what do you think gives best fuel mileage

1. 21cm
2. 18.5cm
3. 16cm
4. 12cm waste gate

 

Just cause I was first to vote don't mean I know what I'm talking about.

 

I have a 21 housing. When I finally replace it I will cut it up with the plamsa cutter, smash the peices with a sledge and then sprinkle them in the dumpster

How's that for a owner performance review?

Den

 

I'm thinking up to 250 rwhp or so the 12wg is the way to go---provided the afc settings are reasonable. In my mind, the 'instant' boost provided by the 12 as compared to the other contestants would provide for the most efficient burn of the available fuel. 250 rwhp on up (read:more fuel) and the 12 prolly just gets in the way
greg

 

I have the stock 18 cm and my mileage is pretty good around town it's 18.6 mpg. I bought a WH1C off ebay and when I get all the little pieces together I'll put it on and hopefully it will improve my boost around town and my mileage.

I really feel for people who are stuck with the 21cm. I'll probably have an H1C for sale soon.

Edwin

 

The 21 cm is best for high speed fuel mileage. I don't think the other 2 non wastegated choices are so small as to make much difference compared to the 21, but I can tell you from personal experience that the 12 cm hurts mileage at high speed (75 and up). At 80 mph in an empty truck, you don't really need any boost at all, but the 12 cm will give you 12-15 psi just because the engine RPM is high. As long as you can keep cruising boost down around 5 psi, highway mileage will be OK. You might want to ask guys with 16 cm housings what their boost is at 80 mph cruising empty.

My 21 cm went to the scrap yard.

 

Does drilling the WG hole to equalize the front cylinders help this problem?

Edwin

 

No. The hole in the divider only functions when the wastegate is open.

It's only a problem if you cruise at 75 and above.

 

Now I wish there was a FSM answer for this

I am so confused now

 

In our application the 16cm is a great compromise......
It will flow pretty well the same amount of gases/air as the 18.5cm housing does at the top end and it also gives decent spool-up. You can improve the initial spooling by doing some careful pump tweaking and still maintain the advantage of the better flow that the 16 provides on the highway.
The non-gated 14cm (which I have run in the past) is a pretty nice housing to get you on top of boost quickly. It also flows better than the 12cm of course but it does suffer from choking at the higher fueling/HP levels so keep that in mind.
At my HP level I saw a 100*F improvement in EGT's by going back up to the 16cm from the 14.
The nice thing about the 14cm and, even the 12cm is that they will move air for you pretty much right from idle RPM....this means that if you have a fairly aggressive set of nozzles/fueling you'll see your boost come one quicker and the smoke clean up real fast... but as noted they choke sooner too....you can get some nasty drive pressures when you push the small housings hard, that's why they are not the best at highway speeds...

pb....

 

When you add a turbo to a diesel engine, you go from having a fixed displacement engine to a variable displacement engine. . .

Acceleration, frictional losses, etc. determine how many hp you are "asking" for. This then determines how much fuel you introduce to the engine for combustion. As you introduce more fuel, the exhaust gas temperatures increase, and the turbo compresses the intake air to a higher pressure, increasing the volume of air that flows through the engine for each cycle. Increasing the manifold pressure allows you to add more fuel, and thus generate more hp -- until pumping losses get out of control with all that air trying to flow in and out of the head, or until the head/block grenade from the combustion pressure.

The point is that while many other details are important, the choice of turbo centers around the planned hp output. If you are running over 300 hp, you probably want the 16. If you aren't running that much fuel, you probably want a smaller housing.

 

Alec, thanks for explaining it that way. I think I understand now