High ratio rocker arms?

[scottydont]

I'm a big fan of high ratio rockers as an easy bolt on mod for warming up an otherwise mild engine. I haven't done a TON of digging, but from what I have done, I haven't seen or heard much talk about ratio rockers for corvair engines at all. Are there many choices available for corvairs? I was thinking the rockers were compatible with other chevy engines, but not sure....

So am I just missing the posts and builds that people used ratio rockers?

Thanks

[UNSAFE]

I'm not sure but I don't think that there are any increased ratio rockers readily advertised for the vair.

I don't think chevy V8 rockers will work.

As far as I know the Ford small block rockers will work and I'm pretty sure that you could find different ratios with those .

Hopefully someone with more solid info will chime in .

I am using roller rockers as sold by Clark's but I think the ratio is stock.

[bbodie52]

How does an increase in Rocker Arm Ratio improve the engine's performance?

The lobe lift of the cam is increased by the ratio of the rocker arm to produce the final amount of valve lift. A cam with a .320" lobe lift using a 1.50:1 ratio rocker arm will have a .480" valve lift (.320" x 1.50 = .480"). If you install rocker arms with an increased ratio of 1.60:1, with the same cam, the lift would increase to .512" (.320" x 1.60 = .512"). The engine reacts to the movement of the valve. It doesn't know how the increased lift was generated. It responds the same way it would as if a slightly larger lift cam had been installed. In fact, since the speed of the valve is increased with the higher rocker arm ratio, the engine thinks it has also gained 2° to 4° of camshaft duration.

The end result is an easy and quick way to improve the performance of the existing cam without having to install a new one. See the Buyers Guide section for availability of increased ratio rocker arms. Remember, whenever you increase the valve lift, with either a bigger cam or larger rocker arm ratio, you must check for valve spring coil bind and for other mechanical interference.

http://www.cranecams.com/faqview.php?s_id=11


For some additional Corvair-related discussion on this topic, see: http://corvaircenter.com/phorum/read.php?1,152621


http://www.corvairspecialties.com/rollerrockers.html

ROLLER ROCKER ARMS

"At Reasonable Prices"

My roller rocker arms provide two very important attributes for the Corvair engine. First they significantly reduce valve stem to guide wear. Secondly they significantly increase cooling. I currently have stock of two styles...the 1:56(OEM ratio) in a single design for the 140 late model which are color coded for easy installation. I also have 1:7 high lift rocker arms(also late model) with two rocker arms mounted on a pedastal.

[scottydont]

Thanks for the links Brad. $450 for rockers is more than I'll probably ever spend on a $1000 vehicle, but at least I know that they exist. I'd be more likely to try to find a higher ratio OEM style rocker.... I'll have to do some research on Unsafe's suggestion that ford SB style rockers may work....

That first link leaves out one of the benefits of increasing rocker ratio. Aside from being an inexpensive, quick and easy way of increasing lift and duration, they give the added benefit of being able to run lighter springs and put less wear and tear on the valvetrain than a big aggressive cam. Since half of the valvetrain is moving at a lower speed, you need less spring pressure to fight the inertia and keep the valves from floating.

[Luke Geis]

I am using a set of ford 1.6 ratio rockers in my engine. I believe the stock ratio is 1.4? I believe the rockers are from a small block V8

[MAXREVS]

Part #1442-16 non-rail type roller tip steel ball pivot rockers are 1.6 ratio 7 will fit. About $150

[martyscarr]

Are there many choices available for corvairs? I was thinking the rockers were compatible with other chevy engines, but not sure....

Corvair rockers are very similar to small block Chevy rockers, but since they are in a horizontal position in operation they have the oiling hole for the rocker ball relocated. The oiling hole is placed so the rocker ball is lubricated by oil spray from a hole in the side of the pushrod. Additionally, they have a wider slot for the stud mount as the valves in the Corvair are canted slightly. This makes the rockers unique to Corvairs.

MAXREVS is correct that the Comp Cams roller tip rockers for small block Fords will work on Corvairs, but some modifications are needed. The slot on the Comp Cams rocker needs to be widened to accommodate the canted valves of the Corvair; stock rocker slot is about .075" wider than the Comp Cams rocker slot.

stock and 1.7 Comp Cams rocker #1450

Oiling to the rocker ball pivot should be provided, either by drilling a new oiling hole similar to the stock rocker, or installing a spray bar in the head. The original oiling hole in the Comp Cams rocker should be plugged. The Comp Cams rocker is made of 8620 chromemoly steel, and is very hard. You'll need carbide tooling.

Stock rocker ratio is somewhere between 1.5 and 1.57; the Comp Cams rocker #1450 is a 1.7 ratio. The 1450 rocker is a "rail type" rocker, meaning the rocker has extra metal at the roller tip to keep the roller on the valve (you can see them in the above pic). These "rails" can be ground down if they contact the retainer as they're not needed - the guide plate keeps the valve in contact with the valve. The #1442 rocker from Comp Cams is a 1.6 ratio, and does not have rails. The -16 means the package quantity is 16, they're also available in -8 and -12 quantities.

There are knock off roller tip rockers available, I will stick to Comp Cams products.

this rocker is off it's rocker ;)

Some people have used roller shaft/roller tip rockers made for the small block Chevy, but they impart a large side load on the valve and guide wear is increased. Harlan Sharp makes a very nice roller rocker correctly drilled for the canted valves, but it is only available in the stock ratio.

Marty Scarr

[scottydont]

Thanks for the info guys....
I'm wondering how much benefit going from nearly 1.6 (assuming the top end of the range that martyscarr gave) to 1.7 would actually give.... It's probably worthwhile, but I didn't know what the stock ratio was when I asked and was honestly thinking of a bigger jump. The air cooled VW's I used to wrench on had 1.1:1 stock ratio and aftermarket rockers were available up to about 1.6 ratio. 1.4:1 was a pretty popular choice for street engines. That's a much bigger percentage of change to lift and duration than what we're talking about here.

At least I know what to look for now. It's a low priority (I'm working on brake/suspension upgrades at the moment). As far as tooling to modify the rockers goes. I've got a little mill in my garage that would be perfect for the task.... And I'm always looking for excuses to buy tooling.... :)

[erco]

That first link leaves out one of the benefits of increasing rocker ratio. Aside from being an inexpensive, quick and easy way of increasing lift and duration, they give the added benefit of being able to run lighter springs and put less wear and tear on the valvetrain than a big aggressive cam. Since half of the valvetrain is moving at a lower speed, you need less spring pressure to fight the inertia and keep the valves from floating.

I've been considering 1.6 rockers and some of the reasoning above sounds wrong from a physics perspective. The "rocker ball stud to valve" distance is fixed, so the only way to get a 1.6 rocker is to move the pushrod dimple 6.5% closer to the ball. Comparing a 'regular' cam with 1.6 rockers to a higher-lift cam with 1.5 rockers, assuming the same total valve lift:

1) Valve motion/acceleration/forces remain the same: valve floating is not reduced. Spring pressure and stem wear the same.
2) 1.6 rockers increase forces & wear on the cam, lifter, pushrod, rocker & ball.
3) 1.6 rockers move the pushrod closer to the rocker ball, possibly rubbing on the guideplate hole at the extremes.
4) Rocker travel/rotation is the same, for similar valve lift.
5) Lifter & pushrod travel is 6.5% less on the 1.6 setup, corresponding with more force per #2.

I suppose #5 is what he meant by "half of the valvetrain is moving at a lower speed". Not sure if that compensates enough to reduce valve spring pressure or justifies increased stresses on the cam, lifters & pushrods.

Just thinking out loud here. Every mod is a compromise in performance & reliability, and stock parts have a lot going for them. As said in HTHCE, "It's hard to second-guess the factory engineers."