old I'm building a mild 403 for my 72 88 ht
its going to have 350 heads
a howards cam 270 advertised duration
4 barrel intake
holley 600 dual feed vac 2ndary
and long tube headers
what kind of performance can I expect for this as a mild build

 

Carb is small but probably fine, what are the specs on that cam, lift and duration wise? What gear and converter, stock?

 

camBrand:
COMP Cams
Manufacturer's Part Number:
K42-308-4
Part Type:
Camshaft Kits
Product Line:
COMP Cams Magnum Hydraulic Cam and Lifter Kits
Summit Racing Part Number:
CCA-K42-308-4

UPC:
036584461418
Cam Style:
Hydraulic flat tappet
Basic Operating RPM Range:
1,800-5,800
Intake Duration at 050 inch Lift:
224
Exhaust Duration at 050 inch Lift:
224
Duration at 050 inch Lift:
224 int./224 exh.
Advertised Intake Duration:
270
Advertised Exhaust Duration:
270
Advertised Duration:
270 int./270 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:
0.501 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:
0.501 in.
Valve Lift with Factory Rocker Arm Ratio:
0.501 int./0.501 exh.
Lobe Separation (degrees):
110
Grind Number:
OL 270H-10
Computer-Controlled Compatible:
No
Lifters Included:
Yes
Lifter Style:
Hydraulic flat tappet
Valve Springs Included:
Yes
Outside Diameter of Outer Spring (in):
1.437 in.
Retainers Included:
Yes
Locks Included:
Yes
Valve Stem Seals Included:
Yes
Timing Chain and Gears Included:
Yes
Timing Chain Style:
Double non-roller
Assembly Lubricant Included:
Yes
Pushrods Included:
No
Rocker Arms Included:
No
Gaskets Included:
No

the rear gear is a 373 posi
with a yank 2000 rpm converter

 

Now that see you have gear and some stall, dump that carb and get either a Street Demon 750 or the Quickfuel Slayer 750 cfm or a custom 800 cfm Qjet. Put 2.07/1.625 valves with the bowls opened up and matching springs on your early 350 heads.

 

Sounds like a nice build. I thought about a build like this, but with B big block heads. Are you just swapping the cam and going to 350 heads on the 403 you have or building a new 403?

 

building from the short block up I need to figure out push rod lengths

 

"815cut" big block heads have 84cc's in the chambers. The reason for the 7a heads, they have around 64cc's.
With the BBO heads you need to mill them a bunch.
Also you have to drill the head bolt holes for 1/2 inch bolts.

Gene

Well I just read thread from "cutlassEFI" and he did a 403 with BBO heads, says they work great.

 

BB heads are a nice big port job for a 403, without ever touching a grinder. Either you have to cut them big time to get a good chamber, or run a flat top though.

I am very happy with my 0 deck, (3cc valve relief) flat top arias pistons, and 80cc big valve E heads on my 403. Gives me 10:1 and it hauls pretty well.

 

I'm using a set of G heads with 2.07/1.71 valves on my stock 403. These things need a lot of air.

 

I'll bet with bb heads and 10.1 that thing runs real good. What kind of intake are you using and what of mods to get it to work?

 

Stock 7a heads are 68-69 cc and so are #5 6 and 7 heads.

1967?# 4 heads are 64 cc stock.

Carry on

 

It does run good, plenty of power for my heavy brougham with all the options.
It has a performer rpm on it which has been port matched to the heads. Effectively you need to raise the port roof a bunch (I think its about .100), and supposedly from what I've read, the rpm is the only one with enough meat to do it to, but I cannot verify that nothing else would work.
Otherwise, nothing else is different.

 

64Rocket here is my 403 Mark spoke of


Built by Mark Remnel- Cutlassefi(here on classicoldsmobile.com check him out) Look under 403 Cutlassefi post in the small block section. He will answer any questions about this.

.039 over 403, KB 6cc piston, .020 in the hole
N crank
4 main halo
Stock rods
455 C heads, 2.07/1.68 Built by Champion Racing Heads
221/228@.050 on a 112, in at 107 Custom Lunati Hyd Roller
5/16 one piece restricted pushrods
HS 1.6 rockers
9.0:1
QF 750 Slayer
Performer RPM intake matched to the heads
Accel HEI 30* Timing

Melling HV pump with purple spring

451hp@5600/512tq@3600. Run on 91 octane pump gas.

 

Pete,
That was a good read.
I did not think the big heads would work that well. I stand corrected.

Should be a very good runner.

Gene

 

Thank you now just need to find something to put it in

 

A nice '64 Cutlass or a '73 to 75 Omega.

Gene

 

403s are a great upgrade to a 1979 HO or a 1980 442.

 

Olds could have done it, the same way they snuck in the Olds 350, should have in 78 as the 10th anniversary edition but would have brought on the wrath of GM.