#920 vs. #675 Heads "Compression vs. Cylinder Flow"

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69 Cuda 440

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Which Cylinder Head Performs Better,

#2658920 {1966 and 1967 '273'}
Closed-Chamber @ 57.3 CC's

#2843675 {1968 '273' ~ 1968 thru 1974 '318'}
Open-Chamber @ 60.6 CC's

On the 'bench' both Cylinder Head Ports flow near identical.

But, a true test, on a running Power-Plant.

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No other modifications, just stock Valves {1.78" Intake and 1.50" Exhaust}.

Does the better Compression of the #920 Head {+.35}, outperform
the better Cylinder Flowing #675 Head which has less Valve Shrouding.

Were going to try this 'test' on a 'restored' 1967 Barracuda '273 Commando',
~ 'stock' with factory cast 10.5-1 Pistons {+.040" oversize}.

Everything else is 'stock'. {ie; Camshaft, Carburetor, Intake and Exhaust}
 
On a stock-type engine I'd say no discernable difference.
 
Subscribed! Might not be much difference but a little can mean a lot on a 273.
 
Yeehawww!.....I love these kinda tests! I'll place my $1.75 bet on the closed chamber ones.
 
In this case 'stock' the increase is crumbs.

Unless you like doing a lot of chamber work, the 675 is the ticket for larger valves and stage 2 and up porting.

I get the numbers close, but overall better #'s and easlier had.
 
moper said:
On a stock-type engine I'd say no discernable difference.
Click to expand...

X's2, but, I'll go for the flow over the squeeze. It'll make more sense once the engine is (re) built up.
 
hi, I assume you measured port velocity in both heads at same lift?? just curious?
 
The Patient

1967 Barracuda 'Formula S'
* Fastback
* 4-Speed
* 3.55 Gears 'Sure-Grip'

All Stock, except
* F-70 x 14" Goodyear Polyglas GT {Vintage Tires}
* Just Suspension 'Bushing Kit'
* Weber Clutch and Pressure Plate {9.5"}
* Fan-Clutch
* 6-Blade Fan
* Fan Shroud

Project
273 Engine bored {+.040}
Factory Cast Pistons {10.5-1 Compression}
Speed Pro Piston Rings
Federal-Mogul Bearings
Melling High-Volume Oil Pump
Speed Pro Timing Chain
Windage Tray

Internals Balanced = {Rods, Pistons, Crankshaft, Harmonic Balancer and Flywheel}

The Cylinder Heads will receive the 'same' ,
* 3-Angle Valve Job {Seat}, plus a 'Top-dress'
* Back-Cut Valves
* Stock '273' Commando Valve Springs
* Spring Height set
* Bronze-Wall Guide Liners
* Teflon Seals
* Milled to NHRA Specifications
* #2658920 = 57.3 CC
* #2843675 = 60.6 CC

Absolutely 'no porting', 'no gasket matching' or additional bowl work........
 
Re;

The Barracuda had run a previous best of '16.06'

The car is ready-to-go.........with the rebuilt engine.

Will test the #2658920 Heads 'first' this weekend.
 
Sweet. This explains ,the "buddy 273 cam thread" earlier.Appreciate the description on the valve seat work,Thank You. Best of luck.
 
Cast Iron Pistons? What top angle did you narrow seats with, or is that classified? Thanks for all the 273 info by the way.
 
66fs said:
Cast Iron Pistons? What top angle did you narrow seats with, or is that classified? Thanks for all the 273 info by the way.
Click to expand...

I meant, Factory Cast Pistons

Sorry About That.... 'Cast Iron'..... :banghead:

Valve Seat Angles.
Intake...... 60* ~ 45* ~ 37* {Top Dress 20*}
Exhaust.... 60* ~ 45* ~ 30* {Top Dress 15*}
 
LOL, I read right past that and never gave it a thought.
 
All the Mopar factory ones do because of the steel thermal limiting struts in them. They keep the piston to wall tight but weigh a ton.
 
We car folk's understand type O nese. My original engine has the 920 heads
 
Test #1 Results are in,

The 67' Barracuda 273/235 'Commando' ~ 4-Speed ~ 3.55 Gears

All stock with #920 Cylinder Heads.

#1..... 15.88 @ 84.93 MPH
#2..... 15.91 @ 84.07 MPH
#3..... 15.80 @ 85.02 MPH
#4..... 15.83 @ 84.77 MPH

Line Launch............... @ 3500 RPM's
Shift Points................ @ 5000 RPM's

Shipping Weight.............. #2940 lbs.
Curb Weight.................... #3067 lbs.
Scale Weight w/Driver.... #3257 lbs.
 
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