Info from that link: The stock C6 ZO6 GM manifold flows a peak of 347 CFM at .650 lift or within 87% of max flow of the modified intake port or within 99% of the stock intake port.

L92 - This new casting is designed for engine sizes of 6.2 Liters and larger. The larger stock intake/exhaust valve size, larger runner volume and larger combustion chamber does not lend itself well to smaller cubic inches engines or bore sizes for street utilization. In stock form, this head would create the characteristic dip in the normal lower torque curve as seen in many larger valve/runner heads used for a smaller cubic inch application. However, if the goal would be to maximize mid range and top end power with sacrificed low end torque, then this head could be considered for performance applications.

These heads are currently sold as new GM castings which are further CNC modified per the customers needs. L92 heads can be modified in several ways. Valve sizing can go up or down. A smaller intake valve and exhaust valve would be more appropriate for engine sizes less than 6.2 Liters. The downside to this head, as well as the LS7 head, is the poor exhaust port. Regardless of the combination, the I/E ratios can be significantly improved. The intake and exhaust ports can both be modified to surpass the LS7 stock ports. The combustion chambers can be CNC machined or left alone depending on application. It should be noted that in the stock form the L92 has more average flow than the LS7 under .600 lift.

GM L92 Stock Port
260CC runners
V= 2.16 1.59
S/I= Max Flow through Stock head with L76 Stock Intake. 91%
S/E= Max Flow through LS2 Stock Exhaust
Lift I E E/I S/I
.200 160 128 80%
.300 226 170 75%
.400 277 209 75%
.500 319 225 71% 289
.550 332 227 68% 299
.600 340 231 68% 306
.650 340 235 69% 311 (S/I= Max Flow through Stock head with L76 Stock Intake. 91%
AVG 285 203 71%

and just for comparison only: (WHY WOULD YA WANNA START WITH A LS6 HEAD??)
Stock 4.8/5.3L Stock 5.7L
CCCC= 62 67
RCC= 200 70 200 70
V= 1.89 1.55 2.0 1.57
Lift I E E/I I E E/I
.200 128 93 73% 122 97 74%
.300 179 121 68% 178 133 75%
.400 210 145 69% 215 156 73%
.500 218 163 75% 219 170 78%
.550 221 168 76% 223 176 79%
.600 226 174 77% 227 180 79%

 

BTW, manifolds knock down flow by a certain amount with slight variance due to the intake charge draw, not down to a specific level. For example, a heavily ported FAST may knock down flow by around 25cfm, a stock one would be closer to 35cfm. So on a 360cfm head, you'll still see 335cfm or so overall. It won't knock down flow to 280 or 290, unless the head was only flowing 310-320 at the start.

Same thing applies to the L92/L76. If it's knocking down flow 25-30cfm, then subtract that from the ported 360+ levels and you'll see how much power you can get. Unfortunately, there are only a couple of cathedral port heads that can flow 350+, so with a ported L76, you might be able to get that flow delta closer to 20-25cfm and make better power with the L92/L76 combo. Anything better than 20cfm and you'll need a ported Victor or a sheetmetal intake.

But in comparison, most cathedral port heads have better I/E ratios and therefore can run larger cams without adding excessively to the overlap caused by large splits required to overcome poor I/E ratios. With that said, if an ETP/FAST90 combo can see 320-330cfm with more intake duration, of course it will make more power than a 310-320cfm L92/L76 combo with less intake duration.

 

Kurt, I'm really interested to see what you find with the ported setup. Although I haven't run a carb style intake but it looks like it's the only economic solution for high rpm work. Too bad it has to have an elbow on top of it to fit most cars. I undertand ET is working on an intake for the LS7/L92 heads and I'll bet it proves to be an excellent piece. As soon as I quit chasing my tail I'd like to explore other intake solutions. It also looks like 90mm ttbs are going to be too small for most of the ported setups.

Richard

 

A stock 90/90 setup can and will stall. Those intakes can really be worked over to continue a good flow. Problem is, most who claim tthe port work only has the entrance and exits ported with ridges taken out.

 

With some creative work, there are intakes already out that can be used for it. It pertains to Nascar stuff if that helps.

 

Assuming its the L76 intake?

 

Why dosen't someone just flow the L76 intake by itself to see it's full potential? By this, I mean, no head, intake only. Then you'll know it's max potential.

 

I asked for that.... I even offered to loan my intake to someone to test!!!

 

I'm aware of the Nascar intakes being modified to fit, but they still have a carb flange. I guess the Wilson billet style is more what I had in mind.

Richard

 

I think most guys can't justify the time spent fixturing and testing a part that has little room to modify. If reshaping/resizing the runners of the plastic intakes were easy there would be a whole industry devoted to it.

Richard

 

It seemed that there were always results from other LS intakes. I wasn't aware that it would take "alot" of time to flow a intake. Seems as if you could make a adapter from plywood so the intake would be able to be clamped to the bench without much effort. While there are only miniscule, if any gains to be had by porting these intakes, one would still think that vendors whould be interested in the max potential of the intake. However, time is money.

 

Just got a PM back from Greg G. down in Houston... he offered to flow test my L76 on his unbiased bench..... Hopefully will have results in less than a couple weeks...!!!

maybe he will flow the heads with the intake and see what the difference is??
Might as well contribute to the knowledge.

 

Max flow is around 380CFM.
Max potential on head is around 345CFM.

 

Guys.... you really can't generalize that a intake will knock a certain CFM off of a head. If a head flows 370cfm with a intake on it could flow less than a head that moves 320cfm once the intake is on.

Bret