Dr. Scott M. Baker

Turbo Components

Now that we’ve discussed the¬†fuel components, let’s take a look at the turbo itself.

I decided to go with an IHI RHB5 turbo, the same model that I used on the manx build. There were a couple of reasons for this. First of all, since I already had one RHB5, I was already familiar with how they worked, how to rebuild them, and the performance. It maintains parts compatibility with my other turbo so I could swap them if necessary. Second, it’s a relatively cheap turbo and just about the right size for the 1776 engine.

Let’s revisit the issue of dynamic seals versus carbon seals. The manx build used a draw-through turbo configuration where the carbureator was placed upstream of the turbo. This puts an input restriction on the turbo. If the turbo has a dynamic seal, then it’ll suck oil right out of the turbo housing into the engine – blue smoke, lots of it. for this reason we had to rebuild the manx turbo with a more expensive carbon seal.

The fuel injection setup on the other hand is going to use a blow-through configuration. There is no input restriction on the turbo. Thus we can use the dynamic seal that comes with most modern turbos. No need to rebuild it or add a carbon seal. This is very good news as it not only saves some cost but also reduces the overall complexity of the system.

However, I ended up rebuilding the turbo anyway. The shaft felt just a little bit too sloppy to me and it had a bit too much end-play. This is common of some of the turbos that you’ll find on ebay. What a seller might describe as “very little endplay” really means that it rocks back and forth like a loose rod. What’s described as “spins freely with no friction” usually means nothing more than it wasn’t frozen in place. Plan on rebuilding an ebay turbo. It’s not that hard of a job; the most trouble you might encounter is some stubborn bolts or screws.

In a blow-through configuration, we also need a blow-off valve. This is because the throttle-body will be placed downstream of the turbo. If we rapidly let off the throttle, then the there will be large surge of pressure between the turbo compressor and the throttle body. This is not good for the compressor and may cause it to stall or stop spinning as fast as it should. The blow-off valve is responsible for noting when you let your foot off the accelerator and releasing the excess pressure. Your turbo can keep spinning at full speed and be ready to deliver full pressure when you put your foot back on the throttle. It makes a coool “Pssshhhhtttt” sound whenever this happens.

Finally, we need an intake filter. This is the easy part as we don’t really need anything fancy. I used a leftover K&N-style filter that I had laying around somewhere.

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