I have just finished a frame off restoration on my 68 nova. I have a 1970 motor. Its a 396 with a 454 crank 454 heads, extreme energy cam, 9.5 to 1 compression, edelebrock dual plane intake, holly carb. I am having a problem with my timing. The lowest I can set the timing is 12 before top dead center without it starting to backfire. The problem is it sounds like jingle bells when I hit the throttle. I disconected the vaccum advance with no help. The car runs, and starts great at about 15 degrees. At 12 degrees I'm loosing power, but no matter what I still ger predetination.  I have a stock HEI ditributor with stock springs and weights, do I need to change my timing curve or could it be something else.  I'm also runing 94 octane fuel with octane booste with no change. PLEASE HELP!  thanks Rich from Mebane NC  

you sure you got the distributor pointed to number one with the number 1 cylinder at top dead center? sometimes you jump a gear on accident.  

Doesn't  it have to be there (#1 tdc)  if the distributor is adjusted with a light? Should I try restabbing the distributor one gear back? thanks Rich

What are the cam spec's?? Are you sure you're at 9.5 : 1?  Almost sounds like a valve timing problem.  

When we ordered the pistons at the machine shop they said with this package I'll be at 9.5 to 1 compression. They done alot of street strip motors in this area. Its an extreme energy cam, 284 intake/  296 exhaust/  valve lift intake .507/  valve lift exhaust .510/  lobe seperation 110 degrees.  what do you mean by valve timing problem?  Pull timing cover and check the marks. thanks Rich  

Sometimes cams with really short durations are installed in motors with fairly good compresion. With 9.5 and 284 intake duration you should be ok.  Check your cranking compresion if you are below 190lbs its ignition. You're marks are lined up right?  Sounds like a pretty good combo.  

well, it doesn't nessicarilly have to be at their number one, as long as they are firing at the right cylinder at the right time, but i do use the factory set up. but if you can check it, pull the spark plug, put ur findger in there, turn it over till you feel it poof,and make sure its at top dead center, then pull you take off distributor cap and see if it is pointing at the number one plug wire.

I think by valve problem, it could be mis-seated valves. I've had the problem running older heads that were supposed to be rebuilt with new seats having old seats that needed lead, so they sunk in. it caused a popping sound in the exhaust.

Valve float often sounds like detonation. Comp cams recommends changing the valve springs on any cam with more lift than stock. Extreme Energy cams have drastic valve opening ramps and will cause major valve float with stock springs. They recommend part #924-16 which requires machining the heads because of their larger diameter. You could maybe use their new beehive springs which have stock diameter and don't require machining the heads.My sbc 383 has a much smaller Extreme Energy cam (XE-274, 230-236 dur at .050, 487-490 lift) and the push rods were getting dragged on holes in the heads when the valves opened caused valve float and beating the crap out of the push rod tops.

Also, check to see if your valve retainers aren't hitting the valve guides because of the high lift on your cam.

I hope this helps. Should be a wild motor.

Cool car. So, when ya gonna paint it?

Edited 5/22/2006 12:21 am by rebldryvr

thanks for your message.  I hope its not the valve seats, I spent alot of money on this build. Do you think a lead additive might help?

thanks for all that information.  The car is completly done now.  Its white with blue/teal flames, all new custom interior, total frame off resto.  411 richmond gears, eaton posi, th 400 trans, hurst ratchet shift, disk brake conversion.  Everything new from bumper to bumper, and its killing me not to be able to drive it. I'll pull the covers this week and start lookin.  The machine shop assures me the right springs were used, how do I tell? How do I tell if my valve retainers are hitting my guides.  thanks again Rich  

I dont think  the additive would fix the problem after it started. but go back thro the timing and all the stuff other people told ya, and if it doesn't fix it, I'd take it the seat have sunk in.

hello

sounds more like a timing issue to me. since you have changed the motor from the stock configuration, the stock timing specs don't necessarily apply any more. set the timing where it runs the best, the motor doesn't know what is stock any more. also i'd recalibrate your dist. to come in sooner on the advance, again this is something you'll have to play around with on a long stretch of road, or if you are lucky enough to have a shop with a dist.  machine near by they can usually get you close and then you play with it to dial it in for  a better et. As for running unleaded gas on a pre leaded head, my experience has taught me that it only really becomes a problem when either doing a fair amount of towing, or you race it alot and hard. My heads are old 041 castings and they still have a decent seat, don't race every weekend, but when I do, I race her hard!!!

hey, that sounds like the problem with the timing. I put a new hei distributor in the car and that helped, but I went the other way with the weight springs.  I need to go with lighter springs for a quicker advance. I will try that next.  thanks for you time  

I don't know Chevys real well but my 66 283 did that when the rocker studs started to push out of the head.  I don't know if big chevy has screw in studs or not  

has the harmonic balancer been replaced? the problem just about sounds like the outer ring of the balancer has slipped around,giving you a false indication of your timing,have you tried winding on more timing? a couple of other things may be;running extremely lean or cam timing.