Thru-Hull exhaust

[bluewater19]

I was wondering what Kinda performance increase I would see by using a thru hull exhaust on a 1991 4.3L mercruiser LX 4bbl motor. The stock Y-pipe somehow got a crack in it when I took it to the retired boat mechanic to replace my outdrive bellows and gimble bearing .I found it when my bilge started filling with water after the repairs. After buying a manual I realize I should have done this myself like I did switching to the 4bbl carb and manifold.I think it would be worth it Because it looks like I have to yank the motor to take the y-pipe off anyhow.<br />thanks

 

[Ralph 123]

Re: Thru-Hull exhaust

I have thru hull. You don't get any improvement. In fact, you may get a slight decrease. When it is below the water line, the prop creates a vacuum that sucks the exhaust out. What you get with thru hull is noticed If you wanted to add headers (where the performace increase comes from) you need thru hull.<br /><br />Search these forums for thru hull and you will find a recent post with a rather extensive discussion of the topic.

 

[ndemge]

Re: Thru-Hull exhaust

On our river trip this summer, all the guys with I/O's with us had through hull.... loud and obnoxious when sitting in the locks. Did I mention LOUD?<br /><br />One guy had a switch he could flip to send it down through the prob, but it was still noisy because of the blowby coming out top.<br /><br />did it sound "cool"? ..heck yeah,.. but I don't think I would switch personally.

 

[kdmiller8251]

Re: Thru-Hull exhaust

I have got a thru hull on mine and hate it...<br /><br />Yeah it sounds neat, but it is to freaking loud...<br />When you have people in the boat you can barely talk...

 

[bomar76]

Re: Thru-Hull exhaust

There are not very many perfomance type boaters ont this board so the opinions expressed here are kinda skewed....<br />With a 4.3 a thru hull is gonna be a complete waste of effort if you are looking for HP gains. They really don't even sound too great with the V6.<br />With high perfomance big block engines there is definitly a HP gain but even then I would use a "Captains Call" type system to be able to switch between tru hull and prop exhaust for noise reasons.<br />On stock engines it's pretty much a waste of money.

 

[Doug Durako]

Re: Thru-Hull exhaust

I'd like to do it, but after reading the book Ralph Spencer recommended, I see it is a wasted effort without headers. Don't have $3K to spend right now, so guess I'll stay quiet a couple more seasons---unless someone knows where to get this stuff a lot cheaper.

 

[Ralph 123]

Re: Thru-Hull exhaust

Keep trolling eBay for the stuff. Sooner or later the stuff you need will show up there. You just need to be patient.

 

[bomar76]

Re: Thru-Hull exhaust

I'd like to do it, but after reading the book Ralph Spencer recommended, I see it is a wasted effort without headers. Don't have $3K to spend right now, so guess I'll stay quiet a couple more seasons---unless someone knows where to get this stuff a lot cheaper. <br />

You don't need to go to headers....use these exhaust manifolds as recommended by the God of GM Marine engines, Dennis Moore: http://www.mooreperformance.org/Two.html

 

[Ralph 123]

Re: Thru-Hull exhaust

bomar76 - that's the book he's talking about. In the book the performance improvement comes from the headers not the thru hull

 

[bluewater19]

Re: Thru-Hull exhaust

I checked out the moore performance website and I am ordering his manifolds and risers.I need new ones anyway(still has stock 1991 manifolds). I also have a set of roller rockers and new comp cams marine cam and timing set that I was waiting to put on. Why I'm at it I was thinking about doing the heads maybe a little pocket porting and polishing. I bought a set of used heads a while back to do this with but haven't gotten around to it. But now winter is here and dad(retired GM master Tech with lots of GM V-6 and V-8 truck experince.) has loads of free time to help out. How much do you think these changes will help with top end? I am 44 mph on gps now bone stock except switched from mercarb 2bbl to volvo 4bbl marine system I found on ebay used.While I don't run around at WOT all the time I do like to open the old girl up once in a while when the water is calm. There is no horsepower limit on the capacity plate and I know these boats were availible with a v-8 and had planned to swap one in. but I don't want to put in a set of motor mounts and all that stuff.