I had a chat with some people from federal mogul (oe aftermarket parts distributor) AND a comp cams tech support person.
the springs can take about .550" of lift with comp, and that's a little more than the oe-style from fed. mog. at .510 I read somewhere that the ideal valve lift is achieved at .44" for maximum flow (any more is almost pointless/for the iron head the H/O 2.8 uses). stamped rockers don't carry consistent ratio (wont lift at 1.5x consistently, which is why a roller-tip option is slightly better) a 1.6 rocker is fine if you want a little more hp, even better if they are roller/roller-tipped.
The 60*v6 has intake restrictions with all oe intake setups (not including the carbureted version) so cam lift is essential. BUT to gain more power after one has a cam with a .44" valve lift with an assumed 1.5 rocker ratio, one has to increase the intake valve duration. (Almost no problem on the exhaust side, especially after its ported to 1.5" (with or without a cam upgrade))
I'm doing research on what to look for in a camshaft, I'm doing an engine rebuild on a 2.8 next week and will most likely get a custom grind if I can't find one that meets my requirements. (.44" lift with assumed 1.5 ratio, and longer intake duration than exhaust duration).
edit to add: I use stamped 1.6 ratio rockers from a later model 60* V6, (3.1?) and I run 4qts 10w30 diesel and mix in a qt. of 15w-40 diesel I also use a sbc dual spring setup on the valves. I have no problem climbing past 7k, 8k max because then the 2.8 oiling system becomes an issue, even with all the modification on the crank and oil galleys. (it stops pulling around 6500, but will reach the 8k)
[This message has been edited by AL87 (edited 03-09-2015).]
I had a chat with some people from federal mogul (oe aftermarket parts distributor) AND a comp cams tech support person.
the springs can take about .51" of lift with comp, and that's a little more than the oe-style from fed. mog. v6 performance guide for early 60* engines (not including 3.4) state that ideal valve lift is achieved at .44" for maximum flow (any more is almost pointless). stamped rockers don't carry consistent ratio (wont lift at 1.5x consistently, which is why a roller-tip option is slightly better) a 1.6 rocker is fine if you want a little more hp, even better if they are roller/roller-tipped.
The 60*v6 has intake restrictions with all oe intake setups (not including the carbureted version) so cam lift is essential. BUT to gain more power after one has a cam with a .44" valve lift with an assumed 1.5 rocker ratio, one has to increase the intake valve duration. (Almost no problem on the exhaust side, especially after its ported to 1.5" (with or without a cam upgrade))
I'm doing research on what to look for in a camshaft, I'm doing an engine rebuild on a 2.8 next week and will most likely get a custom grind if I can't find one that meets my requirements. (.44" lift with assumed 1.5 ratio, and longer intake duration than exhaust duration).
Think you are missing part of your "thinking" .44 lift might be ideal.. from whatever book you read, and whatever head work they listed.. BUT.. take 2 cams, both with the same intake duration, one with your magical .44 lift at the valve (not lobe lift) and a cam that has a lift of .500 or greater,, what cam held the valve at or past that magical .440 lift longer ?? remember both have same duration.. lift is the only thing changed.. if you get max flow at .44 lift, the cam that gets it to that point and holds it there or past it longer will flow more air.. so going past .440 lift isn't pointless.. as more of those intake duration degrees will be flowing at max flow(per whatever you were using for your math) .. and is why roller cams make more power, in the flat tappet world, you have to go past your Goal lift to get the valve to that max flow lift longer..without adding duration.. Not knowing what book you are going by and how old it is.. the info on ideal lift. might be questionable.. tulip valves, serdie 5 angle valve jobs, all can change at what point in lift something else becomes the choke point
Think you are missing part of your "thinking" .44 lift might be ideal.. from whatever book you read, and whatever head work they listed.. BUT.. take 2 cams, both with the same intake duration, one with your magical .44 lift at the valve (not lobe lift) and a cam that has a lift of .500 or greater,, what cam held the valve at or past that magical .440 lift longer ?? remember both have same duration.. lift is the only thing changed.. if you get max flow at .44 lift, the cam that gets it to that point and holds it there or past it longer will flow more air.. so going past .440 lift isn't pointless.. as more of those intake duration degrees will be flowing at max flow(per whatever you were using for your math) .. and is why roller cams make more power, in the flat tappet world, you have to go past your Goal lift to get the valve to that max flow lift longer..without adding duration.. Not knowing what book you are going by and how old it is.. the info on ideal lift. might be questionable.. tulip valves, serdie 5 angle valve jobs, all can change at what point in lift something else becomes the choke point
If you actually read, I said "almost pointless" beyond .44" valve lift. There are a few things that can be done, BUT the flow is limited by the head at this point (with this^ meaning; that if the intake flowed even better than the head (which I doubt), THE HEAD will limit flow at this point) I was commenting on what I read, AND I am also saying that if what the author did in terms of their performance research is correct, then flow remains just about constant from .44" lift and greater, this to me implies that a longer duration at the max lift of .44" would yield better results than a cam that has .5" lift for a standard duration, if the heads are a limiting factor. if .44 was where the cfm flow plateaued, then having .5 lift would not matter and it would only flow incrementally better, as decided by whatever the lift is and said duration degree. (most companies use duration at .05" lift)
because .5" duration is "going into the grey area" where coil bind can possibly happen, you are getting into having to start measuring tolerances for everything, as well as stressing the valvetrain to the MAX, slamming the valves shut from such a high lift and standard duration, and doing that is a recipe for BOOM. that is why using a .44" valve-lift cam with a longer duration is better to me, its SAFER. less stressing on the valve train, no coil bind, no valve slapping the head as it shuts (no snapped off valves), and something I personally love, SEXY CAM LOPE.
[This message has been edited by AL87 (edited 03-09-2015).]
it's about ramp speed, that's hard on parts.. move past the 80's we have things like beehive springs, and such.. higher lift,without coil bind.. longer valves, cam lobe ramps have changed tons even on flat tappet cams, over the "tech" in that book.. we have fast lift and lazy close.. no bouncing off the seat.. "no snapped off valves" I haven't seen a one piece valve loose a head, or "snap" in anything I'd call anywhere near streetable.
I guess stick with what you know.. good luck..
if a 5 angle sergie valve job, and tulip valves would give you that max flow from .320 lift on that you by the book only get at .440 lift or more would you do it.. or stick with what was the norm. back then..
[This message has been edited by E.Furgal (edited 03-06-2015).]
it's about ramp speed, that's hard on parts.. move past the 80's we have things like beehive springs, and such.. higher lift,without coil bind.. longer valves, cam lobe ramps have changed tons even on flat tappet cams, over the "tech" in that book.. we have fast lift and lazy close.. no bouncing off the seat.. "no snapped off valves" I haven't seen a one piece valve loose a head, or "snap" in anything I'd call anywhere near streetable.
I guess stick with what you know.. good luck..
if a 5 angle sergie valve job, and tulip valves would give you that max flow from .320 lift on that you by the book only get at .440 lift or more would you do it.. or stick with what was the norm. back then..
I will say my commenting is a bit dated, because it is being referenced to an article that is at least 20 years old, and advancements in tech/engineering have continued forward.
something in relation to ramp speed: comp cams has a "thumpr" cam with ramp speed in mind. looking more into it, that tech has been around since the 60's with endurance racing where race motors would have to last the 24hrs or 12hrs depending on the event (the 12hrs of sebring and the 24hrs of lemans come to mind) those motors with that cam setup were meant for high rpms, over a long period of time, you have to take into account they are race motors, and will be torn down and rebuilt right after the race ends and are by no means fuel efficient at or near idle. PLUS the amount of programming it would take for such a radical cam to be used in a fiero.
WE here on PFF are the most genius of people and are excellent at what we do in contribution to Fiero culture, but I doubt most of us actually race any more than a few scca, or 1/4 mile events, let alone an endurance race with a built 2.8.
I am trying to match my suggestion to the mold of the op being a regular ordinary person who will be happy doing what I suggested, if they do it, without having to deal with all the headache of meeting/exceeding the max tolerance of STOCK components, assuming they are on a budget or don't want to "waste money" on a 2.8 only meant to putt-putt from home to work on a daily basis with a little extra zoom for the seat of their pants.
Many of us hop up our Fieros, and I love that, but I have yet to read about anyone running that high of a lift on their 2.8, or in a similar ratio of increase on any motor they have.
So would 1.52 rockers work with a 272 cam and get better performance than a 260 with 1.6's?
As Arn posted, they should be about the same. That is based upon the premise that the duration would work out the same. I'm not sure if that's the case, however.
If I were starting with a clean sheet of paper (or a bare shortblock) i'd just go for the 272 (or whatever cam you wanted.) IMHO, 1.6 rockers are okay, but are just a shortcut to higher lift without having to go into the engine to change the cam. If you're going to be starting out with a new cam, just choose one that has the specs that you want, to begin with, and use 1.52 rockers. The 1.52 rockers will place marginally less stress on the valvetrain pieces than the 1.6s. Especially the cam lobes and lifter faces.
Again, just to be clear, the 260 cam should work with stock valve springs. The 272 likely won't. Neither will the 260 with 1.6 rockers, since the resulting lift will be about the same as the 272.
Hi Fiero Friends, This may make you feel more comfortable about the 1.6 rockers. Several years back I rebuilt my 2.8 as a stroked 3.1(0.030" overbore) using a kit from ARI in Missouri. I used the 1.6 rockers with the Compucam 2020or 2030 (don't remember exactly). The motor now has about 90K miles on the rebuild and runs strong still. The motor made 138 WHP and 200 # of torque on the dyno after about 25K miles. With the stock exhaust manifolds restrictions removed the exhaust tone is great. The only drawback with this build is that when the engine is cold it is really rough, most likely the cam/computer aren't designed for open loop operation. Once at operating temp it idles really smooth and is very responsive to throttle requests. Fuel mileage on the open road is 28 -30 MPG, 33 when driving at 5000 feet elevation. This is almost as strong as my 3.4TDC, only the 7000rpm makes the TDC nicer.
Larry 85SE 3.1 stroker 87 4 cyl coupe 88 3.4 TDC coupe
keep in mind max lift before any coil bind is .500' with .510' being the average coil bind
EDIT: NOTE: The stock valve springs are different from sbc valve springs, and sbc springs will allow a higher lift and a slightly higher seat pressure. (most cam companies recommend using their springs, and their recommended springs are for sbc)
[This message has been edited by AL87 (edited 03-10-2015).]
keep in mind max lift before any coil bind is .500' with .510' being the average coil bind
EDIT: NOTE: The stock valve springs are different from sbc valve springs, and sbc springs will allow a higher lift and a slightly higher seat pressure. (most cam companies recommend using their springs, and their recommended springs are for sbc)
I like those 1.6 w/260 cam numbers.. ---- Being that the max lift at .500 before binding. It's almost just there with the .470 listed. Thanks for the calculation AL87
keep in mind max lift before any coil bind is .500' with .510' being the average coil bind
EDIT: NOTE: The stock valve springs are different from sbc valve springs, and sbc springs will allow a higher lift and a slightly higher seat pressure. (most cam companies recommend using their springs, and their recommended springs are for sbc)
I believe there are two '260' cams...from different manufactures with different specs. I believe the other one H-260-2 has .427" intake lift with a 1.5 rocker arm...and the exhaust is similarly reduced to .454" over the H-272-2 cam. http://www.engine-parts.com/GMV6/28camspecs.html
Also, years ago, I used a Compucam 2030 and made 142 rwhp and 203 ft*lbs of torque with a mildly ported intake and heads with Sprint manifolds on a 3.4L build. the H-260-2 cam made 149.8 RWHP and 199 ft*lbs on another build with the same heads and intake.
All with 1.52 Magnum rollertip rockers...
[This message has been edited by lou_dias (edited 03-10-2015).]
I believe there are two '260' cams...from different manufactures with different specs. I believe the other one H-260-2 has .427" intake lift with a 1.5 rocker arm...and the exhaust is similarly reduced to .454" over the H-272-2 cam. http://www.engine-parts.com/GMV6/28camspecs.html
I believe there are two '260' cams...from different manufactures with different specs. I believe the other one H-260-2 has .427" intake lift with a 1.5 rocker arm...and the exhaust is similarly reduced to .454" over the H-272-2 cam. http://www.engine-parts.com/GMV6/28camspecs.html
Also, years ago, I used a Compucam 2030 and made 142 rwhp and 203 ft*lbs of torque with a mildly ported intake and heads with Sprint manifolds on a 3.4L build. the H-260-2 cam made 149.8 RWHP and 199 ft*lbs on another build with the same heads and intake.
All with 1.52 Magnum rollertip rockers...
so if I have a 260H cam can I switch to 1.6 roller tip rockers without upgrading any other components? ie springs or push rods?
No they are not. The ones I listed from Summit worked fine. They are "narrow body" style.
My motor:
If you are truly worried about clearance, you can always run the gasket from other 2.8 motor as an "EXTRA" one - I'm talking about the thin flat one that looks like someone scrammbled cardboard and rubber together...
If these rockers fit the stock valve covers, why did you eventually make valve cover spacers? Did something change?
I used Comp Cams roller tip rockers in my 3.2 turbo build with a Crane 272 cam and it worked very well. Had Ross Racing flat top forged pistons - no clearance issues.
You will get a bit more wear despite the roller tips as the stroke is longer and it pushes a tad sideways at the extreme so results in guide wear a bit more than a stock cam will.
Ran it for 10 years, sold it, and as told by the buyer that it needed guide replacement when he had it looked at.
[This message has been edited by BillS (edited 05-30-2022).]
---- Being that the max lift at .500 before binding. It's almost just there with the .470 listed. Thanks for the calculation AL87
