806 - 1206 pistons difference???

Larry B 1486 · Sep 16, 2011

Wanting to do a overhaul on the DT 361 motor. Was looking a piston sets and it list different pistons for a 1206 than a 806. Said 1206 has a lower comperssion piston than the 806. The 856,1256,1456 with a 407 uses the same pistons. What happens if you put 806 pistons in a 1206? They all use the same head so whats with a lower compression in a 1206? To me that should be the other way around. If you put 806 pistons in a 1206 motor won't it give more power?

Owen Aaland · Sep 16, 2011

With everything other than the pistons being the same the change in compression has the result of a larger combustion chamber. With a turbocharger the dynamics change a bit compared to a naturally aspirated engine. In the 806 the amount of air entering the cylinder (ignoring any outside restriction) is dependent on the displacement of the engine. With a turbocharger the lower compression will allow more air to be pumped in at the same boost pressure.

If the differences in compression ratio are enough to make a noticeable difference in power I don't have a clue.

karl f · Sep 16, 2011

less compression in a turbo engine makes it easier
to prevent detonation and other high cylinder temp
problems. It sacrifices maximum power for
simplicity and reliability. Cost reduction in
research and development too. High compression,
higher turbo pressures often require more complex
fuel and air controls that monitor and change the
air and fuel real time based on various sensor
inputs. A wastegate and modern computer control
(or many mechanical devices) are definitely
required when you get into higher manifold
pressures and higher compression. My info is
based on conversations with a guy that was
modifying the heck out of his turbo car.

karl f

FC Andy · Sep 16, 2011

I didn't know there was a difference in pistons. Good to know for the future. (I'm sure I'll have to overhaul the 806 eventually.)

A lower compression ratio would allow for higher boost pressures to be ran, which would result in more power and cooler EGT's. It's why my old chevy 6.5 supposedly only runs 5-8 lbs boost. I don't have a gauge on it. It has 22 to 1 pistons in it. Later ones and all your 7.3's and 5.9's are at 17 to 1 (Give or take) and run 15-20 lbs boost.

My best understanding is that with a turbo engine, a little lower compression and lots more boost pressure is beneficial rather than the other way around. More potential pressure would also allow the turbo to better adjust for altitude changes, too. Of course, a stock engine running stock rpm's can only support so big of a turbo...

Neat conversation. I hope my understanding is pretty close. If not, I'd like to be set straight.
-Andy

Anonymous-0 · Sep 16, 2011

The pistons are different on 806D361, DT361 for 1206, D407 for 856 only, DT407 for 1256 only, 1456 DT407 is different also. Compression ratio and Bore must match, 1456 has larger wrist pins.

tjiniowa · Sep 17, 2011

I put 1206 pistons in my 806 when I o.h. it. It was recommended by a friend that has worked on several of these engines. Not sure I notice a difference, because it was tired before I took it apart. If you do change pistons you may have to check the injectors, the 1206 takes a little more pressure if memory serves me correctly. I had mine all shimmed a little and had to have one rebuilt at the time

ejr-IA · Sep 17, 2011

Piston height on 806 is 3.043,1206 is 3.040 .003 diff.

806 - 1206 pistons difference???

Larry B 1486

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Owen Aaland

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karl f

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FC Andy

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Anonymous-0

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tjiniowa

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ejr-IA

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