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Message started by DragBikeMike on 03/24/20 at 20:16:39

Title: Pop-Top vs Tight Quench - Wiseco Piston Install
Post by DragBikeMike on 03/24/20 at 20:16:39

Pop-top vs tight quench - Wiseco Piston Installation

There are two options for increasing compression on our LS650 engines. One is to install a Wiseco pop-top piston. The other is to reduce the height of the cylinder (tight quench setup). Each has distinct advantages and disadvantages.

I had been running my engine with a tight quench setup. It ran great but I got a little careless and melted the piston. This was a good opportunity to compare the two approaches.

I installed a 94mm Wiseco. It was easy.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:17:47

I used my original stock cylinder. It was in excellent condition but the forged Wiseco 94mm needs a bit more clearance. Wiseco specifies .0025” clearance but I run my hotrod pretty hard, so I opted to give it just a tad more. I set it up at .0030”. When finished, it was round and straight within .0002”, still not perfect but pretty good. If you do this yourself, I suggest you use a rigid hone and torque plates. If you don’t have the equipment, get it done at a machine shop.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:18:42

I know I will probably get an earful, but please don’t use one of these if you are re-sizing the cylinder. Spring hones are fine for de-glazing, but any re-sizing should be done with a rigid hone. The spring hone follows the existing bore, so any existing taper or out-of-round will just be made worse. Use a rigid hone and torque plates to re-size.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:19:15

Same thing goes for ball hones. Good for de-glazing, but don’t use to re-size.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:20:28

I monitor the cylinder size using an inside micrometer and a dial bore gage. That way I can make sure I’m keeping it round and straight. Then I verify clearance with feeler strips.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:21:04

When finished with the hone, you must wash the cylinder with hot soapy water. You should be able to wipe the bore with a clean white towel and not pick up any evidence of honing debris. No black stuff on the towel, it must remain white. If the towel picks up anything, wash the cylinder again.

Since I had reason to suspect my prior failure was related to ring butt gap, I gave it a little more than specified. I ended up with .022” for the top ring and .024” for the second ring.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:21:54

When you reassemble, it’s tough to support the piston while you drop the cylinder down over the rings. It’s a juggling act. The ring compressor can only do its job if the top of the piston remains exactly perpendicular to the cylinder. That’s tricky with the piston wobbling all around on the wrist pin. This simple piston support works great. Just three chunks of mahogany (1”x 2”) held together with wood screws.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:22:36

With the piston support under the piston, both hands are free to work the cylinder down over the rings. I love this piston support. You want the base gasket adhered to the cylinder, not the crankcase. That way you don’t damage the gasket.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:24:43

BTW, don’t get confused by those pics of the cylinder installation. I forgot to take pics when I was installing the Wiseco piston, so I took some photos using spare parts. I’m sure you get the idea.

Once the cylinder is in place, you can run the piston up to TDC and get a look at the deck height. You can see that the Wiseco is situated well below the deck (.143” to be exact). No effective quench on this motor. With the Wiseco, you have to rely on port tumble/turbulence to get the mixture stirred up, not gonna be any squish working on it.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:25:28

In contrast, raising compression by machining the cylinder results in tight quench clearance. There is no pop-top to impede flame propagation, and relatively tight quench clearance to generate turbulence and improve combustion. Two different ways to skin a cat.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:27:04

With the Wiseco piston, I installed the 340b cam on the factory timing marks. The initial compression check showed 185 psi. That improved to 195 psi after about about 500 miles of very easy break-in. 195 psi is right where I want to be. I should be able to run 92 octane without ever having to worry about the dreaded spark knock.

Since installing the Wiseco, I have been able to do a lot of testing. I have loads of comparative data.

One thing I noticed immediately is vibration. The LS vibrates a lot more with the Wiseco piston. The 94mm Wiseco is 52 grams lighter than the stock assembly. The mirrors are blurred continuously, and long freeway hauls really put my hands and butt to sleep. It’s manageable, but I think the 97mm Wiseco would be a better choice. It’s only 11 grams lighter than stock and will most likely run much smoother.

In terms of performance, the tight quench setup kills the Wiseco. The tight quench has a lot more compression and you really feel it. It has torque that starts low and never stops. Second gear acceleration from 4K to 7K is much faster (2.60 tight quench vs 2.90 Wiseco). That’s a comparison using exactly the same cylinder head, camshaft, carburetor, airbox, exhaust system, etc., the only difference being the method of compression enhancement. The additional compression is clearly an advantage. I also believe that the tight quench setup yields much better combustion. If you imagine that 0.3 second acceleration advantage over five gears, you start to see what a big difference it is.

From a practical perspective, you can’t beat the Wiseco. You may not achieve the same all out performance, but the simplicity of installation makes it a better choice. It’s still plenty fast, and you don’t need a machine shop to install it. There are no cam chain tensioner hurdles, and valve-to-piston clearance isn’t a problem. Installation is easy. It really offers a lot of bang for the bucks.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/24/20 at 20:29:18

The details of the tight quench engine are in this old post. It gives all the gory details plus an explanation of why I feel tight quench is good.

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

I think the tight quench engine had too much compression. With a DR650 cam timed to the factory marks, that engine pumped 245 psi. It ran good, but I had to feed it octane booster. I switched to a Web 340b cam (timing retarded 5°). That brought the cranking pressure down to 220 psi, still too high. I was able to run on 92 octane but was always conscious of the big squeeze numbers. I really should have opened up the combustion chamber a bit and brought the cranking pressure closer to 200 psi.

Since I got the engine running again, I have been able to finish up testing on the Hayden KrankVent and also do a carburetor comparison test. I hope to finish up those reports soon. Plenty of time on my hands these days.

I hope this post gives you a little perspective on the two compression enhancement options that I have tried. I’m sure there are others.

Knowledge is power.

Mike

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by Armen on 03/24/20 at 20:41:52

Thanks so much for the detailed write up and sharing!

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by kamelryttarn on 03/25/20 at 05:36:35

What is the maximum reasonable compression ratio that can be achieved? In Sweden the regular gasoline is 95 octane and premium is 98 and I even found something called ED95 which is 95 percent Ethanol and 5% "combustion enhancers" and I think it can safely handle 18:1 compression ratio. Are there benefits to be had with going higher than stock compression if 95 octane is available everywhere?

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by Armen on 03/25/20 at 06:48:38

Kamel
With all due respect, there is no way a simple carburated air cooled motor can run 18-1 compression.
My guess is that 10:1 is about as high as you'd want to go, unless you want a hand grenade.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by DragBikeMike on 03/27/20 at 23:35:28

Kamelryttarn, with .040" quench I estimate you end up with 11.5:1 CR, cranking pressure about 255 psi. With .060" quench I had about 11:1 CR and 245 psi, too high for pump gas here in Hawaii.

That 95% ethanol blend you mentioned would allow you to run very high CR, most likely around 15:1. I agree with Armen that 18:1 is probably not doable. Problem with alcohol is it's so darned corrosive. It's hydroscopic and sucks up water like crazy. Your carb and fuel tank will be a corroded mess in no time. Additionally, you have to really increase the ratio of fuel to air to run straight ethanol. You would probably end up with A/F ratio well below 10:1. You will be washing down the cylinder. I suggest you stick with gasoline.

I don't know all the specifics on European octane ratings, but here we use R+M/2. We add the research number to the motor number and divide by 2. So if I am not mistaken, 92 octane here is equivalent to a higher octane rating in Europe. I imagine your high octane fuel is probably at least as good as ours. Once I installed the long winded cam with timing retarded, my tight quench engine ran good on the fuel available here. But I always had concern over detonation, I knew I was on the ragged edge. I was willing to run it like that because it made so darned much power. I just got careless. You can't be careless when you run on the ragged edge. ;)

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by srinath on 03/28/20 at 14:59:38

I have a MZ scorpion - Yamaha 5 valve 660 that someone installed a high compression 676 piston in, and I cracked the piston because I didn't know it had high compression piston. Its now getting back together with a 10:1 690 or so.
I had bought another 660 stock 660 this time, and the biggest difference between the 676 high compression that I ran for a few 1000 miles before it blew was actually torque - the high compression bike was actually worse at getting revved up and nearing its redline it was more anaemic - likely cos it didn't have the cams to fill it right nor the jetting - which may have been why I cracked the piston. That bike was always hard hard hard to start.
Anyway I am thinking is it the cams and carbs that get you that extra power or is it the high compression piston.

Cool.
Srinath.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by Armen on 03/28/20 at 20:54:20

Hey Srin,
I was at Daytona in the 80s when the 5 valve Yamahas debuted. They were so fast! Funny thing, in a few years, they weren't. Everyone else took off and they did't get faster.
Kevin Cameron, my fav bike tech writer in the world, spent a lot of time ranting about what a bad design the 5 valve heads were for racing. Part of the problem was that with a high compression piston, the combustion chamber looked like an orange peel. Flame travel was so convoluted that the bikes were running 40 degrees of advance at a time when good 4 valve heads were running less than 30. Needing that much advance was a sure sign things were unhappy in combustionland.
Finally Yamaha ditched the design.
Wonder what other changes the PO made to your motor besides the high compression piston. Prob didn't do much.

Title: Re: Pop-Top vs Tight Quench - Wiseco Piston Instal
Post by srinath on 03/29/20 at 07:00:46

The high compression piston was the only change the bike had. I actually like running the airbox, he had a K&N in the airbox, I reverted back to paper. It made better torque but was low on top end revs, it may have had a fatter and taller rear tire causing it to choke up as well. It wasn't wanting to rev basically.
I am reassembling it now with a 692 or some like that CC but 10:1. Will have to finish it when I finish building my addition to my house and getting it here etc.
The stock MZ has a horrible starter clutch issue, someone in 2012 made me the starter clutch for the other one, I gotta get him to make me another and put it on the stock one as well.
Cool.
Srinath.