78 replies to this topic

[Liam Kelly]

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/

 

[RallyRed]

Serious valve lift?

[claysummers]

Serious valve train wear...

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[yel327]

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.

[N/A-PWR]

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.

[Liam Kelly]

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

[warrenm]

You may have to move the head over to allow the inlet valves to miss hitting the cylinder wall.

[Liam Kelly]

Thanks mate, sounds like you encountered something like that in previous posts a while ago.

Just ordered a dial indicator and a dual lens borescope to do some non invasive snooping whats going on before getting more serious

Hopefully with the 1.68 valves and 40 thou over pistons its doable but doubt im that lucky.

[Liam Kelly]

Did you end up shifting your head over to stop the inlets hitting?

[N/A-PWR]

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 

[Liam Kelly]

Hey NA , you mean if offsetting the valves from std location rather than whole head?

[warrenm]

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.

[S pack]

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.

[Bruiser]

Don’t the designers change the length at the pushrod end to change the ratios?

Hey Warren, I remember your thread about valve to bore contact from a while ago
with the pictures of the marks on the bore walls
Was that with the 1.68” valve and .040” bore?
Wondering if there might be a clue there about how much lift before the valves hit

[N/A-PWR]

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.

[N/A-PWR]

 Screenshot at 2023-08-10 07-59-38.png   429.15K   6 downloads

[Liam Kelly]

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

[Bruiser]

It’s cool you are exploring this idea, I have the 1.7s in the back of my mind for a much further down the track thing to try.
Never got as rad as 1.8s, though.
Warren has been much further down this path than I have
Tk did unshroud the chambers,, also sunk the valve seats .020 when he re-did them from memory
No special shifting of the head at all. I think my valves are the 1.68 size, yells terras with the letters still on them,
and I am .040” up in the bore as well with .550 and no expensive noises
He has done a head and relocated the valves closer together, but big job and pretty dear
Early on in the piece, he chose a cam for me and recommended using 1.7 rockers to get very near .600 lift
Only had .550 in the end, not sure why. He did not mention a clearance problem
After the initial recommendation, I ripped off a valve spring and check measured everything to see just how much machining this big idea might
need and how many bucks it might cost me. The retainer to stem seal ended up being quite close for what it’s worth (in my case)
Might be worth checking
I did check if the valve would hit anything at a big drop, though
I put the piston up top AND put a wire bread bag tie in the collet groove so valve wouldn’t drop into cylinder
Can remember letting it down until the tie stopped it going any further down and not touching anything
Only did number 1 cylinder though, so probably lucky and not thorough enough
Perhaps you could try it? You could compare vernier measurements from valve tip to spring seat and see if you’re safe

I would love to give you an absolute guarantee it won’t hit, but I can also recall a post by straightlinemick here a while back
saying he had seen inconsistencies in blocks allowing some valves to clear yet some still hit.
Dunno what size his valves were. He has an eBay shop with his phone number in it
Unless there are 2 straightline performance people

[N/A-PWR]

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.

[Bruiser]

That thought is a good thought, Dave
It leads back to Clay’s earlier comment about wear and tear
Can spring loads like this survive long in a street driven car?

Is your car a street cruiser or a racer, Liam?

[N/A-PWR]

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.

[Bruiser]

Beefier pushrods would become a must at some point, but I was thinking more about the poor old cam lobes and lifter faces
grinding away on each other at low revs while sitting at the lights

[N/A-PWR]

In case of high load,

 we need a roller cam, roller lifters and even roller cam bearings.

[RallyRed]

....and no fibre timing gear..

[N/A-PWR]

and for the high rollers,

 Roller thrust race:

https://www.gmh-tora...m-thrust-plate/