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converting conventional sr20det rockerarm to later model roller rockers.


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6 replies to this topic

#1 Darryn

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Posted 25 September 2012 - 05:47 PM

Hey guys, I have been doing a bit of research into using roller rocker arms from later model fwd versions of the sr20 found in Japan and the US in the redtop sr20 from an s13 that I am building. There is very little to no info regarding this but so far I have found that the heads are basically identical, meaning everything is interchangable.
So everything is sweet for me to go ahead and bolt in some roller rockers into my head... Except for the fact that the roller rocker requires valves that are 3mm shorter due to the larger size of the roller. All good as I can search for an aftermarket upgrade if they exist for the RR head or get my factory redtop valves shortened and machined to suit. Here is the part where I am stuck is the valve springs... Obviously the RR head would have different valve springs to suit the different size of valve. I have already ordered myself some tomei valve springs that are (a) stiffer and (b ) flat on the top and bottom of the coil for more compression of the spring. So all in all if I were to bolt it all up into my s13 head with roller rockers and shortened valves with the tomei s13 springs I would effectivly have 3mm of preload on the springs, would pre loading the springs that much be bad/cause them to fail? I could test fit everything once I had all the parts and turn it over by hand to see if they bind up but it wouldnt really give me the same result as if the engine were rotating at say 7000RPM.

Anyone have any idea wheather that much pre load would be fine? I seem to think it would be ok but yea another voice/opinion would be great.

Edited by Darryn, 25 September 2012 - 06:02 PM.

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#2 lukemonty

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Posted 25 September 2012 - 08:23 PM

I would think if your not getting any coil bind you would be fine. But I can see your cause for concern, 3mm is a lot of preload.

#3 SFort

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Posted 26 September 2012 - 03:29 PM

Thats an interesting idea, haven't heard of that. Got any links?

I have no experience to share, but the first thing that comes to mind - Why haven't we heard more of this? Broken rocker arms have been an SR issue forever and some of the 'solutions' like rocker stoppers are not all that crash hot. Don't let me put you off though, you're clearly more learned on this!

#4 Darryn

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Posted 26 September 2012 - 06:58 PM

Well I stumbled across the info randomly, but then thought why not give it a shot and started to look a bit further into it.

I have absolutely no idea why it is unheard of, maybe its just a little known fact to rwd sr20 enthusiasts that they even exist. As for broken rocker arms, from what I can gather, it isnt the arms design or even the material it is made from that is the problem. The reason they break is when they become dislodged from the pivot of the lifter and float/shift to one side, then when the cam rotates the lobe back onto the shifted rocker arm the force of it trying to open the valve is too much for it to withstand in the position that it is in and with the lifter applying force in the unusual spot that it may be resting on they then snap.
The only two causes for the rocker arm to lift or float that I am aware of is either the hydraulic lash adjuster (lifter) bleeding down at high RPM causing an excessive clearance between the pivot and the rocker arm and then the float occurs... or Valve bounce at high RPM causing the two feet to lift off of the shims on the valves, this clearance then leading to the shifted rocker arm.
As you mentioned, rocker arm stoppers are one of the fixes... they do work pretty well in keeping the rocker planter firmly on the lifter but they dont eliminate the possibility of the rocker arm floating all together. This is where solid lifters come into play to eliminate the possibility of it floating from the pivot and stiffer valve springs to make sure no valve bounce ever occurs.

I think I covered it all in there lol. Anyway, I am running the RAS, Solid lifters and stiffer valve springs which will bring the chances of a broken rocker arm down to very bloody low :thumbsup_anim:

A bit sidetracked, but none of the broken rocker arm issues were why I was considering the roller rockers for my build. After a bit of reading I had found that due to the lesser friction between the rocker arm and cam lobe the RR engines were found to have more grunt down low and a better torque curve... partially due to their higher comp ratio as well which I will also be using to my advantage in my build (If machining permits a 10:1 comp)
The RR engines also run without the oil rails above the cams because they dont need them as the friction is so low... Thinking I might keep mine for peace of mind though :yes:

As for links... sorry, all of the info I got was from an hour or so searching google and thread after thread on various forums to piece together the relevant info. All very vague, I could not find anyone who had said they have RR's in their DET head and they work fine with proof... massive grey area.

but here are a couple of pics of the RR's

Posted Image
Posted Image

3mm is ALOT of pre load isnt it Luke lol. Im thinking that with the fact the tomei ones have the ability to compress further and with a stiffer spring rate that it should be fine... :huh: I hope.

Edited by Darryn, 26 September 2012 - 07:02 PM.

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#5 lukemonty

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Posted 26 September 2012 - 08:12 PM

Nice comp ratio, you should make some descent grunt. I take it pump fuel is out of the question LOL.

My next engine build will be based around higher comp ratio. A bit off topic here, but interesting none the less. There is a bloke in NSW running an FJ in a tc Gemini running a TA45 turbo. From memory it's currently running boost in the high thirties and ran low 9s on its first outing.

Anyway he was discussing the power loss you get running an auto, and the way to compensate that is more boost. He is doing R&D to run 65psi reliably. I just about fell over when I read that. Here is a pic of the engine bay.
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#6 james

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Posted 26 September 2012 - 10:07 PM

As said above, your biggest issue would be binding.
The springs are loaded the whole way through the cycle, so it's nothing new to them.
They may wear out a little sooner, but consider how long a spring lasts anyway. Something else is sure to wear first.
3mm is a lot, but if these springs are slightly thinner, you'll be right. Higher spring rate works against you here though if they're preloaded a bit more than usual.

Pity you can't just angle grind these springs down to size, hey Darryn! :P

Luke, 65psi would be a hell of a thing to hear running.

#7 vegasS12

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Posted 23 October 2012 - 01:29 AM

Are you talking about the sr20 vvl head and swaping it onto the sr20det block?
Or just swapping out the guts from the two heads?

Swapping the two heads can be done and is a great head to get big numbers from.

The vvl head actually has way better flow than the det head which would be a better idea swapping out the complete head rather than just the guts. .

http://www.mazworx.c...-conversion-kit

This is a kit that mazworx makes for it. There are other company's as well.

There is also the option of having solid lifters in the sr20det head.




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