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Old 07-11-2003, 07:15 PM
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Whats wrong with my set up??

I built up a 355 sbc engine and its not putting out the power it should....whats wrong here??
350 chevy engine bored .030 over. About 9.5 to 1 compression. Brodix aluminum heads CNC ported, 2.08 in 1.60 exhaust valves. Solid roller cam with .618 lift, 248 in 250 ex duration @.50. wiend single plane intake. edelbrock 750 cfm carb. MSD ignition, 8.8 wires, 1 7/8 Hustler headers. The engine has alot of power but not like it should. It seems to have a dead spot in power between 4000 and 5000 rpms but it pulls pretty good from 2500 to 4000 and 5000 to 7000 rpms. What could be wrong here, not enough compression? I had a small block 400 with 2.02 cast iron heads and a dual plane intake and a mild cam and it pulled just as hard as this motor. Any suggestions??

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Old 07-11-2003, 08:08 PM
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with a cam that big, it needs at least 11:1 or more compression. the 400 pulled harder due to a longer stroke and dual plane intake, plus the 50 more cubic inches helps. the overlap of your cam likely has the compression ratio in the low 100`s or less until enough RPM`s build up. I take it this isn`t a street machine, and if it is, there will be some changes you`ll have to make.
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Old 07-12-2003, 10:27 PM
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oh this is a street machine all right, its a daily driver haha
but can i figure something out wher i wouldnt have to go with so much compression i dont want to go that high with a street machine ya know
too much money into this car for it to not work right you know?
why does it back fire too?? every time when you rev it up
it back fires
any ideas??
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Old 07-12-2003, 10:43 PM
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with that compression ratio and that cam your cylender pressure is way too low, so if you feel you have to have such a large cam then you need more compression, theres no way around it. and i imagine it backfires because it runs out of gas, with such a large cam and low cylender pressure there isnt enough of a vaccum signal getting to the carb in the low range, thus its pulling no gas from the boosters.

Last edited by Dozier768; 07-12-2003 at 10:49 PM.
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Old 07-12-2003, 11:33 PM
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Yep.. you have WAY to low compression for that cam. Either you can get bigger pistons for more compression and then you would really have some HP.. or probably the cheaper way and easier drop your cam size down to a solid flat tappet and like a 520 lift and it will run better than it does now.
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