Cam regrind , need suggestions ?

[ET2]

your right roach its dynamic not static the point I was trying to make is matching the right cam to your engine quote A mild cam with an early intake valve closing point will work well at low RPM. But at high RPM the intake valve will close before the maximum amount of air/fuel mixture has been drawn into the cylinder. As a result performance at high RPM will suffer. If a high static compression ratio is used with a mild cam (i.e. and early intake valve closing point) then the mixture may end up being "over-compressed". This will lead to excessive compression losses, detonation and could even lead to head gasket or piston failure.

On the other hand, an aggressive cam with a late intake valve closing point will work well at high RPM. But at low RPM the intake valve will close too late for sufficient compression of the intake charge to occur. As a result torque and performance will suffer. If a low static compression ratio is used with an aggressive cam (i.e. a late intake valve closing point) then the mixture may end up being "under-compressed". Thus a high performance cam with long duration should ideally be combined with a higher static compression ratio. That way the engine can benefit at high RPM from the maximized amount of intake charge afforded by the late intake valve closing, and still achieve sufficient compression of the mixture as a by-product of the dynamic compression ratio.

[riced_roach]

Its all about give and take. A mild cam will have more static compression than a larger duration cam but there is no such thing as "over compressed". Yes since the overlap in a mild cam is smaller you'll get good low end performance but the problem is that in the higher rpms you'll close the exhaust port too soon and the intake isn't open long enough to take advantage of the momentum of the a/f charge. So basically you'll have great volumetric efficiency at low rpms but crap at the top.

You can have a high static compression with an extremely large cam since the large cam will "bleed" the compression at low rpms. BUT you'll have alot of negative reversion of the air fuel charge since the intake valve is open longer and the piston at bottom dead center (BDC) will start to travel upwards while the intake valve is still open.

people always talk about duration but advertised duration is meaningless. You want to know what the duration is at .050. This is where actual effective flow happens (theoretically) advertised is at the absolute beggining of the ramp where the valve hasn't even opened yet.

[skull1441]

what is meant by reground cam ?? ... is it something u do to the cam or is it a stock cam replacement ooor woot????

[k-roy]

Its when you take a stock camshaft and have the lobes reshaped.
This is the only option for us since there are no aftermarket camshafts available for the A20.

[racerx]

there are 2 things involved when regrinding:

1. raising the lift of the lobe. This means letting your valves open wider, thus allowing more air in/out.

2. increasing the duration of the lobe. This means (obviously) giving the valve more time to be open, and consequently allowing more air in/out.

if you want, I have a cam for sale now (click on link in sig) and you can see a picture of the cam and its lobes.

[skull1441]

ok thnx .........

[riced_roach]

Pray the the company that does the regrind hardens it well after the process. Too big a duration is meaningless unless the intake port cannot accomidate more cfm. Otherwise negative reversion will be more apparent while gaining minimal benefit from a larger duration cam that wont flow alot more due to head port limitations.

As far as cam lift is concerned I am not certain a regrind will add material to the stock camshaft to achieve higher cam lift. I was always under the impression that a regrind only increase duration and NOT cam lift.

[k-roy]

As far as cam lift is concerned I am not certain a regrind will add material to the stock camshaft to achieve higher cam lift. I was always under the impression that a regrind only increase duration and NOT cam lift.

Thats exactly what I was thinking. How exactly can you reliably add lift? You would need to add material to the lobes, I don't think you can do that and have it last for long.

[ET2]

I asked the same question when I ordered my cam from delta and they told me they dont add anything to the cam, imagine looking at the end of the cam shaft and say the diameter is 1 inch with out the lobe's and they grind down the size of the diameter to 3/4 inch with out removing material from the lobe's so now the cam has 1/4 inch more lift, hope that make's sense

[Robs89LXi]

I still don't understand that though. Reducing the radius of the cam journals would necessitate using "thicker" cam bearings to make up the difference, thus negating the raising of the cam. Seems the only way to increase lift would be to:
a) add material to the lobes- don't think I like that idea, or
b) raising the cam in the cam towers, thus bringing the cam closer to the rockers (lift).
I guess this could be done by building up the bottom half of the cam tower, and machining out the top half (bearing caps). By doing this, you could retain the original bearings, and would not need to reduce the journal radius. Can someone find out for sure from one of the reputable cam builders?

[riced_roach]

I asked the same question when I ordered my cam from delta and they told me they dont add anything to the cam, imagine looking at the end of the cam shaft and say the diameter is 1 inch with out the lobe's and they grind down the size of the diameter to 3/4 inch with out removing material from the lobe's so now the cam has 1/4 inch more lift, hope that make's sense

1/4 inch more cam lift sound like BS to me. Look at the cam profile sheet that shoud have come with the cam. try to get a spec sheet on the stock cam profile. it'd be interesting to see what duration they get supposedly.

[ACE_14]

[ACE_14]

If you grind it down, doesn't it loose it's surface. With less surface to lift the lifters, won't it be less of a lift. I'm confused.

[A20A1]

to a point yes... but I think they grind the entire lobe smaller and then use the valve lash adjustment to take up the slack, so it almost acts as if you just added a different cam instead of grinding in one spot and losing lift in that area. I'm not sure if valve timing is thrown off any... you can always get a new cam or get a hard weld.

I wonder if lowering the rocker arm assembly some would make up for the decrease in the lobe material?

[ACE_14]

Where can i get a naw cam? What exactly does hard welding do?

[smufguy]

i think it does change the valve timing, Not only the duration of the lift is increased, but also the valve lash time is longer too. But i am not sure about them.

U can get regrind from crane, crower and some other companies like Delta and such.

[Gregg86DX]

A simple way to imagine a re-grind is just think about taking material off of the back side of the lobe (base circle). Then you have to reset the valve lash and the net effect is more lift (and possibly duration)

[ACE_14]

The change in valve timming, is this a good thing or bad? And would i need an ajustable camgear?

[ACE_14]

Who does the best "Reginds"? Would i need to modify anything else if i got one?

[smufguy]

The change in valve timming, is this a good thing or bad? And would i need an ajustable camgear?

it could be considered good for ur performance, bad for your emissions. But an adjustable cam gear would boost ur performance even more, and when tiem comes to go to inspection, it would save ur butt too.

[300700'88lx-i]

On single cam engines like ours, an adjustable cam gear mostly allows for moving the power band. You can change it to favor the low end, or move the power band up more towards the top end, but on SOHC engines, an adjustable cam gear doesn't really allow for one to "build" on the power band. I'm also not sure how much it would help with emmisions inspections, you might be able to adjust it to a point where it would lower emmisions, but it would be a long process of trial and error. Actually, in Cali, you can't pass smog inspection with an adjustable cam gear unless it's set to zero degrees. They won't let it pass the visual inspection.

[smufguy]

Its not only to move the power band, its also has the ability ot use EVC (early valve closing) to improve volumetric efficiency, Its more of a manual v-tech u could say. Thats why the moving the power band is named as such. Having the intake valves stay open for a longer time, gives u more power at the top end, and having them close early, gives u more power at the lower end of the band. also matched with a reground cam, u can do some serious magic with it.

[ACE_14]

I'm kind of a dumbass when it comes to these things, negative degrees on the cam, would it give me low end or top end power? Does anything else need to be done when I get my regrind?

[smufguy]

I'm kind of a dumbass when it comes to these things, negative degrees on the cam, would it give me low end or top end power? Does anything else need to be done when I get my regrind?

I think negative degrees, makes the valves (intake valves) close early, which then would boost ur low end.

If the negative degrees makes the intake valves close late, then it boosts ur high end.

When u get ur regrind, its best to get a cam gear too. But its not needed. Changing your timing belt would be a best bed if u have to change it or wanna. Besides that its all good. I woudl say inspect all ur springs and rockers and see if they are all good and go on from there. nothing major has to be done to em, but always adjusting the valves and the lifters are always a good thing to do while u got the cam off.

[ACE_14]

Still looking for the best way to go. Let me know What kind of Cams you guys use, so that I can get a better idea. Also, do you use a Camgears? How many degrees is it set at?