roller rockers, why?
Discussion
The higher the cam lift the more the need for roller rockers - normal rockers create more side load the ligher the cam lift. I suspect the link between high revs and rollers is not so much that rollers are needed at high revs, but that rollers allow higher revs because of the reduction in stress on the valvegear.
Why no side load on the valve stem? Instead of pushing the stem sideways as well as down, the roller spins and the only real force imparted is the downward one. Less friction on the valve stem as much reduced sideways forces, so less wear, less noise, and potential higher revs as there is less "drag" imparted by the valve gear.
Why no side load on the valve stem? Instead of pushing the stem sideways as well as down, the roller spins and the only real force imparted is the downward one. Less friction on the valve stem as much reduced sideways forces, so less wear, less noise, and potential higher revs as there is less "drag" imparted by the valve gear.
Smaller capacity Rover V8s inherently rev higher and produce peak torque at higher rpm, unless you want to spend serious dosh, in which case you can get a 5.X to rev its nuts off !!
My preference is a 4.5 @ standard bore, or 5.X @ 96mm bore, but the latter costs quite a bit more.
Tim
My preference is a 4.5 @ standard bore, or 5.X @ 96mm bore, but the latter costs quite a bit more.
Tim
The advantages are:
1. Lighter weight ( but not in all cases ), which will allow the engine to RPM quicker and if valvetrain is lightened enough ( we are talking grams now ) the RPM range is increased over stock, and so is the HP curve.
2. Stronger...able to withstand valvetrain harmonics better.Hold their adjustment much better also. They act as a heat sink to absorb valve spring heat. Heat is the KILLER of valvesprings
3. Accurate ( very ). Mass produced valvetrain components vary by incredible amounts. The fulcrum points are off, rocker to valve contact points sometimes don't even come close ( side loading ), pushrod pockets vary also. An old trick was to go through about 300 rockers at a lenient dealer and pick the highest lift ones to use for stock classes. Very legal, as they carry mfgrs. part numbers. just one of a thousand little ways to strech the " rules ".
If you are going to the trouble to cc heads to ensure compression is right on,check the deck height of the block and how far pistons are down in the " hole ", why use rockers with ratios that vary. When you " blueprint " do everything. Can't have cylinders all pulling different hp figures, can we ?
Another old trick is to adjust valves with a dial indicator, warm engine to operating temp. and recheck. Now readjust to correct cam mfgrs. specs when hot. Takes a little longer, is much less messy this way, insures dead-on adjustment. After all, you can come close with feeler gauges......but not exact.
Hope this may be of some help....Alan
1. Lighter weight ( but not in all cases ), which will allow the engine to RPM quicker and if valvetrain is lightened enough ( we are talking grams now ) the RPM range is increased over stock, and so is the HP curve.
2. Stronger...able to withstand valvetrain harmonics better.Hold their adjustment much better also. They act as a heat sink to absorb valve spring heat. Heat is the KILLER of valvesprings
3. Accurate ( very ). Mass produced valvetrain components vary by incredible amounts. The fulcrum points are off, rocker to valve contact points sometimes don't even come close ( side loading ), pushrod pockets vary also. An old trick was to go through about 300 rockers at a lenient dealer and pick the highest lift ones to use for stock classes. Very legal, as they carry mfgrs. part numbers. just one of a thousand little ways to strech the " rules ".
If you are going to the trouble to cc heads to ensure compression is right on,check the deck height of the block and how far pistons are down in the " hole ", why use rockers with ratios that vary. When you " blueprint " do everything. Can't have cylinders all pulling different hp figures, can we ?
Another old trick is to adjust valves with a dial indicator, warm engine to operating temp. and recheck. Now readjust to correct cam mfgrs. specs when hot. Takes a little longer, is much less messy this way, insures dead-on adjustment. After all, you can come close with feeler gauges......but not exact.
Hope this may be of some help....Alan
Decent roller rockers tend to have fully floating bearings which reduces friction. On the Rover some people place oilway restrictors in the oil feed holes in the heads. The rockers don't need as much oil because they also get lubricated by oil film in the air which in the upper half of the engine. This helps maintain high pressures to the lower half of the engine. IMHO of course.
I was lead to believe that with roller rockers on my Crossflow with a high lift cam,the tip would roll across the top of the valve and prevent the valve being pushed sideways and damaging the guide and valve also.The pad on the rocker can also wear and be difficult to set the gap,not so on the rollers,oh and the look smart(Titan) when you took out the rocker cap!!
Adjustable Pushrods
Generally used in engines that have been machined to the maximum, which dictates their use. The use of "Stock Length" pushrods can no longer be used due to:
1.The amount of adjustment in the rockers ( if any ) has been machined out.
2.Engines that never had adjustable rockers or any aftermarket ones available.
3. The use of VERY high lift camshafts.
Adjustable pushrods are also a cheaper alternative to roller rockers, but yes a pain to service.
Remember also that some roller rockers are taller than stock, so therefore require either different rocker covers to be bought/made or the use of multiple gaskets to raise cover away from rockers.
Hope this may explain a little bit...Alan
Absolutely correct on the roller/needle bearings for the rockers, not to mention the minute gain in HP. We will take any gain we can get, won't we ?
Using restrictors is an excellent way to control where the oil stays. Depending on the orifice size used, you can "almost" keep the oil in the pan, where it belongs.
Deep pans,windage trays/crank scrapers,kickouts all help, as well as increase capacity, not to mention reducing windage in the bargain.
Not many people realize exactly how much oil is pumped up into the rocker covers at 6000 plus rpm, especially on those long high speed runs, and that's where it stays as the drainback holes don't allow for the rapid recovery of lube, as a dry sump system does.
You may find that in the grand scheme of things, the real purpose of upper end oil is for the cooling of the valve springs. I'm not saying that rocker lubrication does not enter into this, but as you stated, spray takes care of "some ' of the oil needed for this job. The majority of engine heat is located in the cylinder heads. That's why many people use reverse cooling systems, to pull the heat out of the heads first..block second....decreasing the cooling effect of oil on the springs only makes the cooling system work harder. It also takes the "temper" out of the springs, not to mention what the increased conditions due for valves/guides/seals,etc.
Many a racer has lost their expensive springs due to this problem over/over again....never suspecting the restrictors that had been installed. Granted these are extreme cases, but never the less must be taken into consideration. Some racers use the restrictors along with "spray bars " installed in their rocker covers, directing oil onto the spring directly, not massive volumes now, just enough to keep the springs within there working range.
Cylinder to cylinder temperatures MUST BE taken into consideration by any serious racer/tuner. This is just another "blueprint" area or tuners knowledge area. To ignore this will gather a fairly large collection of burned pistons and valves, DNF's,or subpar performance for you investment and a large outlay of cash......Alan
Using restrictors is an excellent way to control where the oil stays. Depending on the orifice size used, you can "almost" keep the oil in the pan, where it belongs.
Deep pans,windage trays/crank scrapers,kickouts all help, as well as increase capacity, not to mention reducing windage in the bargain.
Not many people realize exactly how much oil is pumped up into the rocker covers at 6000 plus rpm, especially on those long high speed runs, and that's where it stays as the drainback holes don't allow for the rapid recovery of lube, as a dry sump system does.
You may find that in the grand scheme of things, the real purpose of upper end oil is for the cooling of the valve springs. I'm not saying that rocker lubrication does not enter into this, but as you stated, spray takes care of "some ' of the oil needed for this job. The majority of engine heat is located in the cylinder heads. That's why many people use reverse cooling systems, to pull the heat out of the heads first..block second....decreasing the cooling effect of oil on the springs only makes the cooling system work harder. It also takes the "temper" out of the springs, not to mention what the increased conditions due for valves/guides/seals,etc.
Many a racer has lost their expensive springs due to this problem over/over again....never suspecting the restrictors that had been installed. Granted these are extreme cases, but never the less must be taken into consideration. Some racers use the restrictors along with "spray bars " installed in their rocker covers, directing oil onto the spring directly, not massive volumes now, just enough to keep the springs within there working range.
Cylinder to cylinder temperatures MUST BE taken into consideration by any serious racer/tuner. This is just another "blueprint" area or tuners knowledge area. To ignore this will gather a fairly large collection of burned pistons and valves, DNF's,or subpar performance for you investment and a large outlay of cash......Alan
I agree with Motorman. Loads of oil gets stuck in the top end of a high revving rover. It won't drain back fast enough on it's own so you have to either stem the supply or increase the drainback areas to the valley or even install additional holes at the rear of the heads maybe with a suction pump draining back to the sump. Roller rockers such as Kenne Bell items are nice to have. I don't think there is any increase in rocker ratio though so any power gain (due to the rockers alone) must be very minimal. The KB items also fit on standard diameter shafts and yet some people want larger diameter shafts. If you go down the roller rocker route you may end up with adjustable pushrods, (you have to make sure they don't foul the guide holes in the heads) or you may use shims to set up your lifter preloads. On the other hand a lot of people just fit the rockers and change nothing else which makes the excercise a bit pointless IMHO. The other option is to use the Volvo set up which I think has thicker shafts and certainly has adjustable rocker arms. Personally I like to keep things simple so would hope to make preload adjustments with shims or by machining the pedestals. I wouldn't go for the expence of adjustable pushrods for a stock/ish engine.
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