89 coupe l98 LPE219 cam- going to split ratio roller rockers 1.5 & 1.6 I have a set of springs that will accept a .570" lift, will these work?

 

We need more info than you provided. What do you mean by "... will this work?

Jake

 

Why are you splitting the ratio? Whats the theory behind it....?

Does this work? I read about this in some magazine, they did it. I cant remember why, or how much more HP it made than 1.6 roller rockers all the way around.

Yet forum members (well ex-forum members) like Nathan Plemons have switched to 1.7's all the way around and got proven dyno gains on an actual LT-1, not some random small block chevy.

Please share the theory!

 

with the 219 cam lift ratio is .525" lift with 1.5 RR & .560" with 1.6 RR so I'm wondering if a spring with a .570" max lift is acceptable? Is there a "rule of thumb" on determining spring lift?

 

SPRINGS: It's always best to use the spring that is recommended by the camshaft manufacturer. That spring has been tested by them and is the one which is most compatible with that particular camshaft.

You do not necessarily have to buy THEIR springs, but the springs you buy should have the same seat pressure, open pressure and spring rate as the ones they recommend.

The maximum lift that a spring is rated for is not a good indicator of that spring being the "right" one for your specific camshaft. Just knowing that the spring cam handle .570 lift isn't enough. Many springs can handle that lift but may have way too much seat pressure for a hydraulic roller or may have way too much open pressure or may be the wrong diameter, etc.

Higher ratio rockers, especially full rollers, do a few things to valve action, which most often are positive in power production. They lift the valve to a higher level off the valve seat, thus allowing a greater opening for flow. They accelerate the valve quicker so that flow is started sooner and full rollers reduce friction which translates into more power. The ratio is much closer to being accurate than stockers too.

Power increases are on the order of low double digits, like 10/12/15 HP and more torque also.

Since the exhaust duration is the one most often increased in a dual setup, whether you need to use split ratio rockers - or a split ratio camshaft for that matter - depends on the efficiency of the exhaust on the car.

Everything in the exhaust tract, from the exhaust port in the cylinder head to the muffler tip should be considered. If there is a significant restriction in that area, a dual pattern cam or higher ratio exhaust rockers will generally show better power. The longer duration of the exhaust duration on a dual pattern cam and/or the higher exhaust lift and additional duration achieved with higher ratio rockers on the exhaust helps to offset that exhaust restriction.

There are a couple of other on-going threads on this Forum dealing with the same topic now. Do a search to pull them up.

Hope this helps.

Jake


[Modified by JAKE, 11:44 AM 12/1/2003]

 

Thanks Jake-I was trying to save a few $ by using springs I already have, but from your info I'll get with LPE and get the ones they suggest.

 

Thats a good idea to check and see whats recommended, don't go cheap on valve train parts. Sometimes doing so it will come back and bite you hard on the butt :eek: I knew a guy once that dropped a large flat tappet cam into a big block that had GM truck heads on it. The heads had the stock valve springs complete with the valve rotators on the valves! I had warned him that doing so may cause coil bind and or valve float. His reaction was the same, he wanted to save some cash. In the end he dropped a valve and seriously damaged the engine.