Fitting Exhaust 3 or 4 inch?

[Scott Pearson]

OK Guys,
Need some info. I am fitting my exhaust on my boat. The transom is filled and I will be cutting new holes. Remember this was a Ford with a Volvo drive, Now a Chevy with a Alpha. I was going to re-chrome the stock exhaust tips and use them but they are 3 inch. so I was going to come out of the motor with the 4 inch and then down to the 3 inch into the tips. Or should I buy new tips that are 4 inch. ****... is everyone following this? Any ho, what do you think?

[seano]

Scott,

If it were me, I would definitely go with the 4" tips, now I'm not sure about your feelings on keeping the boat original, but that is the only drawback I see to switching to 4". Additionally, the 3" exhaust is more restrictive...although I don't really know to what extent it will affect performance. Just my two cents.

Sean

[PaulO]

Seano,
Personally, I can't believe that 3" exhaust would ever be restrictive for any small block except some 6500 RPM beast so, I don't think that is a concern. I woould definately go with the 4" risers because to my eye, they appear to be a much better design and dump the water in further downstream than the 3". Now, I want to inform you of a problem I have with my exhaust. I have the same setup (SBC/Alpha) and I have 4" all the way through. The problem is that you have little or no choice as far as placement of the through-hulls and the placement you must use presents an interference problem with the power steering unit. I have had to go to great lenghts to remedy this. If I had it to do over, I would have put 3" through hulls and 4" risers. I have been curious as to whether anyone else has had this problem.
Paul

[Scott Pearson]

Paul,
What problem did you run into? I too have 4 inch exhaust risers.It looks like if I did go 4 inch all the way that everythig would clear but I dont know. Let me know what you ran into.

Thanks (NJ) Scott

[seano]

PaulO,

I had the same exact problem with my 28ss, and here was the problem.

Twin small blocks with Bravo drives(2000 350 Mag MPI, although it really doesn't make a difference), but the problem came when I wanted to keep the exhaust below the gunwale. If I followed the line from the elbow to the transom, the exhaust came out right in the middle of the rubrail. (Oh, I forgot to mention I raised the x-Dimension nearly 2")

Well, I had to use Sheilds soft-wall exhaust hose and I actually ran the starboard exhaust just about 1.5" further starboard of center to avoid the power steering ram. I'm not really thrilled with it, and unless you know about it, it isn't noticeable, but I notice it and it does bother me. Did you do the same? Also, I think IMCO or GIL has a stainless "elbow" that could possibly be used here also. I'm gonna look into a better soln for next year. Take a look at their websites

[PaulO]

I have Gil transom mount silencers just like the ones used on the new 18s. I dont't think this changes the situation any as they are the same dimesions (as far as flange diameter) as my original plain thru-hulls. The problem is that if I attempt to mount the starboard thru-hull, the inner section of the 4" tube will hit the high spot on the steering valve. Again, there is no place else to place the thru-hulls on my boat. As it is the tops of the exterior flanges butt up against the rub rail. moving it inboard or outboard will not get it far enough away and of course, down is worse. What I did was shorten the inner tube on the thru-hull so it falls just short of the steering and then attach a short section of 4" stainless tube that I worked an indent into. This piece then attaches to the hose that runs to the riser. I don't like it (too many clamps and pieces of hose in a hard to access area)but until I find another way, this is it. What makes me curious is that this is mostly a Mercruiser thing. Any boat that this setup is in is forced to run the thru-hull just above the steering (which, by the way, is a little high as far as drainage is concerned)and hope that it ends up below the rub rail.
Paul
Paul

[Scott Pearson]

I raised my X-dim. 1 inch, so Im fine with the rub rail clearing.I do see what you mean by having problems with the steering. It looks like I just might clear. Im waiting on some Vernatube Fiberglass exhaust tubing then I will be able to tell better. I will let you know how I make out.

(NJ)Scott

[RichF]

Scott:
Go 4" !

------------------
Rich mailto:fngrht@aol.comfngrht@aol.com</A>



[This message has been edited by RichF (edited 05-12-2000).]

[Forrest]

If you want 4" chrome plated bronze tips that look like the originals, Buck-Algonquin makes them, but they are a little bit pricy. I have a pair of their 3-1/2" tips on my 16 since everything is 3-1/2" back from the Kodiak risers. One neat thing about these tips is that you can get them with about a 20-degree angle up inside of the boat, and buddy boy, that helped me with my installation big time. Buck-Algonquin is located somewhere in Delaware and most large prop shops, like Admiral Propeller in Tampa, sells their stuff.

[This message has been edited by Forrest (edited 05-12-2000).]

[GeneD]

Ah ha!
I went through this when I restoed 007.
I had to move the exhaust up 1.5 inches to clear the power steering valve, and boy was I pissed.
Yeah, the 4 inch is the way to go...all the way. The four inch pipes just sound so much better. The ones with the flappers on them are cool, but the pipes like I got just make it sound so nice. A bit obnoxious, but then, you know!
And, Yeah! You are limited on where you can exit. It IS a bitch. But I do not have to explain this to people that have done this already. And Paul, the way I solved the angle problem was to put on spacers, we think on the same plane. I was very nervous about this too, but it just clears the cover. 1 inch spacers did the trick. Check out my story on my Donzi resto in the tech page. I was so pissed! It took me $25 and two days of work to fix it. I had to buy a 4.125 inch hole saw.
BTW, if anyone has a need for 3 or 4 inch Mercruiser riser spacers, I have a bunch and you can have them for the shipping cost.
AND, I would consider it a big thrill to go and buy you the same type of pipes as I got. Used, under a hundred, I think. New about $175-180.

------------------
GeneD
007
Melbourne, Florida

[This message has been edited by GeneD (edited 05-12-2000).]

[This message has been edited by GeneD (edited 05-12-2000).]

[Scott Pearson]

Scott,
Send a picture if you can. I can always use some Ideas.

(NJ) Scott

[Scott Pearson]

Gene,
Sounds like the 1 inch spacer on the risers did the trick. Is that a Mercury product?
Or do you know where I can get them? I have plenty of room to go up one inch. What did you run between the risers and the tips? Its about 16 inches between the two. I was going to run some of the wet exhaust fiberglass tubing. let me know your thoughts.

(NJ) Scott

[Scott Pearson]

Forrest,
I will check them out. thanks for the great info!
(NJ) Scott

[Scott Pearson]

Gene,
Almost forgot... What type of pipes did you run. When you say pipes do you mean the exhaust tips?

[Scott Pearson]

Scott
I will keep you in mind. These also need to be re-chromed but are in real nice shape.

(NJ) Scott

[Spitfire Dave]

I put Powerflow exhuast on my 1981 18' 2+3 Merc/Alpha setup. It was a real pain in the butt. I had to machine the riser where it meets the manifold from thick in the back to thin in the front. This brought the transom end of the riser up to clear the power steering( still had to grind a tab off the end of steering ram). The tips (4") come out just below the gunwhale. I had to machine part of the flange on the tip off in order fit it under the gunwhale. This a being said, I would do it all over again in a heartbeat. The exhuast looks great both under the hatch and out the back. Spitfire Dave

[Forrest]

. . . and I have a pile of original Donzi 3" cast-bronze exhaust tips that need rechroming as well. Not a rare item!

------------------
Forrest

[This message has been edited by Forrest (edited 05-15-2000).]

[GeneD]

The one inch spacers should be a standard Merc part. I got mine from a surplus joint in Ft. Pierce. I think they were $20 ea? A rip, but when you need something, well, you know.
The pipes (tips) are your standard run of the mill, stainless steel, 4 inch pipes, about 8 inches long and slash cut. With the slash pointed down.
Interesting what someone said about not being able to fit them properly under the gunwale. A situation I didn't encounter due to the barrel-back type set up I have. Thank Don too, I would have committed Sepeku (ritual suicide).
Oh, and of course with the spacers, you'll need to get new bolts or studs.
Also, I ran the 4" exhaust hose with the wire in it from the risers to the exhaust "tips". I think about $10/ft?

------------------
GeneD
007
Melbourne, Florida

[This message has been edited by GeneD (edited 05-16-2000).]

[Scott Pearson]

Gene
thanks for the info. It looks like I will have no problem with the 4 inch. I will know more by the weekend. I will have the rest of my parts to see how everything will fit. I will wait to see if I need the spacers but as it looks now I wont need them...I hope. Just another thing to keep me from moving on with this project.

thanks (NJ) Scott

[CDMA]

Madpoodle,

How much for the tips??

Chris

[Scott Pearson]

Scott,
Man, this is an old thread. I went with 4" on mine. I went with Gil polyurethane (plastic) exhaust tips. There gloss black and have internal and external (Salsbury) flaps. They look awsome against the transom with a black drive and Bennett sport tabs.

Your right about the risers not being a true 4".

(NJ)Scott

[MarkG]

Old thread good topic. I'm about to add 4" tips to my SBC with EMI exhaust.

Has anyone considered that not enough back pressure may cause a loss in performance?

Currently the 3" runs great but I was hoping to add some simple perforated steel baffels with the 4" tips, & have a slight reduction in noise. How much louder were the 4" over the 3" ?

Mark
&gt;=^;&gt;

[BigGrizzly]

First, very few companies make 4 inch exhaust. Stanless is 3 id, impco also. CMI does and they have 4.5 od. On the Corsican the headder gave it the life not the tail pipe, My Criterion had well over 600 hp and it breathes through 3inch ID exhaust and it is a 502. Think of car headders, the collector is (on most) 3inch. So it doesent matter. Mercruiser ar 4inch od but 2.5id in the riser. So make tour choice .PaulO is correct you won't notice below 6000-&gt;6500 rpms. As for loosing horse power, up top -NO, down the bottom, below 2200, slim but possible with a big cam. With a good marine can I doubt it

Randy

[Eddie Eastwood]

Scott, I ran 4 inch exhast all the way from the risers thru the transom on my 18 Donzi. I have hydrolic steering and had no clearance problems at all. I even have Mercriser mufflers inline. If you plan on running a SBC over 5000 RPM go with the 4 inch, the engine needs to breath. Volume wise a SBC at or over 5000 flows as much exhaust as a BBC in the 4200-4600 rpm range. If you need to see the exhaust system installed in a boat give me a call, you looked at my Donzi last summer and it's not to far away from you. Eddie.

[jwright]

On my 1976 GT-21 I had stock exhaust on my 350 chevy. They were the log type with the riser in the back. I went to 4" Stainless Marine with custome risers. It was louder then the 3". So after I got out of a noise ticket I put GIL clamp on mufflers on the tips. Now I am right at 89 dba at idle. WIth out the muffles I was at 94 dba at idle.
What was interesting is that my hole shot improved when I put the mufflers on, back pressure helped out the low end. But I lost rpm on the top end. So after all this money I do not know if I am aheadd or not (with the mufflers)... but it looks good! Maybe I will take them off at AOTH for fun...

[Chops]

Ok, everyone should get a kick out of this- I just converted my 18 2+3 SBC from Merc iron manifolds to EMI with 4" stainless risers and Teague selectable silencer tips. The funny part is that I was really paranoid about having a silencer assembly (even in the open position) blocking some of my 4" exhaust stream. Solution: Teague's system solves this by making the OD of the exhaust tip 4.5" (that's right, 4.5"). You guys might think I'm nuts but this looks REALLY cool! I haven't fired it up yet so I don't know how it sounds. From what I'm hearing I might have to run with the silencers closed just to get enough back pressure!

(I'm sick enough to find humor in that)

BTW, I had to buy EMI's "S" pipes to clear the power steering.

[boldts]

Does anyone know if someone makes a clamp-on muffler for a 3" outlet or what looks like a bolt-on with the securing bolt coming out the center of restricting baffles. Hard to explain. Inside the exhaust pipe coming through the transom is a bracket that holds a threaded rod. The baffles press up against the exhaust outlet with a end plate (chrome) and a cap nut then tightens everything up. Must be a early 70's attempt at quieting things up. http://www.donzi.net/ubb/smile.gif

Scott Boldt

[Formula Jr]

4 inch SS tips Forsale: http://www.boatered.com/topic.asp?TOPIC_ID=10455&FORUM_ID=8&CAT_ID=6&Topic_Title=STAINLESS+4%22+Exhaust+Tips+45degree+F orSale&Forum_Title=Buy+And%2FOr+Sell

[Voodoocanoe]

Originally posted by Formula Jr:
4 inch SS tips Forsale: http://www.boatered .com/topic.asp?TOPIC_ID=10455&FORUM_ID=8&CAT_ID=6&Topic_Title=STAINLESS+4%22+Exhaust+Tips+45degree+F orSale&Forum_Title=Buy+And%2FOr+Sell (http://www.boatered.com/topic.asp?TOPIC_ID=10455&FORUM_ID=8&CAT_ID=6&Topic_Title=STAINLESS+4%22+Exhaust+Tips+45degree+F orSale&Forum_Title=Buy+And%2FOr+Sell)

Those look like they are from a side exhaust application from the angle of the mounting flange

[Edward Donnelly]

[QUOTE]Originally posted by boldts:
[B]Does anyone know if someone makes a clamp-on muffler for a 3" outlet or what looks like a bolt-on with the securing bolt coming out the center of restricting baffles. Hard to explain. Inside the exhaust pipe coming through the transom is a bracket that holds a threaded rod. The baffles press up against the exhaust outlet with a end plate (chrome) and a cap nut then tightens everything up. Must be a early 70's attempt at quieting things up. http://www.donzi.net/ubb/smile.gif
Those are marine Supertraps. My buddy has them on his 30' Scarab

[boldts]

Edward,
Thank-you very much for the name of these things. I'll use the vast Internet to see if I can find the company that makes the Supertraps.

Scott Boldt

[RickR]

Beware!
The supertraps exit the exhaust around concentric rings. Not out the back.
You may end up with too much exhaust residue on the transom.
Can you even use them on a wet exhaust?
Also it may end up being quieter behind the boat and louder in the cockpit.

------------------
RICKR
mailto:riggerb@aol.comriggerb@aol.com</A>

[boldts]

RickR,
The ones that were on my boat were being run on a wet exhaust. Back when I first test drove the boat, it was toooo quiet. That was 16 years ago. Now, I have a 4 yr. old that won't go near my boat because of the exhaust sounds. I still love the sound of an open exhaust, but I'd like my daughter to enjoy the boat also, so I thought maybe I could find these baffles again and try putting them back on her. Since I had them taken off when I bought the boat, I really don't know how they worked and I didn't notice any more noise in the boat compared to now with just having the black flappers on the exhaust.

Scott Boldt