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sr20det cylinder head blues...lifters springs and more
I have a sr20det i am trying to rev over 8000rpm. I have 280 tomei cams and bc single springs and retainers. I did have the bc 272 cams but something happened and bent valves and damaged the cams twice. I think there may be some sort of frequency where the valves float, the shims pop out, and i have a catastrophic failure. This has happened to me twice now. The second time i installed tomei solid lifters. I revved it to 8000rpm, a rocker popped off and bent a valve. I think the second time i may have weakened a rocker from the first failure and it broke. I am just not sure what to do or where my weak link is... w/ my current setup i have bc single springs and retainers, solid lifters, and the 280 cams but have not installed it yet. I ordered the tomei ras but i do not like them. they hover over the lifter side of the rocker and do not even touch the rocker. I think i may need dual valve springs this way if the one spring has a frequency that causes the valve to float or bouce, it will be compensated by the second spring. After both of these failures, the second with solid lifters, i dont even know if i want to rev over 7700. I want to get 9000rpm out of it. I am probably going to order the dual springs but i want to know if i should run the ras with the solid lifters. Is anyone revving over 8000 and what parts are you using. help appreciated. Thanks
generally it is not a good idea to use hydraulic camshafts with solid lifters. hydraulic cams ride the rocker(almost), while solid type cams have to retain a min clearance of 0.008-0.010" intake and 0.010"-0.012" exhaust. due to this gap now present with a solid type camshaft the design of the lobe actually changes. hydraulic cams can use much steeper and more aggressive up and down ramps, while for solid type cams they have to be about 10 degrees longer in duration for the up-ramp and down-ramp.
i compared about 6 sets of camshafts use a cam doctor camshaft profiling software and there is a visible difference in ramp. ramps are usually described in thousand lift per degree of duration.
basically BC and most other crap cams out there are kids play made in china and cheap copies of HKS and other Japanese companies. All of these cams made for the SR20 to be used with hydraulic lifters. When you convert the engine to solid lifters and retain the same aggressive lobe ramps you are literally slamming the rocker arm when it is opening and closing the valve too fast as well. Minor valve float occurs when the valve is closed too rapidly, hit the seat, and bounces back off. This type of float does not cause bent valves due to piston contact. It can cause loss of power or surging at a certain rpm and in extreme cases the stem of the valve is weaked, eventually leading to valve head braking off and then causing catastrophic engine failure. In cases where valve springs are voewfully inadequate and wrong type of cam is used, can lead to launching of the valve off the lobe while opening the valve and causing piston-valve contact.
In the cam doctor i compared the following camshafts:
I need to locate that folder and I will post it soon.
If you really want to rev an sr20 really high you need an sr20ve head and mounted rockers. Last august at Bonneville salt flats while running my old boss's car I met a fellow from New Zealand running an NX2000 with an sr20ve NA engine. I got a lot of engine info out of him and a lot of ideas. His engine was a 2000cc, making about 320hp and revved a high of 10,000rpm on one of the last days. Most other days he was revving at least 9500rpm.
thanks for the post. i am now running the tomei 280 cams, and i hope they are designed for the solid lifters with a more friendly lobe. i looked at one of mazzworx motors and they are running them too along with the solid lifters and supertech springs of the strongest spring rate. i just cant afford to rebuild my head every week revving to 9k. i remember talking to a guy running about the same parts to a little over 9k and he was running into valve float soon after. what sr20de engine have mounted rockers?
Tomei 280 degree camshafts for the SR20 motor as the "Procams", meaning they require solid lifter conversion.
Installing a strongest spring you can find does not necessary mean you need it. What size valves are you using? What brand valve and how much does it weigh? Higher pressure springs are needed to prevent valve float when using heavier valves(bigger OD), revving to higher rpm, or using a camshaft with more lift than stock.
Supertech dual spring will work but the next weak point are the solid lifters. At high RPM the cam lob will try to move the rocker arm to push open the valves. Since spring rate is so high it may actually cause the lifter to collapse(give) before opening the valve.
Yep again proper engine design is key and "bigger is better" does not necessarily work.
I'm working on a way to convert OEM hydraulic lifter and make them into solid style. This is a cheaper alternative to Tomei solid lifter kit but requires more time to set clearances and you need access to a surface grinder to do this.
i already have tomei solid lifters so i am going to run those along with the slotted shims on both sides. they sell the slotted ones in different sizes through tomei so i wont have to grind down the valve stems. now with that being said is there any more mods possible other than mounted rockers. also what would be the highest possible rpm on stock stroke.
I had my valve stems ground because I had the head rebuilt including some new valves, JWT bronze valve guides, BC springs/retainers, etc.
Measure your factory shims, so you can replace them with the slotted shims that are the right size, after you've modified the rocker arms.
I have no experience with solid lifters/cams, I'm using the DET oil pump with 2000 + roller rocker hydraulic lifters, so they self adjust to some extent.
If you read my thread (and the other's I listed) you can see everyone concurs that I'm good for at least 8500 RPM, and 9000 shouldn't cause any problems. Other people have had the same results with stock stroke.
I see your goal is 9000 RPM, but the question is, can you still make power that high? (for me it's just a safety net)
i dont feel like taking my valves out so i already have a bunch of those slotted shims off another head. i took one and ground off a few thousands with my belt sander and it worked perfect. i think im going to do the same with the rockers to make the shims fit. thanks so much for your help. i am running a turbo similar to a gt35r and need the rpms so when i shift it stays closer to boost.
I wasn't suggesting you remove the valves and grind the stems, like I said, I only had my valve stems ground because I had to replaced some of the valves and guides, so I had to have the head rebuilt.
Just go slow grinding the rocker arms and make sure they're "centered" on the slotted shims.
The DET high port head may not be the best flowing SR20 head but it is definitely capable of the highest RPM. Good luck with your build.
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