'78 SR500 street tracker

[hoffman900]

Playing around with things a little more. He has a special valve shape that works well in his Chrysler Hemi work (sorry, I'm holding the shape of that close to my chest). He had a blank come in for another project, so after he got done playing with that, he cut it down so it was ~2mm larger than standard and flowed it. Keep in mind the seat is still at sized for the 47mm valve. Pretty cool to see how it picked up low through the mid. You can see as valve lift increased, the throat/seat became the controlling factor in airflow, hence it didn't really change.

Of course, once the seat is cut, numbers will surely shift around.

The next step is to order valves after the retainer and locks for the 7mm valve stems come in, and open up the valve seat.

I also found someone who will machine a velocity stack with a elliptical profile and a full radius around the periphery.

 

[hoffman900]

Here is the finished chamber and valves. The head has since been blasted and decked to get the combustion chamber volume where we need it.

and again, the photo of the intake port:

Valve retainers to fit the 7mm valves:

So as you can see above, we flow tested the Mikuni VM-36 (36 mm venturi) with a more traditional style velocity stack.

and the flow numbers at WOT

After that test and testing the combination on the head (was losing almost 30cfm at .600" lift), I decided to pick up a Mikuni TM-38 flatslide (38mm venturi), which works out to be an increase of 11% in area. Now the venturi matches the spigot and the port entrance diameter.

Here is the TM-38 attached to the spigot and being flowed:

and flowbench figures:

So a 11% more area and 12% more flow, and that's without a velocity stack of any sort.

Here are the final flow numbers with the spigot attached (but without the carburetor):

Went up from a 1.85" valve to a 1.90". The port actually lost about 1.5% of flow by doing so, but made the port VERY stable on the bench. I'll take some flow if it means a smoother and more stable port.... especially when you start thinking about the kind of depression is actually occurring in the engine.. If the port is starting to break up at 28" H20, it'll be a mess at 3x that.

The right side is the exhaust. Those numbers are without a pipe. The .800" number is .700 valve lift but with a pipe. Was just really looking for the port to sound clean, which it did.

Keep in mind, this isn't what I would call a 'race' port. The goal with this was port efficiency. This is a nicely sized port with very good velocity. To take this further, we would go with a larger carburetor (40-41mm) which is where the port face would open up to. The intake valve size would be reworked a bit and the port just touched up to get it working better with everything sized differently.

Going forward, I'm looking to possibly get JE or Arias to update their dated piston designs. Something a little lighter and something with the top ring moved up to the .200" range to minimize crevice volume.

In the future, I'd like to ditch the pod filter and build an airbox with a flat panel filter underneath. This will help with some flow losses that are inherit to the individual pod filter design.

Lastly would be camshaft development. We'd give back some of the low lift flow we too away and probably take 15-20* of seat to seat duration out of the camshaft.

Cheers,
Bob

 

[hoffman900]

Pictures of the stack for the TM-38 from the machinist. Will see how it works out on the flowbench.

(had these guys make it up http://www.racerxfabrication.com/ )

 

[hoffman900]

Forgot to update this...

Final head flow numbers:

The left side is with a radius plate on the spigot, right side is with the carburetor and stack. Lost about 8% of flow at peak lift with the entire system in place. Nick said anything under 10% is acceptable. Still super steady on the bench, moving only .1 of an inch of depression at any given valve lift.

 

[hoffman900]

More photos, courtesy of Nick at http://smithbergracing.com/
Intake port:

 

[hoffman900]

Making a combustion chamber mold.

and looking down the bore...

I'm having Racetec make me up two pistons. They don't have a minimum order ($30 set-up fee for anything under 4). Racetec is Wayne Brook's company, of JE fame. He and Barry Calvert built JE up to what it is today. Wayne and Barry sold JE pistons, with Barry cherry picking staff to form CP pistons with the idea to work exclusively on NASCAR stuff (obviously they have since expanded). Wayne retired, but got bored, and started up Racetec / Autotec. The latter being more a street, off the shelf line, where the former is their racing / custom line.

 

[Jack]

The RS and XS share similar flow characteristics from low to max lift with low flow coming on to strongly thus opening the door to reversion and over scavenging. Looking at last the flow chart ,I'm a little confused as to why you changed the exhaust valve head shape for further gains as you're nearly approaching 90 to 100% flow ratio from low to.400 lift,where as before IMO you had the optimum flow ratio giving you a cushioning tool for an exhaust system up grade if needed,but that's just me,port the EP a bit lazy and let the exhaust system do its job in pulling.

It's a cool build and hope it all comes together for you. You don't see many SR500 these days,at least not in my region.

 

[hoffman900]

The RS and XS share similar flow characteristics from low to max lift with low flow coming on to strongly thus opening the door to reversion and over scavenging. Looking at last the flow chart ,I'm a little confused as to why you changed the exhaust valve head shape for further gains as you're nearly approaching 90 to 100% flow ratio from low to.400 lift,where as before IMO you had the optimum flow ratio giving you a cushioning tool for an exhaust system up grade if needed,but that's just me,port the EP a bit lazy and let the exhaust system do its job in pulling.

It's a cool build and hope it all comes together for you. You don't see many SR500 these days,at least not in my region.

Jack,

The flow chart I posted is just of the intake. Left column is with a radius plate attached to the spigot, right column is the intake with the carburetor and velocity stack attached.

Here is the exhaust flow chart:

The .700 lift number is really .600, but with a pipe attached to the port. Keep in mind the exhaust valve has been sunk a bunch and is smaller than stock.

 

[hoffman900]

Custom RaceTec pistons

The piston is a 2618 alloy, machined with the Johnson J2 camshaft (.540" i, 515" e lift) in mind, a 49mm intake valve, and a 37.5mm exhaust valve. It also has dual pin oilers, and lateral gas ports. The dome volume will give me about 10.1 for my set-up, but will be around 12.1 for a stock combustion chamber. Rings are spec'ed for Total Seal's offerings for this bore size (1mm top, 1.2mm second, 2.8mm third). It also has a coated skirt and the top ring sits .220" from the deck which reduces crevice volume. The one thing that could take this piston further, and it's an option box I didn't check, is a tool steel pin (lighter).

In addition to the mold, there is a spec sheet that I filled out from the piston manufacturer. I also sent my Wiseco piston to them as well. Basically it was one of those, 'this is what I need, this is what I have / is available, make it better' kind of things.

Also, some history… Pankl owns CP pistons, which owns Carrillo as well. C(alvert)P(ankl) is a combined effort of the Calvert brothers, who started out working for Nick Arias, before going to JE. Wayne Brooks bought JE from Harvey Crane and Wayne and Barry Calvert became co-owners in JE. When Barry and Wayne sold the company to that owns Wiseco, Barry partnered with Pankl to provide high end pistons to the NASCAR world (and cherry picked the staff at JE). Obviously, they since have expanded. They later bought Carrillo and now the company overall is called CP-Carrillo. Wayne Brooks came out of retirement after his non-compete clause expired, and opened up Racetec/Autotec pistons with some of the former talented JE staff as well; Racetec being their custom piston line.

Cheers,
Bob

 

[hoffman900]

Update:

Courtesy of Curtis at Full Circle V Twin (flattracker94)

 

[hotdog]

Did it throw the rod..? Or just beefing it up.?

 

[hoffman900]

Did it throw the rod..? Or just beefing it up.?

Beefing it up. Shooting for 1.6hp/ci on pump gas. Everything is sized to peak at 7200rpm, so I'm right on the cusp. With the the Carrillo in it, I can grow into the bottom end.

I forgot to add, the rings for this feature a Napier cut 'hook style' cut on the 2nd ring. This is an option that you have to pay extra for with Total Seal.

 

[hoffman900]

Horsepower is made where the rings meet the bore...

Custom torque plate assembly and work done by Curtis (flattracker94) (www.fullcirclevtwin.com)

 

[hoffman900]

Engine bling:

 

[TwoManyXS1Bs]

Yum!

I'd like to shoehorn a pair of those side-by-side into mine...

 

[hoffman900]

Finally got around to graphing the flowbench data:

Also, had to source new to me cases since the previous ones had a botched repair job that was uncovered when we popped the bearings out (crack through the mainshaft bearing housing):

 

[hotdog]

Wow, 200cfm @ 0.400" - good numbers.
What lift Cam are you running.?

 

[hoffman900]

Wow, 200cfm @ 0.400" - good numbers.
What lift Cam are you running.?

I have a Johnson J2 roller in the drawer from before I started this project.

I only have the .040" numbers and valve lift.

Intake: .540" lift, 105* LCA , 287* @ .040
Exhaust: .515" lift, 105* LCA, 280* @ .040"

I want to degree the whole thing and measure valve to piston clearance at TDC, *10 BTDC and ATDC, and lift to valve clash before talking with other cam designers.

Coil bind is at .600" lift, unfortunately, and you can't go any higher than that with the stock geometry of the valvetrain. Ideally, I want to use as much lift as possible, with the seat to seat duration I need. For more power goals, I'd like to see a little less duration and more lift than the J2.

 

[hoffman900]

So three years into this motor build and FINALLY something is happening.

I have all the parts I need, dropping the cases and all bearings all to the local machinist on Saturday to have washed and bearings pressed in (need an oven).

I also wanted to mock up the cylinder head and checked the installed height of the springs as well as the retainer / valve stem seal clearance. I'm a bit short. To show you how good my cylinder head guy is, both valves came out to 1.653" installed height on a spec that is 1.650. I'm pretty confident that there is .003" of error in how I measured it. This wasn't as clear cut as we moved around the valve's placement on the seat, but he got it first shot.

Both valve stem seal to retainer clearances were 0.551". I'm running .515" lift on the exhaust and .540" lift on the intake. That's just not going to do. I really prefer about .060" of clearance, and it's a simple machine job to do, so I'll have that done as well.

I also noticed the spring cups foul on the little step between the head and the guide. So either the pad will have to be machined down or some of the ID of the spring cup will have to be turned. If the machinist is set up to cut the guides down a bit, it should be pretty simple to clean this up.

Additionally, I noticed a small chip on one of the retainers. That is no good. So a call to R/D Valve Springs and another is on its way. This is a custom piece for a 7mm valve stem, but Zach had two on his shelf ready to go, so no hold up there.



As an aside, RD's PN #1002 springs, which is what they use in the SR/TT kits, are made by PSI now. That's as good as you can get.



I also installed all the studs and the through bolt reinforcements.