Anyone tried out the Yella Terra platinum 1.8 ratio roller rockers ? just noticed them when looking at the 1.7s
https://store.yellat...-ratio-yt-6768/
Posted 09 August 2023 - 10:56 AM
Anyone tried out the Yella Terra platinum 1.8 ratio roller rockers ? just noticed them when looking at the 1.7s
https://store.yellat...-ratio-yt-6768/
Posted 09 August 2023 - 12:04 PM
Serious valve lift?
Posted 09 August 2023 - 12:09 PM
Posted 09 August 2023 - 02:22 PM
Aren't the standard 6cyl ones 1.5:1? Just go to 1.6 like a 253 or 308. Or if you must the Pontiac 1.65:1.
Be careful though, I have had issues on a 350 where I tried to use 1.6 rockers on a mild off the shelf cam with recommended springs (kit of cam and springs), was going to hit coil bind on exhaust valves. Had to use 1.5 on the exhaust and 1.6 on the intake. Just have to pick the right springs to suit the cam and rockers. Some of those off the shelf SBC cam grinds come with more exhaust duration and lift, can't remember the reason. It was a budget build so just using what was on hand.
Posted 09 August 2023 - 04:20 PM
Also you would need wider lobe centres cam grind,
as a lumpy cam with say 106 degrees makes the valves almost open all the time using 1.5:1 rocker ratio.
Edited by N/A-PWR, 09 August 2023 - 04:21 PM.
Posted 09 August 2023 - 05:58 PM
Thanks for the info all, when an off the shelf product likes this comes out it does get you thinking.
Currently have 12 port yella terra alloy head, .HQ (1.68 inlets) race valves, springs and valve train apparently can handle .600 lift, currently running solid crow cams .495 lift (both inlet and exhaust) with 1.60 rockers so about .520 odd after lash etc.
Head has a bit more flow in it up to .600, and if the valves have enough clearance etc was thinking maybe give it a shot (was originally looking at 1.7 rockers, but noticed these)
I think the cam LSA is 108 at the moment but with the higher rockers anyway prob behaves a little different anyway. Car has ITB and fuel injection controlled with an Autronic ECU so is really tuneable and idles 100 times better than previous iterations with smaller cams, less flowing heads etc.
but yeah requires a bit of testing and measurements etc , but you know what its like the stupid things you think of to do to your cars
Cheers
Posted 09 August 2023 - 10:28 PM
You may have to move the head over to allow the inlet valves to miss hitting the cylinder wall.
Posted 09 August 2023 - 10:48 PM
Posted 09 August 2023 - 10:52 PM
Posted 09 August 2023 - 11:51 PM
At a guess,
you would also need to shift the rocker post,
to accommodate the extra leverage to be central on the valve top.
However longer the 1.8:1 rocker is,
compared to the 1.5:1 is from the pivot,
is how much the off-set has to be, hmm
Posted 10 August 2023 - 12:06 AM
Posted 10 August 2023 - 06:46 AM
I was using 1.68" valves & +.040" bore, .540" valve lift & 1.6 rockers.
Yes the head was moved to allow the valves to be located in the middle of the cylinder & now 1.7" valves & over .600" valve lift.
Posted 10 August 2023 - 07:01 AM
Hey NA , you mean if offsetting the valves from std location rather than whole head?
I think Dave is comparing the contact position of the roller tip to the end of the inlet and exhaust valve stems with the 1.8:1 rocker to the std 1.5:1 rocker, without any mods to anything else.
Edited by S pack, 10 August 2023 - 07:01 AM.
Posted 10 August 2023 - 08:51 AM
Posted 10 August 2023 - 09:19 AM
Don’t the designers change the length at the pushrod end to change the ratios?
I think your right,
this snipet from manufacturer:
Easy installation, no cylinder head modification and all hardware supplied
Edited by N/A-PWR, 10 August 2023 - 09:20 AM.
Posted 10 August 2023 - 03:20 PM
yeah nice and 'off the shelf' product, except for the valve hitting bore issue lol.
should get the scope camera and dial indicator this arvo to have a gander whats going on at .520 at the moment. Stuck my old camera in there and cant see any witness marks roughly in that area and only carbon.
The yella terra platinums are a pair so cant have different ratios on the inlet vs exhaust without buying two sets and slipping them on the same shaft
Bruiser, did TK move your valves over a bit in your head to unshround etc ?
Curious to hear any of Warrrens wisdom also
Posted 10 August 2023 - 04:54 PM
Posted 10 August 2023 - 06:23 PM
Another thought,
is the spring pressure on the cam bearings and valve train.
My cam for instance,
need 600 lbs springs to keep the valve from bouncing at 8500 cam specification rpm.
This means @ 1.5:1 ratio = 900 lbs
whereas
@ 1.8:1 ratio = 1080 lbs on the push rod.
Posted 10 August 2023 - 06:58 PM
Posted 10 August 2023 - 07:17 PM
That's right Bruce,
Here is a link to pushrods:
https://blog.trendpe...-wall-thickness
In this case we have to increase the pushrod diametre, depending on the load.
7/16" to 9/16" diametre rod @ 9 inch long for 186 head on a 202,
with 5/16" ball ends.
Posted 10 August 2023 - 07:54 PM
Posted 10 August 2023 - 07:59 PM
In case of high load,
we need a roller cam, roller lifters and even roller cam bearings.
Posted 10 August 2023 - 08:32 PM
....and no fibre timing gear..
Posted 10 August 2023 - 08:45 PM
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