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A65 camshaft. full race vs. Spitfire #367052
04/07/11 2:15 pm
04/07/11 2:15 pm
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Posts: 198
Tynset Norway
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oleandreas Offline OP
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I wonder if somebody has any opinions on the SRM "full race camshaft"

The SRM camshaft has a higher lift, AND A LONGER DURATION. So far I have been adviced by different specialists, included SRM, to use the Spitfire camshaft, but my engine is changed from 650 to 883 with bigger inlet valves, ported to 32 mm, 32 mm carburettors increased ccm by 233, wouldent longer duration and a slightly higher lift be excatly what the engine need to breathe better, to produce better torque a lower rps because of longer duration AND more power on top rpm due to slightly higher lift ?

I NOT buliding a racing engine, just a engine for fast street use. IM specially conserned about the longer duration of the cams, that should give me more torque at lower rpm, or ? I also have slightly stiffer titanium springs and titanium collars, I have pictures of the camshafts on my facebook profile. http://www.facebook.com

http://www.facebook.com/photo.php?fbid=4...556&theater

Last edited by oleandreas; 04/07/11 2:36 pm.
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Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #367055
04/07/11 3:02 pm
04/07/11 3:02 pm
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Seattle
Alex Offline

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Now, I'm no cam expert, but this is the way I've come to understand it and my experience supports it: Increasing only lift will generally increase torque throughout the rpm range. Longer duration will generally push torque and power up the rpm range because it generally produces more overlap.

Increasing lift will increase load i.e. wear on your cam and lifters. Also, higher lift cams will require machining the cases for clearance. Increasing duration does not increase it directly, though to take advantage of more power at higher rpm, you will want to rev higher, requiring lighter valve gear and/or stiffer springs. Stiffer springs increase load on your cam and lifters. Also, valve/piston interference must be tested for increases in both duration and lift.

Do you know what the specs are on the SRM cam? I've run the stock A65 (spitfire) cam and Megacycle X1 (full race, .400" lift) cam. The X1 really woke up the bike giving an impressive response and buildup of torque and power, though peak power is pushed beyond 8000 rpm (I've been to chicken to chase it). I would be reluctant to put this in a street bike...particularly since the stock cam is really quite good all around and already pretty rev happy. I think it's come up before but if all you want is more torque, perhaps increasing the lift with the offset rocker buttons would be an option?

BTW, you can't increase torque independent of power...they are intimately intertwined.

Cheers and good luck.


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Re: A65 camshaft. full race vs. Spitfire [Re: Alex] #367058
04/07/11 3:25 pm
04/07/11 3:25 pm
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Ohio
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Ohio
Hey Alex,
Talking about cams [ NOT trying to hyjack the thread! ], is there a difference between the 'stock' A65 cam, and this "Spitfire" cam?

Other than aftermarket cams, I am unaware of any factory cam for A65's, other than the 473 cam... I THINK that's it's number...

I know for A10's, there were the 356, 357, and the 358 cams from the factory..

I'm kinda asking, because I think all the A65 cams I have, need to be reground, or replaced.... And so do the A10 cams I have... I'm going to be needing 3 of each... As do all their followers...
Brett

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #367063
04/07/11 3:44 pm
04/07/11 3:44 pm
Joined: Sep 2002
Posts: 7,813
Seattle
Alex Offline

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The "Spitfire" cam (68-0473) appeared on sporting (Rocket) A65's starting in '64 and became standard on all A65's in '65 and stayed that way 'til the end of production. I believe the "spitfire" nomenclature came from the A10 spitfire which use the same grind cam (358).


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'40 Silver Star
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Re: A65 camshaft. full race vs. Spitfire [Re: Alex] #367098
04/07/11 9:27 pm
04/07/11 9:27 pm
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newcastle australia
trevinoz Offline
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Alex,
That would be 357.
Trev.

Re: A65 camshaft. full race vs. Spitfire [Re: trevinoz] #367103
04/07/11 9:49 pm
04/07/11 9:49 pm
Joined: Sep 2002
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Seattle
Alex Offline

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Originally Posted By: trevinoz
Alex,
That would be 357.
Trev.


D'oh! You're right. Thanks for catching that.


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'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #367105
04/07/11 9:56 pm
04/07/11 9:56 pm
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Tynset Norway
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oleandreas Offline OP
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Thanks Alex.
I will ask SRM for the spesification, and measure myself tomorrow too.

what do yo mean by : "higher lift cams will require machining the cases for clearance" where on the cases ?

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #367107
04/07/11 10:19 pm
04/07/11 10:19 pm
Joined: Sep 2002
Posts: 7,813
Seattle
Alex Offline

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The lobes on the higher-lift cams may not clear the casting, so be prepared to do some machining. Also, they may not clear the barrel castings around the tappets. All this will have to be clearanced depending on the amount of lift and how your particular casting came out.


A smattering:
'53 Gold Flash
'67 Royal Star
'71 Rickman Metisse
'40 Silver Star
'37 Rudge Special
sixtyseventy Lightboltrocket road racer...and many more.
Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #367123
04/08/11 12:35 am
04/08/11 12:35 am
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new jersey usa
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pushrod tom Online content
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Just a note from my own experience. I have used 3 different cams in my A-65 Hornet which is standard 650 size. I use it for Land speed trials and, so far, the stock cam has been the best for overall power and top speed with mufflers. I have tried many combos on the dyno and found this to be the best.
But then there is always the Fourth cam. Haven't given it a sporting chance yet. Cheers PRT

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #414784
01/23/12 11:09 am
01/23/12 11:09 am
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Tynset Norway
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oleandreas Offline OP
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SRM sendt me this numbers:

Spitfirecam 68 - 0473 with 5 degrees retarded grind,
All measured at 0.020 :
intake
Lift 0.344
lca 105 degrees
Lash 0.006
tappets stock radius
duaration 281 degrees
open 36 btdc
close 65 abdc

exhaust:
Lift 0.337
lca 105
Lash 0.008
stock radius tappets
duration 277
open 62bbdc
close 35atdc

SRM fulll race camshaft, at 0.020:

intake
Lift 0.375
lca 102
Lash 0.008
stck radius tappets
duration 300
open 49 btdc
close 71 abdc

exhaust:
Lift 0.375
lca 110
Lash 0.008
stock radius tappets
Duration 300
open 80 bbdc
close 39 atdc

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #414786
01/23/12 12:18 pm
01/23/12 12:18 pm
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derby england
wak Offline
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derby england
Use a spitfire cam,the porting will get the gas in ,it aint going to rev higher than a 650 so forget the race cam it will just make it crap to ride,you can file a woodruf key up to get the 5' retard ,most dirt trackers do this.


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Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415008
01/24/12 7:49 am
01/24/12 7:49 am
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Bega NSW Australia
Mark Parker Offline
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My view; a big motor will naturally generate more gas speed in the ports for a given RPM, so a bigger motor will come on the cam earlier, because what is happening is the inertia or energy created by the moving charge overcomes the piston rising while the inlet is still open, and as the piston comes up charge still rams in. Because of its displacement a smaller motor will not generate that energy in the inlet till higher RPM, so until it reaches critical gas speed the piston will push the charge back out, and your 325cc cyl may fire with the strength of a 125cc or worse. So in that respect its likely a 440cc cyl can tolerate more cam timing and still give a good power spread.
An interesting thing I have found is what seems to have a very big influence on power delivery is the exhaust. It effects the above scenario because gas speed in the exhaust predetermines alot of what happens in the inlet.
With 38mm carbs 44.5mm inlets and 39mm exhausts a 79.5mm X 74mm A65 with std dia headers and Spitfire cam has a very sweet power spread. With bigger headers it takes way longer to come on the cam but at about 5,500RPM really lights up, with more cam duration one would have to wait longer and I expect it would be counter productive. Experience tends to make me think more gains can be had from making an A65 head breath than trying to gain breathing with a longer duration cam.
On my 880 more lift lifted power, but also moved it 1,000RPM up the rev range, which is what I wanted, maxing out around 7,000 rather than 6,000. I think what happened is the flow of the head was maxing out restricted by valve lift, so increasing lift slightly made a decent gain. The same head, pipes and cam on a 750 and it would be maxing out around 9,000.


mark
Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415016
01/24/12 10:04 am
01/24/12 10:04 am
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Tynset Norway
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oleandreas Offline OP
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I think its important to realise this is NOT a 650 but a 880 ccm engine, ported, bigger valves, bigger carburettors, the race cam from SRM seems to be quite moderate in my opinion, the stock Spitfire camlift is around 0.335", the SRM race has lift on 0.375, the magacycle as Alex informs has a lift of 0.400.

also the duration is not that extreme on the "so called" Race cam from SRM. Even if my bike is for street use Im still tempted to try the SRM race cam.

By the way, Any one knows where to get the offset rocker buttons ?

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415019
01/24/12 10:37 am
01/24/12 10:37 am
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Bega NSW Australia
Mark Parker Offline
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That's what I was getting at, if it were me I'd be fitting the SRM race cam and see what it's like. Just need to check clearances.


mark
Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415020
01/24/12 11:08 am
01/24/12 11:08 am
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Pete R - R.I.P. Offline
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Cam duration is not a function of rpm.Cam duration is a function of piston speed.If you doubled your stroke and kept the same cam,the cam would be happy at 1/2 the rpm in the long stroke engine.
At 6000 rpm,you'd need 20 degrees more duration on your long stroke engine,compared to standard stroke.The 300 degree cam would be about right.

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415230
01/25/12 3:01 pm
01/25/12 3:01 pm
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im not sure i agree with the above statement ,personal experience aside ,the volume of the cylinder controls how much gas can be pumped in per cycle not piston speed , and 300' duration will put the power up the rev range ruining what a twin is good at ,low end stomp.but dont take my word for it read what our tuning greats,David Visard,Graham Bell,Phil Irvine,Stan Shenton andDes Hammil have writen, all more or less state 300' will give little below 4000 rpm,great in a road engine !!!not


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Re: A65 camshaft. full race vs. Spitfire [Re: wak] #415255
01/25/12 4:58 pm
01/25/12 4:58 pm
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The earliest reference I can find,concerning long-stroke engines requiring more duration for a given rpm,goes back about 90 years.It's mentioned in "Dyke's Automobile and Gasoline Engine Encyclopedia" back in the 1920's.

It's not a new concept,and it explains the wives' tale "long stroke engines make better low rpm torque".Short stroke engines can do it too,with the right cam timing.

There is subtle mention of it by A.G. Bell in "4 Stroke Performance Tuning".You need to read between the lines.Look at his chart for recommended cam timings on different size engines with approximately square bore/stroke dimensions.The ratio of valve area to piston area is constant,so that's not an issue.The larger engines require more duration at the same rpm.The larger engines always have longer stroke,if bore/stroke is square.

Among other things,it takes a longer time for a pressure wave to travel from the piston back to the intake valve at the end of intake stroke (after BDC),on a long-stroke engine.The engine travels more degrees past BDC,before a high enough pressure reaches the intake valve to stop intake flow.

Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415265
01/25/12 5:37 pm
01/25/12 5:37 pm
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derby england
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i will gladly research this idea as knowledge is power,excuse the pun !!!!But this thread started as a 883 road engine, how long are you going to want to keep a big unballanced paralel twin at over 6000rpm for ?Why rob power where you can use it to get power where its never going to be used?im sure this will get a lot of response from people that have 863s which sit all day at 8000rpm smooth as silk !!!


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Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415316
01/25/12 8:22 pm
01/25/12 8:22 pm
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Personally I fitted an H&C roadrace cam to an OIF '72 w/ the SRM 750 kit and some porting .This had 32mm miks and megasand a lotta fettling .Prolly the quickest (pre hinckley) Britbike I have ridden but it was pure misery in any sort of traffic.I have no experience with the SRM cam and I know this is a whole art in itself but I have been more than happy with the standard late A-65 cam for street use . I recently aquired an A-10 SR with high compresh pistons and a 358 cam ,all fresh and ready to go ,I'm almost considering installing a 357 cam but I just have to see what this will do .Looking fwd to comparing it to my low compresh,356 cam,ironhead ,siamesed piped A-10 superbimbler ...

FWIW-BONZO

Re: A65 camshaft. full race vs. Spitfire [Re: ] #415331
01/25/12 9:00 pm
01/25/12 9:00 pm
Joined: Aug 2001
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Michigan, USA
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"68 , I have to believe we are on the same page . Here in the "D" things happen fast , my typical commute tends to be 0-70-0 MPH in a matter of seconds .I pretty much quit riding 2 wheels for the commute when I took a day shift job, we just don't have enough roads to light it up but there are a great number of modern sportbikers tend to be the "donors"b that we all hear about

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Re: A65 camshaft. full race vs. Spitfire [Re: oleandreas] #415344
01/25/12 9:45 pm
01/25/12 9:45 pm
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Bega NSW Australia
Mark Parker Offline
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Wak, here is a demo, your right about 4,000RPM, good power on this is actually after 4,500 and if you were racing you would want to stay above that. But it's not particularly little below 4,000. When I measured the cam timing, I don't know how accurate I was, but it must be close, anyway at 020" 53-68 inlet and 80-43 exhaust, around 300deg, thats with offset rocker buttons and spitfire profile.
In this video 883cc 38mm flatslides. The bike is also light, another factor in choosing a cam.
RPM is just at key level MPH above, shiftlight on at 7,000. The last little bit is overtaking in top gear where it picks up about 30MPH and starts at about 3,000RPM. The twin spar alloy frame is vice free and the brakes are very good.
http://www.youtube.com/watch?v=uncK4P1gyUw


mark
Re: A65 camshaft. full race vs. Spitfire [Re: ] #415438
01/26/12 8:18 am
01/26/12 8:18 am
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Oslo Norway
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Per B Offline
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I wold go for the race cam in the engine Ole Andreas is building, where he lives there is not much trafic to worry about, not many cars around in rural countryside in Norway. The cam timing of the SRM cam is not that radical compared to Clubmans Goldi set, in this on the duration are 330 degre, I am running that in my bigbore longstroke Goldi and there is no problem with that, good torque all the way down, it realy coms on the cam at around 4000rpm, by the way I am living in Oslo city centre, but who cares, I dont drive in the city.

I am also building a a 1000 cc R3 in a Rob Nort frame and I am putting quite wild cams in that one, much more radical than the SRM cam Ole Andreas is using, the duration of the cams in the R3 is 315 degree,


best regards

Per
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