engineermike

Tried this in Advanced Tech, with few takers...

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

reamo04

those L92 heads have to basically have cams ground specifically for them in order to make good power. Ive seen several builds use them with cams that work amazingly on the cathedral port heads and they were nowhere near the power the cathedral port heads power. This were on bigger cam's as well. So, not sure why this is, but that may be something you should check on. Maybe call cammotion and talk about a custom grind for those heads that would be similar to your current one?

T/A KID

Mike I say go for it

Wckd94Z

i thought the reason for that was because they (L92s) have CRAPPY exhaust ports. i was really thinking about a converted 18x topend for my 388. Conventinal port volume thinking doesn't really apply when you have an 18 or 15 degree head, the runner gets longer, but the cross section of the port doesn't suggest a 240cc port. At least the 18x heads have a decent combustion chamber, and not a <50cc chamber like alot of the 15* and splayed valve heads have.

Wckd94Z

guess no help on the lt1 forums either?

engineermike

I guess that's what happens when you think outside the box...