Hi Mini13
A 2ins roller would be good but it won't fit the problem being the physical size of the lobe, by boring the block out and not fitting cam bearings then making a bigger cam you can start to get some where near it.
Back to back testing was one cam in one cam out, just not worth the effort.
As for the .875 lifter i have been up to .012 per degand that starting to get over the top very hard on the lobe once again the size of the lobe is just to small then you get into trouble with valve springs trying to keep the follower on the lobe.
Graham Russell

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"It's better to be not informed than ill-informed"

Hmmm,

12 thou per degree eh, that's a good improvement.

Part of the reason that I started looking at rollers is due to the removal of anti scuff additives from oils these days, which I can only see getting worse,
Also my motor sees a significant amount of road miles that hot cams seem not to like particuarly, although cams over here in the UK tend to be particuarly pointy, one of your RE13'' on a wide LCA(112-114 deg) might live quite well in comparison.

oh the motor is a 1380 7 port turbo BTW, hence the wider LCA.

Pointy lobed cams don't last, I wore out a VP3 grind in 45,000 miles. Valve lift dropped from .470" to .270".
So far, after 12,000 miles my RE282 hasn't lost any lift at all, I still have .493" at the valve.

(rockers used on both cams are MSC 1.5:1 forged ones)

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I think in a road motor, rollers would be an improvement but at what expense? The road motor would create earlier and stronger torque and may no be hindered by the need to rev as high for outright hp. Therefore there is springs that would do the job.
Done properly would be less likely to wear.

I am no mathemetician but assuming,on a given cam, the best springs allow valve float (of flat tappet arrangement) at 8500rpm. Is anyone good enough to calculate the spring rates required to achieve the same rev limit (of roller), if I can give the increase in valvetrain weight, acceleration and velocity?

Is it as simple as increasing spring rate by the percentage of weight increase and then follower acceleration increase or are there other forces?
ie. 140%heavier on the follower side = X% increase in required spring rate + percentage of accel. increase?

Also at what valve accelleration rate does a valve pocket need to be cut in the piston and what trade off does this have on combustion shape?

come on there are some smart cookies on here!!

mini13, what device were you planning to use to stop the lifters rotating? keyway?linkbars?

LOL

i do love to get a good debate going!

I have been looking at using keyways to prevent rotation,

for valve spring rate i have used engine sim software to predict it, it seems that some of the currently availabe race springs should be more than enough to keep the valves in check with the roller setup.

regarding piston cutouts with the simsIi have run I have not managed to get close to a point where the valves might his the pistons, but I am looking at shortish duration cams.

The debate is great for progress. The greater the argument against something , the better the final result!!
Oh beware the sim sofware. I was really keen on it at one stage but a wise (old) head has told me its limits. Make sure it is asking you for the base circle diameter of the camshaft. Even then it will still let you design a valvetrain that wont work in the real world!! Try to put an almost square cam profile in and see if allows it! A square cam profile would be the ultimate as it would almost simulate the operation of a pneumatic valve syatem. Almost instantly open and shut.

As Graham has already said the small cam and ther way it relates to the follower is a very limiting factor. even though all cams have 360 degrees, a small cam has less surface area in which to carry out its duty. ie. if you were to unwrap the face of a 2in dia. cam. and do the same to a 1.5in. lobe which has the longer area to operate the follower? The smaller cam has to have a actual angle sharper than a larger one for the same accell?

If you are well away from piston to valve contact then work out the path of your valve and I would almost bet Graham has already got a cam that is similar and reliable on flat tappet, as he said he is up around the .012 per deg.
I would love to know how you go with the software!!
cheers b.

Indeed, me and my boss often have a good debate over new product, we'll take oposite sides and just argue for argues sake and see where we go often has interesting and worthwhile results!

I hear what your saying about sims, any form of calculation needs to be terated with suspison.



GR what can you offer in the way of cams for a turbo engine on a std diameter follower? an what is the cost likly to be?

curently i am using a cam 268 deg, 290thou lift (lobe) inlet 294deg peack acc approx 4.5 thou/deg, 320 thou (lobe) lift exhaust peak acc approx 4 thou/deg on a 108 deg LCA .

HI MINI13
Try the RE13T its ground on 112 lca it'll make heaps of HP and torque one motor we did made 248hp on 15lb boost and not very nice to drive,you can get one from Keith Calver over there.
Graham Russell

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"It's better to be not informed than ill-informed"

Cheers Graham

I thought that might be what you would suggest,

I shall get in touch with Keith.

Thanks Again

Joe