We get really excited about head flow, porting mods, and all that stuff. And spend alot of money on it too! For some reason though, exhaust just seems to be an afterthought.

Maybe, its because, most guys build a combo, bring it to their local dyno guy, he dyno's it with race car headers, and it makes the number. But most dont' dyno with their actual exhaust they are running in the boat, so they don't see the losses on paper.

Tim's build is fairly close to BCK's. Esp when BCK had the victor jr 4150 carb combo. Cams close, compression close, bck had the 315 afrs, tim had the 325 afrs. Almost a 50hp difference. I'd be willing to bet, if tim had dyno'd with some 2.25" open race headers with a decent collector, those numbers would have been alot closer to each other.

I think its all a package. And it should be a package, of how it goes into the boat. I would like to think, if Tim was to upgrade exhaust, intakes, carbs, and maybe a cam change, he'd have a noticeably better performing boat. I don't think changing just ONE of those things, is going to do much for him. What I'm saying, is if he had a 700HP engine, dynoed with accessories, marine exhaust, flame arrestor on, etc.

Come to think of it, thats how I dynoed my engines this time around. At 6000rpm with old combo, dyno sheet showed 798HP. That was with 2.25 race car headers, no accessories. This current combo, with accessories, my exhaust system (1 7/8 stellings with tails that had baffles in them), my flame arrestor, at 6000RPM, the dyno sheet showed 782hp. At first I thought, well that sucks. I lost 16hp with the new combo. But then I ran the boat, with the same props, and realized , it didnt suck at all! I gained a solid 4-5mph. As we know, to gain 4-5mph in a straight bottom 38ft boat, with no other mods besides engine, takes a decent amount of power.

I gained 5mph in my little ski boat just from rejetting the brand new QF carb. Once the hardware is set in place then it's a matter of finding where I'm losing performance, and from what I can tell, that's a bagillion places on a boat and the most tenacious will have the best results. On motorcycles the most gains are had on the exhaust side of things. My last racebike I went from 165hp to over 185hp with little more than timing the cams but mostly blending in the exhaust ports. It was pretty significant.

Ok, so as far as headers go, I will see what I find, but what is the brand to have? Stellings? CMI?

Going from a full length header to a shorty style header, cost almost 50hp on this 600ish hp 427 ci. If that were the case on say, a healthy 540ci build, its almost safe to say, the money spent on fancy cylinder heads, may have been better spent on a good exhaust system?

https://www.youtube.com/watch?v=O1bXPNy1Yn4

Sell me yours lol

M/T - We did put the flame arrestor on mine to see if it made any difference- there wasn't any. I'm running CMI big tubes which might even be bigger than the dyno headers dumping into 5 in. tails dry to the very tip, so I figure there shouldn't be any loss there. I have the 305 heads. I was planning on running all accessories and marine exhaust for the final dyno but lost interest and just wanted it finished.

Same place smashed a header's primary tubes near closed all over the place and reported near 0 hp loss.:faint2:

Just as a reminder on some of these tests...lol

I will say that when looking at boats everyone running 700 hp ish or more have headers unless boosted...

Me Being a broken record, NA the more overlap you have, the more exhaust id's and lengths are critical.

That said, we need more tests with SM's exhaust to put a better finger on the issue/ no issue. They seem to be fine on approx 600hp 502's. I don't know of data past that.

I dyno'd mine in full marine dress, CMI sweepers and tails that were going in the boat, why do it any other way ? because several, maybe most, of the shops are not set up to run wet exhaust, its really that simple.

The interesting thing, would have been, to see what your build made for power with say, a set of Gil's, or the stainless marine standard manifolds. Irrelevent, since you have CMI big tubes.

You eventually made 700hp with the complete package. Intake, carb, exhaust, etc.

On another forum, theres a guy there from Long Island, who does some offshore builds. He said he has done some similar builds to your guys. 540ci, RHS 320 iron heads, no porting, dominator, 9.75:1, 730hp at 6200, 700ft lbs at 4500. Hyd roller comp cam grind. Bolt together build. No trickery. Thats in dyno form, no accessories. I asked for the cam specs on those builds. I will report back.

I remember my buddy years back, had a 9.5:1ish, 540, dart 320 heads, mild lift solid roller, dominator, brodix intake , made 720hp at 6200. He installed them in his boat, but could only turn the props he had to 5000ish. He got with bob m, and asked for some smaller cams, that would help make some more low end torque, to help pull those props. Ssm setup. They reduced duration quite a bit, and increased lift a little bit. Went back to dyno, engines made 690ish hp. I dont recall the torque change. Anyhow, the engines went back in the boat, and it gained a big fat zero. They did idle a little smoother. The boat was a 30ft twin vee race style boat, and accelerated awesome with both combos. I think if he had just went to smaller props from the start, he would have picked up acceleration, and top speed.

Anyhow, thats neither here nor there. What we really need, is a guy like articfriends, to do some marine exhaust testing for us on his dyno!

FWIW....and since you bring up sprint cup, we experimented quite a bit with the 4-2-1 & 4-1 on the D2 midgets we run. Granted, we are only running a 2.4l GM Ecotec, but we spin them up to 8500rpm. We build our own headers so we were able to experiment quite a bit. We liked the stepped 4-2-1 in terms of what it gave us mid-range and coming off the corner, but it wouldn't carry the car as well down the straights at high rpm. With the Ecotec and the ECU I'm using, I was able to take advantage of the variable cam timing (we can swing the cams ~25 degrees) and position them for maximum torque coming out of the corner (~4500rpm), vary the timing as the car went down the back straight to carry the horsepower up to 8500 and maximize this with a 4-1 short tube header. So, in our application, a short tube 4-1 gave us the best upper rpm power and we were able to improve lower rpm torque with cam timing. This was good for about 4 tenths of a second off lap times and clear visual of our car pulling away from the competition down the straights. This stuff is a blast!

Yes. Would've been very difficult to run my exhaust and with me having real headers it probably wasn't worth it. As far as front accessories it's the same thing. The hassle of plumbing power steering and raw water to see how much hp it absorbed wasn't worth it as there is nothing I can do about it anyway

Good thinkin don't have power steering to deal with lol

Bobs Marine Kinetics cams seem like they should work , prove me wrong , swap some different cams exhaust , I cant handle Bobs dateline , call week after week , way of doing biz

Im getting ready to start soon on my 540 NA project on dyno using efi, at one point maybe ill pull my dyno headers off and substitute on a set of manifolds and dump the water on the ground , my hp goal is 700 btw with sub 9-1 compression, not saying its going to make it but thats the goal

In all our dyno testing there was only about 15 HP difference using full length dyno headers and exhaust manifolds with 15" runners. It is pretty hard to beat the value of the Stainless Marine exhaust.

In the testing I've done over the years a good manifold like stainless marine, or imco gives up around 15 - 30hp on a build that makes 625-650hp with decent headers. I run 1 7/8 primary headers with full length 3" exhaust into magna flow mufflers on every engine during initial testing and break in, so I can monitor 10 O2 sensors and egt's. It's also easier to hear the motor during initial run up. This setup is very close to what a set of cmi e-tops makes for hp in the 600 - 650 range; the e-tops give up a bit of torque, but no hp. Once you get in the 700 - 800hp range, e-tops start to lose a bit, nothing major, but a set of big tubes or lightnings could be a benefit if you're chasing every last hp. One very important note is, cams with a bigger split on the exhaust show far less power difference between exhaust systems then the ones with the tighter split. This is why we run 8 to 10 degrees even on heads with good exhaust ports. Underperforming exhaust is a reality, and should also be part of the design criteria. The same way a crappy intake port needs more duration to carry the rpm. If you spec a cam based solely on flow numbers you could be giving up quite a bit of power. Not that it applies to this thread, but blower motors literally dont give a chit about exhaust in terms of hp percentage. It's amazing to see on the dyno

COOL Haxby nice to have you on board subscribed

Do you guys run the standard stainless marine, or the GEN 3 manifolds ?

Standard, single bolt pattern, I drilled the flange for the AFR's

Edit: mine are CMI not Stainless marine

That is interesting what haxby mentioned about seeing cams with more split, not being as affected as much by the poor exhaust setup.

Anyhow. Heres some 1600hp sterlings with Stainless Marine Gen 3's .

So my 5 degree spit and exhaust sucks just wonderful lol

Here's some dyno info on a 582 low rpm deal for a big white water jet boat. It shows a couple things. The first pic is with a custom cam 250 - 256 @.050 Dana exhaust with 2" divided riser extensions. The second is a few months later when we had to go through it because of reversion issues. I put a much smaller cam in it after running it in the boat and realizing that the pump was really inefficient over 4400rpm. 234 - 244 @.050. I believe the reason there is little change in peak torque rpm, is because the exhaust is holding it back and controlling the curve even more then the cam. Also, even though the engine ran at very low rpm, there was evidence of valvetrain instability with the bigger cam with higher lift. Second pic is with my dyno headers (which give very similar power numbers to E-tops) and last is with the Dana's back on, which is what the first one with the bigger cam was running too. I would agree with the gravel haulers suggestion that Tim's exhaust is more likely holding things back then the intake side of things. Oops, they posted in the wrong order. last one is 250-256, first one is smaller cam with headers, middle is with Danas. sorry

So, in your opinion would I see anyone enough gain at the gps in a boat like mine if I bought headers?

What's holding it back from going over 53-5400rpm?

https://www.youtube.com/watch?v=Y6EcyKygxTg Just for fun...... full marine dress with Dana Marine manifolds. This was just getting it tuned. We eventually pulled it to 6500.

Bill, i think the cam was too big. You need more torque. :)

Oh we found quite a bit more torque before we were finished..:)

Even better, was that was an engine that actually ran on the water. For quite some time too. She was no dyno queen

That would fit nicely in my ski boat. ;)

Were the exhaust housings on the turbos water cooled?

The housings were not water cooled but there were water cooled heat shields over the top of them.

From an engine builder in Long Island who does some offshore stuff. The RHS heads he mentions, are the Engine Quest iron heads now. He doesnt mention cam specs though

Have a number of similar units out and running for some time now.

Dart S/D, 540", RHS 320's, Comp retro-hyd-roller, 9.75:1 C.R., 2527 Edel, and a 4500 Holley. Bolt-together build, absolutely no HP chasing at all!

All off the dyno at/above 730 HP @ 6200 and 700 Torque @ 4500. Have many of these still in service after 15 years or more, not a single problem to date an any!

These are tested without any accessories however.

Thanks, Gary in N.Y.

P.S. With a change to a solid-roller, some very minor head work, and 10.5/10.75:1 C.R., we see above 775 HP/725 Torque, very similar RPM band. The RHS heads flow 375/275 @ .700" from the boxes. Just tested some recent "brand-X" heads we took on for a line, and still see just above 700. The cost on these heads is about 1/2 price!

That had pretty big camshaft you can watch the screen on the holley and see it did not make much vacuum at idle.

Do you know what heads they where?

I wanna say, 370cc . Don't hold me to it though. It was a fairly long duration solid roller, with a decent amount of lift if I recall.

Price difference isn't much btwn profilers and rhs. Valako is adiment about me getting the 320 profilers due to the extra thickness above the runner. We never discussed rhs but I always seem to hear and read great things about them.

Typically, if you are going to have heads ported, you get what your head porter wants you to. Doesn't mean you can't battle alittle. LOL. IMHO.

The only time we disagree is with the very same subject were on "cam selection". He always *****es cause I tend to wanna over cam everything. I understsnd his reasoning with his ported heads.