This is a 2 part question, the first part being more a general question on how people select the rocker ratio they use, and the second part, Whether or not in my case, I would gain any advantage in increasing the rocker ratio in my engine.
1/ What factors influence the rocker ratio you choose for your engine? With todays camshaft technology, can more valve train stability be gained with lower cam lits, and higher rocker ratio's etc?
2/ I have a 360 Chrysler engine that I will finally start freshening next year. It has been run before and made around 600hp. I bought the engine disassembled minus the camshaft and the pushrods. It has 1.5:1 Harland Sharp rockers that have been blueprinted by Hamburger. I would like to run ball/ball one piece 3/8" thickwall pushrods , so I will need to change the adjusters, but I may just upgrade to a set of Jesel Sportsman rockers in a higher ratio. Here's is what's in the engine-
4.02" Flat top Venolia Gas ported & lightened pistons
BME rods, replacing with Groden or MGP's
W2 early castings, flow 313cfm@0.600" 296@0.500"
2.08"/1.60" 3/8" stem Manley Pro Flow Valves
Solid Roller, Yet to be purchased, either going Comp or LSM
Harland Sharp 1.5:1 Roller rockers
Factory Block, half filled
Factory Cast Crank
Drag only engine
Compression is around 11.5:1 , calculated with the rods cold
Anything else, don't hestitate to ask.
Let the discussion begin
AL...
Rocker Ratio's
Moderator: Team
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bill jones
- Guru
- Posts: 2650
- Joined: Sun Sep 05, 2004 6:38 pm
- Location: salt lake city, ut
- Contact:
-What choices do you have for rocker ratios other than 1.5:1?
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-Where you have the shaft centerline locked into place the only way the rocker ratio can be changed is to move the rockers adjustment screw closer to the shaft.
-One of the main advantages of increased rocker ratios happens when you can move the shaft away from the valve, to get a longer arm from the trunnion or shaft over to the valve tip.
-This improves the ratio over the full sweep very dramatically, but it means the pushrod end of the rocker is moved closer towards the valve cover and gasket usually to where there becomes interference issues.
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-Have you ever profiled the activity at the VALVE in a race ready condition?
-If you haven't, then now is the time to find out what the VALVE has been doing with your existing combination, and then see what you gain with the supposedly latest greatest changes you buy.
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-One problem you always face with shaft mounted rockers is getting the geometry right especially when you try to use different ratios between the intake and the exhaust, and/or when you have a difference in basecircle diameters and lobe lifts.
-Like if you wanted to run 1.65 intake rockers and 1.5 exhaust rockers you end up having to change the exhaust valve length to a longer valve because if you get the intake geometry worked out real nice, the exhaust will be way off until you get a longer exhaust valve in there.
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-In looking at your engine specs I wonder why the low compression ratio if you are not limited by rules.
-Second deal is if you change to 3/8" pushrods with ball & ball ends you have to remember that the Chrysler uses a larger diameter ball in the lifter than Chevys do so you can't just drop in the easy to get SBC pushrods.
-If you attempt to run lots of lobe lift at the valve with 1.5's the sweep across the valve tip is real ugly when you start getting up into the .550" plus range so you really need to get the high rocker ratio's in there just to get the sweep across the valve under control.
-The amount of sweep you have now, and how much better you can make it will require that you get serious on understanding the geometry and get in there and seriously look at what's happening.
------------------------------------
-Where you have the shaft centerline locked into place the only way the rocker ratio can be changed is to move the rockers adjustment screw closer to the shaft.
-One of the main advantages of increased rocker ratios happens when you can move the shaft away from the valve, to get a longer arm from the trunnion or shaft over to the valve tip.
-This improves the ratio over the full sweep very dramatically, but it means the pushrod end of the rocker is moved closer towards the valve cover and gasket usually to where there becomes interference issues.
----------------------------------
-Have you ever profiled the activity at the VALVE in a race ready condition?
-If you haven't, then now is the time to find out what the VALVE has been doing with your existing combination, and then see what you gain with the supposedly latest greatest changes you buy.
----------------------------------
-One problem you always face with shaft mounted rockers is getting the geometry right especially when you try to use different ratios between the intake and the exhaust, and/or when you have a difference in basecircle diameters and lobe lifts.
-Like if you wanted to run 1.65 intake rockers and 1.5 exhaust rockers you end up having to change the exhaust valve length to a longer valve because if you get the intake geometry worked out real nice, the exhaust will be way off until you get a longer exhaust valve in there.
---------------------------------
-In looking at your engine specs I wonder why the low compression ratio if you are not limited by rules.
-Second deal is if you change to 3/8" pushrods with ball & ball ends you have to remember that the Chrysler uses a larger diameter ball in the lifter than Chevys do so you can't just drop in the easy to get SBC pushrods.
-If you attempt to run lots of lobe lift at the valve with 1.5's the sweep across the valve tip is real ugly when you start getting up into the .550" plus range so you really need to get the high rocker ratio's in there just to get the sweep across the valve under control.
-The amount of sweep you have now, and how much better you can make it will require that you get serious on understanding the geometry and get in there and seriously look at what's happening.
Thanks for the reply Bill. I have not done a dummy assemble on the engine as yet to test these things out, and to be perfectly honest, the compression ratio is just an approximation. I still have to sit done and mic up everything, and see what the bore clearance etc is like.
The engine was originally built in 1981 by Seymour Pederson , who I believe is now very much involved with the Slant 6 Racers association these days. It was imported to Australia after Seymore did a season or two on it, and it has sat around ever since. I bought the engine very cheap, so cheap that selling off a set of new bare W2 heads, a set of Arias Pistons, Eagle rods and a second hand gear drive basically paid for the engine.
Anyway, I haven't really played around with checking the rocker sweep at all, so it's something I should take a look at. From what little reading I have done on the subject, depending on the design of the rocker arm itself will determine the rockers tips rate of sweep over the valve tip through it's sweep. What should I be look for here Bill? Should I be trying to centralise and minimise the sweep, what will determine the needing of longer valves etc? Obviously the camshaft profile will affect all of this as well I would imagine, unfortunately , the two Roller camshafts I have sitting here are much bigger than what I would put in the engine, unless I increase the compression ratio up to around 14.5:1-15:1. Lastly, I would not imagine needing anymore than a 1.65:1 rocker in this engine, The heads peak at 0.600" and fall over after that, so I would think anymore than 0.650"-0.700" would be a waste. If I am wrong, feel free to explain why, I am here to learn off you guys.
Thanks , much appreciated
AL...
The engine was originally built in 1981 by Seymour Pederson , who I believe is now very much involved with the Slant 6 Racers association these days. It was imported to Australia after Seymore did a season or two on it, and it has sat around ever since. I bought the engine very cheap, so cheap that selling off a set of new bare W2 heads, a set of Arias Pistons, Eagle rods and a second hand gear drive basically paid for the engine.
Anyway, I haven't really played around with checking the rocker sweep at all, so it's something I should take a look at. From what little reading I have done on the subject, depending on the design of the rocker arm itself will determine the rockers tips rate of sweep over the valve tip through it's sweep. What should I be look for here Bill? Should I be trying to centralise and minimise the sweep, what will determine the needing of longer valves etc? Obviously the camshaft profile will affect all of this as well I would imagine, unfortunately , the two Roller camshafts I have sitting here are much bigger than what I would put in the engine, unless I increase the compression ratio up to around 14.5:1-15:1. Lastly, I would not imagine needing anymore than a 1.65:1 rocker in this engine, The heads peak at 0.600" and fall over after that, so I would think anymore than 0.650"-0.700" would be a waste. If I am wrong, feel free to explain why, I am here to learn off you guys.
Thanks , much appreciated
AL...
-
bill jones
- Guru
- Posts: 2650
- Joined: Sun Sep 05, 2004 6:38 pm
- Location: salt lake city, ut
- Contact:
-Depending on what you intend to use it for and how hard you want to run it, IE: how greedy are you for power, what you have for tools and equipment & ambition, and of course money & time all end up having a part in what happens here.
-You have to have a baseline and check it out really good, then get an idea and try a change, then run that change to prove it was or wasn't worth anything.
-Guys who run stud mounted roller rockers or separately mounted shaft rockers have life real easy when it comes to getting the rocker geometry correct, and when wanting to make ratio changes with great success, and we can run any ratio combinations we want and about any basecircle size without too much problem other than maybe a pushrod length change.
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-BUT--where you have BOTH rockers geometry initially dictated by the single shaft and the fixed height (and distance from the valve tip) of the saddle in the head, you are just sort of between a rock and a hard spot when it comes to doing neat tricks with the final out come.
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-I think you need to look at all the choices that are available, the amount of machine work expense necessary to move the shaft up or down or back away from the valve tip, decide whether or not you want to buy special length valves and pushrods an all that stuff.
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-From what I've seen of cast iron heads of that era, most seem to respond to about all the INTAKE lift you get regardless of the flow numbers, and you are usually limited in lift by the poor (long) sweep patterns of the low 1.5:1 ratios.
-I haven't necessarily seen where on cast iron or low port SB Chevys where high exhaust valve lift ever did anything for power but intake lift alwyas seems to help , as long as it doesn't get into a relaibility problem.
-Much of my thinking comes from asphalt oval racing experiences from too many years ago but I still think you need to get your big eyeballs on and get in there and see what-when-why & how it all relates to "at-the-VALVE" activity.
-I could maybe help you out if you had the engine assembled in a race ready state and could get me some numbers of where the valve is in relation to the degree wheel, in .100" valve lift increments.
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-Part of the idea is to know how far the roller tip moves back and forth across the valve tip, and this also is directly related to how far the pushrod moves in relation to the shaft centerline, and you want the least amount possible to get the max lift at the valve.
-An example is the roller tip may move "out" something like .100" and then back in maybe .020" on a typical SB Chevy but if you could get the numbers down to .045" out and .045" back and still get the same total lift at the valve, AND at the same time the roller tip pressure point is fairly well centered on top of the valve, which do you think is best?
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-One other problem I've seen is when machining for larger OD springs and smaller ID springs is hitting the water jacket (I think it happens when cutting for the inner springs) so you need to know what's right there in the castings.
-One other advantage of a longer rocker arm/higher ratio/relocated shaft pivot is that you can get a larger valve spring under the underside of the rocker body.
------------------------------------
-There's a guy who's posted here named RyanJ from Shady Dell Speed Shop in PA. somewhere that is a specialist in these small block Mopars that if we could get him involved we'd probably all learn something.
-You have to have a baseline and check it out really good, then get an idea and try a change, then run that change to prove it was or wasn't worth anything.
-Guys who run stud mounted roller rockers or separately mounted shaft rockers have life real easy when it comes to getting the rocker geometry correct, and when wanting to make ratio changes with great success, and we can run any ratio combinations we want and about any basecircle size without too much problem other than maybe a pushrod length change.
-------------------------------------------------
-BUT--where you have BOTH rockers geometry initially dictated by the single shaft and the fixed height (and distance from the valve tip) of the saddle in the head, you are just sort of between a rock and a hard spot when it comes to doing neat tricks with the final out come.
---------------------------------------------
-I think you need to look at all the choices that are available, the amount of machine work expense necessary to move the shaft up or down or back away from the valve tip, decide whether or not you want to buy special length valves and pushrods an all that stuff.
----------------------------------------
-From what I've seen of cast iron heads of that era, most seem to respond to about all the INTAKE lift you get regardless of the flow numbers, and you are usually limited in lift by the poor (long) sweep patterns of the low 1.5:1 ratios.
-I haven't necessarily seen where on cast iron or low port SB Chevys where high exhaust valve lift ever did anything for power but intake lift alwyas seems to help , as long as it doesn't get into a relaibility problem.
-Much of my thinking comes from asphalt oval racing experiences from too many years ago but I still think you need to get your big eyeballs on and get in there and see what-when-why & how it all relates to "at-the-VALVE" activity.
-I could maybe help you out if you had the engine assembled in a race ready state and could get me some numbers of where the valve is in relation to the degree wheel, in .100" valve lift increments.
--------------------------------------------
-Part of the idea is to know how far the roller tip moves back and forth across the valve tip, and this also is directly related to how far the pushrod moves in relation to the shaft centerline, and you want the least amount possible to get the max lift at the valve.
-An example is the roller tip may move "out" something like .100" and then back in maybe .020" on a typical SB Chevy but if you could get the numbers down to .045" out and .045" back and still get the same total lift at the valve, AND at the same time the roller tip pressure point is fairly well centered on top of the valve, which do you think is best?
--------------------------------------
-One other problem I've seen is when machining for larger OD springs and smaller ID springs is hitting the water jacket (I think it happens when cutting for the inner springs) so you need to know what's right there in the castings.
-One other advantage of a longer rocker arm/higher ratio/relocated shaft pivot is that you can get a larger valve spring under the underside of the rocker body.
------------------------------------
-There's a guy who's posted here named RyanJ from Shady Dell Speed Shop in PA. somewhere that is a specialist in these small block Mopars that if we could get him involved we'd probably all learn something.
Thanks for the info Bill. I actually know Ryan through a Mopar web Board, Moparts.com, He has helped me quite abit in the past with identifying W2's etc, he is abit of a wealth of knowledge when it come's to the Small Block stuff. I will have to contact him.
Thanks again Bill, Much appreciated.
AL...
Thanks again Bill, Much appreciated.
AL...