427R Drive Ability

[patrickt]

Alright, 244/256 with a 112 LSA is a just hair larger than mine, but I have 20 cubes more, which helps, and I have no problem whatsoever. I'm now thinking that a really careful tune-up might be the answer, and certainly it's the first step.

[blykins]

That is the laziest cam I’ve ever seen and the amount of overlap is what causes the low rpm bad manners. You can’t compare .050” durations and lobe separations to judge which cam is more aggressive or less aggressive. You have to look at all the specs.

[patrickt]

Alright... can he swap a cam out in that car without having to pull the engine?

[blykins]

Why does he need to? Just needs tuned and he needs to know he can’t lug the engine around at 1200 rpm. Easy.

[patrickt]

If it's the laziest cam you've ever seen, then he might just want to spend a couple of hundred bucks and pop a better one in... especially if he can do it without pulling the engine.

[eschaider]

Originally Posted by blykins

That is the laziest cam I’ve ever seen and the amount of overlap is what causes the low rpm bad manners. You can’t compare .050” durations and lobe separations to judge which cam is more aggressive or less aggressive. You have to look at all the specs.

Originally Posted by blykins

Why does he need to? Just needs tuned and he needs to know he can’t lug the engine around at 1200 rpm. Easy.

Amen, Brent!

To the OP, things just got even easier for you, if that is possible. Time to learn how to tune your car.


Ed

[14vision]

Originally Posted by olddog

It occurred to me that the OP has never actually explained the bad manors. We have all assumed that he just doesn't like the low rpm tendency to want to buck and hop if you try to make a quick blip on the throttle or open the throttle too much at very low rpm.

An engine running too lean can hesitate, even pop up the carb and backfire. It can also cause surging. Not all engine builders take the time to tune anything other than WOT on the dyno. In fact most do not. Especially if they are a large shop that builds cookie cutter engines (100s of the exact same engine). They may tune one or two and just set all the rest the same.

Then there is the timing. The big three engineers spend hundreds of hours finding the ideal timing to make maximum break torque at every rpm and every % load combination. Then they change the commanded fuel ratio and do it all over again. All this while measuring emissions. This is how they maximize mpg, minimize emissions, and get good manors and good Hp.

Most engine builders will not even make a low rpm dyno pull. This is the danger zone where engines self destruct from detonation. They will argue that you should never operate a performance engine in that range anyway. Fair enough, but this is the proof that nobody has spent the time getting a good tune down in the low rpm range. This can be done with EFI, but there are not many tools to work with on a carb and mechanical distributor.

Does your engine have vacuum advance? If not, one less tool, and a terrible way to run a street engine. It's fine for a race only engine, because it will spend little time at low rpm.

I have digressed. My point to all this is: Take your car to a good tuner with a chassis dyno. The best dyno for this is the type that can hold a set load or a set speed and can change this on the fly. I forget the name for this. The dyno that just spins a heavy wheel is better suited for WOT pulls. You can do some tuning, but not everything. Then they have to take the car out on the street to finish up.

With the engine well tuned, it may resolve most of your issues. Then it is a matter of training the driver not to try to run the engine where it does not want to run. At some point in time you just have to realize this is not your fathers station wagon. It's a fricking race car, and you need to treat it as such.

Very valuable information and I certainly appreciate it. I am in a unique situation as I live relatively close to BDR down here in south Florida , but I bought the car from an out of state dealer for several reasons. Car is brand new, 3 month old build with now 100 miles on it. The issue I see mainly is in first gear starting out I experience surging and even if I try to just drive at 10mph steady car runs rough unless I increase rpms and get into 2nd gear. As speed and rpms increase car runs strong. I probable agree the car needs a good overall tune. Engine was installed at speed fanatix in Boynton which is bdr’s engine installation sister company. The real challenge as I have experienced in the past with my former bdr cobra is BDR lack of customer support etc. This is 2nd time I have experienced this and I thought over the last couple of years as they grew they would address this and other issues many customers have had issues with. I know there are many in the community that have had a great experience with BDR which is good, but unfortunately I haven’t been that lucky. I am obviously not as mechanically inclined as many out there and that is ok, and I am willing to pay for what is needed. I will try to locate a shop in south Florida like you mentioned that has the experience to handle high performance engines for a tune. I have learned a lot from reading many of the valuable posts. The warranty as stated probably would end up being a waste based on parts only and having to pay $135 hour for labor to deal with a warranty issue.

I certainly appreciate all the great feedback....

Thanks
Doug

[fastd]

have an air fuel gauge installed so you can see how you carb is delivering fuel and air to the engine. that way you can tell where your issue is and it’s a good way to see what kind of job your tuners have done.

[Anthony]

With the cam having duration @ .050 of 244/256, I would say it’s too big. I think something like 226/236 would bring the power band to 2000-6000 rpms with much better street ability still retaining good mid range power

[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

[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.

[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?

[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.

[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.