SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: KonaCole on November 15, 2007, 03:45:54 PM
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Does anybody know what a general HP difference whould be between headers and exhaust logs?
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I believe that it is a difference of about 4 or 5 hundred rpm.
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Possibly as much as 20% after tuning (adding headers) Tom
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Does anybody know what a general HP difference whould be between headers and exhaust logs?
It is kind of funny the amount of port mismatch that most of the logs that I see have. It would help a bunch if you spent the time just blending the entry of the log manifolds to the same size as your exhaust port. I do that on every pair that I have to replace the gaskets on, it helps reduse the chances of it happening again real soon.
I also surface them so they are nice and flat and use copper gaskets.
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Thanks for the info guys. I was curious b/c the kona came with Hardin Logs. I decided that I wanted to stay with logs and bought a new set of Glenwoods as I will mostly be water skiing with it.
:o 20%! That is about 80 horse on a 400 horse motor! That would be worth the money for headers if I was going that route.
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AHHHHHH did you say copper gaskets!?!?! On a boat!!!????!????! Really?
Headers brought me up an extra 500 RPMS, from 4900- 5400 with the standard Berkeley 12JG and Aggressor A-cut impeller.
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Why, what's wrong with copper gaskets? Copper gaskets and copper RTV...That is what I was planning on using with my new build and eldelbrock water logs....
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Headers with some tuning will definatley be a gain over the logs ,coppers OK but we always use our "composits" Tom
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Correct me if I'm wrong , but when your running logs doesn't the water going into the motor get "pre-heated" not that that's a bad thing ??? I run a thermostat kit and the thought of 60* water hitting my 160* block makes me cringe :-[
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There are two common log "routing methods' "preheat" and "cold water" both work fine IMO Honestly the only time i could see that scenario being an issue is if the block was bone dry & hot ,and then suddenly plunged into the H20 and started .The bigger issue is critical piston to wall ,ring and valve guide clearances (different than auto ) To allow for cold block and "loaded pistons" Tom
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Tom "loaded piston"? I think I know what your talking about? Ummmmmm maybe not. BTW is a hyperetic sp? piston worse for that ??? Also before i drilled a couple holes in my thermostat my temp shot up and down up and down.
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Coppers wear out quicker, leak a little easier, more sensitive to unequal torquing of the bolts. Personally I use the SCE's. My friend was dating the owners daughter for a while and he was more than happy to stamp out gaskets quite frequently.
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A thermostat will help prevent exhaust valveseat cracks, and will give a fuel economy gain. Other than cost and looks, there is no downside to a thermostat setup. OT headers are especially hard on cylinder heads as there is no preheat. Most cracked heads have installations that restrict the water to the engine to help it run warmer. The problem arises when after a hard run, the motor is shut down and the water in the engine drains back into the lake, leaving a dry, hot cylinder head. Then before the heads cool, the engine may be restarted and the driver stomps the throttle. With the engine empty of water and the incoming water restricted, it may take up to 40 -50 seconds of full throttle operation to fully fill the engine with cold lakewater. This cold water then hits the hot head and causes cracks in the hottest area of the head, around the exhaust valveseat area. On the jetboat engines with OT headers that we rebuild, about 1 in 5 heads are cracked, and about half of those are not repairable. TIMINATOR
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I like the cometic gaskets. Dont know if I spelled that right
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I never put that much thought into it..... However I always made sure water was flowing overboard before I did anything more than idle. Thanks for the in depth Timinator.