Ric232

Anyone done this or know anything about the advantages / disadvantages? I was thinking of doing this swap on my 454 Mag MPI. It would increase the effective lift from .483" to .520".

I've been told this is not a job to be done at home (unlike swapping to roller rockers in the stock 1.7 ratio) because there are numerous clearance issues to watch out for.

Any input would be appreciated.

HighPriority

on a stock motor I do not think that you will have any clearance problems, but I do not think you will see any gain. My 2 cent worth.

HighPriority

PS With that said I do have a set of 1.8 roller rockers that were run on a race motor for one racing season if you would like to try them. Just let me know.

Crazyhorse

We installed 1.8's on Dyno's, but only on the intakes. At least I think it was the intakes. It's been 3 years and my memory tends to get a little fuzzy after a day or so.

Raylar

You should not have any problem with the 1.8 rockers as long as you adjust the preload properly. The extra lift will give you slightly more area under the lift curve and possibly a little more power, but it depends on your exhaust system. If you have factory manifolds, I don't think you'll will see much of a difference, because the air flow is restricted by the exhaust manifolds.
Raylar

HARRISONMIRAGE

OK I'll try and confuse every one with my oppinion(I should try sleeping at night rather than thinkin about this stuff).For argumentive reasons cams are generally compared at .050 lift wich is .085 valve lift.So it is fair to say we should do our duration comparisons at .085 valve lift.So if we change the the rocker ratio to 1.8 we only need .047 cam lift to get the same valve lift(.085).If we now degreed the cam we can figure out the duration at .047 and see how much greater it is than at .050.With your new duration number(wich is higher)you can check overlap for reversion reasons and also valve timing for compression reasons(longer durations require more compression).Remember your lsa is the same only your duration and lift has increased.I would think if you had a fairly mild cam in a stock motor and were upping the compression a bit this would work good because it essentialy gives you a larger cam.The down side is more load on the cam lobes.If the cam already has overlap it could push you into reversion issues.If you have an engine on the stand and a good degree wheel you can have lots of fun figuring this out.Wow that was harder to say than do!

mcollinstn

I don't know anybody with dyno results, but it's a pretty good choice if you were already planning to go to roller rockers anyhow.

But, let me say that I don't feel that 1.8's are a good choice for ALL applications, especially cams with aggressive accel/decel ramps.

The stock cam has very conservative accel/decel ramps on it. The heads have moderate spring pressures. To increase the ratio will add load to the cam lobes, lifters, and pushrods BUT in this case all of the mentioned parts can easily tolerate that increase without any problems. Your heads flow well to .540 lift in the stock untouched configuration. Your springs will tolerate .540 lift (some say .550). The duration figures on the Merc cam aren't all that bad (224/224) so it may offer an increase worth messing with.

BUT if you plan to use a hot cam in the future, I'd stay with 1.7's. Good cams are ground with aggressive ramping and are conceived around the stock ratios.

To make sure you know what you are in for: you will have to buy the correct studs to convert from bolt down rockers to adjustable rockers (they have a 3/8 stud on the bottom and a 7/16 stud on the top). The rockers should come with poly locks already so you should be okay there. The guide plates may need clearanced for the 1.8 ratio - maybe not.

enjoy.

Ric232

Thanks, Mc.

It seems logical that I would gain some performance for not a lot of money, unless I run into clearance issues that require machining. I'm not ready to do a full performance rebuild with cam. If I ever do that, I'll just go back to 1.7's.

The thing that puzzles me is that when I plug this into Desktop Dyno, it shows a slight loss of power on the upper end if I adjust the cam lift from .483" to .520" without changing anything else. Any ideas why that might be?

mcollinstn

odd.

No idea. DD can be weird.

ragtop409

Well for starters 0.483 divided by 1.7 (stock rockers) = 0.284 (lobe lift) times the 1.8 (roller rockers) now = 0.512. Correct?
I also agree with the fact that it gives you more duration but I think that is very minimal.
I had my engine builder go through my 502 (rectangle port) heads before I put them back on and he said they did not need clearenced to run the 1.8's

Rag's