| Author | Message | ||
     Jeff Martin Frequent User Username: jeff_r_1 Post Number: 676 Registered: 07-2018 |
This is an interesting service that Flying Spares is offering. One of the things they do in their description is "combustion chamber enlargement" When that was done, won't that decrease the compression ratio ? They are also adding larger valves and valve seats, so I'm assuming that's why the combustion chamber has to be enlarged ? They are charging £ 1295.00 for this service. I guess that doesn't sound that bad for what seems like a lot of work. I would like to see some before and after photo's and find out exactly how they go about doing this. https://www.flyingspares.com/cylinder-head-6-6-1-to-8-1-cr-conversion-ue2299conversion.html | ||
| Jason Watson Frequent User Username: crikeydawn Post Number: 216 Registered: 07-2023 |
wooooh snuck in there by 12 vehicles, I feel for the car that got the last low compression head. I see your point on enlarging the chambers, possibly the skimming of the head raises the compression by lower height. If you're interested for interest sake, I can measure mine assuming it has the 8:1 and FS build date is correct. Not uncommon to have random bits on or off other models as parts get used up. Do you know what size valves the 8:1 should have? | ||
| Daniel Shepherd Experienced User Username: 1957_grey_cloud Post Number: 66 Registered: 12-2021 |
Looks like our '57 (SDD264) has the low compression head. Does the higher compression head result in much of a power increase? | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 677 Registered: 07-2018 |
8:1 is still low by todays standards, but quite the jump for 6.6:1. It should (I dare say will) get better fuel economy because it will take less fuel to do the same job. Should run and idle better over-all because of more complete burn of the air/fuel mixture. The more complete burn will result in a less sooty and dirty engine as well. And should result in more power, but with the F head design and the poor exhaust flow, I wouldn't expect anything that's mind blowing. Just from memory, 8:1 roughly corresponds to 150 PSI in the combustion chamber. My MK VI engine with its low compression head is doing well at 100 PSI. Jason, I have some intake valves that are from a low compression head, I'll measure them later and post the size. I have no idea how much bigger the 8:1 valves are though, but if you have the larger type, you can compare. | ||
| Jason Watson Frequent User Username: crikeydawn Post Number: 217 Registered: 07-2023 |
Jeff you got me curious so I went and unpacked the head to see what it is. According to FS UE3764 is an 8:1. So I ran a ruler across the centre of the internal stud holes and grabbed the vernias. The valves are 55mm wide, and on one side to the valves there is a small shoulder, depth is 16.5mm. On the other more rounded side the depth is 17.25mm. I'll leave it out for a few days if you need anything in particular. Pic with ruler is to show the shoulder not the width.    . | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 678 Registered: 07-2018 |
Here are some photos of an earlier head from a 4.5 litre engine. Note the difference in the shape on the combustion chamber where the exhaust valve is, your 8:1 head is flat in that area and slanted away from the edge of the valve seat and the overall depth of the chamber appears more shallow. I measured the intake valve on my head, and they're 47.06 mm, so quite a bit smaller. Flying Spares is over-boring the intake valve area to accept the larger valve, and adding aluminum in the exhaust valve area to make the compression higher. If that's so, that would be a lot of work, and quite tricky to get all the chambers the same.   | ||
| Jason Watson Frequent User Username: crikeydawn Post Number: 218 Registered: 07-2023 |
you have a good eye Jeff, some pics for comparison. With Daniel's enquire, would one step hotter spark plugs make a low compression engine burn/combust/run better?   . | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 679 Registered: 07-2018 |
I can't see running a hotter plug would do anything to get the compression up, thus making it run better, if that's what you're thinking. A hotter plug simply extends deeper into the combustion chamber where combustion takes place, thus it gets hotter. It may cause pre-ignition _ I would advise just sticking to what's supposed to be there. Each engine is designed to take a specific plug to run at its best depending on the design of the combustion chamber. If he wants it to run better, setting the mixture is crucial, not too rich as the low compression is already not burning the fuel/air very well. Looking at your head, it's pretty obvious how RR got the compression up. The area back from the plug is flat and very shallow compared to my head. My head is "domed" a bit there, RR was probably thinking that it would create some sort of vortex to keep the exhaust gasses flowing out and into the manifold. In fact I think it just had the opposite effect where it took longer to evacuate the exhaust to an already poorly designed set up with the valves in the block. Having a smaller "ramp" like design in your head would certainly be more helpful of getting rid of the burned fuel. Even the area on the centre line of the valve looks to aid in getting rid of the exhaust _ note the ramps there. I think they finally started to understand the dynamics of the whole thing. Took-em long enough !  | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 680 Registered: 07-2018 |
 Notice where the red arrow is, how this part is "ramped" and not the same height like the old head. I think it was to help evacuate the exhaust and decrease the combustion chamber size.  Further ramping here to aid escaping exhaust gas, it may also help with combustion action efficiency. Also gets narrow from red to green arrows to help with flow. I think RR finally realized the short comings of this engine design with the exhaust valves in the block and how choked off it was after it got by the valve. I think they did everything they could to improve things here. Why didn't they go just one step further and put all the valves in the head. Yeah, it would have made the engine longer, but it would have been so much better, they could have gotten around the water gallery problem too. All they would have had to do is look at a Chev in-line six at the time. These photos are great Jason, it clearly shows the improvements and all one has to do is look them, and one can identify a high compression head. I would like to see the head design of the Bentley Blizzard, apparently it's compression ratio is higher still. | ||
| Jason Watson Frequent User Username: crikeydawn Post Number: 219 Registered: 07-2023 |
Well, they did have a rush of blood and shoe horn in a V8 that doesn't fit, so meh why do anymore with and old 6 pack. I find it all good stuff Jeff to learn bits and bobs, I feel very lucky to have picked up what I have and glad to help out while its apart. Now I'm a Standard Steel guy, these two door coach built things on the whole don't do much for me......until I came across a Bentley Blizzard. If that is not one of the prettiest cars ever made then I'll be blind. What compression did they run.  | ||
| Daniel Shepherd Experienced User Username: 1957_grey_cloud Post Number: 67 Registered: 12-2021 |
I've found this pretty interesting too, and most educational. As for the hotter plug and pre-ignition, is this not a risk that increases with increased compression anyway? For now I'll keep running the low compression six, and one day if the head needs to come off then we can consider the Flying Spares service. That Blizzard is indeed a piece of eye candy and no mistake... | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 682 Registered: 07-2018 |
Not with modern fuels, otherwise every car with 8:1 compression ration and above would have that problem, even before the days of computer controlled fuel delivery systems. No matter what compression you're running a hotter plug (one that reaches down into the combustion area further) will get hotter then a shorter plug and can cause pre-ignition. You're talking 8:1 and buy todays standards, that's a low compression ratio. There are lots of S1's running around with 8:1 heads and they run just fine. | ||
| Jason Watson Frequent User Username: crikeydawn Post Number: 222 Registered: 07-2023 |
Well that's a bit interesting but makes sense. I was under the impression from my crash course in spark plugs from reading the net. Or NGK and Champion web sites in particular. You can get a standard or protruded electrode, which does not make it a hotter plug. Rather a protruded electrode is exactly that, penetrating further into the combustion chamber for better ignition, as it is better placed in the thick of the bang. You can then go hotter or cooler within that plug depending on requirements, cooler lower compression motors use hotter plugs. High compression performance motors use a cooler plugs. Which once upon a time was easy to read as the plug reflected fuel mixture, a stick choke, dirty air filter perhaps. However now days with unleaded fuel it's black and sooty every time. My handbook suggest for an 8:1, a Champion N8BR which no longer exists, however cross references to RN10YC with reasonable confidence. I have some old NGK BP6ES (P for protrude) that came from the motor before its rebuild. Between the two brands they cross reference to each other. I was leaning towards putting BP5ES (hotter) plugs in because the old were black and sooty, but then discovered the unleaded fuel factor. I'm sure there is more to consider. |
