Caveman

iTrader: (2)

SO I want better flowing heads on my 4.070 bore L92 motor in my 2002 Formula. Richard at WCCH says that a 2.20 intake valve will work on a 4.070- 4.080 bore as in LS7 heads but that the 1.61 exhaust valve is too big. Ferrea makes a 2.20 Hollow stem intake valve for the L92 heads but none of the vendors on this site offer these as an option for CNC'd LS3/L92 heads. It would seem that going from a 2.165 intake to a 2.20 valve could make the L92s flow better on the intake side, like maybe close to as good as CNC'd LS7 heads.
The Mast new mid bore 12* L92 heads only flow 12 - 15 cfm more in the mid lift then my PRC cnc'd L92s and the same at low lift and .500+ .600 lift. That would not be a good option for over $2500!

Bandit28

iTrader: (28)

ONLY!! That is quite a bit in the mid range.

formula17

iTrader: (4)

Wish Richard would step in here and shed some light on this...I too have been holding off on doing anything with my heads until this is cleared up and I know for sure if it will or will not work and if well see gains from it more importantly.

formula17

iTrader: (4)

Dave...the history on our computers probably looks a lot a like. I've been looking back and forth at the flow numbers on texas-speeds site on the L92's and then over to mast's site on those 12 degree L92 heads. I hadn't found the hollow 2.20" valves though good work on that! I might call texas speed tomorrow and ask them about putting those valves in see what they have to say.

Nick

KCS

iTrader: (20)

Don't you think a 2.20" diameter valve might be just a tad too big for a 4.070" bore?

Beaflag VonRathburg

iTrader: (176)

^ I do.

Especially at the exspense of having to down size the exhaust valve. L92 heads are extremely intake biased. I fail to see why you would want to continue to extend that bias. If you want better heads I would back away from the L92 stuff and step into a really nice cathedral port option. The cost will be larger, but so will the performance.

njc.corp

How can you compare the prc cnc l92 vs the mast small bore head

2 different heads and 1 got more options then the other and a different valve angle-

formula17

iTrader: (4)

You don't need to downsize the exhaust valve. Obviously we could buy better flowing heads, But isn't half the fun of going fast doing it at the lowest expense possible??Wouldn't it be nice to find out their are a few more horsepower left on the table here? my .02

SUCK MY SS

iTrader: (14)

you really dont see any companies offer a hollow valve w/ a stiff dual valve spring.
i would think with a large valve head diameter like 2.20 it would be prone to breaking.

1CAMWNDR

iTrader: (21)

Yeah, those heads don't need anymore intake valve. They need more exhaust valve/port.

1lejohn

iTrader: (9)

I looked at putting larger valves in the 92 heads. The machine shop and I decided against it. Its not worth the expense and there is not a lot of material in the casting to work with. It will need chamber work and will shroud the intake.

Beaflag VonRathburg

iTrader: (176)

When you are going from a 2.165 to a 2.20 intake valve a 1.61 vs 1.59 exhaust valve is not that much of a difference. To make a 2.20 intake valve work in an L92 chamber and avoid shrouding issues you would have to downsize the exhaust valve or open the chambers up with deshrouding cuts.

Then you are running a massive 70+ cc chamber pre milling. To reach a higher compression you are into domed pistons, large chambers (milling would only exacerbate what you just tried to fix in the chambers), and undesirable of getting towards the edge of having to deal with flame propogation, quench, burn, and other issues (versus a smaller chamber and slight dish). L92 heads are good for OEM setups and massive cubes. Beyond that you can spend slightly more on a few different sets of heads and have a lot better setup.

The other thing I'd be interested to know is how large can an L92 intake seat actually go?

1CAMWNDR

iTrader: (21)

I know a few folks managed to put 2.04" valves on a stock LS1 valve seat, so the .035" difference from 2.165" to 2.200" is probably possible on a stock seat. I still say a 1.65" exhaust valve would be much better.

NemeSS

iTrader: (127)

perhaps the best solution would be to improve with stock intake valve with some minor work in the valve throat area, improved valve job with backcut on valve. with same operation on the exhaust side and if possble,use the larger exhaust valve instead

KCS

iTrader: (20)

If I remember correctly, there was a shop that used epoxy, basically reducing the cross sections in the L92 port and intake runners, and picked up ~70ft-lbs at lower rpm, and I think actually gained about 10 peak hp...and that was on a 427ci motor.

Not to mention, and don't quote me on this, but I think there are some really good head porters out there having better results actually reducing the valve/venturi diameter as well.

NemeSS

iTrader: (127)

a SAM student got the l92 ports to around 370cfm and with a shrunk port and with stock valve. iirc

KCS

iTrader: (20)

That doesn't surprise me, and that's just a student.

Beaflag VonRathburg

iTrader: (176)

I had a set of 806 heads with 2.04s on the stock seats that I just sold. I've seen quite a few 2.055s, but doubt it would pick up too much over a 2.04 on a stock seat.

I remember reading about the epoxy too. I was going to mention it also, but typing on my phone is a giant pain in the ***. I'm going to try and find that thread.

Richard@WCCH

iTrader: (3)

We've worked on a variety of chamber and port configurations for the L92 heads over the last eight months. Before we release any new programs we want to see resulting trends and developing markets. As engines trend in the larger displacement catagory port and chamber configurations will want to grow as well. With the release of the new FAST intakes for LS3 heads further development of the ports can yeild some nice gains. Reflecting on the title of this thread regarding hollow valves, it's always nice to see more options available. I don't see a lot of applications where a light weight valve is necessary but there are some guys who will benefit. As larger displacement engines are built the operating peak rpms will come down. Solid valves can safely cycle to 6500 rpms with hyd. roller cams and that handles 98% of the street cars we deal with.
The L92/LS3 intake seat rings measure approx. 2.200". A 2.180" valve will comfortably fit while the 2.200" valve could cause fragmentation to the outer edges of the seat. The seats can be changed, but will make for a more expensive pair of heads.


Richard

1CAMWNDR

iTrader: (21)

Great info as usual Richard. I look forward to one day having your Stage II(or one of the new versions) heads and a matched Victor Jr. on my 4.07" bore iron 427.