Rockers to suit cam

[maldotcom2]

Hello. I have a cam ready to install into a project engine (ecotec V6), now i'm looking for some higher ratio rockers to suit. Here are the cam specs, please advise what is the highest ratio rocker i can use with this cam on a standard crank with high comp pistons. Also what springs and pushrods will be required.

 

[acarmody]

I wouldn't go any bigger than 1.8:1. You will need 105lb springs and modified retainers and oil seal I think. Give Steve from MACE a call, he can fix you up. Sells all these parts at very reasonable prices.

 

[Immortality]

.520" max lift stock heads
.540" with slim valve stem seals
.550 with modified retainers
.570 with modified retainers and new slim valve stem seals

for total valve lift greater then .570 you need to machine the top of the valve guide off.

push rods depend on how much you have machined of the deck and heads, head gasket thickness etc

the cam supplier should really suggest a appropriate CR but i'd suggest a little more then stock will be a good starting point. maybe 10:1

you will also need suitable springs

.294 and 1.7 rockers = .4998" lift
.294 and 1.8 rockers = .5292" lift
.294 and 1.9 rockers = .5586" lift

personally i'd go for the 1.9's with new seals and retainers, you will need new springs so you will need new retainers, may as well get the ones with the extra .030 clearance and the new seals. MACE sell all of these

 

[MACE]

"Hello. I have a cam ready to install into a project engine (ecotec V6), now i'm looking for some higher ratio rockers to suit. Here are the cam specs, please advise what is the highest ratio rocker i can use with this cam on a standard crank with high comp pistons. Also what springs and pushrods will be required."

Assuming you're running a double row timing chain, shorter retainers, shorter stem seals and 130lb springs then I would recommend a set of 1.9:1 ratio rockers. This is also assuming that the piston to valve clearance is ok at this level of lift.

Cheers
Steve

 

[maldotcom2]

Hi Steve. That is essentially the crux of my question, if I use 1.9's am i gonna smash a valve through a piston? Is there a calculation i can do? I know how to do it with the rockers in place but obviously i need to know what rockers to buy.

I have the double row timing chain, everything else i'll probably buy from you shortly.

 

[chargedvx6]

Hi Steve. That is essentially the crux of my question, if I use 1.9's am i gonna smash a valve through a piston? Is there a calculation i can do? I know how to do it with the rockers in place but obviously i need to know what rockers to buy.

I have the double row timing chain, everything else i'll probably buy from you shortly.

You will need to measure the piston to valve clearance with some ratio of rocker. Maybe start with a stick rocker and plot the PTV through out the combustion cycle, especially the exhaust valve as the piston is very good at playing catch up when the ex is closing.

Looking at the specs of that cam I'd suggest not going crazy with lift. It doesn't have a crazy duration and the LSA is tight. Looks to be a very efficient grind so I wouldn't go messing with that by having un needed lift. Keep in ming your engine is N/A and would not out flow that cam with stock rockers.....................that is unless you are running heavily worked heads and some kind of more efficient fuel like E based.

What ratio did the cam manufacturer state?

 

[maldotcom2]

I was under the impression you can never have enough lift. I figured some more lift from rockers might help low down without adding duration. The heads are ported and polished, but nothing crazy.

Once i work out the PTV clearance with stock rockers how to i work out clearance for higher ratio? Measure clearance, divide by stock ratio, times by new ratio and add the difference to the PTV measurement?

 

[MACE]

You can calculate the PTV clearance theoretically if you plot everything out, but if your not handy with a calculator and geometrical equations then your best bet would be practically determine what that is. You can use dial indicators to do this however the cheapest easiest method (considering the engine is apart) would be to use the plastacine (spelling?) or clay method for the job as shown in the link below.

FORDMUSCLE webmagazine: Fundamentals - Checking Piston to Valve Clearance

As for going higher ratio rockers on a roller cam, it’s not a problem provided the spring seat pressure and stiffness is there (to stop valve float). Assuming that the cam itself still has a hardened layer on the surface (which can be compromised with heavy regrinds unless they’ve been nitrided after regrinding) then they’ll be able to with stand the contact stress associated with the increase in seat pressure with no local deformation of contact surfaces (chewed lobe, roller bearing on lifter etc). The “theoretical” forces acting on the various valve train components can be worked out here.

valve train dynamics

In saying this though in, very rare cases, where an engine has done many many km’s or where the contact stresses are very high using extremely stiff springs (as found on NASCAR engines), fatigue cracks can occur on the contact surfaces as shown in the link below.

www.mechanicsupport.com: Some thoughts on camshaft lobes

In saying all of this though it would be best to contact cam supplier, as they may have removed .100” off the base circle for the job which would certainly have an impact on the forces in the valve train, or haven’t re hardened the cam after a regrind etc. For the cams we supply though this isn’t a problem nor are the springs which are designed to be used with aggressive LS1 cams (same spring we use for the eco 6’s) as has been proven time and time again.

If it was a flat tappet cam then I would definitely say no, as they’re much harder on the cam lobes as it is LOL.

As for going higher lift here are my thoughts on the matter as cut and paste from another forum…

Going higher lift even a little beyond the flow capability of the heads, is as close to one will ever get to achieving a "free lunch" with a cam. By that I mean will have minimal impact on low end performance, unlike going a narrower LSA or greater duration which can. Show in the link below is a good example of the impact that going a set of higher ratio rockers can have on power production

http://forums.justcommodores.com.au/mace-engineering/96813-v8-performance-parts-2.html#post1529663

It's for this reason our 2.15:1 ratio rockers or an standard ecotec cam are very drivable even with a standard tune, though valve lift has increased by around .130"!

Yes people may say that it's pointless going past a certainly valve lift on a cylinder head as as there are no peak gains in flow rates, however the average flow rate per given amount of time and duration at .05" would most certainly have increased! So ramp rate is also something to consider.

At the end of the day it depends on what you want, however if your after a more streetable cam, best to err on the side of less duration with more duration and more lift

My 5 cents

Cheers
Steve

 

[delcowizzid]

just have to watch with big cams the lifter acceleration rate is allready huge then you add rocker ratio and the valves accelerate and close even faster slamming on the seats and wanting to bounce.ide stick with the lowest ratio possible the cam is ground to suit stock ratio.with higer ratio youll change the 50 though lift duration as well

 

[maldotcom2]

Hmm, maybe it's a bit risky to go with high ratio. I do after all want to play with the cam timing as well. It just pisses me off that i have to pay the same for stock ratio and get no added performance.