Detonation under hard acceleration

I've been getting detonation under hard acceleration, even when I run 91 octane. I know the easiest thing to check would be the timing, but one thing I've been wondering is how do you know what to set your timing to? My cam is to radical to listen to the engine at idle to set the timing... and I've heard abit about spark plug gap and how it could affect things, I'm at 0.045" plug gap. I'm using autolite platinums standard heat range. I'd appreciate some input on this... I used to have a feel for this but now a days it seems like I'm just feeling around in the dark... Thank you.

 

Make sure your getting enough fuel and not running too lean.This will cause your problem as well as a vacuum leak or timeing.Generally these engines like 12 to 14 deg initial timeing and a total of around 28 to 36 deg.You will get more accurate responses if you list your cam specs...carb type/size and compression ratio you are at. Good luck!!!

 

You have to set your timing with a timing light!
Seat it at 34 degrees at 3000 rpm.

 

I do have a timing light but I used to have better luck of setting timing by ear for the engine sents timing changes depending on your specs but not with my cam on this car...

My specs are;
Comp Cams Magnum 280H, 280 duration, 230 @ 0.050" lift, 0.512" lift.
Edelbrock 1405 carburetor, 4 bbl, 600 cfm, I can't remember the exact Jet and Rod sizes though...
My compression ratio is around 9:1 to 9.5:1 (I don't know my piston to deck clearance).
I installed a O2 sensor and a narrow band air/fuel gauge (sunpro from autozone... the cheaper one) and it stays between ideal and rich.

What would be the next thing be after timing to look at as a cause for detonation?
That 34 degrees @ 3000 rpms and or 12 to 14 degrees... what octane gas should I expect to use? I've been running 91 lately/most often and sometimes I've been able to get away with 87.

Thank you,

 

Just checked my timing... I have a vacuum advanced distributor and at 800 rpms with vacuum disconnected it's at 0 degrees... with vacuum connected it's at 20 degrees... I'd appreciate any input. thank you.

 

it should not be reciveing vacuum at idle. the vac line is probly hooked up to the wrong port.
whats the timing at when you rev the motor to 3000 rpm with the vacuum disconected?

 

I have the vacuum line to the distributor coming from the vacuum port on the front right of my edelbrock. I'll check the total later when I get a chance.

 

Connect the vacuum hose to the port on the other side of the carb.The one your useing is constant vacuum...You need ported vacuum (other port on left front of carb)

 

Time your engine with the vacuum advance disconnected - it doesn't play any role at wide open throttle or under hard acceleration. Total number of degrees at 3000 should be no more than 34 degrees on the 289/ 302 small block.
That includes any initial timing!

 

According to the manual the constant port is for non-emission vehicles and the ported vacuum is for emission controled vehicles, should I still use it even though my car is not emission controled?

 

there is no dist. vac. advance that would use manifold vac. hook it up to the ported vac. now this probly wont fix your detination but it is still something that you have hooked up wrong.
have you checked what you timing is at 3000 rpm with the vac like disonceted yet?

 

Not yet I was visiting my wifes family today so I didn't get a chance to do anything with it yet. I try to check it tomarrow afternoon after work assuming my wife can help me by keeping the car at 3000 rpms while I check the timing...

 

you should be able to reach your hand over to the carb linkage and rev it up your self. if you dont have a tach on your timing light just get the rpms pretty high. the total advance should be in fully by 3000 rpm. you can watch it advance on the balancer with the timing light till it wont advance any more. thats the number were asking for.

 

Yes...

 

At 3000 rpms it's at 24 degrees with vacuum advance disconnected and plugged at carb.