HELP!! my 427 runs like a two stroke

Printable View

05-12-2011, 01:26 PM
Cooter1989

HELP!! my 427 runs like a two stroke

my 427 has no low end torque and wont really run untill about 2000rpms. has a 850 demon air gap intake solid non roller cam and factory hi-perf corvette rectangle port heads flat top pistons roller rocker t56 6 speed and a 342 gear all in a 79 trans am. I am curious about the heads i have been told these heads arent great to use with a mild street motor and are better off on a high rpm motor. could this be my problem? The timing has been set every way possible and i still come up with the same problem
05-12-2011, 02:16 PM
34_40

Do you know who made the intake? Some of those Single Plane High Rise Intakes don't start working good 'til 2 grand or better. I don't know any info about those heads.
05-12-2011, 02:21 PM
Cooter1989

edelbrock the rpm range is suppose to be 15-65 but its also a dual plane manifold and in 90 percent sure the castings are 840s on the heads but its been a bit since ive looked
05-12-2011, 04:44 PM
pat mccarthy

what cam ? any hot cam with a low CR goiong to hurt you. rec heads are better for bigger CID bbc and some to lot of CR .your not getting that with flat tops .small O ports heads would work much better then them heads and if it has any cam with a small CID engine its not going to like any thing under 2000
05-12-2011, 06:00 PM
echnidna

I tend to agree with Pat, the cam might be too wild for you OR the valve timing is not set correctly
05-13-2011, 05:15 AM
Cooter1989

I didnt get to build this motor so im not sure on the cam specs i know it has a pretty choppy idle and when we ran a compression check it only has 165 170 psi cranking compression which would mean its a low compression motor right?. i have a set of built oval port heads on A 462 not sure on the casting numbers would it be a better idea to change heads and cam or say to hell with it a put the 462 in?
05-13-2011, 05:25 AM
Dave Severson

Would depend on what the chamber size is on the oval heads, the flat top pistons are killing the compression so a pair of oval port heads with the same cc or larger won't do much for improvement. For what it's worth, I've never build or had built an engine that made poop for power below 2,000 rpm, always aimed for the power to come in at about 2,000 and then the engine starts pulling good. Anything 2,000 or thereabouts is barely a cruise rpm, even with the overdrive transmissions and lazy rear gears of today's cars.....
05-13-2011, 05:46 AM
Cooter1989

What would be a good cc chamber to run with flat top pistons? The 462 is built with the oval port heads oversized valves 10.5/1 dome speed pro pistons scat i beam rods lunati 590 lift cam and 1.6 roller rockers but when you spin it over with a ratchet it has a stiff spot in it and havent messed with it to figure it out and if i change motors i will have a flywheel issue unless i can have the balanced changed on it. just not quite sure which motor would be better in the long run
05-13-2011, 04:03 PM
pat mccarthy

Quote:

Originally Posted by Dave Severson

Would depend on what the chamber size is on the oval heads, the flat top pistons are killing the compression so a pair of oval port heads with the same cc or larger won't do much for improvement. For what it's worth, I've never build or had built an engine that made poop for power below 2,000 rpm, always aimed for the power to come in at about 2,000 and then the engine starts pulling good. Anything 2,000 or thereabouts is barely a cruise rpm, even with the overdrive transmissions and lazy rear gears of today's cars.....

well yes and no dave ..you ford ... guy you:D rec port heads will not work that hot in low rpm engine +big cam ....small CID...... two heads with the same chamber size with big port runner and smaller port runners .the smaller port s will work better in this case the O ports you may get away with to big of cam .but not a big cam. low CR + big intake runner for the street = turd