horsepower
09-10-2003, 12:05 PM
#11
Scarab31excel,
An aftermarket exhaust system will not ever hurt performance----it's like bolting on free horsepower only we all know it's not really free. An aftermarket exhaust system always gives the engine the potential to do better----especially as you add hi-perf parts to your engine(s). As you add the parts, the aftermarket exhaust will already be there to allow the engine to breath better-------and that's really what any person is trying to do to go faster is trying to get the engine to BREATH BETTER---that's what it all boils down to.
Aside from that, if you used the stock Merc cast iron exhaust manifolds from your 365's and bolted them on to your 425's then you aren't going to see much----and in your case it sounds like that is exactly what happened. I'm not always right, BUT I honestly believe that once you bolt those CMI's on those engines are going to WAKE UP because the 425hp engine are more of a hi-performance oriented powerplant and with the stock Merc exhaust you have all that power CORKED UP in there!---At least those are my thoughts! That is of course if there isn't any other problems with the engines/boat that we don't know of. Besides, you can't really lose with aftermarket exhausts anyway---they will benefit you in the long run should you decide to want to add more hi-perf parts. Yes, they do cost $$$, but aftermarket exhausts will enhance any engine with looks, less weight and sound.
If you had 330hp engines and were expecting an increase in speed only by bolting on an aftermarket exhaust system alone, then you would be disappointed.
Just my .02. Be sure to let us know what the outcome is----I think it will be positive.
An aftermarket exhaust system will not ever hurt performance----it's like bolting on free horsepower only we all know it's not really free. An aftermarket exhaust system always gives the engine the potential to do better----especially as you add hi-perf parts to your engine(s). As you add the parts, the aftermarket exhaust will already be there to allow the engine to breath better-------and that's really what any person is trying to do to go faster is trying to get the engine to BREATH BETTER---that's what it all boils down to.
Aside from that, if you used the stock Merc cast iron exhaust manifolds from your 365's and bolted them on to your 425's then you aren't going to see much----and in your case it sounds like that is exactly what happened. I'm not always right, BUT I honestly believe that once you bolt those CMI's on those engines are going to WAKE UP because the 425hp engine are more of a hi-performance oriented powerplant and with the stock Merc exhaust you have all that power CORKED UP in there!---At least those are my thoughts! That is of course if there isn't any other problems with the engines/boat that we don't know of. Besides, you can't really lose with aftermarket exhausts anyway---they will benefit you in the long run should you decide to want to add more hi-perf parts. Yes, they do cost $$$, but aftermarket exhausts will enhance any engine with looks, less weight and sound.
If you had 330hp engines and were expecting an increase in speed only by bolting on an aftermarket exhaust system alone, then you would be disappointed.
Just my .02. Be sure to let us know what the outcome is----I think it will be positive.
09-22-2003, 03:28 PM
#12
Geronimo36
Gold Member
Re: Should be going faster
Originally posted by Ratchet
With 425hp, you should be going faster.......
I have a 31 scarab with twin 425-450 Hp (355 small blocks) and I run 70-72
Another with ~ 500-525 509's (77-80)
Another with ~ ???-??? 540's (77-80) still in progress
Another with ~ 385 502's (70-71)
Another with ~ 700 555's (over 90)
I say you need to do some tweaking, or the engines aren't making that much power ?
Just a thought
RJ
With 425hp, you should be going faster.......
I have a 31 scarab with twin 425-450 Hp (355 small blocks) and I run 70-72
Another with ~ 500-525 509's (77-80)
Another with ~ ???-??? 540's (77-80) still in progress
Another with ~ 385 502's (70-71)
Another with ~ 700 555's (over 90)
I say you need to do some tweaking, or the engines aren't making that much power ?
Just a thought
RJ
What kind of Drives are those boats running? Are they Bravos or TRS. I am running a Panther with 550hp, 502's and getting 76 mph with Stainless Marine Exhaust, spinning 25" Mirage Plus props to 5100.
Panther
09-22-2003, 04:41 PM
#13
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That baffles me Panther. I too run a panther and with 25p mirages (non plus) and 5k rpm only see 68mph. I been meaning to get more info on what you are doing better than me. I know you have more power, but the rpm and pitch are similar. Have you done any hull work and are you running 1.5 gears? Any suggestions would be appreciated. Gotta break that 70mph barrier!
Sorry for the sidetrack scarab31excel
BT
Sorry for the sidetrack scarab31excel
BT
09-22-2003, 09:47 PM
#14
I can't help either. I am just posting to make everyone feel bad. I am running 454/425s in an S-Type (basically the same as a Panther hull) and I got 76.4 mph (gps) last year and I had carb issues at the time. 
SURFACE DRIVES ROCK!!! (16.5x25 props turning in.)
SURFACE DRIVES ROCK!!! (16.5x25 props turning in.)
09-27-2003, 01:52 PM
#15
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Re: Re: Should be going faster
Originally posted by Panther
Ratchet,
What kind of Drives are those boats running? Are they Bravos or TRS. I am running a Panther with 550hp, 502's and getting 76 mph with Stainless Marine Exhaust, spinning 25" Mirage Plus props to 5100.
Panther
Ratchet,
What kind of Drives are those boats running? Are they Bravos or TRS. I am running a Panther with 550hp, 502's and getting 76 mph with Stainless Marine Exhaust, spinning 25" Mirage Plus props to 5100.
Panther
