First79vette

How much duration can I go before you start having severe vacume problems? I would like to go with about a 280 + or - a little. Comp Cams tech guy told me I should not go above a 262 duration or I will start to lose vacume signal...sure would not want to lose my headlights, I've heard of that happening! :crazy: :eek:

LiveandLetDrive

280? Is this engine otherwise stock? I have a 268 and vacuum might be a little worse, but not noticably, especially not with headlights that don't work anyway!

Very much more information is needed. How do you plan to drive the car? What have you changed already? If you haven't changed anything, cam is not the first place to go. Exhaust is where you should start, change to duals, no cats if emissions laws allow, and some freeflowing mufflers. Then intake, cam, heads, gears, trans, and at that point, you can start replacing everything you start breaking :lol: Don't forget to think ahead to further mods (don't restrict yourself to a part that will have to be replaced with a higher performance one in the near future if possible) but also don't look so far ahead that you ruin the balance of your current setup. A 280 would obliterate that balance on a stock engine. Oh yeh, and rip out all that emissions crap!!

-Chris

Glensgages

I would think that duration @ .050" lift, not the 'advertised duration', would be key...
:confused:
For example, the CC 292H I had in my Z28 was 'only' 244* @ .050" lift...
Might a vacuum reservoir help-out? I ran the above cam on the street (altho primarily to/from the strip) for a few years, until I got a truck & trailer, with little problem; it even 'held' the car on the line @ 4000RPM launches...

Just my $.02 worth...

page62

I'm with RUXperienced. It's the whole system, of which the cam is but one component. They all gotta work in harmony. So give us the big picture... :yesnod:

Glensgages

:iagree:
Thanks, page62:
I didn't mean to imply that duration, whether 'advertised', or '@ .050"-lift', was the key;
just trying to clarify CompCams' recommendation.
:thumbs:

First79vette

Ok sorry guys, been a while since I've been on here, Yes i'm in a teardown of the whole thing. It had a .30 over bore when I bought it not sure of the cam thats in there now, but the kid put everything that I can see back in stock, no noticable lope now. I am tearing all that emissions crap off now going to put a Torker 2 on, headers and a holley or Edelbrock carb on with a dual chambered exhaust. (cats are coming off :jester ) Whats the answer now? :D Thanks!

Smokehouse69

I wouldn't go bigger than the XE262 Comp, even then you'll need to replace your valve springs. You didn't say if your car is an automatic or a 4 speed, if it's an automatic then if you go with a really high lift cam, you'll need a high stall torque convertor, otherwise you'll never get the car going. The best performance for a street driven car with a stock rear end is acheived with a cam that accentuates the low and mid-range torque of the engine. A high lift long duration cam will make most hp and torque at higher rpms than you'll typically find in most normal driving.
So unless you are planning on spending a lot of time at the drag strip or running all out, you'd be better off with a smaller cam. Talk to the Comp guys, if you're lucky, you'll get someone who knows what he's talking about. Remember your engine is a low compression engine with smog heads on it, you'll want a cam that will increase your dynamic compression, without a lot of overlap. Good Luck! :thumbs:


[Modified by Smokehouse69, 9:52 PM 3/6/2004]

First79vette

Thats what the tech guy at comp cams told me, a 262 with about 480 something in lift...I dont think I have to replace the springs with that lift but I'll ask the comp guys..It has I think it is a 3:78?? rearend I know at 55 Its turning 2800 rpm and its a 3 speed auto. Definitly going with headers, the stock logs....are off now :lol: Thanks! any thoughts on Cranes? I put one in my truck many years ago and was a nice one. Seem to be cheaper than the Comps. :D

Glensgages

Boy; I don't know...I'd be tempted to put fresh springs on with THAT tall (.480") a cam...I swapped springs going to a .450" lift cam 'back-in-the-day' just to be safe.

I ran 3.42:1 gears with a 224* @ .050" lift cam on the street w/ no problems (14.40/97);
a buddy had a 236* @ .050" lift cam and 3.70 gears w/ similar street manners (a bit quicker);
when I threw-in a 244* @ .050" lift cam, 4.11s made it 'tolerable' at best, but I only drove to the strip & back (13.30/104).

55 MPH @ 2800 RPM with 27" tall tires (255/60R15s?) and non-lock-up THM350/400 is very close to 3.70:1 gears

Ganey

W / a stock auto. & 3.70 gears you could run Comp Cams HE268H, which will give a noticeable cammed idle. Max. cam w/ 1.52 rockers for stock springs.
Run a dual plane intake.
For exhaust see what many refer to as my Exhaust topic. http://www.corvettefaq.com/c3/ganeyexhaust.htm

SpyderD

To directly answer your original question I have a comp cams 280 (which is the advertised duration, @.050 it is 230). I have a vacuum of 15" at idle and all accessories work.
To get this however I had to correctly match everything - high compression, high initial timing, stall converter @ 2,000 (probably needs to be larger). low gears, carefully adjusted carb for idle mix and speed.
Everyone above provided pretty good advice with this cam - don't use it on a stock engine. For a high compression modified engine it works great. I do love that lumpy idle, everyone think I have a big block in the engine.