Need advice on new exhaust/upgrade for 21ft Howard V-drive cruiser

[kurtis500]

So the old manifold and snail combo is at the end of its life and I need to replace them. I need some new exhausts before Thanksgiving (next trip) and would like some advice on your experience with BBC exhausts... Heres a few important facts:

-Engine is under a fully enclosed engine cover
-454 11:1 closed chamber rect port heads. Original LS6 motor that i replaced the mech cam with a slightly less aggressive hydraulic cam. I will probably switch to a flat tappet cam or maybe hyd. roller at the same time. (cpuld use advice in that area also!)
-Exhausts go straight out the back with the Harding marine manifold/snail setup so a similar alignment would be needed
-I use an O2 sensor to a gauge so i can watch and tune for A/F ratio when needed.

I am not looking for any more MPH or HP gains although I will take it if they are possible with a switch. The boat is used for wakeboarding and skiing, it was my comprimise with the wife to keep the V-drive in the family. Also, I have a 6-71 sitting here that I never put on and probably wont anytime soon. but maybe one day now that my youngest kid is off to Baylor next month!!

I would like a good exhaust that gives the same or more air flow and allows for an O2 sensor. I have room under the hatch for almost any existing exhaust so they are all options to consider.

What are your experinces going from manifold/snails to anything else? Do you think the manifold/snail setup is just fine and buy a new set or is the Dana/CMI/Lightning jacketed headers the way to go? I dont mind a little extra $ for something nice but dont want to pour money into something that doesnt have a good benefit.

Thanks in advance

 

[obnoxious001]

How are you running an O2 sensor with your current Hardin aluminum logs?

 

[kurtis500]

How are you running an O2 sensor with your current Hardin aluminum logs?

I drilled in the the non-jacketed section in front of the #1 cylinder and welded an aluminum bung on top. I used to have a full Holley MPFI HP system but couldnt keep the sensors alive no matter how far I put them from the back of the boat.

 

[obnoxious001]

I have a set of the Glenwood, which flow better than the other "log" type exhausts, but not sure you use an O2 sensor in them.

If the hydraulic flat tappet cam has worked out well for you, why change it? Solid flat tappet would require periodic adjusting, and hydraulic roller would mean new springs, lifters and pushrods, so $1000 or so. (Don't use cheap hydraulic roller lifters in a marine engine).

Header type exhaust may gain a tiny bit, maybe not necessary for your combination.

 

[kurtis500]

I have a set of the Glenwood, which flow better than the other "log" type exhausts, but not sure you use an O2 sensor in them.

If the hydraulic flat tappet cam has worked out well for you, why change it? Solid flat tappet would require periodic adjusting, and hydraulic roller would mean new springs, lifters and pushrods, so $1000 or so. (Don't use cheap hydraulic roller lifters in a marine engine).

Header type exhaust may gain a tiny bit, maybe not necessary for your combination.

I took the flat tappet out after a lobe rounded off and just went with a hydraulic cam. My thoughts then were to not go faster since I had 3 pre-teen kids that were wakeboarding and skiing and I was racing 2 hydros in the IHBA/LODBRS. The hydraulic saved me money so it was a win-win back then. The problem was the cam I picked was too mild. The 850 Demon at the time worked nicely with the flat tappet but with the new hydraulic flat tappet the 850 was too big and ran better when I put an old 750 vac secondary on. With the mechanical flat tappet cam the 850 out performed the 750 noticeably when i did some testing before the lobe rounded off. I think the CC rect port heads just didnt like the cam IMO.

With that said I am willing to do a little more with the motor now that I have to replace the exhaust. We still wakeboard and ski so reliability is important but a good healthy sounding powerplant with reliability is my goal. An increase in performance somewhat without having to change out major items like the Velvet drive, upgrade to 1 1/8th shaft/couplers, an aftermarket block and you know the rest. Im open to anything at this point that can be done with the 4-bolt gen IV and CC rect heads that isnt crazy but modest and reliable and better performing that what I'm doing now.

 

[obnoxious001]

Regardless of what style cam you run, you do have to be aware that too much duration will run the risk of reversion and getting water in the cylinders.

I recall the time my buddy ran out and bought an 850 Demon to replace his "stock" 715 CFM Holley (yes, I do mean 715). We did a bunch of tuning on the Demon to get it to where it would run as well as the Holley, but never better. It just wasn't necessary for a 5,000 RPM jet boat. Yours being a V-drive may let the engine run a bit higher RPM, depending on gear and prop. The RPM range you plan to run will also help determine the cam. I am still scratching my head a bit wondering what fuel you are running with an iron head 11-1 engine in a boat application where the engine constantly has a load on it.

 

[kurtis500]

Regardless of what style cam you run, you do have to be aware that too much duration will run the risk of reversion and getting water in the cylinders.

I recall the time my buddy ran out and bought an 850 Demon to replace his "stock" 715 CFM Holley (yes, I do mean 715). We did a bunch of tuning on the Demon to get it to where it would run as well as the Holley, but never better. It just wasn't necessary for a 5,000 RPM jet boat. Yours being a V-drive may let the engine run a bit higher RPM, depending on gear and prop. The RPM range you plan to run will also help determine the cam. I am still scratching my head a bit wondering what fuel you are running with an iron head 11-1 engine in a boat application where the engine constantly has a load on it.

91 and cut it with avgas. For a few years i had the 291 heads off and 990's on to drop the CR. I put the 291 heads back on hoping to bring the performance up a touch.

BTW, which lifters for a hyd roller? I cant remember which ones are junk..

 

[sintax]

I dont think there are any cheap options. I'd see if IMCO can weld some bungs in their risers, or i've seen dudes make a spacer between the riser and the manifold for an o2 bung.

the IMCO powerflows would be a nice setup, and they do a great job on their risers to fit your boat.