Promaxx 200 dyno before/after porting

[bcjjones]

I’m really tempted to pull the heads (Promaxx maxx series 200) off my 385 SBC and have them professionally ported. They have CNC’d runners but I’m sure some pocket porting etc would help. How much is really the question.

Anyone have some before/after results of dyno numbers when getting heads ported? Preferably an SBC and preferably some aftermarket aluminum heads.

I’m trying to justify the time and more so the cost compared to the results.

50 hp is worth it for sure. 15 hp is not!

 

[94K3500PROJECT]

Gain is likely to be small I’d imagine.
I’d have them flowed and then go from there.
Un-shrouding the valves more seems to help on everything.
Beyond that I’d think a 5 angle valve job would boost low lift numbers which they probably need.
With a 200cc runner I’d go easy on the intake.
My guess is that most good reputable head porters haven’t done much work with them and the less reputable head porters will ruin them.

This just a point of discussion as I don’t have experience with them.
I wish a 175cc cheap Chinese aluminum head was on the market.

 

[L31MaxExpress]

Gain is likely to be small I’d imagine.
I’d have them flowed and then go from there.
Un-shrouding the valves more seems to help on everything.
Beyond that I’d think a 5 angle valve job would boost low lift numbers which they probably need.
With a 200cc runner I’d go easy on the intake.
My guess is that most good reputable head porters haven’t done much work with them and the less reputable head porters will ruin them.

This just a point of discussion as I don’t have experience with them.
I wish a 175cc cheap Chinese aluminum head was on the market.

Why such a small runner? 190-200 works excellent on a 350 and even better on a 383. Can keep the cam mild yet still make decent powet.

 

[94K3500PROJECT]

Why such a small runner? 190-200 works excellent on a 350 and even better on a 383. Can keep the cam mild yet still make decent powet.

Yeah I sometimes (always) forget that not everyone has the same goal as me

 

[94K3500PROJECT]

Why such a small runner? 190-200 works excellent on a 350 and even better on a 383. Can keep the cam mild yet still make decent powet.

You may be onto something. Even for my application (willing to sacrifice HP for TQ and to shift the power band lower)
This is helps explain why the LS3 based engines don’t really give up any torque to the cathedral port LS engines.

Check out this video from Holdener

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