Jimmy Hilton's Titan Rocker Set

So there has been some interest in Jimmy's Titan rocker setup and I figured I might as well display it now since it will save me a lot of e-mails and private messages. Plus everyone seems to be enjoying this "series", so why not?

I'll give a quick overview with all the photos, but if you'd like to learn more about Rockers and how they work, I wrote more about them in these two posts:

Rocker post #1

Rocker post #2

Now on with the show!

All you really need to figure out rocker geometry is a sketch and a calculator. With an MGB (where the push rod axis and the valve stem axis are parallel) there is no complex mathematics involved in deciding where the shaft should be located. Nonetheless, I did a study on a mock-up engine to see just how the ratio changed as the rocker arm went through it's motion. By using the setup seen here, along with a degree wheel on the crankshaft, I was able to map the valve opening per each degree of crankshaft rotation. This takes some time, but allows you to compare the valve motion to the camshaft profile, to determine where in the lift curve maximum rocker ratio is occurring, as well as where it's the lowest.

What's really important about rockers in general, but roller's in particular, is the shaft height relative to the valve tip height. This is because the shaft height determines where in the lift curve the angle of the rocker will be 90* to the valve stem axis (which is the point of maximum ratio for that side of the rocker). For the most efficient use of any given rocker (of any given ratio), maximum ratio should occur at the half lift point. It's noteworthy that real aftermarket rocker manufactures like T&D, Jessel, etc. all use this arrangement. This allows the rocker to transmit the most amount of camshaft movement to the valve with the least amount of wasted rotation. Concomitantly, this also results in the least amount of roller "sweep" across the valve tip, for the least amount of valve guide wear and tear.

There are various ways to alter the rocker shaft height, but shimming the pedestals is the most obvious. The shims you see here were for another customer, but typical of what you might use to achieve a higher stand height.

In the case of the Titan rockers, I found that the shaft height is too low. It is a good thing that Titan supplies the assembly with custom made pedestals to ensure that the distance of the shaft between the valve tip and push rod is correct, however their height choice leaves a little to be desired. I firmly believe they chose the height they did because even though it does not result in the best geometry possible (most efficient transfer of motion or greatest lift available), it does allow you to use the stock push rods without having to go to the trouble of buying custom ones. I should also mention that all cylinder heads are different, you can do a valve job and the valve may sink in to the combustion chamber .030" which leaves the tip that much higher on the rocker side. Naturally that is an aspect no rocker manufacture can take into consideration while building their assembly, however they were fairly far off and we wanted them perfect for Jimmy's project.

I briefly considered making shims like those seen in the last post, however I figured it would be better if we made them fool-proof. I have this kind of "kinship" with Mr. Murphy and if something can go wrong in the way of a custom made shim getting lost at the least advantageous time, he'll be sure it does. So we side-stepped Mr. Murphy and welded them on...

After milling the stands to the correct shaft height, we also milled the top of the stand down to make up the difference of the shim underneath. The concept here is to keep the top of the stands from getting too tall and interfering with the rocker cover hold downs, or simply losing thread engagement on the head hold-down studs. I tested everything out for good clearance before packaging it up to send to Hap.

Below is a shot of the finished assembly, ready to bolt to the engine.

Now, I know we're all sitting at our computers asking, "well Sean, that's terrific, but what did it do for the engine?"

Good question! I'll give some answers below, however the real answer (being as to how much power this adds) could only be found in back-to-back dyno work, which I'm guessing is not going to take place.

The increase in peak valve lift after adding the shims was .012" or about 1 CFM @ 28" H2O

The greatest increase in lift anywhere in the curve was .024" or about 4 CFM @ 28" H2O

That doesn't sound terribly impressive, but remember that the engine will be sucking much harder during those points on inlet valve opening and the airflow values at 60-80" H2O are going to be far more significant. By calculation, I figure the increase in HP should be around 4 HP.

The real question however, is how much better is this setup than a stock rocker assembly? Well I just happened to test one of those as well and here is what I found.

Increase in peak valve lift from a properly set up stock assembly was .076" lift or about 8 CFM @ 28" H20

The greatest increase in lift anywhere in the curve from the stock assembly was the peak lift point, but remained nearly the same over a very wide band starting around 47* ATDC and ending near BDC. Again though calculation, I figure this is equal to around 10 HP increase in performance. These results are very close to what Peter Burgess finds in his book "Power Tuning MGB 4 Cylinder Engines."

For those of you wondering about the validity of using a rocker assembly such as this on the street. Realize that these offer very similar to the gains in airflow you would achieve by going from a stock cylinder head to a well ported version. Of course for those who already have a ported cylinder head, these gains are like having your head ported again (if that were possible).

In Jimmy's case, it was all about getting the best setup available. I wasn't going to leave anything on the table after having put so much work into all the other aspects of his build. In his case especially, I think the gains will pay off.

Sean

wow!

Very impressive wow!

Wow, I am absorbing all of that and find it fascinating!

Nice Job,Looks like a square wave weld job on the shims too.

How did the outer rockers perform versus the inner rockers? Did you see any loss of lift due to shaft flex?

I guess I need to open those boxes and look at all these goodies one day :) The building of the bottom end will happen in early next year, so everything both Sean and Jimmy have sent me is sitting there sealed in the boxes as they sent them until the time is for this build to happen, right now I have two MGB race engines to contend with, and finish up. I normally work on two engine builds at a time, it looks like the engine that I will be working at the same time as Sean and Jimmy x-flow head build is a 948 Sprite motor that will be stock, but for mild cam, wow, talking working on mutt and Jeff at the same time. :)

Cool stuff Sean

Wow! is right. Those shims appear to have added better than .125" to the height of those pedestals. That engine, when it is finished is going to run like a striped a$$ed ape late for dinner. Great write up, thanks Sean.

Jim B.

Sean fantastic work... thanks Mr Wizard!!

Quite impressive. Like porting the head again. Wowwee.

Wowwee is right

I'll add a couple of comments to Sean's and Hap's latest posts:

I believe the Harlan Sharps have a larger roller diam ( heavy) than the Titan and therefore would need more shim to get the roller axle in the optimum position.

More critical to valve float than seat pressure or nose pressure is the spring rate and damping characteristic of the spring. My observation is that a race B with an agressive cam needs dampers and a fairly high rate to prevent coil surge from lifting the valve back off it's seat.