Rayzor32

iTrader: (1)

Ditched my idea of building a 406 and I got a 350 short block from my buddy and some 906 vortec heads. The 350 pistons aren't quite flat tops they have a slight dish in them, im going to run a thin head gasket for compression.

I was planning on running a solid flat tappet cam but may go to hydraulic because of more choices/cheaper.

My question is on the heads whats the TRUE max lift stock? Can I gain more lift by changing the seals to umbrella's or the springs or retainers?

Once I figure out my max lift I can choose a cam..

skinny z

Max lift in stock trim.
.470"
With Comp Beehive springs.
.540"+ ( witness my engine). No machining required.
Check out this link.
http://www.carcraft.com/techarticles...ade/index.html

Rayzor32

iTrader: (1)

Trying to find a cheaper route, im thinking of using isky's z-25 cam which has a lift of .488" . I don't know if I can use different seals or have the valve guides ground down to make this work.. read a lot of different things about them, not sure if stock springs will work either?

skinny z

The stock springs aren't worth much. I floated a valve on a missed shift ( 6500+ ) with a .458" flat hydraulic. I wouldn't recommend it.
>488" is too much for the OEM configuratioon.
If you go for new seals, you may as well cut a little clearence into the lifter boss however you're still limited to the small spring pocket. That's where the economy of the Beehives come in.

Rayzor32

iTrader: (1)

The article isn't very clear, can you use the stock retainers and keepers and just swap the springs? or do you have to buy new retainers and keepers?

skinny z

Retainers and keepers because the valve spring id is very small at the top. .885" if I recall. That also has the added benefit of being very light.

Sonix

iTrader: (1)

Keep in mind a solid cam has about .020" of valve lash, so you'll have that much less than the shown lift...

Don't trust anyone telling you that .470" is the max. They didn't machine the valve guide tops to bearing clearances, I wouldn't trust them all to be the same within .030".

MEASURE IT and find out. Don't ever (EVER) pick a cam based on valve springs that you have, or cylinder head max lift. Machine the heads, and buy new springs. Don't ever compromise your combo because of something as easy as springs/clearance.

skinny z

That's what makes the Beehives a no-brainer.
In my case there's no chance I'd ever exceed the lift capabilities of those springs.

Atilla the Fun

Truly wise men (and women) will accept that the vortec intake ports stall at around .475", and choose an intake lobe accordingly.

skinny z

That raises an interesting point.
Although you say the intake port doesn't flow any greater amount at .520 than it does at .470 ( stalls ) dosen't it make sense to keep the valve open at that point longer by using a larger lift ( you pass .470" twice in a cycle) ? It's the area under the curve that fills a cylinder.

Atilla the Fun

good thought, but the dyno disagrees. Comp has a line of HR lobes for SBCs called the Xtreme 4x4 line, all of which have .474" lift with a 1.50:1 rocker. Durations at .050" range from 210 to 234. And Vortec heads don't flow well enough to need more than 224 on a 350.

skinny z

That's also interesting.
So the science follows that anything above .470" (+/-) with 224 duration will return little in performance increases? That would make the application of 1.6 rockers to said camshaft pointless as well.
Hmmm.

Atilla the Fun

You can go farther, and find some improvement in final HP numbers, but if so, you're passing the point of diminishing returns.

ls six

Speaking of lift under peak, the OP will be leaving significant power on the table by not using a roller cam.

The greater exceleration seen with any roller profile goes hand in hand with skinnyz's theory.

It's just a wild guess but it could be that with a hydraulic roller like the one atilla reffered to you are allready using up that good under peak flow potential.

Adding lift/duration and the effect on either overlap or LSA depending on where you place your compromise simply pushes the port out of it's envelope and results in minimal gains.

With a flat tappet extra lift would be a necessary evil on the way to creating good duration at a lift where the heads flow best.

Atilla the Fun

true, unless using a "lift rule" cam like the circle track guys. But then you can have more duration than the Vortecs can make best use of, and that leads to losing more midrange than any top-end gains can make up for. Vortecs are great for mild 350s. And they do rival many aftermarket 180cc heads. But they are NOT the hot ticket for taking a 350 above 6000 rpm. They can do it, but almost every 200 cc head would be a far wiser choice. I still say the Sportsman II heads are obsolete fot their poor short-turn.

skinny z

That makes sense. Vortecs are a budget oriented cylinder head and as such I would expect them to be limited in out right power potential. I wouldn't consider them ( or my OEM cast crank ) for any sustained high rpm operation ( 6000 and beyond ). However I do like my bang for the buck ( see sig ).
Even though, had I heard about the Comp 4x4 line as Mr. Fun alluded to, I may have considered those over the XE276HR I ended up with.

Thanks for the thread Rayzor32!

Rayzor32

iTrader: (1)

I think im going to get the beehive's then and go with an isky z-25, it would be a lot cheaper than the machine work though but I still have to find a vortec intake too, vortec's are cheap upfront but they take a lot of money into them.. should of bought my buddies fuelie heads for 500 when I had the chance but i got these vortecs for 75 bucks!

The engine I built for my camaro I used vortec heads from scoggin dickey and an LT4 hot cam which is a .525 lift roller cam and I put an eldebrock perfromer RPM on it its pretty nasty going to do almost the same thing with this motor but use a solid cam because its not a roller block and im trying to be cheap!

Rayzor32

iTrader: (1)

ok guys just another question because im about to start ordering all the stuff for the build so far i need:

springs: 26918-16
retainers: 787-16

Do i need to buy comp's 7* locks or can I use the stock ones?? thanks

skinny z

New retainers AND new ( 7* ) locks.
Keepers, 7-degree
Comp Cams 648-16