Pelican Parts Forums - How about a destroked 3.6?

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How about a destroked 3.6?

Will an SC crank fit in a 3.6 case without modification to the bearing journals, etc?

Assuming that custom J&Es would be required, would a short stroke 3.5 (70.4x102) be possible using a 3.6 case and an SC crank & rods?

TIA

For the same reason someone bothered with a short stroke 2.5, 2.6., 2.8, and 3.2. Those engines seem to work well for people so Im curious if the same principle could be successfully applied to a bigger, newer, and more readily available engine with common parts.

Sherman, Check out the latest magazines at the store, There is an articlein either GT or Excellence about a 993 destroked to 3.3 with an SC crank. I don't remember the particulars.

Quote:

Originally posted by Shuie
For the same reason someone bothered with a short stroke 2.5, 2.6., 2.8, and 3.2. Those engines seem to work well for people so Im curious if the same principle could be successfully applied to a bigger, newer, and more readily available engine with common parts.

Generally engines are destroked in order to fit within a certain capacity limit. Destroking also will allow the bottom end to spin to higher rev's, but in most 911's, it's the valve train that limits the rev's more then the bottom end. The "short stroke" 2.5 was created because the long-stroke version kept having vibration issues that were backing out the flywheel bolts. As soon as they could solve that problem, Porsche went on to the comparatively "long-stroke" 2.7 and 2.8.

Compared to "short stroke" engines, "long stroke" engines generally have better combustion chamber charactoristics for a given CR. Specifically they have lower ratio of combustion chamber surface area to volume then short stroke engines of the same design.

BUMP!

lurker no more. Hello...

So is it possible to use a 3.0 crank in a 3.6 case? What about destroking the 3.6 crank? The Excellence mag (sept 05) noted custom rods. Why?

The following I think has relevance:

Quote:

Originally posted by Henry Schmidt
If your only criteria is horse power, the answer is no. It is reasonable to assume that a larger engine (all other things being equal) will make more horse power.
The benefit of the SS 2.8 over the 3.0 is that the engine will spin at a higher RPM safely.
The rod length to stroke ratio is better.
A relatively low conrod-to-stroke ratio such as the 3.0 produces greater rod angularity with the cylinder’s centerline as the crankshaft turns from top dead center (TDC) to 90 degrees after TDC than that of engines with higher conrod-to-stroke ratios. (Note: conrod-to-stroke ratios in Porsches range from about.1.66:1 [3.3 - 3.8] to 1.97:1. [2.0-2.8 ss] As rod angularity increases, the piston accelerates away from TDC more quickly than in an engine equipped with a longer rod; engine designers refer to this phenomenon as “piston dwell.” Short rods generate abbreviated piston dwell; long rods have prolonged piston dwell. The trick for designers is to match piston dwell with the fuel’s burn speed to produce an acceptable increase in cylinder pressure without introducing detonation (a destructive, power-sapping combustion defect). Many experts believe that the most important benefit associated with long connecting rods is the reduction in piston side thrust, which increases friction and promotes cylinder-sleeve distortion.

http://forums.pelicanparts.com/uploa...1128097398.gif

Everything that has been posted in this forum about rod stroke ratios is true. But the research to back up these findings is skewed (turn of the century) if the rod stroke ratio was 1.3 and you went to 1.5 ,1.75
or so you would be correct. But everything is 1.5 or better, and it does not change piston position more than 1 degree if you lenghten the con rod 5mm. Currently even the the Porsche DP engines that are running have a long rod so they can make the piston skirt smaller and reduce the ring drag, as the ring and skirt combine for most of the drag in the short block and in a limited displacement engine the production of power at elevated RPM is crucial. Packaging (engine bay dimensions) are dominant in engine design for most of the racing organizations now days " so look before you leep". Also the dwell deal is just not the case.

Best regards