Question on BBC Rocker Ratio

[Camaro_nut2001]

I've got a buddy that's runnin a 454 in his '68 GMC. He has asked me what the advantage/disadvantage is on runnin a 1.8 ratio roller rocker versus a 1.7. I cannot answer his question other than it raises his lift a tiny bit, lol so I need ya'll's answers please. He put a cam in goin off another buddy, that dirt track races, recomendations. Says he can't really hear his cam hit & was told to raise his rocker ratio to 1.8 opposed to puttin a bigger cam in. I told him he had to mate his cam with his heads, CR., etc.. & over cammin would kill his power. It's a stock bore '84 model 454 with peanut port, 236 I think, heads on it. It's a 262/268, .505/.515 with a 112 lobe sep. Would changin to a 1.8 ratio help him "Hear it Hit"? I would also like to know the adv/disadv. lol. Thanks.

[moggey01]

112 lobe seperation will help with idle and vacuum for a streetable smoother idleing engine. Tighter LSA may be choppier at idle . As far as a 1.8 rocker try them at the track or on a dyno. You can try them on the exhaust also, alot of people did that a long time ago with older grinds.

[Camaro_nut2001]

Originally Posted by moggey01

112 lobe seperation will help with idle and vacuum for a streetable smoother idleing engine. Tighter LSA may be choppier at idle . As far as a 1.8 rocker try them at the track or on a dyno. You can try them on the exhaust also, alot of people did that a long time ago with older grinds.

Thanks for the info. I have ran split ratio rockers a long time ago but I don't really know how to explain to him that goin up on the ratio won't make the cam any different as far as sound & also what he's gonna gain from them.

[soxplayer]

Higher ratio will have the valves open more at overlap. This should lead to greater overlap effect for a rougher idle and possible more torque up top.

[Marv D]

I sincerely doubt he will ever feel or hear any difference. Adding .1 to the rocker ratio does increase his gross valve lift to .535 / .545,, which means that if the valve is opening further, it has to be open longer at all incremental lifts (.1, .2 etc) but... it does NOT change total duration. It will STILL be the same 'seat to seat' timing will NOT change. Remember 0.050" is the TAPPET LIFT, has nothing to do with rocker ratios or valve lift.

Now the question is,,, that 262 / 268 has to be seat to seat???? Even a duration gobbeling big block is going to thump and bump HUGE if that were 0.050" timing. That's solid roller race cam territory if it were 0.050"

Without knowing the ramps (which are going to be pretty mild with a mild hydraulic like this) he is going to increase the 'typical' 0.050" duration about 1-3 degrees. Which I'll be a dollar to a donut the only thing he notices is that his wallet is lighter. (that is assuming his valve springs and valve to piston clearance doesn't lighten that wallet a lot more)

[regan wilson]

Tell your buddy ....Dont talk to Dirt Trackers !
(anynyone offended by this post please just dissregard it)

[ulakovic22]

Originally Posted by Marv D

I sincerely doubt he will ever feel or hear any difference. Adding .1 to the rocker ratio does increase his gross valve lift to .535 / .545,, which means that if the valve is opening further, it has to be open longer at all incremental lifts (.1, .2 etc) but... it does NOT change total duration. It will STILL be the same 'seat to seat' timing will NOT change. Remember 0.050" is the TAPPET LIFT, has nothing to do with rocker ratios or valve lift.

Now the question is,,, that 262 / 268 has to be seat to seat???? Even a duration gobbeling big block is going to thump and bump HUGE if that were 0.050" timing. That's solid roller race cam territory if it were 0.050"

Without knowing the ramps (which are going to be pretty mild with a mild hydraulic like this) he is going to increase the 'typical' 0.050" duration about 1-3 degrees. Which I'll be a dollar to a donut the only thing he notices is that his wallet is lighter. (that is assuming his valve springs and valve to piston clearance doesn't lighten that wallet a lot more)

^^^This

Mine is 262/270 @ .050 Yes it's a solid roller.

[BigDan3131]

Originally Posted by ulakovic22

^^^This

Mine is 262/270 @ .050 Yes it's a solid roller.

That's still not the max for an aggresive street ride 280/288 @.050 would be.

[regan wilson]

But really he needs a new cam . My best 468 had a 110 cl and was setup at 105.5 for tq. Good rockers are way more expensive than a cam and I can tell you rockers are not gonna help.

[Camaro_nut2001]

Originally Posted by soxplayer

Higher ratio will have the valves open more at overlap. This should lead to greater overlap effect for a rougher idle and possible more torque up top.

Thank you for your imput.

Originally Posted by Marv D

I sincerely doubt he will ever feel or hear any difference. Adding .1 to the rocker ratio does increase his gross valve lift to .535 / .545,, which means that if the valve is opening further, it has to be open longer at all incremental lifts (.1, .2 etc) but... it does NOT change total duration. It will STILL be the same 'seat to seat' timing will NOT change. Remember 0.050" is the TAPPET LIFT, has nothing to do with rocker ratios or valve lift.

Now the question is,,, that 262 / 268 has to be seat to seat???? Even a duration gobbeling big block is going to thump and bump HUGE if that were 0.050" timing. That's solid roller race cam territory if it were 0.050"

Without knowing the ramps (which are going to be pretty mild with a mild hydraulic like this) he is going to increase the 'typical' 0.050" duration about 1-3 degrees. Which I'll be a dollar to a donut the only thing he notices is that his wallet is lighter. (that is assuming his valve springs and valve to piston clearance doesn't lighten that wallet a lot more)

Thank you but I'm not gonna tell him this as it would be openin a whole nother can of questions, lol.

Originally Posted by regan wilson

Tell your buddy ....Dont talk to Dirt Trackers !
(anynyone offended by this post please just dissregard it)

I will pass this on! Thank you.

Originally Posted by regan wilson

But really he needs a new cam . My best 468 had a 110 cl and was setup at 105.5 for tq. Good rockers are way more expensive than a cam and I can tell you rockers are not gonna help.

I have told him i'd help him choose & swap the cam, so we shall see. Thank you for your imput.