Aftermarket exhaust and Silent Thunder
04-26-2006, 02:36 PM
#11
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Re: Aftermarket exhaust and Silent Thunder
Originally Posted by RedDog382
Is this with silent thunder application?
If it is, 4" downslope seems generous.
Unless you have a very mild cam, I will be surprised if you do not have reversion problems.
Only speaking from my very extensive personal experience.
If it is, 4" downslope seems generous.
Unless you have a very mild cam, I will be surprised if you do not have reversion problems.
Only speaking from my very extensive personal experience.
My cams are not mild but i did take extra precaution against reversion going to 114* lobe seperation. Of course this reduced the aggressive idle and moved my torque range higher but I was okay with that.
If I have problems after this, I guess I'm going partially dry with dumps!
As for the 89' 311SR-1 being a TRS set-up........opps....I stand corrected
I believe 88' was the last year for the 454/420hp TRS set-up.
04-26-2006, 02:58 PM
#12
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Re: Aftermarket exhaust and Silent Thunder
Originally Posted by offthefront
mtgbiker ....that is some very good information .. I was planning to modify my silent Thunder so the exhaust exit without the sound box ... I had planned to eliminate everthing below the platform itself ..I would leave the outer supports. If you notice the outside exhaust actually go thru the transom inside the outer part of the box ( toward the drives) and then the box angles the exhaust out. My problem is that the stock holes are too high. I think they would need to be lowered but I wasn't quite sure exactly they need to be . And if I do the mods it was mean new exhaust or at least pipes ... I want to retain the look of the 311 from the side.. m
Oh and Dogs correct 89's (most if not all) are Bravo ..
Oh and Dogs correct 89's (most if not all) are Bravo ..
I have read where other members made 4" round openings in the bottom of the ST box where the drain plugs go and had bad vibration problems. I think your idea of cutting out those areas is very good as long as you can add back structural integrity.
04-27-2006, 05:53 AM
#13
Re: Aftermarket exhaust and Silent Thunder
Originally Posted by mtgbiker
I cut out the baffles in the Silent thunder box and sealed the cuts with 3m 4200. As for modifying the box, I would be careful doing that.
I have read where other members made 4" round openings in the bottom of the ST box where the drain plugs go and had bad vibration problems. I think your idea of cutting out those areas is very good as long as you can add back structural integrity.
I have read where other members made 4" round openings in the bottom of the ST box where the drain plugs go and had bad vibration problems. I think your idea of cutting out those areas is very good as long as you can add back structural integrity.
04-28-2006, 11:26 AM
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Re: Aftermarket exhaust and Silent Thunder
Originally Posted by offthefront
Outlaws 311 before retirement .... .Stock Thru Hull location ... What I worry about is how much to lower the holes and how low would be a reversion Hazard ....
.Stock Thru Hull location ... What I worry about is how much to lower the holes and how low would be a reversion Hazard ....LMFAO........
I went with Eddie Marine's alluminum risers and manifolds and had to have 3 inch custom riser spacers fabricated out of solid aluminum billet in order for the riser would line up with the stock holes.
04-30-2006, 04:17 AM
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Re: Aftermarket exhaust and Silent Thunder
Originally Posted by formula1
Formula Outlaw, did you notice the boat run any better with the Eddie's?
No doubt about it.
First, the stock Merc exhaust units from a performance perspective are pure junk. All the exhaust dumps into this big cavern, bounces around and eventually finds it's way out. The Eddie Marine units have individual runners inside there. Plus the Eddie Marine units weigh 84 lbs. LESS on EACH motor. There's 168 lbs. of dead weight right over the props you eliminate. Then I yanked off that silent thunder platform and that saved me probably another 225lbs. At the dock, the azz end of my boat now sits a minimum of 2 and a half inches higher out of the water. So right there I have less drag.
Between the performance value and the decreased weight/less, I picked up about 5 or 6 mph. Midrange is stronger and cruise speed went up by about 3 mph.
Right now with basically stock 454 Mags, running 24" Hydromotive Quad IV's, which are stern lifting props and our boats are REAL azz heavy anyway, I am now seeing 73 and kissing 74 mph. (gps) and that's with about three quarters of a tank of gas and 2 people onboard.
04-30-2006, 09:00 AM
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Re: Aftermarket exhaust and Silent Thunder
You got any pics of that setup on your engines? 73-74 MPH w/stock 454 mags on a 311 is fantastic! Have you tried Bravo 1 4-blades on your boat? I'm using 24 pitch Bravo 1's and they were a big improvement over the 3 bladed Mirage as far as cruise speed and hole shot. I haven't run WOTwith them, though 
. I see cruise speeds on the speedo of 43 MPH @ 3200 RPM. The bow doesn't point to the sky when I get on plane either! 
What pitch Hydros are you using?
. I see cruise speeds on the speedo of 43 MPH @ 3200 RPM. The bow doesn't point to the sky when I get on plane either! What pitch Hydros are you using?
05-01-2006, 04:10 PM
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Re: Aftermarket exhaust and Silent Thunder
Originally Posted by formula1
You got any pics of that setup on your engines? 73-74 MPH w/stock 454 mags on a 311 is fantastic! Have you tried Bravo 1 4-blades on your boat? I'm using 24 pitch Bravo 1's and they were a big improvement over the 3 bladed Mirage as far as cruise speed and hole shot. I haven't run WOTwith them, though . I see cruise speeds on the speedo of 43 MPH @ 3200 RPM. The bow doesn't point to the sky when I get on plane either! What pitch Hydros are you using?
. I see cruise speeds on the speedo of 43 MPH @ 3200 RPM. The bow doesn't point to the sky when I get on plane either! What pitch Hydros are you using?The Quad IV's are a much stronger stern lifting prop than the Bravo 1's. That's the main reason I saw such a big difference, the azz ain't so friggin' deep in the water anymore....
Anyway here's a couple of shots of the engine compartment, not particularly pretty, but functional.
Also went with the Stainless Marine "Superflapper" exhaust tips. Got everything through Fred who was just TOO cool to work with.....
