Compare Vizard head with Holbay head

[jdoclogan]

Saw this Holbay head for sale on UK Ebay.



And noticed the similarity of a Vizard head's valve chambers. So did Vizard influence the Holbay head composition or did the above Holbay head influence Vizard's alteration?


The valve chamber difference between the Vizard and Holbay is that the Holbay inlet area is slightly opened up on the manifold side of the head. For the Vizard only the exhaust area is mostly opened up on the manifold side and slightly on spark plug side of the head. Also note the coolant crest at each cylinder on a standard head. The Holbay head only has two coolant holes per cylinder.

 

[husky drvr]

jdoclogan,

I think I found that Vizard's book on how to port different cylinder heads was first printed in 1971. The H120's came to market in 1972. The differences could be both a way to use existing casting technology and a way to keep from infringing on DV's copyrighted information. It's even possible that DV possibly consulted or collaborated on the design, since he is a UK citizen.

IIRC, the intake ports are different as well. I think they are the same diameter as the exhaust ports instead of larger as in a normal head. That might also be part of the reason for the differences.

The head in your first picture has been repaired by welding three of the four crescents. It appears that it may need the #2 crescent AND the adjacent chamber edge repaired again. Maybe the #1 and #4 crescents as well as the large water ports on the manifold side need attention, considering the head discoloration. Hard to tell with a picture.

 

[alpine_64]

Just a quick chime in.. The head on ebay UK is not a production holbay head.. Its a later head thats had the chambers modified to a holbay-esque shape.

It could be someone trying to do the holbay "marathon" style head which was a mod done to stock heads to try and get some performance gains but also loses quite a bit of compression.

As noted the water crescent passages on 3 of 4 cyclinders have been welded and drilled.. A comon mod... But why not all. 4? And yes the standrad holbay heads had smaller intake ports to help air speed into the chambers with a venturi style dcoe manifold that gave better low down torque for the street engines. This was done by also taming the original holbay cam and the original proposed cam became the 128 tornado cam iirc.

 

[alpine_64]

A stock holbay H120/ GLS head

 

[RootesRooter]

I thought the narrower intake ports were standard on Arrow Range heads, with engine smoothness the goal rather than power. IIRC the rated hp for the Alpine GT fastback was about 5 hp less than the Series V.

Just a quick chime in.. The head on ebay UK is not a production holbay head.. Its a later head thats had the chambers modified to a holbay-esque shape.

It could be someone trying to do the holbay "marathon" style head which was a mod done to stock heads to try and get some performance gains but also loses quite a bit of compression.

As noted the water crescent passages on 3 of 4 cyclinders have been welded and drilled.. A comon mod... But why not all. 4? And yes the standrad holbay heads had smaller intake ports to help air speed into the chambers with a venturi style dcoe manifold that gave better low down torque for the street engines. This was done by also taming the original holbay cam and the original proposed cam became the 128 tornado cam iirc.

 

[alpine_64]

Rich,

I would have to check.. I think the Hunter GT head had the same port size as the Series Alpine, the very late SV alpine used the revised castimg heads without the spark tubes... Would they have had smaller ports too?

I was under the impression that it was only the Holbay head that had the smaller intake ports which when i read about the evolution of those motors was to help the low down torque as the
development engines while powerful lake low and mid range response.

Iirc this was in the McGovern book where they also discussed that twin 2" SUs were trialled and proved as powerful and more responsive but the marketing of twin DCOE was the draw... Id have to find the book again to check.

Re the port size.. Maybe an easy check would be measure the manifold ports of a series V alpine vs those of the hunter slanted 150CD manifold

 

[husky drvr]

I thought the narrower intake ports were standard on Arrow Range heads, with engine smoothness the goal rather than power. IIRC the rated hp for the Alpine GT fastback was about 5 hp less than the Series V.

RootesRooter,

A possible reason for the down grade would be the carbs are regulated for emission compliance.

 

[65beam]

RootesRooter,

Two possible reasons for the down grade would be carbs regulated for emission compliance and the exhaust manifold is only a single outlet instead of the 4 into 2 into 1 Series type manifold.

The series 5 owners manual shows the HP to be 99 @ 5500 RPM. The 69 GT fastback owners manual shows the HP to be 92 HP at 5300 RPM. FYI, the U.S. GT version of the fastback does have a four into two exhaust similar to the series 5. Here's a photo of the engine bay of our 69 GT showing the carbs and a partial view of the exhaust manifold.

 

[alpine_64]

Horse power ratings changed over the years also by way of measure, the original ratings were engines on a stand in a room without filters, exhausts etc and being fed cool air... As times went on the rating was based on having auxiliaries attached and eventually with exhausts and even conditions to replicate enigne bays... So the change in HP rating over the life of the rootes motors also indicates changes in the method of measurement

 

[husky drvr]

The series 5 owners manual shows the HP to be 99 @ 5500 RPM. The 69 GT fastback owners manual shows the HP to be 92 HP at 5300 RPM. FYI, the U.S. GT version of the fastback does have a four into two exhaust similar to the series 5. Here's a photo of the engine bay of our 69 GT showing the carbs and a partial view of the exhaust manifold.

Thanks for clarifying about the exhaust manifold. I wasn't sure but thought that was discussed a while back. The only Arrow range car I've ever had dealings with was an iron head standard engine in a wagon (complete with alloy sump). The other possibility would have been a change in camshaft timing, but I don't have an Arrow range service manual to check for that possibility.

Are the intake ports on a GT head the same size as the Series Alpine heads?

 

[65beam]

[QUOTE="husky drvr, post: 201639, member:

Are the intake ports on a GT head the same size as the Series Alpine heads?[/QUOTE]
Some say the ports are a different size but I've never bothered to measure them.

 

[RootesRooter]

GT intake ports are definitely narrower than on most, if not all, Series heads. [side-by-side, it might be hard to eyeball the difference. Sticking your thumb in each port is telling] The question is whether the narrowed ports first appeared only on the Arrow Range, or were they introduced at the same time with the recessed spark plug heads found on very late SV's.

 

[alpine_64]

The question is whether the narrowed ports first appeared only on the Arrow Range, or were they introduced at the same time with the recessed spark plug heads found on very late SV's.

Yeah thats what i was asking a few posts up... Did rootes change the size when they updated the head design. There was the change to the spark plug area but also on the intake side.. They changed the profile elevation of the intake side with the ridge above the the ports following the intake opening.. The holbay heads were based on these heads casting... So was it from the holbay research or the general rootes head.. It would incease intake air speed and density.. But dont recall much difference in torque rating?

 

[65beam]

FYI,
There were three aluminum heads used on the fastback Alpines dependent on model number ( H,J, K) . H was the Rapier, J was the H120 and K was the Alpine GT in the states. The standard Alpine used the cast iron head but the Model K (Alpine GT in the states) used a different head than the aluminum head 1725 engine for the H120 or the Model H. Model K used a different exhaust valve than the Model H and the intake valves were the same. H120 valves were specific to that head.. Some where in late production of the series 5 there must have been a change to the single valve spring according to the parts book because my parts book for series Alpines from February 1968 shows the double spring being superceded by the single spring used on the Model K. The 1725 intake manifold locating rings for cars sold in the states are the same part number thru out the 1725 production. I have spare heads but haven't looked at them for years but wasn't the late head without the spark plug tubes from a different vendor?

 

[65beam]

GT intake ports are definitely narrower than on most, if not all, Series heads. [side-by-side, it might be hard to eyeball the difference. Sticking your thumb in each port is telling.

Dick, We may all have different size thumbs.