16 replies to this topic

[Da11yn]

Does anyone know if i can replace my sintered 1.2? rockers with 1.5 ratio without any detrimental affect to the running of the car until i can get it set up on a rolling road?

I am interested as have limited funds and can't afford to do all at once, but am having to replace the sintered ones due to high levels of wear, which i noticed when i removed the head to have some new valve guides fitted.

Thanks

[KernowCooper]

What engine are you dong the mods on? and what spec is the engine now DA11yn?
If its a standard engine then there are more beneficial items to consider before roller rockers and fitting 1,5 roller rockers is not recommended on a 998

Tell us a bit more about the engine and what your plans are for it, but I;m sure on limited funds there are better ways to tune the motor

[Cooperman]

Higher ratio rockers are a high-cost item for very little increase in power and a loss of bottom end torque. On my car I gained 2 bhp at only over 5700 rpm, which was about 2% increase.

[HUBBA.HUBBA]

If you need to change them anyway, just be mindful of what cam you have.

[Turbo Phil]

Depending what valve springs you currently have you may need to change them, you'll need to check they will not go coilbound at full lift with the rockers fitted.
To see any benefit your cylinder head will need to be able to flow at the higher lift the rockers provide. Otherwise the higher lift is pointless.

[Ethel]

I'd agree about the springs, even if they don't bind it could cost you power and increase cam wear. I'd only agree to a point about the head. True the limiting factor will be whatever restricts the flow , but there will still be a point where the valve lift matches the flow capabilities of the port. With higher lift rockers that will be reached earlier so the average flow across the whole induction & exhaust cycles will be improved. The downside is the effective valve overlap will also increase, which is where you can lose a little low rpm torque, just the same as a more racey cam. If this is for an original cam I don't think will you see much low end loss, if any, but you may well get better results for similar money from a cam swap with standard rockers.

As far as setting up goes, it shouldn't make much difference to the fueling if the ports remain the same; you may need a fraction less ignition advance - nothing that would make it undriveable or liable to blow up.

[Da11yn]

Thanks ethel your last sentence is what i was after.

Thanks to everyone else's responses some very useful and informative information.

To answer the questions it is a 1310 with md266 cam, compression ratio of around 11, head is of unknown origins as bought cheap on ebay, but has bigger valves than the big valve metro head, appears to be ported and chamber volume is matched at 21 cc. has double valve springs, but no idea of poundage, under compression with the current set up they looked no where near being coil bound. Omega 4cc pistons, cente main cap, hif 44, aldon red distributor, stage 2 lcb, with single back box silencer. rings have worn a bit and am now down to around 160 PSI across the board.

Totally agree that there are better ways to spend money initially for performance gains and am well aware that if any it will only be around a minimal increase (Am i correct in thinking around similar to going from 266 to a 276 cam?) in power at top end. the car currently does a lot of autosolo and is my daily driver so i don't want anything too racey, but as I am having to replace the rockers thought i might as well investigate an upgrade at the same time. I am debating replacing the cam next time the block is out, but to be honest I do not suffer from lack of power, but more lack of traction so in-terms of pound per second reduction in lap time, an LSD is top of my list.

Thanks

[Turbo Phil]

Yes you will see more lift at any given point, but once peak flow of the valve is reached, simply lifting it further will achieve nothing. The primary restriction is the valve. So fitting high lift rockers to a standard or almost standard head will see no peak horse power gain if the cam fitted lifts to the peak flow point already.
It's a different matter when bigger valves are fitted & the head still flows at the lifts achieved with the higher ratio rockers.

[govig]

They aren't something I'd consider on their own but 1.5 rockers and the SW5 cam are a proven good combination in the right motor.

[Ethel]

First off I'm not sure a a 266 qualifies as a standard cam, you'll already have 20-30 degrees more duration. I still don't think you'd have to worry about running it without a rolling road setup, but it is debatable that it'd be an improvement - depending on what sort of use you want out of the engine.

If you do manage to improve breathing the cylinders will be fuller resulting in a faster burn so requiring less advance. It is true that more duration means the inlet valve closes later, which can mean less fuel/air is trapped in the cylinder, cancelling out the breathing improvements.That'll happen more at low rpm, the power you are after will be found at the top of the rpm range. Ideally you'd reprofile the ignition advance across the rev range, but that isn't an option for the OP at the moment. Less overall advance should let him see some of the power increase he's after (at the top), and it's certainly safer to have too little rather than too much (as you might get if you optimised the bottom end advance) . It is only a prediction of where I think he'll want to be, there's nothing to stop him experimenting using a real road.

All of what Phil says is true, but an increased rocker ratio means you open the valves faster as well as further. This is actually the real benefit of high lift rockers: you get the valves open far enough to no longer be the greatest restriction to flow sooner and keep them above that point for longer. This is why the effect is similar to fitting a longer duration cam and people complain of losing some low rpm performance. It reduces the impact one of the biggest limitations with an old 8 valver like the "A", it's ability to breathe at low valve lift.

[carbon]

Da11yn - I have used higher lift rockers with the MD266 and found it improved the responsiveness of the motor from mid-rpm upwards very nicely. The 1.5 rockers should work well with the MD266 in a 1275, as this cam is very conservative on valve lift compared to a lot of more recent profiles.

In my experience you will need to change the ignition timing profile, about the same amount of advance at mid-high rpm but at low rpm you may need to advance by 5 degrees or so. I'm running about 10:1, and needs Shell V-Power to avoid pinking. Ultimately will need to be set up on rolling road to get the best out of it, but you should be able to get close.

Your compression numbers are well down from what I would expect, but think you know this already. With new rings you should be getting 210-230 psi on 11:1 with this cam.

[Gulfclubby]

My tappets were noisy so had a go at adjusting them today. Quickly found the reason for the noise too: the rollers of my 1.5 rockers have started to eat into the alloy rocker arms. Not just one either, several.
Consequently clearances where way too high and the rocker assembly is scrap. Now looking into buying a replacement.
Been eyeing the MED LD rockers, as they seem to be the only significantly different design and address a couple of issues the other designs have. What are your experiences and can anyone recommend a particular make or can share some good/bad experiences?

[Gulfclubby]

where would I get these, please?

[HUBBA.HUBBA]

or roller tip rockers from mini spares

[summs116]

Titan are £560 direct from Titan as no 1 seems to sell them or stock them as most buy the cheaper craps 1s,

Med ld rocker are ok but mine didn't like being revved over 8500 and holding that rev as the kept jamming and sticking the valve open and smashing bits together,
That was 2sets tried and tested

The titans ave cured it.