr run 11.7's

 

Orr, that is what i was wanting to hear....

 

11:1, IMHO, is too high for cast iron heads on pump gas. I would like to hear explained how a large cam, that will increase cylinder pressure through the engine's power band, is going to help run too high CR on too low octane.

To the OP: I would hope that on any serious build you are using a good machine shop that has alot of experience building and tuning high horsepower engines. Talk to the machinist about your build plans and listen closely to their advice. The worst thing that could happen is to go to the expense and time of building this engine to end up with something that won't run, or worse yet that destroys itself in short order.

 

Thanks for the reply, but I can in no way imagine the combo i have being anywhere near 11:1 CR, even with .020 off the heads, and the block trued up..Eagle shows this setup as 9.6:1 with 64 CC Heads, (3.480 Stroke) I was under the impression this is a decent Street/Strip Combo for 93 octane pump gas...Am I missing something here??? I will definitely listen to my Machinist, as I am great at bolt ons, but not Machine work....

 

It looks like 10.5-10.6 depending on actual gasket thickness and cc of heads. Cc the heads to be sure

Big cam wont make cyl pressure down low where detonation is more prevalent due to slower piston speeds. It will need a big cam to turn rpm to reduce pressure but the right valve events can make it work. May want to talk to a custom cam grinder.

Will need to run it as cool as possible. Big rad and fan. Low temp thermostat. Maybe even an oil cooler. A cold spark plug as well. Back off timing some as vortecs are fast burn

 

^^THAT'S^^ the way ya do it

 

9.6 is generally good for cast iron heads. I forget that the Vortecs are fast burn. They have a good chamber design with plenty of quench area. That and keeping quench at or below .040 will help prevent detonation. I would be nervous at 10.6 on any cast iron head on pump gas. You certainly run the risk of limited tuneability, having to keep timing back from optimal in order to avoid detonation. Talk to your machinist. Like Orr says, keeping temp down will help.

As 86LGBird says above, precise measurement of the rotating assembly and chamber volumes is critical, especially when you start cutting things down to set CR and quench. This is the essence of blueprinting and as we tighten things up for more power, it becomes more critical.

 

So it comes down to a balance between CR and Quench with proper cam Shaft selection to avoid detonation, and produce max power.....Damn this started off sounding so easy........You know I think I suffer from "information overload."

 

Could also have someone hand port the chamber abit to open it up some cc's. Round the spark plug boss, theres some excess metal there

Always a compromise in things

 

Gallileo, right now you're worrying needlessly. Get some accurate measurements instead of postulating all these "what ifs". And then if necessary you can do what Orr suggests, and you can also get fancy by relieving the edges around the valve reliefs in the pistons if the engine's not yet balanced....just be careful and consistent....get an accurate +/- 1 gram scale and keep weighing the pistons as you work on them.

9.6 CR? .. come on, that's what I run for an economy Vortec with 87 OCTANE! ...with a cam that gives me 8.0 DCR. thin gasket....minimize that quench!
With good fast-burning heads like the Vortecs, I wouldn't even think of shooting for under 10.0 SCR for an engine with any pretense of high performance.

 

Havop Been there and done that with 10.4:1 SCR/8.4:1 DCR with iron heads. Cranking pressure was 200 psi plus with a roller 276 cam. To keep out of detonation, it was necessary to pull out a lot of timing. It was especially problematic at cruise. That's when I want the most timing to offset the lean cruise fuel trim I developed to obtain good highway fuel economy.
For what it's worth, timing has a greater effect on engine performance than compression. My approach now is to back off on the compression by about half a point, keep the quench as tight as possible and optimize the timing curve.
One of the best all round performers I've built around Vortec heads was 10:1 SCR/8:1 DCR. Cranking pressure was about 190 psi with an aggressive timing curve that maxed out at 34 degrees. The vacuum advance added another 14 at cruise.
Having said that, I wouldn't hesitate to build a 10.5:1 SCR Vortec 350 with a cam of 288 intake duration provided the intake valve closing event is where it should be (not horribly advanced).