Destroking - Facts or fiction

[turbo89]

Been thinking about this topic from a different perspective. More power pulses per second is key to the destroked motor making more power. When comparing a 600 hp 231 @ 2.5 hp per cubic inch vs a 280 ci (at equal RPMs) the extra 50 ci is a huge difference in potential power.

People can say and think whatever they want .. I can tell you my observation from this season ... IT WENT MUCH FASTER with the smaller engine .. I will leave it at that as I need to make 1 final trip to the track in the next few weeks...

In the street the car is an absolute mineshaft and so much easier to harness the power ...

Only pissed I didn't do this years ago ... If I didn't trip over that short throw crank I probably wouldn't have given the combo a chance.. live and learn.

 

[Mike T]

How fast did it go?

 

[turbo89]

How fast did it go?

6 mph faster than the previous setup .. and it has gained some weight from last season ( both car and me )
had to add in some safety items prior to my return to the track .. can't believe how pricey safety stuff is !!
I bet the car would pick up another 1-2 mph if I didn't have all the extra weight added in .. these cars are TANKS !!!

 

[Ttype6]

In the street the car is an absolute mineshaft and so much easier to harness the power ...

Are you saying that the power comes on at a slower rate which lessens the chance of wheel spin on the street?

 

[turbo89]

Are you saying that the power comes on at a slower rate which lessens the chance of wheel spin on the street?

No .. its how you can apply the power ..

 

[Pronto]

6 mph faster than the previous setup .. and it has gained some weight from last season ( both car and me )
had to add in some safety items prior to my return to the track .. can't believe how pricey safety stuff is !!
I bet the car would pick up another 1-2 mph if I didn't have all the extra weight added in .. these cars are TANKS !!!

Yes, stronger parts all seem to weigh more. Roll bars are at least 120 lbs. As much as we think these cars are heavy, the new ones like the Challengers and Camaros are heavier.

 

[Ttype6]

No .. its how you can apply the power ..

I still don't understand what you are saying. Please explain.

 

[TexasT]

Can we get a recap on the engine?
By some of the above thoughts a 4" bore on a Siamese block and the shorter crank throw might be a nifty setup. Just have to get the rest(block, valve train, rods, trans) to be able take the higher rpm. The bigger bore will get a better flow unshrouding the valves in the bore. And you can really move some air with these newer turbos.

Now you have me causally hunting a bms crank for my 291 block. With the stiffer crank and some billet caps I would hope it could stay together better than the flimsy stock crank flopping all over the place. Have to calculate the rod/piston combo and with these newer available custom pistons can get something to where I can make a clean up bore of the cylinders and get a zero or near zero deck. I guy can dream.

 

[Mike T]

I would also depends on if we're talking 8,9,10 or 11 second power. I could see a lower 10 second (and faster) car benefiting from a higher revving short stroke.

 

[Mike T]

Assuming VE is close a 215 ci would need to turn 6200 RPM to be equal to a 231 @ 5800

 

[434nova]

I would think with talking 109 or stock blocks. You would want to build the biggest motor possible to keep the boost levels down cause the 8 head bolts and keep the revs down for the block not to flex. If it’s a stage or a ta block you can run rpm and tons of boost.

 

[turbo89]

I would think with talking 109 or stock blocks. You would want to build the biggest motor possible to keep the boost levels down cause the 8 head bolts and keep the revs down for the block not to flex. If it’s a stage or a ta block you can run rpm and tons of boost.

Nope ... who cares about boost numbers

if your goal is to keep boost numbers down .. put a 106 on it .. but you won't go fast
The block isn't the blocker to RPM's

 

[Mr.Spool]

6 mph faster than the previous setup ..

what turbo did you use?and did it make more less or the same boost to go 6 mph faster?

 

[Turbo6inKY]

Been thinking about this topic from a different perspective. More power pulses per second is key to the destroked motor making more power. When comparing a 600 hp 231 @ 2.5 hp per cubic inch vs a 280 ci (at equal RPMs) the extra 50 ci is a huge difference in potential power.

Not really. More power pulses is a result of increased RPM, which may or may not be something you get from a destroked engine, depending on how you build the engine around the crank.

There are only a few direct effects of reducing the stroke:

1) Reduced displacement
2) Reduced piston speed
3) Crank rod pins are closer to centerline of the crank


What do you do with that? Reducing displacement is easy to overcome with forced induction. So we move on to #2. You can calculate the benefit there:

http://www.csgnetwork.com/pistonspeedicalc.html

That'll get you your average piston speed quickly. Then if you know the weight of the piston and convert everything to metric, you can use F= MA to figure out the force the piston experiences at TDC on the exhaust stroke (maximum tension on the rod since there's no combustion chamber pressure canceling out the force from the piston travelling up in the cylinder).

If you do the math, you'll find the difference between a 3.4" stroke and a 3.0" stroke end up only being ~3%. If you're at the bleeding edge, being able to reduce the mass of your rod due to the decreased load might be worth it. Maybe. Or leave the rods along and enjoy the added margin.

But that's just the force of the piston at the end of the rod. The shorter stroke has a rod journal closer to the crank centerline, which moves the rod pin mass inward 0.4" (think of a figure skater pulling their arms in, they spin faster) so it'll take less force to accelerate the crank. That probably has more to do with the destroked engine wanting to rev than the piston speeds.

But if you don't lower the deck height, you'll need a longer rod, and on and on.

 

[GNBRETT]

Nice Joey!

What if you could do all 3.

Build a 272 ci motor and spin that bitch to 13000 with 45 pounds of boost!

Yea baby!

 

[GNBRETT]

All I know is Don Cruz told me years ago that when he went 109 "Stroker" he went 2 tenths faster in the 1/4. Same combo just a stroker. Im sure there are all kinds of opinions and combos to make an argument for either and maybe with todays Turbo's its not apples to apples but I would think more CI means more power. Sure seems to be that way with a Stage or TA motor.

I'll wait for the Bison "The rocket scientist" to chime in lol.

 

[Ttype6]

The shorter stroke has a rod journal closer to the crank centerline, which moves the rod pin mass inward 0.4" (think of a figure skater pulling their arms in, they spin faster) so it'll take less force to accelerate the crank. That probably has more to do with the destroked engine wanting to rev than the piston speeds.

I like this and have only ever thought about engine speed. The figure skater analogy is a good one. To experience what happens to a figure skater when she puts her arms and hands in tight to her body while spinning,spin yourself on a stool with your arms out away from your body then pull them in tight while you're still spinning. It's amazing how much your rotation speeds up.

 

[NY Twin Turbo]

I like this and have only ever thought about engine speed. The figure skater analogy is a good one. To experience what happens to a figure skater when she puts her arms and hands in tight to her body while spinning,spin yourself in a stool with your arms out away from your body then pull them in tight. It's amazing how much your rotation speeds up.

Who says the figure skater has to be a woman?

I used to figure skate.

 

[Ttype6]

Who says the figure skater has to be a woman?

I used to figure skate.

Who looks at men who figure skate?

 

[~JM~]

Who looks at men who figure skate?