De-stroking

derost · Post by **derost** » Tue Jun 27, 2006 10:47 pm

This might be a silly thought/question, but how feasible would it be to de-stroke the 1.6? What does it take anyways? My understanding is that it's a shorter crank throw (terminology) and a slightly longer conn. rod. What benefits would this give other than making it rev quicker and higher? Probably want to overbore it a little to keep it close to 1.6L though.

I know F1 cars have insanely short strokes and I have heard of at least 2 Jeep guys de-stroke their 4.0L I-6's.

Post by **PrecisionBoost** » Wed Jun 28, 2006 4:50 am

Well.... destroking does decrease the piston velocity... and help keep the angle the rod moves through smaller.

In short... this helps keep the piston more stable and it allows for higher RPM.

Think about it this way.....

If engine #1 has a 100mm stroke and engine #2 has a 50mm stroke...... it means that piston #1 has to move 200mm for every revolution while piston #2 only has to move 100mm for every revolution.

So.... if you rev engine #1 to 5000 RPM it would be the same as reving engine #2 to 10,000 RPM.

So by decreasing the stroke you decrease the piston velocity/acceleration/deceleration.

It's a linear equation..... between piston velocity, stroke and RPM

there are also more advantages to having a shorter stroke with respect to the burn pattern and expansion forces inside the engine but it would take a while to explain.

As far as rods.... well.... rod ratio is important for a number of reasons having to do with things like piston dwell time at TDC and BDC... as well as angles of the connecting rod..... If I have a spare half day perhaps I will explain it

There have been posts on this stuff before.... use the search tool and look for things like "rod ratio"..... you might be able to narrow things down by using me as the author in the advanced search

MMamdouh · Post by **MMamdouh** » Wed Jun 28, 2006 7:53 am

nice info chris but you still have the rev limiter holding you from going past 6500 RPM... right?

what about the top end of the engine? valve float is a concern

and finally the ever lasting question: what are the HP gains??

MMamdouh

wolfhound · Post by **wolfhound** » Wed Jun 28, 2006 10:17 am

Destroking does increase the "revability" of an engine. I am also a classic Mini fan and in SA we had a 1275 motor that Leyland destroked to make an 1100. What the guys in the UK are doing is putting our South African cranks with 1275 pistons and decking the block to get a really high reving 1100 with light weight pistons.

Unfort, you can see from above, destroking losses cubic capacity - using longer rods or infact pistons with higher compression heights like leyland SA did to get the compression ratio back up again, does not get that capacity back.

Another negative is that you could gain HP but loose torque.

Séan

woo · Post by **woo** » Wed Jun 28, 2006 1:17 pm

wolfhound wrote:
Another negative is that you could gain HP but loose torque.

Séan

F1 cars make something like 700hp, but they make the same amout of torque as a stock WRX

Rodd1s · Post by **Rodd1s** » Wed Jun 28, 2006 2:58 pm

woo wrote:
wolfhound wrote:
Another negative is that you could gain HP but loose torque.

Séan
F1 cars make something like 700hp, but they make the same amout of torque as a stock WRX

u sure? arent F1 cars pushing 1500 HP? if i remember correctly the max HP for an F1 car used to be 1500, but that was decreased to 1000 HP cos the speeds attained were becoming stupidly high.

woo · Post by **woo** » Wed Jun 28, 2006 9:33 pm

Rodd1s wrote:
woo wrote:
wolfhound wrote:
Another negative is that you could gain HP but loose torque.

Séan
F1 cars make something like 700hp, but they make the same amout of torque as a stock WRX
u sure? arent F1 cars pushing 1500 HP? if i remember correctly the max HP for an F1 car used to be 1500, but that was decreased to 1000 HP cos the speeds attained were becoming stupidly high.

i dont know how much power they make, but they only make the torque of a wrx

Post by **PrecisionBoost** » Thu Jun 29, 2006 5:02 am

Who needs torque when you can rev to 15,000 RPM

kinkyllama · Post by **kinkyllama** » Thu Jun 29, 2006 5:11 am

chris@PrecisionBoost wrote:Who needs torque when you can rev to 15,000 RPM

I think it's closer to 22,000rpms now.

Rodd1s · Post by **Rodd1s** » Thu Jun 29, 2006 12:52 pm

chris@PrecisionBoost wrote:Who needs torque when you can rev to 15,000 RPM

+1... i would love to have a high-revving engine.

Edit: come to think about it... if someone does this (de-stroking) and the mods proves to be good... i'll join in and do it aswell. can anyone list the parts that will need to be replaced?

chronoti · Post by **chronoti** » Thu Jun 29, 2006 2:32 pm

you need a modded crank for a lower stroke, shorter rods, higher comp pistions, diffrent cams, dual valve springs, way over bored block, and your engine will idle like crap or at around 2k.

also rotory engine? they rev to 10k but you need to take it that high to get anywhere.3

also there was a toyota engine (4a) that was modified like this as well by formula atlantic to be reving that high, here is the discusion on it.

http://toyotanation.com/forum/t136441.html