engineermike

I was thinking about the advantages of L92 and LS7 technology and, up until their release, I would have said that SBC tech was similar to LSx potential. However, the rectangle port LS items are clearly head and shoulders above conventional SBC parts. Understanding that the cylinder heads are the biggest technology gap between SBC and LSx, I posed the question - what would it take to give an SBC those same advantages. Of course, there are plenty of 18, 15, SB2, and canted valve heads, but they are very expensive. I landed on the Brodix -18x head because you can use conventional SBC headers and valvetrain, and they are only about $1500/pair bare.

Conventional SBC wisdom (as well as advice from my friend, who builds high-powered dirt track engines) tells us that the -18x heads, mainly because of the large ports, require large displacement, turning high rpm with a long duration cam (260++ deg @ .050), and high compression. However, when you compare the -18x to the L92 head, you can see they are amazingly similar:

Item L92 -18x

Valve angle 15 18

Intake runner cc 260 245
Chamber cc 70 68

In valve 2.16 2.14
Ex valve 1.59 1.60

Intake flow
.2 153 157
.3 225 212
.4 277 260
.5 313 303
.6 336 319

Ex flow
.2 121 106
.3 157 145
.4 176 179
.5 188 195
.6 194 205

As you can see, the heads are extremely similar. If anything, the L92 head is a tad more aggressive. However, you don't hear anyone saying that the L92 heads need 400+ cid, 15/1 compression, and a 270@.050 cam.

I'm considering installing a set of these -18x heads on my turbo 388 LTx in an attempt to gain power without affecting the street-worthiness of my combo, but my cam is only 224/236 and my compression only 8.4/1.

Thoughts?

Mike

rskrause

I think you need to look at minimum and average cross sectional area in addition to flow numbers and port volume. I don't know what the numbers are, but I think you need them to make an educated guess.

Good topic! Maybe someone can help clear it up.

Rich

engineermike

I spent some time googling today and found these shady numbers.

-18x CSA
2.15, stock
2.66, ported

L92
3.1, stock

The numbers admittedly from varying sources, and I'm not even sure if they are minimums, maximums, or averages. Either way, looks like the L92 has a larger CSA.