427R Drive Ability

[blykins]

Originally Posted by tomshep

The cam card specs are quoted with 1.6 rockers. Is it possible to get 1.5 ratio for those heads? That will tame the cam.

Tom

Lift has nothing to do with how tame a camshaft is. You need to focus on durations and LSA. All of those work together to create overlap, which is the amount of time both valves are open at the same time. If both valves are open at the same time, no vacuum is being made. If no vacuum is being made then you have reversion. The OP’s cam has 88 degrees of overlap. Normally I would aim for somewhere around 65-70 with these engines while keeping the powerband the same. It’s just a lazy old lobe to keep guys from hurting valve springs and burning pistons up. Crate engine. Assembly line, universal....

An NHRA stock eliminator camshaft can be a very nasty mannered camshaft but in a lot of cases will only have about .400” lift. I can also grind a very docile cam that has .700”-.800”-.900” lift.

[FredG]

Talk about complicating something.....When I purchased the car the previous owner told me the 427r was a bit finicky in that it didn't like lower RPM's specifically under 2k but past that the power comes on very quickly. I think it took all of about 15 min to adjust my driving habits and shift points. Problem solved.....nothing else need.

Fred

[twobjshelbys]

Originally Posted by FredG

Talk about complicating something.....When I purchased the car the previous owner told me the 427r was a bit finicky in that it didn't like lower RPM's specifically under 2k but past that the power comes on very quickly. I think it took all of about 15 min to adjust my driving habits and shift points. Problem solved.....nothing else need.

Fred

And the IR is even more finicky! The faux-8-stack trumpets and throttle bodies don't deliver a manageable air flow to optimize the fuel injection into the cylinider resulting in a system that can be optimized for idle or top speed but not both. I ended up running my idle at about 1200 RPM.

[Anthony]

Originally Posted by FredG

Talk about complicating something.....When I purchased the car the previous owner told me the 427r was a bit finicky in that it didn't like lower RPM's specifically under 2k but past that the power comes on very quickly. I think it took all of about 15 min to adjust my driving habits and shift points. Problem solved.....nothing else need.

Fred

Yes. The only issue I have had regarding a cam, is with an all aluminum engine, and solid roller, that do to thermal expansion, I had to try to adjust the lash so tight when cold, I had some issues starting and running the engine until it warmed up, and then was fine after that, although I had to run the lash a little looser than recommended.

[olddog]

Originally Posted by blykins

Lift has nothing to do with how tame a camshaft is. You need to focus on durations and LSA. All of those work together to create overlap, which is the amount of time both valves are open at the same time. If both valves are open at the same time, no vacuum is being made. If no vacuum is being made then you have reversion. The OP’s cam has 88 degrees of overlap. Normally I would aim for somewhere around 65-70 with these engines while keeping the powerband the same. It’s just a lazy old lobe to keep guys from hurting valve springs and burning pistons up. Crate engine. Assembly line, universal....

An NHRA stock eliminator camshaft can be a very nasty mannered camshaft but in a lot of cases will only have about .400” lift. I can also grind a very docile cam that has .700”-.800”-.900” lift.

Well yes and no. The Chevy sbc guys have changed out their 1.5 ratio rockers for 1.6 ratio rocker for 50 years, or more, to get a bit more performance. It increases lift, but it also increases the 0.050" duration a tad bit, too. We all compare the 0.050" duration because it is generally accepted that nothing significant is happening below that. I read where they have actually measured the 0.050" duration before and after a rocker ratio change, but I cannot recall the actual numbers. It seems like it was a degree or two on each end for a total of 2 to 4 degrees duration change. It can be around 25 hp on a dyno. Nothing huge, more like a little, but never the less some change.

Now if you were to tell me that it is so minimal an impact on idle quality and low end manors that it is not worth the work to change out the rockers (let alone the cost), I'm totally with you. However changing out the rockers is a lot easier to do than changing a cam, with the engine in the car. So then the question would be, is a few degrees less duration going to make much of a change in manors? Theoretically going in the right direction, but is it insignificant?

[blykins]

Originally Posted by olddog

Well yes and no. The Chevy sbc guys have changed out their 1.5 ratio rockers for 1.6 ratio rocker for 50 years, or more, to get a bit more performance. It increases lift, but it also increases the 0.050" duration a tad bit, too. We all compare the 0.050" duration because it is generally accepted that nothing significant is happening below that. I read where they have actually measured the 0.050" duration before and after a rocker ratio change, but I cannot recall the actual numbers. It seems like it was a degree or two on each end for a total of 2 to 4 degrees duration change. It can be around 25 hp on a dyno. Nothing huge, more like a little, but never the less some change.

Now if you were to tell me that it is so minimal an impact on idle quality and low end manors that it is not worth the work to change out the rockers (let alone the cost), I'm totally with you. However changing out the rockers is a lot easier to do than changing a cam, with the engine in the car. So then the question would be, is a few degrees less duration going to make much of a change in manors? Theoretically going in the right direction, but is it insignificant?

Changing to a higher rocker ratio will affect duration, but it does it by a rather insignificant amount, like 1-2°. A 1-2° change at .050" duration isn't going to be enough to change the engine's manners or driving characteristics, or in this case, change the engine's personality into something docile.

[patrickt]

Well, it's not going to fix itself. I'd like to see the OP move on a plan of some sort by Monday.

[FredG]

Although I have enjoyed the theoretical/practical expertise being expressed here, all of this brings me back to the advise I received from the best mechanic I ever knew from back in the mid 70's. He told me to make sure I have the right tool to do a job properly and to never try and fix something that isn't broken. Well, no tool advice is needed here so..........part 2 applies.

Fred

[olddog]

Originally Posted by blykins

Changing to a higher rocker ratio will affect duration, but it does it by a rather insignificant amount, like 1-2°. A 1-2° change at .050" duration isn't going to be enough to change the engine's manners or driving characteristics, or in this case, change the engine's personality into something docile.

As always, I value your input and experience. You provide a great service to this site.

Thank you for humoring an old dog.