I was talking with my dad about rocker arm ratio's and the extra load they put on the lifter and cam lobe. We sorta agreed on some load must change, but is it enough to worry about? I have read that it doesn't matter, and also read that it does increase the load, and with all the problems with flat tappet cams, I would want to minimize what the cam sees. So my question to you is, what effect does raising the ratio have on the camshaft? Will the cam lobe have a higher pressure on it? Will the rocker stud have more side loading? I understand you gain lift and duration, thats not the question.
It works like adding spring pressure as far as adding load goes. I’ve talked with engine builders about this and they say use the correct camshaft and you don’t need to change rockers ratios. If you do change rocker ratios it should be specifically for a cam that is ground for it. I personally have seen instance’s where Increasing the ratio generated harmonics in the motor going from 1.5 to 1.6 on mopar big blocks. You need to check piston to valve clarence and coil bind before using and I would also check spring pressures. I read your post again and yes it effects load on camshaft and all parts connected, one other thing it is going to be a parasitic power loss that is it takes more power to spin the camshaft…
The question, will you gain with more valve lift. like oldiron 440 said piston valve clearance coil bind and retainer to guide clearance.
Yes it will increase the load on the camshaft. Using a stronger spring to contain the movement of lifters with a high performance cam profile/more lift will increase the load on the camshaft. A higher lift camshaft will increase the load on itself. All these things will cause differences in camshaft loading. Generally the problem with ruining a cam is that the springs are too stiff during break in. Many people use a lighter spring during break in. All that not withstanding, improper lubrication of the cam and lifters not rotating due to varnish buildup in the lifter bores will wipe a cam no matter what rocker arm or spring you are using. I would not worry about the difference a higher ratio rocker arm makes, as cams have a margin of error if everything was installed correctly and broken in properly.............still some people manage to wipe out new cams......even with stock ratio rocker arms.
I prefer not to run them, for that reason For most stockish / street applications, I consider it a crutch... just get the right cam. I have used it for tuning, swap 1.6 rockers on intake or exhaust, run the car, see if the car is faster and I want to step up a cam.
Thanks for the input, I totally agree, if you want more lift, do it with a camshaft swap. Dad had a set of 1.65 rollers that actually measured 1.7, if one wasn't attentive and just slapped them in, you could shut down a engine very quickly. I like to see more lift spread out over more of the lobe, just seems to me the load on the valve train would less then trying to get it all in in less duration.
I agree with @ekimneirbo , these are just another tuning tool. The OEMs use multiple ratios depending on application, but in most cases prefer a lower ratio for longevity/reliability reasons over performance. Pretty much any changes you make in the valve train for added performance is going to increase stress. Higher rocker ratios, bigger valves, stiffer springs, larger pushrods, more cam lift, each and every one of these will increase loads. With all that said, they do have a use. With just a rocker change you can get a meaningful increase in valve lift without increasing duration, which may be important to some. The big issue with flat-tappet cams is when increasing lift, do you increase duration by using a gentler ramp, or use a faster ramp limiting duration increase but possibly compromising cam wear? Less duration usually means better street manners. This is where roller cams shine; you can get high RPM performance without killing low-speed power. Every motor will be a bit different, as with any changes you need to check things to see if this is right for it.
I'm with crazy Steve, Factory had a tendency to use them in higher performance vehicles of the day. Also as Steve stated just about anything that raises performance in a motor especially valve train adds strain somewhere. Remove stock cam, add a bigger cam and you just added more stress, add bigger springs to handle that cam and more stress. Then add thicker, heavier push rods and more stress. Raising horse power raises stress thru out the entire engine, higher compression, higher rpm etc etc. Now to the original question, if I had top quality parts and was looking for a little more lift I'd have no problem adding the 1.6 rockers, I don't see it adding anymore stress than what I've already added to the entire motor as a whole. .
Funny though, with RA ratio. An SBC (stock) uses 1.5, doesn’t a a Ford small engine like 302, ect use 1.65? And a BBC 1.7 or something like that? Gotta be others I think.
Unless there's a problem with rocker-arm alignment, it comes down to your net valve lift, whether acquired by increased lobe lift/rocker ratio. The higher the lift, the more spring pressure required. Pedestal rockers are more prone to alignment issues than shaft-mounted rockers. Usually, a cam with more lobe lift will also have more duration, particularly if it's an off-the-shelf cam. Depending upon your particular application, a custom grind might be called for. If you're going from 1.5 to 1.6/1.6 to 1.7, a long as they're quality rockers/w no alignment issues, I see no problem with going with the increased ratio. Make sure you have compatible valve springs for your net valve lift.
Rocker ratios are your classic lever. You change it.... you change everything about the cam lift and you may be like 'Star Trek.... "going where no man has gone before". Lift ratios are another way to skin a cat. As long as you can do the math, you should be able to get your head around what the pros and cons are of each option. Just remember "two rights can equal a wrong" sometimes. Your friendly, neighborhood cam grinder has the best answers.
You also gain a bit more duration at 0.050" because it tightens up the ramp angle [and/or lash is set on the valve side of the rocker. Ford Cleveland's have 1.73 rockers. Ford roller rockers bolt onto BBC's which were 1.7 Engine designers used long rocker ratios in the quest for the holy grail of zero overlap and 180 deg of maximum valve lift [an impossibility] and to lower valve spring pressures which is one of the biggest internal frictions in an engine . Roller cams have helped with both these issues ^^^^ [in diesel engines originally where they needed short duration to maintain high cylinder pressures] Both methods have been adapted into the high performance engine arena
That's (in red) a pretty funny comment when you think about it..! Just HOW do you know...what...to buy ? I know that my crystal ball sometimes needs fresh battery's. Adding or subtracting a given amount of ratio, with different ratio rocker arms...will HELP...you pick that "right" cam, over your existing cam ! See how that works !? Mike
429/460 are also 1.73, '72-up use the same parts as Cleveland. Many of the aftermarket roller rockers marketed for Cleveland and 460 are actually the BB Chevy part. Geometry is wrong for the Ford, so you have to make sure the part is designed for a Ford before buying. The Chevy rocker will bolt on and work, but the roller tip is not centered on the valve.
Ted Eaton told me that he does not use lighter valve springs when breaking in a flat-tappet cam. Why? If there's going to be a problem, he wants to know/w the valve springs the engine will normally use. He doesn't want his customers to come back later/w complaints. If your engine builder knows what he's doing and backs his work, using lighter springs during break-in shouldn't be necessary.
Using some simple numbers and not accounting for any valvetrain friction, and assuming a linear increase in valve spring pressure: Scenario 1 is with a 1.5 to one rocker ratio. 0.333" cam lobe lift equals 0.5" lift at the valve, and a wimpy valve spring that has 100 lbs seat pressure and 200 lbs at 0.5" lift, the lifter/cam interface sees 300 lbs of pressure at 0.5" lift. Scenario 2 Now lets swap just the rocker arms, to a 1.6 ratio. 0.333" cam lobe lift equals 0.533" lift at the valve. The valve is now open a bit further, so we see some additional valve spring pressure at the new lift number. Based on a linear increase in spring pressure results in a 6.6% increase, or 212.12 lbs at the new maximum lift number. The cam/lifter interface now sees a maximum of 339.39 lbs of pressure, or an increase of approximately 13% over what there was with a 1.5 ratio rocker arm.
Don't forget the inertia. You need to move the weight of the valve etc. faster, meaning you need to accelerate it faster, and I don't think that comes with a linear change in the load, probably something more like the change squared. I.e. if it accelerates 10% faster, the load increases 1.1*1.1=1.21 = 21%.
Very interesting, Lets go with the above numbers and assume the same lobe shape on each one. cam A with .333" = .500" lift @ 1.5 ratio, cam B with .333" = .533" lift @ 1.65 ratio cam C with .355" = .5325" lift @ 1.5 ratio Cam C has more lift built in, spring pressure remains equal, so would the inertia be the only thing changing? To me its like using a short wrench verse a long one, it just takes way more effort with a short wrench.
Its well known that the initial break in period is critical and many people have different visions of what works, usually based on minimal experience. There are lots of variations in the components used, not only in quality but in the skills of the assembler. Its impossible to say that something will always help a situation as there may be some overlooked reasons for the failure. Putting lighter pressure springs in can help but still does not guarantee no problems.....its only a solution to one possible problem. Many cam manufacturers recommend not using anything but the external spring when breaking in a cam with a multi-spring set-up. Going with a lighter spring during break-in may help. If changing to the heavier pressure springs after initial break-in causes failure.............then it seems likely that those same springs would have caused the same failure if they were used in the initial installation. Spring pressures vary quite a lot, so its impossible to quantify when taking the initial lighter spring precaution might have helped prevent a problem. Its just one of those things where (in my opinion) it doesn't appear to have any negative outcome. If a cam fails with a lighter spring it most certainly would have failed with a higher pressure spring. Again, thats just my opinion.
I believe where you use and run your engine had a lot to do with rocker ratio and valve springs. All the old Motor Manuals show the SBC under 70 psi even at 270 hp and those engines turned in the 6000 range when asked. Your typical street car MIGHT see 5 to 5500 when hitting passing gear. Mine shifts at 4500 in drive when I stand on it at a light. I replaced the stock 1-1.45 with 1.63 I had made and didn’t change the the springs on my GMC racing engine.. cam lift is .380”. Cam engineers design cams for the job they are asked which is always a compromise. The first .100 to .200” of lift is the most important as the piston is really sucking the most. When the valve gets to .600” the piston is close to BDC and not much is coming in.
Maybe it's already been said, but if you do not use the valve spring pressure recommended by the cam manufacturer, the cam warranty will be invalid. My personal experience has been that the cam manufacturer recommended a higher open pressure than required. That tells me they're more concerned about coil bind and valve float.
I lost a bet one day because a good friend of mine asked me if I knew how to change the performance of a cam shaft without changing the cam itself. Increasing the rocker arm ratio, the correct answer. This whole discussion happened because he had just had a 358 engine built for racing by one of the Best Engine builder money can buy for short track racing. My friend had built many of these engines himself, and they all produced around 650 hp on s dyno but the one question he asked of the engine builder was what was the rocker arm ratio and the guy refused to tell him because he said if I told you that you would not need me any longer. It was something 1.8 range or higher if I remember correctly. Every time I went to me friends race shop I learned something new. One day he saw me looking at a 350 block when I noticed the pins for installing the heads had all been machined off set the heads could be moved to work better. Another time he had 3 brand New Edelbrook manifolds sitting on the bench, and he asked to take a close look at each one to see if I could detect which one had the runners all tricked up. I looked at each one a few times, and then he said to me one of them made 32 more horsepower on the dyno then the other 2 manifolds. I asked how much did that cost you and remember this was back in the mid 90s, and he said about $2,000 dollars. He said that cheap to gain 32 H.P. Jimbo Jimbo
This is way out of the league of anyone who is looking for a slight performance increase from a street-driven car. If you make your living racing, you'll do what you have to do to win, which can be very costly, and you'll be happy if your car lasts the race. Some of us old guys would like our cars to last as long (or longer) than we will, run on pump gas, and be docile enough for the street.
55blacktie: Your comment about being happy if your car last the race is very true. When you start building a race engine with a 14 to 1 compression ratio, they can explode very fast. Watching on many times, they installed the pistons and then checked it with the clay to see how close the tolerances were and then removing the piston and fly cutting the pistons for the valves was very time-consuming for sure. Jimbo
Maybe, but if you don't wipe the cam out when using a lighter spring, you don't have to worry about the warranty or all the metal that is inside your engine from the cam. If it wiped out using the lighter spring, it most certainly would have also failed with the heavier spring. The concern I would have is that the lighter spring might not have sufficient travel to prevent coil bind, then it would be the installers fault. Another way is to use the correct spring and not shim it for full pressure, then shim it after the break in. At any rate the spring of choice will need to have sufficient travel to prevent coil bind. Here is what Comp Cams Warranty says.............. Below you will see two pages from the Comp Catalog for common Chevy Cams. There is a note at the bottom of the first page that says "7 Stock Springs CANNOT be used". On the second page you will see that this note does not apply to all the cams they sell...........so apparently those cams may be used with stock springs. Generally it appears that as lift gets to .454 or more, stock springs cannot be used. Logically that is because they don't have enough travel before they bind. Notice also that this is with a 1.5 ratio rocker arm. The key here is that they sell a kit which would additionally have their recommended springs which undoubtedly will have more travel and higher pressure than stock springs. So the thing here is that they sell cams without springs and builders can use their stock springs. If someone buys a kit containing aftermarket springs, they can use either spring for break-in. Often people do not use the cam grinders catalog spring.....very common. I think as long as someone is using a similar spring they should not have a problem with the warranty.........especially if its less pressure......But I can't say every cam manufacturer is going to agree. As I mentioned earlier, these specs are for 1.5 ratio rocker arms. If someone used a 1.6 or 1.7 ratio rocker, then would they not be just as incorrect as someone using a different spring ? There really isn't one perfect answer because there are lots of variables when gathering parts. Sometimes the manufacturer is at fault and sometimes its gonna be the guy building the engine.
Comp Cams used to have a few cams that only a few engine builders could their get the hands on, and they were not listed anywhere in their catalog. When we needed a new camshaft the engine builder told us to call Comp Cams and ask for a certain cam which we had the numbers for and the guy from Comp Cams asked where we got those numbers from, so we told him, and after he made a phone call they called us back and agreed to ship us the cam. Made me wonder how often this practice goes on in racing. Jimbo
Some cam manufacturers are more picky than others. For instance, I know of at least one that requires that their cam lube be used. Years ago, I read something about valve springs having "memory." If, for instance, the rocker ratio were increased/higher lift cam installed without replacing the valve springs, the springs could fail. For that Reason, I had Al Hubbard's machine shop put my new springs on a valve-spring tester and compress them to max lift for the springs. I think the practice was called "defatiging" the valve springs. Maybe the quality has improved, because I have found no such recommendation online. What you have to consider is that cam, valve springs, rocker arms, and pushrods all work together; if you replace one, it's wise to make sure that it will be compatible with the rest, and all components should be in new/serviceable condition. I would not reuse flat-tappet lifters when replacing the cam.
I find it interesting that the part that is hard to come is finding a good set of lifters. The lifters seem to made out of junk material today, and sometimes new lifters don't ever make the first 600 to 1,000 miles before they fail. Lifters can be an engine builders nightmare today with their failure rate. Jimbo
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