SuzukiSavage.com - Oil System Evaluation & Upgrade

zevenenergie

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Re: Oil System Evaluation & Upgrade
Reply #180 - 03/20/26 at 15:30:24

Hi Mike, I'm going to say a few things purely for the sake of reflection. So I'm not trying to state it definitively

That clean spot could also be caused by the cold mixture flowing into that side of the head, and the temperature being too low to form a layer of black carbon.

I don't think that if there is detonation, it is caused by a compression ratio that is too high. I think it is caused by a squish gap that is too large.

I have seen people increase the crankshaft stroke before https://www.youtube.com/watch?v=pxGF8KyH2NQ&t=91s.

I have been thinking about using that method to make the stroke slightly larger so that the compression increases and to make the squish gap smaller, without running into problems with the length of the timing chain.

It detrimental to hone away the ring that has formed at the top of the cylinder due to wear on the cylinder if you don,t use an oversized piston and hone the cilinder.This creates a larger space above the piston rings. This not only lowers compression, but also allows liquid gasoline to accumulate, potentially causing vapor blasting and other phenomena that are difficult to foresee or interpret.

It is actually beneficial to make the space between the piston and the cylinder above the piston rings as small as possible.

I wouldn't say that no detonation occurred, judging by the sandblasted appearance. But I would like to rule it out(ore rule it in) out by mounting a detonation sensor.

I know from experience that you are going to ask me questions, but I think I already know that I won't know the answer due to my limited knowledge of 4-stroke tuning.
I am afraid that my ignorance about this will become apparent, so I want to preempt that.

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Fast 650 Senior Member Offline SuzukiSavage.com Rocks! Posts: 420 Valrico, FL Gender:	Re: Oil System Evaluation & Upgrade Reply #181 - 03/20/26 at 21:57:11 How much will increasing the stroke affect the balance though? Would it change enough to require altering the balance shaft to match then?
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zevenenergie

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Re: Oil System Evaluation & Upgrade
Reply #182 - 03/21/26 at 09:00:24

It is quite a substantial job, and as far as I am concerned, that includes balancing the crankshaft itself, although that small increase in stroke won't disturb the balance much. In theory the balance shaft would then also need to be modified, but Mike didn't do any of that either, even though his piston is heavier than the standard piston.
And he experienced no problems with extra vibrations—at least, I haven't read anything about that.

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Fast 650 Senior Member Offline SuzukiSavage.com Rocks! Posts: 420 Valrico, FL Gender:	Re: Oil System Evaluation & Upgrade Reply #183 - 03/21/26 at 10:34:08 That is good to hear then. The only stroker cranks that I have used were already lightened and balanced as purchased so I didn't know how much it would change the balance.
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DragBikeMike

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Re: Oil System Evaluation & Upgrade
Reply #184 - 03/21/26 at 11:34:59

Zevenenergie, thanks for your comments.

I agree with you, good tight quench will allow an increase in compression ratio without running into a detonation problem, but there are limits. I set up the quench clearance (squish gap) at .038" on this iteration of the test engine. The "squish" is very tight. I won’t reduce the quench clearance below that value on a street engine. On a drag race engine, I have run my quench tighter, but I routinely saw evidence that the piston was kissing the head. OK for drag racing, not OK for street cruising.

I am sure this damage is a result of detonation. The broken ring land wasn't caused by vapor blasting. This piston incorporates "detonation suppression bands" intended to mitigate this exact problem in the exact area. If you search around on Google, you can find several examples of the same type of damage. Mahle Pistons has a nice spread of photos.

Also, if you research suitable compression ratios for street engines, you will find that the general rule of thumb is not to exceed 195 psi cranking pressure on a street engine that doesn’t utilize an engine management sytem (i.e electronic fuel injection incorporating a knock sensor). Of course, I generally ignore all that sort of stuff and give it a try anyway. In this instance, it looks like I'm not gonna get away with it. I believe I went too far. I'm sure the fix is simple, and I'm sure the engine will still be killer fast with the reduced compression ratio.

Your comments on the stroker don't fall on deaf ears. I have long considered that option as a good way to increase compression ratio and displacement. But just as The Fastman mentioned, the balance issue would be a hurdle. The balancer shaft complicates things. The vibration levels were certainly affected by the different weights of the various pistons I ran. All were manageable, but the lighter pistons seemed to make freeway cruising a bit hand-numbing. As I recall, the smoothest setup was the Wiseco 97mm pop-top; the weight was very close to the stock piston.

A stroker would be sweet since it would increase the CR and displacement. Another option would be to simply install a longer rod on the same 94mm stroke crank. That would increase the CR without increasing displacement, and the longer rod engine makes better power by taking advantage of a more favorable angle of attack on the crank throw. Also, given the high rpm that the LS650 operates on the freeway, the long rod motor would keep the piston velocity at a more reasonable speed.

I went through all my parts bins yesterday to see what I needed to order. As it turns out, I have all the necessary material in-hand, so I'm getting started right away.

Fastman, how ya been?

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Re: Oil System Evaluation & Upgrade
Reply #185 - 03/26/26 at 17:22:35

DragBikeMike wrote on 03/20/26 at 12:52:57:

I also can’t explain why this thing gets into the detonation biz with the 97mm flat-top but not with the 94mm flat-top. I understand that the larger bore raises the compression ratio a bit. I guess it's just on the ragged edge of detonation and the bore increase takes it over the cliff.

The problem might be related to the cam. Of all the available cams, the DR650 cam has the earliest intake closing event. I might try revisiting the Web 402. I’m also gonna try a bit less compression, see if I can get cranking pressure down to 190 -195 psi. So, bring the compression ratio down to 9.7, install a cam that closes the intake about 8 degrees later, and pull out 2 degrees of the ignition advance. Maybe that’s the secret recipe.

I am not as well versed in the details of your science project - but it seems a cranking pressure of 190-195 would be a bit low. The stock Savage has a compression ratio of 8.5:1, and the Workshop Manual allows a cranking pressure of 140-203psi....I assume the 140 is a well worn engine and 203 is one that is loaded up with carbon deposits. On this YouTube video a stock Savage had a cranking pressure of 190.

Perhaps a hotter cam with more duration/overlap will lower the cranking pressure by allowing more air to escape before the valves close.....does that really help an engine survive once it is turning 3,000 rpm and upwards?

Is a compression ration of 9.7:1 really going to be able to have a cranking pressure down around 190-195?

Perhaps that old DR650 Wiseco 97mm with 9.5:1 isn't all that bad? Huh

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DragBikeMike

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Re: Oil System Evaluation & Upgrade
Reply #186 - 03/27/26 at 16:16:24

In my experience with the LS650 (and other engines), compression ratios in the 8.5:1 range result in cranking pressures around 150 - 160 psi. The 97mm pop-top pumps around 190 - 200, the 94 mm flat-top pushed around 220 psi, as did the 97mm flat-top. My crazy tight quench engine pumped 245 (CR was well north of 11:1). I have no idea how the service manual came up with 200 psi being in the normal range for a stock engine. Only way that could be normal is if a 1/8" layer of carbon is normal.

One very important factor is the intake valve closing event, not overlap which occurs at TC, but intake closing which occurs at the beginning of the compression stroke (just after BC). The stock cam closes the intake pretty early, and the DR cam closes it even earlier. Even with the early closing intake valve my stock compression engine didn't pump anywhere close to 200.

If you Google "compression ratio vs cranking pressure" you get all sorts of info on this subject. Since this is an adiabatic process combined with other dynamics such as gas intertia, it's pretty tough to arrive at a simple rule of thumb. But the general consensus seems to be keep the cranking pressure below 200 psi on a street engine. Some publications suggest 180 psi.

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DragBikeMike

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Re: Oil System Evaluation & Upgrade
Reply #187 - 03/27/26 at 16:21:43

This is an example of the type of stuff you can find using a Google search.

MotorTrend 09/01/2002 Tuning Engine Compression

Compression ratio is a fixed geometric measurement, while cranking pressure (PSI) is the actual pressure measured during cranking, heavily influenced by cam timing, engine speed, and sealing. Generally, a higher compression ratio increases cranking pressure, but a radical camshaft can lower PSI despite high compression.

MotorTrend +4

Key Differences and Correlations

• Compression Ratio (CR): The volume ratio of the cylinder at Bottom Dead Center (BDC) to Top Dead Center (TDC). It is a passive calculation.

• Cranking Pressure: The actual PSI measured using a gauge in the spark plug hole while cranking the engine, indicating the engine's dynamic sealing efficiency.

• The "Rule of Thumb": A common, rough estimation is that cranking pressure (PSI) is roughly 15-20 times the compression ratio (e.g., 10:1 ratio x 15-20 = 150-200 PSI).

• Impact of Camshaft: A "hotter" cam with2 early intake valve closing (IVC) increases dynamic pressure; a cam that keeps the intake valve open late (long duration) lowers cranking pressure.

Commonly Observed Values

• Street Engines: 8.5:1–9.5:1 CR often shows 160–190 PSI.

• Performance Engines: 10:1–11:1 CR can yield 200+ PSI, requiring premium fuel.

• Consistency: Consistent readings across all cylinders (within 5-10%) are more critical for diagnosing engine health than the absolute PSI number.

MotorTrend +3

Factors Affecting Cranking Pressure

• Camshaft Timing: Long duration/high overlap decreases cranking pressure at low RPM.

• Engine Speed (RPM): Slower cranking speeds result in lower pressure readings.

• Altitude: Higher altitudes reduce atmospheric pressure, resulting in lower cylinder pressure.

• Ring Seal/Condition: Poor ring seal allows pressure to leak past the piston (blow-by), lowering PSI.

MotorTrend +4

If you're the classic hot rodder, then you're already thinking, "Hey, if some is good, then more is better!" True to form, if you do that, you will be disappointed. Higher cylinder pressure also means that you will need more octane to slow the burn rate in the cylinder. The limit for street engines seems to be around 200 psi of cranking pressure. Numbers higher than 200 psi create excessive cylinder pressure at low engine speeds, which turns the engine into a detonating monster. A classic example of this would be an 11:1 compression engine with a short-duration camshaft that features an early closing intake valve, such as 50 degrees ABDC. This would create excessive cranking pressure and an engine that would rattle its brains out on 92-octane fuel. Our current HT 383 engine actually tested at 195 psi with the original stock cam and later at 185 psi with the large hydraulic-roller cam and does not detonate.

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DragBikeMike

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Re: Oil System Evaluation & Upgrade
Reply #188 - 03/27/26 at 16:33:42

Of course, I generally fall into the category "Hey, if some is good, then more is better!" I've always gotta try a little more. Sometimes I get away with it, sometimes I don't. As it turns out, the 97mm flat-top is not gonna let me get away with it.

I feel pretty good about my plan. I think bringing the cranking pressure down, installing the 402 cam, and pulling 2 degrees out of my ignition advance will solve this problem, and I think the engine will still run very strong.

I should probably continue the post I did on the original detonation problem. A cylinder is in my lathe right now and I'm making the final cuts on the bore. It shouldn't take too long to get it back on the road. The saga continues.

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Re: Oil System Evaluation & Upgrade
Reply #189 - Today at 04:37:04

Mike:

I know you are busy on your Science Project and trying to get the engine back in your bike and go back to wearing out tires - the detonation issue with the 97mm Wiseco Flat Top just has me confused. On the one hand getting 30,000 miles from a performance engine is likely not too bad - however history has shown that you have run high compression ratios before and never had a problem with detonation....something is just weird about that 97mm Wiseco Flat top piston.

Comments on the stock 94mm piston with the shortened cylinder/head.

DragBikeMike wrote on 03/24/20 at 20:29:18:

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.

Comments on 97mm Wiseco Pop Top (DR650).

DragBikeMike wrote on 09/22/20 at 01:01:13:

The forged 97mm runs quiet, it’s not rattling around in the cylinder. The dreaded forged piston slap is not a problem.

The 10:1 compression ratio and 210 psi cranking pressure do not cause detonation problems. It runs great on 92 octane pump gas.

The ignition timing is critical to limiting oil and cylinder head temperatures. Retarding the timing just 2° makes a big difference.

Comments on 94mm Wiseco Flat Top (LS650_

DragBikeMike wrote on 04/26/21 at 19:10:19:

I had logged 2250 trouble-free miles on the Wiseco Flat-top and it was time to start my next project. I figured I would update this post to let you all know how the new Wiseco is holding up.

The piston has performed admirably.

Power is outstanding. I’ve managed to squeeze a bit more steam out of it with a PWK40 carburetor. It’s killer fast, everywhere.

Fuel mileage continues to run in the low 70 mpg range. I almost never get less than 70 mpg (it’s usually around 72 to 73 mpg).

The subtle piston rattle has remained about the same. Doesn’t bother me in the least. On 92 octane pump gas, there have been no audible detonation issues.

The engine operating temps are still well below what I observed with the 94mm pop-top and the 97mm pop-top. The temps are also well below what I have observed with a completely stock 8.5:1 compression LS650. This flat-top piston is much more efficient. It’s converting more thermal energy to work instead of rejecting the heat through the cylinder & head. The flat-top engine runs a good 20°F cooler on surface streets and about 40°F cooler on the freeway.

A quick compression check prior to teardown showed the Flat-Top is pumpin a solid 235 psi. Things are still fresh as a daisy under the hood.

DragBikeMike wrote on 10/20/22 at 18:04:00:

The 94mm flat-top now had over 14,000 miles on it (actually 16,250 miles if you consider the 2250 miles I logged on the first build). It was running exceedingly well. Power was great, vibration normal, temperatures normal (180 oil/280 CHT), oil pressure normal (7psi @ 4000 rpm with 200°F oil temp), fuel economy excellent, and oil consumption the same (about 8 ounces every 1100 miles).

I have just "re-installed" the 94mm Wiseco Flat Top in my Cafe' bike and it is running great. I have 220psi cold cranking pressure and I am running a Webcam Stage 3. I am going to keep running that engine with this setup, as it appears you got 16,000 miles without any signs of detonation and you had 235psi cranking pressure.

On my Retro-Touring motor I have installed the 97mm Wiseco Pop Top (DR650 piston) and I have adjusted the C/R to 9.5:1, and I believe that will have somewhere around 200psi of cranking pressure, and I am going to to leave that where it is as you put a lot of miles on that engine without any detonation issues. You did comment on a lot of carbon build up on that piston, and similarly my 95mm Wiseco had a lot of carbon. I currently have the DR650 cam installed - I will likely take that out and install a Webcam Stage 1 that I have.....this motor is intended for many miles of cruising (Geezer Glide) and having a milder cam and less cranking pressure may be desirable.

I hope all is going well on the next chapter of your engine (Version 6.015) and it will be back on the road soon!

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Re: Oil System Evaluation & Upgrade
Reply #190 - Today at 06:05:28

One other thing that had me wondering - is why the detonation was occurring on the back (intake) side of the cylinder.

I thought that maybe the rear of the cylinder was not getting as much cooking and perhaps was running hotter than the front of the cylinder.

When I did a Google search about this - it tends to be the complete opposite issue. The exhaust side of a cylinder is hotter and the fuel/air mix burns faster on that side of the cylinder - then as the flame front spreads to the intake side of the cylinder the pressure/heat is such that the mixture "detonates" rather than burning normally.

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Re: Oil System Evaluation & Upgrade
Reply #191 - Today at 09:13:41

In another forum, a member experiencing similar issues with pre-ignition on a bored out, performance modded, Royal Enfield single, is converting the engine to run dual spark. This is relatively easy with the particular RE engine, since some machines were factory equipped with duals, and there's a suitable spot in the casting to drill at.

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Re: Oil System Evaluation & Upgrade
Reply #192 - Today at 10:15:09

Axman88 wrote on Today at 09:13:41:

In another forum, a member experiencing similar issues with pre-ignition on a bored out, performance modded, Royal Enfield single, is converting the engine to run dual spark. This is relatively easy with the particular RE engine, since some machines were factory equipped with duals, and there's a suitable spot in the casting to drill at.

This was done on the Suzuki DR650 by the factory, and there has been a bit of discussion about it long ago on this forum.

It is not all that easy on the LS650 as it will require a significant amount of machining to get the hole in the proper place, and with a proper seating surface and thread depth for the spark plug.

But is anyone could do it - I would bet on DragBikeMike to "GETRDONE"!

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