GarrettM

iTrader: (6)

Anybody had any experience with the CNC LS3 heads offered by SDPC? Looks like a pretty good deal for around $1500 assemebled with .650 springs.

Im looking to do an LS3 top end on a forged 370. Any advice if this is a good decision or not? I have read about valve shrouding being an issue, also tight PTV clearance.

Mainly curious if they are worth the extra over what I can pick up stock L92s for.

1lejohn

iTrader: (9)

Depends on what pistons your running. How much are the heads milled. They performed well in a GM High Tech article. SPDC does good work.

GarrettM

iTrader: (6)

Well motor hasnt been built yet but if i went that route then i would choose pistons accordingly with the correct valve reliefs. It will be a turbo motor so I just don't know if the ported gains would be worth it with it being forced induction. And beyond that are they really worth it over 243s?

bww3588

iTrader: (49)

Valid point, but it's a magazine. Everything performs well when someone is paying you to test it and publish the results.

To the op, the cnc ls3 heads flow a lot of air, a lot more than a 370 is ever going to need. During my research and 370 build with ls3 heads, I've noticed that the best setup using ls3 heads on a 370 is stock, with light clean up work on the intake ports and some to help the exhaust ports out.

A full cnc job on ls3 heads will most likely not help you as much as the same cnc work on a set of cathedral heads. Simply because the ls3 heads in stock form already out flow the best of the stock cathedral offerings.

I've noticed with cnc ported ls3 heads on a small cube engine such as the 370, top end power picks up decently, but low end under the curve power suffers slightly because of the low volume of air moving slower.

On a larger cube engine such as a 408 or ls3 based 413, the cnc heads will provide killer gains because of the engine's demand for more air.

Also keep in mind, ls3 heads like a different cam profile than cathedral port heads.

The custom(ish) cam I had spec'd for my 370 with ls3 heads is an EPS grind, 230/242 .603/.605 113.

bww3588

iTrader: (49)

I just re read your post and seen you will be going turbo. In that case, you could probably see very good gains with cnc ls3's over stock. How much? I'm not sure, but I'd say it would be more than the same comparison on an n/a engine.

GarrettM

iTrader: (6)

See I wasnt sure if the CNC would be worth the cost over stock or not on a turbo motor seeing as how the amount of airflow is dictated more by the output of the turbo than the heads themself like if it was an N/A build. Make sense? I know there would be gains, minimal or not, just not sure if that money is better spent elsewhere. Not concerned if I leave 5-10hp on the table and save a grand.

bww3588

iTrader: (49)

Cylinder head and intake air flow is just as, if not more critical on a boosted engine. Port velocity however is not as critical. Of course all that is dependant on turbo dynamics and such as low port velocity can make low boost scenarios less powerful.

But in general, cylinder heads are seriously important, regardless of aspiration.

GarrettM

iTrader: (6)

Ok I see.

1lejohn

iTrader: (9)

The problem when porting stock GM castings are they become weak in some places.They generally are light weight castings to begin with. Theres not alot of material left and they become brittle. They may develope small cracks or pin holes where they are thin. Just speaking from past experience.

Yes Sir the mags are driven by ad $$$.