The Delta Project

Why this name? Well, when Suzuki went from the flat square-4 (RG500B) , to the stepped square 4 (RG500 “C”, or “Gamma” ) it was generational change, from Beta, to Gamma. What we were proposing to do was also a major change to the powerplant: an upgrade to modern Grand Prix technology. The Gamma engine was a significant evolution of the RG500B, so, I chose Delta to designate the next stage..so now it’s an RG500 Delta!

From “Gamma” to “Delta”

The Delta project would ultimately involve modified crankshafts,different rods, all-new cylinders, and custom-built heads, not to mention a new, completely adjustable digital ignition. To round off the project, I incorporated massive bracing to the frame to try and shore up a classic weak point on my RG500.

How this all started

I am not the smartest guy in the world. For some reason, after developing my RG500’s motor to the point where it made 127 hp and 66 ft-lbs of usable torque, I junked it and started over by swapping TZ250 barrels onto my RG500s cases. I thought a home-brewed, disc-valve RG/TZ500 would be pretty cool. Well, the search for killer power has been a cruel -and expensive- mistress. Nontheless, it has been a very interesting experience and I got to work with some great people. Ever wonder what goes into building some crazy special? This is our story...The Tale of the RG500 Delta!

Before Project Delta even began, my RG500 had made over 45 dyno pulls. It now (Sep 2002) has over 100 dyno pulls on it. I spent a fair bit of effort in the last few years learning how it responded to different compression, porting, pipes, intake systems, ignition curves, you name it. When the smoke cleared (literally) we had an amazingly flexible disc valve motor than pumped out great power from 7500 rpm, and over 60 ft-lbs from 8500 to 10000 rpm, peaking at 66 ft-lbs on the Dynojet. With the addition of an exhaust water injection system, the powerband started 1000 rpm lower. A fully programmable ignition would have fattened the power spread even more. It would have been easy to get higher peak power, but I do track days and the occasional race with this bike and longevity was the order of the day, so we kept the revs reasonable. The motor made good BMEP, pushing 160 psi using net hp, so we did OK with a motor that was designed in 1985!

Then I got greedy.

An innocent discussion on the RG500 mailing list (RG500@xs4all.nl) brought up the topic of what it would take to get really insane power from one of these things. 127 hp pushing a 350 lb (fully wet) bike isn’t bad, but I slavered at the prospect of 150-160+ hp and bottom end, to boot. A few guys have swapped on barrels from the RGV250 streetbikes, but it was a pretty big job, and for modest power gains. I had seen reports of 135 hp - no dyno sheets though- but we could do that with the current motor if we wanted. Hardly worth the effort when we were already at 127. A lot of guys had done 550cc kits but we creamed them for midrange and peak with the well-sorted 500cc motor. (This was before Mark Dent showed up!) Again, not worth the effort.

We tossed around the idea of making modern barrels from scratch, and one list member even had access to the facilities to do it. However, this was a bit too daunting- no takers. Then a friend suggested skipping all the streetbike BS and installing TZ250 top ends. Same bore and stroke, 56 x 50.6. hmmm! A parts supply as close as the Yamaha dealer, stretching into the forseeable future. Upgradable to latest-model TZ cylinders whenever money allowed it. Race-bred breathing that had the potential to develop 160-180 hp in 4 cylinder trim. Irresistable! I knew this would be a heavy job and enlisted the aid of my unofficial tuner, Darcy Rosentreter, of Darcy’s Race Pipes in Winnipeg. As far as I am concerned this guy is next to God for making a 2 stroke go. No BS, just incredible results. And nice, to boot. I suppose most 2 strokers feel the same way when they hook up with a really good tuner. He built a normally aspirated, 230 hp Vmax snowmobile and kicked the hineys of pretty much all the big-name opposition at the World Series. . Will that do?

Rocky Stargel, a friend who raced a late modelTZ250, had spare barrels he measured out for us, and Darcy figured that it just might be a doable swap with a bit of machining on the barrels and a set of adaptor plates. From this point on, I have to give 90% of the credit to Darcy, as he designed the adaptors, set up all the clearances, and facilitated the necessary crank work. So when I say “we did this” and “we did that”, it was me chasing Darcy around yapping like an excited pup while he figured out how things would fit together.

Rocky also happened to have 4 spare complete top ends he was willing to sell cheap, to help out with the project. I couldn’t resist- I sold my ZX6R supersport bike and bought the TZ250 parts.

Rocky shipped me the stuff asap and in a week I was like a kid at christmas, opening boxes of menacing-looking TZ cylinders, heads, and powervalves. Darcy had already seen TZ stuff and was forming his battle plan, but for me out came the ruler and I got my first impression of what he had been talking about.

Just to lay a bit of groundwork, the RG500 Gamma is a stepped, square 4 engine. A pair of twins, on a common case, geared to a single intermediate shaft in the center. 56 x 50.6mm layout with individual cylinders and paired cylinder heads. Front cylinders exhaust out the front, rear cylinders go straight out the back. The TZ250 we wanted to use is a V twin, with individual heads but the same bore and stroke.

The TZ barrels were not ideally suited to bolting onto an RG500 case. The TZ parts attach to studs, while RG cylinders have through bolts at the base, in the coolant passages. TZ has coolant coming up under the exhaust port, RG feeds coolant next to the boost port... so the coolant inlet was on the wrong side of the barrels. The TZ barrels were a bit too wide to fit, but we had enough material on the outer wall of the transfers to shave a few mm off the facing transfer walls and gain clearance. The massive triple port of the TZ requires a piston with a full skirt to seal on the exhaust side, so the Rg pistons absolutely would not work, as they were cut away next to the pin- this would uncover the exhaust ports. Unfortunately, the RG rod takes a 14mm wristpin as opposed to the TZs 16mm part, so we could either swap to a new rod, or make rods to fit, or find another suitable piston, or get pistons made. RG pistons use an offset wristpin on 2 cylinders to counter pin thrust. The TZ also uses offset wristpins, but since 2 barrels would be facing ‘backward’ from their usual orientation, for a TZ, the pin offset would in that case be in the wrong direction. It was impossible to reverse the TZ pistons on the 2 ‘backwards’ cylinders bacause of a relief on the backside of the skirt, so the rear pair would just have to suffer additional side thrust.

The whole project was this sort of exercise.

The swap broke down into major and minor areas of consideration.

Major:

Adaptor plates: thickness? to be determined by the final desired piston protrusion, but we had to

settle on a connecting rod first.

what to do about coolant routing from the case into the barrels

max external dimensions

material

placing all the stud holes, thread holes, transfer ducts, coolant passages, and sealing surfaces so they didnt get in each other’s way.

do we handmake the pieces, or get them digitized and CNC cut so my pack of drooling friends could follow in my footsteps? cast them or machine from solid stock?

Crank mods: we needed to buy enough room for an adaptor plate to fit under the TZ barrels. The RG uses a 100mm rod, the TZ, 110mm. It seemed logical and convenient to look for a suitable 110mm rod to more closely emulate the TZs setup, as this would also gain us precious room under the barrels. The yet-to-be-found rod would need to fit my RGs crankpin and the yet-to-be-found piston’s pin. The yet-to-be-found pieces were beginning to stack up. Of course, after all these new parts were hung on the crank, it would need to be rebalanced- but to what balance factor?

Pistons: Must have a full skirt (aha! a starting point) and fit the TZs 56mm bore. Offset pins a plus if reversible. Single ring preferred. Must be able to withstand 350 Bhp/liter, so no 1962 Bultaco stuff. Can use a larger pin than the con rod, if it comes down to it, as we could use crowded rollers on the small end if need be. An example would be using a piston designed for a 16mm wristpin on a rod intended for a 14mm pin. Just use the 14mm pin and pack in 2mm roller bearings with no cage, just install as many as will fit in and pack it with grease so they stay put till you get the pin in place. Apparently this is yet another racing trick as the cage, at ultrahigh rpms, has enough inertia to slam against the rollers and make them skid when its time to reverse direction. Get rid of the cage, and all the roller element have to do is reverse their own rotation, with no cage bashing into them every revolution. That’s the story, at any rate. Don’t call me on any of this stuff because I had never heard of half of this before!

Page two: Project analysis