 Cam Timing Specs for 270 engines?
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Could someone please post the cam timing specs for the 790cc and 865cc 270 degree engines, if this subject has been discussed before, please post link to previous posts.
Thks and Cheers..........Agro
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Re: Cam Timing Specs for 270 engines?
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The 790 cams are:
inlet, 19 before, 43 after
Exhaust, 31 beore, 5 after.
Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python
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Re: Cam Timing Specs for 270 engines?
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Quote:
Could someone please post the cam timing specs for the 790cc and 865cc 270 degree engines, if this subject has been discussed before, please post link to previous posts.
Thks and Cheers..........Agro
If I gave you the specs for the 865 270`s you wouldnt believe them - really!
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Re: Cam Timing Specs for 270 engines?
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Ok. Thruxton/T100 Inlet open 4deg btdc. close 48deg abdc duration 232deg Speedmaster 865 ahem...ZERO deg btdc 24deg abdc wahey! 204deg Thruxton/T100 Exhaust open 33deg bbdc close 7deg atdc Duration 220 Speedmaster 865 open 39deg bbdc close 7deg BEFORE!!tdc (recheck the inlet opening figure gentlemen - Briggs and Stratton have more bleedin overlap - really!) Duration 212 So there you have it - factory figures. The book quotes the lift as 9.5 and 9.4 respectively for inlet and exhaust for both models, first one we measure that actually does that will be the 1st - they dont even do that much. Rather underwhelming to say the least, and lots of potential for some valve lift and duration  Watch this space....
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Re: Cam Timing Specs for 270 engines?
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Speedmaster 865
inlet...ZERO deg btdc 24deg abdc wahey! 204deg
exhaust open....39deg bbdc close 7deg BEFORE!!tdc (recheck the inlet opening figure gentlemen - Briggs and Stratton have more bleedin overlap - really!) Duration 212
That's -7 deg. overlap or 7 deg. underlap!!! hahaha
That is sick man!
Ok here's the big Question.......... what's the specs on your cams??
Cheers..........Agro
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Re: Cam Timing Specs for 270 engines?
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I wonder how much of a power gain the new S/M would get with a pair of *STOCK* 790 cams? And to think they did the same miserable thing to the poor scrambler, which SHOULD have had the Thruxton engine.
The only thing I can think of that would justify this is that they might have been trying to get the same emissions effect as an automotive exhaust gas recirculation system.
Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python
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Re: Cam Timing Specs for 270 engines?
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Loquacious
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how much effect would the thrux cams have? would they move the powerband much? or even make any difference over stock 790 cams
Frank
(Former)05 BA tbike pipes, ai removed, Freak, mikuni hsr 42's, 904, ported/polished head, 1mm oversized valves
NOW-2010 silver and black tbird
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Re: Cam Timing Specs for 270 engines?
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Quote:
Quote:
Speedmaster 865
inlet...ZERO deg btdc 24deg abdc wahey! 204deg
exhaust open....39deg bbdc close 7deg BEFORE!!tdc (recheck the inlet opening figure gentlemen - Briggs and Stratton have more bleedin overlap - really!) Duration 212
That's -7 deg. overlap or 7 deg. underlap!!! hahaha
That is sick man!
Ok here's the big Question.......... what's the specs on your cams??
Cheers..........Agro
I do like the term "underlap" I hope you dont mind if I use that in future :-D
As you can see they are crying out for some attention. With regard to our figures they will be remaining firmly under our hat for the time being, market forces etc.
We will be more forthcoming with results though once they become finalised.
Please realise the results will be improved performance from zero to hero on the tachometer with NO holes in the power, and more grunt right through. These motors DO respond well and there is real performance gains just waiting to be unleashed with some correct attention, very satisfying of Mr Bloor to make them in that manner, and with the strength and reliability built in.
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Re: Cam Timing Specs for 270 engines?
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I wonder how much of a power gain the new S/M would get with a pair of *STOCK* 790 cams? And to think they did the same miserable thing to the poor scrambler, which SHOULD have had the Thruxton engine.
The only thing I can think of that would justify this is that they might have been trying to get the same emissions effect as an automotive exhaust gas recirculation system.
We did consider going a similar route but the price of modifying or even replacing Triumph cams with similar Triumph items have made us decide otherwise. I suspect a noticeable improvement with some minor irregularities in the torque curve would be the outcome, I couldn`t say accurately though without some actual testing.
And yes, what were they thinking of putting the 270 in the Scrambler?, Steve McQueen will be turning in his grave now they are associating him with it. I cant believe they have done that - some camshafts and a pipe with your Scrambler sir? www.Thunderbike.co.nz coming soon.....
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Re: Cam Timing Specs for 270 engines?
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Quote:
how much effect would the thrux cams have? would they move the powerband much? or even make any difference over stock 790 cams
Frank
They would give the characteristics of a Thruxton - not exactly hold on to your hat stuff but an improvement in mid range without the top end I suspect of a 790 with our pipes, and now we have the 865 270 cam specs we can see how they were able to say the Thruxton was the sports model in the range when it was introduced.
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Re: Cam Timing Specs for 270 engines?
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Old Hand
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Quote:
how much effect would the thrux cams have? would they move the powerband much? or even make any difference over stock 790 cams
Frank
Without the rest of the Thruxton package, ( more compression, bigger carbs) I would think Thruxton valve timing would give the S/M pretty much the same power/torque curves that the T100 has. Unfortunately, this isn't a drop-in change because the Thruxton has a proper 360 degree crank.
Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python
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Re: Cam Timing Specs for 270 engines?
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We did consider going a similar route but the price of modifying or even replacing Triumph cams with similar Triumph items have made us decide otherwise
Yes The Thruxton is a bit of a dog on the top-end and i have considered getting the 790 Bonney cams for mine.
For interest, what would the cost be for 790 Bonney intake and exhasut cams and America/Speedmaster 790 intake and exhaust cams ???
Cheers.......agro
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Re: Cam Timing Specs for 270 engines?
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3/4 Throttle
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Yipe! Those stock cam specs (both of 'em) are really weak!
For those of you who think metric measurements are a French (spit) Commie plot, the lift translates to .374" IN and .370" EX. At first blush, this seems short, but remember that this is a 4 valve per cyl. head, and they can get away with shorter lift.
And, yes, the shorter ex. duration is to help with smog reduction.
The duration figuers of 242* IN and 216* EX are probably "design" duration. On solid lifter type cams (as opposed to hydraulic cams), this duration is usually measured at .006" lift. This makes that small cam seem larger, but, the first few degrees of stock cam lifter movement is a slow rate, so that the valve lash can be taken up before the faster movement is applied to the lifter. This helps keep the valve train pounding to a minimum.
The slow lift rate lowers valve opening speed, so the cylinders don't get a chance to fill very well; read, lower horsepower.
CAM SELECTION TIP: The Bonny twins translate to around a 2400 cc V-6 car engine. Go to your favortie cam grinder's catalog to see what grinds he offers for V-6, 4 valve engines. Crane, Comp Cams, Isky, or others, will have their basic street grinds listed. ANY mild cam they do would make a decent choice for recamming a Triumph twin, I should think. Look for solid lifter grinds, but a hydraulic grind would be fairly close.
There's lots more to this, but it's 2 am after a rather big Thanksgiving day and I'm pooped out. Beddy-bye time for Grandpa.
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Re: Cam Timing Specs for 270 engines?
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3/4 Throttle
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I just came from the Isky web site, after looking at his cam lobe specs pages for flat tappet lobes.
Of course, almost all these lobes are designed for rocker arm engines, so the raw lobe lift is on the short side for the particular duration.
What I did come to realize is that the stock Triumph cams have a seriously fast lift rate compared to even custom lobes from a specialty grinder. That's how Triumph can make the HP is does with seemingly short duration cams. The only downside to fast lift rate lobes is possible cam and valve train wear. Putting a large amount of oil up top is the countering measure. Not only does the extra oil keep things lubed better, but it takes the heat away, down to the crankcase for dissipation.
Coming up with a a new - and better - grind could be a little tricky. As Red Green would say, "This is best left for professionals."
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Re: Cam Timing Specs for 270 engines?
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I suspect that the stock valve timing is also a big part of the amazingly flat torque curve. The difference in the exhaust timing between the 360 and 270 degree engines is probably to match the different exhaust system.
Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python
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Re: Cam Timing Specs for 270 engines?
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To be fair I should have mentioned when reporting the cam figures earlier that all measurements are at 1mm lift which is fairly normal practice for those who may be unsure.
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Re: Cam Timing Specs for 270 engines?
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3/4 Throttle
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QUOTE: "To be fair I should have mentioned when reporting the cam figures earlier that all measurements are at 1mm lift which is fairly normal practice for those who may be unsure."
Here in the States, it's always been duration at .050" lift from the aftermarket cam grinders, as that lift is about where effective flow starts past a valve. SAE has several different standards for measuring cam duration, and some car manufacturers - Chrysler, for instance - use something different from .050". Zero, .006" and .020" come to mind. (Zero is the instant the lifter starts to move and is popular with hydraulic lifter cams.)
Long design duration specs on a flat tappet cam have a fair amount of low and slow lift rate at the start, which is intended to take up the valve lash softly, so as not to pound the valve train pieces. Once the lash is taken up, the faster lift rate kicks in.
1 mm translates to .03937", which will give a slightly longer duration than the oldtime .050", but this extra bit of info tells us that the Triumph 790 cams are not all that bad, but that smogger ex. cam could be a little bigger. Going with the same grind on the ex. that the intake has would be a decent step up
Thanks for the additional info, Graeme!!
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Re: Cam Timing Specs for 270 engines?
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Learned Hand
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I didn't think it was possible to have valve timing with no overlap; when my VW was on the street, the accepted wisdom was that it was almost essential to have some overlap in the works. With the air-cooled engines, the overlap actually helps cool the exhaust valve by letting some of the incoming charge flow over it, and also helps pull more charge into the cylinder. Kind of like having to open the door and an opposing window in an apartment to get a draft going.
Michael D. Rodriguez
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Re: Cam Timing Specs for 270 engines?
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Normally, that is so. It's true for the new S/M engine as well, as you can see from the dismal performance gains in another thread. For years, car engines have had a valve that injects some of the exhaust back into the intake to screw up the mixture for the purpose of reducing the nitric oxides, and I suspect that's what they are trying to do with the S/M by slamming the doors too soon.
Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python
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Re: Cam Timing Specs for 270 engines?
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Quote:
I didn't think it was possible to have valve timing with no overlap; when my VW was on the street, the accepted wisdom was that it was almost essential to have some overlap in the works. With the air-cooled engines, the overlap actually helps cool the exhaust valve by letting some of the incoming charge flow over it, and also helps pull more charge into the cylinder. Kind of like having to open the door and an opposing window in an apartment to get a draft going.
I`m sure your mild old VeeDubya cam had both valves shifting a whole lot more air than these 865 Speedies, remember 1mm open 7 degrees underlap! My lawnmower valves have more overlap - honest. And yes you are correct to mention the relationship between inlet and exhaust flow, the mediocre opening of these std cams almost entirely eliminates any benefits there may be available though.
Cheers
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Re: Cam Timing Specs for 270 engines?
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Learned Hand
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I dunno about that one :-) 85.5mm Bore, 69mm stroke, 35.5mm intake valve, 32mm exhaust valve. Wish I had that car still intact.. Eitherways, good technical discussion, it's cool that someone's been able to really conduct a good study on the valve timing for these engines. Still amazing though about that stock cam for the 865cc. We can only hope that they had some over-riding reason why they did things the way they did.
Michael D. Rodriguez
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Re: Cam Timing Specs for 270 engines?
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Quote:
The 790 cams are:
inlet, 19 before, 43 after
Exhaust, 31 beore, 5 after.
Hey Greybeard, were did you get these specs from?
Just got quoted these from RAT forum member..........
Specs for Bonneville America 790cc from Issue 2 - 03.2002
Intake
Open - 19deg btdc
Close - 43deg abdc
Duration - 242deg
Exhaust
Open - 46deg bbdc
Close - 20deg atdc
Duration - 246deg
(All are measured at 1.0mm lift, per Manual)........
Cheers,,,,,,,,,,agro
Last edited by Whale_Oil_Beef_Hooked; 10/02/2007 10:10 AM.
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Re: Cam Timing Specs for 270 engines?
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Quote:
Post #64128 - 05/11/23 08:17 PM
Rua gravedigger?? LOL
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Re: Cam Timing Specs for 270 engines?
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Quote:
Quote:
Post #64128 - 05/11/23 08:17 PM
Rua gravedigger?? LOL
Yes but were did he get these specs from which versin of the manual.
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Re: Cam Timing Specs for 270 engines?
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Specs that have been sent in so far;
Specs for Bonneville America 790cc from Issue 2 - 03.2002
Intake
Open - 19deg btdc
Close - 43deg abdc
Duration - 242deg
Exhaust
Open - 46deg bbdc
Close - 20deg atdc
Duration - 246deg
My manual states;
Triumph Workshop Manual for Bonney/Thrux/America/SM, P/n T3859909-1, Issue 4, 10.2004
Checked the cam timing specs for the 790cc America/SM in Chapter1, Page 13 - General Information, states:
IO 19* btdc, IC 43* abdc, duration 228*,
EO 37* bbdc, EC 11* atdc, duration 216*,
Intake duration as listed is wrong, should be 242*
Exhaust duration as listed is wrong, should be 228*
Another RAT member posted;
Specs for790cc America/Speedmasterfrom Issue 2 - 01.2006
Intake
Open - 22deg btdc
Close - 46deg abdc
Duration - 248deg
Exhaust
Open - 42deg bbdc
Close - 7deg atdc
Duration - 228deg
Is there any more cam timming events for the 790 BA/SM ?????
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