VN1700 pistons to raise 1600 comp ratio

[andyvh1959]

Well hmmm. if the crank throw is changed and the same rods are used, the result is no change in stroke length, just piston position at the top and bottom of the stroke. If longer rods are used with the same crank throw, the piston position at the top of stroke will be higher into the combustion chamber. At the bottom of the stroke it'll just be a bit higher in the bore. At least that's how I envision it, and maybe I am wrong. I do understand how a longer rod increases piston dwell time at TDC, which may produce more power.

Looking at any specs on the 1500 Mean Streak shows the same 9:1 compression ratio as the 1600. So how is a Mean Streak piston in the 1600 able to increase compression? All the pistons I've seen for a 1500 are the similar dished style as in the 1600, unless I'm not looking at the right pistons.

I have a pair of 1700 pistons/con-rods I bought from a cycle salvage yard, for $125. In the 1700 the comp-ratio is 9.5:1. Now I realize that is not due alone to the pistons. But the 1700 pistons are clearly crowned (with valve reliefs) and the 1500 or 1600 pistons are dished. Then I found this info about rod lengths and power:

https://www.thirdgen.org/forums/tech...ion-ratio.html

https://www.enginebuildermag.com/201...ng-rod-ratios/

[Mechaniac]

If the crank throw is changed so is piston travel, Piston travel = stroke length. Rod length is just how far the piston pin center is from the crank throw center. But realize if the crank throw is 1/2" the total piston travel from top to bottom is 1" as the crank rotates 180*. 1/2" up and 1/2" = 1" total travel.

From what you say Kawi increased the stroke by 2.5mm but a the same time reduced the rod length by 2.5mm. This means at the top of the crank stroke the total height of the piston is still the same as before. But as the crank hits BDC it is pulled 2.5mm further and has a 2.5mm shorter rod. So at BDC it's actually 5mm further down. If they had left the rod length alone it would travel 2.5mm higher and lower, but they shortened the rod so the piston didn't hit the head.
This is important because it establishes the pistons have the same bore, pin size, and combustion height (distance from the pin to the top). It just travels further down on the 1600 with the longer stroke.
Now compression ratio is the total displacement of the pistons bore and stroke divided by the remaining open volume of the combustion chamber and the piston top at TDC when everything gets squeezed the tightest. 9 to 1 means the total swept displacement of the piston is 9 times the size of the area left at TDC. The higher you make the compression ratio the more you're volume squeezing into a set space. Divide total swept displacement by left over at top and you get compression ratio.

If a single 1500 meanie piston travels 750 cc and at TDC there is 83cc of left over space in the chamber and on top of the piston the compression ratio is 9/1. Likewise on the 1600, if the piston travels 800cc's of displacement but the piston is dished or not quite as tall leaving 89cc's of left over space you still have a 9/1 compression ratio. Two different pistons (AFAIK). Combustion chambers could vary as well making another variable. I'm going to use the better 1500 meanie heads so I'm going apples to apples there and looking at piston differences assuming the heads have same chamber volumes.

So if you stuck 1600 piston in a 1500 because it fits the same bore, pin, and compression height you would have less compression because it's designed to have 6cc's of extra space on top of the piston left open than the 1500 piston, to account for the longer stroke in the 1600 that isn't being used by the 1500. Likewise if you put the 1500 piston on the 1600 crank you will have more compression than the 1600. This is because the 1500 piston top is going to have less void or a slightly taller flat top to make the 1500's left over chamber volume 1/9 of the total 1500 displacement. But use that piston that takes up more room in the chamber than the 1600 piston does, with the 1600's added displacement, and you end up with a smaller left over volume at TDC. I did quick math the other day and it was like 9.6/1 (total swept displacement / left over room in the chamber at TDC). The piston doesn't get much if any closer but it starts coming up from further down. The 1500 piston was designed for 9/1 at 750cc (half of the 1500 total) so putting the same combustion chamber on but with 5mm more stroke the 1600 makes, the left over space only 1/9.6 of the total. So 9.6/1 compression ratio of the tighter piston in the same head but coming from 5mm further away.

Rods only connect them, rod to stroke ratio is a tuning variable but it only needs to connect the crank to the piston at the correct length to end up close as possible to the chamber at TDC and clear any obstructions in the case at BDC etc. It doesn't effect compression ratio. It does effect piston speeds at different crank angles, your links describe this well. They can to an extent be tuned to work together but it's not the end all. At the specific output and RPM it's really just what fits as long as it's within reason.

The 1700 piston could make more compression, but how much more and at what cost? If it turns out to be 9.9/1 but cost custom pins and machine work and or rods etc. then is it worth it or just use the 9.6/1 Kawi $125 each piston that bolts right in?

Now take a custom made piston and max out the bore size and make the compression as high as you're willing to support, i.e. 93 octane pump gas, and make it where it just fits the pin and the compression height puts it right in the chamber at TDC with the factory rod length and the only machine work you need is to make the bore for it. At that point you get the right compression, the biggest displacement and spend less on machine work. That's why I think this is the ultimate answer. If it was low budget just for fun or cost prohibitive I would say just use the 1500 piston an call it art. But if the custom piston is affordable the gains of it are worth the cost.

I will talk with RacinRay tomorrow if he's availible and see what he says. He did this for the 1700 already and has been doing this kind of thing for decades so he knows what to expect.

Hopefully this all make sense, I've done writing like this in the past but I've been drinking Whiskey tonight, lol. I may be rambling trying to make sure it's understood as I see it.

Vernon

[andyvh1959]

Right. Assuming 5mm longer stroke increase is only 2.5mm additional offset at the crank journal, to make the 1500 by 5mm more stroke to get the 1600 displacement. Then like you say the rods shortened 2.5mm means the pistons at TDC are no higher in the bore than on the 1500. When I get into the engine I'll see if there is additional space at TDC to allow a higher crown piston. Going up to 9.6:1 compression like in your calculation would be a healthy increase assuming no pinging/knocking issues. Surprising that Kawasaki never really bumped up the comp ratio for the Mean Streak versus the Classic or Nomad. My 2007 BMW R1200RT has a comp ratio of 12:1, in an air/oil cooled engine, overhead cam 4-valve heads and a good fuel/air management system to keep any pinging/knocking at bay. I only run premium fuel in it. Perhaps the better airflow around a flat twin heads is that much better than a big v-twin. But the Vulcan has water cooling going for it, and some air cooling as well.

I too have 1500 Mean Streak heads/cams/throttle body/injectors going onto my 1600 crankcase and jugs. So at least I'll get the increased flow into the combustion chambers with the larger valves and increased/longer valve lift. I'm anxious to hear what your contact RacinRay has to say about it.

It would be interesting to calculate the volume difference of the 1600 piston versus the 1700 piston, and determine the compression ratio difference. If I slide a 1600 piston into a tube fitted tight to the piston, at a set distance, say 30mm, from the top of the tube to the top outer diameter of piston, and then fill the tube to 10mm from the top I'll have a volume of fluid to reference. Pour the fluid out and set it aside. Then do the same with the 1700 piston, set to the same position in the tube. Then pour the fluid from the 1st test into the tube and note the fluid height difference. With the difference in fluid height I can calculate the volume difference between the two pistons. That should relate to the increased compression in the combustion chamber at TDC. Then use that volume difference like your calculation to estimate the static comp ratio.

Did some parts digging and found three different part numbers for the 1500/1600 piston. The 1500 Mean Streak piston is 13001-1628. The 1600 Classic piston is 13001-0054. The 1500 Drifter piston is 13001-1566. All are the same bore, so why would Kawasaki have three different pistons when all three use the same wrist pin #13002-1107. The 1500 Mean Streak use the same con-rod #13251-108011. The 1600 Classic con-rod is #13251-1147HH. I know on the 1600 the pistons got longer skirts to reduce noise in the engine.

Did some research into the Mahle piston catalog, and the pistons for the 3.6l turbo Porsche are also 102mm bore, just interesting. Mahle also has a compression ratio calculator that accounts for bore, stroke, deck height, head gasket and other factors.

[Mechaniac]

Good stuff. A crowned or domed piston would have to fit into the space made by the chamber and any unused bore at TDC. I'm curious to hear what you find in this regard. Leaving dead space on top of the piston isn't very efficient internal combustion or detonation resistance but OEM's don't always sweat the small stuff.

I did speak with Ray today for about thirty minutes, very easy to talk with him. A pleasant guy who happens to love motorcycles and makes his living building them. He was very knowledgeable and willing to work on this, he's done this kind of thing more than a few times. He has experience in how thick a cylinder wall needs to be to last in a street engine and how much compression to build in for pump gas. He says he needs a sample 1600 piston, a 1600 cylinder to determine maximum safe overbore and a combustion chamber that will be used to measure it or a mold of one. This was mandatory for him to go beyond a flat top design. I'm getting those pieces together now to send over to him, I'm sure I'll send him my heads as well to have it all machined or rebuilt together. I know some good automotive machinist we use here but this is his area of expertise. I have professional automotive knowledge and experience and have built many performance engines but leave the machining to the machinist even if I know what I'm doing and they have no clue IYKWIM. In this case I'll leave it all up to him, much easier and faster because he knows bike engines and tuning much better.

While looking on Ebay for suitable 1600 jugs and pistons I came across a 1600 listing that has some really good pics. In the pics of the piston tops a plain to see dish design is present. I've seen many of the 1500 and they are all flat. So that settles that, the 1500 flat-top in the 1600 engine would be a modest increase in compression for not much loot. Listing with pics: https://www.ebay.com/itm/255208730323

Ray was describing his fees and the cost of the 1700 pistons last time, it seemed reasonable (I left my notes at work, will update tomorrow). He will charge $125 engineering and design fee which includes dealing with the piston manufacturer (Wiesco) to get them made to his specs. Wiesco charges a set up fee for custom runs, which was similar to Ray's plus the cost for pistons. He was going to get with them to see what current pricing is and let me know the next time we talk. So if more than one set is ordered the price per set drops because the set-up fee is split by how ever many people buy a set. I told him that you and I were interested, not sure if there will be others. I think one could come along later and order the same pistons but have to pay the set up again.

I forget exactly what he said about the factory 1700 pistons but I think he mentioned some dish. I do remember him saying he was able to increase the CID to 110 along with a good increase in compression ratio.

He went into the need to have a tunable fuel injection system after this modification. He endorses the Dynojet Power Commander V. He said I would need to find a dyno tuning shop in their lists that could tune it properly after the build up. I live near Houston so there were several listed but I didn't see any that were motorcycle specific. I'm not sure if the others will dyno tune bikes. Cross that bridge when I get there.

That's about it for today.

Vernon

[andyvh1959]

Good stuff. I looked at those pistons on that ebay link, and those are exactly the pistons I have in my 2003 Classic 1600 right now. So they are dished, not flat at all. I found a reasonable picture of a 1500 Mean Streak piston/jug for sale on ebay:
https://www.ebay.com/itm/38339696532...IAAOSwf~NeMexn

Looks to me like the piston still has a dish versus flat, perhaps less of a dish shape than on the 1600 engine. That's why I got curious about the 1700 pistons as they are definitely not dished, though they are flat, with a definite squish band and valve reliefs at the top. Here are some pics of one of the 1700 pistons I bought:

[andyvh1959]

Here is a link to the page in the Mahle piston catalog for the 3.6L Porsche:

https://www.us.mahle.com/media/usa/m...e-ap-guide.pdf

Maybe RacingRay can reference this info and see if a 102mm bore Mahle piston has an application in the 1600 Vulcan engine.

[RACNRAY]

The 1700 pistons ARE DISHED, or also known as a reverse dome. It does not take much of a reduction in the reverse dome volume in that dome style piston to raise the compression alot. When I designed the 109 kit for the 1700 the displacement increase by itself raised the c/r .5 point so I had to calculate how much smaller in volume the dish had to be for my target c/r. I do feel the 1500/1600 engines will tolerate a higher c/r with a larger margin of safety against spark knock due to dual plugs per cylinder.

[Mechaniac]

Thanks for checking in Ray.

Got my notes, the surcharge is for a custom run set up is about $100. Pistons were about $750 last time, not sure if that's gone up like every other thing. Ray charges design fees of $150 if it's a flat top or $250 if he has to design a dome.

One other thing, he was adamant about the need to go into the transmission and back cut the gears on this type of project. He feels that once power is increased in this manor and the rider is prone to wring it out the transmission will soon show signs of overstress and pop out of 2nd under WOT. He says that he can back cut the gears now and they will last but if one wears the gears out (esp. 2nd gear) then decides to get the transmission repaired after the problems arise their is less good heat treated metal on the face to work with than there was before the problems. I don't know what the cost of this is. I was thinking about replacing the 5th gear with the standard drifter/classic gear for less RPM in 5th but I'll have to see how much work and money is involved. I'm old enough to have power and only use it when necessary these days.

Vernon

[andyvh1959]

I got this reply from ppgflyer when I PM'd about the rebuild he did on his 1600, which too had a failed 2nd gear like my 2003 1600. He did a bunch of machining updates inside his rebuild. I asked him about undercutting the tranny:

Initially I thought that the gears needed to be undercut in order to help prevent this problem, in actual fact they are undercut, even though the faces are not machined the dogs and the mating portion of the gear they mesh with are definitely trapezoidal. Once you have the gears in your had you will see this. Unfortunately, if the previous owner was unkind to his transmission you have now inherited their abuse of the bike, much as I did. However, going forward, after you have replaced the gears, I know you will treat the bike with a lot more respect, just as I do. As far as I'm concerned, if you shift gears correctly the only maintenance required for 100,000 miles the transmission should last would only be the clutch, especially on a cruiser.

He indicates the shift dogs are undercut from the factory. I'll check the Mean Streak tranny parts I have to see if the undercuts are obvious as ppgflyer says they are.

[Mechaniac]

I can say the gear engagement feel and mess noise it makes when moving definitely says they already are. Might be a characteristic of the Mean Streak close ratio gear sets.

[andyvh1959]

I bought me a burette so I can measure the volume difference of the 1600 dished pistons versus the flat 1700 pistons. From that I can calculate the comp ratio gain assuming it all fits. Is getting a set of custom con-rods a reasonable option to fit the 1700 pistons into the 1600 jugs?

[Mechaniac]

I my opinion getting a set of custom pistons is the reasonable option. Fit the existing rods, get the maximum bore increase, get the compression ratio I want. Most likely a more durable engine with more power. The rods are not a limiting factor, pistons are.

Using the 1700 pistons is a viable option if you get increases with little to no adaption work. Then it's a low buck gain.

[andyvh1959]

Right. I don't plan to spend a bunch of bucks and I want a really reliable engine. Just lots of speculation until I get into the engine and find what the limitations or opportunities may be to build some additional power into the 1600.

[Mechaniac]

It's been a minute but I was able to get back to this project recently. I've been communicating with Ray and the plan was to remove a sleeve from a 1600 jug and measure the size for potential overbore. I was able to do this at home in the oven and sadly it was not very thick. There isn't enough wall thickness to go much further, considering the cost of a set of custom pistons it wasn't worth it to me. So I pursued installing the 1500 Meanie flatter top pistons that should amount to about a half a point of compression. I ordered a couple in 0.50mm O/S but the order bounced back as "Unavailable" even though the rings were still there. So I ordered a set off Ebay that looks really good. I'm going to send a set of 1600 jugs, 1500MS pistons, rings, intake, Throttle Body, and 1500MS heads w/cams to Ray for machining and head work. Once he has everything in hand he may decide to mill the heads down a bit to increase compression.

I've ordered Classic 5th gear sets. I put pics in the flywheel post but for those who didn't see I've had the flywheel lightened quite a bit as well.

That's the direction of my build at this point.

I studied the jug and sleeve relationship closely. With more time and money it may be possible to install a larger sleeve and bore the jug openings to match. One would have to carefully relieve the bolt bumps in the water jacket of the jug to maintain coolant flow area against a larger sleeve. Do able but experimental and expensive. I'm not going to do that at this point.

Vernon

[andyvh1959]

Lots of good info, thanks. When I finally get into my 1600 engine this winter I may have a project for Ray, especially if it looks like the 1700 pistons will work. I already have the other goods: 1500 Meanie heads/valves/cams, Meanie throttle body, Meanie gearset/shifting forks (but I'll use the Classic 5th gear). I'll update the cam chains/sprockets, clutch, output bearing in the final drive. Goal is a stronger 1600 with a potential goal of 85 to 90hp at the crank. Already have a Baron intake, all the smog crap is long gone, got a Power Commander and a set of Vance & Hines True Duals. I do plan to build extended baffles in the True Duals, I want deep tone with no harsh barking so I can comfortably ride at 70 to 80 in 5th gear with no exhaust bark tiring my ears.

No way will my 1600 perform like a HD 114 or Indian 1800, but I have a weight goal of 800 lbs for the bike, so the weight to power ratio could be comparable to the much heavier Harley's and Indians. I think I can create a dresser with performance comparable to a Harley 103 or 107, certainly better than anything earlier than a 103.

I finally "see" the stroke/con-rod/crank offset/piston position now: the crank "throw" is increased 2.5mm and the con-rod length is decreased 2.5mm. So at TDC the piston is in the same position relative to the deck as it was in the previous engine, and the crank offset and con-rod changes negate each other. At BTC the crank throw is lower relative to the deck, AND the con-rod being shorter make the changes additive, so the effective piston stroke is 5mm longer. Longer effective stroke times the cylinder bore means more CC's. So IF the 1700 piston pin centerline to piston top is the same as on the 1600, IF the 1700 piston pin diameter to the con-rod small end is the same as on the 1600, then the 1700 piston will fit in 1600 bore but the CC's does not change. But the shape of the 1700 piston dish is higher than that of the 1600 it will bump up the compression ratio without a conflict with the valves.

Makes me wonder, say the 1700 piston pin centerline to top of the piston is even 0.5mm taller than the same distance for the 1600 piston, would the 1700 piston work in the 1600 bore as long as it doesn't interfere with the 1600 Mean Streak higher lift valves. Does the top piston ring have to stop some specific distance from the cylinder deck top?