Reply With QuoteDid you try asking R.C. Olsen(72nd & Blondo)? They do alot of blower work.
JIM
Fellas,
Brand new member here in Omaha, looking for any help since marine tech's around here are hard to find. Am running a blown 454 in my 26 ft Wellcraft. Bored 30-over, older style B&M (671 ???) blower, Merlin iron-cast heads, single Holley 850. Twice this summer I have dropped a valve seat and conveniently had it bounce around my back four cylinders. Theories abound as to why... Most common is that these Merlin heads are not designed to hold up in a marine application. Another is that we were running way too much compression (approx. 8.7 to 1 with 5-6 lbs. of boost.)
Has anyone ran into such a problem? Any ideas on how to spec my upcoming rebuild? Compression? Carb? Are Dart heads any good? Thanks!
Shallow Minded
Did you try asking R.C. Olsen(72nd & Blondo)? They do alot of blower work.
JIM
Jim,
Sure did. He thought I was running too much compression (recommended something closer to 7.5 to 1), but didn't offer a ton of help. Stated he's seen valve seats pop out before, but that was about it. Looks like you're in Omaha?
Shallow, think about this! At sea level you can run a combination that equates out to 13 to 1 on pump gas. If you keep that blower, don't waste money on 'trick' heads. Polish the chambers, and or use a .060" gasket to reach 8.2/8.3 to 1. (the boat will not stay on plane @ 7.5 to 1, it will ALLWAYS BE ON BOOST!) Use a cam, .550/ 235 @ .050 I, and .565"/ 240 @ .050, on 112 centers, in @ 3 degrees advanced. With iron heads run an intercooler, and INDEX the carb the the boost! Put in 10 initial and 32 degrees total (dist timing) You will NEVER have enough oil cooler, and "pressure feed only" to the intercooler, the faster you go, the more it cools. Keep water temps. @ 120/140 ALL OF THE TIME! If you go with the aluminum heads, it is a different story and I can help you there too. wink
do you have a way of controling the engine temp? and at what temp are you running it? in a jet boat that gets its cooling from the water thats being drawn through the pump, it is very easy to run the engine with too much cool/cold water. this will allow the valve seats to pop out from the expansion and contraction of the metals. when running hard there is a very hot combustion chamber, and with a rush of cold water surrounding it, you get problems. cracking is a possibilty, and popping out valve seats is aswell. i am thinking you definatly do not have a jet drive boat, but is there a possibility that you are running it too cool?
Hey guys, REALLY appreciate the feedback. Not an abundance of marine knowledge in land-locked Nebraska. Also, to clarify a couple of things, using a 177 cfm B&M blower and this is not jet-driven boat.
Following a come-to-Jesus meeting with my mechanic, I am now leaning toward aluminum heads and a cam similar to the one BigKat mentioned. If I go with aluminum heads, do I still need the intercooler? Previously, I did not have one installed and ran approx. 170 degrees. Stay at WOT very long and she'd get hot. Pretty sure that's what happened this last time.
Another idea I've heard is to up the compression to 9 or 9.5 to 1 and decrease the boost to 4 or 5 lbs. since this blower is not exactly huge.
Any suggestions for aluminum heads? Thanks guys!
SM, From reading your thread I am guessing that the seats or heads have lost their temper & are not able to retain their size or shape at a given temperature. I would also check your springs to make sure the valves are not bouncing due to lack of tension. I had a similar problem almost 20 years ago with some aluminum heads & they kept dropping seats, finally got rid of them. I see nothing in your setup that alarms me & you have a very similar setup to mine except for the Merlin parts. I have the 177, very reworked stock heads, 8.75:1 6 #'s boost & it has been good.
If I had the budget I would definitely switch to aluminum, they will let you run a little more timing & compression and better dissipate the heat generated. Don't worry about 6 #'s, thatÂ’s not the problem & make sure you have an ample oil cooler & enough flow on the exhaust so it lets out what you are putting in. Do you have a picture of your engine? Send it to me.
Shallow, Yes I am here in landlocked Omaha at Sandpiper Cover with a green Pachanga.
Going with 355 Dart heads? DUMP THAT P O S WAN'NA- BE BLOWER!
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