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Vanapplebomb
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Joined: November 03, 2010
Posts: 5411
Location: Holland, MI
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 Posted: Sun Mar 07, 2021 8:36 am Post subject: 1800 AN High Compression Pistons |
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Does anyone know how many CC the dome was on these pistons? Was it the same size/shape as the 1.7 Djet dome, or was it larger? Height? Diameter?
If anyone has any information on these pistons, I would appreciate it. Looks like they were last reproduced in the 1990s by NPR in Japan.
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1800 Type 4 Berrien 295
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raygreenwood
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Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Sun Mar 07, 2021 9:39 am Post subject: Re: 1800 AN High Compression Pistons |
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| Vanapplebomb wrote: |
Does anyone know how many CC the dome was on these pistons? Was it the same size/shape as the 1.7 Djet dome, or was it larger? Height? Diameter?
If anyone has any information on these pistons, I would appreciate it. Looks like they were last reproduced in the 1990s by NPR in Japan. |
I have only seen one set of high compression, domed 1.8s in my life. And.....they were KS......if memory serves. Just got to fondle them.....because I could not afford them 
But.....they have the same dome shape and I would say.....same height. The important thing observation wise....is that the margin ......the flat area .....between the outer edge of the dome and the piston edge......seemed to be very close to the same as a 1.7L dome......so the dome volume....could be crudely interpolated.....to be 3mm larger than the 1.7L in the calculation if you know what I mean. Ray |
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5411
Location: Holland, MI
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| Posted: Sun Mar 07, 2021 5:04 pm Post subject: Re: 1800 AN High Compression Pistons |
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Ray, you may be on to something. That would make sense that they would be 3mm larger in diameter and maintain the same margins.
If anybody has specifics on the size, that would be awesome.
I have a contact who develops pistons for Mercury Marine, Chrysler, professional racing teams, etc... Anyways, he has the ability to make reproductions as well. Although he can make cast and forged pistons, the most cost effective for a small run are billet pistons.
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1800 Type 4 Berrien 295
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5411
Location: Holland, MI
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| Posted: Sat Mar 27, 2021 7:14 pm Post subject: Re: 1800 AN High Compression Pistons |
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Ray,
Does ~3mm dome height sound about right on the 1.7? It has been a few years since I had one in my hand. From what I remember, it wasn't much. Figured your guess would be a lot better than mine since your the 1.7 Djet guy. Cool
Also, would you happen to know if any specs for such things would be in any factory literature?
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1800 Type 4 Berrien 295
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raygreenwood
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Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Sat Mar 27, 2021 7:31 pm Post subject: Re: 1800 AN High Compression Pistons |
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| Vanapplebomb wrote: |
Ray,
Does ~3mm dome height sound about right on the 1.7? It has been a few years since I had one in my hand. From what I remember, it wasn't much. Figured your guess would be a lot better than mine since your the 1.7 Djet guy. Cool
Also, would you happen to know if any specs for such things would be in any factory literature? |
I thought I had put the doe height measurement in my Nural piston review. I was looking for the same thing today thinking about that other thread.
I will be at my storage unit in the am and can measure a Nural and KS before noon.
I think its about 3.5mm...but its deceptive due to the radius around the edge.
Ray |
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raygreenwood
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Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Sun Mar 28, 2021 12:51 pm Post subject: Re: 1800 AN High Compression Pistons |
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| raygreenwood wrote: |
| Vanapplebomb wrote: |
Ray,
Does ~3mm dome height sound about right on the 1.7? It has been a few years since I had one in my hand. From what I remember, it wasn't much. Figured your guess would be a lot better than mine since your the 1.7 Djet guy. Cool
Also, would you happen to know if any specs for such things would be in any factory literature? |
I thought I had put the doe height measurement in my Nural piston review. I was looking for the same thing today thinking about that other thread.
I will be at my storage unit in the am and can measure a Nural and KS before noon.
I think its about 3.5mm...but its deceptive due to the radius around the edge.
Ray |
Here is a sketch from measurements I took this morning. The Nural pistons and a Mahle piston were within .002" in almost all dimensions.
The dome is shorter than I thought...right at 2mm.
As to the other conversation...the thing people have to be careful of when "detuning" or decompressing a 1.7L either by shimming and increasing deck...or detuning by dropping advance and idle timingh...is that a fair portion of the "effect" that is generated by the higher compression domed pistons...happens due to the interaction of this dome with the dimple shape and quench area of the 1.7L head.
Removing that dimple from play/interaction....say....physically due to excessive porting (even if you do maintain compression)....or by going to flat top pistons or dish pistons....which also takes that dimple and quench area out of play.......just absolutely ruins the performance and makes it a ht running dog.
Likewise....there is a lot more interaction going on than meets the eye. One needs to be careful with the timing when keeping the stock high compression pistons and head set up.
Ray |
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5411
Location: Holland, MI
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| Posted: Tue Mar 30, 2021 6:30 pm Post subject: Re: 1800 AN High Compression Pistons |
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Thanks Ray, that gives me a good starting point on the original shape.
I think that with a similar profile and a tighter deck, I should be able to get north of 9:1. I will have to run some numbers and see what things look like. 9.5:1 would be nice. Not sure I could get there without making the piston crown look like the Mahle 1600 Super Vee Type 4 pistons. A buddy of mine had some original Super Vee goodies. Factory 87.5mm pistons/cylinders, Solex 40PII carbs/manifolds, etc. I should have pounced on them when I had them in my hands. Cool stuff. You would have enjoyed that, Ray.
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raygreenwood
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Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Tue Mar 30, 2021 8:54 pm Post subject: Re: 1800 AN High Compression Pistons |
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| Vanapplebomb wrote: |
Thanks Ray, that gives me a good starting point on the original shape.
I think that with a similar profile and a tighter deck, I should be able to get north of 9:1. I will have to run some numbers and see what things look like. 9.5:1 would be nice. Not sure I could get there without making the piston crown look like the Mahle 1600 Super Vee Type 4 pistons. A buddy of mine had some original Super Vee goodies. Factory 87.5mm pistons/cylinders, Solex 40PII carbs/manifolds, etc. I should have pounced on them when I had them in my hands. Cool stuff. You would have enjoyed that, Ray. |
I have thought about this as well! You are thinking of a 1.8L right?
For the moment...think of either 1.7L or 1.8L...just about the pistons for a moment. On the 1.7L....you have right at 0.600" all around the dome...flat piston edge. Its far enough from "most quench areas. You could make that deck area right at .040".
Since on the 1.7L the deck in this surround area is 0.075" to 0.079"....you could get there by a combination of things. On the 1.7L...this is simple. You remove the head gasket which "about" 0.025" when crushed...plus the stock cylinder base shim....and you are .045".
That helps...but to really get much over about 8.4:1...maybe a little more....and still keep a sane deck.....you need more dome...right?
Most good racing shops ...as long as the pistons can stand it...can mill say...0.030+...off the surround area making the dome 0.030" higher. Then deck the case to make up the difference keeping the 0.040" deck in the surround area. The quench area and the dimple in the 1.7L...can handle this extra height with no issues.
So...lets look at a 1.8L....with 1.7L heads. Mill a flat top 1.8L piston to get a 0.077" stock height dome....flycut the heads to match a 93mm bore...maybe expand the dimple shape a little in the heads...deck the case to keep the surround area at .040"-ish....and thats a bad ass combo. Ray |
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Vanapplebomb
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Joined: November 03, 2010
Posts: 5411
Location: Holland, MI
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| Posted: Wed Mar 31, 2021 4:50 am Post subject: Re: 1800 AN High Compression Pistons |
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Those are good points Ray, thanks for your input, as always.
Right now, I am kicking around the idea of an experimental engine, just for fun. I have always been a big fan of the 66 stroke Type 4 platform, so I figured 1.8 or 1911cc would be a good starting point. Last year, I talked to Webcam about a similar engine and they recommended a 163/86b cam... which sounded way to big to me. Other things happened and the idea of building another engine just or the heck of it kind of fell by the wayside. Now I am thinking of picking it up again, but not in any hurry. I’m still puzzled by the 163/86b in such a small engine, so I posted in the performance forum, trying to understand it a bit better, and some suggested it may work. How well, I don’t know. If Web suggests it, it can’t be too far off.
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raygreenwood
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Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Wed Mar 31, 2021 12:02 pm Post subject: Re: 1800 AN High Compression Pistons |
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| Vanapplebomb wrote: |
Those are good points Ray, thanks for your input, as always.
Right now, I am kicking around the idea of an experimental engine, just for fun. I have always been a big fan of the 66 stroke Type 4 platform, so I figured 1.8 or 1911cc would be a good starting point. Last year, I talked to Webcam about a similar engine and they recommended a 163/86b cam... which sounded way to big to me. Other things happened and the idea of building another engine just or the heck of it kind of fell by the wayside. Now I am thinking of picking it up again, but not in any hurry. I’m still puzzled by the 163/86b in such a small engine, so I posted in the performance forum, trying to understand it a bit better, and some suggested it may work. How well, I don’t know. If Web suggests it, it can’t be too far off. |
Some of that cam....I dont fully understand either......but lobe center down around 104° ....trying to wrap my head around how that will affect vacuum signature. It may not be an issue....depending on what systems you will use ro control the fueling and ignition.
I would suggest.....going to a CB blackbox on a locked out stock distributor for full ignition control . Ray |
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