Stroking

[Lextreme II]

This is an interesting topic since its being develop as we speak. Couple of things I would like to share with our members. Stroking is no easy task. Couple of issues should be consider:

1. Rod clearance
2. Rod length
3. Piston design
4. Interferrence

1. Rod Clearance:
Some people think its so easy to sell a stroker crank like 3.85" stroke. If 3.85 stroke is possible, then there are few issues above need to be address. However, it will take more then a stroker crank to make the engine run. From what we found out, anything over stock 3.31" stroke will require block modifications. The uzfe block has limitation on clearance. Above and beyond stock stroke, then u will spend big money on modifying the block to make things clear.

2. Rod Length:
Assume this person made a 5.85" stroker crank. What size of rod would this person use? If the rods is too short, then the counter weight will hit the piston and if the rod length is too long, then your piston design will be compenmise with decrease compression height and ring lands. So choosing the right rod length is very essential.

3. Piston Design:
The pistons must have certain specs in order to function properly. As stated on number 2. The rod length will affect the piston design and compenmises. However, there are ways you can get around it, but still compenmises.

4. Interferrence:
Since the stroke increase from 3.31" to 3.85", interferrence is unavoidable. Rod swing or counter weight. Basically selling a 3.85" crank is only part of the solution. However, stroking is more complex than just adding stroke.

In conclusion, stroking will require lots of engineering and testing. Simple crank wont do it.

 

[jtucci]

it was my understanding that the tundra 4.7 crank & rods + SC400 pistons would clear the valves and block in my 93 SC400 as long as i used the stock SC400 heads/cams/valves. correct me if i'm wrong.

 

[ed_ma61]

5. Compression Ratio
With the increase swept volume, and fixed combustion chamber size in the (stock) head you will put your static compression ratio through the roof. Youll need to consider what impact this will have on your piston crown design, and what necessary changes with thence have on the dynamic combustion process and knock tolerance.

6. Rod Stroke Ratio
These days, anything under 1.6:1 is just plain unacceptable.

7. Piston Speed
4500ft/min is the maintainable max piston speed for a variety of reasons. Sure stroking improves capacity per stroke and torque, but significantly limits RPM (capacity per min and thus HP).

Conclusion
cubes vs rpm - your choice. everything is a compromise. My thoughts? dont try and make an engine something it isnt. a 4L engine just isnt in the same league as the 5 and 6L v8's. dont try and make it one. optimise the aspects of the engine and make it work as well as it can, dont try and make it another engine altogether - if thats your aim, buy that engine to start with

Ed

 

[ed_ma61]

lol - and its lextreme's birthday today - cheers!

ed

 

[928s]

You are right in many ways Ed, I would just add that some engines have the capacity to be increased built into them in the factory when they are first made. Porsche thought of this when they made the 928 engine. They started off with 4.5 litres and went to 5.4 litres. The guys these days are making 6.5 litres with the same blocks but different cranks and pistons. They rev to about the same but need better materials to do it. They make about N/A 500 to 550 rwhp in a reasonable state of tune. This engine though is not a compact 4 litre engine, it never was.

Cheers Greg