My new CC 503 cam is supposed to be 108. I have measured it a dozen times and it comes out at 110. Will that be a problem?

Eddie

 

racers move the cam as little as 1* to tune (we have 'belt' drives that make this ez)...'dumb thumb' rule is your butt won't notice less than a 4* change...normal timing chain wear will retard your cam, first few miles are the fastest retard till all bits 'seat'...for street 106* will probly run better...your car will drive at 116* (typ oem emissions set-up)

 

Yes it will be a problem.

It's only 2 degrees, but Retarding a camshaft Intake Centerline lowers cyl pressure and bias' the powerband higher up in the RPM range. Also the Intake Centerline retards itself when the engine is running by approx 2-4 degrees depending on how much slack is in the timing chain/belt and how much valve spring you run. This only gets worse as the timing chain and gears wear.

Buy a bushing kit - If you can't get it to degree in close using the multiple keyways on the crank sprocket (or if you have a stock timing set with only 1 keyway).

http://www.summitracing.com/parts/CCA-4760/

Will

 

I didn't change the timing set as it still seemed pretty tight. It has the LT4 single chain that comes stock.

I assume that you drill out the cam sprocket and use the bushings to advance or retard the cam? How do you do that on an LTX with the opti dowel?

Is 110 retarded versus 108?

 

Guess I will call Comp Monday and see what they say.

 

Yes. First you drill out the 3 camshaft bolt holes (to allow for movement). Second you drill out the dowl pin hole (from the rear of the gear) - but not all the way thru. You drill just deep enough for the bushing to fit flush on the back side of the gear leaving a small ledge on the front of the gear to retain the bushing.

It won't affect the opti being driven off the dowl pin one bit.

Yes 110 is 2 degrees retarded. The higher the number from 108 the further the camshaft is retarded. The lower the number from 108 the more advanced the cam is.
Will

 

Actually with the CC 503 (XR276HR-12) The LSA is 112 and the ICL is 108. That means that the cam is installed 4 degrees advanced with those settings.

Will being installed at 110 really make enough diff to justify the bushings?

Is the discrepancy due to an error on CC's part or stretch in my timing set? I believe stretch will retard the cam timing. Yes/No?

What is the effect in degrees in advancing one tooth on the crank gear?

Eddie

 

Right.

Most cam grinders like to grind 4* advance for the ICA and want it installed there due to the cam retarding when the engine is actually running. Is 2* enough to warrant all the work with the bushings? For me that is too much variance from the mfgr's recommended installed ICL angle. I do everything in my power to get a cam installed where I want it but on lower class engines if I can get it within .5*+- without using the bushings - I honestly let it go at .5*+-.

The discrepancy is mostly due to "tollerance stack".

1. Error from when the cam mfg ground the cam

2. Error from when the timing set mfg machined the timing set

3. Any slack in the timing chain

4. Error from when the keyway was cut in the crank snout

I see it all the time - Even with brand new timing chains and cams. Usually with top quality parts it adds up to about .5* to 1*, but I've occasionally seen worse than yours.

Moving one tooth would be way too far. I think about 15* or 20* change.
Will

 

Some Engine Builders advance most Cams 2 or 3* on a new build, to compensate for the Chain Stretch.

 

Looks like I will be buying a bushing set.

At least I learned something. I haven't installed a lot of cams and this is the first time I have seen this.

Eddie

 

Run a simulation with the two Intake Center Line angles if you can.

You may find that 110 is preferable over 108. Considering that this is an LT4 and that the 503 is a relatively small cam to begin with, you may benefit on the top end with 2 degrees less advance.

Try and get some input from other cammed LT4s as to what works best.

 

Just got done with my hot cam, it measured up at 109.5° which was okay. It's suppose to be 109°. .5° makes the dynamic compression ration lower by .3 in this case. The Pat Kelley calc works well. I would not choose to install it at 110° unless you want lower dynamic compression!

 

I don't understand this thread. I posted yesterday, then removed it since Will is more experienced. (But today, I'm overcome by blind stupidity! LOL)

My approach would have been the same as above. With my build, there was evidence that retarding my cam (to 112) would have produced a better result in terms of HP.*** A simulation shows it would produce more power up top (as indicated by Will biasing of top-end power). Since it was also apparent (during my last 2yrs in C4Tech) that damn near everyone would prefer more top-end, I would question how an 108ICL became so darn important! Stronger motors build more cylinder pressure anyway and MOST people would say getting more isn't nearly as important as making power! It's how you boost HP numbers for cryin' out loud!

So, why get all bent out of shape by a 2-degree issue like this? More importantly, if it's a big deal, why not buy a new timing set, install in the 4-degree adv slot and wait for the instant 2-degree stretch? Voila! You're back at 108! (BTW,,,I hope that 2-degree stretch applies to a double-roller chain as well. If so, I'll get an exact compromise of the 108 vs 112 simulations I was looking at!

So, I'm actually happy that I could end up with a 110ICL. By contrast, it's a big problem in this thread! I just don't get it......


***Footnote: L98's come with the factory cam installed at 112ICL. I know we're talking LT1 here, but we're also talking about generalities of installation.

Also, to this cylinder pressure thing. Anyone wonder how retarding a cam can make more power up top? Seems pret-ty ODD if static cylinder pressure were the ONLY consideration!

 

FWIW,,, the simulation for my build showed a 4-degree alteration in cam orientation shifting ~10hp/tq from lower rpms to upper rpms. From that, I'd estimate a 5hp/tq alteration. And, somewhere around 4k rpms would be the pivot point of that shift.

As RedRose pointed out, I'd bet the change would be impossible to feel. If this is for track times, wouldn't launch technique have more of an effect?

 

not at all...LSA is only the relationship of the exhaust-to-intake lobe centers...if you put the cam in upside down the LSA would still be 112...the ICL is the relative position of the intake lobe with PISTON position (usually TDC).

actually, where you put the cam is only anybody's guess until you drive the car and determine if you want more low end , more top end, or maybe the engine peak power is right where YOU want it for YOUR pruposes.

btw, we move cam timing for track condition/temp/etc between heats and feature, as do all the other competitive teams...and altho i won't share speed secrets that belong to others as much as to me, i will say that it's more than a couple degreees.

 

it's quite logical, actually, but cyl pressure isn't a major player...as you already know (hopefully) air is compressible AND has mass...mass means inertia...sit back and contemplate (me too lazy to type all which you can do in your own gray pile) what happens in the intake tract (and exhaust) based on inertia/compressibility when the door (valve) opens at varying engine speeds and you will realize why retarding the cam helps top end.

btw, when discussing retarding vs advancing, be sure to be 'on page' with your respondent, some 'big heads' talk in terms of advancing/retarding the ENGINE relative to the cam (opposite what is common in 'hot rod' circles).

 

To further muddy the waters, I just read on another website devoted to the LT1 that stated that advance and retard must be built into the cam because of the dowel pin driving the opti. That using the bushings would alter the timing.

I will talk to Comp tomorrow before I do anything. What I have now would be advanced 2 deg from straight up.

How do you run these simulations.

Eddie

 

Eddie,
Ther are offset keys available for the crank also.
That may be a simple way to solve your problem without altering the cam sprocket.

 

Seems to me that the effect would be the same regardless of where you make the adjustment. I am leaning toward leaving it alone. As someone said, the CC 503 is not a large cam and is 2 deg advanced as it sits with a 112 LSA and 110 ICL.

 

He bought the cam to have power where he wants it. If he's forced to install it in a way to shift that power into the upper RPM, he may not want to do that.