Topic: 125-75 or CX-7

[Turbogrimace]

So I recently pulled my bike out, fired it up, and noticed it was running a little off.  Last season, it had been a bit off as well, but I was fiddling with a new carb/exhaust combo so I attributed it to that.  This time around, I ran a compression check and found out one of my rings was shot.  That being said, I'm tearing down and rehoning. Since I'm going into the engine, I was also going to swap out my decades old Yosh Daytona cam with something fresher and maybe a tad more aggressive. 

First off, I have an 836 with 10.9:1 CR, JMR Stage II Ported head with 33.5 mm intake valves, vm29s with ramflos, and a relatively open 4-2 exhaust.  I'm also running a late model F tranny for a closer top end gearing.

I've been looking around at some of the dyno results posted here and some other discussion on the very streetable curve of the megacycle 125-75.  It has slightly more lift and duration than my Yosh cam and has 4* more overlap.  Cycle X offers a modified version of the 125-75 with 3 more degrees of duration (they call it the CX-7).  Im assuming that they've left the lobe centers the same and therefore it has an added 3* of overlap over the 125-75.  I'm thinking this will push the power curve up the rpms a bit more.

1.  How is the idle and bottom end feel with the 125-75?  Is it relatively streetable or is it finnicky? How is torque off the line?

2.  Has anyone found any benefit to advancing the 125-75 to drop the power curve down the rpms a bit?  If so, have you had any issues with clearance?

3.  Does anyone see a benefit to the added duration in the CX-7 cam for overall performance while still maintaining somewhat comfortable day to day performance?

I typically use this bike for touring around with the occasional thrashing.  Sometimes with a huge pile of gear on the back... and eventually a trailer.  I'd like to maintain decent bottom end torque while attempting to get most of the potential out of my combination.  Yeah, I know, best of both worlds. 

As always, the advice and perspective if very much appreciated.

[Sam Green Racing]

You can't have the best of both worlds with the 125-75, it don't Kick in until 7,000rpm.
I don't know how much you will gain by advancing it but what you gained at the bottom, you'd loose at the top.
For the best spread of power, try the DP295 from Dynoman.

Sam.

[Turbogrimace]

Yikes.  I hadnt really looked at the DP295.  But with 64 Degrees of overlap, how does it pull down low?  It has a little less lift, but a good bit more duration than my yosh cam.  I feel like i might be looking at it wrong, but a lot of the older torquer cams (I.E. RC240) use a lot of duration, but limit the overlap to prevent pressure loss in low revs.

Sam, have you run both in similar engines?

Is there any standard correlation with these engines?  For example:  More duration = more top end power, more lift = wider torque curve.

[Sam Green Racing]

Yes and they were both run in an automatic on a drag strip. I guess this is probably the best way to test a cam because with the auto, there is no variation in the launch and the strips timimg tickets give you all the increaments along the track.
It was like a snail off the line with the 75 until 7,000, then BANG, time to hang on.
The DP295 completley transformed the bike, really strong power from around 3,500 to 10,000rpm.
Best of both worlds is what you wanted, the DP295 will give you just that.

Sam.

[Turbogrimace]

Thanks for the info.  Any clearance issues with so much lift and duration?  I'm runnig a wiseco forged kit with the valve reliefs the size of craters.

Also, did you ever put it up on the dyno with the DP295 in it?

[MRieck]

I ran the 75 cam for years with no problem with torque. The reason the 295 cam worked well in Sam's bike is because it doesn't measure up to the specs. On paper the 295 and 75 are close but in reality the 295 in the auto closes the valves earlier and increases compression giving more torque. With close to 11:1 you have plenty of static compression. I remember Doctor D changed from the 125-65 to the 75 cam and picked up something like 4 or 5 lbs of torque. I haven't seen a cam that fouls a Wiseco 836 valve relief.

[Turbogrimace]

So you're leaning toward the 75 over the others?

The 295 shuts intake at 46 ABC, whereas the 75 shuts at 56 ABC.  Clearly the 295 would develop more pressure initially, and it also holds the cylinder shut longer.  lot more stressssss.

[Jerry Rxman Griffin aka MuthaF'er]

You can't have the best of both worlds with the 125-75, it don't Kick in until 7,000rpm.
I don't know how much you will gain by advancing it but what you gained at the bottom, you'd loose at the top.
For the best spread of power, try the DP295 from Dynoman.

Sam.

Turbo, don't know if you'd agree but Sam's description of the 125-75 sounds identical to the Yoshi Daytona we have been running. That plus his "BANG, then hang on". Wish I could compare to my 125-75 but it hasn't had any real throttle time plus the engine is a MUCH different beast than my 812 and Daytona. My contention is the Daytona was NOT intended as a strong street cam. Hence the Daytona name. WFO on a long track. It does well above 7000. Sounds like you are really looking for this plus some earlier torque for the street.

What do you guys thing about the 315 vs the 295? Does he need that much duration for a 836 or wouldm the longer duration be better suited for 900+?

Perhaps get Kenny's opinion of the CX-7 (was that what he used in the road racer?) vs whatever he's going to use on the strip?

Also keep in mind that SamAuto is running 2 speeds and can use more torque as he is not at top rpms 5 times like non-autos.

[Turbogrimace]

Very good info.  And yes, the Daytona was an absolute rocket above 7k.  It was good until about 10,500 when I started to pee my pants and slide off the seat. Bottom end was hesitant until about 4500-5000 where it started to pick up.  This is why I was running a 15/48 final drive.

I was interested in the 315 vs the 295, but that thing looks like it's an absolute screamer.  it has similar timing to the daytona intake but milder lift and a lot more duration.  I know these engines like duration, but with that comes an ever upward drifting power curve.  Also of note though, the published durations for DP's are @ .050" and megacycles are measured @ .040".  Therefore, if the published numbers for DP cams were measured @ .040", they'd be even bigger.  Are the DP cams exact copies of Russ Collins old line? 

There are significant differences is in the design basis between the megacycle cams and the DP cams.  Megacycle being more in the lift, and DP more in the duration.  DP cams hold the cylinder shut longer (curious what the benefit is here).  DP cams also have a lot more overlap, which could bleed the pressure at low rpms.  The long duration with both valve closed on the upstroke probably compensates for this.

I talked to Ken at Cycle X about the CX-7 cam and why they added more duration, but his answer was "no reason".  I'm wondering if it was just to modifiy the profile so it could be consider "made for Cycle X only".  Nothing wrong with that.

[Billys mate]

Newbee here thinking of goin drag racin also want info on cams. Av got wisco 836 lumps thinkin of goin with Megacycle 65 cam, wots the best tork figre for this set up? (CB750k stoc carb- kerker 4 in 1.)

bubba.

[Bill/BentON Racing]

Cams, cams, cams, sticks with bumps on 'em! Sam we did change to 915cc, lighter pistons, and with 75 advanced and a little more lash, still ran 2.0, 2.1s, with 836 and 75, but I agree it likes the set up now! 295 cam and 915cc Kennys kit, 32mm CVs, Vance&Hines sidewinder.But what makes it REALLY work? Mike Riecks beautiful headwork!! Thank you Mike, and a shout out to Mr. Automatic, Jon Weeks, thanks for the help.I got to get busy, might have to run Kenny one day!!! Bill

[Sam Green Racing]

Yes William, them there cams with the bumps on them are the best.

Sam.

[Turbogrimace]

Ooops.  I made a mistake when compiling my cam specs.  The overlaps I had for the DP cams were very high.  And it turns out that the DP315 has identical timing to my old Yosh Daytona cam, but with milder lift and much longer duration.

Am i correct in this thinking:  If a cam is spec-ed with the duration based on .05" valve lift, then the duration given for the same cam spec-ed with the duration based on .04" valve lift would be larger. 

[Bill/BentON Racing]

Less lash, more lift, of course lift limited by valve springs.Once completely compressed can't  open valve any further. More lash, less duration,compression builds sooner, intake closes a little earlier, opens a little later.Bill.

[Turbogrimace]

Does anyone know where I can buy megacycle cams?  I'm a little bit between the 125-65 and the DP295 at this point.  I think I'm pushing the limit for overcamming if I went with anything larger than these.  Although the profile of the DP315 has had me giddy.  medium lift with long duration.  This is what Jerry Branch recommended way back when.  Although he was probably out for max hp at high revs, which is what the long duration is going to give.

[Bill/BentON Racing]

Try Megacycle! Still in business,may be out of billets,Mike Rieck keeps up,PM or ask him.Bill

[Doctor_D]

Since my bike's been mentioned, I want to throw this out there:

First, the disclaimer; an engine is the sum of many parts working with (or against) each other.  We spent a lot of hours on a dyno getting my engine set up and tuned correctly, and not everyone's experience will mirror my own.

As for the cam, I've gotten some real miles in on my 836, and this engine - with the 125-75 - is very streetable.  The engine is quite happy being short-shifted or burbling along at 2500 rpms. Can you whack the throttle open down there?  No, you need to roll it on until about 4k.  Does it hit hard when it comes on the cam?  Yes, so be careful if you go to WOT around the transition point (4500-5000 rpms) or you'll wheelie past the police station.  But, other than the powerband coming on somewhat aggressively, it's a pussycat that will chug up the steepest Seattle hills at 3k in 3rd every day of the week.

Having tried both, the 125-65 is a nice cam, but the 75 outperformed it virtually across the board.  The only place the 65 made more power was below 4k - and that was marginal.

[CrazyRocketMan]

Awesome thread!  After reading sounds like the 125-75 is what I'm looking for.  I like high rpm cams on the track and still streetable is perfect. Power wheelies and dirt tracking the corners at HPR in Colorado is exactly what I'm looking for. Love the 7,000 rpm descriptions SOHC4.net ROCKS!

[Jerry Rxman Griffin aka MuthaF'er]

And I look forward to seeing you on HPR!

[CrazyRocketMan]

Jerry,

HPR soon my friend.. Soon.. 

Maybe when things slow down a bit for ya we can meet there?
Beers after.

Bruce will probably come along too.

 - George

[Sam Green Racing]

You must be real crazy if you are mates with Jerry. 

Have fun Guys, wish I could be there.

Sam.

[CrazyRocketMan]

There's no set date yet for HPR Sam. All the places listed on your profile make it look like you might do a little traveling. Maybe you could be there? Just going to be some track fun..  Couple days maybe. That is probably the most I could reserve the track for.

 - George 

[Bill/BentON Racing]

You'll be real happy with 125/75 , I love it, yes it comes on nicely, as Sam said around 7000 and above, you best be paying attention or you'll be paying a ticket fot too much fun!! Mike Riecks favorite! Bill

[CrazyRocketMan]

Bill,

Very clever name, I dig it!

Thanks for the input on the 125/75. That cam sounds perfect! I cant wait. So close to assembly time its killing me..

[Jerry Rxman Griffin aka MuthaF'er]

Sam,

Why CAN'T you come??!! I'll put you up for a while. We got Mexicans all over the place, surely they'll let a Brit into Colorado. High Plains Raceway, which I have yet to see, is a world class race course that's supposed to be better than Loudon back Michael's way, which I haven't seen either. It ain't flat and it ain't straight so we'd have to loan you a ride anyway. You take the Vette and I'll take the bike?! Let's see you could go to Bonneville and AHRMA @ Millers Motorsport Park with me in Aug too. Bonneville is flat and REAL straight. Get Bill to ride SamAuto out we're on. Or he could combine it with a trip to AZ too. I better quit thinkin and start drinkin.