DRC 7 Cam

Has anyone come across a Commando cam stamped DRC 7 ?
The engine had been worked by HPI in California back in the day, so presumably one they supplied/fitted?
I'm told it looks more suitable for drag racing than road riding - which might in part at least explain the Dyno chart i posted a while back where the power was less than spectacular until over 4000rpm.

Only drag racers builders alive today that might know are TC Christensen and Ron Fratturelli. If Ron will speak to you he may point ya to others that may know and still around. http://nortoncommando.com/ Another possibility is Kenny Dreer or his friend Doug McQuire in Oregon. I think your powerband is right up my alley, normal legal operation engine power below 4000 with just a down shift away for 3000 rpm head room to take your breath away, yeah man music to my ears!

The DRC #7 was ground by Dunlavy Racing Cams for George Gjonovitch at HPI back in the late '70s or early '80s. It had .375" lift at the cam, .427" lift at the valve. Timing specs for the cam at .020" lift are Intake opens at 53 BTDC and closes at 84 ABDC, and exhaust opens at 84 BBDC and closes at 53 ATDC. Intake lobe center is set at 106 ATDC. It was sold as a serious race cam, and probably isn't very suitable for a street bike. They sold a milder #3 grind as a road race/TT grind that was better for the street.

Ken

I don't agree about drag cam use in slow school campus, parking lots or stop/go city rush hr or riding in pits on full dragster configured engines, extreme cams and light flywheels from what I've experienced and seen at races. Mostly what I ran into was avoiding too much throttle ups creeping about or instantly turn any surface into loose flat tracker excitement. My P!! didn't need brakes to do rolling burn outs yet would lug hands off throttle in 4th plowing through Fla sugar sand tire deep spraying sand out like water wakes about 15 mph even up some grades, though for the steeper ones just snapped throttle to rooster up em then let go again for the pleasant drum beats of Hi Compression no detonation lugging d/t the aggressive cam lowering low rpm CR. This is where selectable curve programmable ignition comes in handy. If i'm wrong Ms Peel will be about totally useless failure.

Thankyou Ken, excellent info.
When i bought the bike in '84 it had a planed RH4 head (HPI stamped) and a full Dunstall exhuast (earlier type not 2-1-2) so i had always wondered about the cam but never quite got around to investigating.
The bike came apart this week so that a PW3 could be fitted, given the complete lack of low end grunt shown on the Dyno. I had always wondered why the "torque monster" comments didn't tally with my riding experience. Only took 30 years to get there.
One main bearing was found to be on its way out in the pull down so a lucky save.
iain.

lain do ya have info on the CR in your lack of low rpm torque set up?

hobot - sorry i didn't check how much had been removed from the head, or do any sort of comp calc when i had the head. The pistons did need healthy sized valve pockets. I sold the head for race use, if i don't forget i will ask whether he has worked that out when i next see the current owner.
iain

lain I'm hoping Peel's upper 10 CR will make up some for low end bog though yours sounds like it had over 10 CR too. If noting much wrong in condition of the drag cam I may want to try it on Peel if the Norris D don't work as hoped.

hobot

you may wish to look into considering a Megacycle 5600 cam for your Peel bike.

Three years ago I had Jim Mosher (who built the Bonneville Norton) rip my engine apart and go through it carefully renewing everything. He chose the Megacycle 5600 cam to install as he felt that it gave superb performance for all around road, and even some track, riding.

here are the specs from the Old Britts cam page, and the link for you to review below

560-00 .395"
.395" 277
277 104.5
104.5 3" Best all around road/road race performance. Strong mid-range, increased top-end. Wide smooth power band. OK with stock pistons in 850 Commando. Check in all others models Must use racing spring. 34 btc/63 abc
63 bbc/34 atc .010"
.010"

Click to expand...

https://www.oldbritts.com/11_30cam.html

lcrken said:

The DRC #7 was ground by Dunlavy Racing Cams for George Gjonovitch at HPI back in the late '70s or early '80s. It had .375" lift at the cam, .427" lift at the valve. Timing specs for the cam at .020" lift are Intake opens at 53 BTDC and closes at 84 ABDC, and exhaust opens at 84 BBDC and closes at 53 ATDC. Intake lobe center is set at 106 ATDC. It was sold as a serious race cam, and probably isn't very suitable for a street bike. They sold a milder #3 grind as a road race/TT grind that was better for the street.

Ken

Click to expand...

Ken,

For clarity, the timing numbers you quoted relate to cam lift, not valve lift?

hobot said:

lain I'm hoping Peel's upper 10 CR will make up some for low end bog though yours sounds like it had over 10 CR too. If noting much wrong in condition of the drag cam I may want to try it on Peel if the Norris D don't work as hoped.

Click to expand...

hobot,

Just to be clear, the Dyno chart i posted a while back was when the engine still had (unknown to me then) the DRC 7 cam fitted but by then i had changed to a FullAuto head, so the lack of low end power at that stage was at standard 850 compression ratio. I expect that will only have exaggerated the situation.
iain

WZ507 said:

Ken,

For clarity, the timing numbers you quoted relate to cam lift, not valve lift?

Click to expand...

Good question. The spec sheet I got from George doesn't say. I've always assumed it was lift at the valve, with adjusters set to zero clearance, which is pretty common way of specifying, but can't say for sure. I use lobe center to set timing, not opening and closing points, and that works either way, using cam or valve lift as is convenient. For Nortons I use cam lift, with a dial indiator on a pushrod, to measure cam timing. On overhead cam engines with rocker arms, I usually use a dial indicator on a valve spring retainer. On OHC engines without rockers it's usually off a bucket.

Ken

1up3down, I used dynamic compression calculators to decide on Peel Norris D to not over compress in ordinary legal-ish &ugh THE Gravel travel on 87 octane w/o need of anti-detonation fluids. I'll mostly use 91 oct but can't tell where she'l take me. With water or windshield washer fluid on full tilt boogie ignition advance, calculators say detonation will not be an issue hi rpm throttle with or w/o boost. Kelly George runs a 5600 in his winner flat tracker and told me he and his riders want more spikey top end power so will try the Norris D someday. Road racers want to avoid rear spin but flat trackers want more of it on tap. Basically I want the P!! back that can lean and not vibe ya to death. Kelly's Norton shake sort of disappeared as the sonic blasts impacted to bone conduction on cam/pipes which kind of nullify each other so ya don't feel it in same sense as a road racer or tourer would.

lain CR matters a lot down low on aggressive cams so hope that was missing factor in your delights. Ken is pleasing me with nearly 11 CR in Peel's 1st set up, against his better judgement to do so. I think I know enough now to have custom asymmetric cam made for the Drouin use yet still work decently w/o boost, with enough CR to start with. Almost everyone wants their blowers to boost significantly soon off idle into mid range but while I hope for some mildness till suddenly after midrange. Ya don't take off in races from idle don't ya know, just city traffic lights or very loose steeps.

Bytheway, Wesuson's oval 'cushioned' track when dampened and groomed was a shocker to me how freaking sticky duct tape like it was yet everyone but the best pilots on best bikes complained how loose it felt, sheeze. The air ya see Kelly pilots catching in mid turns is exactly what I call Phase Four on Peel, but don't know if their cycles can handle the frame loads/rebounds low to hi side saves to understand what they are missing out on taking more advantage of its harsh sharpeness > at both entry and exits so the sweeper part is a short upright straight all hooked up out of there, then can let air out and used up blood to drain from brain. The speedway guys try too but still too afraid or something to get their leg out the way before really Throwing yourself At The Ground and Missing IT!

With supercharging near redline + hi CR on cam maybe Peel can perfect Phase FIVE> that keeps front down thru turns- for straight steer aim.

lcrken said:

WZ507 said:

Ken,

For clarity, the timing numbers you quoted relate to cam lift, not valve lift?

Click to expand...

Good question. The spec sheet I got from George doesn't say. I've always assumed it was lift at the valve, with adjusters set to zero clearance, which is pretty common way of specifying, but can't say for sure. I use lobe center to set timing, not opening and closing points, and that works either way, using cam or valve lift as is convenient. For Nortons I use cam lift, with a dial indiator on a pushrod, to measure cam timing. On overhead cam engines with rocker arms, I usually use a dial indicator on a valve spring retainer. On OHC engines without rockers it's usually off a bucket.

Ken

Click to expand...

Ken, I asked because I was looking at some cam plots (courtesy of COMNOZ) to see which cam might fit the timing numbers you provided @ 0.020" lift (either valve or cam as we're only talking a few deg difference between cam and valve numbers anyway) but there are too many large cams (D+, JS3, 560-00, 86C, PW3, etc) with timing similar to the numbers you quoted, that the entire undertaking is of questionable value. Adding further to the uncertainty is the fact that at 0.020" lift some cams are on the ramp, some just off the ramp and some well off the ramp, so this essentially renders the exercise mute. Your comments about the cam being large and perhaps best suited for all out racing are likely more valuable than anything that can be gleaned from the cam timing numbers, since they tell essentially nothing about the cam profile.

Ken when you set the timing using lobe centres do you calculate the centre point from the specified open and closing points, and try to get maximum lift at that point ? I once had a discussion with a friend who has been a much more dedicated racer than I've ever been - a top A-grader on a manx in the fifties and sixties. He suggested the important thing in timing is the lift of both valves at TDC. My take on it is that the inlet opening and exhaust opening points are critical as they set when the 1st node of the standing waves occur. I find it difficult to get my head around the concept of 'mass transfer' such as occurs when an earthquake causes a tsunami in the ocean. The waves hardly cause a ripple as they pass under a ship, however can appear as a sequence of 100 foot waves on the beach. I believe that is how gas flows out of an exhaust pipe - not like water out of a tap. With my 850, I use a two into one exhaust - like a Dunstall but only with one muffler and tail pipe. I open the exhaust at about 92 degrees before BDC. It would be impossible to use that timing with separate exhausts, however I believe the two into one needs more time to establish the standing wave in the header pipes and keep the tail pipe resonating at twice the frequency as the header pipes. (An error fixes an error).
When I first fitted the two into one pipe to my short stroke 500cc Triton. I kept modifying it and adjusting the valve timing until it worked. I found that opening the exhaust valve before 90 degrees BBDC, the bike got louder and lost power. Also, if the header pipe is smaller in cross-sectional area than the total of the two header pipes, the motor lost a big number of revs off it's top end. With the 850 cam, if the exhausts opens at about 92 BBDC the inlet opens at about 60 BTDC. I believe the inlet opening point has a major effect on where the 'cam spot' occurs. I don't believe the closing points are nearly as important as the opening points. When the nodes of the two standing waves coincide is more important, that is the when the whole system resonates in unison. In the end the exhaust valve opening point must suit the exhaust pipe.
The cam this guy has got would give a commando some hurry up, however as cams go it is not the most radical I've seen. I don't know anything about lift, however my short stroke Triumph had a lot less than the normal kit cams used in 650 bonnevilles. It used to rev to 10,500 RPM regularly without blowing up, and it was a nasty piece of garbage.

acotrel said:

Ken when you set the timing using lobe centres do you calculate the centre point from the specified open and closing points, and try to get maximum lift at that point ?

Click to expand...

Alan, aside from cams with asymmetrical opening and closing profiles, the lobe center is both the axis of symmetry for the lobe and the point of maximum lift. If the manufacturer doesn't specify the lobe center, you just calculate it from the published opening and closing points. To measure it, all you need do is measure two points at the same lift, one on the opening flank and one on the closing flank. It doesn't really matter what lift you use, as long as it's off the clearance ramps. I usually use .020", but on something with large clearance ramps like the 4S, I use .040".

I've only seen one Commando cam with asymmetrical lobe profiles, Axtell's "Allegro" grind, and for that you'd measure the lobe center using the lift points specified by Axtell, if you could talk him into letting you have the cam. That was his "house" grind, not a customer grind, and I don't think he let it out of his sight much. I know Ron Wood used it on some of his engines, and I think that was what was in the engine that Axe took over to Norton in the early '70s to demonstrate that his horsepower numbers were real. I don't know where else it got used. I was never able to talk him out of one for my use! I remember him telling me that most cam grinders wouldn't do an asymmetrical cam because it required them to use a smaller diameter grinding wheel to allow the right curvature on the closing ramp, and that meant that the expensive grinding wheels didn't last as long. I don't know if that would be such an issue now with modern CNC cam grinders. There may be someone out there grinding asymmetrical profiles on Commando cams, but if so, I don't know who it would be.

I always time the cam to the manufacturer's specification for lobe center. Absent other information, I have to assume he knows where it should be set. I've not had the opportunity to play with different cam timings on a Commando on a dyno, but I doubt if there's much to be gained, and plenty to be lost, by straying from the recommended settings. If it were a twin cam engine so you could advance or retard the intake without changing the exhaust, you could use that to tune for more top end or more low end power, but with the fixed lobe separation angle of the single cam, you can't do that. I have had the opportunity to try identical cam profiles, but with different lobe separation angles, in a Commando, and the differences are noticeable. I've also had the opportunity to try different cam timing on a Rotax twin cam single on a dyno, and found that I got the best performance at the recommended settings (Megacycle custom grind). Other folks will surely have other opinions and experiences, but mine convince me that unless you've got some weird engine mods (supercharger, nitromethane, etc.), or you're building something unusual like a Commando trials bike, the cam grinder's recommended timing is the way to go on a Commando.

Just my opinion. YMMV.

Ken

Ken , with my 850 I'm using the standard cam and I've advanced it 12 degrees. There is a considerable increase in torque, and one other person on this forum has reported the same thing. My feeling about race cams is that the person who develops them would only specify timings for customers which offer either a margin of safety or a slightly more rideable bike. If I was using separate pipes I wouldn't advance the cam as much, however I would still try advancing it progressively to see if there is a performance gain. The first thing I did when building my motor was soften the cam sprocket and broach two more key ways into it at random. I've always understood that the shape of the trailing face of the cam is important. Apparently cams that allow the valve to snap shut too quickly can cause valve dropping. In a commando motor the shape is not so important - we don't rev them very hard. And I think this is the whole point of the design. Revving a commando to 8 or 9000 RPM would be a good way of getting more power, however the cost of getting it to stay together would be horrendous. The reality is that the heavy crank, long stroke define the strengths of the design to lie in producing more mid-range torque rather than top end power. Then gearing becomes a problem. As far as cam timings are concerned, I suggest we always need to find the optimum combination of cam and exhaust and inlet configuration which suits the application. In building a competitive bike it is not simply a matter of buying all the hot bits and bolting them together to the specified numbers. With my own bike, it has had virtually nothing done to it, yet surprisingly it is fast enough - the rest depends on the rider.

1up3down said:

hobot

you may wish to look into considering a Megacycle 5600 cam for your Peel bike.

Three years ago I had Jim Mosher (who built the Bonneville Norton) rip my engine apart and go through it carefully renewing everything. He chose the Megacycle 5600 cam to install as he felt that it gave superb performance for all around road, and even some track, riding.

here are the specs from the Old Britts cam page, and the link for you to review below

560-00 .395"
.395" 277
277 104.5
104.5 3" Best all around road/road race performance. Strong mid-range, increased top-end. Wide smooth power band. OK with stock pistons in 850 Commando. Check in all others models Must use racing spring. 34 btc/63 abc
63 bbc/34 atc .010"
.010"

Click to expand...

https://www.oldbritts.com/11_30cam.html

Click to expand...

1up3down,

Sounds like you have a well prepared Norton with a Megacycle 560-00 cam in it. What size engine do you have the cam in and what is the CR? Has any head work been done to increase airflow? What carb(s) are you using?

I too like this cam but have yet to hear any first hand feedback from a 560-00 user. Since you've had 3 years of experience with it, was wondering if you would share your impressions of the bike's performance. With the 560-00 some sacrifice of low end grunt has likely occurred, yet I suspect you've gained significantly on the other end where the bike should want to rev well beyond 7000 rpm. Do you miss the torque associated with the stock cam or is it fine to sacrifice a little on the bottom to gain some on top? Do you visit 7000 rpm often, seldom or never? If you frequently visit 7000 rpm, are you disciplined enough to resist winding it past 7000 rpm?

Any insight you offer would be welcomed. Thank you.

If you found you had loads of torque, wouldn't you increase the overall gearing ? When I found I was getting to 7000RPM too quickly, I raised the gearing and the bike simply accelerated faster. I always try to change up, below 7000 RPM. The needle often hits 7,500 RPM during the change up.

Yeah man Alan that's exactly what I found in prior Ms Peel, which with tire expansion could not pull but 6000 in slight down hill opens yet very few sport riders would dare to keep up. Very strange to see tach drop as speedo raised. What I found for me is torque rules in turn handling while horses rule the bee line opens to top end. I got more low end torque out of dual amals but more mid range and top end out of the 34 Miki, so confused by the reports - must have duals for Nortons to get ahead of the pack. I really think the 2-1 system helped a lot with the small port head and 2S cam.