Page 16 of Weiand Superchargers by Holley Performance Products, Inc.

superchargers technical information cylinder head and valve train preparation for marine use weak valve springs or burned valves can lead to backfires when an engine has been run more than 500 hours the entire valve train should be inspected if the valve springs require replacement factory heavy duty or equivalent springs should be used if a new camshaft is to be used follow the camshaft manufacturer s recommendation for valve springs intake valves should be treated to a three-angle grind to provide better sealing exhaust valve edges should be as thick as possible to avoid burning and the exhaust valve seat could be treated to a one or two-angle valve job thin valve edges are extremely susceptible to burning and have no place in a high performance marine supercharged engine that operates for extended periods at full load full boost and high rpm wide valve seats should be used because they will provide a much greater contact area between the valve and the valve seat for maximum heat transfer if porting work is contemplated effort should be directed to the exhaust ports the supercharger will overcome most minor restriction on the intake side of the cylinder head a supercharged marine engine should never be set up with a through-the-prop exhaust system this is overly restrictive and can substantially reduce power and could cause engine damage due to excessive back pressure marine cooling system superchargers particularly when run at higher boost pressures produce a lot more heat in the combustion chamber this heat must be transferred from the cylinder head to the coolant that passes through it in a quick and efficient manner in many cases the standard marine cooling system is not capable of pulling this heat out of the cylinder heads fast enough the stock cooling system however can be modified to substantially improve cylinder head cooling this is accomplished by replacing the o.e recirculating water pump with a holley universal crossover adaptor the stock thermostat housing must also be replaced with a holley water distribution block these parts are listed elsewhere in the catalog marine carburetion at full throttle a supercharged engine can require 50 more air than a naturally-aspirated motor this means a larger carburetors will be required to produce maximum power typical non-supercharger calibrated carburetors will need to be enriched by 5 10 on the primaries and 10 20 on the secondaries the idle mixture screws may need to be enriched by 1 2 turns in either case the carburetors need to be properly jetted to prevent a lean condition for initial start up it is better to have a slightly rich condition to help prevent the engine from overheating after initial start up check the spark plugs for proper reading color and adjust the carburetors accordingly you want to see a medium to dark tan color while holley offers specific supercharger carburetors they are not suited for marine use unless modified by appropriate professionals marine camshaft selection a supercharger can overcome inadequacies in a stock cam up to about 4500 5000 rpm you will typically find that performance with a blower will not be significantly enhanced below these speeds with a camshaft change however for optimum performance at high rpm a more aggressive camshaft profile will provide a substantial power increase select a cam that has higher lift and longer duration on the exhaust side for the best performance non-race performance will usually be best with a camshaft that is ground on 112 114 degree lobe centers supercharger cams can typically be run straight up note that a supercharger does have the tendency to lessen the rough idle characteristics of radical cams note call the lunati tech line for professional help in selecting a camshaft to suit your marine application at 662-892-1500 superchargers marine fuel systems an inadequate supply of fuel can cause a lean condition which could lead to detonation and overheating an excessive supply of fuel can cause puddling of fuel in the manifold which could lead to backfiring upgrading the stock fuel system should be considered especially if the engines will be run hard on occasion to upgrade a high volume mechanical or electric marine fuel pump used in conjunction with a fuel pressure regulator is recommended the electric fuel pump should be mounted near the fuel tank holley offers a variety of high flow mechanical and electric marine fuel pumps for example a 120 gph electric fuel pump under p/n 712-815-1 larger diameter marine fuel lines may also be necessary especially on high-horsepower engines use a good quality high flow filter other preparation flame arrestors a good quality flame arrestor must always be used especially if the engine sits in an enclosed bilge always use the largest flame arrestor that you can a flame arrestor that s too small will hurt top end power because it will be too restrictive marine exhaust systems the more horsepower an engine develops the better the exhaust system has to be the stock cast iron exhaust that is supplied on mercruiser 330 and 365 horsepower engines both based on the 454 cid block and the 420 horsepower engine based on the 502 cid block are adequate only up to about 500 horsepower the horsepower series of mercruiser engines utilize a high performance exhaust system that flows well and can handle the higher horsepower levels high performance marine aftermarket exhaust systems are expensive but if you want serious horsepower this is mandatory 76 www.weiand.com

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