valve lift and rocker arm ratio |
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Lizer
Member Joined: 04-January-2020 Location: SW Michigan Status: Offline Points: 70 |
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Posted: 28-November-2020 at 6:06PM |
I'm rebuilding my 351M (it's going to become a 410) and Comp recommends an after market rocker arm to accommodate the cam lift. They recommend something like their Magnum roller tip rockers (which require converting my pedestal mount heads to stud mount, Crane has a screw in kit to do this fairly easily.)
The thing is the stock rockers on my heads are 1.73 ratio, and the Magnums are 1.72 ratio, so the stock rocker arms should still allow for plenty of lift--even a little more than the aftermarket. Is there something I'm still missing? Here are the cam specs. Intake lobe lift for instance, is 0.298. Multiply that by 1.73 = .52, which gets me right where I want to be with the cam's rated lift at 0.513. Grind Number:XE262H Engine Family:Ford 351C, 351M-400M 8 Cylinder (1970-1983) RPM Operating Range:1,400-5,600 Cam Type:Hydraulic Flat Tappet Lifter Style:Hydraulic Flat Tappet Camshaft Series:Xtreme Energy Camshaft Gear Attachment:1-Bolt Usage:Street/Performance Valve Springs Required:Yes Camshaft Material:Cast Iron California Proposition 65:WARNING: Cancer and Reproductive Harm P65Warnings.ca.gov Advertised Intake Duration:262 Advertised Exhaust Duration:270 Intake Duration at .050 Inch Lift:218 Exhaust Duration at .050 Inch Lift:224 Intake Valve Lift:0.513 Exhaust Valve Lift:0.52 Lobe Separation:110 Assembly Lubricant Included:Yes Intake Centerline:106 Lobe Lift Intake:0.298 Lobe Lift Exhaust:0.301 |
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78 LTD II sports touring package (blue), father original owner
67 Mustang (5.0) 69 Mach 1 428 SCJ Drag Pack |
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72FordGTS
Admin Group GTS.org Admin Joined: 06-September-2005 Location: Ontario, Canada Status: Offline Points: 5802 |
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The cam on my 408 has .321" of lobe lift. My engine uses the Scorpion pedestal mounted roller rockers and they work fine. They are the correct 1.73:1 ratio which gives me .555" of total valve lift. I know lots of others have used these rockers as well.
Edited by 72FordGTS - 29-November-2020 at 2:01AM |
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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Lizer
Member Joined: 04-January-2020 Location: SW Michigan Status: Offline Points: 70 |
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Did those work with stock valve covers or do they require taller ones? And do you know what the difference between those and the Endurance 3024 are? Or the Race 1024?
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78 LTD II sports touring package (blue), father original owner
67 Mustang (5.0) 69 Mach 1 428 SCJ Drag Pack |
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72 RS 351
Senior Member Joined: 04-September-2014 Location: Knoxville TN Status: Offline Points: 2765 |
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Those are decent moderate cam lift figures. The studs of stud mount rockers are a weak link, and pedestal mount studs are smaller(5/16") and worse case scenario, weaker link still. I'm just cautioning, the pedestal mount studs are not very strong, those should never be used with high rpm or long term use. It's a big subject that doesn't get discussed hardly ever. So I'm sorry to be pointing out something that engine builders should think about, but virtually nobody does. Any stud mount roller rocker is less reliable than a stock OEM pedestal mount, no roller, cheap slide, rocker system. The OEM type can last for decades easily. The studs of the other type are experiencing high side load forces. It typically isn't a problem for an engine raced at a track occasionally, or sees very low miles per year. The issue is often from long term, many miles of street use. At some point wear and stress on the studs will break one, and that is bad and you don't want that. Keep an eye on your rocker studs, R&R the VC's yearly to inspect the studs where the trunion rides. The ideal rockers are shaft rockers, but those are crazy high($1000-$1700). That lift level of the low .500" range is best for stud mount rockers, and anything ratio in the 1.7-1.73 range is fine for a Cleveland head(they can all attain a good valve geometry).
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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72FordGTS
Admin Group GTS.org Admin Joined: 06-September-2005 Location: Ontario, Canada Status: Offline Points: 5802 |
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They clear the stock valve covers without issue (I am running stock valve covers). I pulled up my parts list, and it looks like my engine has the 1056 arms, which are the race series. From what the decription says, the race series are decribed as:
" They're precision-crafted by high-tech manufacturing methods, then fully CNC-machined. These rockers offer more clearance for retainers and springs, and can easily handle .950 in. lift and 950 lbs. of open spring pressure." Tim Meyer of TMeyer Inc was the one who suggest those rockers. He's built a ton of engines 335 series engines, so I trust his experience. I was looking at converting to stud mounted rockers but he talked me out of it. He said for stock heads the machine work cost makes it better of to go to aftermarket heads (which I didn't want). Here are some pics of my engine: |
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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72 RS 351
Senior Member Joined: 04-September-2014 Location: Knoxville TN Status: Offline Points: 2765 |
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You guys are keeping your rpm's down I'm sure, that helps a bunch. I had that kind of pedestal rocker on my first 351C in 1981. I was young in College and knew very little about engine concepts. I had just built that as my first engine. I did have one valve spring break, they were a used set from a friend's son, I forgot about that, when one header pipe was cherry red, scary.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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Steve M.
Senior Member Joined: 08-June-2019 Location: Florida Status: Offline Points: 1740 |
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Yup,
Remember having no money in the early days. I learned the hard way about torque settings and stretch the hard way.
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Steve M.
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Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
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1.72 vs 1.73 won't make a ratsasshair's worth of difference in the real world. the Crane stud kit will hold up to the spring pressure the XE262 requires if it's installed properly, but don't forget bolt down pedestal rockers are adjustable by shimming the pedestal and altering pushrod length to achieve correct geometry and lifter preload. you still have to check for correct pushrod length when changing to an aftermarket roller rocker, there's no guarantee the critical points are in exactly the same locations as the stock rockers
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72 GT Ute
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Lizer
Member Joined: 04-January-2020 Location: SW Michigan Status: Offline Points: 70 |
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The crux of my question is really if it's safe to stick with my stock rockers (what I'd prefer) or if I need to use something with a roller fulcrum. The stock rockers have the ratio necessary to achieve the lift, but somebody else pointed out to me the fulcrum slot in the stock rocker is the limiting factor. So the part about that which is confusing to me is the slot would still have to allow the rocker to attain a 1.73 ratio, otherwise it wouldn't be able to achieve the lift that ratio should be able to achieve. I don't do high RPM driving. On my Mustang, which I felt like I drove a lot this year, I only ended up getting 300 miles on it for the year (didn't even get my new rear end fully broke in :( ) and rarely do I exceed 4000-4500 rpm. I don't know that I ever have actually.
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78 LTD II sports touring package (blue), father original owner
67 Mustang (5.0) 69 Mach 1 428 SCJ Drag Pack |
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72 RS 351
Senior Member Joined: 04-September-2014 Location: Knoxville TN Status: Offline Points: 2765 |
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I don't know the limit of the stock rockers, but I think that very low .500" range is okay. If it was above .550" I'd worry about that. I too don't push rpm's high much, everything I own is an automatic and nothing special. I see 5000rpm in two of my three 98 SUV's, that's the stock point for the 302 and 4R70 trans as programmed. I'd call over 6k getting high rpm's. You might research more and see if someone knows what the lift limit of the stock rockers is. Rock may know or know where the answer is, he's a great source of information. I appreciate that too, that's invaluable for solving many issues, odd or common problems.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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72FordGTS
Admin Group GTS.org Admin Joined: 06-September-2005 Location: Ontario, Canada Status: Offline Points: 5802 |
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I am not going to pretend to be any sort of expert. I am just sharing my experience with my build, which doesn't sound too far off Lizer's engine. I can see high RPM use being an issue for the pedestal mounted rockers, but my engine sees maybe 5500 RPM max (WOT upshift). It's not a 351C spinning to 7K. I had many of these same conversations with Tim Meyer about the pedestal mounted roller rocker arms, and he reassured they were more than fine for my build. I am sure Rock will have more to say, he's our resident forum expert on these engines. Rather than retype things out, I went to the ultimate source on the matter - George Pence. This is what he has to say on the subject. He also mentions the Scorpion arms, but says to limited them to 400 lb over the nose springs.
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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72 RS 351
Senior Member Joined: 04-September-2014 Location: Knoxville TN Status: Offline Points: 2765 |
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Thanks Vince, that is excellent information about detailed guidance for the rocker arms and valvetrain. I was being conservative in my estimates of what would be reliable for the stock rockers. I like that one paragraph the most, about the Yella Terra rockers. I hadn't read about that part which bolts onto the stud pad as a base for a "shaft" for twin roller bearing rockers. That sounds very promising for long term use. For the 400 Lizer is building, I think the stock rockers or the Scorpion type of pedestal mount roller rockers would work well. His cam is not a radical lift or duration part, the springs will be under 400lbs I'll bet. The ARP bolts available to replace the stock rocker bolts are another great item to have available, for stock rocker uses. "If your motor’s cylinder heads are milled and tapped
for 7/16” stud & guide plate type rocker arms the Yella Terra
YT-6321 rocker arm is the hot tip. This very rugged rocker arm also
performs like a shaft mounted rocker arm therefore it requires no studs,
guide plates or hardened push rods. Internet pricing for the Yella
Terra YT-6321 rocker arm is in the range of $785 US dollars for a set of
16." |
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000+ rpm 351-4V &4R70W 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
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the 1st issue with using stock rockers is if they're used or new, if they're used they'll have a wear ridge set in at the travel limits. the wear ridge on the lift side is the one that causes trouble with a cam that has more lift than the cam that wore in the ridges. when the new cam causes the rockers to travel over & past that wear ridge the rocker will balk and jump over the bump like a parking curb. this shock occurring every cycle of the rocker will definitely piss off the cam & lifters new stock stamped rockers may be up to the task if they're set up at mid-lift, to have equal available travel both ways from center. and depending upon the rocker bodies themselves whether they're able to travel the needed amount at all? in the Ford OHO Newsletter there's an article describing how some rockers are formed a little different than others, you need to check them to make sure the 'bulge' doesn't inhibit travel in the fulcrum or interfere with the pushrod on the outside. |
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72 GT Ute
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Rockatansky
Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6059 |
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and beware discount offshore rockers, Billy Ray does a lift comparison of 2 rockers out of a set and the results are, not good |
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72 GT Ute
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