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TECH5 is a regular feature where EngineLabs [2] asks industry leaders five technical questions. This week’s guest is Jack McInnis, marketing director for PBM Performance [3], which is the parent company of World Products and Erson Cams.
EngineLabs: First, please explain the relationship between PBM, World Products and Bill Mitchell Products, as many enthusiasts might not be aware of the transactions from late last year.
Jack McInnis: PBM Performance Products is an engine parts supplier located in Louisville, Kentucky. In October of 2012, PBM bought the World Products cast-iron aftermarket division and moved the operation to its Louisville location. All World blocks and heads are now manufactured and sold by PBM and through the same dealer network as in the past. The line of aluminum blocks and heads which World had offered were not purchased by PBM, and are no longer marketed under the World Products name. PBM has five warehouse locations across the country and is well known for their customer service and technical support, elements which they intend to bring to the World Products line as well.
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The Motown LS block from PBM Performance.
EngineLabs: The Motown LS block is being reintroduced. What makes this version different, and what technology is used in the design and construction of the Motown LS block?
McInnis: The Motown LS was introduced as a means to use the high-flowing LS cylinder head design with a standard small-block bottom end. The concept was that all the familiar and readily available SBC components could be used, making it easier and less costly to build an engine with the newer cylinder head design. There were drawbacks however, which stemmed from the differences in camshaft configuration between the LS and the SBC engine designs. The most significant revisions PBM has made to the Motown LS block are to address the limitations of the first generation design. These include revising the cooling system to accommodate the LS cylinder heads reverse flow design, and altering the cam tunnel. The camshaft location in the block has now been raised by +.134-inch. This feature allows the use of a 55mm cam and also allows the use of a 4-inch-stroke crankshaft with H-beam connecting rods. So, it is now possible to build up to 440 cubic inches with the Motown LS block, utilizing the appropriate components for high horsepower applications. Another drawback engine builders faced was the expense of custom cam cores, because the LS cylinder heads have a different valve train layout than a standard small block. Camshaft cores are now available and in stock at an affordable cost from Erson Cams, alleviating this situation.
EngineLabs: Since most LS engines are aluminum block, what are the advantages of using an iron block with LS heads?
McInnis: The advantage of this design is affordability. The LS cylinder heads are where the power is made in those engines. The Motown LS allows the use of LS heads and also allows the use of a huge assortment of readily available and affordable SBC rotating assemblies, oil pans and accessories because the bottom end is all standard SBC. The SBC style block also means that it can easily be used in any chassis where a standard small block fits, without all the conversion pieces that an LS engine would require. Another advantage is that the standard SBC oil pan rails and sump eliminate the high rpm windage issues associated with the LS platform and offer superior oil control with proven components.
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Features of the Motown 220 assembled cylinder head.
EngineLabs: Are there still frontiers in designing and/or modifying iron cylinder heads for classic engines?
McInnis: There are always frontiers available, it’s more a matter of how much demand there is. The only real difference between iron and aluminum heads is the weight. Other than that, it’s mostly glamour. Aluminum dissipates heat faster and so will tolerate a bit more compression, but iron holds heat better and so extracts a bit more energy from the combustion, so the power is not much of a factor in most cases. Iron is less expensive than aluminum so a good set of iron heads offer a lot of performance for the money if weight is not a big issue.
[8]Combustion chamber of Motown 220 head.
EngineLabs: Some enthusiasts still think rebuilding junkyard heads is less expensive than a new set of iron heads. Can you enlighten them?
McInnis: I think that if you already have a set of heads that aren’t cracked and haven’t been re-machined too many times, you might save money by rebuilding them. If you have those heads and happen to own a machine shop, then you’re looking good. Otherwise, it becomes more doubtful. Here are some of the issues you face. 1) The supply of used cylinder heads is not what it used to be. Most of the desirable castings have been scavenged from the junkyards years ago and have been rebuilt many times over by now, so if you can find a good set for sale, they won’t be cheap. If you can find a cheap set for sale, odds are they won’t be good. 2) Machine work, seats and guides, and labor are expensive at most reputable shops. You get what you pay for. These expenses will likely make up for anything you might have saved on the head cores. 3) Assuming the above things did work out in your favor and you have saved a hundred dollars or so over the price of new aftermarket castings, you will still be faced with ports and chambers that are thirty years behind the airflow technology available today. This adds up to a significant power difference which would require specialized porting and blending work to compensate for. Then you have spent your savings plus, and probably still are down on power compared to the newer designs.