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Message started by DragBikeMike on 09/30/21 at 19:21:19

Title: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:21:19

This is the ninth in a series of reports intended to document the results of progressive modifications to the LS650 engine. You can find Parts 1 through 8 here.

Part 1 Stock: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1620523526

Part 2 Airbox: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1621150483

Part 3 Exhaust: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1623048749

Part 4 Carburetor: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1625732492

Part 5 Cam: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1626391255

Part 6 Flywheel: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1626921647

Part 7 Head: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1627891507

Part 8 Compression: http://suzukisavage.com/cgi-bin/YaBB.pl?num=1631491370

In Part 9, we will increase the displacement by installing a 97mm piston. We will compare the Wiseco 97mm pop-top piston (9.5:1 CR) to the Wiseco 97mm flat-top piston (11.2:1 CR).

What I am about to describe worked good for me. If you decide to try this stuff on your own, you assume responsibility for the outcome. If you don’t have the skills, don’t do it. If you don’t understand something, STOP and get help. Get a manual. Read up. Comply with ALL the safety requirements outlined in the manual. Make sure you know what you are doing before attempting any of these modifications.

Let’s get started.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:22:23

Rather than give you a blow-by-blow on the 97mm pop-top piston installation, I am going to provide a link to the final post on my 97mm pop-top Big Bore engine. I think it’s a good series of posts (six parts). The series will give you all the nitty gritty on the 97mm pop-top installation and testing. Most of the info is applicable to the flat-top installation too. Eventually, I did a complete test regimen on the 97mm pop-top engine with the special high flow muffler. So, unlike the 94mm pop-top, I have a complete set of data for comparison.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1600759429

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:24:33

Up to this point, we have increased power and economy by improving volumetric efficiency and thermal efficiency. Now we are going to take the “bigger is better” approach. There’s no substitute for cubic inches; no replacement for displacement.

The stock LS650 engine has a 94mm (3.701”) bore and stroke. That works out to 652 cc (39.8 cubic inches). If we increase the bore to 97mm (3.819”), the displacement increases to 695 cc (42.4 cubic inches). That’s a 6.6% increase in displacement. Bigger should be better provided we can supply the engine with enough air.

Increasing the displacement will also increase the compression ratio (CR). The stock engine has an 8.3:1 CR. The 94mm pop-top brings the CR up to 9.2:1. The 97mm pop-top yields 9.5:1. The 94mm flat-top steps it up to 10.4:1. Throw in a 97mm flat-top and we’re lookin at 11.2:1. I think that’s pushing the limit for premium pump gas.

We’re gonna see if the old Twin-Swirl Combustion Chamber (TSCC) can hack a CR over 11:1. Up to this point, it has handled increased compression well. The centrally located spark plug and turbulent combustion chamber handle pump gasoline quite well. Adding the tight quench associated with the Wiseo flat-top also helps to stir things up. At 10.4:1, the 94mm flat-top engine ran fine on 92 octane. No problems with detonation. Now we’ll see what happens with more displacement and a little more compression.

As mentioned earlier, I’m not going to give you a blow-by-blow on building the big engines. The prior posts provide plenty of how-to. I’m just gonna hit on some of the unique issues I encountered on the 97mm builds, and then provide the test results for comparison.

In the interest of full disclosure, we need to talk about the clutch. Once I took the engine up to 42 cubic inches, the stock clutch wasn’t up to the job. It just couldn’t handle the power. The same holds true for the 94mm flat-top piston. Although I never tested the 94mm flat-top with the stock clutch, the 94mm flat-top runs just as good as the 97mm pop-top. That means the 94mm flat-top must produce a similar amount of horsepower and torque. If the clutch couldn’t hold the 97mm pop-top, it probably won’t hold the 94mm flat-top. If you wanna play you gotta pay. See this post for clutch options. You might need em.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1615547049

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:25:26

To install the 97mm piston you need to bore the cylinder 3mm oversize. I did that on my 97mm pop-top build. The 97mm cylinder only had about 1583 miles on it so a quick pass with a hone had the cylinder ready to go.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:26:02

It ended up just a bit looser than I wanted. I would have preferred .0030” clearance. Looks like .0035” will have to do. I set the ring gaps using Wiseco’s guidance for “Blown Race Only”. This is an air-cooled engine with really high compression, so I’m taking the conservative approach. I’ve learned my lesson. I set the gap for the top ring at .025”, and the gap for the second ring at .027”.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:26:46

The jug was an eBay beater. It was ugly. I left it ugly for the pop-top build. Since the 97mm flat-top would probably be my final build, I decided to slap on a coat of paint. This Dupli-color engine enamel with “ceramic” really goes on nice. Have any of you used this stuff?

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:27:44

The Dupli-Color went on easy and looked great. Made a silk purse out of a sow’s ear.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:28:33

I opted to go with a factory DR650 cam for this 97mm flat-top engine. I am not too happy with the welded cams. IMO, they don’t hold up well. The 340b cam has pits after only 7272 miles. The 402 cam has signs of failure after a measly 1583 miles. But the old DR650 cam is still pristine after 5073 very hard miles, even without the oil holes in the lobes. To be fair, the Web cams require heavy valve springs with more travel, so the lobes are subjected to a lot more pressure. Using the factory DR cam will allow retention of the stock valve springs. Less pressure on the cam lobe, less parasitic loss, less heat. All good.

Look at this old DR cam. Ain’t she pretty?

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:29:22

In contrast, the Web 402 after only 1583 miles. Same oil, Mobile 1 V-Twin 20W-50, Phosphorous 1600 PPM, Zinc 1750 PPM, full synthetic.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:30:17

Check out the 340b after 7272 miles. They were hard miles, but I really would like to get a little more service life out of my camshafts. Again, same oil. I recall Dave had a failure that looked very similar. I’m not likin these welded cams.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:31:16

Let’s look at some of the differences between the 97mm pop-top and 97mm flat-top.

The pop-top has a shorter compression height. At TDC, the top of the piston is situated about .125” below the cylinder head, there is in no tight quench zone. It bumps up compression using a pop-top, and increases displacement with a 3mm increase in bore size.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:31:56

The compression height on the flat-top is significantly taller. At TDC it is flush with the top of the cylinder and will permit setups with a tight quench zone (.030” - .060”). Instead of a raised top that sticks up above the basic top of the piston, it has a spherical dish that extends down into the basic top of the piston. Like the pop-top, it increases displacement with a 3mm increase in bore size.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:32:45

The pop-top doesn’t have a full-circle skirt.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:33:19

The flat-top has a full-circle skirt.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:34:04

At 496 grams, the pop-top is only 4 grams lighter than the stock piston.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:35:00

At 535 grams, the flat-top is 35 grams heavier than the stock piston.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:36:23

The ring sets are different. The pop-top uses Wiseco ring set 3819XH. The oil control ring has this cool wire guide in the expander. I think it’s used to prevent overlapping the butts of the expander.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:36:58

The flat-top uses Wiseco ring set 3819XS. No wire guide in the oil ring expander.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:39:28

I used the same cylinder head on both engines (97mm pop-top and 97mm flat-top). It’s my stage III head with the larger 34mm intake valves and the 1.79” exhaust port. All the details are in this post.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1595224521/0

The factory DR650 cam doesn’t need the high-lift valve springs, so I replaced the SuperTech springs with stock valve springs. The KibbleWhite spring retainers and cotters fit OK. The lower pressure stock springs will be gentler on the cam lobes. The old DR650 and the LS650 use the same valve springs. They work OK and have served me well in the past. Best keep it under 7500 rpm with the stock springs.

The special Cagiva valve adjusters I installed in Part 7 would not fit the Stage III head. The intake valve stems are a bit longer and there was not enough available adjustment with the Cagiva adjusters. I was satisfied with the performance, it just would’t fit this particular head. These adjusters are a good upgrade if you are using stock LS650 valves or DR650 valves.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:40:46

The bigger bore requires a special head gasket. The stock gasket hangs over the edge of the 97mm cylinder. I don’t recommend trying to use a stock gasket. Copper Gaskets Unlimited (CGU) in Phoenix, AZ can provide the correct head gasket for the 97mm bore, and they also have a variety of thicknesses. Lani at CGU gets these gaskets out quick. Please don’t try and use a stock head gasket with these 97mm pistons (especially the flat-top).

The copper head gasket is not nearly as forgiving as the stock multi-layer steel gasket. The head and deck surfaces must be perfectly flat. On the 97mm pop-top build I wasted a lot of time resolving oil leaks. Take a look at the Big Bore Engine Project Part 6. It provides a lot of details on my gasket fiasco. On this flat-top installation, I had zero problems with oil leaks.

For the flat top piston, deck height is critical. I suggest you try and adjust the cylinder height using the base gasket. Shoot for “zero” deck, meaning that the piston is exactly flush with the top of the cylinder at TDC. Adjust the thickness of the cylinder base gasket to achieve “zero” deck, and then use a .042” thick cylinder head gasket. That will set your quench clearance right at .042”. Mockup your engine, take some measurements, and then order the appropriate thickness gaskets. Just shoot Lani an eMail at coppergasketsunlimited@yahoo.com.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:42:06

Once the correct thickness gaskets have been determined, it’s time to check valve-to-piston clearance. Don’t even think about skipping this step. Install the piston and cylinder. No need to install rings or wrist pin clips for this check, but the correct thickness cylinder base gasket must be used.

To keep the piston-top centralized, I apply tape around the top of the piston until it will just fit into the cylinder with light force. You should be able to push the piston into the cylinder, but the piston should not move on its own. Three layers of blue masking tape were just right.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:42:42

Once the cylinder is in place with the correct thickness base gasket (for “zero” deck), apply modeling clay on the valve reliefs in the piston.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:44:36

Apply a liberal coat of grease to the valves to act as a release agent. Then install the head along with the cam and head cover. Make sure that the cam is timed perfectly. Adjust all the valves to .004”. Then slowly rotate the engine through at least two complete revolutions. I do four or more. Needless to say, if it gets hard to turn something isn’t right. Investigate. Don’t just force it and break something.

Remove the head to see if any valves are getting too close to the piston. This is why you should ALWAYS do clay checks. The intake valves were touching the piston. Certain death. The intake valve reliefs needed to be enlarged. The exhaust valves had plenty of room.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:45:40

Granted, my intakes are 1mm larger than stock (34mm vs 33mm), but that’s only 0.5mm (.020”) on the radius. Even with the stock valves, there would not have been enough clearance.

I addressed the clearance problem by increasing the radii on the intake valve reliefs. I’ll go through the process I used, but keep in mind there’s more than one way to skin a cat.

You can use a 17/64” transfer punch through the valve guides to mark the top of the piston.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:46:33

Place the piston at TDC. Then install the cylinder head gasket and cylinder head. Insert the transfer punch through a valve guide and lightly tap the punch to mark the piston. Repeat for the other valve.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:47:46

Now you have punch marks exactly on the centerline of each valve.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:48:21

You will need a fly cutter adjusted to cut the appropriate radius (.709” for 33mm valves, .728” for 34mm valves). You also want a generous radius on the tool point, like the one shown here. I didn’t use a radiused tool point on my original tight quench engine and I believe the tight corner in the relief contributed to the failure I experienced. The radiused tool point is important.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:49:19

Set up the piston in a drill press or mill. Adjust the angle of the piston top to the appropriate angle (117° for the intake valves, or 63°depending on how you look at it).

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:50:03

Using a center finder (pointer), adjust the X & Y axis until the punch mark is lined up on the centerline of the mill/drill head. Lock the table in this position. The piston is now aligned at the correct angle and centerline.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:50:46

Raise the mill/drill head and install the flycutter. Then slowly and carefully plunge into the piston top with the flycutter until you reach the depth you want. In this case, there was more than enough depth, the problem was on the radius, so I just plunged in until I reached the depth of the existing relief.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:51:23

To be safe, I didn’t even use the motor. I removed the belt and just turned the mill/drill by hand. Only took a couple of minutes to do each relief.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:51:56

This is what you end up with.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:52:50

Now, both the intake and exhaust valves had more than enough room. There was ample clearance, both radial & vertical. Lancer is working with Wiseco to resolve any interference issues. The valve-to-piston clearance is critical on the flat-top installations. It’s affected by the cam, quench clearance, valve size, and cam timing. YOU MUST CHECK THIS CLEARANCE, EVERY FLAT-TOP BUILD.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:53:31

I did a sketch that depicts the layout for the flycuts. If you already have a 97mm flat-top, this might be useful.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:54:19

The rest of the 97mm flat-top assembly was straight forward. I used a .042” copper head gasket and applied a thin, uniform coat of Permatex Optimum Grey 27036. Since I had “zero” deck, the quench is about .042” to .045”. The DR650 cam was set exactly to the factory timing marks. The valves were adjusted to .005”. I filled it with Rotella T4 for break-in. It looked pretty good too.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:54:50

Initial compression was 240 psi. Pretty high but as I previously mentioned, this engine never ceases to amaze me. It’s a large bore air-cooled engine. You wouldn’t think it would tolerate that much compression. We shall find out.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:55:57

Break-in went well. No leaks. It ran perfect. I hardly had to spend any time dialing in the carb. The engine starts easy and idles smooth. It didn’t use a drop of oil during break-in. It’s quiet but the vibration levels are robust. The interesting thing about the vibes is they are heavy at low rpm but tend to smooth out as the rpm rises. At freeway speed, it doesn’t shake any more than the stocker. The mirrors are clear. It has tremendous power and torque.

After 500 miles I changed the oil. It was time for the usual dose of Mobile 1 V-Twin 20W-50. A quick clearance check showed the valves were all within .005” - .006”. Things were lookin good.

Note: Consult the old posts for the performance evaluation of the 97mm pop-top engine. I had some problems with an oil leak. It took me a while to figure that out, but it was worth the effort. The 97mm pop-top was a great motor, lots of power and torque. The stock clutch couldn’t hold it. I will provide comparative data in the acceleration results of this post. Keep in mind that the pop-top motor was running a different cam & carb.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:58:16

Acceleration Tests - 97mm Flat-Top Tight Quench Engine

This was the setup for the 97mm flat-top engine. Stage III ported head, factory DR650 cam, 3” flywheel, 97mm bore with 94mm stroke, Wiseco flat-top piston (11.2:1 CR), modified airbox with K&N RD-0710 cylindrical filter element, Keihin PWK40 carb (actually 38mm), Mac 1.79” exhaust header with LCGP high flow muffler.

Second Gear 4K to 7K: 2.29 seconds 0.13 seconds faster than 97mm pop-top

Third Gear 4K to 6.5K: 3.79 seconds 0.42 seconds faster than 97mm pop-top

Third Gear 4K to 7K: 5.19 seconds 0.53 seconds faster than 97mm pop-top

Fifth Gear 3.5K to 5K: 3.70 seconds 0.34 seconds faster than 97mm pop-top

Fifth Gear 3.5K to 5.5K: 5.95 seconds 0.43 seconds faster than 97mm pop-top

As you can see, the 97mm flat-top is significantly faster than the 97mm pop-top. I might also add that the 94mm flat-top is just a bit faster than the 97mm pop-top in the lower gears, and just a bit slower in 5th gear. They are really pretty close to even. These flat-top pistons work great.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 19:59:49

Switch to Stock Header

I wanted to see how much the stock header would affect performance on the big flat-top engine. I installed the stock header and dialed in the jetting. It took a lot less main jet to achieve 12:1 A/F ratio.

Second Gear 4K to 7K: 2.37 seconds 0.08 seconds slower than Mac header

Third Gear 4K to 6.5K: 4.14 seconds 0.35 seconds slower than Mac header

Third Gear 4K to 7K: 5.78 seconds 0.59 seconds slower than Mac header

Fifth Gear 3.5K to 5K: 3.80 seconds 0.10 seconds slower than Mac header

Fifth Gear 3.5K to 5.5K: 6.56 seconds 0.61 seconds slower than Mac header

Wow! That really sucked the wind out of the sails. This engine puts the big Mac header to good use. It’s still plenty fast with the stock header, and it feels great. It’s very responsive. But you give up a lot. I guess the 1.79” port likes to be matched to the 1.79” head pipe.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:02:09

Switch to Smaller Carburetor

I have a PWK36 now so I figured I would match that up with the stock head pipe and see if I could create a torque monster. The PWK36 was a breeze to dial in. Had to reduce the main jet even more. I was all the way down to a #132.

Second Gear 4K to 7K: 2.40 seconds 0.11 slower than the PWK40 & Mac header

Third Gear 4K to 6.5K: 4.55 seconds 0.76 slower than the PWK40 & Mac header

Third Gear 4K to 7K: 6.37 seconds 1.18 slower than the PWK40 & Mac header

Fifth Gear 3.5K to 5K: 3.69 seconds 0.01 faster than the PWK40 & Mac header

Fifth Gear 3.5K to 5.5K: 6.46 seconds 0.51 slower than the PWK40 & Mac header

That’s just leavin way too much on the table. Yes, it was a torque monster. It felt fabulous on the surface streets. Key words & phrases, “felt”. In reality, it was way slower. The carburetion was excellent. It ran clean and had great response. But merge on to the freeway and it was evident that a lot of the old zip was gone. It would just fall on its face around 5K.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:04:22

Fuel Economy

Unfortunately, I did not check fuel economy on the 97mm Pop-Top. I have no idea how much fuel it used. All I can say is that it ran fine on 92 octane.

Fuel economy for the 97mm flat-top averaged about 67 mpg. I checked it eleven times. Worst was 62 mpg; best was 74 mpg. The flat-top was efficient, just like the 94mm piston. I also checked it three times with the 36mm carb and stock header. It was about the same, 67 mpg.

Operating Temperatures

Cylinder head temperature (CHT) was always higher on the engine with the 97mm pop-top. CHT ran around 310°and would routinely approach 330°-340° CHT. The 97mm flat-top piston always ran around 280°-300° CHT. We’re talkin cruise, not stuck in traffic.

Oil temperature followed the trend. The pop-top would motor along with oil temp around 200°-220°. The flat-top runs around 180°-200°oil temp.

Noise & Vibration

Like the 94mm Wiseco pistons, audible noise was highest on the flat-top piston. It had this rattle at light load. Nothing alarming. Just a faint rattle. The pop-top had a hint of the same rattle. The forged pistons need more clearance and it’s not uncommon to get a bit of slap. The fins on the air-cooled engine amplify the noise. I am also running the 97mm flat-top on the loose side.

The vibration levels on the 97mm pop-top piston are very close to stock. That makes sense since they are almost the same weight.

The 97mm flat-top is significantly heavier than the stock piston. As a result, the flat-top shakes a bit. I refer to it as Harleyesque. It’s got a pronounced shake at low rpm but get it up around 4000 rpm and it smooths out. On the freeway it’s about the same as stock. IMO, this (the freeway) is the area of concern. Long hauls at a constant rpm can take their toll. Lucky for us the heavier flat-top doesn’t cause high vibration in this critical range. The low rpm stuff makes the bike feel more muscular. I don’t see vibration as a problem with this piston.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:05:12

Durability (Pop-Top)

The 97mm pop-top piston looked fine after a little over 1500 miles. However, you can see the heavy carbon buildup. These pop-tops really seem to accumulate a lot of carbon. Other than the carbon buildup, the pop-top piston didn’t present any problems. I don’t count the oil leak. I shot myself in the foot on that one. I also don’t count the cam. The piston won’t make your cam wear out.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:05:50

Here’s another view of the carbon accumulation. It seems a little heavy to me for only 1583 miles.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:07:11

Durability (Flat-Top)

I haven’t inspected the 97mm flat-top (sorry, no pictures). It’s running great. No oil leaks, zero oil consumption, no accumulation in the catch can. Still running quiet and cool. Carburetion has been flawless, never requires any adjustment. The 13-plate clutch is handling the power, no signs of slipping. The whole package has been flawless (2300 miles). I don’t intend to open it up.

Notes:

The 13-plate clutch has about 6500 miles on it. It has been subjected to countless full throttle tests (97mm pop-top, 94mm flat-top, all of the exhaust system tests, all of the Evolution of a HotRod tests, and this 97mm flat-top). It performs good. No slipping, smooth engagement, no drag, easy to find neutral, light lever pull. It’s a good mod.

The factory DR650 cam now has 7354 miles on it. I don’t hear any gnarly sounds comin from the top end, and the valve clearance checks have been good. Inspections through the valve covers don’t reveal anything ugly. Won’t know for sure until I pop it open.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:08:31

Driveability

Both engines run great. They start right up, idle smooth, have good throttle response and broad useable power bands. But the flat-top piston is better at everything. More horsepower, more torque, broader powerband, faster acceleration, instant response. Pump gas (92 octane) works fine, no hint of detonation. The only advantage the pop-top has is ease of installation.

The cams behave exactly the same. The Web 402 doesn’t seem to have any advantage over the factory DR650 cam, but you have to run stiffer high-lift springs with the 402. I don’t think it’s worth it.

The carburetion is superb with either carb (VM or PWK). They both run great.

The part throttle performance is very good on the pop-top and excellent on the flat-top. As I mentioned on the prior report, this is the area where the higher compression really shines. The flat-top with its tight quench steals the show again.

These bigger high-compression engines pull like crazy in 5th gear. You can lug it all the way down to 2500 rpm, whack the twist grip, and it will accelerate hard all the way to 6500. It really pulls. The 5th gear performance is stellar.

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by DragBikeMike on 09/30/21 at 20:10:05

This completes the displacement portion of the project. The 97mm Wiseco pop-top adds a big boost overall, and the 97mm Wiseco flat-top seems to be the pinnacle of performance. Both are improvements worthy of your consideration.

Installing these big-bore high-compression pistons is a little more expensive. You have to foot the bill for a bore job. The increased compression associated with the increased displacement provides a measurable improvement in performance and fuel economy. If you go one step further and tighten up the quench (flat-top), you will bring your operating temperature down significantly, get even better fuel economy, and have the ultimate Savage HotRod. The flat-top is a little harder to set up but it’s well worth the effort.

I’m outa stuff to try. The next report will summarize the results and conclude the project. We started with a motorcycle that took 22.4 seconds to crawl from 55 mph to 85 mph. Now it will dash to 85 in 5.9 seconds, and it uses less fuel. It’s quiet and has good manners. I think that’s impressive.

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, post a reply so we can discuss.

Best regards, Mike

Title: Re: Evolution of a HotRod - Part 9 - Displacement
Post by Armen on 09/30/21 at 20:37:25

That was awesome!
Thanks so much.
Can't wait to get mine back on the lift and start to finish it!