Thread: '92 CSB 350 TBI heads. Junk?

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Are the original heads on my '92 CSB 350 engine worth modifying, or are they just junk who should be swapped with Vortec heads or something?

By the way, the engine is modified with Air Gap intake, carb, headers, no AC / PS, and 2,5" double exhaust.

Originally posted by staleg
Are the original heads on my '92 CSB 350 engine worth modifying, or are they just junk who should be swapped with Vortec heads or something?

By the way, the engine is modified with Air Gap intake, carb, headers, no AC / PS, and 2,5" double exhaust.

hmmm chevy? junk? need i say more

No they aren't junk.

They get called that because very few people ever bothered to look at them, measure their airflow, and explain why the factory designed them the way they did (with the swirl ramp under the intake valve) and considered what they were intended for. The popular (and ignorant) knee-jerk reaction from auto magazines, and many web sites (like Thirdgen.org), is that they are junk because they look like they won't flow well.

First they're not performance heads, but then again they weren't designed for that. No iron production GM factory head qualified as a "performance" head until the LT1 heads issued in the 1992 Corvette.

The Vette did get aluminum heads in late 1986 IIRC, but those were clones of the 083 iron casting and didn't flow any better until 1988 when they got D-shaped ports on the exhaust side. So the L98 aluminum L98 heads weren't really that great (as far as airflow and burn speed) when they were introduced so they weren't performance heads either, but they did weigh a lot less than the iron heads. They got much better later on when GMPP cleaned up the ports, and back cut the valves, and improved the casting.... but that occured after the LT1 was issued, and the L98 abandoned in production. The alum L98 version (113 casting number) sold now by GMPP is MUCH better than the 1st alum Vette L98 heads, as shown by the much better flow numbers as compared to the c. 1990 data shown in Vizard's book on Chev Cylinder Head Porting.

So the TBI swirl port heads, 187 casting number on 305s and 191 or 193 casting number on the 350s, are about as good/bad as the iron heads used on TPI 305s and 350s (081 or 083 casting #). The don't flow quite as well on the intake side as the TPI heads but they flow much better on the exhaust side. The tradeoff is either a wash or it slightly favors the swirl port head because the SP heads are better burners (better & faster combustion, so less ignition advance to get optimum power). There is a long thread at TGO that lists the flow numbers for the SP and non-SP production sbc heads, so you can see the numbers yourself, and the links to the original source material is also provided.

There are people on Thirdgen.org (TGO) that have modified engines (both LO3 305, and LO5 350) without touching the SP heads, and run in the 13s or 14s (350, 305) in the quarter mile. There are also people that have ported the SP heads and had even better results. So in either case, stock or ported, they respond to engine mods the same way as earlier Chevy sbc engines did. The only caveat is that once the exhaust and cam are modified, the engine will make enough power that the stock unported heads (either SPs or non-SPs!) will be the choke point for airflow through the engine. And remember, they are non-performance heads and they were cast to be fairly light, so they won't take an infinite amount of abuse.... and it makes no sense to spend a lot of money in modifying them because you can buy new heads for that purpose.

There are several long threads on TGO and on the Fullsizechevy.com websites that discuss swirl port heads, with accompanying head flow data, dyno data, and track data to suppport the assertion that the SP heads are not the junk they were claimed. The best one is probably the garage ported 193 casting thread that Fast355 started:

http://thirdgen.org/techbb2/showthre...ght=garage+193

The people that still cling to the junk/garbage comment tend either to be people that spent a lot of money on Vortec heads (and compatible Vortec manifold), or people that have been bashing the SP heads for years without anything to back up their claims.... or both. Hope this helps.

If they aint leakin they aint junk.