Teague On Tech: Q & A with Bob Teague March 2021

As seen in Speedboat Magazine’s
March 2021 Issue.

454 Camshaft Upgrade

Dear Bob:
I am going to do a camshaft change I’ve been planning for a number of years with my 454 MerCruiser. The heads are iron GM which have been ported by a reputable builder to blend the valve work and clean up the pockets. The chamber CC with the combination results in a compression ratio of 9:1 and the flow is respectable. I just want to get a sanity check on my spring selection. I’m will be running an Ultradyne HR 276/286 hydraulic roller camshaft that has a duration measured at .050” lift of 222 degrees on the intake and 230 degrees on the exhaust with a gross lift of .600” on the intake and exhaust.  I have a set of 8205-Plus ISKY springs which when installed at 1.900” closed will result in an on-the-seat pressure of 150 lbs., and provide 414 lbs. open, however this set up will be .180” from coil bind. Should I shim to 1.850″/172 lbs. closed, and 1.250”/436 lbs. open? This would put me at .130” from coil bind. I understand the cur-rent thinking is springs should be set .060” to .120” from coil bind to avoid any potential coil surge. The maximum RPM for this engine will be 5,100 to 5,200 RPM. I am looking forward to your reply.
Rich Chrzanowski
Warrington, PA

Rich, you are correct about the trend to tighten up valve spring installations closer to coil bind but I am not sure it really makes a big difference with your milder set up.  We are running hydraulic roller lifter set-ups with high on the seat spring pressures but in order to do so, you must have a good quality lifter.  We have developed a lifter with Johnson that allows us to run over 200 lbs. on the seat.  With your mild duration and reasonable lift, I think you are in the correct range for this spring.  ISKY prefers that the coil bind on the 8205-Plus spring is not less than .100” to .120”.

Coil surge is somewhat of a concern with aggressive cam lobe profiles at higher RPM.  I have no concern with your set up for your intended RPM range and cam profile.  I would be concerned about running near 190 lbs. of seat pressure on hydraulic lifters that are not designed for the extra load. Also, make sure that your camshaft has an iron gear on it.  If it is a steel camshaft without the iron gear, you will have distributor gear issues.  In combination with the iron gear on the camshaft, the distributor gear needs to be melonized.  Most automotive after-market gears are not adequate for performance marine use.  The MSD marine distributor comes with a GM melonized gear that is reamed to their .500” shaft diameter.  We were involved with that improvement on the MSD marine distributor offerings. Depending on your exhaust system, you need to make sure the camshaft lobe center line is in the range of 114 degrees or it is likely that you will have an exhaust water reversion problem at idle speeds.

Check with your cylinder head builder to make sure that he replaced the exhaust seats.  The original GM Stellite are notorious for falling out or breaking into pieces.  New hard-ened exhaust seats must be installed with increased interference press.  I recommend the Tucker “H” series seats in combination with Inconel or Super Alloy exhaust valves.  This set up will insure maximum reliability because of the compatibility of the materials.  If you don’t change the seats, there is a high likelihood that you will have a failure.  If you don’t use the correct valve seat, over time the valve will hammer the seat causing it to deteriorate.  The reason for this necessary procedure is primarily because of the Ethanol if our gasoline which increases combustion temperature and the lack of lead which served as a “cushion” for valve seating surfaces.

Most new engines are built with aluminum heads. We almost never rebuild or use iron heads in our engine builds. The aluminum heads are superior for dissipating heat.

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