Chevrolet "305" Cast iron Small Block Cylinder Heads

Win More Races with our "UnderCover Ported" Cast Iron 305 Heads

'601 casting with "UnderCover Porting"

Let’s face it: Stock Chevrolet 305 heads do not perform very well on a race engine.  With our "UnderCover Porting" air flow on 305 castings is improved from 165 cfm to 195-200 cfm.  This is an amazing 35 cfm improvement at .400" lift.

Exhaust air flow on stock 305 heads is 115 cfm at .400" lift. With our “UnderCover Porting” this is increased to 140 to 150 cfm. These air flow improvements have gained over 22 horsepower on the dyno.

We use a variety of 305 heads available: ‘601, ‘450 & ‘416 casting numbers.

Our bare 305 heads start as quality, pressure tested and magnifluxed castings. They are machined for screw-in studs, pushrod holes opened, new guides are installed, “UnderCover Porting” and a Serdi valve job designed specifically for the 305 heads is performed.

Will installing larger valves improve performance of a 305 cylinder head?

Thinking that "bigger is better" many people install 1.94" intake valves in 305 heads.

Well, the fact is, a 1.94" intake valve in a 305 head will hurt overall air flow of the head, especially under .400" lift.  Many tracks that require 305 heads have a valve lift rule. 

Air flow facts on 305 heads.

Test head:  '450 casting number Chevy 305 head with "UnderCover Porting".

Air flow with 1.84" valve. Ferrea # F5060.

.200          126

.300          173

.400          206

.500          212

.600          213

After the head was flow tested with the 1.84" valve, we machined the valve seat to accept a 1.900" valve. If all you look at the high end flow numbers, you would think that the larger valve was a improvement.  However, the small improvement at .500" and .600" lift was more than offset by a sizeable reduction below that point.  

Air Flow with a 1.900" valve Ferrea #F5072.

.200         124      -3

.300         170      -3

.400         198      -8

.500         214     +2

.600         215     +2

Our complete 305 heads start with all the same machining and “UnderCover Porting” as described above.  They are assembled with stainless steel valves, flat tappet springs, steel retainers, machined locks, ARP rocker studs and guide plates. For more information on our complete head assemblies click here. Use this link for a list of options for our complete heads.

Part# Description Price
LMS-305-UC Complete 305 heads with "305 UnderCover Porting". Assembled with 11/32" stainless valves, flat tappet springs, steel retainers, machined locks, rocker studs and guide plates. Flat surfaced to your specifications. 1,995.00
305-UC 305 castings machined for screw-in studs, pushrod holes opened, new guides & "305 UnderCover Ported". Bare, pair. 1,395.00

Free Custom Camshaft: With your purchase of a complete set of modified heads and a matching, modified intake, we will supply a custom ground flat tappet camshaft designed specifically for your application. 

Cylinder Head Design Form: Fill out our online form for a recommendation and pricing on a set of heads built specifically for your application. Also, here is a link to more detailed information on our Complete Cylinder Head Assemlies.

Cylinder Head FAQ'S

Sending your cylinder heads to us for modifications?

Brzezinski Racing Products, Inc. The #1 Name in Cast Iron. Call us toll free at 866-236-6300


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