MILD THUNDER

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!

rvander68

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!

bck

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

Full Force

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

hotrodford

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

articfriends

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

Knot 4 Me

http://www.offshoreonly.com/forums/s...mi-e-tops.html

BenPerfected

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.

HaxbySpeed

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

hotrodford

COOL Haxby nice to have you on board subscribed