me and my friend want to put a bigger cam in his gm 350 ho crate engine and would like to know the max lift on the vortec cylinder heads.

 

I am not 100% sure, but I think it is .550

 

You have to check guide/seal to retainer clearance to be sure, but .480" is all you can hope for with unmodified heads. .450" would be safer.

(Moving to General Engine where it belongs.)

 

Having first hand experience I can tell you the average lift allowed before the retainer touching the valve seal becomes an issue is .540". Subtract the "standard" .050" clearance and you're left with .490".

It's safe to say (as five7kid said) .480" is a good rule of thumb.

The problem comes with finding valve springs to fit in the spring pockets without machining the valve guide down to a smaller diameter. The Comp Cams 981 springs fit, but only if the damper inside is removed (which I don't recommend for an engine you're looking to put some miles on). Ironically those springs are also limited to ~.490" of valve lift.

Comp Cams does make a "bee hive" spring that supposedly works, but by the time you spend the money on buying the kit you could have the machine work done and be able to use much better springs.

 

Does anyone make a spring that will fit in a l98 head to take .509 lift?

Right now I have a lt4 cam with 1.5s (~.450) and I am just running stock everything on my heads. I am getting a set of l98s soon and I want to run a xe270hr cam. I need the heads to be able to take a .509 lift.

I thought about having them machined for 3/8'' screw in studs and bigger springs. I have no idea how expensive that is though.

 

dude those ovate 'beehive' springs are state of the art LS6 technology
I'd choose them over a regular dual spring + head machining anyday.

 

First, ovate wire springs and "bee hive" shaped springs ARE NOT the same thing.

Learn the proper terms before you debate.

Second, there are much better springs. Just about any dual spring is better at controlling valve train stability. Just because GM used bee hive springs in an LS6 doesn't not make them "state of the art technology".

If you would rather use them then that's your choice. But that doesn't make them better.

EDIT: Perhaps there's some confusion from me using the term "bee hive". By saying that I was talking about the conical springs that Comp Cams sells. I wasn't aware that Comp Cams used the term "bee hive" to describe the ovate wire.

Just thought I'd clear that up in case it caused some confusion.

 

Those beehives got nothin on my Isky 9945's And theyre dual with damper.

And yes there is a difference between Comps ovate wire springs and the "bee-hive" springs that simply fit stock spring pockets down at the bottom, but cone out to be, i think it was, around 1.46" OD. They are great springs if you dont want to enlarge the spring pockets. But, like AJ said, that doesnt make them any better.

Spring technology has come a long way since the days of the "good ol" 80 or so lbs of seat pressure stock springs. yes factory LS6 springs have advanced a long ways. But any advances Gm has made on their engines can easily be surpassed by aftermarket companies.

 

so would ether of yall suggest a spring and cam to go with the gm 350 ho. we would like to us a full roller setup with his 350 (lifters and rockers). thanks..in advance

 

Well, comps 986 or 987 is always a good spring for the money. Either would require you to enlarge the spring pockets, but that isnt too big of a deal if the heads are on the shop now, or at least, still un-assembled. Basically, whatever cam you get, get the spring that the cam manufacturer suggests or any spring with similar specs.

As for the cam, what RPM powerband are you after? What is your stall speed at? What is the compression ratio? What is the rear gears? For a decent suggestion, i really only need the powerband and stall speed. But for the most 'fitted' cam, the more info about your setup you can share, the better. For cams, it really comes down to 'what do you want to get out of your car and how much are you willing to change to get that?'

 

1,500-6,500, 2400 stall, 3.42 gears, 9.1-1 compression

 

A cam that is very close to the Xe274h (if you need a hydraulic flat tappet) or the Xe276hr if its a hydraulic roller cam you need. You should take a peek at Cranes cams as well, their Powermax grinds are also something to consider. But when comparing, those 2 cams are probably the best that would fit you.

 

alright so who makes these cams, are those part numbers? im not seeing them on summit or jegs

 

I upgraded my springs to be able to handle .550. I have a .490 cam in there right now. If you have stock springs, I would definitely recommend upgrading the springs. Stock springs can't handle big lift.

Steve

 

These are Comp cams. The numbers i am feeding you is the grind number. The corresponding summit part numbers are:

<A HREF="http://store.summitracing.com/partdetail.asp?part=CCA%2D12%2D246%2D3">XE274h hydraulic flat tappet</A>

<A HREF="http://store.summitracing.com/partdetail.asp?part=CCA%2D12%2D423%2D8">XE276hr hydraulic roller</A>

 

To take a .550'' lift I would think you probably need screw in studs to.

What is the lift limit on press in studs?

 

i don't think there is a limit...

FWIW, the stock LG4 in my z28 pulled a rocker stud.

 

Yup, there really isnt a limit. As a rule of thumb for myself, any time i go over .480 valve lift and increase the spring pressure i switch to screw in studs.

 

I'm about to get a set of l98 heads and I'd like to run the xe276hr cam with them.

About how much money do you think your average machine shop would charge to tap them for screw in studs and machine them for bigger springs?

 

Go into your phonebook, grab a few numbers and call around. Rates will vary. I have a connection at my local machine shop so i get cheaper rates.

 

will the vortec l31 heads handle the lift of the xe276hr cam, or will it need to machined for screw in studs?

 

the amount of lift a head can take and the rocker studs have very little to do with eachother. In the case of the vortecs its a matter of guide-to-retainer clearance when talking about lift. As for screw in studs, You cant go wrong with them.

From the factory, no, L31 vortecs will not have sufficient clearance for the 276hr lift figures. The guide bosses are too tall and will create guide-to-retainer clearance issues around .480" of lift. You will have to take the heads into a shop and have them mill the guide boss down. You might also want to enlarge the spring pocket as well, if you havent already done so. An alternative is the bee-hive springs. They fit the factory spring pocket size, but get bigger a the top to a 1.46" diameter i think it was. but be cautious, many dual springs ive seen, and some single with damper as well, the innermost spring does not clear around the guide boss. So there may be machining needed there as well.

Yes, for the kind of lifts you will be entering with the 276hr, you will want to replace the pull-out studs with screw in ones.