CNC BLOCKS N/E

We build a lot of circle track engines with flat tappet cams and we use 1.8 and 1.9 ratio rockers and on these engine that the rules don't allow for roller cams we blue print machine the cam tunnel to the BBC size 2.120 which is only .020 smaller then a 50MM cam and by going to the bigger base circle cam we now can run more rocker arm without tearing the nose of the cam as the cam lobe has a much rounder nose which gives the lifter more area to ride on.

And runing the bigger base circle cam when we run more rocker ratio we run less duration as the valve accelerates alot faster and farther and we build more dynamic pressure using this set up and works great on restricted compression engines.

And a engine that turns under 7500 and we need more torque we will go from a 1.8 ratio rocker on the exhaust to a 1.5 which seems to pick the torque up if needed.

And going with a bigger core there is much less torsional twist over the standard SBC cams and better seat timing events from one end of the block to the other.

And either a flat tappet or roller cam with the bigger cam core the valve action is alway smoother then the smaller cam cores.

And once we blue print bore the cam tunnel then we correct the lifter bores by either bushing them back to standard or go to either .875 or .904 lifter bores depending on the application.

As we find lifter bores off up to .025 and on a flat tappet engine it really does not hurt to much as far as seat timing events because the lobe is riding on a slightly convexed surface, But when talking a roller lifters and they are center line to center line and if the lifter bores are off .025 or less it changes the seat timing events a ton now times that by 16 lifters.

We work with a lot of shops all over the country and Canada on preparing blocks for performance applications and my engine shop and the engine shops and engine builders we do work for do see a big gain on the dyno with bigger cam cores and bigger rockers.

Alot of the newer engines have bigger cam tunnels and higher ratio rockers HMMMMMMMMM

nesikachad

I guess I'm an opinion. I'll go kill myself now.

Nice post!

CNC BLOCKS N/E

The quote in my signature is on all my posts and it on all the websites I post on and don't be offended by this as that statement was not directed at you and don't go kill yourself it's just not worth it!!!!!!!!!!!

Another note we use alot of the .904 Jesel roller lifters where the rules allow with the bigger wheel which picks up on the opening ramp earlier and leaves later which does affect seat timing events which the cam grinder has to be made aware of the wheel size, But again it makes the valve accelaration that much more faster.

edcmat-l1

iTrader: (10)

Some people you just cant tell. I think we should just go back to 1.5s and be done with it.

nesikachad

No worries buddy. Didn't take offense, I thought it was a good one!

Eagles soar, but weasels don't get sucked into jet engines!

PortPros1

If you go with a higher rocker ratio you will pick up a bit of upper end power. If the heads you running continue to flow air at the same rate or better at the new lift number.

The question of stress on the valve train; the closed pressure will be the same. The open pressure will go up depending on the springs you have. Let's say you are running a Comp Cams 26120 spring installed at 1.950, closed you have 140lbs on the seat. At .600 lift you have 325lbs open, add .063 to the lift and you have 350lbs open. This will not put any undo stress on the valve train. As long as your .060 away from coil bind.

The gain you'll get by changing cams (going bigger) is more duration and more lift. The bigger cam with the 1.7 rocker ratio will in most cases make more power throughout the range than a small cam with a higher rocker ratio. The higher rocker ratio will open the valve further but the valves will be open for the same amount of time. The bigger cam will have more duration (the valve will be open for a longer period of time) and more lift, which will make more power.

Give me a call if you have any questions,
Advice is free.
Harold
Port Pros LLC

CNC BLOCKS N/E

On the engines we build and just going to a bigger cam seems to hurt the torque on our circle track engines we build andwe work with a lot of shops accross the U.S and Canada and on some of the top engines being built today the bigger cam tunnel and higher rocker ratio seems to be the hop set up.

I wish just installing a bigger cam would help our engines as It wolud save alot of time machining cam tunnels and lifter bores. Some of the DRC blocks are being machined for 70MM cams no and they are into some high ratio rockers.

Some of the cup teams are near 2.5 rocker ratios on some of there engines and the newer engines have higher rocker ratios and bigger cam tunnels so there must be something more to it then just stuffing a bigger cam in.

The higher rocker ratios aids in the valve acceleration rate alot and on some of the engines we build where we use bigger cam tunnels and 1.8 and 1.9 ratio rockers on the flat tappet engines we are only around 248 @ .050 and building a ton of torque and power and to get a cam in there to make that much power would have to be quite a bit bigger in duration which would kill the torque in the engines.

At our shop and the shops we deal with we all try build both torque and horse power.

Most guys that argue this point don't do this type of work machine work at there shop so they have nothing to compare against.

Gary Z

I'm considering going the 1.8-rocker route because it will be easy to switch back to 1.7 when I need to pass emissions testing. I just want another tenth off my ET.