jz06man

What is the acutal valve lift for a .551 cam with 1.7 rockers vs 1.79 vs 1.89.

These high ratio rockers will add how much duration or lift in a comparable cam with stock 1.7 ratios... Does/will adding high ratio rockers 1.79/1.89 increase idle chop.

Lastly, the Patriot gold springs are rated for how much lift.

Thanks

ROGERSPERF.

what is your cam lift

2k2blkss

.551/1.7 = 0.324
0.324*1.79 = 0.580
0.324*1.89 = 0.613

Patriot Golds are good to .650

2k2blkss

Oh yeah,

I'm not sure how to figure the increase in duration but it will increase some.

If the duration increases then the idle chop *should* increase some but probably not enough to tell any difference

Importdestroyer

iTrader: (1)

I plan on running cranes 1.8 variable ratio rocker arms with my stock 02 LS6 cam ,they come off the seat at 1.89 and then settle to 1.8 when the valve is fully open. A simple way you can tell what your new lift numbers will be is to take the current lift of .551 and divide it by your current ratio: 1.7 and then multiply that number with the new ratio in this case 1.8, you now have your new lift number with that rocker arm.

Example:

02-04 ZO6 cam .551/.545 ( I think)

.551 / 1.7=3.241 x 1.8=.583

I dont know what the specs are on your cam but one thing you have to take into consideration is that duration is also affected, by as much as 6 degrees per 1/10th of lift increase, so going from 1.7's to 1.8's will increase your duration as well.

You will have to worry about ramp rates as too much lift too fast may collapse your lifters, and then theres piston to valve clearance. I wouldnt go over .600 regardless of the dual gold's springs to handle that kind of lift. Only really a concern on your exhaust lobe as thats when the piston returns to TDC (top dead center) and your exhaust valve may still be open, especially if you have a lot of duration.

During the intake stroke the piston is diving towards BDC (bottom dead center) and piston to valve clearance isnt critical, unless you have a really low lobe separation angle in which your intake valve remains open longer during the exhaust stroke.

I purchased a set of crane 1.8 rocker arms and right now Im torn between using them in conjunction with my stock 02 LS6 cam or a TR 224 similar california friendly cam.

Oh yeah one more thing, if the 1.89 ratio rockers in question are the crane 's gold's then the final lift number must be attained by multiplying the #'s by 1.8 not 1.89. The crane 1.89 ratio rockers are actually variable rate rockers that as stated before come off of the seat at 1.89 and then settle down to 1.8 before the valve is fully open, which is neat because you have more lift in the middle of the valve events and less peak lift. Same with their gold 1.79's, actually peak at 1.7.

I purchased a set of stage 2 patriot heads about 6 months ago, I plan on using them with LG longtubes, and the rocker arms. How did you dyno with them? I havent had a chance to throw them on as Im still over here in Afghanistan doing time, cant wait to get back in April.

jz06man

Well thanks for the input.. I currently have one of these Crane(Acce.Lift) cams with the crane 1.79-1.72 rockers. The set-up works great with the stage 2 head. It makes great torque down low and mid rpm's.

I'm torn with the posibility of changing out the cam with another more aggressive cam, since this will cost me TQ, but gain some peak hp. This is a trade off I'm not looking to make. Therefore, i was thinking of just adding these 1.89-1.82 rockers to give this extra lift- pick up a few hp & tq...But I'm wondering if it will increase idle chop(added duration???), which I'm not looking to do. Right now this VHP 062(Crane) cam idles near stock, with a slight chop at idle.
Considering this cam is small by many standards (210/218 .551 lsa112), but makes great flat torque, 405 peak and nice hp at 420(make excellent power under the curve).

Well this is the delima. Any input is welcomed.

jz06man

Well using this formula 551 / 1.7=3.241 x 1.8=.583, then that's means my lift will go from .551 to about .583, well looks pretty good and i should pick up a few hp & tq.

Right?

mrr23

iTrader: (3)

one thing to remember about the accelerated lift rockers. they only start and end with the 1.79 or 1.89 ratio. about .250 cam lift then move to 1.72 or 1.82. so, your max valve lift isn't going to change much when comparing stock 1.7 and 1.72. .551 / 1.7 * 1.72 only gets you .557. and .551 / 1.7 * 1.82 = .589 valve lift.

jz06man

Mrr23, you are right about the 1.72-1.79 lift times and seat intervals, but still a .032 total valve lift difference still should a positive impact- But do you think the idle quality might/should change? I've been told it will not, just the exhaut note will be a bit/slight higher- like a slight pop more. If this makes sense.

mrr23

iTrader: (3)

here's the dyno sheets of when i went from stock 1.7 to the VHP/Crane 1.89 rockers and dual springs. do not pay attention to the torque peak as there was a spike at the beginning of the run. reminder, this was on a stock cam as well. they did a great job of growng the upper rpms.

jz06man

Ok, so you picked up a few ponies and a little tq on this stock cam. I assume you felt the difference and what did it do too the idle quality- from the point of sitting inside the, and what did it do to the sound of the idle from outside the car?

Well ,I'll assume that the hp & tq gains maybe 1/2 of what you got since I already have the 1.79 rockers.
Thanks Mrr23

mrr23

iTrader: (3)

well i didn't really notice anything different about the idle. just that, as the graphs show, the better acceleration in the upper rpms. hell, i have ported heads on the car now. did nothing to the idle at all. cams are where you'll get your idle differences.

mikey

iTrader: (6)

mrr23, you have some knock retard going on in that blue graph. That curve is not right. Right where the dip in the hp curve is about 4600rpm. The retard carries all the way out. I've seen that a million (exagerating a bit) times.

mrr23

iTrader: (3)

did you read the notes for the blue (before) lines? 1* knock from 4800 up. but, good eye from noticing it on the graph. it's long gone. went away when the rockers and springs went on. must be the noisy stock springs and rockers i have taken off. VHP/ Crane don't lie when they say they have the quietest springs and rockers available.

mikey

iTrader: (6)

Ok. The quick lift rockers are standard equipment on our Dominator package and all of our upper end crate motors

mrr23

iTrader: (3)

good move on that part.

mrr23

iTrader: (3)

hey jz06man just looked over my current graphs. and here's a recent dyno #14(1/20/05). even more gain over time.so using dyno 9 before rockers and dyno 14, about 8 months later, you see a 17 rwhp gain the dyno 11 was about 2 weeks later and 250 miles on them.

jz06man

Nice, i guess I'll look to do this as aspring project with the LSX intake and 90mm t-body I'm concedering.

Thanks

jz06man

Well after all these cam & valve event question & discussions- Will the idle quality rock/shake more with these 1.89-1.82 rockers???
this is the real test at idle & then at low, mid, & high rpm's what can be the effect of them.

mrr23

iTrader: (3)

there was no idle change when i put the 1.89 rockers on. maybe with a larger cam, you might hear something more. but very little change.