Six Cylinder Heads

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Original submission by T Mar 30th 2007:

Back to the Engine Section

A 3.3 Engine from a VC or VH Commodore with the standard 12 port head. Note there are undrilled bosses for the Unused Air Injection Ports above each Exhaust Port in the Head. Click to Enlargen. Photo by SleakVH.

Six Cylinder Heads:

Original Thread
See also the

173_Head_On_a_202 page.


Submitted by v8slrtorana on Tue, 27/03/2007 - 09:49.
Holden 6 cylinder heads are stamped with L & H. Low and High compression.

Casting Numbers:

Casting Number
EngineAdditional Info
 7429477 161  
 7420081  179 - 186
 179 & early 186 head 5-11-64 to 30-6-65
 7429461 186  
 7429929  2850  
7429928 202 early 
 7429930 202  late  
 2811929 173
 2811930 202  GTR 
 2815843 202  XU-1 
 7420081 179 & early 186
 92013755 2850 2.85 Low Compression Head
 9937263 2850 2.85 High Compression Head 75-76 to 4-9-79
   These are a few cast codes I know of.
The dates below these are dates I have casting dates for, they may have been from before or after these dates as well.
The engine types are what I have been told they are for so I would like to confirm them too. 6cyl_7420081__h? normal 179 & early 186 head
5-11-64 to 30-6-65 6cyl_7420105__L
24-8-64 6cyl_7420109__H 149
dated 25-3-64 to 4-10-65 6cyl_7429461__L
12-9-67 6cyl_7429477__H
24-5-66 to 23-2-67 6cyl_7437395__L Is used for both 186 high compression and 161 low compression.
13-11-67 to 24-11-69 6cyl_7437397__L I suspect this may actually be a 395 cast head. 6cyl_7438296__H 161
18-4-64 to 16-2-70 6cyl_2811929__H 173 HG adjustable and HQ non adjustable
26-9-72 to 24-5-74 6cyl_2811930__L 202 HG adjustable and HQ non adjustable
15-4-71 to 22-3-76 6cyl_2815843__H XU-1 head P/N
14-5-70 to 27-6-73 6cyl_2817134__ 186X 6cyl_9937262__L 202 ADR27A head
5-5-75 to 7-79 6cyl_9937263__H 173/2850 ADR27A head
75-76 to 4-9-79 I would be very interested in any information for any of these heads as far as what is for what and other casting dates.
I have pictures of the chambers of a few of these Here
If anyone has pictures of the chambers of any of the others can you send them my way please. ( actually a picture of the chamber and the cast number would be even better )
Cheers Paul.  

Casting Date Decode:

Submission by Ben Simpson.

E186 will be the casting date. 18/5/1966 E = may 18 the 18th of may, 6 for 1966 8 is just a casting id, maybe the 8th time the mould was used that shift etc?? H for high comp

477 is what i recall as a 161 head.

End of Submission by Ben Simpson.


This refers to the amount of metal removed from the shared head ports.

A stage I head. The Iron around the Head Bolt is still in place. Click to Enlargen. Photo by HQ_SS.

Stage 1:

Another shot of  stage I head. The Iron around the Head Bolt is still in place. Click to Enlargen. Photo by HQ_SS.

Stage 2:

A stage II head. Note there is still iron surrounding the Head Bolt but is has been reduced in diameter. Click to Enlargen. Photo by HQ_SS.

The port has the Head Bolt removed as far as possible. The Head Bolt and support is still in place.  
A stage II head. Note there is still iron surrounding the Head Bolt but is has been reduced in diameter. HQ_SS had added details to show details of a Stage III head. Click to Enlargen. Photo by HQ_SS.

Stage 3:

The port has the Head Bolt completely removed. The Head Bolt and support is no longer in place. A short hex head bolt is usedin the lower position of the head and a plug inserted in the top to seal the port from the atmosphere.  HQ_SS Shed 

Adjustable Rockers:

The earlier 149, 161, HP, 179, 186 heads have adjustable rockers which can be an advantage.
See Hydraulic_Lifters.

Non-Adjustable Rockers:

173 and 202 use the same rocker gear as the later blue and black heads, non adjustable.
From what i know, all reds where available in either high or low comp versions, so anything is possible.
See Rockers and Pushrods.

Blue Engines:

In the blues, only the 173's came out high comp.
The blue VC 173 head is probably the best to modify as it is the only high comp, 12 port non exhaust emission control head.
Red Cylinder Head with adjustable rocker gear. See Thread 1. Click to Enlargen. Photo by Verdoro70.
161 Low and 186 High Compression Head. Photo by Blissy. Click to Enlargen.


2850 blue low compression Head. The head is originally from a 2.85L (173) blue. The correct spark plug for this head is (as already mentioned) NGK BP6EFS-13 or equivalent. Jeff.

Black Engines:

Black engines were fitted to EST and EFI 6 cylinder VK Commodores. Blacks have the low comp heads only.
The black EFI head is different to the EST head, it has no exhaust emission control and has better port work than any of the factory heads.
Unleaded petrol can only support a maximum of 9:1 static compression, so as Dusty says, fitting a high comp head might not be a good idea.
End of submission by V8slrtorana.
2850 (173) VC, VH Head (blue) Left, 3.3 EFI VK Head (Black) Right. Image by Dusty. Click to Enlargen.

EST and EFI VK Heads:

There is major differences between the Blue and Black A black head will be the way to go, if you are going to do the mod might as well get the full benefit :)
End of submission by Hem_Den

Interchangeable Parts:

Submitted by Qute on Thu, 29/03/2007 - 12:49.
In short, a 202 head is a direct replacement for a 186 head.
You will need to run the rocker gear and pushrods for the 202 head as the 186 gear is not compatible (the pushrods are longer in a 202 and the rockers should be obvious...).
Everything else will be a direct swap.
End of submission by Qute.
2850 Cylinder Head on a 3.3 Engine. Photo by Cameron Rutter. Click to Enlargen.

Further Head Details:

There is a lot of incorrect info out there !! Firstly, in the case of 149, 161 & 173 engines, it is the size of the combustion chamber (in the head) that determines the compr. ratio. With a small chambered head they are a normal (hi-comp) motor, but if they fit the head from the larger engine (179, 186 or 202) which has a larger chamber, the engine becomes an lo-comp version. 178 [sic], 186 & 202 hi-comp engines had regular pistons & large chamber heads. Of the larger engines, only 186 & 202 had lo-comp available & this they achieved with special dished pistons. These motors are extremely rare. The odd ones out were the XU1 engines, they did the reverse, they put the smaller head on the larger motor, resulting in very high compression (10 plus). Dr Terry