LS heads vs traditional SBC heads (why?)

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LS heads vs traditional SBC heads (why?)

Postby mtrhead » Tue May 14, 2013 2:28 pm

Ok - I would like to hear some reasoning on the following. I've been trying to find an answer for sometime.

Hot street heads for 383-420cu inch SBC's (pump gas normal street/strip cruisers) have been somewhere between 185cc-230cc 23 degree offerings.
Many examples of excellent HP combo's can be found on this site utilizing these size heads (450-650+hp) (I have a set of Chads Pro-Filers on mine)

Hot street heads, including OEM, for LS series motors are anywhere from 200cc-300+cc with 12-15 degree angles. GEN V GM has 12 degree as OEM
I have been in a Z06 with All-Pro 300cc LS7 heads and a Katech cam and it idled better than almost any hot SBC I have heard and it makes more USUABLE power than I have ever felt in a normal street car.

My question is why wouldn't one buy heads like that for the traditional SBC with an angle between 12 to 15 degrees (250-300cc) for their 406cu street motor if they wanted hot heads? What would be the negative if the cams are equal in design? Block angles are the same, EFI or CARB's can be the same Is the air-speed that bad? I'm lost since the technical data like CSA's are similar.

I would really like to know "technically" what is wrong with that idea. I'm sure there are others who have thought the same

Thank you,
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Re: LS heads vs traditional SBC heads (why?)

Postby Orr89rocz » Wed May 15, 2013 8:08 am

Ports are completely different in shape so a 200cc cathedral port ls head isnt the same as a 200cc 23 deg sbc head. Even if valves are the same, csa are different for sure. Afr 210cc ls1 heads have a csa of 2.57 inch square. Afr 215 ls1 heads are 2.64 inch square. Look at Chad's heads. His 2.50 head is 227cc. 2.72 head is 245cc. Most consider 210-215 cathedral heads about as big as you want to go on a street 346 inch ls1 for sub 7000 rpm operation.

I also assume the laid back valve angle of ls and the port shape can tolerate more airspeed. Chad can perhaps comment to this as he has done an ls1 head now. Most sbc 12-18 deg heads have way to large csa and valves to target street rpms, sub 7500. If you could make one with a smaller valve and csa, keeping overall cc size down i bet a sbc would match the ls1 for power. Its just expensive to go 13-18 deg sbc

The big square ports like ls3, lsa, l92 however have much greater cc size but still have good airspeed to make them liveable on 6-6.2 liter motors. They do have big valves but based on flow across that valve size it still has good velocity. I love my 6.2 L9H truck, very torquey off idle to redline
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Re: LS heads vs traditional SBC heads (why?)

Postby mtrhead » Thu May 16, 2013 6:20 am

Thank you - I really wasn't referring to the first generation LS heads but more the LS3 all the way to the new LT1's

In your response you mention the BIG square ports. That is what I'm referring too, my friends ZO6 with the big AllPro's are just shy of 300cc's and the car absolutely is unreal. The spec on the heads appears to a layman like a 12 degree SBC race head. The car runs on pump gas, has air cond, and idles good.

Again, just curious
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