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

Bullitt347

Could it be that the L92 head has better low lift velocity in the ports as opposed to the -18x head? That is one of the great things about the LS series cylinder head is that the low lift and low rpm velocity in the port is significantly better and yet delivers high cfm flow at higher lifts and rpm's.

engineermike

Velocity comes from having high flow and a small cross-sectional area (related to port volume). Since the L92 has a larger port and valve, with a larger cross-sectional area, I believe its velocities will actually be a tad lower than the -18x.

Bullitt347

I will take another stab at this.........maybe the -18x and L92 head are best suited for the large displacement, high rpm, big cam application, but that does not mean they can work just as well in a boosted application. The real issue is, are they going to be such a mismatch when in off-boost operation. What is the LSA of the camshaft you are using? Chances are the overlap is considerably less than in a high compression N/A application. Also what cylinder heads are you currently running? If they are significantly smaller, then the jump to the bigger heads with no other changes is going to certainly hurt bottom end performance. If the camshaft is also changed to take advantage of the bigger head, then maybe the trade off in low end performance will not be such a issue..........Also forgot to ask...how much boost are you running, that would have an impact as well.

XtraCajunSS

iTrader: (2)

Mike,

I believe you've answered your own question on this one...

If this is who I think it is, long time no see man... When are you going to come by the new shop?


Shane

engineermike

Hey Shane! I just heard a rumor about the new shop, but haven't made it by. Where are you guys?

Daryn

iTrader: (19)

they are right by stanghi

XtraCajunSS

iTrader: (2)

You got it, right around the corner from Cody, on Hollyfield. Come on by when you get a chance...

Shane

pantera_efi

iTrader: (1)

My opinion, I'm an EFI guy and I have rebuilt many street/offroad LS-92 head engines.

First is compression, 12:1+ is needed to get good BSFC. (pump gas)
Next is camshaft, with "wide" L/C of 116 or even greater.

A normal 416 CID engine, GMPP "spider", 13:1, 246*/252*(.580/116C/L) will make 650+ SFHP@7000 RPM.

At "peak torque" the BSFC will then be .313 with a 12.5 AFR.

Good work from GM.

Lance

LSwonderfull

Close, i made that power with 11.4 to 1 and 111*lsa on pump gas, and 402" Fuel specifics were around .40 lbs

topend

i would not recommend using -18x cylinderhead. There much better sbc heads out there.

engineermike

You mean the ones that require shaft rockers and spread-port headers? No thanks...

topend

well if your on a budget i can understand. u could go with a brodix track 1 head and use all the conventional parts. Or u could go to racingjunk.com and get a package deal on some high end stuff.

engineermike

If I wanted 23 deg standard port location heads, I'd stick with my AFR 210's and maybe have them ported. However, I was specifically looking to get the advantages of a raised intake runner and shallower valve angle.