068 alone or -68+1.7 rockers? or ???

fredjchavez · 04-22-2008, 11:47 AM

Currently have factory cam (066 or 067...from what i gather, 350hp was 067) and was wondering how the 068 would work given that I have a/c, pb, and a 293 gears, 16 heads. My current cam idles nicely in gear at 650 (prolly will idle lower) and gives a hint of something there and hoping that a 068 would be more obvious but not kill my accessories or not require in gear idle more than 750-800!

I expect to loose a little bottom end response, but a little loss is ok because the bottom end is mostly unusable at this point (open rear and remaining so for the near term). I do not wanna have to deal with slow power brake response due to lower vacuum or stalling when a/c is running (although I do have an electric solenoid). I also wanna counter/mitigate pinging risk by going to a bigger cam. I have no plans to change heads or deck block to increase quench at this time. (I'm totally subscribed to the dynamic compression theory).

Another possibility is to install new rockers and be done which if I recall will give around 4 degrees more duration which is not a whole lot but may give me the edge I am looking for to run pump gas. Another possibility is both!

Any opinions?

05GTO · 04-22-2008, 05:45 PM

My 67 has a larger cam that was in the car when I purchased it last year, I have the problems you are speaking of regarding pinging that can't be removed with timing. When I'm in a parking lot at low speed the power brakes feel manual although they are 4 wheel disc.

I am considering changing the brake booster from ported to manifold vacuum to see if that will correct the braking problems and maybe install thicker head gaskets to lower the compression and hopefully correct the pinging.

I'm not sure which cam is in my car but it sounds good while driving through car shows.

Rukee · 04-22-2008, 06:57 PM

Why in the world would your booster be plumbed to ported vacuum?? Every one I`ve seen is plumbed into manifold vacuum, you need the brakes when your off the throttle, not on it !

05GTO · 04-22-2008, 07:26 PM

Both the 66 and 67 brake boosters are ported, neither have a vacuum inlet in the manifold other than the PVC valve.

I agree with your statement;

Rukee · 04-22-2008, 08:23 PM

That`s just crazy. The Tri-Power set up has a manifold plug. That would be the first thing I would do, T into that PCV or tap a new one in a carb spacer plate or something.

fredjchavez · 04-23-2008, 11:03 AM

I would advise not using thicker head gaskets to lower compression for most engines of this design (I'm no wise pontiac sage so I defer to those that are). As I understand, doing so reduces the quench area and if a thick enough gasket is used, this will result in a worse problem than before (counter intuitive but I've experienced this ). Sufficient quench is required for good combustion and creates turbulence which basically causes a swirl and cools hot spots which is a good thing.

Cutting/milling piston tops while also lowering static compression, creates a similar situation and I too have experienced this!

So, I plan on obtaining static compression and going from there. There are calculators out there that estimate dynamic compression and so I'm gonna plug in cam intake time to get me to about 170 based on recent reading/research.

Thanks for the input/comments!

geeteeohguy · 05-05-2008, 02:59 PM

I've run an 068 cam in my '67 for about 15 years. Idles just as good as the 067 cam, has more power, better fuel mileage, and no loss in lower end performance. My car has an automatic and power brakes. It pulls about 20 inches of vacuum at idle. I'm running stock 1.5 rockers and 9.2 compression (87cc heads). It's not the screamer my '65 tri-power is, but it runs very well and gets 16mpg on the hiway at 70mph. the only thing negativ I have to say about the 068 cam is that you may be disappointed that it is not "radical" enough. (Smooth idle, etc.). For the money, and for 99% of driving conditions, it does fine. The 744 ram air 4 cam is much hotter, but has noticable low end power loss, rough idle, and poor drivability at "normal" speeds. Hope this helps!
Jeff

Eric Animal · 05-09-2008, 08:49 PM

Fred, Leave it as it is.......

Eric