Question out of left field..ZX11, ZRX1100 pistons

[Guest]

Considering the ZX11 had a 76mm bore and 18mm wristpins, does any know if these pistons would work in a bored 1150 block to get me a cheap 1197cc lash up? I guess I'd need to know the compression height of a stock GS and ZX11 piston to know for sure. Just wondering if anyone had tried it. It would be a hell of a lot cheaper than a $600+ piston kit from the usual sources.

[TheCafeKid]

Trying to remember off the top of my head, and if you can wait til morning I canlikely get you for sure numbers, but IIRC the ZRX12 has 10.1:1 CR.? I'll double check that. Not sure if the 11 used a different CR but considering it's nearly the same motor I wouldn't think so.

[7981GS]

Is this for your '83 1100E?

Daniel

[Roger P.]

Yes, it's for the 1100. I just got a bit peeved when I saw how cheap performance pistons for import cars were, so I decided to think outside the box a bit. I know Toyota pistons have been used in XS650 big bore projects successfully, so I was hoping something similar could be done with the GS.

I know the CP, MTC, WISECO, JE, ROSS etc pistons are probably much stronger units, but I'm not going to be racing, so anything that would work satisfactorily is good enough for my needs. I'm looking for a cheap 1200cc solution for a $50 GS1150 block I won on Ebay that needs boring.

By the way, it's compression height I'm interested in, not compression ratio.

[7981GS]

Well, I only have KZ1000 and GS1100 pistons to compare and the compression height difference is roughly 1.5mm:



Waiting to see what TCK comes up with.

Daniel

[rapidray]

Call CP & ask if "Snake" or someone else can tell you the compression height for the ZX 11 & then you will know if it will work in your 1100. I like your thinking outside the box!!! Call me at 714--356-7845 if I can be of any help. I build & race 1100s & 1150s & have literally tons of engine parts for them. I am at CP every other week or so picking up pistons & am a WD dealer for them. I can call on Monday & ask also. Ray.

[TheCafeKid]

Sorry I misread what you were asking. I looked through the shop manual and didn't see anything regarding compression height so I will ask on the ZRXOA if ya like. I've not dug into the motor on this thing at all so I have only the book to go on.

[trippivot]

I see no one here knows the difference between water cooled pistons and air cooled.

Well you don't want to hear some brainiac quote the top 10 reasons why it is a TERRIBLE idea. or do you?


#1 the compression height 1.065 for the GS. I just bought a set of CP and they include a engineering drawing of the product.

I have yet to fiind the spec for a ZX1100 "C" or "D"

but all the piston prices are in the same range as a set of air cooled GS pistons by weisco and MTC.

[posplayr]

I see no one here knows the difference between water cooled pistons and air cooled.

Well you don't want to hear some brainiac quote the top 10 reasons why it is a TERRIBLE idea. or do you?


#1 the compression height 1.065 for the GS. I just bought a set of CP and they include a engineering drawing of the product.

I have yet to fiind the spec for a ZX1100 "C" or "D"

but all the piston prices are in the same range as a set of air cooled GS pistons by weisco and MTC.

does that mean yes it will work or no it wont work?

[Roger P.]

I see no one here knows the difference between water cooled pistons and air cooled.

Well you don't want to hear some brainiac quote the top 10 reasons why it is a TERRIBLE idea. or do you?


#1 the compression height 1.065 for the GS. I just bought a set of CP and they include a engineering drawing of the product.

I have yet to fiind the spec for a ZX1100 "C" or "D"

but all the piston prices are in the same range as a set of air cooled GS pistons by weisco and MTC.

I was thinking stock ZX11 pistons, not aftermarket. I assume the water cooled vs aircooled has to do with metallurgy and expansions rates. I also remember Honda touting water cooling in a 500 Shadow brochure many centuries ago that clearances were able to be kept a lot tighter in a water cooled motor, so maybe the initial bore to piston clearances are unacceptably tight or loose for an aircooled motor? I'd welcome any info, as this is a clean sheet idea, and certainly has it fair share of reasons why it can't be done, compression height being the most obvious. The successful use of Toyota pistons in the XS seems to suggest it is possible though.

[TheCafeKid]

Dunno if this matters or not as im no engine designer but youll also have the issue of the stock Rex rings if you chose to use those. ZRX cylinders are coated in Nikasil (lypophilic nickel silicon matrix carbide) which is hard stuff. Thus the rings stock are softer material. You know the rule I'm sure. Soft against hard hard against soft. The GS bores are soft in comparison, the rings are harder. So I'm not sure if that will have an effect on bore clearance/tolerance etc but I'm guessing it would come into play

[Nessism]

Pistons in a water cooled engine may run a tighter bore clearance, but that doesn't mean they won't run in an air cooled engine assuming the appropriate clearance is used (although determining that may be tricky).

[Roger P.]

I'm thinking if ring material comes into play, a properly sized set can be obtained from Hastings. Sorry to beat a dead horse, but there are Acura rings that fit an XS perfectly.

[Roger P.]

Hmmm, according to this thread,

http://www.zrxoa.org/forums/showthread.php?t=169771

the top of the wristpin bore to the top of the piston on a ZX11 is .658". Adding 9mm to get to the middle of the wristpin bore gets me to 1.012". Now assuming that all these measurements are taken from stock pistons and in the same position on the piston, the CR should drop a little. I have calculated the combustion chamber displacements to be:

GS1100 CC 29cc

GSXR1127 28cc

using Swept Volume/4/Compression ratio, so they may be off.

So, if the piston is 1.052" - 1.012" = .040" farther down the bore at TDC, we are looking at

7.6cm X 7.6cm X .7854 = 45.365 square cm piston area X .040" (.1016cm) = 4.7cc "lost displacement" per cylinder. Added to the combustion chamber, we have 32.7cc or 33.7cc at TDC.

7.6 X 7.6 X .7854 X 6.6 = 299.4cc swept volume per cylinder

divided by 33cc, we get a CR of 9.07 : 1, which is a bit low, but I'm sure .040" is skimmed off of lots of heads to bump up the CR. You could certainly run on regular gas with this setup, but I'm wondering how much of a performance hit you would take with such a drop in CR. I believe there are formulas to calculate this, but it's a bit too late to be at that at the moment. Of course, if you are into skimming heads, I wonder if there is any cost advantage to running these pistons at all.

If there is a problem with the math, please let me know.

[GregT]

Your math for the CR is slightly off. Conventionally, it's total cylinder volume (incl combustion chamber) divided by chamber volume.
this would seem to be 299.4 plus say 33 equals 232.4 divided by 33
which gives approx 7 to one compression ratio.
But I see on your post how you arrived at the chamber volumes.....

Start your calculations again for the chamber volumes - it's a little harder but it's still possible to come up with a close answer

Clearances for pistons originally in water cooled motors should be as specified for the air cooled motor they're going into - the piston material will be very close unless you change to a forging.