Don Terrill’s Speed-Talk

I've got a set of those heads on my '88 K1500, although the engine was a service-replacement crate engine intended for a '92 Caprice, so it has flat-tops instead of the truck's dish pistons, and a (very mild) roller cam instead of the truck's very mild flat-tappet.

If there's a way to pep those heads up, I'm interested. As is, I am NOT impressed with the performance. The older "HO 350" crate engine went from 300 hp to 330 by losing the swirl-port heads for Vortecs. Looking at the ports in the swirl-port heads, half the port area is blocked by the ski-jump.

The exhausts aren't too bad but they do have a double crossover. The intake is tougher and I did my work on these with my low pressure homemade bench ages ago. I would cut for a 2.02/1.6 valve combo, reduce ramp thickness, smooth the square prp, serious ssr shaping and chamber deshrouding. The advantage of the high helix swirl port that seems to be ignored is it uses the entire perifery of the valve. These heads do not flow as well as standard ports but use the air they can pass. Just a guess but with some work I think these can move about 220 cfm on the intake and 200 cfm on the exhaust. Thanks, Charlie

The old 350 HO heads (300 hp GMPP crate) were not swirl ports. They used '217' castings with a chamber that looked like swirl port heads, but no ramp in the bowl. These were the same heads used in OE F-body 350 TPI applications. They also had the double exhaust crossover.

novadude wrote: ↑Thu May 17, 2018 7:10 am The old 350 HO heads (300 hp GMPP crate) were not swirl ports. They used '217' castings with a chamber that looked like swirl port heads, but no ramp in the bowl. These were the same heads used in OE F-body 350 TPI applications. They also had the double exhaust crossover.

I have never worked on 217's so I have no reference on them. My work has been on 193's which had a tight chamber about 69 cc after working. 171's I think have a different chamber size but not 100% sure on that, I have never cc one. Thanks, Charlie

The iron TPI 350 head '217' chambers I checked were right around 65cc without any work.

I've used two sets, both on trucks. I did a little work on the exhaust side and left the intake ports alone, including the sharp edge from the bowl cutter.

On a 350 4x4 used primarily for trails, the owner was happy with the snappy throttle response and a very flat torque curve.

On a 307-powered 3/4 ton truck, the owner was also happy, and reported the fuel economy went up several mpg.

As far as throttle response and economy go, I'd say they work great. I don't know what the flow pattern looks like with air, but directing the water hose at an intake port resulted in a big funnel-shaped vortex of water coming out of the port. A standard head, the stream just came out mostly to one side.

https://www.thirdgen.org/forums/tbi/336 ... dflow.html Here's a huge amount of information about the swirl port heads. But you have to take the time to read it.

Yup-if you can DIY and have realistic expectations may be worth it.

To pay someone to monkey with them heck no

This is an example of a high helix swirl port. The GM version has a poorly designed pinch.

I found this page for an example of a high helix port vs. Standard port.