Cam Profile - Regrinding

[kylestyleup]

Does any one know a good cam profile for carbureted engines?
How do we reground cams?

I am planning for a reground on my cam.

Long Duration
Concave flank for the intake
Convex (egg shape) for the exhaust

[abently]

Check how close the base circle of the lobes are to the actual common axis mass. If there's a good 4+mm of material there then you should be able to get a reasonable grind out of it.

If your 100% set on staying carby, go external carby pump and get an EFI Head (if they exist) as that will let you run whatever cam you want with little mods if any.

It is very expensive (labor intensive) to machine up a carby Head on top of needing a custom one-off camshaft built as well for it.......

[w810sc]

Here is a you tube link on how cams:
http://www.youtube.com/watch?v=VTsivFJjMwY
It shows you how a cam is constructed.

Sometimes they weld it and grind to suit the profile.

What motor is the cam for?
What is done to the motor?
What rev range do you want to find power in?

You might need to adjust your shims/buckets/rockers/push rods to suit the cam too.

fonz

[kylestyleup]

What motor is the cam for?

It's for an 18R.

What is done to the motor?

Nothing done yet. (gathering info)

What rev range do you want to find power in?

At 7000rpm

Please don't advice for another engine, this is what I have...
Machinist here are cheap, so work is not a problem.


.

[-GT-]

Can you explain why you want a concave flank on the intake cam? And what you're planning on doing to your valvetrain to help it cope with a profile like that?

[kylestyleup]

Can you explain why you want a concave flank on the intake cam? And what you're planning on doing to your valvetrain to help it cope with a profile like that?

Well... I want a concave flank because I think it snaps and don't restrict air flow. This only for the intake.

I would try to have a convex (egg shape) for the exhaust.
I want to go bigger vales, hardened vale seats and after market springs and maybe racker arms.

[timbosaurus]

Here are some 18R profiles from an Australian company.

http://www.camtechcams.com.au/cat/toyota18R.html

[kylestyleup]

Here are some 18R profiles from an Australian company.

http://www.camtechcams.com.au/cat/toyota18R.html

This is great timbosaurus
only if I know how to read this profiles (how this is applied)
so I could somehow modify a little into this.

[oldcorollas]

If your 100% set on staying carby, go external carby pump and get an EFI Head (if they exist) as that will let you run whatever cam you want with little mods if any.

It is very expensive (labor intensive) to machine up a carby Head on top of needing a custom one-off camshaft built as well for it.......

err... what are you talking about abently? what is so different between this "carby head" and "efi head" you are talking about?

kylestyleup, think about what happens to the bucket when the cam lobe pushes down...the bucket is flat, and has a finite width.
or is 18RG rockers? in that case, you still have limited range for changing the shapes of the ramp.
the movement of the valve is a function of the interaction of the two surfaces.
even if you had a "point" on the bucket.. ie, a roller follower, then you may have issues where that concave part binds due to putting too much side load on the follower.
you also need to think about having "constant push" on the valves so that they don't bounce.

18R already has hard valve seats. all toyota alloy heads do.
rocker arms? planning on roller rockers? that will allow you a more aggressive lift. but the more aggressive the lift, the stronger the springs have to be (or lower rev limit) to stop the valves bouncing..

here is a pic of a TRD 272, 7.5mm lift cam

and toda 272 7.9mm

[timbosaurus]

A couple of sites that may help you understand all those variables...

http://www.camshafteng.com.au/calc.htm
http://www.rbracing-rsr.com/camshaft.html

and most importantly, have a look at the coloured image halfway down this page:

http://auto.howstuffworks.com/camshaft.htm

It will explain WHY the inlet valve opens before TDC (top dead centre) and closes after BTC (bottom dead centre). It also explains why the opposite happens for exhaust.

The "cam timing" and "advertised duration" columns describe these characteristics of a camshaft.

22-63 means that the inlet valve opens 22degrees before TDC and closes 63deg after BDC. The advertised duration is therefore 22 + 180 + 63 = 265 degrees.

63-22 means that the exhaust valve opens 63degrees before BDC and closes 22deg after TDC. The advertised duration is therefore 63 + 180 + 22 = 265 degrees.

The lift is the total lift of the valve in "thousandths of an inch" at its peak.

You can make an entire career out of this stuff, so I don't claim to be an expert. I say that you should take these figures into a camshaft machine shop and ask them what they recommend for your goals

[kylestyleup]

18R already has hard valve seats. all toyota alloy heads do.
rocker arms? planning on roller rockers? that will allow you a more aggressive lift. but the more aggressive the lift, the stronger the springs have to be (or lower rev limit) to stop the valves bouncing.

My 18R has an iron head. Not sure if it do have hard seats.
So concave profile is complicated.

herewith my original plan on the cam.
I first got the idea from the word "mild" and convex egg shape

Option 1 - is to add lift
Option 2 - is to add lift but also I think is mild - convex
Option 3 - milder but staying to the original lift - convex

Thanks, now I just need to know/understand how to apply the info timbosaurus gave. Or machine shops already know..? But I still want to learn it though.

[timbosaurus]

Hi Kyle,

You are correct... 18R has an iron head. As I understand, iron heads can withstand unleaded fuels without hardened valve seats. It is the alloy (aluminium) heads, like the 18RG, that require hardened valve seats for unleaded fuels.

If you are looking for a path to follow, I would suggest that you find some larger valves and have the head machined to suit.

Install some heavier duty valve springs to allow higher lift and/or high rpm.

Research porting strategies and have a go at porting the heads yoursefl, or have a proffesional do it for you.

Have a cam ground to a profile that is proven... like the "stage 4" from camtechcams. This has the specs of 38-76 inlet, 76-38 exh, .325 inch lift with a 108degree lobe separation.

Have your bottom end balanced with high comp 11:1 pistons, if you can find them over there. Use high quality fasteners and pay careful attention to the clearances and lubrication system.

That should be a good start

[oldcorollas]

sorry my bad, i assumed that 18R was alloy head like most toys
if it has valve seat insets already, they will be "hard". if it just has the seats machined into the head with no insert (ala old holden/ford heads) then an insert will be better.

most shops that specialise in cam grinding will have a bit of an idea about the profiles, but not all shops are the same..

just having someone "machine it up for you" may not be as good as having a shop with years of experience with actual camshafts do it..
cams are cheap and having one sent OS to be ground, while not the cheapest strategy, is not that expensive.

as for applying the info, what you wan tto do is to work out the valve lift vs cam angle for the cams rotation. the lift cur ve should be smooth and not have bumps etc.. from this curve it is possible (but i don't know how) to calculate the chance of valve bounce, and spring harmonics etc....
all this will depend on the geometry of th ehead. ie, the arc of movement of the rockers with respct to cam and valve etc... you can model it, it just takes a bit of time.

[kylestyleup]

Thanks Tim...
I am gathering info and researching. I am aiming to be able to finish it all within the year.

Though I'll use a proven stage 3 or 4 profile, I will still do the concave cam.
I do believe there is something about that quick open/close (snapping behavior) on the intake valves.

[Joshstix]

I first got the idea from the word "mild" and convex egg shape

Are you saying that the word "mild" made you think that the shape was convex? I am not too sure if this is just a cross language issue. The term "mild cam" in English just means not too much bigger than standard. I have never heard of and never seen a cam with a convex ramp like you showed before.