I will shortly be rebuilding my V6 and I have purchased a GM performance cam that is .050 @ 208 intake / 208 exhaust. Can I use 1.6:1 ratio roller rockers, or wil that be too much lift and duration for the stock 2.8 ECM?

What is the lift of the GM cam you bought? You gave us the duration spec. Using 1.6:1 rockers instead of 1.5:1 does not affect cam duration, but does slightly increase valve lift. If the rockers you are thinking of buying are only the roller tip type, don't waste your money. Studies have shown that under the normal high valve train pressures, the roller tips do not actually roll. The true roller fulcrum rockers do give a couple extra HP due to their reduced friction, but very few are narrow enough to fit on the 2.8 engine (most are made for the V8's). Also, the 1.6 ratio rockers creates excessive binding of the valve train geometry.

Those of us that use 1.6:1 rockers would disagree with that statement. Some of us have even used them for years and thousands of miles with absolutely no indication of premature wear. While I do agree that a higher ratio rocker can pose a problem on a V8 head, this simply does not apply to the 60° HO heads. There are even standard methods available to prevent problems associated with higher ratio rockers on the V8 heads.

To determine the change in lift resulting from the higher ratio, simply divide the current lift spec by 1.5 and then multiply by 1.6. You can do a rough prediction of the effect of this on the computers control capability by comparing these numbers to cam charts. They usually give a very good indication of the limits to follow for acceptable computer performance.

Mike

I believe the stock Fiero V-6 rocker arms are actually 1:4.2 ratio.

I'd love to put the 1:6 rockers in my new engine but that would void the warranty. I'll have to live with stock for the next 18 months.

Bathboy, where do you get this infomation about roller tip rocker arms being a waste of money? Everything that I have read about roller tip rockers contradicts your theory. An article in Hot Rod Magazine were they installed Comp Cams roller tip rockers on a mustang showed that they do improve power about 15% or so at higher RPM's. Accoring to Comp Cams, stock 1.5 rocker arm ratios vary as much as 1.42-1.48. Comp Cams claims that there ratios are super accrurate @ 1.52 and are a lot stiffer in desiegn compared to stock rockers arms. Because they are stiffer and more accurate, you get more valve lift than a stock unit and hence, more power. Also roller fulcrum rocker arms can not be used in a stock engine because of longevity problems as there is not enough of an oil supply to lublubricate then at idle.

I have 1.8 ratio al. roller rockers on my 'Burb and have had no durability or any kind of problems out of them what so ever. As far as not enough oil at idle, I have never heard that before. If a roller bearing starves for oil at idle, then the stock rockers should also fail sooner for the lack of oil. Regardless, I installed a high volume oil pump and have no problems. Pumping the oil pan dry is not an issue on this truck because it has a 7 quart capicity. To take advantage of the higher ratio, I went with a milder than recommended cam and made up for the lift with the rockers, this helps keep overlap low to build low end torque. The cam was advanced 4 degrees, also to help low end power. I used Mr. Gasket's Desktop Dyno when buying parts to see how they affected power output. The actual dyno results of the engine were within a few horse power of the comp. simulations.

88formula, roller tip rockers like Crane or Comp Cams are very well built and are far stiffer than the factory rockers as you pointed out. Any power gain is for this reason, there is less flex in the rocker. Also, if you are using a higher ratio, you are making a few horsepower from the higher lift too. The roller tips look cool, but they rarely actually roll.

Oiling and head design on the 60 degree V6 is similar to the small block V8. Therefore, true roller fulcrum rockers will work if you can find some that are narrow enough. The Chevrolet Power book describes a method of converting Crane V8 roller rockers to fit.

Increasing the rocker ratio helps gain a few HP, but in my opinion, not enough to justify spending the extra money or the extra stress on the valve train. If you guys want to use 1.6 rockers--then go for it. I was just pointing out that maybe roller tip rockers are not as great of a deal as the first might sound.

Cooter, 1.8 ratio sounds impressive, but of course a big block is 1.7 even stock, if I remember correctly. So, that's about the some as increasing from 1.5 to 1.6 on the V6.

Crane Cams 1.6:1 Ratio Gold Race (Extruded Narrow Body) Full Roller Rocker Arms for Chevrolet 60° V-6:
Part # 25759-12
http://www.cranecams.com/master/goldrace.htm

Available from Summit:
CRN-25759-12 $361.99

Competition Cams 1.6:1 Ratio Magnum Roller Tip Rocker Arms (10mm stud):
Part # 1414-12

Available from Summit:
CCA-1414-12 $133.99

And YES, they do "Significantly" enhance performance when used with a stock cam.

Mike
(See Fiero details in my profile)

Batboy- that was my point in listing the 1.8 rocker ratio. I took for granted that everyone would know that the big block had 1.7 factory rockers. Sorry about that. On the computer simulation, the engine picked up a few horsepower by using the higher ratio rockers, but using the bigger cam and the high ratio rockers reduced low-end torque. That was another point that I needed to make- Too big of a cam with high ratio rockers could also cause valve to piston interference which could result in severe engine damage. It is a good idea to always check these clearances when changing to high comp. pistons and big cams. Sorry if my previous message mislead anybody.

I called Comp Cams help line (1-800-999-0853) on this matter and that is what he told me. He didn't recommend the roller fulcrum rockers for a stock engine even though you could gain extra HP. He said they wouldn't last because they wouln't receive enough oil in a stock engine, and this application was for a chevy 350 engine. Basically there made for highly modified engines. I was also confused about the oil thing to, it doesn't make sense.

Also...Crane Cams said that if you want to order their Gold Race Roller Fulcrum...there is a back order ti'll next year....probably around February or March...

Are "they" referring to a stock oil pump. Would a high volume/pressure pump satisfy the oil needs for roller rockers. Fieros have high volume pumps.

What difference did they make for your engine and was it worth the cost. 2 high volume oil pumps eat HP if you did not know.

Yes, a high volume oil pump(cast iron)would use more HP than the standard aluminum oil pump which came on base 2.8 and 3.1. The Fiero's 2.8 is an HO and came with a high volume pump. My question was did Comp-Cams know that the roller-rockers were to be used with a "stock" fiero and not a base 2.8? Would shimming the bypass spring to up the pressure help with the lack of oil to the rockers? Maybe increasing the diameter of the oil passages to the rockers would be a work around. For a vendor to say their product might cause harm to your engine is unusual I think.