Bolt On H.P.

[Tomtall]

A while back there was a discussion about bolt on horsepower. Nitrous Oxide kits, Turbo Kits, Big carb manifolds etc.

A few examples of this were the use of nitrous on the world record setting OMC V-8 outboard driven by Bob Wartinger. This engine was rigged with nitrous to give the engine an added boost just before entering the traps. 15 seconds of boost is all they gave the motor. But it seemed to be enough.

Land & Sea had their Turbo powered outboard record setter also.

Who on BRF has played with such things and what was your outcome? :rolleyes:

[kevin beaulier]

I'm 98% sure the hydro in the ad was built by Tom Drozd in Dallas. Thats a really cool picture. Thanks for posting it.

[Skoontz]

Educate me here. In the olden days, when motors were motors and gas was mixed with oil as how it should be, turbo and supercharging was tried and it shoved the gas through the engine so fast that much of the combustable charge was pushed right through to the exhaust.

How are they making compressed induction systems work in this day and age? Unless a valve was used to hold in the charge, I'm having a brain fart here and can't visualize how this would work/benefit....

[Roy Hodges]

so let's say that a V-6 merc uses 40 gallons /hour ? ok ? (for an example) . o k. Now ,let's say that supercharged /turbocharged - it uses 3 times that much? That's 120 gallons/hour . for DRAG racing, who cares? That would be 2 gallons /minute. divided by 6=10 seconds . 8quarts/6=1 &1/3 QUARTS !that's affordable for just about anybody ,and you would not need a big fuel tank, for the drags , anyway .

[7500Blizzard]

There's tonnes of guys running Nitrous nowadays in drags and pleasurecraft. There's been a guy working on a twin turbo merc for a few years haven't heard much lately, this motor is from New Zealand

[Mark75H]

Educate me here. In the olden days, when motors were motors and gas was mixed with oil as how it should be, turbo and supercharging was tried and it shoved the gas through the engine so fast that much of the combustable charge was pushed right through to the exhaust.

How are they making compressed induction systems work in this day and age? Unless a valve was used to hold in the charge, I'm having a brain fart here and can't visualize how this would work/benefit....You are correct, a normal belt, gear or shaft driven supercharger just looses pressure out the exhaust ports because they close last ... but ... a turbocharger causes a restriction that stops the pressure from falling to atmospheric pressure. One way of thinking of it is that the piston motor is now functioning completely inside the high pressure part of a jet engine; another way to think if it would be that the piston motor is now operating at the bottom of a great hole and the atmospheric pressure is much higher than sea level - the exact opposite of running your motor on a lake near Denver or Mexico City where you loose power at altitude due to reduced atmospheric pressure.

Supercharging a normal piston port spark ignition two stroke engine does not work ... unless it is turbosupercharging

[MN1]

You are correct, a normal belt, gear or shaft driven supercharger just looses pressure out the exhaust ports because they close last ... but ... a turbocharger causes a restriction that stops the pressure from falling to atmospheric pressure. One way of thinking of it is that the piston motor is now functioning completely inside the high pressure part of a jet engine; another way to think if it would be that the piston motor is now operating at the bottom of a great hole and the atmospheric pressure is much higher than sea level - the exact opposite of running your motor on a lake near Denver or Mexico City where you loose power at altitude due to reduced atmospheric pressure.

Supercharging a normal piston port spark ignition two stroke engine does not work ... unless it is turbosupercharging


Some how this doesn't sound right. Both produce pressure, how can one produce a different type of pressure that stays in the cylinders and the other doesn't?
Mark N

[Mark75H]

Some how this doesn't sound right. Both produce pressure, how can one produce a different type of pressure that stays in the cylinders and the other doesn't? Mark N
Both push in, but only a turbo has something hanging around outside the exhaust port. Its not that the pressure is different, its that a motor is basically inside it's turbo - and the whole inside system is at higher pressure

[mac19f]

In a 4 stroke engine supercharging or turbocharging results in a higher initial pressure inside the cylinder on the intake stroke before the compression stroke. That is its main contribution to increased power.

On a 2 stroke there are different factors at work. Other than on direct injected 2 strokes there is always mixing of the fresh intake charge with the spent exhaust gases. Normally the final charge in the cylinder during the compresion stroke has a significant amount of exhaust gases included. This is because the amount of fresh charge pumped from the crankcase into the cylinder is slightly less than the volume of the cylinder. This "dirty" charge results in less power per stroke than a 4 stoke engine would produce. That is a lower "break-mean-effective-pressure"(BMEP). Direct injected engines over scavenge the cylinder with clean air and then inject the fuel into the cylinder. The resulting clean charge is why they have significantly better performance than traditional 2 strokes.

Now if you don't care about fuel economy or emissions you can overscavenge the cylinder with a fuel/air charge with a supercharger, wasting a lot of it out the exhaust. But "BMEP" will be increased with a net increase in horsepower.

[Mark75H]

you can overscavenge the cylinder with a fuel/air charge with a supercharger, wasting a lot of it out the exhaust. But "BMEP" will be increased with a net increase in horsepower.BMEP will be increased some because volumetric cylinder effiency will be increased to 100%, but the net power cost to do this (because of the loss driving the pump) will not be much above break even or will be a net loss. In other words, power will be increased at the piston, but not necessarily at the output end of the crankshaft

Complete cylinder scavenging is not always 100% desireable .... in some situations residual (or reintroduced exhaust) gas is helpful in reducing detonation and increasing power ... on a 4 stroke it is called exhaust gas recirculation or EGR. It was new to production cars in the 1970's but researchers had been using it on test motors for decades before we ever heard of it.

[NERSTROM]

Jim Booe, creator of the TURBO propeller line, built an OMC V4 with turbo-charger and mechanical fuel injection (Hilborn I believe) in the early 70's. He did this with Bob Thompson, Just-Add-Water Racing. Jack Leek, Jimbo and I went to Indy where Jimbo tested the engine on the lake by Bob's dealership. The engine was impressive(fast), when we saw it Jim was still working out bugs in the fuel system. A little know fact, but in addition to making some really fast race props Jim is an excellent engine guy. Also, much more modest than RH.

[Tomtall]

Here is a neat little program for sizeing a turbo for the engine your bolting it to. Just in case your getting the itch. :D

http://www.smokemup.com/tech/turbo101.php

[mac19f]

BMEP is significantly improved by a clean fuel/air charge with resulting significant power improvement. This is evidenced by the fact that 4 stokes of the same displacement are generally torquier (is that a word?) than normal 2 strokes. Also why we see significantly better performance from direct injected 2 strokes than traditional 2 strokes.

EGR was introduced primarily for emission control. Exhaust gas particles provide a neucleation site for the chemical reactions of combustion. They act similar to a catylist in that they are not directly involved in the reaction but help start it going. This results in a more complete burn of the fuel for better emissions but with very little increase in power. However where a very small amount of exhaust gas mixing may be beneficial, the large amount of remaining spent gases in a traditional 2 stroke are far more detrimental. Some estimates I have heard state that a traditional 2 stroke final cylinder charge is only about 70% fresh fuel/air due to mixing. The other 30% consisting of exhaust gases obviously can make no power. Furthermore because they are much hotter than the intake charge they actually rob power by reducing volumetric efficiency.

Sam, I know you have always disagreed with this but the main power enhancing feature of a tuned open megaphone exhaust on a 2 stroke is the overscavenging effect of removing the hot spent gases from the combustion chamber so it can be replaced by the cooler clean intake charge. The return positive pressure pulse, which is the 4th pass, up and down the pipe, is so weak it has almost no effect in stuffing to increase cylinder pressure. Just look at the amount of raw fuel that always dumps out of a megaphone pipe.

[Skoontz]

HAVING tekn in and absorbed this thread, (thanks guys) let me axe this one....If an engine had a tuned pipe with Super Trap style silencers, which are quite restrictive, could that produce enough back pressure to make a supercharger set up werk on a 2 stroke? I'm gathering back pressure is needed so the charge does not push out the ports, but, with enough back pressure, could this werk?????

[Mark75H]

I just reread Harry Brinkman's explanation of how tuned exhaust megaphones work. Harry claims that a pipe designed primarily as a scavenging pipe will be in the 12 inch (from piston to pipe end) range - much shorter than pipes that actually work. If you can figure out what is wrong with Harry's math you will have me convinced.

My pipes run pretty dry, nothing ever drips out of them. There is never any odor of fuel, if any thing, my pipes are slightly sticky with oil residue (the delicious aroma of burnt castor!). I'm running jets bored out to just under .070 and getting a nice medium dark chocolate spark plug color. Without the pipes the same motor runs about the same plug color with .063 jets, so you are definitly right about the pipes pulling.

A restricted exhaust pipe/supercharged 2 stroke would produce extra power but only at a certain rpm/load and would be nearly impossible to keep at that load/back pressure condition on a boat without sometimes getting into an over restricted/over heat condition. There would still not be any guarantee that there would be a significant power increase at the crankshaft.

[Skoontz]

Another thingy. It was mentioned the old school 2 stroke had a dirty air charge. I find this especially interesting, simply because of EPA regs...I.E., lets tweek the numbers to prove our point. The dirty charge would be burned next round, thus creating the effect like a Cat, or as I affectionately call them, intergalactic BF'ers.

Sam what yer saying is to make the blower work, we need to maximize RPM to gain HP, or prop turns/i.e. speed. I'm thinking outside the box here, but a variable waste gate could just handle that in conjuction with the blower. After turbo charging a Kohler 25, and supercharging a Techumseh, I see a possible play with project on the horizon for me........

Add a different note....

I'm getting closer to opening that contain with the Belgian made stacks for the V-4. Once I get to it, I have'nt forgotten about your picture.

[Mark75H]

I don't think you have to "maximize rpm" if I gave that impression I made a mistake in my wording

Your waste gate would have to be pretty sensitive and work over a wide range ... and like I've been saying still no guarantee of significant power increase

I think you'd have better results going straight to a turbo, esp since you've done it once already

[Tomtall]

One mans sollutions to the pitfalls of nitros and the 2 stroke outboard.

"It was really fairly simple," he explains. "I just had to start thinking in terms of what was happening in the engines. All the systems I had used were being built by guys building kits for cars and inboard boats, and they simply did not have a clue as to what was going on in a two stroke outboard.

Read his story at - http://hydrodynamics-usa.com/index.php?option=com_content&task=view&id=22&Itemid=45

[7500Blizzard]

Tuned pipes should be 12-13 inches from exh port to front side of chamber to work, And most factory tuned pipes do run right around that length.

[Mark75H]

Tuned pipes should be 12-13 inches from exh port to front side of chamber to work, And most factory tuned pipes do run right around that length.What motors are you talking about?

[7500Blizzard]

Almost all my sleds tuned pipes measure right about there from the factory. The pipes for my Blizzard are just a bit over 13'' and that motor is 436cc's 95HP and runs at 9000rpm in sstock form.

[Mark75H]

I must have been bleary eyed when you first posted
Tuned pipes should be 12-13 inches from exh port to front side of chamber to work, And most factory tuned pipes do run right around that length.

I missed the "from exh port to front side of chamber" part. The length we are talking about would be the same as from the exhaust port all the way to the fattest part of the chamber, not just to the beginning of the diffuser cone. Now do you see why I am saying 12" is too short?

[7500Blizzard]

I've always been told to the beginning of the diffuser. I'm probably almost around 20'' to fattest part of pipe.

[Mark75H]

The critical tuned length for an expansion chamber is half way down the final cone taper. You can find this information in any technical description of an expansion chamber or description of how to design and build an expansion chamber from scratch.

[7500Blizzard]

The head pipe should be 12 inches.