Camshaft tech thread!

[Rookie]

Roman, you have to remember that when Rawb says big cam, it means BIG cam.

[Testament]

i.e. .600" lift 240 deg duration @ 50 thou is only mild

[Beaver]

Might be worth putting your credentials/background in the first post Rob, just so people dont think you are pulling all this our your ass! haha

[BobbyBreeze]

Chur, updated original post.

[Testament]

Hello OS! 

 

So I thought I would start this thread to answer any questions I can on camshafts. I am hoping I can help educate you guys as much as possible & also get asked some tricky questions that helps further my own knowledge on the topic too. I might also throw some updates / photos in here of interesting & relevant stuff I am up to at the moment.

 

I'm Bobby Breeze and I've been doing voodoo stick magic at the black tracks for twenny years so roll your dice and pray for snake eyes!

 

Cheers,

BB

[RUNAMUCK]

Valve acceleration I think?

as much thou as poss, for as few degree's of rotation as it'll take without punching the side of the profile into the edge of the lifter.

[Rhyscar]

Hey Rob, 

 

Here's a new-school cam question (markku has prob already chatted to you about it), but essentially a lot of the new japanese (when I mean new I mean 2000's) engines have vvti/vvt on either cam such as my 2zz. 

 

Firstly, knowing nothing about the difference in the cams and the maps these VVTI systems run, how could the map be optimized at different revs to bring the cam on earlier or provide more boogie up top etc. Essentially toyota/honda etc did these systems for a reason which hopefully aren't 100% emissions based - I'm really just wanting to get the most out of what the engine/cams have. 

 

Secondly, how would a cam profile for use with VVTI differ to your 'standard' non VVTI type engine and if/how could these systems be used to optimize the engine for a more aggressive cam? or is non-VVTI always going to be a better option (application I'm thinking of is throttle response, good torque from 4000rpm and still plenty of power and reviness through to 9500rpm which is normally quite a bit to ask for from a non-VVT/VVTI cam)

 

 

 

Thanks

[Yowzer]

I believe Simon has a flowchart regarding altering VVTI systems

[Testament]

from my understanding with i-vtec and VVTL-i  you have 2 cams effectively and you can switch between them PLUS the cam phasing of at least the inlet cam is adjustable

 

basically the two cam profiles give you wildy different engine torque curves (hence booooo and baaaaaaa)

altering the phasing can give you the best performance for that profile at x rpm

 

so for what you want I'm thinking you need to get profile A = some kind of rally/fast road cam that pulls hard from 3000 or 4000 - 6000 or 7000, then profile B as all out race/drag/extreme cam 6000-10000rpm

 

something like that Bobby?

[Rhyscar]

I'm not really too interested in the high/low cam side of things but in how the phasing of the cam from the VVTI/VVT can increase performance. 

 

For now I'm just looking to get the most out of a standard cam but will be looking at going as aggressive as I can in the future - hopefully the VVTI/VVT can help me make an aggressive cam work over a wider range of revs but I'm not sure exactly how this would happen.. (if at all possible)

 

 

Simon - Interested to see VVTI info. 

[kpr]

vvti  is just cam timing.  so you get the benefits of an adjustable cam wheel, with no drawbacks.  eg; advance inlet cam for more midrange, while still retaining top end power and idle by retarding it in these areas.     main reason you cant stick with vvt on  a big cam, is the valve to piston, and valve to valve clearances start to get tight. but stick with vvt/i as long as you  can. carefully ground cam and engine setup will have the max vvt travel stop before the valves eat the pistons. also  if you are going for something massive. for something like a drag car, will likely be pointless retaining vvti. as your engine will only be using a small hi rev power band

[BobbyBreeze]

Valve acceleration I think?

as much thou as poss, for as few degree's of rotation as it'll take without punching the side of the profile into the edge of the lifter.

 

Maximum lift rate, or velocity is determined by lifter diameter. You can work out the max lift rate by taking the lifter dia. in inches and multiplying by 0.008726 (i.e. a 1" dia lifter can run 8.7 thou per degree lift rate).

Working the lift rate out yourself isn't really that useful unless you are designing profiles i.e. there isn't really a good rule of thumb on how much lift you can use for a given duration  We can dwell velocity at the maximum to increase lift for a given duration, so it depends on the cam profile designer as to what is possible. 

 

Firstly, putting a larger lifter in and still using a profile that is designed for the smaller lifter isn't going to do jack. You're just adding weight to your valvetrain. You need a profile designed to take advantage of the extra velocity you can run with the new larger dia lifter - in some cases this means a custom profile and therefore isn't really economical for your average build. 

Secondly, the main advantage of added lift rate is you can run more lift for a given duration. So if you are limited in lift in some other area of your valvetrain/cylinder head design it is a pointless exercise. The extra performance gained by running increased lift rate at the same peak lift isn't great. Sure, if it is a 10/10ths race profile that we want everything we can get out of it we will do this. But on your general 'hot' street motor it isn't a huge deal. 

 

 

Hey Rob, 

 

Here's a new-school cam question (markku has prob already chatted to you about it), but essentially a lot of the new japanese (when I mean new I mean 2000's) engines have vvti/vvt on either cam such as my 2zz. 

 

Firstly, knowing nothing about the difference in the cams and the maps these VVTI systems run, how could the map be optimized at different revs to bring the cam on earlier or provide more boogie up top etc. Essentially toyota/honda etc did these systems for a reason which hopefully aren't 100% emissions based - I'm really just wanting to get the most out of what the engine/cams have. 

 

Secondly, how would a cam profile for use with VVTI differ to your 'standard' non VVTI type engine and if/how could these systems be used to optimize the engine for a more aggressive cam? or is non-VVTI always going to be a better option (application I'm thinking of is throttle response, good torque from 4000rpm and still plenty of power and reviness through to 9500rpm which is normally quite a bit to ask for from a non-VVT/VVTI cam)

 

 

 

Thanks

 

Yep, you can make good gains on motors with variable timing over factory. Generally on the Intake you run retarded at idle to reduce overlap and give a good idle, then advance decently through the midrange for good grunt. After peak torque you start retarding again to get the top end back - as kpr has stated. Exhaust you would advance up top to reduce pumping losses. To get the most you are going to have to do a lot of testing, exact numbers are different for every motor. But yep, definitely worth playing with. 

 

The difference in cam profile between vvt and non vvt motors is minor and depends on the motor. On some setups the variable phaser pulley can't handle the increased acceleration on the cam profile and heavier valve springs and can stop working correctly. Unsure if this is the case with the 2zz, I haven't had a lot to do with them. If you can run vvt then do - even in full drag motors it is worthwhile. Often with really large cams they will disassemble the variable pulley and fit a solid stop as to limit advance - in case the setup fails and advances to the limit (some motors run up to 50degrees advance, this + big cam profile = valves tag a piston)

[Yowzer]

So how about diesels? My previously NA 3L is now eating 22psi, what could be done to the cam to complement this?

[kpr]

grind us a TD42 cam rob

[RUNAMUCK]

I would have thought (As we discussed on FB aaages ago) with a larger lifter, you can get your duration@50, closer to your advertised duration. More power, "under the curve"

But more importantly, if one was working with a cam piner/fiend like yourself, and had a lifter face of .902" then the above formula could be implemented to dream up a profile with more ability to bleed manifold pressure off into the cylinders for a given advertised duration, than another cam with less aggressive ramps. I've seen first hand how much the boost decreases with fatter cam. (Boost friendly grind too)

[Celica RA45]

im using a 14.65mm lift cam on my altezza engine and its 263 at 50 thou .still moving the inlet 1 and half teeth of vvti.. std is 3 teeth of movement

on the exhaust ,moving that 1 tooth ,both cams are the same in lift and duration .they also fit onto a 33mm bucket ,had to do shit loads for the cam to turn thou

not using std pistons thou up to 14.5 to 1 comp and have deeper fly cuts on the valve pockets .currently running 80 thou piston to valve with max vvti movement

[flyingbrick]

grind us a TD42 cam rob

back when I had mine every bloke was saying that cams gain sfa on the td42. I'm keen to know why diesels are different

[BobbyBreeze]

I would have thought (As we discussed on FB aaages ago) with a larger lifter, you can get your duration@50, closer to your advertised duration. More power, "under the curve"

But more importantly, if one was working with a cam piner/fiend like yourself, and had a lifter face of .902" then the above formula could be implemented to dream up a profile with more ability to bleed manifold pressure off into the cylinders for a given advertised duration, than another cam with less aggressive ramps. I've seen first hand how much the boost decreases with fatter cam. (Boost friendly grind too)

 

Not at all - because the velocity doesn't peak or get close to the limit under 0.050". This is why I asked what your definition of 'ramp rate' is, there is a bit of confusion around. I personally call the ramp the low velocity portion of the profile that is designed to pick up / drop the valve to the seat. We can change this rate easily, irrelevant to lifter diameter. 

The minor intensity (degrees it takes to go from 0.010" duration to 0.050" duration - what you mention), is independent of lifter diameter. To make the cam open faster and reduce this number we need to increase acceleration.

 

Found a wee diagram to make it easier to visualise - Lifter diameter only limits the maximum velocity which occurs around ~0.100" lift on this profile. You can see here - red is velocity. It doesn't peak til much after 0.050" (blue vertical line)

 

 

 

im using a 14.65mm lift cam on my altezza engine and its 263 at 50 thou .still moving the inlet 1 and half teeth of vvti.. std is 3 teeth of movement

on the exhaust ,moving that 1 tooth ,both cams are the same in lift and duration .they also fit onto a 33mm bucket ,had to do shit loads for the cam to turn thou

not using std pistons thou up to 14.5 to 1 comp and have deeper fly cuts on the valve pockets .currently running 80 thou piston to valve with max vvti movement

 

Nice yep, I think I may have ground your cams? Have you had any issues with the vvti playing games with those profiles? 

 

So how about diesels? My previously NA 3L is now eating 22psi, what could be done to the cam to complement this?

 

I'm sorry, I have no experience with performance diesels so couldn't really tell you what works. I think more lift if definitely going to help breathing, just unsure as to what opening/closing events work well with diesels.  

[Celica RA45]

yes you did the 205 profile ,they marked up straight a way like the toda cams do  and that bigger 1 had to much velocity and lost power every where  ,but that super tourer that you fixed was good  ,these were made here and are fine so far ,no problems with vvti, seated pressure are 90 lb springs with ti retainers and steel valves

[BobbyBreeze]

I just checked the L205 profile and it has too much velocity for a 33mm bucket. That will be why they marked up. Did you let us know they did this? 

 

What makes you say that too much velocity is what lost power?