Which Cams Are Which ??

[sportyone]

Hello,

there seems to be some confusion, ( for me anyway ) as to whether or not the cams fitted to Thruxtons are different to Bonnevilles.

I'm talking of the later model 865 carbyed motors not the 790 ones. does anyone out there actually know, according to my info from the dealers workshop, the part numbers are the same for both Thrux and Bonne 865's so in theory they should run the same.
so does the Thruxton rely on it lighter weight to go harder as many parts are identical ?

I have heard of guys using Thrux needles but my Asian mechanical Guru tells me they are not needed.
and by the way my Bonneville runs, he could be right !
I have since found out that the later 865's have the Thrux needles anyway !

so what are the 813 cams people on here often have fitted, do they give something more ?

I did notice in some of the latest models (EFI ) I mean, they do have quite a noticable longer straight pipe distance before the first bend on the header pipe, which I imagine could provide abit more power, does anyone know that for sure either ?

cheers,

 

[ivar]

2 things that give the thrux an ever so slight edge in performance:
- better headers
- lighter alloy wheels, 1" less front wheel diam.

813 is a cam grind from TPUSA

 

[Craigore]

I don't mean to hijack but I have a question also- which years of the 790 have the "hot" cams??

 

[KingBear]

Floating front disc, preload adjustable front suspension, slightly shallower rake, and a few other minor differences but the 865 motors are all the same, needles and firing positions (270 for the Scrambler) notwithstanding.

 

[coopv2]

i have a 8/2007 bonnie, and was in the local dealer today, I asked him to check the needle part #s against my engine # and same month thruxton, result was different numbers, and $20 each, so I ordered some to test them out.

a note to those interested in a cam change, which I will try to keep basic.

a mild cam change will gain mild results, as you go for a longer duration on the cam lobe, you end up closing and opening valves at a different degree on rotation of the crank, the position the piston is in at the closing point of the exhaust valve, determines how much volume can be compressed from that point on.
basically wilder cams lower compression. this will result in low end power loss. therefore to take full advantage of a wilder cam change you must raise the mechanical compression ratio...ie. high comp pistons, thinner head gasket, milled head surface, weld filled combustion chambers.
So a motor with a mild cam and 10:1 mechanical compression ration, may have a corrected ratio (takes into account cam timing) of 9.8:1
fit a wild cam to that 10:1 motor and you could end up with corrected comp of 8.5:1
CAM LIFT.... can be determined by some basic factors. eg piston to valve clearance at top dead center. TDC. valve diameter. valve spring coil bind, spring pressure, and Head flow.
So stock heads with poor port flow , require less lift than a ported head. to make the best cam choice and the most performance out of your motor requires.... a cam with duration that matches compression, and lift that matches port flow.
there is much more to consider, and changing just the cam is never enough.
at least raise the compression to match the cam timing.
enough rambling from me.

 

[ivar]

i have a 8/2007 bonnie, and was in the local dealer today, I asked him to check the needle part #s against my engine # and same month thruxton, result was different numbers, and $20 each, so I ordered some to test them out.

When you swap out the needles, there should be a 4 letter code stamped on them. The 865 is supposed to be marked "NBTZ"

 

[coopv2]

When you swap out the needles, there should be a 4 letter code stamped on them. The 865 is supposed to be marked "NBTZ"

Thanks Ivar,
so is that for the bonnie and thruxton as both are 865
or will my stock Bonnie needles be NBTZ and the thrux be different. ???

 

[ivar]

from what I understand, they should both be the same. (even if part #'s differ)
I guess we'll see when you get your needles

 

[coopv2]

yes that is true, I stayed up late tonight to bid on ebay, scored a modded airbox, twin opening with polaris venturi, uni filter, 'D' tool, pro-com ignitor, jet kit , AI removal kit, ignition key relocation brkt. and pingle hi flow tap, all for $175.
pat me on the back!

 

[ivar]

not bad...!

 

[thearcticsea]

yes that is true, I stayed up late tonight to bid on ebay, scored a modded airbox, twin opening with polaris venturi, uni filter, 'D' tool, pro-com ignitor, jet kit , AI removal kit, ignition key relocation brkt. and pingle hi flow tap, all for $175.
pat me on the back!

wtf did you search for??

 

[Carnation]

Hello,

there seems to be some confusion, ( for me anyway ) as to whether or not the cams fitted to Thruxtons are different to Bonnevilles.

I'm talking of the later model 865 carbyed motors not the 790 ones. does anyone out there actually know, according to my info from the dealers workshop, the part numbers are the same for both Thrux and Bonne 865's so in theory they should run the same.
so does the Thruxton rely on it lighter weight to go harder as many parts are identical ?

I have heard of guys using Thrux needles but my Asian mechanical Guru tells me they are not needed.
and by the way my Bonneville runs, he could be right !
I have since found out that the later 865's have the Thrux needles anyway !

so what are the 813 cams people on here often have fitted, do they give something more ?

I did notice in some of the latest models (EFI ) I mean, they do have quite a noticable longer straight pipe distance before the first bend on the header pipe, which I imagine could provide abit more power, does anyone know that for sure either ?

cheers,

It's the header that makes all the difference.

All 865 Bonnies (not just later ones) have the Thruxton needles.

 

[sweatmachine]

all the 865cc Bonnies and Thruxes have the exact same cams, which all suck. Early 790 cams are a decent improvement over the stock 865cc cams. I picked up a dyno-verified 5hp improvement with NO LOSS ANYWHERE by installing some 790 cams in my Bonnie.

The real deal are the 813 cams from TPUSA.

 

[coopv2]

wtf did you search for??

was just lucky while checking out bonnie parts, someone had some used parts for sale in West Aust.

 

[Aussie_T100]

basically wilder cams lower compression.

That statement requires clarification and I'd like to attempt to do so if I may.

You need to differentiate between static compression and dynamic compression. Static compression is just that - static, it does not vary because it is mathematically derived from the swept volume of the cylinder and the volume of the combustion chamber both of which are non variable. Static compression assumes 100% volumetric efficiency, that is, that the swept volume of the cylinder is filled to 100% of its capacity. Naturally aspirated engines rarely achieve 100% VE and if they do it will be only over a narrow rev range.

The actual compression ratio of an engine varies according to the conditions it is operating under at the time, for example when the throttle is wide open more air can get into the cylinder than when the throttle is only partially open so the achieved compression ratio is higher with a wide open throttle than a partially open throttle because more air is getting into the cylinder. Thus the actual compression ratio of an engine varies according to the operating conditions and is therefore dynamic being dependant on airflow or volumetric efficiency.

The whole point of fitting performance cams to an engine is to increase airflow or VE which has the effect of increasing the dynamic compression ratio. If such was not the case there would be no performance improvement gained from altering the valve timing by fitting performance cams.

Of course there are trade offs when altering the valve timing of an engine because valve timing is non variable during operation (in most cases), that is, you can only optimise the valve timing for a given rev range. Performance cams usually have valve timing optimised for higher rev ranges which results in the valve timing being less optimal for lower rev ranges.

Valve overlap, that is, the time that both inlet and exhaust valves are open together measured in degrees of crank rotation, is often increased on performance camshafts. Increased valve overlap capitalises on inertia of the airflow through the engine to improve cylinder filling which results in a higher VE and increased dynamic compression however it is only effective at higher RPM. At lower RPM increased valve overlap has a detrimental effect on cylinder filling which results in a lower VE and thus a lower dynamic compression ratio.

To sum up, performance cams typically have a detrimental effect on dynamic compression at lower RPM's but also have a positive effect on dynamic compression at higher RPM's, this is where the performance improvement comes from. It is quite common and good sense to increase static compression ratio when fitting performance camshafts in an effort to counter the loss of dynamic compression at lower RPM's.