Series V Cylinder Head Questions

[RootesRacer]

I understand it may not be strictly necessary, I've replaced a head on my motorcycle without it and been fine too. But, both the machine shop and a few people on here said to use it, and I figure it can't hurt? Besides, the can is $10, if it helps even a little, it's worth it.

I am a fan of the copper spray.

If nothing else, I helps with heat distribution of the gasket to the head which can prevent certain types of combustion ring burnout.

Also helps seal marginal cooling port passages.

 

[Stick]

Just measured my combustion chamber and I seem to be coming in at 36cc pretty consistently. From what I've read, 39.2cc is normal? Is it possible I'm that far off (it seems like a significant difference!) just from shaving the head? Tested with brand new NGK BP6ES plugs installed in the head

I'm not 100% confident my method is completely accurate, but I don't see any way I'm not significantly below the 39 mark if this syringe is accurate. Tested 3 cylinders (skipping #2 due to it's damage), filling the syringe twice to 60cc and once to 50cc, each time coming up with as near as I can tell 36 each time. Took a small 6x9 piece of plexiglass, drilled 2 holes, Vaseline around the combustion chamber to help the plexi seal, filled the syringe with 50 or 60cc vegitable oil, and filled until I worked the air out.

What sort of compression ratio am I looking at with the standard headgasket and 36cc in the combustion chambers? Tom?

 

[Tom H]

You lose 1 cc for every 0.0114" you mill the head. I think the starting depth of the wear bars is about 0.065". So measure your wear bar depth. If it's about 0.020" , your head has been milled about 45 thou, which would reduce head volume 4 cc.

It seems you did the measurement correctly. But I would use denatured alcohol, rather than vegatable oil. You want something with low viscosity and low surface tension. Add some food color to make it more visible. That will minimize the miniscus (curved surface of the liquid) in the syring and make it easier to gauge the amount of liquid ejected. I assume you fill the syring and then eject enough to get the air out and set the amount exactly as possibel to 50 cc. Then fill the chamber as you did, and see hwo much remains in the syring. Volume = 50- what left, of course.

36 cc should give you a CR of 9.74


Tom

 

[Stick]

My wear bars look to be .035", maybe a bit more (with the slope and rough casting it is hard to be exact) which should mean no more than .030" has been shaved from this head since new. From your figure of 1cc per .0114", I come up with 2.63 CC lost from shaving using the wear bar method. Assuming it started at 39.2, that works out to 36.57cc which is well within my margin of error for the 36cc I measured.

As much as I would just like to put it back together, I can't help but think I'm maybe better off doing the vizard? An effective compression ratio of 9.65 to 9.75 (depending if I have 36 or 36.6cc) will almost certainly result in pinging without a drastic reduction in timing will it not? 91 (R+M/2) is the highest octane fuel readily available (there is 93, but it has ethanol).

 

[Tom H]

Makes sense to me. I'm not very knowledgeable on interaction of CR, timing, and octane (that's why I tried to maintain stock CR) , but I hope Jarrid (RootesRacer) or someone else chimes in. But it seems to me that doing the Vizard would bring you back quite close to stock CR. And again I caution that the Vizard drawing shows sloped walls, not rounded, so you will only remove a little over 2 cc per chamber. (2.17cc per my calc)

Tom

 

[RootesRacer]

Makes sense to me. I'm not very knowledgeable on interaction of CR, timing, and octane (that's why I tried to maintain stock CR) , but I hope Jarrid (RootesRacer) or someone else chimes in. But it seems to me that doing the Vizard would bring you back quite close to stock CR. And again I caution that the Vizard drawing shows sloped walls, not rounded, so you will only remove a little over 2 cc per chamber. (2.17cc per my calc)

Tom

I would first ask if Stick measured the depth of all 3 wear bars. The photo that sparked the debate looked pretty near the end of the road on one of them. Dont recall which.

WRT the vizard/compression/timing compromise, the stock rootes engine HC alloy engine is what is known in the trades as a knock limited timing motor.
Simply speaking, the timing that is needed for peak torque cannot be delivered across the entire RPM range since the available gasoline detonates becuase of lousy chamber design. The area that is knock limited on these motors is low to mid RPM at full throttle.
The engine would like 34 degrees, but unless you feed it 96+ octane it will knock and break ring lands (why Sticks #2 cyl chamber has dents).

Lowering compression helps reduce the knock threshold and allows added timing without detonation, but there is also typically a .25% loss in torque for each 1% drop in compression due to reduced thermal efficiency.

The Vizard mod helps by taking a thoroughly awful chamber design and makes it less awful. This speeds the flame front propagation, prevents front collisions and allows the engine to make peak torque with less timing, which improves the detonation threshold.

Were it mine, I'd go whole hog and put in flat-top pistons to maximize the benefit of the better chamber, while keeping compression as high as is practical for the fuel available.
If I was on the cheap, I would determine the exact loss of chamber volume on your head and perform a "compromised" vizardectomy so that I got some chamber benefit while keeping the compression ratio stock. This is IMO the only way you will be able to safely run factory timing specs.

The alpine engines were designed to run on higher octane than we have today so many find that a stock motor either needs the best possible gas, or a few degrees taken off the advance.

 

[alpine_64]

Vizard mod on a skimmed head.

i have been thinking about the implications of performing the Vizard mod on a skimmed head. the template in the Vinzard book gives you the chamber shape at the face of the head and a sectional view showing the straight line angled profile from the head face to the chamber face where the valves are.

What I have been thinking is that often people perform this modification on a head that has probably at least been skimmed once... and in some cases several times. However we simply scribe the chamber shape onto the head as per the diagram.. but in fact.. that's probably not correct. In doing so you require a steeper side wall profile to get the chamber face. The shape of the chamber profile at the face would be a smaller version the more that had been shaved and would thus remove less material.

i can model the chamber in 3d software and then section the chamber at given skimmed depths to create what I would assume is the correct chamber shape for the given depth of the combustion chamber .. if that makes sense.....

 

[Tom H]

Jarrid wrote:

If I was on the cheap, I would determine the exact loss of chamber volume on your head and perform a "compromised" vizardectomy so that I got some chamber benefit while keeping the compression ratio stock.

It seems to me that he HAS determined the loss of chamber volume, when he measured it and found it to be 36 cc, and only used the wear bars to confirm.

But it might be a good idea for Stick to re-measure using alcohol with coloring added, instead of vegatable oil. I think that will be more accurate measurement.

Michael wrote:

The shape of the chamber profile at the face would be a smaller version the more that had been shaved and would thus remove less material.

Michael, you have it backwards. The more the head is shaved the more material you need to remove, to regain chamber volume and retain stock CR.

For my Vizard mod, I made a template from sheet styrene and used it to mark the outline and also to keep checking the shape (surface shape)

Tom

 

[alpine_64]

Jarrid wrote:
Michael wrote:


Michael, you have it backwards. The more the head is shaved the more material you need to remove, to regain chamber volume and retain stock CR.

For my Vizard mod, I made a template from sheet styrene and used it to mark the outline and also to keep checking the shape (surface shape)

Tom

Tom,

I'm not confused about the CR.. I know the more you shave the head the larger you open up the chamber to compensate.. i might not have made my point clear...I'll try again.

The Vizard diagram shows a revised combustion chamber shape.. this shape is drawn at the face of the head to the block.. and one can assume the shape and size of chamber was done based on a new head with stock depth and stock volume. In the diagrams there is a sectional view showing the angle at which the material is removed from the chamber walls.. and as per your comments originally.. it is straight were as often people curve them (adding volume and probably having some effect on the flow characteristics)

The point i was trying to make is the template assumes a stock head depth.. when you draw that shape at that size on a milled head... the wall profile will become more angled (open) to meet the chamber head. Is that clearer?

What i am saying is in theory you can measure the depth of the camber and compare that to the vizard section and appropriate the correct profile for the head chamber at that depth... maybe i need to sketch and scan what im talking about...?

 

[alpine_64]

explination

OK.. here is what im referring too.. hopefully this makes it clearer.

 

[Tom H]

Michael, Your first statement in your reply made clear to me what you were describing. Duh! Sorry I misunderstood your earlier statement. And your sketches make it even more easily understood and should help others understand about how to do the Vizard mod.

Tom

 

[alpine_64]

OK.. now that my thoughts are clearer to others..

what say we about the revised shape?.. i didn't do a diagram illustrating what i see as the issue (a shallower wall profile if the head depth is reduced and the original vizard template is used) should the shape be scaled down?

I guess without a flow bench and testing a stock height head with vizard chamber vs a skimmed head with standard vizard mod vs skimmed head with reduced profile vizard mod it would be har to tell advantages vs disadvantages.

regardless.. Should I model up the chamber and mod and then do comparative plans with set milled levels? I guess we can at least see the variation in size then.

 

[RootesRacer]

OK.. now that my thoughts are clearer to others..

what say we about the revised shape?.. i didn't do a diagram illustrating what i see as the issue (a shallower wall profile if the head depth is reduced and the original vizard template is used) should the shape be scaled down?

I guess without a flow bench and testing a stock height head with vizard chamber vs a skimmed head with standard vizard mod vs skimmed head with reduced profile vizard mod it would be har to tell advantages vs disadvantages.

regardless.. Should I model up the chamber and mod and then do comparative plans with set milled levels? I guess we can at least see the variation in size then.

For flow, anything that opens the bathtub around the valves, (particularly the exhaust) translates into power.

With flat top pistons set to the deck, you can go to a chamber volume of 48cc or so, and still have more compression than you will know what to do with. This is where the Vizard turns to a holbay.

 

[alpine_64]

Hey Jarrid, i am aware of that.. I have modified chambers that were opened up a fair bit 10 years back and were a point of discussion on a previous iteration of the forum re: did i have enough squish left.. I had flattops and running them at deck height.. which took a bit of mucking around and an electronic ignition to get to run right.

However.. what I would like to know is what if any affect the increased angle of the walls of the head would have if one performs the standard vizard mod on a shaved head... i might just go model it all up for the heck of it and might prove some interest.

Perhaps i should contact Vizard... a fellow sunbeamer is currently working with him on an engine project... not rootes based though.. maybe he can slip in a question or two....

 

[RootesRacer]

Hey Jarrid, i am aware of that.. I have modified chambers that were opened up a fair bit 10 years back and were a point of discussion on a previous iteration of the forum re: did i have enough squish left.. I had flattops and running them at deck height.. which took a bit of mucking around and an electronic ignition to get to run right.

However.. what I would like to know is what if any affect the increased angle of the walls of the head would have if one performs the standard vizard mod on a shaved head... i might just go model it all up for the heck of it and might prove some interest.

Perhaps i should contact Vizard... a fellow sunbeamer is currently working with him on an engine project... not rootes based though.. maybe he can slip in a question or two....

Actually the angle of the bathtub would function better if the chamber were much flatter (less slope on the chamber walls).
The best chamber you could possibly make would be one that is the size of the piston and has the least surface are possible (AKA hemi).

The last thing in the world the flame front wants are sharp edges and lots of surface area,

 

[alpine_64]

I note that the rootes chamber according to Vizard book has a very slight wedge. Apparently wedged shaped hemi heads are the ideal..

I found this head on the net a while back.. it was prepared by Coltec racing (who took over holbay) from one of their 1922cc motors. A few guys down under have done similar on their stroker motors.. always wondered if it had to much taken from it... maybe not.

i have started to model up the chamber.. can post it in the next day or so.. other things in the way this afternoon.

 

[alpine_64]

here is the coltec modified head

 

[alpine_64]

Vizard diagram errors

Ok, i was modelling up the vizard chamber.. and low and behold.. plan does not match section!

The vizard diagram gives a section at the center line of each of the valves, however the section through the exhaust valve is larger in width than the plan... so something is not right there. its more noticeable at the face of the head than the chamber.. but in the diagram at that point none of the wall is being removed... odd... will try and post some 3d views in the next day or so..

 

[alpine_64]

vizard model

test model

 

[Stick]

Another inconsistency I noticed with the vizard diagram is the shape of the combustion chamber. If I'm reading it right, it shows a different original shape that is more "peanut" like for the 1725 engine, vs the "bathtub" shape it has listed for the 1500 and 1600 engines. My head clearly has the smaller "bathtub" shape without the bump out around the intake valves that is shown on the diagram.

the "peanut" shape I am referring to is the line through the middle of the hashed area.