I just did smog and was thinking about getting an offy intake and a demon 625. Possibly a 4.0L head in the future. Would the 625 be too big for the lame 120HP 4.2L. thanks.

Uh, yeah. WAAAAY too much.

Even with the 4.0 head, you'd need to do some MAJOR internal engine modifications to even come close to being able to handle that much air...

Without any mods, the engine is gonna fall flat on it's face...

Jake

what about a cam? my lifters are ticking anyway, probably should replace them.

Think about this, Busch series cars only run a 500 cfm 2-barrel. Hell yeah, 635 cfm is a waste of money. Save your money for something else - for instance fuel inhection that will help you on inclines and steep side hills.

Originally posted by Taso Stambolis
what about a cam? my lifters are ticking anyway, probably should replace them.

I'm thinking you could have the hottest came out there for a 258, cam, Offy intake, borla header, ported, polished 4.0 head, supercharger, and a full roller valvetrain and you STILL wouldn't need a 635 CFM carb on that thing.

Look into a Motorcraft 2100 or a Weber 32/36. Both great carbs for a 258.

HTH,
Jake Harsha

I ran a Holley double pumper 600 cfm on my 69 mustang with a large cam, bored .040 over and a Torquer 2 intake and i still never could get the air/fuel ratio right. I could light the tailpipes on fire:D:D For a 4.2 i would not go any bigger than 550(even that is pushing too much air) and if you are going to trun a K&N with the filter top just get a 500.

I ran a 450 vacuum secondary Holley on my bone stock 258 for a while, it was OK, but would occasionally "load up" when idling for a while.

There is a formula that goes like this: CID X Max RPM/3456= CFM. I know it is just an estimation, and it is based on displacement and max rpm that the motor would see and it is based on 100% volumetric efficiency. So that 258 running at 6000rpm would only require a 450cfm...and that is at 100% V.E.! Assuming an 80% V.E. it would only require about 360cfm. If your running blowers or turbos you may run close to and/or exceed 100% V.E. But a normal engine in good sound running condition is about 75-80% V.E. I do know for a fact that on a trail/crawler you definitely do not want to overcam or over carb. All those big lopey race cams and large carbs are for the strip (dragstrip...not our favorite strips....;) )

any one want a 4160 holley 650 I got one pm.........................ltr