Stock head flow data

The Mad Cadder

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Cadillac 902 '69 200cc intake /145cc exhaust

.100............200.............300.............400........... .500.......... .600.................700
83/73.....134/107 .... 180/140.......215/164.....248/181......263/191......277/206


Cadillac 493 '75 185cc intake port /124cc exhaust port
2.00 in valve/1.625 ex valve 120cc combustion chamber

.100...........200..............300.............400..............500................600
68/67.......130/97......190/130...... 215/160......233/172........ 246/-turbulant
 

The Mad Cadder

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I have always maintained the smog heads are inferior. Both in stock form
and in ported.. if your gonna look for power..

An above average home port job on a 120 head yeilds about the
same flow as a stock 76cc head.. Actually less..

Using small valves 2.11/1.77 compounds that becuase larger valves
can help cover a infeior port ! Yes the smaller valves can be made to
work but the big draw is they are easier to fit and take less porting
Less porting less volume and flow..

There is alot of material in Caddy heads and alot alot alot needs to come
out to make an appriciable difference

I know 120's can come close to 300 on the intake but without
exerience on those heade no one is going to get their without
alot of help.. The home porting guy mainly is waisting his time..
Not only that by the time your done it costs damn near as much
as just having either vendor do them right

I have never waisted my time or money on them..
The only Caddy I had that didnt want to rev or pull even with a aftermarket
cam was a 500 backup motor I had that had stock 120 heads
The 472 I had in the same car would have made a joke out of it
 

8ad-f85

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Looks like the smoggers could still allow 500hp, potentially.
The torque curve is still the beauty of these engines.

You can strongly guess by the #'s that the short turn loses the air at higher lift.
Being that the stock VJ isn't exactly magical for flow, there's always room for help.

If you measured the MCSA and got some before and after porting airspeed #'s you could plan your power curves pretty close.
 

Member 3508

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For comparison's sake, i have '250 castings. Previous owner told me they are 1968. I did a home port job, and did what i thought was alot of material removal, but actually i did just about nothing. I had MTS clean it up for me. Here are the flow numbers for a "mild" clean up job. The word porting is probably a stretch. Valves are 2.11/1.77 int/exh. respectively.

.100-67/59

.200-128/101.3

.300-182.1/121

.400-225.7/149.9

.500-249/180.8

.550-256.2/195.7

.600-263/OOO


Here is what the ports look like. Very last pic is the exh port.







 

8ad-f85

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It's not that so much work did nearly nothing...those mods just aren't needed yet at that phase.
Many times you are going further up the line to steer the air where you need to for the next mod to make sense.
Most of the time the pocket/throat area and/or short turn just isn't ideal yet.
For fun (accident) I've done this; Re-create a fully developed flowed port in reverse or random order and re-checked mods step by step on the bench.
It's rather disheartening to see $1000 worth of time produce 'nothing' just to see that one little thing bring the #'s right back :D .
The beauty of any flow measuring device is that you can probe the port to look for areas of too much/little airspeed, turbulence/separation, etc.....
You have an idea where you need to end up based on throat area vs MCSA and the airspeeds you are seeing, compared to the casting shape (kind of), and it's apparent limitations.
I have a few sets of Pontiac heads now that have the entire top of the ports cut out, all the way to the spring pads, lol.
 

goodspeed

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What vehicle(s) do you drive?
Ford Focus
I have a similar issue and I don't know what to do with it
 
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