To advance the cam or not to advance the cam, that is the question.

[TheSilverBuick]

On my Skylark I'm trying to think of changes to make to it with out actually having to do any major lifting. I'm real happy how the car runs right now, but it seems like at 6,000 rpm it's still pulling for more and with the fact I've left the bottom essentially stock I'm thinking of getting an adjustable timing set and advancing the cam. Here is the rub though, do to the rush of getting ready for Drag Week and not having an adjustable timing gear even if I did find it off I didn't degree it when I popped it in.

So one, I need to degree it first anyways, so if I find it advanced 4* already I'll look at taking it up to 6*, if it's straight up I'll take it to 4*. Does that sound reasonable or should I leave it alone?

Second part is I want to chassis dyno it at some point this year. Do to where I live I'd kinda like to only do it once, so should I do it before moving it and expect the power curve to simply move downwards, or should I advance the cam first and if it noses over on the dyno simply move the cam timing back? Or am I simply stuck dynoing a before and after (remembering its easy to spend other peoples money).

I'm not sure there would be a down side to advancing the cam from where it sits now. It makes power above the rpm I'm willing to turn it and it can run on 87 octane now so if the DCR goes up I may have to run a higher grade gas, and as long as it's 91 or lower I'm okay with that too. Is there a downside I'm not aware of?

[A/Fuel]

You could take a before and after compression test and post those numbers up so we can see what they are.

[Barry Donovan]

I had this question too..
if to need to think of advancing, retarding..
duration is not enough.

I did play with pointy cams in a boxer engine, each cam on just two cylinders...so simple my eyeballs made a decision.

I got mad, either way has a something annoying.

increasing duration (that does not mean overlap), or better defining a more robust path of the curve (round versus pointy), that finally made me happy. Lift was not even a factor.

[TheSilverBuick]

You could take a before and after compression test and post those numbers up so we can see what they are.

That isn't a bad idea. I haven't done a compression test on this engine since the new pistons, thin rings, aluminum heads and roller cam went on it.

[JeffMcKC]

Yeah they have a good chamber so I would try to stay under or around 205 lbs of comp. Comp does not start till the intake valve closes so duration is everything. Lift is power. Its a manual so you have to watch the lugging if you get the comp up to much. I advance the heck out of stuff watching piston to valve along the way

[TheSilverBuick]

I have deep valve relief's in the pistons. I do cruise around ~2200rpm in overdrive, so lugging is a concern. My old set up would ping on hot days with 91 in the tank, this set up seems happy with 87, though I haven't ran it on a truely hot day, and it only had around 145psi if I recall (at 6500ft elevation, 85kPa atmospheric pressure) and now my static compression is about .7-.8 more. So now I am curious to see what it's sitting at.

If my pipemax settings are right and depending how it calculates it, if the cam is straight up it's estimating 159.3psi, at 4* advance 164.6psi, 6* advance 167.3psi.

Review of cam spec's

Hydraulic Roller with a 4-7 swap -Probably the smallest roller cam TA has made
VALVE LIFT
STOCK 1.55 RATIO:
IN: .512”
EXH: .512”
DURATION
AT .050
IN: 232
EXH: 232
ADVERTISED
IN: 298
EXH: 298
LOBE CENTER: 110

[TC]

Advancing or retarding the cam is just going to move your power range around in the rpm range.......If you don't feel you have enough low end then advance the cam, but realize by doing this you will sacrifice top end power, the opposite goes for Retarding the cam you'll lose low end power to gain power up top........You might find a small gain in doing it, but to really do it right, I'd suggest installing a Belt Drive, where changing the cam timing is a snap............

[TheSilverBuick]

Advancing or retarding the cam is just going to move your power range around in the rpm range.......If you don't feel you have enough low end then advance the cam, but realize by doing this you will sacrifice top end power, the opposite goes for Retarding the cam you'll lose low end power to gain power up top........You might find a small gain in doing it, but to really do it right, I'd suggest installing a Belt Drive, where changing the cam timing is a snap............

Yeah, belt drives and Buick's don't work well together... Plus as my first post says, the power band seems to go well and above where I want to rev the engine, so that is part of the reasoning for looking at advancing the cam.

[CDMBill]

Unless there is an easy wasy to access the cam gear with most of the front dress in place I odn't see how making a blind cam timing change helps the cause. While the engine is newish its a good idea to do a cranking compression test to see where you are and if the tool is available I'd run a leak down on it as well so you'll have a baseline.

Did you get enough runs to s determine the optimum shift RPM? Many engines will rev well past the power peak but ET's will actually suffer. I always found the John Ligenfleter guideline of making max torque at the shift recovery point to be a good starting point for street cars. Your datalogs will tell you that bit of information. The cranking compression wil give you some feedback on the cam timing by backing into it from your PipeMax calcs.

By any chance did you index your timing pointer to actual TDC on the balancer? if so you can do a post install check of where your Intake events are actually occuring with a dial indicator and one of those stick on timing tapes. or make one. You could do that in your sleep. If you didn't index your dampener and pointer you can do that after the fact too with piston stop. I've got one I could send you if one isn't handy there.

With all that information you can decide if advancing the cam is warranted and then maximize the use of your chassis dyno time. Always be sure to fully plan your dyno time so you have your tuning priorties set and as many contingencies covered or anticipated as possible. Arrive with all sub systems as solid as you can make them: fresh plugs, full tank of good gas and clean filters, your drag radials mounted and balanced, a clear idea of where the tie down straps should go, a spare AFR bung on each side for the chassis dyno system ( so you can calibrate yours vs theirs); all tools and parts you need to change what ever you anticipate changing and finally spares like fuses, relays and anything else that is really peculiar to your car.

[TheSilverBuick]

With all that information you can decide if advancing the cam is warranted and then maximize the use of your chassis dyno time. Always be sure to fully plan your dyno time so you have your tuning priorties set and as many contingencies covered or anticipated as possible. Arrive with all sub systems as solid as you can make them: fresh plugs, full tank of good gas and clean filters, your drag radials mounted and balanced, a clear idea of where the tie down straps should go, a spare AFR bung on each side for the chassis dyno system ( so you can calibrate yours vs theirs); all tools and parts you need to change what ever you anticipate changing and finally spares like fuses, relays and anything else that is really peculiar to your car.

That's good info Bill, I wouldn't of thought to install a couple O2 bungs for the dyno, but would be simple enough, nor did I think about bringing the drag radials. All the run time on my car, the sub systems "should" be pretty solid and reliable. You've given me some things to think about for sure.

The timing cover is a PITA to remove but I could "probably" advance the cam and get it back together in an hour. That's draining the coolant, pulling the hoses, distributor (crank trigger now!), balancer and timing cover. I can almost pull the engine and trans quicker =P

[JeffMcKC]

I would advance it. N/A the best way to improve ET is in the slow part of the track. TC once again your simplistic Magazine approach leave a lot on the table.

Randle if you want to get serious with your pipe max, then you can figure the lobe of the cam, against the CFM demand for cylinder fill, remember where the valve is in relationship to the piston and reversion going on in the cylinder......... this is better done when getting a cam than now but I would advance it if it does not make the cylinder pressure to high to deal with.

[dieselgeek]

Advancing or retarding the cam is just going to move your power range around in the rpm range.......If you don't feel you have enough low end then advance the cam, but realize by doing this you will sacrifice top end power, the opposite goes for Retarding the cam you'll lose low end power to gain power up top........You might find a small gain in doing it, but to really do it right, I'd suggest installing a Belt Drive, where changing the cam timing is a snap............

Magazines say that, but it's nowhere near factual. I can think of three different domestic v8 N/A engines I tuned recently on an engine dyno where we moved the cam around, and each time the change was almost undetectable. In all cases the engines were well-sorted cominations with large flat powerbands... so maybe that's why it didn't shift things around much. Anyways, the point is, magazine articles are full of crap 60% of the time.

[JeffMcKC]

Lash looping is a good idea before you tear it down to see what you need if you have not already dis joined the parts yet. LOL

[CDMBill]

Randall do you have a solid roller or hydraulic?

[TheSilverBuick]

Hydraulic roller and non-adjustable valve train (shaft mounted, stock rockers).