Are there advantages to running a destroked 7M?

[JtWo]

this thread is so informational and gets me in trouble at work.

 

[tekdeus]

Glad you "caught" that

Actually that is the new version of the anti-lag system based on EGR. It works both ways for them

The NEW ALS system that particluar car uses (EVO) is actaully pretty intresting. The "valve" you see on the exhaust manifold serves as the basis to bypass air into the exhaust system while the ECU adds fuel. But instead of the old style where you are dealing with pumping losses to get the air through the engine, this way, unrestricted air is injected directy into the exhaust stream while the unlit fuel comes into the exhaust, at the right time the valve closes, the mixutre lights and you have an ALS that reduces the EGT, is less destructive to both turbo and exhuast parts but still able to maintain race level boost when off throttle with less fuel consumed.

It is actually pretty f'ing brilliant. Also notice no BOV All that work the turbo did is used to keep the turbo spinning off throttle. So no venting to atmophere for them anymore and if you think about it, why would you when you can keep all that nice pressurized air in the system and help in keeping the turbo spinning.

Essentially a BOV into the exhaust to keep the turbo spinning?! If this works, why isn't it seen more often? Any street cars doing this? Or is a huge Tial BOV "good enough"?

 

[Supracentral]

Just to add a comment here, that on a 4 stroke engine, it's the exhaust stroke (where the exhaust valves are open and the piston moves from bottom to top), that is most likely to cause catastrophic failure at high RPM's. When the exhaust valve is open, the pistons are pushing exhaust out, and there is therefore, no compression to slow the piston down as it approaches the peak of its cycle, this causes the rod (and only the rod) to slow the piston down and prevent it from rocketing through the hood of the car... however, this puts the rod under immense tensile stress, and like all metals, tensile stress is where it is weakest.

On two of the strokes the piston is moving down (compressing the rod) and the other stroke the rod is aided by compression in slowing the piston.

Correct. I did a pretty extensive writeup on this very topic quite some time ago.

 

[gofastgeorge]

The rod length/stroke figure is used to determine maximum piston acceleration at top dead center.
(when the piston changes from going up, to when it starts to go down)
Sorry, I am too tired to go dig through my books to find the actual formula.

The accepted limit is 140,000 ft/sec/sec.
A stock stroke 7M with stock length rods reaches this at about 8500 rpm.
Above that point, the G-force of the upper components,
even with top of the line parts,
will exceed the strength of the parts them selves.
It will also cause the rings to lift of the bottom of the ring groves, and allowing pure fire (on the ignition cycle) to pass by the rings.

With ultra light weight components, this can be exceeded a little.
(titanium pins, only one compression ring, etc.)
And the use of a dykes (L style) ring will also help.

F1 pistons from a few years ago (pre-2 race engine rules)
used only the compression ring, no oil ring.

You can also increase this limiting rpm point by:
shorter stroke and/or a longer rod.

And........
Increasing the stroke, and/or shortening the rods will decrease the RPM limit.

Interestingly,
Crower used to show a rod that had the same upper & lower bearing diameters as the 7M, but was a few millimeters longer.

 

[figgie]

Essentially a BOV into the exhaust to keep the turbo spinning?! If this works, why isn't it seen more often? Any street cars doing this? Or is a huge Tial BOV "good enough"?

Well funny that you ask,

the EVO IX has that built in. It is not operational though, but the piping is all connected to allow for this type of system on the street. Remember, they (WRC) must use ALS as they are breathing through a 34mm opening. Not even in the most restrictive street car is the opening ever that small.

 

[Keros]

Correct. I did a pretty extensive writeup on this very topic quite some time ago.

hehe. Sorry SC, but where do you think I learned it from

I should have noted your thread initally. Atleast your wisdom does not fall upon deaf ears :icon_bigg

 

[supradjza80]

F1 motor specifically.

the Bore is double the size of the stroke or put another way. the stroke is excatly half the bore size.

As for your last statement.

WRONG. HP = work but without Torque, nothing will happen (Hp= Work,TQ=Force, RPM = Time). Torque is a force that without TIME (very very important) is does not produce any work (put a 1 lbs weight on your breaker bar that measures 1 ft, means 1 ft/lbs. Problem is the weight is hanging there and not moving. A Force but no work is done). HP and Torque are related. You can have torque but no work done. But you CAN NOT have HP without the Force * time (simple work equation).

I know the equations, this is why i said hp is the important value. Knowing HP implies that you know the Force*time...knowing just the force tells you nothing. So i believe everything written above is correct. If you know you have x amount of HP you know you can always gear the thing for the appropriate torque. If all you know is torque, you really don't know anything because of time...

Furthermore, If you have 500 hp, you have 500 hp. You can gear the torque output of the device producing the horsepower to put out the torque that you need. In a car this is the change in torque at the motor to torque at the wheels.

For example you take the motor out of the semi and properly gear it. This motor produces 425 hp peak in a completely linear fashion, but it only revs to 2000 rpm so the motor produces 1800 lb-ft of torque (i didnt calc this - Im lazy, but its just an example). You put it in a vehicle that weighs 5000lbs total.

Now in the other test vehicle you have a V8 that makes 425 hp in a completely linear fashion and only produces 425 lb-ft of torque (motor revs to 5252 rpm). This motor is properly geared as well and you put it in a vehicle that weighs 5000 lbs.

Now you race - and guess what, since the hp is the same they go the same speed...guess torque is not what really matters and horsepower is really what matters. As long as the vehicle has gears in it, and they are appropriately selected torque means nothing, and HP is what is going to determine how quick the vehicle is.

I know you understand the principals here figgie so I am just guessing any disagreement we have here is semantics based.

 

[supradjza80]

Nope, it's the crossover point and they're equal.

Take two exact cars (assuming they have the ability and aren't already on the edge of max flow) and spin one up higher than the other. The one that revs higher makes more HP. These cars would be equal until they had to shift and the higher reving car would win as it would be higher in the powerband where there is more torque/horespower.

On a side note, the WRC cars run restricter plates and are tuned for the most power at 5252 RPM. They run out of air and getting more under the curve is the way to more power in their application as their max flow is limited.

yeah looks like i mis-typed that, at least i wrote the equation right, but yes hp and tq are equal (HP and lb-ft units) at 5252 rpm. After 5252 hp is always higher than torque, and below the opposite is true.

 

[MRSUPRA]

Generally, when destroking, you are losing displacement. And when you lose displacement, you lose power and torque, especially the amount of power you can make on pump gas. Also, when you have less displacenent you lose the exhaust energy to spool a turbo. So not only will you get less power and torque with a destroked 7M, you will make for a laggier turbo setup. There is a reason why so many guys with domestic V8's use stroker setups to get more power (which do include turbo and supercharged V8's).

And if I recall, Milbrum is reving out his stock stroke 7M to 9500rpm's.

 

[gofastgeorge]

Not really, since higher RPM will make more HP
if the engine is built to opperate in the higher RPM range.

Just look at HKS's sub-8 second 7M powered Mk3.
It used a destroked crank (5M stroke),
and it was making low 8, and sub 8 passes back in the early '90s.

They were turning it to 9000 rpm.

Very few Mk3s are even doing this these days.........

 

[figgie]

I know the equations, this is why i said hp is the important value. Knowing HP implies that you know the Force*time...knowing just the force tells you nothing. So i believe everything written above is correct. If you know you have x amount of HP you know you can always gear the thing for the appropriate torque. If all you know is torque, you really don't know anything because of time...

Furthermore, If you have 500 hp, you have 500 hp. You can gear the torque output of the device producing the horsepower to put out the torque that you need. In a car this is the change in torque at the motor to torque at the wheels.

For example you take the motor out of the semi and properly gear it. This motor produces 425 hp peak in a completely linear fashion, but it only revs to 2000 rpm so the motor produces 1800 lb-ft of torque (i didnt calc this - Im lazy, but its just an example). You put it in a vehicle that weighs 5000lbs total.

Now in the other test vehicle you have a V8 that makes 425 hp in a completely linear fashion and only produces 425 lb-ft of torque (motor revs to 5252 rpm). This motor is properly geared as well and you put it in a vehicle that weighs 5000 lbs.

Now you race - and guess what, since the hp is the same they go the same speed...guess torque is not what really matters and horsepower is really what matters. As long as the vehicle has gears in it, and they are appropriately selected torque means nothing, and HP is what is going to determine how quick the vehicle is.

I know you understand the principals here figgie so I am just guessing any disagreement we have here is semantics based.

and incorrect. Assuming a MATCHING torque curve for each car with the SAME wieght and everything else matching. They should be the same. The problem is that even within the same model cars you have manufacturing variances that effect the torque curve which effects the acceleration curve.

500HP = 500hp. The difference is HOW you get those 500HP. Your hypothetical situtation does not exist on this plane but what the hell. If HP is Flat through out the RPM band then the Torque will have to decrease as RPM increase. This means that there is less force available to accelerate the car. In the situation you supplied, you have alot of missing infomration, what is the area under the curve like for both vehicles? If the gearing is such that both have the same MAX MPH. It still will be difficult to say which does what as we do not know the area under the curve.

The very principle applies to electic motors, There torque is greatest at ZERO rpm when a current is applied and have a linear fall off as they reach their max rpm (almost to zero).

I am not in the mood to debate this point today so in my corner, i Will let my good friend Paul Yaw explain it to you with Gearing graphs why HP is what matters in the end.

http://www.yawpower.com/tqvshp.html


Read up, if you have any questions after practicing those equations. Then lets hear them, you are on the right track but making some odd hypothesis.

 

[supradjza80]

http://www.yawpower.com/tqvshp.html

I don't know what else to say. I have been trying to say this and I guess you just don't get how I am saying this. For the last time horsepower>torque.

 

[Supracentral]

I don't know what else to say. I have been trying to say this and I guess you just don't get how I am saying this. For the last time horsepower>torque.

Incorrect.

Horsepower equals torque times rpm, divided by 5252

 

[gofastgeorge]

Incorrect.

Horsepower equals torque times rpm, divided by 5252

But why use know formulas, and fact,
when guessing, and forum bull S#it is so much easier to post............
:naughty: