1.5 - 1.7 rocker ratio

[rumblefish360]

Just wondering, since you can take a "LA" cam and install it in a Magnum engine and gain lift with the 1.6 ratio, which is probably good... What about making use of the 1.7 rocker available for a Magnum engine on the 1.5 rocker ratio "LA" cam?

Lets also say we have VERY well ported Edelbrock Magnum heads on the engine.

Here is a Howards Hyd. roller cam to start with.
http://www.summitracing.com/parts/hrs-713175-10/overview/

Any thoughts on this? Pro's - Con's....

 

[mderoy340]

I would definitely measure piston to valve clearance before buying. I just swapped in a Lunati roller in my 2003 360/300 HP crate motor. Stock pistons .053 in the hole, Thin Mr Gasket .028 headgasket, .010 cut on heads, OEM 1.6 stamped rocker, .060 lifter preload, 234/236 @ .050 495/475 lift. Intake valve P to V clearance is .057, exhaust is just over .100

 

[nm9stheham]

I'd call the cam mfr that I was considering, and put that question to them. The more rapid lift rates are going to put more contact pressure on the cam and lifters, and the ramps may not quite right for that. Just take the time to be sure for that large a step up in ratio.

It certainly CAN be done; the Ford 351C had 1.73 ratio rockers stock. A piece of cake to get lots'o lift with lower durations.

 

[AJ/FormS]

On my Eddy headed-LA I'm running 1.6ers on an old Hughes fast rate 232* cam. With the KB107s .005 out of the hole and .549 lift It's been running like that for 100,000 miles or more. I can't recall the ptv clearance.
Those 107s have pretty deep eyebrows.

Running a Magnum with Magnum heads, an LA cam, and 1.7's: I have no idea. But if I had a Magnum to play with, I would certainly mock it up to see where the geometry ended up. It would probably be good info to share. Over the nose spring pressure would need to be considered as well.

 

[rumblefish360]

I agree. Another thing popped into my head from an old write up about this. Though it was a flat tappet and not a Hyd. roller as I listed. The lifter as it seemed was not able to keep up and there was a HP loss.

I myself am not considering this as of yet. But I thought I'd entertain the idea here. I do have a 360 short block with slugs approx. .070 in the hole & 57cc W5 heads. A 1.6 ratio is what I'll purchase later. I would like to bring the slug up higher. I like flat top slugs @ zero deck height or right close myself. Then. A stray thought wondered in as to use Magnum heads with the 1.7 rocker.

We do know that lift has a direct impact on HP. As long as the head can breath to allow it. A solid roller would not have a collapsing lifter and make this easier in a manor.

 

[moper]

I thin ka cam designed for 1.5 will need too much spring for hydraulic rollers and a 1.7 rocker. There are plenty of custom lobe designs for higher ratio rockers. Those are what you should be looking for if you believe you need them.

 

[B3RE]

I agree. Another thing popped into my head from an old write up about this. Though it was a flat tappet and not a Hyd. roller as I listed. The lifter as it seemed was not able to keep up and there was a HP loss.

I know which article you're talking about. Since a higher ratio rocker increases the rate of lift, it would naturally have higher velocity rates. However, if the geometry is correct, the valvetrain will still be stable with the correct spring. I think they just took one set off and bolted another on in that article, IIRC, and never changed anything geometry wise. Then when the valvetrain got unstable, it was the lifters fault for not keeping up. I've run big blocks with hyd flat tappet cams and 1.7 rockers for years, and they don't have problems with the lifters "keeping up", or any valvetrain instability for that matter. I don't buy the claims in that article.

I'd say go for it. Hydraulic cams don't have lash ramps to worry about, so the higher ratio means nothing to the lifter following the lobe. It's always in contact. Just make sure the true geometry is spot on.

 

[rumblefish360]

I thin ka cam designed for 1.5 will need too much spring for hydraulic rollers and a 1.7 rocker. There are plenty of custom lobe designs for higher ratio rockers. Those are what you should be looking for if you believe you need them.

Thanks Moper, just tossing around bench talk. I'm still a little far away from making use of that short block I seen you for. I slowed myself down with a new car purchase. Great on one front (Daily driver) crappy on the other front (go fast toy) LOL! Always a catch 22. But forge along I do.

B3RE. I glad you know the article and I do think your right about just swapping parts and no geo check. The 1.5-1.6 rocker change was good though. Often I say, "Take advantage of the heads flow ability as much as possible." (Then let it breath deep!) might as well if you can right?!?!