I've talked to so many people who are running .475+ cams with stock vortec heads though... And I really think the retainer is far away from the valve guide. We'll find out though.

 

I put a pair of 8062 vortec heads on my car with 0.480/0.488 lift. The only change I made was putting Comp Cams 981-16 springs on. I can only tell you that the heads have given my no grief to date.
I haven't measured the coil bind with stock springs, so would have to rely on BMmonte's values- I have no reason to doubt him. It's just that the are so many articles out there with different max lift values for those heads when stock.

I think the best way to resolve this is to pull out a couple push rods and see if they are straight and check the valve seals for any signs of interference or damage.

S-D

 

the lt4 HOT cam is .492" lift with 1.5" rockers. 5.25" lift with 1.6 rockers.

i'm pretty sure the maximum lift on stock vortecs is either .460" or .480", but that would only come into effect at higher rpms, wouldn't it? i thought the problem was the spring wouldn't be able to cycle fast enough and the valves would float. is that wrong?

is there a way to check the coil for output? i know you can take your ignition module to any napa store and check it, but don't know about the coil.

when my car died this summer, i spent over 800 bucks replacing distributors, wires, modules, labor for troubleshooting when i couldn't find the problem, etc. it ended up being a partially functioning ignition coil. before he goes pulling the heads off this thing, i think he ought to try every basic check .... twice.

1. if there's no way to test the coil, borrow one off a car that is working and try it. if i'd done that, i would've saved myself weeks of grief and hundreds of dollars.

2. have a friend check your wiring order. i know it's dead simple, but it could be being overlooked, you might be dyslexic or the victim of a druid curse.

3. pull the ignition module out of the distributor, take it to a napa store and have them check it.

4. check all grounds and fusable links.

5. pull the passenger side valve cover and #1 spark plug. slowly rotate the engine until you feel compression out of the #1 spark plug hole. stick a straw in the spark plug hole and slowly rotate the engine till the cylinder is at the top of the stroke. your timing mark on the harmonic balancer should be at zero. if it isn't, you probably have the balancer installed wrong.

5b. after placing the cylinder at tdc as outlined above, both of the valves on the #1 cylinder should be completely closed. ideally, you should be able to wiggle the rocker arms and have a little freeplay. if the valves aren't closed, you probably have your cam installed significantly advanced or retarded.

before i started pulling heads or pushrods, i'd make sure i'd double and triple check all of the above and more.

 

Yes.... I was focusing only on the head being a problem- there are other things to rule out first.
S-D

 

there is a little more to this. there is a point where the parts start to actualy hit each other, the pushrod his the side of hte hole where it pass through the head, retainer and lock hit the valve guids, or the spring actualy 'bottoms' out. when this happens you start to break parts, it is not fun. the other thing you have to be concerned about is the point at which the rocker arm studs, actualy pull out of the head, the hiehgt varies depending on spring pressure. the more pressure, the sooner they pull. this also isn't costant, one set may be fine with heavy springs, at .480 lift, another might pull at .460 with light srpings, this is sort of a matter of 'chance'

 

first thing I'm gonna do is relocate that bad ground wire, then pull some pushrods and roll em around. after that I'll replace the coil and ignition module. if all else fails, I'll bxtch and moan about it to you guys some more.

 

I've got aftermarket springs, let me dig up the Comp Cams part number...

 

with aftermarket springs, you can probably get .480 lift or so before you bind anything, the question is if you have screw in studs, at more than .460-.470 lift, with aftermarket springs, if you still have pressed studs, you are asking for trouble.

 

Comp Cams p/n 981-16

Specifications:
* Outside diameter: 1.254 in.
* Inside diameter: .880 in.
* Seat load: 105 lbs. at 1.700 in.
* Open load: 295 lbs. at 1.250 in.
* Coil bind: 1.150 in.
* Rate: 423 lbs.

 

:lala:

 

You are good to go on the spring bind issue with the 981's.

The two sets of Vortec heads that I have checked with a dial micrometer have both been consistant at retainer to seal measurements of .465".

If you subtract the .050 safety clearance you are down to the earlier mentioned .415". With the stock LT cams you are going to be close IMHO.

I doubt that anyone sent you the LT4 hot cam. I just bought a new (takeout ZZ4) cam from Sallee chevy and it came in the hot cam box as that was the cam that they take the ZZ4 out for.

Anyway you can correct for any of the LT stock cam clearance problems with shims and .050 offset locks.

Found anything new out?

 

No new data to report... but how much do shims cost? lol

 

Shims Comp Cam 4748-16 $6.98

Locks Crane 99045-1 +.050 $17.98

Goodluck

DM

 

are you calling BS on the pressed studs pulling out with aftermarket springs at the .460-.470 lift range?

if you are, ask me how i know this. ask me why i know how to put in screw in studs with the heads still on the car, in 100*+ weather in a rush to get the car running.

 

If it were me....

BEFORE you pull the valve covers / pushrods etc.

I'd borrow a distributor / coil off a car, or just hit the junkyard.

Sounds to me like your're NOT getting spark.

An engine will RUN with bent pushrods....not good..but it will run.

After that I would verifty TDC, check the pushrods, then adjust the valves again...

 

glad to see some one else also has the same measurements that I got. You also have to acount for casting variables as well as the operator of the seat cutter being a dumb a$$. When I checked some of my older heads I found some that were up to .020 different than the others. I wiped out 2 cams becuase everyone said that .460 lift was fine on stock heads with z-28 springs, including my machinist. WRONG, check yourself. Most older heads get retainer to seal interference at around .460-.465 lift some sooner some later.

 

I was just calling BS to the fact that I had to take the damn heads off the car again

 

I love the fronts of our thirdgens for tool storage as well, it can fit most of my tool box on there, except when the socket you need rolls down and gets down behind the headlights. However i have found it a pain that whenever you have the intake off, those damn throttle, and tv cables love to hang out in the valley, especially when your trying to get the new intake on, and they just wont get outa the way

 

I can bend mine back and have the master cylinder hold them out of the way. I know exactly what you mean and this way keeps them far away and out of your RTV.

 

its all good folks, the car is running. gotta tweak it a bit, but I'll update you on that part later.

 

So what ended up being the problem? I haven't been on in a while and missed it.

 

Continued in another thread...

https://www.thirdgen.org/techbb2/sho...hreadid=231194

 

I had the valve lash set too tight
Anyway, I think I'm running lean. The car heats up very quickly, and it bogs when I floor it (and sometimes pops out the intake but not always).

 

YES they do, i made a lower tpi intake outta sheet aluminium, thinking the hoood would close. little to my surprise its the best place to park your butt during a cam swap and it doubles as a tool tray.

 

I practically had to drop my oil for that blasted front lip, next time a 2 peice cover is going on. I used a ring packing tool to manipulate the seal into cover, basically a round bar with a point and a hook on one end.

 

FAST FORWARD ONE MONTH:



The car is running fairly well right now. It's very fast compared to the stock L03. It's still lacking the power under 1500 rpm (it can't squeal the tires from a stand very well, and it doesn't chirp the tires). I don't know if that's due to a bad AFR or if that's just the property of the cam. In any sense, I probably want a new torque converter fairly soon.

The car is getting bad gas mileage (12-13 combo city/hwy) and I don't know if that's just because it was running lean or not. I have bumped the fuel pressure (like an hour ago) but I don't know the effects of that until the next tank of gas. Am I getting poor mileage because I'm running lean, which the computer then tries to correct for it? Or am I getting bad mileage because the car is heavily modified and my C/R is only ~8.5:1?

 

Its because you have need tuning badly. I was only getting ~8 mpg until I started with good ol WinBin, and now GMECM Edit. From what I read, the ****ty performance under the stall speed means (we) need more pumpshot. Ima hook my wide band O2 up to it in a few weeks here after finals and really start tuning, Im sure you might want a bin of such a similar combo

 

We have very similar setups. First the compression ratio ain't killing your gas milage. I get at least 20 with mixed driving. I go through several heavy throttle runs a day. (Why else did I mod it?) X-way is sometimes stop and go and generally otherwise 75-85mph. The worst I got was with the 350 untuned and it was still 18 mpg.

What psi are you running? And what injectors are you using? (I forgot sorry)

I myself am guilty of not enough tuning because of not haveing a laptop to run Winaldl..but that will change soon. I did run a scanner alot to get this close. Have you got anything to datalog with?

 

haha very similar...

how do I read the bin? I think I need a chip reader, but are they cheap? I'm too scared to goto the DIY PROM boards, those guys are mean too.

approximately 14psi (about three threads left under the screw if that makes sense) and stock 55# injectors that came with my TBI. I'm using the stock TBI because I HATE HOLLEY'S LINKAGES! grr.... Anyway, I have not logged any data, but I've made three cables... NONE OF THEM WORK! I've been using this schematic and I've tried both data terminals (E and M)

 

dude with those mods that thing should destroy those rear tires something is off big time

i know this cause my LO3 runs high 14s and demolishes radial tires from a dead stop and then again in 2nd gear

 

Token, double check how you wired the switching transister. If it's wired wrong you won't get any data. Oh and by the way, where is the M terminal?

Steve

 

I tried almost every combo... I'm not using R3 or R4. I've tried two different NPN transistors. I'm not new to electronics...



And I really don't know what's wrong with my low-end, because I can BARELY spin the tires and they're not sticky tires either.

 

From what I understand you want to use the one WITHOUT the 12V source. That could be your problem...

Bruce (90RS305)

 

the #4 pin is +12v from the computer itself...

 

Do you know anyone in your area that is using winaldl that might let you try their cable and or laptop just to see if it might not be a cable related problem?

Steve

 

I dont knw anyone in the area with a computer controlled thirdgen.