Bolt On H.P.

**NERSTROM** · 10-26-2006

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 · 10-26-2006

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

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

**mac19f** · 10-27-2006

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** · 10-27-2006

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** · 10-27-2006

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** · 10-27-2006

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** · 10-27-2006

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 · 10-28-2006

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.p...d=22&Itemid=45