Good evening. I have some L-29 heads I’m putting on a 330hp 7.4 with cam,intake and 454ho manifolds. I keep thinking of doing some porting on the heads but I’m curious how much extra power it will actually gain with just some mild porting ?

and if it’s worth the time to do a light porting
Thank you

you'd be better off finding oval port heads(larger version)

Check my thread bbc 454 build.

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I have built several L29 engines. Crane 731 cam(or 500EFI take out), holley 750, air gap dual plane intake and good exhaust will get you to 450HP+/-. Most folks think these are peanut port heads, but they are not. Their biggest issue is they fall flat at 5k, at least from all of them that I have built. I would love to see what a engine would with a set worked over would do. This engine is my go to build for a budget big block since you can pick up core truck engines on the cheap and the factory roller lifter set up will work with the 731 or 500 EFI cams. I have gotten core engines for as little as 250 bucks and thrown second hand 200 dollar cams, set of springs, rings, bearings and gaskets at them and have a complete long block for 1000-1500 bucks

I would disagree with throwing the older large oval ports at a 330 short block, you will loose compression with the large CC chambers and flat top pistons. The L29 heads are 99CC which gets you 9.4 compression. If you were to swap pistons out for domed to run larger combustion chambers, you are going to have to pay for a balance job and might as well replace the entire rotating assembly with a stroker kit. Which also at that point, might as well find another block and build the entire engine and keep your stock one as a back up. You can see how that becomes a slippery slope.

Apparently they pick up if you grind the swirl ramps out

https://www.gmt400.com/threads/l29-h...ibility.59936/

Here’s general porting theory. Air gets pushed down and in on the intake side. Goes down into the combustion chamber then up and out the exhaust side. Where this typically goes wrong is the wrong side is ported on the intake or exhaust intakes and a water jacket is ruptured or guys get way too aggressive in chamber and puncture a water jacket or screw up,the seat and guide.

simplest to do is
intake manifold side- smooth the bottom and sides, avoid the roof. Your goal is to smooth out the cast marks for air to flow better. More advanced guys will gasket match and remove ridges if any amd smooth the roof too.
exhaust side- smooth the roof and sides. Avoid the bottom. More advanced guys will smooth the bottom too and gasket match primarily on the tops.
valve bowls- remove the rough casting marks. Smooth the flow around the valve guides. More advanced will start removing the edges near the valve seat and even have a valve ground down to 88-90% intake and 86-87% exhaust (but let’s not get into that argument here) of the opening and use that to reference for valve seat opening. I do NOT recommend messing with the valve seat opening on boat heads but it’s your boat.

suggest buying some dychem and Prussian blue, as well as a cartridge roll or dremel tool with lots and lots of drum sanders and the Christmas tree looking grinding tip for a die grinder. Headflowinc has some really good videos on this. But I’d do very little until you get the hang of it. Smoothing is huge Improvemnt over the cast surfaces.

Good luck. Worst case you have a repair done by shop or buy new heads. Regardless it’s not end of world but can get pricey.

The BBC Vortec L29 heads have similar issues to the SBC truck TBI heads.

They have the massive swirl ramp system.

As mentioned...they snuff flow past 5K rpm.

It would take a lot of effort to get them flowing much better. You would be better off going aluminum aftermarket. There is cost to cleaning up the L29s, as well as porting media/tools as well. Porting iron will make you re-think the whole plan...unless you just do some minor blending etc.