SOHC Cam Sprocket Advance or Retard?

[Frostbyte]

Ivymike might be able to answer this. Would it be better the Advance the cam Sprocket on a SOHC VTEC or would be better the Retard it for All Motor and F/I?

[ivymike1031]

I might be able to give you the wrong answer too (I'll try not to, but I always get this backwards for some reason - perhaps I'm lesdyxic - so somebody please confirm or refute)...

In general, advancing the cam timing (on a SOHC engine) lowers the speeds at which peak torque and peak power occur. Conversely, retarding the cam timing increases these speeds.

(N/A) Since we're talking about a Honda, I assume you'd like to get more power (@ a higher rpm), so retarding the cam timing by a little bit is probably the way for you to go.

(F/I) For forced induction, I would guess that the opposite is the case. My thinking is that you'd want to close the intake valve sooner, to prevent excessive blow-through. Better to get a cam designed for use w/ turbo instead, imho.

[Frostbyte]

Thanks Mike I am going to do a little more research on this but I am going to print out your post and I am going to confirm that for you. I have a Unorthodox Full Race Cam Sprocket on it's way out.

[ivymike1031]

well you'll have a printout of at least one mistake then...

correction for F/I: since the overlap is fixed, I don't think that you'll be able to significantly affect blow-though by changing the valve timing. I'm not sure which way would be the best way to go (I still think that a low-overlap cam would be the right thing to do).

[Tofuboy]

sorry to bug in, but I think if you get a higher cam loop cam and advance the timing a bit on the F/I SOHC motor will help on the "blow-though" and minimumize on the HC emission level which can also give you a better gas milage.

[Frostbyte]

I don't care about the fuel milage. For now I am going to be running N/A but I will be getting a turbo and running on my stock cam with a Adj Cam Sprocket.

[Tofuboy]

a higher cam loop cam and advance the timing a bit on the F/I SOHC motor will help on the "blow-though" and minimumize on the HC emission level which can also give you a better gas milage.

Also it should help you to run the motor at a lower temperture

[ivymike1031]

forgive my ignorance, but what's a "higher cam loop cam?"

[Tofuboy]

what's a "higher cam loop cam?"

Sorry for the bad spelling, what I ment was a higher cam lobe. It is usually called "fast cam", and commonly used in race cars which are running in high RPM rage. The cam lobe actually will lift the rocker arms higher and open the valves more to allow more A/F mixture to enter and exhaust gas to exit the engine.

[ivymike1031]

well if that's what you meant, then I'm going to have to disagree with your statement that it will help to reduce blow-though. If you maintain the same lift periods and overlap, but increase lift, you'll very likely make blow-through worse.

I'd support going with higher-lift cams on a turbocharged engine (it will still help breathing). The concern I had was with the charge going in the intake and straight out the exhaust during overlap, and it seems to me that the best way to prevent that would be to reduce the overlap. The stock cam probably doesn't have much overlap anyway, so it's not necessarily going to be a problem. Using a "racing" or "fast" cam designed for a naturally aspirated engine seems like a sure way to cause trouble on a turbocharged engine - those cams generally have more overlap than the stock cam, and would waste a bit more charge as a result (not to mention potential probs w/ cat, etc., if so equipped).

[Tofuboy]

well if that's what you meant, then I'm going to have to disagree with your statement that it will help to reduce blow-though. If you maintain the same lift periods and overlap, but increase lift, you'll very likely make blow-through worse.

What I meant by it will help on "blow-through" has to do with the RPM speed, SOHC and for racing purpose.

During high engine speed (racing), the valves will have less overlap time, due to this the exhaust gas will not have enough time to escape through the exhaust valve since air does not move as fast as the mechanical action of the valves during high speed. This will result in exhaust gas remaining in the cylinder during compression stroke, therefore reducing HP output.

Even though a F/I system will help forcing the exhaust gas out of the cylinder before the exhaust valve closes, but the valve opening area that allow the fresh A/F mixture to enter and the opening that lets the exhaust gas to exit are still restricted by the stock cam lobe, especially during high RPM and SHOOK.

By installing a "fast cam", it will help the F/I system further to reduce the possibility of exhaust gas being trap inside the cylinder at high RPM during compression stroke. And by advancing the timing correctly, it will reduce the problem you have concern about the charge being going in and straight out of the exhaust manifold. Also by doing the above, the engine should run in the coolest temperature possible while putting out the highest HP possible.

I do agree with you that by doing this will waste some fuel and require a high quality exhaust system as back fire and flames coming out of the exhaust tip will occur (not to mention you will need a stronger bottom end).

This is what my philosophy on this topic, but please feel free to discuss or correct me if anyone has a different point of view (this is what this forum is for):smoker2:

[ivymike1031]

Originally posted by Tofuboy
[b]

What I meant by it will help on "blow-through" has to do with the RPM speed, SOHC and for racing purpose.

During high engine speed (racing), the valves will have less overlap time, due to this the exhaust gas will not have enough time to escape through the exhaust valve since air does not move as fast as the mechanical action of the valves during high speed. This will result in exhaust gas remaining in the cylinder during compression stroke, therefore reducing HP output.

Perhaps it would help if I explain what I mean when I use various terms:

Overlap: the amount of time (usually measured in degrees of crankshaft rotation) when the intake and exhaust valves are both open

Blow-through: A condition in which intake charge passes straight through the cylinder and out the exhaust valve without being burned (happens during overlap).

Valve Lift: The valve height above the valve seat (how far the valve is open)

Duration: the amount of time (in degrees of crankshaft rotation) that a valve is open. A similar number is often quoted in cam ads, that is the duration @ a given height, and refers to the amount of time (in crank degrees) from when the lifter reaches a certain height above the cam base circle 'til when it reaches that height again.

Now back to what you were saying - yes, with a given overlap in degrees, the higher the rpm, the lower the amount of time during which overlap occurs. Two cams with the same overlap, in degrees, will have the same overlap, in seconds, at every rpm..

Even though a F/I system will help forcing the exhaust gas out of the cylinder before the exhaust valve closes, but the valve opening area that allow the fresh A/F mixture to enter and the opening that lets the exhaust gas to exit are still restricted by the stock cam lobe, especially during high RPM and SHOOK.

By installing a "fast cam", it will help the F/I system further to reduce the possibility of exhaust gas being trap inside the cylinder at high RPM during compression stroke.

Yes, that's why I think that increasing lift would be a good way to increase power. BTW, what's "SHOOK?"

And by advancing the timing correctly, it will reduce the problem you have concern about the charge being going in and straight out of the exhaust manifold.

If you keep the same overlap, I'm not sure that you'll really accomplish this on a f/i engine. It definitely works that way at high rpm on a n/a engine, but it seems to me like you won't see nearly the same improvement on a f/i car.

Also by doing the above, the engine should run in the coolest temperature possible while putting out the highest HP possible.

I don't have any idea whether that's (approximately) correct or not, but I usually try to steer clear of blanket statements like "the highest possible" because they're almost guaranteed to be wrong.

I do agree with you that by doing this will waste some fuel and require a high quality exhaust system as back fire and flames coming out of the exhaust tip will occur (not to mention you will need a stronger bottom end).

If you're replacing the stock cam when you add f/i, why not replace it with a cam designed for use with a turbo, instead of one designed for high speed n/a operation? Makes more sense to me to use lift profiles & duration for f/i when you use f/i, instead of trying to adapt a n/a cam for f/i use by tweaking the timing.

[Tofuboy]

BTW, what's "SHOOK?"

It's a stupid mistake from the spell check. What I meant was SOHC not SHOOK.

If you keep the same overlap, I'm not sure that you'll really accomplish this on a f/i engine. It definitely works that way at high rpm on a n/a engine, but it seems to me like you won't see nearly the same improvement on a f/i car.

Yes, I agree that the result won't be as good as the NA set up, but it will help the F/I a little and that's why I mention that it will help save some gas mileage and reduce the problem but no eliminate it.

Also by doing the above, the engine should run in the coolest temperature possible while putting out the highest HP possible.

It's almost the same theory as eliminating the EGR system by cooling down the engine temp with more fuel. Also it will increase HP output.

If you're replacing the stock cam when you add f/i, why not replace it with a cam designed for use with a turbo, instead of one designed for high speed n/a operation? Makes more sense to me to use lift profiles & duration for f/i when you use f/i, instead of trying to adapt a n/a cam for f/i use by tweaking the timing.

The reason I said to have this set up is because I thought Frostbyte wanted to have a NA set up first and then add a F/I system later on down the road. Also for some reason I thought Frostbyte had order the cam already instead of the cam gear. My bad.

[Frostbyte]

I was reading the paper that came with my Cam Sprocket and it say retard the timing -3 to add high end horse power
Advance the timing +3 to add low end horse power.
I figured since the pulley is going to help me a lot on the lower end rpm range then I am going to retard the timing to add to the high end horse power. What do you think?

[A20A1]

My current N/A racing camshaft... nuff said

- COLT CAMS, Custom reground cam
-- (280° Duration / .392 Lift / .008 Clearance / Intake)
-- (288° Duration / .394 Lift / .010 Clearance / Exhaust)
-- (4,000 to 7,500 rpm power band)