ding56

I just give installing a new cam in my 68 289. I installed a comp xe256h and I also have performer intake, 600cfm Holley carb, long tube headers and exhaust. With the cam I replaced timing chain, lifters and springs. I just took the car for a drive and it seems like I took a big step back in performance and hooking someone can help me figure out why. I thought I had the car tunbed up and on the vacuum guage I'm holding steady at 23 at idle.

I don't know the engine history but was never told it was rebuilt. On the old can I found a UA marking and the specks I think I found on it are:

Duration : I 266 e 244
Lift: I 360 e 380

The new cam is

Durration: I 256 e 268
Lift: I 477 e 484.

Did I go backwards on performance out what could be wrong. I just use the car as a weekend cruiser. Any help would be great.

Tim

Gun Jam

Did you make sure the timing marks lined up on the timing chain (cam vs crank)?

Whats your ignition timing like base / advance / total and any vac advance?

23 inhg vac at idle is extremely high with that cam I cant imagine it being above 14. Is idle rpm like 4,000? is the vac gauge bad? that just doesn't add up.

check into those things and let us know what you find.

-Gun

ding56

The timing marks are all lined up when I put it back together. On idle rpms are around 800-1000 so not that high. The vac gauge was working fine before the swap. Not sure what my exact timing is now as the marks are to light. I timed out based on smooth idle and the highest steady vacuum reading.

Tim

Gun Jam

okay so the ignition timing is going to require a light...get that
you are probably running 30 deg initial with and additional 20 of advance for a total 50+ all in (just a guess)
-Gun

ding56

So you think it's under power cause the timing is off? How am I supposed to set the timing of I can't read the marks on the balancer? Over all should the new cam give me better performance than the old one so the issue is tuning and not just the cam?

Thanks

Tim

Gun Jam

well the duration is on average more and the lift is more...im not a huge expert on that but I would think it should not be noticeably less...I would think that it should provide more Hp than your old one...If you said it made only a slight noticeable improvement that could be expected but an obvious loss in power is not in my opinion...maybe someone can apply actual math to the issue and remove opinion from the equation but I dont have the ability to do that nor have you provided enough info for a real world HP estimate.

and yeah ignition timing is a BIG deal...testing it with a light is basically free compared to the alternative. If you tell us is 12 initial + 20 advance with no vac advance for 32 all in a 2500 rpm and that power is crap then we must go on to other things that get expensive or difficult like mechanical timing and cam degree...

BUT with that in mind.....is the firing order correct? your new cam may run a 351 firing order (you must check this) it is a 289 order or the 351????

Is it actually firing all 8 cylinders? use an IR temp gun and check header temps is one running way cold?

is it a roller cam? if not did you grind a lobe off and an intake valve isn't opening?

is there a bunch of metal in your oil?

-Gun

Gun Jam

Oh and to answer the timing question

the best method is to put a white line on the 0 mark and then get a timing light that allows you to set an advance number....for example lets say you want your initial timing a 12 deg advance. you would set the timing light to 12 deg and then rotate the distributor until the indicator was on the zero mark this is 12 deg advance.

Then you could rev the engine up and keep adding advance to the timing light until the indicator is on the zero mark and what ever the light read would be your total timing if the indicator is on zero and the timing light read 34...you are at 34 degrees total.

I have this one:
http://innova.com/en-US/Product/Detail/3568a

the tach is awesome because you know when full timing comes in and can be used for any other tac related uses (curb idle speed to idle mix adjustments) it allows you to set a timing advance as well.

hope this helps

-Gun

Starfury

I ran that cam for quite a while (until I wiped a lobe off). It's pretty aggressive for a 331, let alone a 289.

I'd bank on two problems:

1) Timing. As Gun-Jam has addressed, you need to get the timing right. This includes both base timing (@idle) and total mechanical advance. Setting the base timing for smooth idle is definitely not going to help this cam; it's going to lope, so let it. Set it at 12*. I believe the total timing should be 30-34* for this cam, but you may want to call Comp Cams to verify.

2) Gearing/torque converter stall speed. This cam needs to wind up to about 2800rpm before it really kicks in. If you have tall gears and/or a torque converter with a low stall rpm, the car is going to feel gutless at lower speeds.

As a side note, make absolutely sure you're feeding the engine oil with a high zinc content. The aggressive lobes on the XE series cams are very prone to shearing damage due to inadequate zinc levels in the oil. I recommend Valvoline VR-1 for a conventional oil, or Mobil 1 15W-50 for synthetic.

barnett468

the cam you put in is smaller than the one you removed and it will have more bottom end and not rev as far.

you need t reinstall your old cam if you want your old performance back.

if you want quicker acceleration and more top end, reinstall your old cam or one like it and install numerically higher gears.

you also may need to modify your distributor mechanical advance and plug your vacuum advance and run 10 degrees btdc and around 30 at 3000 rpm.
.

Gun Jam

that cam has 10 deg less intake duration and a 10th+ of an inch more lift and 24 deg more exhaust duration... how is it smaller? does the lift not outweigh the loss of duration?

-Gun