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Wiseco Flat Top Piston - Installation & Test (Read 1031 times)
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Wiseco Flat Top Piston - Installation & Test
02/10/21 at 21:44:31
 
In June of 2020, Dave got in touch with me and asked if I would like to collaborate with him and Lancer on a new flat-top piston.  A flat-top piston with increased compression height will provide a nice tight-quench area, which improves combustion and increases compression.  I had already built an engine with tight-quench and it ran really well, but it required some machining and the installation of a special jack bolt to take up excessive cam chain slack.  A special piston with increases compression height would eliminate the need for machining, and it would allow the use of the stock cam chain configuration.
 
This old post provides the details of the original Tight-Quench engine and the concept behind the approach.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1567201633

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #1 - 02/10/21 at 21:45:36
 
The special flat-top piston with higher compression height would make a tight quench engine a piece of cake.  No machining, no cam chain issues, I was all in.

I got in touch with Lancer and provided this sketch.
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Proposed_Wiseco_FT.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #2 - 02/10/21 at 21:46:22
 
Lancer got together with Alan Pizzino at Wiseco and a few months later we had a prototype in hand.  The Wiseco Flat-Top project was good-to-go.
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Wiseco_Flat_Top_Box2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #3 - 02/10/21 at 21:47:53
 
The two big changes on the new piston are the increased compression height (1.250” vs 1.099”) and the dish machined into the top of the piston.

Here you can see the difference in compression height between the stock piston and the new Wiseco flat-top.  Also note that the rings are situated higher.  This piston won’t tolerate any sort of ridge in the cylinder.  I wouldn’t recommend installation in a high-mileage cylinder, and it’s best to use a rigid hone to clean up the bore.
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Compression_Height_Stock_vs_Wiseco_FT2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #4 - 02/10/21 at 21:48:48
 
This shows the dish in the top of the piston.  I measured it at .074” deep.  Without this dish, the compression ratio gets a bit too high for pump gasoline.  For the dish, I was looking for a trench cut rather than a spherical cut.  The trench cut would preserve more quench area and increase the volume of the dish.  We’ll find out how it works with the spherical cut.
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Wiseco_FT_Dish_Depth__0742.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #5 - 02/10/21 at 21:49:38
 
Here you can see how the spherical cut eliminates some of the quench area.  That’s a .020” pin gage between the tool bit and the piston.  The quench area runs all the way to the edge of the valve relief in the top of the piston.  So, the spherical cut runs through a little over one-half of the quench area.  If I set it up with .040” clearance, it will have .040” at the outer edge and gradually transition to .060” at the edge of the valve relief.  Which is better, .040” all the way or .040” about half-way gradually increasing to .060”?  The gradually increasing configuration might work like a nozzle (possibly good) or it might diminish the desired turbulence (not good).  Again, we shall find out.
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Wiseco_Flat_Top_Quench_Zone__0202.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #6 - 02/10/21 at 21:50:41
 
I was also hoping that Wiseco would extend the skirt to match the stock piston.  I felt it would add stability and allow the piston to run quieter.  I’m no piston engineer so I must defer to Wiseco.  I’m sure their engineering staff looked at all aspects of the design.  Here you can see how much longer the stock skirt is compared to the Wiseco skirt.  The Wiseco pop-top also has a short skirt.
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Skirt_Length_Stock_vs_Wiseco_FT2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #7 - 02/10/21 at 21:51:27
 
This shows the differences in the skirt configuration.  Stock at the top, pop-top on the right, flat-top on the left.  It’s pretty evident that the stock piston, with it’s longer & fuller skirt, will provide the most stability.  The cast material also needs less running clearance.  The stocker should be the quietest of the three, while the pop-top should make the most noise.  I’ve been running the pop-top and it’s only a little noisier than stock.  Hard to guess how noisy the flat-top will be.  It has more skirt than the pop-top, but the increased compression height might add to the rocking and thrust loads.  Another burning question that needs an answer.
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Wiseco_FT_vs_Wiseco_PT_vs_Stock2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #8 - 02/10/21 at 21:52:07
 
Piston assemblies are part of the reciprocating mass.  Their weight is taken into consideration when the crankshaft is balanced.  Change the weight of the piston assembly by a significant amount and you end up with a shaker.  The stock piston assembly (piston, pin, rings & clips) weighs in at about 499 to 507 grams (I’ve weighed several of them).  The 94mm Wiseco pop-top weighs in at 455 grams and it shakes noticeably more than the stock piston.  It takes a toll when you run on the freeway for an extended period.  The 97mm Wiseco pop-top weighs in at 496 grams.  It runs a lot smoother than the 94mm pop-top.  This new Wiseco flat-top weighs in at 512 grams.  It will be interesting to see where it falls on the seismic scale.  The nice thing here is it would be simple to reduce its weight to a value closer to stock.
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Piston_Assy_Wiseco_FT_512_grams2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #9 - 02/10/21 at 21:52:50
 
Here you see the wrist pins for the three different pistons.  Pop-top on left, flat-top center, stock on right.  The wrist pin for the flat-top is heavy wall.  Looks to me like the inside diameter could be ground a bit to bring the weight down a few grams.  I’ll keep that in mind if this thing turns out to be a shaker.
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Wrist_Pins_Pop_Top_Flat_Top_Stock2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #10 - 02/10/21 at 21:53:38
 
To get started, it seemed like a good idea to see where the deck height was.  I intended to use a .021” copper base gasket so I did a rough assembly with and old copper base gasket, no rings, and no wrist pin clips.  Things looked great.
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Deck_Height_Rough_Check_32.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #11 - 02/10/21 at 21:54:20
 
In contrast, here’s how the deck height looks on the stocker.  No quench on this one.
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Deck_Stock_Negative_162_2.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #12 - 02/10/21 at 21:54:56
 
No quench on the pop-top either.  Note the orientation arrow.  It faces the exhaust side.  The new flat-top doesn’t have one of those arrows.  More later.
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Deck_Height_Pop_Top.jpg

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Re: Wiseco Flat Top Piston - Installation & Test
Reply #13 - 02/10/21 at 21:55:32
 
To accurately measure the quench clearance, use lead wire (sort of like using plasti-gage).
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Re: Wiseco Flat Top Piston - Installation & Test
Reply #14 - 02/10/21 at 21:56:10
 
Place the lead wire on top of the piston.  A little grease helps to keep the wire in the correct location.  My lead wire is only about .030” diameter so I stack it up on feeler gages.
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