I have 1993 502's with B&M 420 Blowers. The Rods and Valves have been upgraded, new Pistons, 8.5:1 Compression. twin Nickerson Carbs (930CFM), Stainless Marine exhaust, Crane Ignition running 650SC Ign. Curve, SX Performance fuel pumps, Stock heads, stock crank, B&M Blower cam. Motors have run good for years, Have had both Mototrs Dyno'd several times. Total HP 610 @5100 can't remember torque #'s. Motors don't want to run past 5100 rpm. I have upgraded to XR Drives I was thinking about changing Pulley's to get more Boost and more Power. Total boost now is 5PSI or less. The old B&M chart shows my pulley config to be 6-7 PSI 9% UD 6.3"top Pulley 5.8" Bot. Pulley. Chart shows 5.8" top and Bot. pulley 8-9 PSI 1:1. If I just change the top Pulley from 6.3" to 5.8" What are my expectations as far as power upgrades.?? If I do this will I also have to reprop. Just looking for a little more, Feeling I won't blow up the XR's.Boat is a 370 Baja, Big ,Heavy with a slow hull. Thanks in Advance

Increasing boost 2lbs will probably only get you another 20-30hp or 1-2mph. If you up the boost enough and install chillers, you might see about 60hp.

IMO, unless you plan to change cams and heads, you will not see any major gains.

Also, the XR's are no where near bullet proof with your power and weight. If your current setup is reliable and dialed in, I would leave it alone and enjoy the added reliabilty of the XR's.

I have run into the same issue, run the boat without your flame arrester and see what the boost comes up to....I hade a 177 and made 0 boost checked everything, called weiand, 1st thing he told me was pull the flame arrester...really did not beleive it..but tried, went from 0 to 4-5, now this was a eddie marine h/p arrester, not just a stock peice, tried a larger K & N and lost 1/2 pound, so these things are real sensetive to air going in, also engine room air, are you getting enough in ??? crack the hatch and try....Rob

USE GAFFRIG FLAME ARRESTORS,,,100% flow !!!!!!!!

K&N are very sensitive to dust and beltwear,,,,once installed ,after 2 hours cloged up.

Of course the chart from B&M shows a 100 HP gain going to the smaller pulley config. Is that all only 20-30 HP for more boost. The boat only runs 70-71 with current setup. Still would like a little more. I do have K&N Filters. Flame arrestors are orig. from B&M. If I faxed you the Original Chart & Info. would that help with any more insight.

Thanks

Kevin

Cocktail,,,,i am not kidding u on the Gaffrig.

A buddy of mine had K&N and he tryed my Gaffrig and gain'd 200 RPM just by changing the Flamearrestor.

K&N FILTER ,,,word filter,,,,,dust filter,,,like on cars where there is a dusty invirement,,,,water ,boats ,,no dust ,,,therefor no filter needet.

The only reason wy that thing is on there ,is to keep the birds out and the fire in.

I have K&N Filters on top. Maybe that's the hidden problem. I have never run with out Flame arrestor's on it. I could have an air supply issue. Only air intakes are from side vents, no scoops. I do clean the K&N filters, but if they clog that quickly I certainly don't clean them enough.

Try and run without one time and feel the diffr.

If you call Gaffrig for new ones ,just tell them Scott send you from Daredevil Racing. They give u a deal !!!

Would I still use the top and bottom Plate and put the gaffrig in place of the K&N or would I be buying the whole setup. Dop you have a part # or where is the best place to look up and buy. Thanks

The gaffrigs are 1 piece without a separate element. They make several sizes. I would run with the K&N's off for testing before you buy any new ones.