Budman II

iTrader: (1)

Has anybody run these?

http://www.summitracing.com/parts/cro-72897-8/overview/

Crower says in their catalog that they are used in conjunction with 0.100 + length valves to establish proper mid-lift geometry. They are available in .050 and .090 offsets (at least in the steel versions). I came across these when trying to find a solution to some geometry issues I have been having. I am running a set of the AFR 265's that use the longer than stock valves, and I used Miller's mid-lift method to calculate the pushrod length for optimal valvetrain geometry. When I do this I get a nice narrow pattern on the valve tip, which is showing me that I have good geometry, but the pattern is too far outboard on the valve tip. These look like they would move my pattern back closer to the center of the valve where it needs to be.

Other possible solution would be to just go with a shorter pushrod, but when I do this, the pattern becomes much wider, which is showing me that the geometry is not as good.

I realize that there are probably thousands of BBC's running around out there with less than ideal valvetrain geometry, but since I'm throwing money at this thing, I would like to get it as right as possible.

Thanks for your input.

Young Performance

I have not run the rocker arms that you are talking about. I will say this much. Personally, I would prefer to have the rocker centered in the valve and have a slightly wider arc than to have it running off center with a tighter arc. How wide is the pattern when you shorten the pushrod?
Eddie

Budman II

iTrader: (1)

Eddie, here are some pictures of the intake valve stem tip. The first one shows what I had with mid-lift geometry. The second is with a 7.95" pushrod, and the third is with a stock length GM pushrod. As you can see, the first pattern is the narrowest, but it is probably too far off center. Second pattern is centered more, but we have probably doubled our sweep. Third picture is nice and centered, but also probably has about 0.11" of travel. Too wide, IMO.

Pattern with 8.05 PR using mid-lift calc:


Pattern with 7.9" PR:


Pattern with stock length PR:


These patterns were all achieved using a set of Scorpion roller rockers. These are not the endurance marine rockers like Merc is using, but they are just one step below - still a quality rocker rated at 900+ lbs spring pressure. I am waiting for a single Scorpion marine endurance rocker to arrive to repeat the test. I also mocked it up with a spare Crane gold roller rocker, and it resulted in a little bit better looking geometry, but for the price of a new set of Crane Golds I could be running the Crower's and possibly get my geometry spot on.

Maybe I'm wasting my time on this, but I thought I would try to get it right.

Black Baja

iTrader: (2)

What lift cam? Are lifters 300 tall?

Young Performance

Yeah, the pattern is a little wide, but I would still take that over the first 2 pics. Personally, I would never run one that looked like the first pic. The sweep is small, but that doesn't do any good if you push the valve through the side of the guide
Eddie

MILD THUNDER

iTrader: (3)

Is it just the intake valves?

Heres a thread I read a while back. Not sure if this pertains to your situation or not, but worth a read. Tony from AFR discusses this issue on his older heads.


http://speedtalk.com/forum/viewtopic.php?f=1&t=9025

Budman II

iTrader: (1)

MT, funny you should mention that thread - I was thinking about referring to it. I have a similar issue on my exhausts, but it is much more pronounced on the intakes. I think I may be able to get by with just running a slightly shorter pushrod on the exhausts, but for now I am focusing on the intakes. In the thread, you will see that Tony from AFR references the change to the rocker stud location - the heads I have are less than a year old, and they have the S stamped on them, so they should have the revised stud location. In addition to this, I recently ran a mockup with a Crane gold rocker that I borrowed from a friend, and it did show better geometry than the Scorpions, but still off center to the exhaust side. I considered getting a set of Crane's, but for the cost of them I might as well spend a little bit more and get a set of the offset Crowers and get my geometry squared away. I have some pictures of the rockers on the studs that I might post up in a few minutes to show the geometry issues very graphically. Thanks for the replies.

Budman II

iTrader: (1)

OK, I photoshopped my pictures of my rocker mockup with some lines through the roller tip center lined up with the valve stem to illustrate where the roller is landing on the valve.

As you can see with the Scorpion, the roller is way to the outside of the tip. I agree with others that I would be scared to run it like this. Pushrod length was determined by the mid-lift method, and gives the valve pattern shown in the top picture of the earlier post.



I followed this check up with another one with a borrowed Crane Gold rocker, and once again set the pushrod length with the mid-lift method. As you can see, this one gives better looking geometry, but it is still not quite centered on the valve. This one could probably run like this, but with the cost of the Cranes being what it is, I am wondering if I would be better off putting that towards a set of the Crower centerlines and get this geometry dialed in with no compromises. Is the Crower a quality piece?



Honestly, if this type of geometry is common with the various aftermarket heads that utilize longer than stock valve stem lengths, it is surprising to me that more rocker arm manufacturers are not offering offset trunion rocker arms to correct this. I guess there is also the chance that I have something wrong with my setup, but even a shorter pushrod puts me pretty far off center. I need to get a picture of what the geometry looked like with the stock length pushrod that gave the wide-but-centered wipe pattern, because it didn't look very good to me!

Thanks for the input!

Budman II

iTrader: (1)

Eddie, here is a picture of one of the Scorpions with a stock length pushrod installed. Yes, it does center the roller over the valvestem, but it seems to me that the increased travel would put even more side thrust on the valve guide. Not only this, but I am losing some of my effective valve lift by translating the pushrod motion sideways instead of down.

Budman II

iTrader: (1)

Also, I measured the distance between the center of the trunion and the center of the roller tip on both rockers. The Crane measured 1.630, and the Scorpion came in at 1.660. That explains why the Crane put the roller closer to the center of the valve stem tip.