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Evolution of a HotRod - Part 8 - High Compression (Read 121 times)
DragBikeMike
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #15 - 09/12/21 at 17:29:23
 
The Wiseco pop-top had the most mileage on it.  I logged 5023 miles on the pop-top and it had been used for the carburetor shootout, the muffler shootout, and all sorts of other projects.  It had been subjected to countless WOT pulls and all sorts of grossly rich and lean fuel mixtures.  The skirt still looked new.  No significant wear on this thing.  Not even a scratch.
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DragBikeMike
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #16 - 09/12/21 at 17:30:08
 
The Wiseco flat-top was the baby of the crowd.  Just 2249 miles on it’s odometer.  As expected, it looked great.
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DragBikeMike
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #17 - 09/12/21 at 17:32:04
 
Combustion

Each piston exhibited clues that might be useful in evaluating how well the combustion process was working.  The three pistons had unique deposits and burn patterns.  These deposits and patterns might aid in evaluating efficiency.  Since the flat-top performed best, maybe the location of the deposits and burn pattern might be something to work toward.  I recall reading something about this but don’t remember what book.  If my memory serves me correctly, that expert was of the opinion that if there were areas with no deposits then the burn wasn’t complete.  That would seem to be contrary to my own experience since the flat-top had the best performance and efficiency but the least amount of deposits.  The area around the intake valves had almost no carbon deposits.

This shows the three piston tops, stock on left, flat-top in center, pop-top on right.
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DragBikeMike
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #18 - 09/12/21 at 17:33:01
 
The pop-top was downright nasty looking.  The deposits were thick and looked to me as if they would eventually become a problem.  All these pistons were setup using the same techniques to establish proper air/fuel ratio.  A wide band air/fuel ratio meter was used to achieve optimum air/fuel ratio at cruise and WOT, and timed performance runs were used to verify that the best power mixture was achieved at a ratio of about 12:1.  Oil consumption was zero for all three.  Where’s all this carbon coming from?  Maybe all the carburetor setups.

The build-up on the pop-top was crazy thick.  I got no answer for this one.
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #19 - 09/12/21 at 17:33:49
 
In contrast, the flat-top was clean.  I prefer this.  Note the bright silver area along the back side of the intake valve relief.  I find that interesting.
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DragBikeMike
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #20 - 09/12/21 at 17:37:21
 
Driveability

This is the area where the high compression pistons really shine.  Unfortunately, it is also difficult to measure.  It’s subjective rather than objective, seat-o-da-pants stuff.

All three setups have excellent manners.  They all start right up, idle smooth, have good throttle response, and broad useable power bands.  But the high compression setups are crisper.  The higher the CR the better it gets.  The high compression changes the character of the engine from that of a workhorse to a thoroughbred.  It changes from an engine that’s always willing and able to one that is chomping at the bit.  Sure, the WOT tests show conclusively that the high compression setups are faster, but the real benefit is at part throttle operation.  This is especially evident on the flat-top with its associated tight quench.  Part throttle response is instant and crisp.
 
Where the part-throttle to WOT transition is good with the stock piston, it is much better with the pop-top, and excellent with the flat-top.  The transition from part throttle to WOT is smooth and predictable on all three pistons, but the flat-top is off the hook.  It will kill in the twisties, probably allowing a good rider to run one or possibly two gears higher through turns.  It’s makin good power way down low.
 
At part throttle, the venturi vacuum is highest.  That results in much better atomization and homogenization of the fuel droplets and air.  Throw that brew into a combustion chamber that is more turbulent due to the higher compression and the burn is more uniform and complete.  Add the flat-top’s tight quench and things really get stirred up.   You get more power from less fuel.   More heat is used to do work, less heat is lost to the cooling system, CHT and oil temps go down.
 
I can’t say enough about the part-throttle performance.  Yes, both these high compression pistons are faster at WOT, but it’s the part-throttle performance that makes them worth the entry fee.
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #21 - 09/12/21 at 17:38:49
 
This completes the compression portion of the project.  The Wiseco pop-top adds a nice boost to overall performance and the Wiseco flat-top really kicks it up.  What’s not to like about big improvements in power and economy.

Installing a high compression piston is relatively easy and inexpensive.   The increased compression will provide a measurable improvement in performance and fuel economy.  If you go one step further and tighten up the quench (Wiseco flat-top), you will bring your operating temperature down significantly, get even better fuel economy, and run with the bigboys.  The flat-top is a little harder to set up but it’s well worth the effort.

Next stop on the Power Train?  Displacement.  There’s no replacement for displacement.  In the next installment (Part 9), we’re gonna bump up the cubic inches with the Wiseco 97mm pop-top and the Wiseco 97mm flat-top.

I hope some of you find this project informative and can use the data I collect to help make decisions on your own project.  If you have suggestions or comments on my test methods, post a reply so we can discuss.   As mentioned earlier, if you have a particular component or modification that you would like to see included, let me know and we can collaborate.
 
Best regards, Mike          
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #22 - 09/12/21 at 20:20:06
 
Awesome as always!
Thanks!
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #23 - 09/12/21 at 21:05:46
 
On 1 of my stockers, it was burning a lot of oil and the carbon deposits were very thick all over the piston.  But not bubbly like your pop top.
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #24 - 09/25/21 at 16:42:45
 
Hi Mike, would it be a ridiculous idea to press fit some type of metal slug into the centre of the gudgeon pin when using these lighter pistons to bring the reciprocating weight up to that of the original to help smooth out the vibes.
Thanks for all your great research & write ups
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #25 - 09/25/21 at 19:21:21
 
Sparktfxr, I assume you are interested in the Wiseco 94mm pop-top piston since it is the only assembly that is significantly lighter than the stock piston.

I have thought about installing a plug and decided it wouldn't be wise. You would have to set it up with a lot of interference to have confidence that the plug would stay put.  The wrist pin has very little clearance with the rod and piston.  A plug with an interference fit would most likely increase the wrist pin diameter and cause clearance problems.  I think it would be better to just procure a heavy-wall wrist pin, like the pin that comes with the flat-top Wiseco.

The vibration on the 94mm pop-top isn't that bad, but you will notice it.  Long freeway rides at a constant speed take a toll.  The 94mm Wiseco flat-top is only a few grams heavier than the stock piston so vibration levels are about the same as stock.

I'm currently testing the 97mm Wiseco flat-top.  It's about 35 grams heavier than the stock piston.  It increases vibration at a lower rpm.  IMO, that's easier to live with because the vibration is in a range where you don't typically ride at a steady speed.  Get it up around 4K and it smooths out nicely.  So when I'm on the freeway running steady state, the vibes are pretty low.   The 97mm flat-top is killer.
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #26 - 09/26/21 at 16:01:54
 
Hi Mike, I perhaps wrongly thought the wiseco's were generally lighter, I am currently running a 96mm pop top but after reading your article re the HC flat tops last week  have been in touch with Lancer to try to buy one of the 97mm. Being 35gms heavier if there was enough meat in the crown could the underside of the crown be milled or drilled to bring the weight down.  Just a thought!
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #27 - 09/26/21 at 17:10:29
 
It might be an option.  I didn't take any measurements to see how thick the crown is.  It would certainly be easier to lighten the piston assembly than to add weight.  

That said, I don't think it's worth the effort.  As I mentioned, the 97mm flat-top vibrates more at lower rpm.  Get it on the freeway and it smooths out.  I went for a long ride this morning and paid particular attention to the vibration levels at 4000 rpm.  The mirrors are clear and the hand grips seem to be buzzing about the same as the stock engine.  These are subjective tests but I don't have any sort of vibration analyzer to collect hard data.  

The vibes at lower rpm are higher but you typically drive through the range, so you aren't subjected to the constant steady-state vibration.  It's a non-problem.

I discuss the vibration levels in my posts because I think its important.  To some folks, it might be a big deal, or it might cause concern over reliability.  None of the Wiseco pistons I have tested exhibit vibration levels that are unacceptable to me.  The improvement in performance is well worth the small increase in vibration.  I think you will be very pleased with that 97mm flat-top.

One thing I failed to mention in this post on the 94mm Wisecos.  The stock clutch can handle the 94mm pop-top, but the 94mm flat-top might overwhelm the stock clutch.  It will depend on what else has been done to the engine.  Here is a post that provides some options for the clutch.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1615547049
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Re: Evolution of a HotRod - Part 8 - High Compress
Reply #28 - 09/27/21 at 09:19:13
 
Carbon deposits are the result of incomplete combustion. So the more efficient engine will build up less deposits. And your results really show that, thanks!
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