With so much recent discussions on cams one question came to mind, how much does rocker ratio play in the horsepower role. I have champion heads with 1.65 rockers and stage 2 heads with 1.55 and 1.65 Jesel's . I know cam duration is increased with the higher ratio but when a cam is created are the rocker arms in the equation of making power. Just thinking...
Roller rockers
- Thread starter rag231
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gunzandgearz
gearzandgunz
- Joined
- Aug 24, 2015
Actually this isn't correct, first of all if you have to change the rocker ratio you don't have the right cam in the engine, if you change the rocker ratio and it changes the engine power, you should have had the cam ground for that spec. Secondly the longer rocker ratio does NOT change the duration of the cam, it [the engine] thinks the duration changed, but it physically doesn't change the duration.If you need explanation on why just let me know because a lot of people think this.
- Joined
- May 26, 2001
There is one important word/concept that most people do not understand or follow in the turbo world when building a car or engine, and that is "combination".
The "proper" combination in selecting all the necessary parts to achieve an optimum performance goal is very rare now days.
For example just selecting a cam depends many factors and choices of other parts, how the car will be used, and the goals of the owner?
Since it is rather easy to obtain more power that most people can and will use, there are usually many different methods and parts to achieve performance goals, and the simple way to select parts for a build is to find someone that has achieved the desired result without re-inventing the wheel.
A simple answer to your question is to increase RPM if you are looking for more HP.
The engine does not "think", it responds and reacts to how it is built and the supporting parts to make it perform.
The selection of the cam and rocker ratio is only a small consideration of the final goal.
The "proper" combination in selecting all the necessary parts to achieve an optimum performance goal is very rare now days.
For example just selecting a cam depends many factors and choices of other parts, how the car will be used, and the goals of the owner?
Since it is rather easy to obtain more power that most people can and will use, there are usually many different methods and parts to achieve performance goals, and the simple way to select parts for a build is to find someone that has achieved the desired result without re-inventing the wheel.
A simple answer to your question is to increase RPM if you are looking for more HP.
The engine does not "think", it responds and reacts to how it is built and the supporting parts to make it perform.
The selection of the cam and rocker ratio is only a small consideration of the final goal.
- Joined
- Feb 18, 2006
A little bit of extra lift and duration is not critical on a turbo car. You will get more results turning up the boost!
Like gunz n gears said if you have to change ratio on the rocker to try an achieve more lift then you didn't choose the right cam. It will not change duration the cam is ground like that when you bought it and installed it changing the ratio isnt going to magicly advance or retard the cam to change a few degrees. There is a lot that goes into this you can't just change rockers and think it is correct you have to measure push rods and make sure you have the correct geometry . A lot of people don't check this and think its all good. But it really does hurt valve guides and in the end performance. I have been screwed because of this on a set of heads i bought a few years back for a v8 sbc.
fastblackracing
Well-Known Member
- Joined
- Apr 7, 2009
Rag, I look at it this way, rocker ratio is tool that you can use if you have different sets to see how your engine responds to the change and changing to a higher ratio will make the cam appear several degrees bigger to the engine and of course the extra lift as well......the extra ratio will change the number of degrees of crank rotation that the valve is off the seat at a given amount of lift.....one other point to keep in mind is when specing a custom cam grind to end up with the valve lift and effective duration you want you are limited by what the lobe series has to offer and changing ratios is a great way to get the end result you are looking for......I recently did one for jr's new engine we are putting together and the lobe series I used that had the ramp speed and duration I wanted also had very high lobe lift [ .495"] and with a 1.7 ratio would put us over .800" lift and past the limit of what our spring package could handle so we dropped down to a 1.6 ratio to get it where it needed to be........to just blatantly state that changing rocker ratios means you have the wrong cam is bad information, I think it is just another tool to fine tune with.......and changing rockers is quite a bit easier than buying and changing a cam to see if a bit more or less helps your combo........Gearz I would like to see what T/R cams you have specked out that hit the mark 100% with out any room for improvement.......
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gunzandgearz
gearzandgunz
- Joined
- Aug 24, 2015
Ok so we can agree to disagree,but I have a question for you what part of my statement was not correct, the part where if you change rocker ratios and the motor picks up you didn't have the right cam in the motor to begin with, or the part where the actual duration does not change when you change rocker ratios.Please , explain to me which one of my statements were not FACTUALLY correct since you insist on calling me out.
The rocker ratio should be determined before the springs selected. The total lift and the opening/closing rate will determine the spring requirement and installed height. If you had a .325" lobe lift and 1.55 rockers and needed 150lbs seat and its 1.700and the coil bind height is 1.200" you might run into a big problem with more rocker ratio. Bigger ratios are great because they will increase lift and valve open time more where the head is actually capable of flowing more air and not adding much at all near the seat. You will need more pressure to maintain control with the higher ratio and you will have a harder time finding a spring that will work as well unless you want to run longer valves with wider springs. You could also spend a lot of $$$ modifying iron heads for strong near stock diameter double springs. There usually is a bunch to be gained elsewhere though. The cams 99.9% of TR owners run need more spring pressure because of the fast love design not the rpm.
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Duration increases measurably at higher lobe lifts with increased rocker ratios and decreases measurably with reduced ratios.
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gunzandgearz
gearzandgunz
- Joined
- Aug 24, 2015
I totally agree with that statement wayyyy too many problems messing around with rocker ratios unless your a pro and trying too dial in a specific combo. On a boosted application, call an expert, get close to the right cam and start adding boost,then comes the smiles.
gunzandgearz
gearzandgunz
- Joined
- Aug 24, 2015
Ok so heres the deal, because now we are confusing people, and anybody can agree or disagree with me, but this is fact.The valve duration does not physically change with rocker ratio increase,it only has the valve lifted farther off of the seat at a given lift point,in other words, if you have a 1.5 rocker ratio and you change to a 1.6 ratio the valve will be farther off the seat at that same lift point for the 1.6 than for the 1.5, but the duration DOES NOT physically change with a ratio change.You cannot physically change the duration that the cam was ground at, it will still leave the seat and return to the seat at the same crank degrees no matter what ratio you have.The valve curtain area will change but not the true duration.Now that isn't to say that the engine wont like the change but it still doesn't change the physical duration of the cam.So if you are like 90% of the guys on this board who aren't total pros at this and do it for a living then call a pro tell him what you are trying to achieve and get a cam that is right for your combo and then turn up the boost to reach your goals.
No. I think I'll let you spew your garbage out here. We've analyzed about 50 different cam lobes in the last couple years. No shit you can't alter the cam lobe with the rockers but you still wind up with changes in valve open time (duration) vs crankshaft position when changing ratios.
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mikestertwo
Well-Known Member
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- Sep 13, 2006
You are correct that the actual mechanical duration does not change but the affected duration most certainly does.
Mike Licht
I was here first
- Joined
- May 23, 2001
If you are talking about the seat to seat duration it does not change, if you are talking about the duration at .050 or the duration at .200 it changes measurably since the valve is getting to those opening points sooner with a higher rocker ratio. Its very simple math once you understand it.
Mike
Mike
mikestertwo
Well-Known Member
- Joined
- Sep 13, 2006
That is what I am talking about.
you may not get the answers you seek,there are plenty of guys who go really fast that don't know what cam is in the motor.no engine builder is going to give away every aspect of their build trust me.
True, but there are a few engine builders out there that used to build the Buick V6 that has no interest to do any more. One day I may have to put one back together. There are guys like Bison and many others that don't mind sharing a few technical details not necessarily secrets but a simple understanding of the mechanics. Can you imagine how many questions he gets a day about which turbo is better and why or why their performance doesn't match the TSM car that is running the same turbo? I turn wrenches on my motors and don't need every detail but when I have different motors and all of them have different rocker arm ratios I had to ask the question. Unlike the Mustang and LS crowd we don't have back to back tests on the available heads and rockers or 20 different intakes, and 12 cams, that come out in like every magazine issue, it would be real nice but each engine builder does have their own recipe for power, cam secrets being one. I don't think that there has been a lot of discussion there because up until a few years ago there weren't a need, looking at the TA SE heads there are 5 available ratios and the SI heads have 3. Champions have Harland Sharps, Scorpions, and T and D all with different configurations also.
gunzandgearz
gearzandgunz
- Joined
- Aug 24, 2015
I agree with you Mike and mikestertwo that the area under the curve will change and I stated that in my post that the engine would [think] that the duration has changed but the reason that I put that is most people will walk away thinking that it physically changes the duration and to me that's a disservice for a lot of guys on this board and other boards because they are on here to learn from the guys who are experienced in these areas.If someone makes a statement like and then leaves it open ended then guys don't learn, even me ihave been in this industry and the aviation industry for quite a few years now and have gained a lot of knowledge over the years and am willing to share what I have learned,which a lot of guys wont,they give you only bits and pieces So that being said hopefully we can all learn from each other and not get disgruntled when we have differing opinions,It seems like some guys on here just sit around and wait for someone to say something so they can jump on them and tell them how wrong they are. Even with all of the knowledge I have gathered over the 30 years ive been doing this I am still learning and still wanting to learn ,this is a great time to be a gearhead and I love this industry that I have spent most of my life in.
