Riddle me this Batman...

Comp Cams claims their XE284H-10 cam grind has a "rough idle".

What does that translate into the real world?
1500 RPM idle in park to not die when in gear on an auto with 2500-2800 stall?
10" Hg at idle?
Shake the car?
Die when the AC clutch engages?

BTW, 454 cu in, 781 heads, headers, 800 cfm carb, dual plane intake, TH350, 3.42s, PS, PB, AC.

Opinions welcome...

Thanks,
E.


Part Number 11-250-3
Engine 1965-1996 Chevrolet 396ci-454ci 8cyl.
Grind Number CB XE284H-10
Description
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Intake Exhaust
Valve Adjustment 0 0
Gross Valve Lift 0.574 0.578
Duration At 0.006
Tappet Lift 284 296
--------------------------------------------------------------------------------
Valve Timing At 0.006
Open Close
Intake 36 68
Exhaust 82 34
--------------------------------------------------------------------------------
These Specs Are For The Cam Installed At 106 Intake CL
Intake Exhaust
Duration At 0.05 240 246
Lobe Lift 0.338 0.34
Lobe Separation 110
-------------------------------------------------------------------------------
Recommended Valve Springs 924-16

Thats a fairly hot cam with 240 deg dur@.05 & 110 deg L/S but not that large for a 454. It should idle decent (after motor warms up)being slightly choppy/lopey in a 454 but in a 396 it would idle fairly rough/choppy.

Very often when you have issues like your having its just simple tuning/dialing that needs to be done with carb 7 timing.

But the 1st thing i find when people install aftermarket perf cams is they dont run near enough intitial advance which can causew exactly what your decribing.

So what intial advance are you running?

You should be running approx 16-18 deg btdc intal timing with that fairly long duration cam ,anything less will result in an unstable idle,lower idle vacuume,soggy low speed perf,wasted fuel,and hotter running motor.

So if your intial timing is less than 16-18 deg btdc crank it up where it belongs and you should be plesantly surprised with a crisper throttle reponce, better idle with more vacuum,more power,and run a few deg cooler too. The Motor should at a low idle like 550-600 rpms to set intial timing with vac advance unhooked & plugged. Hook the vac adv back up after your initial timing is set and then raise the idle back up to apporx 900-1k rpms in park with that cam which should get you where you belong in gear.

But listen for detonation after cranking in all that intial timing and if you hear it then you should have the mechaical advance in the distributor recurved to limit it to approx 18-20 deg so you end up with a 36-38 total timing not inc the vac advance.

A quick fix for detonation would be either to run octaine booster or back off the initial timing a few deg at a time untill the ping goes away . But that will reuslt in power loss and likely idling issues again too which is close to ro right back to where you started again with retarded ign timig. So i would do the dist recurve for mech advance at that point to fix it right.

Try this and let us know how you make out.

Scott

I'm running that cam in my 454 right now....and agree 100% with what Scott said.

I used to have a solid Comp CB280S-10 (P/N 11-551-5) (242/250 @.05 .575/.604) ...it was a breeze to set up and tune compared to the current cam. I'm not really sure why?... but it was

The XE 284H-10 has been a total PIA to get set up properly, most likely due to something that I'm doing or did wrong...Then again, I've never really been good at making carb/timing adjustments.

Anyhow, For what it's worth... I idle in N at around 900- 1050 RPM and in gear I'm about 750 rpm. It's kinda rough but doesn't shake the car or anything like that, I run an airgap intake and have power brakes, no problem with vaccuum when using this cam.

When I was playing around with the carb/timing I could get it to idle in N at around 700-900RPM and around 500-600RPM in gear but it would lose RPMs and then die so I had to "bounce" my foot on the pedal to keep it running BUT IT SOUNDED MEAN !!!

My distributor is stock GM with the lightest springs from the re-curve kit and I'm at about 36 deg timing (I have to run retarded because my C/R (~11.75 static) is too high for 91oct)

i run a more agreesive isky cam with 108lsa in my chevelle and i used to daily drive it.... it wasnt that rough

Eric,you have mail,chk it out.

scott

Eric,you have mail,chk it out.

scott

You guys rock the kazz-bah!?! :)

I have not put the cam in 'cause the block is still in the car. Tranny went to the shop today and the block comes out Monday or Tuesday, then off to the machine shop. After that, hot tank, bore, polish, etc. Whatever it needs.

I was considering that cam for the rebuild. I don't currently have any of the issues I mentioned, but know they can results from too hot of a cam for the engine. There is still a possibility I may go 496 instead, which would probably be a smallish cam for that size, but I won't know until I find out what the engine work will cost me. I just have been wondering what was meant by the description CC listed. I figured if they said this is a "rough idle, barely runs, stalls at light without enough timing," they wouldn't sell any cams. :)

This is the excellent feedback I wanted. I expected to run at least 12-14 degrees advance to start with, but wanted some feedback.

I certainly appreciate the input!!!

E.

I have this cam in a 402. It idles at 750-800 but rather rough. You'll want at least a 3500 stall....I made a mistake and only went with a 3000 and the rpm difference between park and drive is like 500 rpms.

It shakes my car somewhat and mine had 10-12" hg....I don't have a/c so I can't answer that one for you.

Scott I dialed in the timing as you recommended and all I can say is WOW :) whatta great tip! My cam is a little lighter Crane 272H. I advanced the initial timing 8 degrees. I was able to back off the idle screw and my idling circuits work properly now. Car idles super nice, super throttle response. Starts no problem. All that because I didnt know to check the timing with the vacuum advance plugged and dial in more timing with a hotter cam. You guys are ALL RIGHT!

A lot of good advise here, my old engine was a solid roller, 244@.050, .645 lift on a 110cl. In a 9.6:1 454 oval ports, 850 holley, it idled at 650rpm in gear, maybe 750 in park. Of course it had a nice lope, but none of the nasty descriptions you are worried about. I was running 14* initial timing with a 21* mechanical, (35 total timing) It nevered died, bogged, hiccuped, whatever. Started real easy and I was runnning a 3000 converter. It is the engine that was in the car in my sig. But is being replaced by a bigger and better 496 now. Later, Brian