94mm Domed Pistons

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Bob Ingman
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94mm Domed Pistons

Post by Bob Ingman » Mon Sep 29, 2003 5:49 pm

Can anyone tell me if the 2.0L 914s were equipped with domed pistons from the factory? Thanks and good luck. Bob Ingman

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Dave_Darling
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Post by Dave_Darling » Wed Oct 01, 2003 12:35 pm

Nope. Dished, all of them.

The higher-compression European 2.0 pistons had a dish, but it was smaller than that in the US-spec piston. As far as I can tell, the "flat top" European pistons were all aftermarket. Even those made by Mahle, who was one of the OEM suppliers.

The 1.7 pistons had a dome. Or at least some of them did.

--DD

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Bob Ingman
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Post by Bob Ingman » Wed Oct 01, 2003 8:35 pm

Thanks Dave. I just found a source for 94mm domed liner kits for $200. I was beginning to think i would`nt find such a thing. Good luck. Bob Ingman

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raygreenwood
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Post by raygreenwood » Thu Oct 02, 2003 7:06 pm

Really? 94's with domes? Where? That would be interesting to convert my 1.7 to....leaving all else. Depending upon pin height and dome shape though. Ray

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Bob Ingman
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Post by Bob Ingman » Fri Oct 03, 2003 6:15 pm

Ray I have asked this supplier to DOUBLE CHECK that they are in fact 94mm Domed 2.0L P&C kits for $200. Will know more first of the week. The price just seemed too good to be true so I asked the supplier to check with his supplier. I do not have high hopes that this will be true but til then we can hope.
I think you think like I do. 1700 heads with 42 intakes and 37 exhaust, and 94mm domed pistons. Wonder where I got those figures? Good luck. Bob Ingman PS disregard my email for now.

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raygreenwood
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Post by raygreenwood » Sat Oct 04, 2003 1:04 am

Yeah! I definately agree. that is the only only way I would stray from the close to stock configuraton on the 1.7. I'm also having a hard time finding another set of 37mm exhaust valves. Apparently I was lucky to get those on my last rebuild. 1.7 heads with domed 94's (can i bore out my 1.7 cylinders that far?) . ..42x37 valves....about 8.7:1 compression....web # 73...some reallly cool injection mods....nice motor....high revving! Ray

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Bob Ingman
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Post by Bob Ingman » Sat Oct 04, 2003 7:31 pm

Ray wrote ( can I bore out my 1.7 cylinders that far? )This is the reason I an skeptical about the price quoted because the price is supposed to be for a complete liner kit. P&Cs 94mm domed for 2.0L(so may not work on your 66mm crank). Anyway well know more Monday. Good luck. Bob Ingman

Rosshawk
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Post by Rosshawk » Sun Oct 12, 2003 6:17 am

This is my first post, but I have been lurking in the shadows for awhile. These domed piston threads are always good, as are the 1911 ones?so as long as I have Ray and Bob in the same place?.

http://www.shoptalkforums.com/viewtopic ... ight=rimco

Ray mentioned in this thread that there might be compression issues with a 1911 with custom made domed pistons. If someone was to build a 1911 with domed pistons and CIS injection what would you recommend they do? (starting with 1.7 heads with bigger valves of course). Could the pistons be modified to offset the higher compression, (shorten dome/dish dome)? I was also wondering about your thoughts on the effects of a domed piston aside from the increased compression, is the dome itself beneficial opposed to flat tops regardless of compression---and how much? Enough to compensate for the extra cost of the custom pistons?

If the pistons are going to be custom anyway then a few modifications shouldn?t be a problem. I?m sure you have thought about this, and I?d be willing to be a guinea pig as soon as funds allow, which might be awhile. Anyway, just keep the different combo ideas flowing, it gives poor jerks like me something to daydream about. I was thinking Euro 1.8, but a Euro 1.9 would be nice.

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raygreenwood
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Post by raygreenwood » Sun Oct 12, 2003 7:25 pm

Good question! I have built 1.7's with flat tops in the past...when I could not get domes. A lot had to be done to use that particular piston...but when all was said and done, the engine was essentially the same except ...no domes. The stock deck on a 1.7 with domes is about .070". Remove the head gasket and shim...you get .040. Thats about what I had to do with the flat tops to get them to have the 8.2:1 compression of the domes. Most would think that the smaller deck area of the flat tops would automatically make the MOST difference. In this case ...no. The domes seem to be made to interact with the dimple...or ramp cut into the edge of the quench area in the 1.7's....forcing fuel mixture up into the quench area faster...with more turbulence. When the domes are missing...even with the same compression...the burn is a little less complete...and tuning the MPS seems to be a little touchier.

As far as mods to the 1.7 style piston...a higher dome would probably be helpful. Here is what I am doing in the next two weeks. My stock 1.7 heads have already been mildly ported....without disturbing the quench area. They went from about 49-50cc...to 53cc. I am leaving off the head gasket and base shim. My deck is .040. This gives a compression ratio of 8.703:1

I am going to have .030" milled from the edge of the piston and radiused into the edge of the dome. That will give a dome of .103". Then..to keep the .040 deck...which is around the edge of the dome..and critical to have clearance to the quench area....I am milling the sae .030" from the cylinder spigot area while truing the spigots to the crank centerline. That will leave me back at the original .040" deck height with a .103" dome.

That will give me a new compression of 8.997:1 static. So...the minor changes in dome will be very signifigant in compression...and i think in moving thefuel mixture around. This may sound like high compression...but...it is static. With the overlap of the web #73...it should give in the neighborhood of about 8.6-8.7:1. I don't yet have the formulas for that type of modeling. Ray

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Bob Ingman
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Post by Bob Ingman » Mon Oct 13, 2003 3:49 pm

The person I asked about the 94mm domed pistons responded that he was about to leave for a trip to China and would find out more for me when he got back. I seriously doubt that a domed 94mm T-4 P&C kit exist. It would be common knowlege if it did. He has access to a 94mm domed kit but I suspect that time will reveal it to be a T-1 kit.
What are the specs on pin height. I know the T-4 uses a 24mm pin and the T-1 uses a 22mm pin but cant remember if rebushing the T-4 rod ig going to meke this a usable component due to tin height.
Ray in a nutshell which do you feel is the more desirable at the same cost, the 96mm flat top or the 94mm domed? Good luck. Bob Ingman

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raygreenwood
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Post by raygreenwood » Mon Oct 13, 2003 6:22 pm

Many may disagree..but the 94 dome would be more desirable in my opinion. With a 96, cutting a 1.7 head will increase the quench area quite a bit. The combustion chambers are still pretty small. The added displacement will make the compression right at 8.92 ...if the pin height of the 96's are the same as the 90's. Thats with an 040 deck. Thats pretty good overall..but not much different than what you can achieve with either a dome or slightly less deck with a dome. If the pin height is lower...then you have to start adding deck. That means less efficient combustion as more is in the cylinder than the quench area. the 94 dome should give 9.35:1 on an .040 deck...with a 53cc combustion chamber. This is assuming that the dome increased in diameter 2mm, with the piston. If this is too much...there is a little more that can be done by porting. I would not lower the deck. That is also static compression. I would bet that with a cam with overlap, it wouldactually be somewhere around 8.8 . The domes should also work well with the head...since it was designed around the dome. But hey...the 96's with flat tops are no slouch if you cant't get 94 domes. Ray

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Bob Ingman
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Post by Bob Ingman » Mon Oct 13, 2003 11:28 pm

Ray this planning I`m doing here is to be using a 2.0L base engine. I want to use the 1.7 heads with larger valves installed. Do you think the Web 73 cam is as good a cam for a two litre engine as it is for the shorter stroked engine? I really liked it on my 1911cc engine. It made more power than I thought it would. I am afraid that the two litre will not live up to my expectations.
You said you cannot find 37mm valves. How about using 37.5mms? I can get them but do`nt know if they will work well in the 1700 heads with 42mm intakes.
Seems like a good cam and domed pistons with a set of 36 Dells should be good medicine for my Thing. They say the 2.0 has better torque and that is what I want.
Do you know what the deal is on using T-1 94mm pistons with T-4 94mm barrels? Would it be practicle to set it up for 8.5:1 CR? Good luck. Bob Ingman

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korijo
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Post by korijo » Tue Oct 14, 2003 2:29 am

This thread may be of some info...

http://www.914club.com/bbs2/index.php?a ... dddeb84195

Image

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Bob Ingman
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Post by Bob Ingman » Tue Oct 14, 2003 3:12 pm

Ray I have a thread going on the t-4rum "type 1 pistoms in T-4 barrels". Help me interpret Shads comment on do the math. Thanks Bob Ingman

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raygreenwood
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Post by raygreenwood » Tue Oct 14, 2003 10:19 pm

I like the web 73 too. It is friendly to FI...because of timing and overlap...and has a bit more lift and duration too. You may get a bit more out of carbs with something else in the web line. I'm sure it will run well...but you may get a bit more. I think 37.5 valves would work. They are just about the limit I think for a 1.7 based engine...but you are going to a longer stroke and a hair more displacement..so it should be close.

Give me a day on themath. I am on the road in Atlanta at a trade show...and I'm having a few beers....I'm un trustworthy at the moment. Ray

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