weird ignition problem on 408w

Rhauf · 04-03-2009, 04:18 PM

Well i have recently built a 408 stroker, and at high rpms (starting around 3,000 and getting worse as it revs higher) it seems to start dropping random cylinders or running rough. at first i thought it could be the carburetor (edelbrock 750) so i tried a holly on it, there was no change. i suspected intake valve float but a vacuum gauge showed steady vacuum at all rpms. is it possible that it could be spark plug blowout? i am really at a loss here but i hope to know before i start throwing money at ignition parts upgrades etc. so any help is appreciated! below is the specs on the engine

408w forged pistons,
10.25:1 compression,
crane roller cam 224/232 duration .540/.560 lift 112lsa,
edelbrock performer aluminum heads 2.02/1.60 valves.
weiand stealth intake
Mallory magnetic pickup distributor
"stock" coil and wires from autozone.
dual 2.5" exhaust w/ shorty headers.

now the strange thing is, i have a jet boat with a high compression olds 455 in it, and it has the same problem! (rough above 3500 rpm at any throttle/load level)

Rhauf · 04-05-2009, 01:06 AM

doesn't anybody have any ideas?

goodyear1984 · 04-11-2009, 09:50 AM

sounds like a coil

04-03-2009, 04:18 PM	#1
Rhauf Registered Member Join Date: Jan 2001 Location: Ojai, CA Posts: 19	weird ignition problem on 408w Well i have recently built a 408 stroker, and at high rpms (starting around 3,000 and getting worse as it revs higher) it seems to start dropping random cylinders or running rough. at first i thought it could be the carburetor (edelbrock 750) so i tried a holly on it, there was no change. i suspected intake valve float but a vacuum gauge showed steady vacuum at all rpms. is it possible that it could be spark plug blowout? i am really at a loss here but i hope to know before i start throwing money at ignition parts upgrades etc. so any help is appreciated! below is the specs on the engine 408w forged pistons, 10.25:1 compression, crane roller cam 224/232 duration .540/.560 lift 112lsa, edelbrock performer aluminum heads 2.02/1.60 valves. weiand stealth intake Mallory magnetic pickup distributor "stock" coil and wires from autozone. dual 2.5" exhaust w/ shorty headers. now the strange thing is, i have a jet boat with a high compression olds 455 in it, and it has the same problem! (rough above 3500 rpm at any throttle/load level) __________________ -1968 Mustang Coupe- 302 roller, gt-40Ys, E-303, t-5

04-05-2009, 01:06 AM	#2
Rhauf Registered Member Join Date: Jan 2001 Location: Ojai, CA Posts: 19	Re: weird ignition problem on 408w doesn't anybody have any ideas? __________________ -1968 Mustang Coupe- 302 roller, gt-40Ys, E-303, t-5

04-11-2009, 09:50 AM	#3
goodyear1984 Registered Member Join Date: Dec 2006 Location: new york Posts: 482	Re: weird ignition problem on 408w sounds like a coil __________________ 347 stroker all forged,arp everything,stud mains w/girdle,7qt pan,full roller, custom cam, aluminum heads swirl valves 5 angle valve job.quick fuel 750,areomotive pump,cobras w/nitto drags,and m/t et drags for the track, ford racing 373 gears,centerforce clutch,tko500,underdrive pulleys,bassani x-pipe,flowmasters ^best et so far 11.6 1.61 60ft coming soon 9sec et's 1992 mustang gt 2001 gmc 1500 4x4 78 century boat 92 skidoo

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