KM steel rocker arms - M20

[82eye]

So you say that turbo engine can't live with properly chosen and shimmed valve springs and std rockers like N/A engines?


You did not answer to my question, but anyway.

sorry forgot this and skipped over.
there's a set of heavier springs as well. i'd say there isn't a street car where the normal dual springs don't suffice. i would say the same for almost all turbo applications as well.

my machinist told me there wasn't even a point to getting new ones for my purposes. we reused the old dual set, and just cleaned up the valves and seats. oh and a little street porting, no fancy.


edit : colt cams suggested a heavier set paired with their turbo grind but i stayed n/a. even then, i'm not sure i could ever have reached the power needed for it, we don't have access to dynos or anything like that here.

[digger]

I don't see a compelling reason to upgrade the rockers when turbocharging unless you've increased cam profile aggressiveness or spring pressure significantly. A turbo doesn't necessarily stress them any more than being stock, it's only the abuse that usually comes with turbocharging. Think about the increases in forces involved; boost pushes down on the valves, exhaust stroke pressure on the face of the valve while open is negligible, increased heat doesn't reach the rockers. If you don't abuse your engine, (i.e. race use, drifting, bouncing off the rev limiter, revving past your power peak) I don't see them being an issue any more than stock. When I had ForcedFirebird rebuild my M20 head, he used resurfaced OEM rockers, I leaned on his spec E30/Chump car race experience to tell me that I was better off using inspected and surfaced OE rockers than buying IE HD. FWIW I have a 272° cam and my limiter is set to 6700rpm. I don't abuse my engine, I probably only hit the rev limiter a few times per month, I usually shift right at 6,500-6,600rpm if I rev it out.

the force required to crack the exhaust valve open could be upto 300lb on a turbo engine which is alot more than the spring force even what you'd use with the RHD rockers. Many turbo engines get abused from what I've seen.

IE HD definitely had issues but most seem to have been resolved e.g. pads falling off, short pads digging into the cam. In my mind there is a bit of a question mark about the surface finish of the pads but i haven't seen tonnes of people complaining about wear of late

[bangn]

I don't see a compelling reason to upgrade the rockers when turbocharging unless you've increased cam profile aggressiveness or spring pressure significantly. A turbo doesn't necessarily stress them any more than being stock, it's only the abuse that usually comes with turbocharging. Think about the increases in forces involved; boost pushes down on the valves, exhaust stroke pressure on the face of the valve while open is negligible, increased heat doesn't reach the rockers. If you don't abuse your engine, (i.e. race use, drifting, bouncing off the rev limiter, revving past your power peak) I don't see them being an issue any more than stock. When I had ForcedFirebird rebuild my M20 head, he used resurfaced OEM rockers, I leaned on his spec E30/Chump car race experience to tell me that I was better off using inspected and surfaced OE rockers than buying IE HD. FWIW I have a 272° cam and my limiter is set to 6700rpm. I don't abuse my engine, I probably only hit the rev limiter a few times per month, I usually shift right at 6,500-6,600rpm if I rev it out.

So couple of reasons for the want of an upgrade - Firstly my originals have done 340k kms and there is no surety they aren't fatigued, I had considered new OE replacements and shotpeening/polishing but Febi quality cannot be relied on as many know and there is a level of risk involved using them on a FI engine. Although I have a spare block, a head is really hard to come by now if something goes wrong. If something did happen that killed the head then it would mean a new AMC head ($2K plus port work to get it to 885 standard) or worse it makes a happy face in the piston if the cam locks up. I would like this engine to survive as long as possible.

Id love to be able to communicate with IE about their rocker arms but they don't answer enquiries, I would hate to think what they're like if there was a warranty issue. Last time I tried to buy off them they canceled my order for being international and then I lost out on the exchange when money was returned.

I desire to have an increased rpm limit to reduce lag going into the next gear. I guess there is a level of risk with all brands at the moment and its finding the set less risky.

[It's Soda Not Pop]

I have a head from Bimmerheads with the HD rockers. I've had this head since 2017. I've never had an issue with the rockers. IMO I rather have something overkill and never use than need it and not have it. But a lot people live by the if ain't broke don't fix it. Bimmerheads use these rockers in all of their head builds. I believe if a lot failures were happening they would have stopped using them by now. Also they are on this forum.

[digger]

metric mechanic sell inspected and peened rockers so that's an option. I've been using them for 15years with almost 12mm lift and stiffer valve springs to 7000rpm and no snappage yet....touch wood

[hasa]

metric mechanic sell inspected and peened rockers so that's an option. I've been using them for 15years with almost 12mm lift and stiffer valve springs to 7000rpm and no snappage yet....touch wood

I'll put all in to bet that your engine is fine as long as the "stiffer" valve springs are stiff. Not too stiff of course. PPF's turbo springs 65kg seat pressure sound hard to cope for other than billet rocker.

[digger]

I'll put all in to bet that your engine is fine as long as the "stiffer" valve springs are stiff. Not too stiff of course. PPF's turbo springs 65kg seat pressure sound hard to cope for other than billet rocker.

if i recall when i had my head redone in 2008 the springs i used were Eibach, the shop measured the seat and force over nose of schrick springs and they were not happy with the 11.95mm lift cam so i got some springs from VAC (the Eibach's) and they were a measurable step up from schrick (a much bigger jump from schrick to Eibach than stock to schrick). These haven't been sold by VAC for years.

i don't know who came up with such craziness in PPF spring choice but when you look at force over the nose, i'd be using steel rockers as a billet aluminium rocker may be at risk. The spring for RHD roller is like 80lb on seat and 280lb over nose and it was way way above that and totally unnecessary

[bangn]

So got pricing for the CAT022 catcams rocker arms if anyones searching to see what they're worth - 145€/piece which is 1740 euro a set plus freight. Bit more than i was anticipating, wouldn't be so bad if I lived in the states but Australian exchange rate kills it.

Im likely going to try out the KMs, if so il measure them up in the head compared to OE and see if theres any differences in lift at set degrees.

[Northern]

At that price, I'd start thinking about the RHD roller rocker/cam setup. Already having springs makes it less attractive, but maybe you can sell to recoup costs on anything you already bought?

[bangn]

So the steel rockers arrived, I put a rocker shaft in it and ran a 6mm stem through the adjuster hole onto both rockers to gauge how different they were in terms of rocker ratio/lift changes
Basically what I found is the centre of the pad is the same height and position as oem. KM Pad is a bit wider and a bit longer. I'm still going to measure them up in the head
so ive got some real data but I think any difference if any will be comparable to wear. At this point it seems the pad arc is comparable to OEM. Here's hoping the steel clamps the eccentric adjuster
with enough side load they don't move.

The KM rockers do sit a smidge looser on a new genuine rocker shaft, its not much but it does rock side to side a bit more than the brass bush type. Noticed a bit more noise audible
with steel against steel instead of the OEM bush when I spun it by hand. Hopefully they don't make a racket. All and all i'm pretty happy with the choice so far.