Turbojack

Yes, if suck thru system, there would be fuel in the line to the waste gate. This would also be the same line that goes to the boost gauge. If you look at any blower setup except for one that has port injection the line would/ could have fuel mixed with the air. That is the reason I always use fuel line for feeding boost gauge & what I use to use to go to the waste gates. The line is sealed. The line would have a good (maybe better, since air/fuel ratio may be close to right) chance, just like the fuel line going to engine might ignite.

REDCHECKMATE

richard What size boat,weight,prop,engine size and max boost are you making.You shouldn't need to reduce the bypass hole size or install wastegates to come on plane. I'm running a banks two carb setup and it works good. Carb settings and ignition advance seem to be a bigger factor getting on plane than high boost.

richard

The boats a 1979 wellcraft scarab. Same shape as their 89 panther. Don't know the weight think maybe 6000 to 6600lb The boat has two engines both 6.2L and runs clever 23 props on trs. The boat had a restrictive exhaust Because of room, the banks exhaust out of the turbo wasn't used between the engines, To which I think provided a imbalance between cylinder bank power. (See pic they are together on the left)All this gas then went through the trs. Which I think is restrictive for a banks engine, and contrary to turbo science.

At the moment the banks system is off one of the engine, so I can address any corrosion issues, and check it. I have just noticed, the inter-cooler separating wall between inlet and outlet water intake has corroded away, allowing the cooling water to by pass the inter-cooler. Losing me more power. There was no flush on it when I bought it, and it was a bastard to open.(also in pic. what remains of the separating wall did not come out in the pic)

This and the new exhaust + transom exhaust should allow me to accelerate much quicker. There is also water injection, but the nozzles are blocked, runs off boost, and I wanted to replace the turbo bearings, as I could push the impeller to touch the side walls (but no damage as yet) on the restrictive exhaust side. I know they float on oil, but from research they were over wear limit. Probably over heating. Now have replacement bearings from turbo city. $800 for 4 sets (2 engines)

I as allot of you, want to get as much out of my boat as possible, without blowing it, and only wanted to have to take the engine apart once to make these options available. If I closed the hole and fixed a external bypass pipe with a spring valve, Of about 1" diameter ( do any of you know of a valve such as this that isn't a waist-gate as I have no where to attach something as big as this as the exhaust has water cooling all over it. see pic). I would then have access to it, and It would give me full boost and spool up sooner for better acceleration onto the plane, as well as limit boost when its reached. Getting onto the plane is where most power is required apart from WOT. Which I think is why clever props have been installed on this boat, as they follow turbo characteristics.

Having control over spool up will allow me to tinker with it, if I decide to change props, and over come any slacking on the engines part.

In time I would like a inlet turbo bleed valve, as this will prevent/reduce boost spiking and ad turbo life + add to response, and again give me more control. I might just plug the hole to 3/8 then implement this kind of air inlet pressure vent, as this would be the simplest form of modification, and very controllable, but not as good as eliminating the hole for some sort of exhaust pressure vent as well.

All ideas welcome.

tomcat

richard: Man, do you have a project on your hands! Turbojack is right, wastegates will prevent the overboosting that would result from a change in turbine housing or plugging the hole. But there are a couple things you need to figure out before you make any changes.

Was the turbo kit originally for a big block or a small block? If it was originally for a big block, then you need smaller turbine housings. If it was originally for a small block, then leave the housings and the holes alone.

Assuming you don't have the mismatch of big block turbos on small block engines, my advice is to get everything shipshape and don't worry about plugging the hole in the turbine and adding a wastegate or valve right now. Gale Banks knew what he was doing. The amount of exhaust gases bypassing the turbine is normally adjusted by changing to a looser turbine housing, so the hole represents some kind of fine tuning. A free floating turbo without wastegates makes sense on an offshore boat for several reasons, so don't jump to the conclusion that you need more midrange boost.

Your real problem is the restrictive exhaust path. Clean that up and the turbine will spool up much quicker for two reasons, a greater pressure difference across the turbine and more exhaust gases to spin it due to the fact that your whole engine will breathe better and make more HP/exhaust.

Forget about wanting more boost. What you really need is more flow. Reducing restrictions to air flow anywhere in the intake and exhaust pathway will help this. (make sure the air side of the intercoolers is not plugged up.) Do this and intake pressure will automatically start to increase anyway as more air is being forced through the cylinder heads.

Changing to tighter turbine housings (or plugging the holes) actually restricts the exhaust pathway, and even though it spins the compressor faster, there are drawbacks for an offshore boat that may run at high RPM for extended periods of time.

- exhaust valves may run hotter

- you need extra components to control total boost at max RPM (extra things to go wrong)

- the increase in total power output may not be what you expect as you will get a little more flow out of the compressors but much of the extra compressor RPM will be turned into heat

- even worse, you will find that your exhaust pressure after the cylinder head is greater than the intake pressure before the cylinder head. This greatly reduces the scavenging of exhaust out of the combustion chamber and reduces HP.

So get everything else working right, open up the exhaust, then measure not only intake pressure but exhaust pressure. I think you will find that a free-flowing, floating turbo without wastegates will do the job.

What do you think would make more power? Intake 10 psi/exhaust 15 psi, or intake 10 psi/ exhaust 10 psi?

richard

I understand your point. Banks made setups for 379's and this was what they are on. I dont know if the manifold would fit a big block. I am manufacturing exhaust outlets similar to the one on the left in pic but a bit flatter, cause of room, and on the inlet side, I have thought about taking my pneumatic grinder to some restrictive areas I spotted. Also might take the head off and have a good look at the surface around the valves. I once grinded and polished a car turbo head with great results.

With all the problems, when she ran, she was not to eager to plane. I knew the exhaust was crap, and you can see why just from looking at it, and that always bugged me+ the exhaust was through the trs, which will add greatly to that back pressure, and cause spool up to suffer.

You are probably right that I should just leave it alone. As you mention I dont want excess back pressure, this can cause pre detonation on overlap and taking it to 3/8 without consulting banks to find out the ins and outs of the kit, if they still have info, that is. Would be a bit naive. As I dont know what housing they used, and even the turbo pressure, as the gauges were not working. But I do know this. Some kind of set by-pass pressure valve would stop exhaust pressure escaping till (using the 10psi in your example) 10psi is reached. Then the valve would open to stop any excess pressure, and exhaust heat, and remove impending restriction, when the revs rise. This I would hope , give you at a guess 200rpm faster spool up, helping eliminate lag, and as she would therefore arrive on plane earlier, would not labour in a state of strain, which also builds up engine heat + the intercooler water is not pumped relying on a bottom scoop, so quicker cooling would take place if rising to the plane earlier, which is another bonus giving less chance of back fire. Mechanics would also be subject to less time at high strain, and it would also help out the days when your accompanied by heavy mates.

Here is a pic from "Turbochargers" by Hugh MacInnes illustrating the resistance a hull with special power requirements gives verses the power of a matched and unmatched turbocharges engine. Note the hump. This is when the boat rises to the plane. Also note that the turbocharged boat with "properly matched turbos" (as the description says) has only a small amount of power in reserve. I think this pic matches my hull/power and most v hulls, and the smoother graph(not shown) in the book (without hump)refers to flat bottoms, or non planning.

Many factors effect this. One being air and sea temp. I know how sluggish a turbo car feels on a hot day compared to a crisp night. I reckon I have felt over a 40hp difference on a 340 car. But as you said with the exhaust, inter cooler sorted I probably wont have a problem getting to plane. But with the new exhausts the boat will have been modified, and may rev right up to 6000. In which case I will look for a set of cleavers with higher than 23 pitch. Which will then bring me back closer to the hump in the pic. Where any extra will be greatly beneficial. Theres always the feel good factor of popping onto the plane with speed, that puts a grin on your face.

Your right in saying I have a project on my hands. I consulted with my girlfriend today, on the prospect of re commissioning my old wellcraft nova xl 23 with twin 190's 35knots (not enough)max 27 cruising for the summer. As I have other work to do on the scarab, and this will give me more time to do the job right+ some boating fun.

tomcat

I was going to say "Get that book" but you already have it so good luck on your project.

The hump is the transition from displacement power requirements to planing power requirements and all planing hulls have a curve that looks like this. Notice that trimming the turbo to have curve #2 reduces the total power and speed. This is because even with the wastegate open the restriction is greater than with a larger turbine housing. Turbonetics sells a NewGen wastegate with a swing valve instead of a poppet valve which they claim gives the bypassed exhaust a less restrictive pathway. This promises to give the control of boost and midrange improvements without giving away as much top end.

Turbojack

I would clean everything up, make sure everthing is in good working order & INSTALL LARGE THRU HULL EXHAUST. I think putting thru hull exhaust will help with takeoff & with WOT.

richard

looking at all the work involved Im starting to agree. Ive got alot to do, and I dont want to be running around in the 23xl for long (nose bounces in the rough). Not now I have a taste of twin gale v8's on a good 30ft hull.

Payton

I gained 300rpm in my spoolup just by having my turbos freshened. So if your bearings are being replaced, you may already have your 200 rpm difference.

I freshened my turbos when they started to look oily wet on the intake side.

richard

300rpm, thats pretty good, and just what Im looking for. Properly looking at waistgates, they are the only thing I should use in the exhaust, as they are operated not just from spring v exhaust pressure, but also from inlet pressure, which opens them up eliminating exhaust back pressure. There goes my valve idea. I didnt really think about too much exhaust back pressure.

Thanks for the wealth of knowledge you guys posess. Will let you know how it runs when Im finished. Dont think Ill install gates, too much work, and I dont think I need them